Microsoft Computer Dictionary, Fifth Edition eBook - ASSA ABLOY ...

PUBLISHED BY 

Microsoft Press 

A Division of Microsoft Corporation 

One Microsoft Way 

Redmond, Washington 98052-6399 

Copyright © 2002 by Microsoft Corporation 

All rights reserved. No part of the contents of this book may be reproduced or transmitted in any form 

or by any means without the written permission of the publisher. 

Library of Congress Cataloging-in-Publication Data 

Microsoft Computer Dictionary.--5th ed. 

p. cm. 

ISBN 0-7356-1495-4 

1. Computers--Dictionaries. 2. Microcomputers--Dictionaries. 

AQ76.5. M52267 2002 

004'.03--dc21 200219714 

Printed and bound in the United States of America. 

2 3 4 5 6 7 8 9 QWT 7 6 5 4 3 2 

Distributed in Canada by H.B. Fenn and Company Ltd. 

A CIP catalogue record for this book is available from the British Library. 

Microsoft Press books are available through booksellers and distributors worldwide. For further information 

about international editions, contact your local Microsoft Corporation office or contact Microsoft 

Press International directly at fax (425) 936-7329. Visit our Web site at www.microsoft.com/mspress. 

Send comments to mspinput@microsoft.com. 

Active Desktop, Active Directory, ActiveMovie, ActiveStore, ActiveSync, ActiveX, Authenticode, 

BackOffice, BizTalk, ClearType, Direct3D, DirectAnimation, DirectDraw, DirectInput, DirectMusic, 

DirectPlay, DirectShow, DirectSound, DirectX, Entourage, FoxPro, FrontPage, Hotmail, IntelliEye, 

IntelliMouse, IntelliSense, JScript, MapPoint, Microsoft, Microsoft Press, Mobile Explorer, MS-DOS, 

MSN, Music Central, NetMeeting, Outlook, PhotoDraw, PowerPoint, SharePoint, UltimateTV, Visio, 

Visual Basic, Visual C++, Visual FoxPro, Visual InterDev, Visual J++, Visual SourceSafe, Visual Studio, 

Win32, Win32s, Windows, Windows Media, Windows NT, Xbox are either registered trademarks or 

trademarks of Microsoft Corporation in the United States and/or other countries. Other product and 

company names mentioned herein may be the trademarks of their respective owners. 

The example companies, organizations, products, domain names, e-mail addresses, logos, people, places, 

and events depicted herein are fictitious. No association with any real company, organization, product, 

domain name, e-mail address, logo, person, place, or event is intended or should be inferred. 

Acquisitions Editor: Alex Blanton 

Project Editor: Sandra Haynes 

Body Part No. X08-41929

Contributors 

Peter Aiken 

Bart Arenson 

Janice Borzendowski 

Jerome Colburn 

Duane Hanson 

Andrew Himes 

Robert Howecton 

Annette B. Jackson 

Larry S. Jackson 

Thomas A. Jackson 

Chris Kinata 

Ilana Kingsley 

Robin Lombard 

Thomas A. Long 

William G. Madison 

Illustrators 

Travis Beaven 

David Holter 

Alton Lawson 

Thomas P. Magliery 

David Mason 

Terrence M. McLaren 

Wallace Parker 

Charles Petzold 

Phil Rose 

John Ross 

David Rygmyr 

Aimée Truchard 

Michael Vose 

Bruce Webster 

Judson D. Weeks 

Tom Winn 

JoAnne Woodcock 

Rob Nance 

Joel Panchot

Contents 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii 

Changes in the Fifth Edition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii 

Order of Presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii 

Entries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii 

Future Printings and Editions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix 

Dictionary of Computer Terms . . . . . . . . . . . . . . . 1 

Appendix A: 

Common Character Sets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587 

ANSI Character Set. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .587 

Apple Macintosh Extended Character Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .593 

IBM Extended Character Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .597 

EBCDIC Character Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .599 

Appendix B: 

Common File Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605 

Appendix C: 

Instant Messaging Emoticons and Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613 

Appendix D: 

Internet Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623 

Appendix E: 

Numeric Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 

v

Introduction 

The Microsoft Computer Dictionary, Fifth Edition is 

designed to be a comprehensive and authoritative source of 

definitions for computer-related terms and abbreviations. 

The dictionary includes terms drawn from a wide variety 

of topics relevant to computer users, including software, 

hardware, networking, data storage, graphics, games, 

information processing, the Internet and the World Wide 

Web, gaming, history, jargon and slang, organizations, programming, 

and standards. 

Although this book covers nearly every aspect of computing, 

it does not include entries on most companies or on 

most makes and models of computers, nor does it contain 

entries on most application software products. The few 

exceptions to this rule of thumb are key companies and 

products that have a historical or universal importance 

within the computing industry. 

This dictionary emphasizes terminology that the average 

computer user will encounter in documentation, online 

help, computer manuals, marketing and sales materials, the 

popular media, and the computer trade press. Because 

most computer users operate personal computers and desktop 

systems at home, work, or both, the majority of the 

entries in this dictionary cover the terminology used in 

describing and working with these systems. However, 

some specialized or highly technical language is included 

that pertains to areas of industry, academia, software and 

hardware development, and research. These terms have 

been included because they have a bearing on more common 

computer terminology or because they are of historical 

significance. 

Changes in the Fifth Edition 

The fifth edition of the Microsoft Computer Dictionary has 

been revised and expanded to include over 10,000 entries, 

reflecting the many advances in the computer field and 

Introduction 

vii 

including several areas that have come into prominence in 

the public eye, such as networking, Web authoring, and 

new technologies, such as .NET. The content from the Year 

2000 appendix has been integrated into the body of the dictionary 

and a new appendix on emoticons and instant messaging 

symbols has been added. 

Order of Presentation 

Entries are alphabetized by letter. Spaces are ignored, as are 

characters such as hyphens and slashes; for example, Baudot 

code falls between baud and baud rate, and machineindependent 

falls between machine identification and 

machine instruction. Numbers and symbols are located at 

the beginning of the book and are listed in ascending ASCII 

order. If an entry begins with a letter or letters but contains 

a number, it is listed alphabetically, according to the initial 

letter(s), and then according to ASCII order. Thus, V20 

precedes V.2x, and both precede VAB. 

Entries 

Entries are of two types: main entries, which contain full 

definitions, and synonymous cross-references, which contain 

See references to the appropriate main entries. Synonymous 

cross-references are generally secondary or less 

common ways of referring to a main entry. The definition 

at the main entry can be substituted as a definition for the 

synonymous cross-reference. 

Format 

Information in each main entry is presented in a consistent 

format: entry name in boldface, spelling variants (if any), 

part of speech, definition, illustration or table reference (if 

any), acronym (if any), alternative names (if any), and 

cross-references (if any).

Introduction 

Main Entries 

Entries that are acronyms or abbreviations for one or more 

words or concatenations of two or more words have those 

words spelled out at the beginning of the definition. The 

letters in these words or phrases that make up the acronym, 

abbreviation, or concatenation are in boldface. 

When a main entry is spelled exactly the same as another 

main entry, the two entries are differentiated by the use of a 

superscript numeral after each term. These entries are 

called homographs, and they are generally different parts 

of speech. For example, 

e-mail1 (noun) 

e-mail2 (verb) 

Spelling Variants 

When a main entry has one or more variations in the way it 

is spelled, each spelling variant follows the main entry, 

after the word or. 

Parts of Speech 

Entries are broken down into four parts of speech, in addition 

to prefixes, abbreviated as follows: 

n. noun 

vb. verb 

adj. adjective 

adv. adverb 

Definitions 

Each of the more than 10,000 entries is written in clear, 

standard English. Many go beyond a simple definition to 

provide additional detail and to put the term in context for 

a typical computer user. When an entry has more than one 

sense or definition, the definitions are presented in a numbered 

list, to make it easier to distinguish the particular, 

sometimes subtle, variations in meaning. 

Illustration and Table References 

Some entries have affiliated illustrations or tables that aid 

in defining the entry. In most cases, illustrations and tables 

appear on the same page as the entries to which they apply. 

viii 

In some instances, however, page layout requirements have 

forced them to a subsequent page. Entries with illustrations 

or tables usually have references at the end of the definition 

for an entry, in the following formats: 

See the illustration. 

See the table. 

Acronyms 

Some terminology in the computer field, particularly computer 

standards and Internet slang, can be shortened to 

form acronyms. Sometimes the acronym is the more common 

way to refer to the concept or object; in these cases, 

the acronym is the main entry. In other cases, the acronym 

is not as commonly used as the words or phrase for which 

it stands. In these cases, the words or phrase constitute the 

main entry. The acronym is given after the definition for 

these entries in the following format: 

Acronym: 

Alternative Names 

Some items or concepts in the computer field can be 

referred to by more than one name. Generally, though, one 

way is preferred. The preferred terminology is the main 

entry. Alternative names are listed after any acronyms; 

otherwise they are listed after the definition in the following 

format: 

Also called: 

Cross-References 

Cross-references are of three types: See, See also, and Compare. 

A See reference is used in an entry that is a synonymous 

cross-reference and simply points to another entry 

that contains the information sought. A See also reference 

points to one or more entries that contain additional or supplemental 

information about a topic and follows any acronyms 

or alternative names after the definition. A Compare 

reference points to an entry or entries that offer contrast and 

follows any See also references; otherwise it follows any 

acronyms or alternative names after the definition.

Future Printings and Editions 

Every effort has been made to ensure the accuracy and 

completeness of this book. If you find an error, think that 

an entry does not contain enough information, or seek an 

entry that does not appear in this edition, please let us 

know. Address your letter to: Dictionary Editor, Microsoft 

Press, One Microsoft Way, Redmond, WA 98052-6399. Or 

send e-mail to mspcd@microsoft.com. 

ix 

Introduction

$0.02 n. See my two cents. 

& n. 1. UNIX command suffix for running the preceding 

command as a background process. See also background1 . 

2. In UNIX, a root user command suffix for starting a 

daemon that is to remain running after logout. See also 

daemon. 3. The default character used to designate a character 

entity (special character) in an HTML or SGML document. 

See also HTML, SGML. 4. In spreadsheet 

programs, an operator for inserting text into a formula 

specifying the relationship between cells. 

* n. 1. A character used in applications and programming 

languages to signify multiplication. 2. In Windows, 

MS-DOS, OS/2, and other operating systems, a wildcard 

character that can be used in place of one or more characters, 

as in *.*, which represents any combination of a filename 

and an extension. See also ?, *.*, wildcard character. 

3. In the C and C++ programming languages, the character 

used to dereference a pointer to a class or structure. See 

also dereference, pointer (definition 1). 

*.* n. A file specification using the asterisk (star) wildcard, 

which means any combination of filename and 

extension in operating systems such as MS-DOS. See also 

asterisk (definition 2), wildcard character. 

.. n. MS-DOS and UNIX syntax for the parent directory. 

A single dot refers to the current directory. 

/ n. 1. A character used to separate parts of a directory 

path in UNIX and FTP or parts of an Internet address 

(URL) in Web browsers. 2. A character used to flag 

switches or parameters that control the execution of a program 

invoked through a command-line interface. See also 

command-line interface. 

// n. Notation used with a colon to separate the URL protocol 

(such as http or ftp) from the URL host machine 

name, as in http://www.yahoo.com. See also URL. 

: n. Colon, a symbol used after the protocol name (such as 

http or ftp) in a URL. See also URL. 

Numbers 

and Symbols 

1 

n. 1. Angle brackets, a pair of symbols used to enclose 

a keyword, comprising a tag in an HTML, SGML, or 

XML document. See also HTML, SGML, XML. 2. In an 

Internet Relay Chat (IRC) or multiuser dungeon (MUD), a 

set of symbols used to designate some action or reaction, 

as in . See also emotag, IRC, MUD. 3. A pair 

of symbols used to enclose a return address in an e-mail 

header. 

> n. 1. Right angle bracket, a symbol used in some operating 

systems, such as MS-DOS and UNIX, to direct the 

output resulting from some command into a file. 2. A 

symbol commonly used in e-mail messages to designate 

text included from another message. 

? n. In some operating systems and applications, a wildcard 

character often used to represent any other single 

character. The question mark is one of two wildcard characters 

supported by the MS-DOS, Windows NT, and OS/2 

operating systems. See also *. 

@ n. The separator between account names and domain 

names in Internet e-mail addresses. When spoken, @ is 

read as “at.” Therefore, user@host.com would be read as 

“user at host dot com.” 

\ n. Back slash, a character used to separate directory 

names in MS-DOS and UNIX path specifications. When 

used as a leading character, it means that the path specification 

begins from the topmost level for that disk drive. 

See also path (definition 5). 

0.07-micron n. A manufacturing technology with which 

400 million transistors, with an effective channel length 

1000 times thinner than a human hair, can be placed on a 

single chip. The extremely small sizes and faster speeds of 

0.07-micron products can be used to create improved-performance 

microprocessors that may extend clock speeds 

beyond 10 GHz. Possible applications of 0.07-micron 

technology range from tiny hearing aids that can be 

implanted in the ear to hard disk drives that read gigabits 

of data per second. 

#

# 

0 wait state 16-bit 

0 wait state n. See zero wait state. 

100Base-FX n. An Ethernet standard for baseband LANs 

(local area networks) using fiber optic cable carrying 100 

Mbps (megabits per second). Also called: Fast Ethernet. 

See also Ethernet (definition 1). 

100Base-T n. An Ethernet standard for baseband LANs 

(local area networks) using twisted-pair cable carrying 

100 Mbps (megabits per second). The 100Base-T standard 

is comprised of 100Base-T4 (four pairs of medium-grade 

to high-grade twisted-pair cable) and 100Base-TX (two 

pairs of high-grade twisted-pair cable). Also called: Fast 

Ethernet. See also Ethernet (definition 1). 

100Base-T4 n. See 100Base-T. 

100Base-TX n. See 100Base-T. 

100Base-VG n. An Ethernet standard for baseband LANs 

(local area networks) using voice-grade twisted-pair cable 

carrying 100 Mbps (megabits per second). Unlike other 

Ethernet networks, 100Base-VG relies on an access 

method called demand priority, in which nodes send 

requests to hubs, which in turn give permission to transmit 

based on the priority levels included with the requests. 

Also called: 100Base-VG-AnyLAN. See also Ethernet 

(definition 1). 

100Base-VG-AnyLAN n. See 100Base-VG. 

100Base-X n. Descriptor used for any of three forms of 

100 Mbps Ethernet networks: 100Base-T4, 100Base-TX, 

or 100Base-FX. Also called: Fast Ethernet. See also 

100Base-T, 100Base-FX, Ethernet (definition 1). 

101-key keyboard n. A computer keyboard modeled 

after the enhanced keyboard; introduced by IBM for the 

IBM PC/AT. The 101-key keyboard and the enhanced keyboard 

are similar in the number and function of their keys; 

they may differ in the way the keys are laid out, the 

amount of tactile feedback expressed when a key is 

pressed, and the shape and feel of the keycaps. See also 

enhanced keyboard. 

1024x768 n. A standard super VGA computer display 

having a resolution of 1024 columns of pixels by 768 rows 

of pixels. See also SVGA. 

10Base2 n. The Ethernet and IEEE 802.3 standard for 

baseband LANs (local area networks) using a thin coaxial 

cable (3/16 inch) up to 200 meters long and carrying 10 

Mbps (megabits per second) in a bus topology. A network 

node is connected to the cable by a BNC connector on the 

2 

adapter card. Also called: Cheapernet, thin Ethernet, 

ThinNet, ThinWire. See also BNC connector, bus network, 

coaxial cable, Ethernet (definition 1), IEEE 802.x. 

10Base5 n. The Ethernet and IEEE 802.3 standard for 

baseband LANs (local area networks) using a thick coaxial 

cable (3/8 inch) up to 500 meters long and carrying 10 

Mbps (megabits per second) in a bus topology. A network 

node is equipped with a transceiver that plugs into a 15-pin 

AUI connector on the adapter card and taps into the cable. 

This form of Ethernet is generally used for network backbones. 

Also called: thick Ethernet, ThickNet, ThickWire. 

See also coaxial cable, Ethernet (definition 1), IEEE 802.x. 

10Base-F n. The Ethernet standard for baseband LANs 

(local area networks) using fiber-optic cable carrying 10 

Mbps (megabits per second) in a star topology. All nodes 

are connected to a repeater or to a central concentrator. A 

node is equipped with a fiber-optic transceiver that plugs 

into an AUI connector on the adapter card and attaches to 

the cable with an ST or SMA fiber-optic connector. The 

10Base-F standard comprises 10Base-FB for a backbone, 

10Base-FL for the link between the central concentrator 

and a station, and 10Base-FP for a star network. See also 

Ethernet (definition 1), fiber optics, star network. 

10Base-FB n. See 10Base-F. 

10Base-FL n. See 10Base-F. 

10Base-FP n. See 10Base-F. 

10Base-T n. The Ethernet standard for baseband LANs 

(local area networks) using twisted-pair cable carrying 10 

Mbps (megabits per second) in a star topology. All nodes 

are connected to a central hub known as a multiport 

repeater. See also Ethernet (definition 1), star network, 

twisted-pair cable. 

12-hour clock n. A clock that expresses the time within a 

12-hour range, returning to 1:00 after 12:59 AM or PM. 

Compare 24-hour clock. 

1.2M adj. Short for 1.2-megabyte. Refers to the storage 

capacity for high-density 5.25-inch floppy disks. 

1394 n. See IEEE 1394. 

14.4 n. A modem with a maximum data transfer rate of 

14.4 Kbps (kilobits per second). 

1.44M adj. Short for 1.44-megabyte. Refers to the storage 

capacity for high-density 3.5-inch floppy disks. 

16-bit adj. See 8-bit, 16-bit, 32-bit, 64-bit.

16-bit application 28.8 

16-bit application n. An application written to run on a 

computer with a 16-bit architecture or operating system, 

such as MS-DOS or Windows 3.x. 

16-bit color adj. Of, pertaining to, or characteristic of a 

display that can produce 216 (65,536) distinct colors. Compare 

24-bit color, 32-bit color. 

16-bit machine n. A computer that works with data in 

groups of 16 bits at a time. A computer may be considered 

a 16-bit machine either because its microprocessor operates 

internally on 16-bit words or because its data bus can 

transfer 16 bits at a time. The IBM PC/AT and similar 

models based on the Intel 80286 microprocessor are 16-bit 

machines in terms of both the word size of the microprocessor 

and the size of the data bus. The Apple Macintosh 

Plus and Macintosh SE use a microprocessor with a 32-bit 

word length (the Motorola 68000), but they have 16-bit 

data buses and are generally considered 16-bit machines. 

16-bit operating system n. An operating system, now 

outdated, that can work with 2 bytes, or 16 bits, of information 

at one time. A 16-bit operating system, such as 

MS-DOS and Microsoft Windows 3.x, reflects the functionality 

of a 16-bit processor because the software and 

the chip must work together so closely. The main advantage 

of a 16-bit operating system over its earlier 8-bit predecessors 

(such as CP/M-80) was its ability to address 

more memory and use a larger (16-bit) bus. Sixteen-bit 

operating systems have since been eclipsed by 32-bit operating 

systems—such as the Macintosh operating system, 

Microsoft Windows NT, and Windows 9x—and by 64-bit 

operating systems, such as some versions of UNIX. See 

also 32-bit operating system. 

/16 network n. IP address class B. This class has 16,382 

networks available and more than sixty-five thousand 

hosts available. See also host, IP address classes, network. 

1999 problem n. 1. A variation on the Year 2000 problem 

in computer systems that have two-digit years in date 

fields and are used by companies and organizations in 

which the fiscal year 2000 begins before the end of calendar 

year 1999. These computer systems may interpret the 

fiscal year as the year 1900. 2. A potential problem, if not 

corrected, with date fields in older code that were (sometimes) 

used to hold values with special meaning. For 

example, the date 9/9/99 was often used as an expiration 

date meaning “keep this information forever” or, worse, 

“destroy this document immediately.” 

3 

1NF n. Short for first normal form. See normal form (definition 

1). 

2000 time problem n. See Year 2000 problem. 

2038 limit n. A consideration in some PCs that use a 

signed 32-bit integer to represent date and time. Because 

such systems determine date and time as the number of 

seconds elapsed since midnight, January 1, 1970, they can 

handle a maximum of 231 seconds, a number that will be 

reached at 3:14:07 a.m. on January 19, 2038. When the 

elapsed seconds exceed that maximum value, the clock 

will overflow, resulting in an incorrect date and time and, 

potentially, causing disruptions. Some organizations have 

defined Year 2000 compliant to mean a system that will 

have the correct date/time and do proper date handling up 

through the year 2038, although this is not universal. The 

extent of the potential problem, of course, is directly 

related to the number of such system solutions still in 

operation at the time. See also Year 2000 compliant. 

24-bit color n. RGB color in which the level of each of 

the three primary colors in a pixel is represented by 8 bits 

of information. A 24-bit color image can contain over 16 

million different colors. Not all computer monitors support 

24-bit color, especially older models. Those that do 

not may use 8-bit color (256 colors) or 16-bit color 

(65,536 colors). Also called: true color. See also bit depth, 

pixel, RGB. Compare 16-bit color, 32-bit color. 

24-hour clock n. A clock that expresses the time within a 

24-hour range, from 0000 (midnight) to 2359 (one minute 

before the following midnight). Compare 12-hour clock. 

2.4 kernel n. Update of the core of the Linux OS, released 

at the end of 2000. Features in the 2.4 kernel emphasize 

support for new buses, devices, and controllers; increased 

USB support; improved Web server performance; and 

increased symmetrical multiprocessing scalability. 

/24 network n. IP address class A. This class has more 

than two million networks available and 254 hosts available. 

See also host, IP address classes, network. 

256-bit adj. Having a data path that is 256 bits wide. 

286 n. See 80286. 

287 n. See 80287. 



#

# 

2-digit year 387SX 

2-digit year n. The capacity for storing only the last two 

digits of the year in a date. In such systems, the century for 

the date is not stored. See also two-digit date storage. 

2G n. Acronym for 2nd Generation. The second generation 

of digital wireless technology, as defined by the International 

Telecommunications Union (ITU). Second generation 

technology delivers data transmission at speeds from 9.6 

Kbps (kilobits per second) to 19.2 Kbps. Second generation 

technology provides greater data transmission capabilities 

and more efficient voice transmission than the analog technology 

first developed for wireless telecommunications. 

2NF n. Short for second normal form. See normal form 


2-nines availability n. See two-nines availability. 

2.PAK n. An artificial intelligence programming language. 

32-bit adj. See 8-bit, 16-bit, 32-bit, 64-bit. 

32-bit application n. An application written to run on a 

computer with a 32-bit architecture or operating system, 

such as Mac OS or Windows 9x. 

32-bit clean adj. 1. Refers to Macintosh hardware 

designed to run in 32-bit mode, which can address up to 1 

gigabyte of physical RAM under System 7. This includes 

all present Macintosh computers; some older models used 

16-bit addressing. 2. Refers to software written for 32-bit 

operation. 

32-bit color n. RGB color that is similar to 24-bit color, 

with 8 additional bits used to allow for faster transfer of an 

image's color. See also bit depth, RGB. Compare 16-bit 

color, 24-bit color. 

32-bit driver n. A software subsystem that controls either 

a hardware device (device driver) or another software subsystem. 

The 32-bit versions of this software take full 

advantage of the instruction sets of the 486 and Pentium 

processors for improved speed. See also driver, instruction 

set. 


groups of 32 bits at a time. The Apple Macintosh II and 

higher models are 32-bit machines, in terms of both the 

word size of their microprocessors and the size of the data 

buses, as are computers based on the Intel 80386 and 

higher-level microprocessors. 

32-bit operating system n. An operating system in 

which 4 bytes, or 32 bits, can be processed at one time. 

4 

Windows 95, Windows 98, Windows NT, Linux, and OS/2 

are examples. See also instruction set, protected mode. 



34010, 34020 n. Graphics coprocessors from Texas 

Instruments (TI), used mainly in high-end PC graphics 

boards, which have become a de facto standard for programmable 

graphics processors. Although both chips use 

32-bit registers, the 34010 uses a 16-bit data bus and the 

34020 uses a 32-bit bus. The 34020 is compatible with the 

earlier 34010, and both chips work with TIGA (Texas 

Instruments Graphical Architecture), a TI standard that 

allows a single application driver to be used with all 

boards based on the standard. See also de facto standard, 

TIGA, video graphics board. 

3.5-inch floppy disk n. Used with the Macintosh and 

with IBM and compatible microcomputers. A microfloppy 

disk is a round piece of polyester film coated with 

ferric oxide and encased in a rigid plastic shell equipped 

with a sliding metal cover. On the Macintosh, a single-sided 

3.5-inch floppy disk can hold 400 kilobytes (KB); a 

double-sided (standard) disk can hold 800 KB; and a 

double-sided high-density disk can hold 1.44 megabytes 

(MB). On IBM and compatible machines, a microfloppy 

can hold either 720 KB or 1.44 MB of information. See 

also floppy disk. 

360K adj. Short for 360-kilobyte. The storage capacity 

for standard 5.25-inch floppy disks. 

.386 n. A file extension for virtual device drivers under 

Windows 3.1. See also virtual device driver. 

386 n. See 80386DX. 

386BSD n. A version of BSD UNIX, different from 

BSD386 from Berkeley Software Development, Inc. 

Freely distributable, 386BSD was released in 1992 and is 

available in two newer versions: NetBSD and FreeBSD. 

See also BSD UNIX, FreeBSD, NetBSD. 

386DX n. See 80386DX. 

386SL n. See 80386SL. 

386SX n. See 80386SX. 

387 n. See 80387. 

387SX n. See 80387SX.

3-D 4GL 

3-D or 3D adj. 1. Short for three-dimensional. Of, pertaining 

to, or being an object or image having or appearing 

to have all three spatial dimensions (length, width, and 

depth). 2. Having the illusion of depth or varying distances, 

as in 3-D audio. 

3-D array n. See three-dimensional array. 

3-D audio n. Short for three-dimensional audio. 

Recorded as stereo sound, 3-D audio enables the listener 

to feel immersed in the sound and to determine its exact 

location (up, down, left, right, forward, or backward). This 

technology is commonly used in video games and virtual-reality 

systems, as well as in some Internet applications. 

Also called: 3-D sound, binaural sound. 

3-D graphic n. Any graphical image that depicts one or 

more objects in three dimensions—height, width, and 

depth. A 3-D graphic is rendered on a two-dimensional 

medium; the third dimension, depth, is indicated by means 

of perspective and by techniques such as shading or gradient 

use of color. 

3-D metafile n. A device-independent file for storing a 

3-D display. See also metafile. 

3DMF n. See QuickDraw 3-D. 

3-D model n. See three-dimensional model. 

3-D sound n. See 3-D audio. 

3-finger salute n. See three-finger salute. 

3G n. Acronym for 3rd Generation. The third generation 

of digital wireless technology, as defined by the International 

Telecommunications Union (ITU). Third generation 

technology is expected to deliver data transmission speeds 

between 144 Kbps (kilobits per second) and 2 Mbps 

(megabits per second), compared to the 9.6 Kbps to 19.2 

Kbps offered by second generation technology. Western 

Europe and Japan lead the world in adoption of 3G technology 

and services. 

3GL n. Short for third-generation language. A high-level 

programming language that was designed to run on the 

third generation of computer processors, built on integrated 

circuit technology roughly from 1965 to 1970. C, FOR- 

TRAN, Basic, and Pascal are examples of third-generation 

languages still in use today. See also high-level language, 

integrated circuit. Compare 4GL, low-level language. 

3NF n. Short for third normal form. See normal form 


3-nines availability n. See three-nines availability. 

5 

3Station n. A diskless workstation developed by Bob 

Metcalfe at 3Com Corporation. See also diskless workstation. 

400 n. HTTP status code—Bad Request. A Hypertext 

Transfer Protocol message from an HTTP server indicating 

that a client request cannot be completed because the 

syntax of the request is incorrect. See also HTTP server 

(definition 1), HTTP status codes. 

401 n. HTTP status code—Unauthorized. A Hypertext 


that a client request cannot be completed because the transaction 

requires an Authorization header, which was not 

supplied. See also HTTP server (definition 1), HTTP status 

codes. 

402 n. HTTP status code—Payment Required. A Hypertext 


that a client request cannot be completed because 

the transaction requires a payment, and no ChargeTo 

header was supplied. See also HTTP server (definition 1), 

HTTP status codes. 

403 n. HTTP status code—Forbidden. A Hypertext 


that a client request cannot be completed because 

access is restricted. See also HTTP server (definition 1), 

HTTP status codes. 

404 n. HTTP status code—Not Found. A Hypertext 


that a client request cannot be completed because the 

server is unable to find an address that matches the URL 

requested. See also HTTP server (definition 1), HTTP status 

codes, URL. 

486 n. See i486DX. 

486DX n. See i486DX. 

486SL n. See i486SL. 

486SX n. See i486SX. 

4-digit year n. The capacity for storing all four digits of 

the year in a date in hardware or firmware products. 

4GL n. Short for fourth-generation language. A programming 

language designed to mimic human language. The 

designation is often used to specify languages used with 

relational databases and is intended to imply that such languages 

are a step up from standard high-level programming 

languages such as C, Pascal, and COBOL. See also 

application development language, high-level language. 

Compare 3GL, assembly language. 

#

# 

4GL architecture 68000 

4GL architecture n. See two-tier client/server. 

4mm tape n. See digital audio tape. 

4NF n. Short for fourth normal form. See normal form 


4-nines availability n. See four-nines availability. 

5.25-inch floppy disk n. Used with the Macintosh and 

with IBM and compatible microcomputers. A microfloppy 

disk is a round piece of polyester film coated with ferric 

oxide and encased in a rigid plastic shell equipped with a 

sliding metal cover. A floppy disk 5.25 inches in diameter 

is encased in a flexible plastic jacket and has a large hole 

in the center, which fits around a spindle in the disk drive; 

such a disk can hold from a few hundred thousand to over 

one million bytes of data. See floppy disk. 

56flex n. See K56flex. 

56K1 adj. Having 56 kilobits per second (Kbps) available 

for traffic on a communications circuit. One voice channel 

can carry up to 64 Kbps (called a T0 carrier); 8 Kbps are 

used for signaling, leaving 56 Kbps available for traffic. 

See also T-carrier. 

56K2 n. See 56-Kbps modem. 

56-Kbps modem n. An asymmetric modem that operates 

over POTS (Plain Old Telephone Service) to deliver data 

downstream at 56 Kbps, with upstream speeds of 28.8 and 

33.6 Kbps. Earlier, slower modems invoke a two-conversion 

transmission process: digital data from a computer is 

converted into analog form for transmission over the telephone 

wire and is then reconverted to digital data by the 

receiving modem. In contrast, 56-Kbps modems achieve 

faster speeds by converting analog data to digital data only 

once, typically at the telephone company's switching 

office near the beginning of the transmission's journey. 

Designed to improve download times for Internet users, 

56-Kbps modems rely on a public phone network that 

allows for a single conversion and on the availability of a 

digital connection, such as ISDN or T1, at the ISP (Internet 

Service Provider) location that provides the actual connection 

to the Internet. See also analog data, digital data 

transmission, modem, POTS. 

586 n. The unofficial name used by industry analysts and 

by the computer trade press to describe Intel's successor to 

the i486 microprocessor prior to its release. In the interest 

of using a name that could be trademarked, however, Intel 

decided to name the microprocessor Pentium. See also 

Pentium. 

6 

5NF n. Short for fifth normal form. See normal form (definition 

1). 

5-nines availability n. See five-nines availability. 

5x86 n. Cyrix Corporation's clone of the Intel Pentium 

CPU. See also 586, 6x86, central processing unit, clone, 

Pentium. 

601 n. See PowerPC 601. 



64-bit adj. Of, pertaining to, or descriptive of the amount 

of data—64 bits, or 8 bytes—that certain computer systems 

or programs can process at one time. 



a 64-bit machine either because its CPU operates internally 

on 64-bit words or because its data bus can transfer 

64 bits at a time. A 64-bit CPU thus has a word size of 64 

bits, or 8 bytes; a 64-bit data bus has 64 data lines, so it 

ferries information through the system in sets of 64 bits at 

a time. Examples of 64-bit architecture include the Alpha 

AXP from Digital Equipment Corporation, the Ultra 

workstation from Sun Microsystems, Inc., and the 

PowerPC 620 from Motorola and IBM. 

64-bit operating system n. An operating system in 

which 8 bytes, or 64 bits, can be processed at one time. 

For Microsoft Windows, the 64-bit operating systems are 

Windows XP 64-Bit Edition, the 64-bit versions of Windows 

.NET Enterprise Server, and Windows .NET Datacenter 

Server. The IBM AS/400 uses a 64-bit operating 

system. 

6502 n. The 8-bit microprocessor, developed by Rockwell 

International, that was used in the Apple II and Commodore 

64 microcomputers. 

65816 n. A 16-bit microprocessor from Western Digital 

Design used in the Apple IIGS. It can emulate the 6502, 

providing compatibility with all old Apple II software. See 

also 6502. 

6800 n. An 8-bit microprocessor developed by Motorola 

in the early 1970s. It failed to gain wide acceptance. 

68000 n. The original microprocessor in the 680x0 family 

from Motorola, introduced in 1979 and used in the first 

Apple Macintosh computers as well as the Apple Laser- 

Writer IISC and Hewlett-Packard’s LaserJet printers. The 

68000 has 32-bit internal registers but transfers data over a

68020 80287 

16-bit data bus. With 24-bit physical addressing, the 68000 

can address 16 megabytes of memory—16 times as much 

memory as does the Intel 8088 found in the IBM PC. In 

addition, the 68000’s architecture, in which addressing is 

linear (as opposed to the 8088’s segmented addressing) 

and in which all address registers work the same way and 

all data registers work the same way, makes programming 

more straightforward. See also linear addressing architecture, 

segmented addressing architecture. 

68020 n. A microprocessor in the 680x0 family from 

Motorola, introduced in 1984. This chip has 32-bit 

addressing and a 32-bit data bus and is available in speeds 

from 16 MHz to 33 MHz. The 68020 is found in the original 

Macintosh II and the LaserWriter IINT from Apple. 

68030 n. A microprocessor in the 680x0 microprocessor 

family from Motorola, introduced in 1987. This chip has 

32-bit addressing and a 32-bit data bus and is available in 

speeds from 20 MHz to 50 MHz. The 68030 has built-in 

paged memory management, precluding the need for supplemental 

chips to provide that function. 

68040 n. A microprocessor in the 680x0 family from 

Motorola, introduced in 1990, with 32-bit addressing and 

a 32-bit data bus. The 68040 runs at 25 MHz and includes 

a built-in floating-point unit and memory management 

units, including independent 4-KB instruction and data 

caches, which eliminate the need for supplemental chips 

to provide these functions. In addition, the 68040 is capable 

of parallel instruction execution by means of multiple 

independent instruction pipelines, multiple internal buses, 

and separate caches for both data and instructions. 

68060 n. The latest and fastest of the 680x0 microprocessors 

from Motorola, introduced in 1995. This chip has 

32-bit addressing and a 32-bit data bus and is available in 

speeds from 50 MHz to 75 MHz. There was no 68050. 

The 68060 is probably the last in the 680x0 series from 

Motorola. 

6845 n. A programmable video controller from Motorola 

used in IBM's Monochrome Display Adapter (MDA) and 

Color/Graphics Adapter (CGA). The 6845 became such 

an integral part of the IBM PC and compatibles that later 

generations of video adapters, such as EGA and VGA, 

continue to support the operations of the 6845. See also 

CGA, EGA, MDA, VGA. 

7 

68881 n. The floating-point coprocessor from Motorola 

for use with the 68000 and the 68020. The 68881 provides 

instructions for high-performance floating-point arithmetic, 

a set of floating-point data registers, and 22 built-in 

constants including p and powers of 10. The 68881 conforms 

to the ANSI/IEEE 754-1985 standard for binary 

floating-point arithmetic. The 68881 can produce a dramatic 

improvement in system performance when software 

takes advantage of it. See also floating-point processor. 

68K n. See 68000. 

6x86 n. An 8086-compatible microprocessor designed by 

Cyrix Corporation. It is socket-compatible with some Pentium 

microprocessors from Intel and can be used in their 

place. See also 8086, microprocessor, Pentium. 



7-bit ASCII n. A 7-bit ASCII character set used for standard 

UNIX mail messages. The leftover eighth bit is a parity 

bit used for error correction. See also ASCII, parity bit. 

7-track n. A tape storage scheme that places data on 

seven separate, parallel tracks on 1/2-inch reel-to-reel 

magnetic tape. This is an old recording format used with 

computers that transfer data 6 bits at a time. Data is 

recorded as 6 data bits and 1 parity bit. Some personal 

computers now use the 9-track tape storage scheme. See 

also 9-track. 

80286 n. A 16-bit microprocessor from Intel, introduced 

in 1982 and included in the IBM PC/AT and compatible 

computers in 1984. The 80286 has 16-bit registers, transfers 

information over the data bus 16 bits at a time, and 

uses 24 bits to address memory locations. The 80286 operates 

in two modes: real mode, which is compatible with 

the 8086 and supports MS-DOS, and protected mode, 

which enables the CPU to access 16 megabytes of memory 

and protects the operating system from incorrect 

memory accesses by ill-behaved applications, which could 

crash a system in real mode. Also called: 286. See also 

protected mode, real mode. 

80287 n. A floating-point coprocessor from Intel for use 

with the 80286 family of microprocessors. Available in 

speeds from 6 MHz to 12 MHz, the 80287 offers the same 

mathematical capabilities that the 8087 coprocessor provides 

to an 8086-based system. Because the 80287 conforms 

to the 80286 memory management and protection 

#

# 

802.x standards 8087 

schemes, it can be used in both the real and protected 

modes of the 80286. Also, if the computer manufacturer 

implements support for it in the motherboard design, the 

80287 can be used in a system with an 80386 microprocessor. 

See also floating-point processor. 

802.x standards n. See IEEE 802.x. 

802.11 standards n. See IEEE 802.11. 

80386 n. See 80386DX. 

80386DX n. A 32-bit microprocessor from Intel, introduced 

in 1985. The 80386 is a full 32-bit microprocessor; 

that is, it has 32-bit registers, it can transfer information 

over its data bus 32 bits at a time, and it can use 32 bits to 

address memory. Like the earlier 80286, the 80386 operates 

in two modes: real mode, which is compatible with 

the 8086 chip and supports MS-DOS, and protected mode, 

which allows the CPU to access 4 GB of memory directly, 

supports multitasking, and protects the operating system 

from crashing as a result of an incorrect memory access 

caused by an application program error. The 80386 also 

includes a virtual 8086 mode (also called virtual real 

mode), which appears to software as an 8086 but whose 

1-MB effective address space can be located anywhere in 

physical memory under the same safeguards as in protected 

mode. The virtual 8086 mode is the basis for the 

MS-DOS prompt available inside Windows. Also called: 

386, 386DX, 80386. See also protected mode, real mode, 

virtual real mode. 

80386SL n. A microprocessor from Intel intended for 

use in laptop computers. The 80386SL has similar features 

to the 80386SX, but it also has capabilities for reducing its 

power consumption. In particular, the 80386SL can reduce 

its clock speed to zero when not in use and return to full 

speed, with the contents of all its registers intact, when 

called on to perform another task. Also called: 386SL. See 

also 80386SX, green PC, i486SL. 

80386SX n. A microprocessor from Intel, introduced in 

1988 as a low-cost alternative to the 80386DX. The 

80386SX is basically an 80386DX processor limited by a 

16-bit data bus. The 16-bit design allows 80386SX systems 

to be configured from less expensive AT-class parts, 

resulting in a much lower total system price. The 80386SX 

offers improved performance over the 80286 and access to 

software designed for the 80386DX. The 80386SX also 

offers 80386DX features such as multitasking and virtual 

8086 mode. Also called: 386SX. See also 80386DX. 

8 

80387 n. The floating-point coprocessor introduced by 

Intel for use with the 80386 microprocessors. Available in 

speeds from 16 MHz to 33 MHz, the 80387 offers the 

same mathematical capabilities that the 8087 provides for 

an 8086-based system, as well as transcendental operations 

for sine, cosine, tangent, arctangent, and logarithm calculations. 

The 80387 conforms to the ANSI/IEEE 754-1985 

standard for binary floating-point arithmetic. The 80387 

operates independently of the 80386’s mode, and it performs 

as expected regardless of whether the 80386 is running 

in real, protected, or virtual 8086 mode. Also called: 

387. See also 80386DX, floating-point processor. 

80387SX n. The floating-point coprocessor from Intel for 

use with the 80386SX microprocessor. It provides the same 

capabilities that the 80387 does for an 80386-based system, 

but it is available only in a 16-MHz version. Also called: 

387SX. See also 80386SX, floating-point processor. 

80486 n. See i486DX. 

80486SL n. See i486SL. 

80486SX n. See i486SX. 

8080 n. One of the first chips capable of serving as the 

basis of a personal computer, introduced by Intel in 1974 

and used in the Altair 8800. The 8080 provided 8-bit data 

operations and 16-bit addressing and influenced the 

design of the Z80. Furthermore, the microprocessors of 

the 80x86 line, which serve as the foundation for the IBM 

PC and all its successors and compatibles, are all based on 

a set of registers organized similarly to the 8080’s. See 

also Altair 8800, Z80. 

8086 n. The original microprocessor in the 80x86 family 

from Intel, introduced in 1978. The 8086 has 16-bit registers, 

a 16-bit data bus, and 20-bit addressing, allowing 

access to 1 megabyte of memory. Its internal registers 

include a set that is organized in the same way as those of 

the 8080. Speeds range from 4.77 MHz to 10 MHz. See 

also 8080. 

8087 n. A floating-point coprocessor from Intel for use 

with the 8086/8088 and 80186/80188 microprocessors. 

Available in speeds from 5 MHz to 10 MHz, the 8087 

offers instructions, not found in the 8086/8088 instruction 

sets, for performing arithmetic, trigonometric, exponential, 

and logarithmic operations on 16-, 32-, and 64-bit 

integers; 32-, 64-, and 80-bit floating-point numbers; and 

18-digit BCD (binary-coded decimal) operands. With

8088 8-bit machine 

application software that takes advantage of these instructions, 

the 8087 can dramatically improve system performance. 

The 8087 conforms to the proposed IEEE 754 

standard for binary floating-point arithmetic. See also 

8086, 8088, floating-point processor. 

8088 n. The microprocessor on which the original IBM 

PC was based. Released by Intel in 1978, the 8088 is identical 

to the 8086 but transfers information 8 bits at a time 

(through an 8-bit data bus) rather than 16 bits at a time 

(through a 16-bit data bus). See also 8086, bus. 

80-character line length n. A standard line length for 

text mode displays. This length, found in the earliest IBM 

PCs and in professional terminals of the 1970s and 1980s, 

is a legacy of the punched card and of mainframe operating 

systems in which each line in a file as displayed on a 

terminal appeared to the computer as a card in a deck. 

Graphical user interfaces support longer or shorter lines 

depending on the fonts chosen. A message composed with 

longer lines using a graphical e-mail program appears broken 

up and difficult to read when viewed by a user with 

only a terminal emulation program and a shell account. 

80x86 n. See 8086. 

82385 n. A cache controller chip by Intel that allows 

modified cache blocks to be restored to main memory in 

parallel with cache accesses by the CPU (or DMA). See 

also cache, central processing unit, controller, direct memory 

access. 

8.3 n. The standard format for filenames in MS-DOS/ 

Windows 3.x: a filename with eight or fewer characters, 

followed by a period (“dot”), followed by a three-character 

file extension. See also extension. Compare long filenames. 

8514/A n. A graphics adapter introduced by IBM in 

April 1987 and withdrawn in October 1991. The 8514/A 

was designed to increase the capability of the VGA 

adapter in some of IBM's PS/2 computers from a resolution 

of 640 by 480 pixels with 16 simultaneous colors to a 

resolution of 1024 by 768 pixels (almost quadrupling the 

amount of information displayed on the screen) with 256 

simultaneous colors. The 8514/A worked only in Micro 

Channel Architecture-based PS/2 computers, and it used 

the interlacing method for display, which can cause a perceptible 

flicker at higher resolutions. Therefore, it never 

gained widespread popularity; the SVGA (Super VGA) 

adapter prevailed because it was designed to work with the 

more prevalent ISA and EISA bus architectures. See also 

9 

EISA, interlacing, ISA, Micro Channel Architecture, noninterlaced, 

SVGA, VGA. 

88000 n. A reduced instruction set computing (RISC) 

chip set from Motorola, introduced in 1988 and based on 

the Harvard architecture. The 20-MHz 88000 set includes 

one 88100 CPU and at least two 88200 CMMUs (cache 

memory management units)—one for data memory and 

one for instruction memory. The 88100 RISC CPU 

includes both integer and floating-point processors and 

has thirty-two 32-bit general-purpose registers, 21 control 

registers, and 32-bit data paths and addresses. The 88100 

is capable of addressing 4 gigabytes of external data and 1 

gigabyte of 32-bit instructions in memory space. Up to 

four chip sets can be set up to work with the same memory 

in a multiprocessing configuration. See also central processing 

unit, floating-point processor, Harvard architecture, 

RISC. 

88100 n. See 88000. 

88200 n. See 88000. 

8-bit, 16-bit, 32-bit, 64-bit adj. 1. Capable of transferring 

8, 16, 32, or 64 bits, respectively, on data bus lines. 

For example, the IBM Micro Channel Architecture 

includes one or more 32-bit data buses with additional 

16-bit and 8-bit data lines. See also 16-bit machine, 32-bit 

machine, 64-bit machine, 8-bit machine. 2. Capable of 

transferring 8, 16, 32, or 64 bits, respectively, on the data 

path of a video adapter. An n-bit video adapter can display 

up to 2n colors. For example, an 8-bit video adapter is 

capable of displaying up to 256 colors; a 16-bit adapter 

can display up to 65,536 colors; and a 24-bit adapter can 

display over 16 million colors. (A 24-bit video adapter has 

a 32-bit data path, although the upper 8 bits are not used 

directly to generate color.) See also alpha channel. 

8-bit color n. A display setting that holds up to 256 specific 

color entries. Any color palette attached to a picture 

is by definition an 8-bit palette. 



an 8-bit machine either because its microprocessor operates 

internally on 8-bit words or because its data bus can 

transfer 8 bits at a time. The original IBM PC was based 

on a microprocessor (the 8088) that worked internally on 

16-bit words but transferred them 8 bits at a time. Such 

machines are generally called 8-bit machines because the 

size of the data bus limits the machine's overall speed. 

#

# 

8mm tape Å 

8mm tape n. A tape cartridge format used for data backups, 

similar to that used for some video cameras except 

that the tape is rated for data storage. The capacity is 5 GB 

(gigabytes) or more of (optionally compressed) data. 

8-N-1 n. Short for 8 bits, No parity, 1 stop bit. Typical 

default settings for serial communications, such as modem 

transmissions. 

/8 network n. IP address class C. This class has 126 networks 

available and more than sixteen million hosts available. 

See also host, IP address classes, network. 

9600 n. A modem with a maximum data transfer rate of 

9600 bps (bits per second). 

10 

99 or 9999 n. A number sometimes given special meaning 

in older programs—for example, as an end-of-file 

indicator or as an expiration date that actually meant “do 

not allow to expire.” Uncorrected programs may interpret 

that date as an end-of-file indicator or expiration date and 

cause problems. See also 1999 problem. 

9/9/99 n. See 99 or 9999. 

9-track n. A tape storage scheme that places data on nine 

separate parallel tracks (one track for each of 8 data bits of 

a byte and 1 parity bit) on 1/2-inch reel-to-reel magnetic 

tape. See also 7-track. 

Å n. See angstrom.

Å n. See angstrom. 

A or a n. See ampere. 

A: or a: n. In Windows and some other operating systems, 

the identifier used for the first, or primary, floppy disk 

drive. Unless otherwise specified by changing the CMOS 

startup instructions, this is the drive the operating system 

checks first for startup instructions. 

AAL n. See ATM Adaptation Layer. 

abandonware n. Discontinued video or computer games. 

Abandonware is often collected and played by computer 

game enthusiasts on refurbished systems or on PCs running 

emulator software. See also arcade game, emulator, 

MAME. 

ABC n. 1. Acronym for Atanasoff-Berry Computer. The 

first electronic digital computer, created by John Atanasoff 

and Clifford Berry of Iowa State University in 1942. 

2. Acronym for automatic brightness control. A circuit 

that changes the luminance of a monitor to compensate for 

ambient lighting conditions. 3. An imperative language 

and programming environment from CWI, Netherlands. 

This interactive, structured, high-level language is easy to 

learn and use. It is not a systems-programming language, 

but it is good for teaching or prototyping. 

Abeline n. A high-performance network developed by 

Qwest Communications, Nortel, and Cisco Systems to 

provide a backbone network for the Internet2 project. 

Abeline interconnects the gigaPoPs created by the 

Internet2 project and its member institutions, enabling 

connected institutions to develop advanced network services 

and applications. See also gigaPoP, Internet2. 

abend or ABEND n. Short for abnormal end. The premature 

ending of a program because of program error or system 

failure. See also abort, crash1 . 

ABI n. See application binary interface. 

ABIOS n. Acronym for Advanced Basic Input/Output 

System. A set of input/output service routines designed to 

support multitasking and protected mode that were built 

into IBM PS/2 PCs. See also BIOS. 

A 

11 

abnormal end n. See abend. 

A-Bone n. The Asian-Pacific Internet backbone that connects 

users in East and South Asian countries and Australia 

at T1 speeds or better, without the need to send data 

through North American facilities. The A-Bone was 

launched by Asia Internet Holding Co., Ltd. in 1996. By 

1998, a total of 13 countries were connected to the A- 

Bone’s hub in Japan. A-Bone also includes links to both 

Europe and the United States. See also backbone. 

abort vb. To terminate abruptly, often used in reference to 

a program or procedure in progress. 

absolute address n. A means of specifying a precise 

memory location in a program by using its address (number) 

rather than an expression to calculate the address. 

Also called: direct address, machine address, real address. 

See also absolute coding. Compare relative address, virtual 

address. 

absolute coding n. Program code that uses absolute 

addressing rather than indirect addressing. See also absolute 

address, relative address. 

absolute coordinates n. Coordinates that are defined in 

terms of their distance from the origin, the point where the 

axes intersect. Graphs and computer graphics use absolute 

coordinates to locate points on a chart or display grid—for 

example, points in relation to the x- and y-axes on a graph 

or the x-, y-, and z-axes used to specify the location of a 

three-dimensional graphic object on the screen. See the 

illustration. See also Cartesian coordinates. 

x-axis 

Origin 

f0agn01.eps 

Absolute coordinates. 

y-axis 

Point at absolute 

coordinates (3,2) 

A

A absolute link abstract machine 

absolute link n. A hyperlink to the exact location of a file 

on a file server, the World Wide Web, or a company intranet. 

Absolute links use an exact path; if you move the file 

containing the hyperlink or a hyperlink destination, the 

link breaks. 

absolute path n. A path to a file that begins with the 

drive identifier and root directory or with a network share 

and ends with the complete file name (for example, 

C:\docs\work\contract.txt or \\netshare\docs\work\contract.txt). 

Also called: full path. See also path (definition 

2). Compare relative path. 

absolute pointing device n. A mechanical or physical 

pointing device whose location is associated with the position 

of the on-screen cursor. For example, if the user of a 

graphics tablet places the pen on the upper right corner of 

the tablet, the cursor moves to the upper right corner of the 

screen or on-screen window associated with the pen. See 

also absolute coordinates. Compare relative pointing device. 

absolute URL n. The full Internet address of a page or 

other World Wide Web resource. The absolute URL 

includes a protocol, such as “http,” network location, and 

optional path and file name—for example, http:// 

example.microsoft.com/. 

absolute value n. The magnitude of a number, irrespective 

of its sign (+ or –). An absolute value is always greater 

than or equal to zero. For example, 10 is the absolute value 

of 10 and of –10. Programming languages and spreadsheet 

programs commonly include functions that return the 

absolute value of a number. 

abstract1 adj. 1. In character recognition systems, of, 

pertaining to, or being a type of symbol that, unlike a letter 

or numeral, has no intrinsic meaning and must be defined 

before it can be interpreted. 2. In programming, of, pertaining 

to, or being a data type defined by the operations 

that can be performed on objects of that type rather than 

by the properties of the objects themselves. See also 

abstract data type. 

abstract2 n. In information processing and library science, 

a summary typically consisting of a paragraph or a 

few paragraphs at the beginning of an investigative document, 

such as a scientific paper. 

abstract class n. 1. In object-oriented programming, a 

class in which no objects can be created. It is, however, 

used to defined subclasses, and objects are created from 

the subclasses. See also object (definition 2). Compare 

concrete class. 2. In Java programming, a class that con- 

12 

tains one or more abstract methods and therefore can 

never be instantiated. Abstract classes are defined so that 

other classes can extend them and make them concrete by 

implementing the abstract methods. See also class, instantiate, 

Java, method, object (definition 2). Compare concrete 

class. 

abstract data type n. In programming, a data set 

defined by the programmer in terms of the information it 

can contain and the operations that can be performed 

with it. An abstract data type is more generalized than a 

data type constrained by the properties of the objects it 

contains—for example, the data type “pet” is more generalized 

than the data types “pet dog,” “pet bird,” and “pet 

fish.” The standard example used in illustrating an abstract 

data type is the stack, a small portion of memory used to 

store information, generally on a temporary basis. As an 

abstract data type, the stack is simply a structure onto 

which values can be pushed (added) and from which they 

can be popped (removed). The type of value, such as integer, 

is irrelevant to the definition.The way in which the 

program performs operations on abstract data types is 

encapsulated, or hidden, from the rest of the program. 

Encapsulation enables the programmer to change the definition 

of the data type or its operations without introducing 

errors to the existing code that uses the abstract data type. 

Abstract data types represent an intermediate step between 

traditional programming and object-oriented programming. 

See also data type, object-oriented programming. 

abstraction n. 1. Broadly, the use of specialized software, 

such as an application programming interface (API), 

as a means of shielding software from device dependencies 

or the complexities of underlying software. For 

instance, hardware abstraction enables programs to focus 

on a task, such as communications, instead of on individual 

differences between communications devices. 2. In 

object-oriented programming, the process of reducing an 

object to its essence so that only the necessary elements 

are represented. Abstraction defines an object in terms of 

its properties (attributes), behaviors (functionality), and 

interface (means of communicating with other objects). 

abstract machine n. A design for a processor that is not 

meant for implementation but that represents a model for 

processing abstract machine language. Its instruction set 

can use instructions that more closely resemble the compiled 

language than the instructions used by an actual 

computer. It can also be used to make the implementation 

of the language more portable to other platforms.

abstract machine language ACCESS.bus 

abstract machine language n. 1. An intermediate programming 

language used by an interpreter or compiler. 

2. See pseudocode (definition 1). 

abstract syntax n. A data structure description that is 

independent of hardware structures and encodings. 

Abstract Syntax Notation One n. The ISO standard 

notation for independent specification of data types and 

structures for syntax conversion. Acronym: ASN.1.See 

also data type, ISO, syntax. 

abstract syntax tree n. A treelike representation of programs 

used in many integrated programming environments 

and structure-oriented editors. 

Abstract Window Toolkit n. A library of Java GUIs 

(graphical user interfaces) that provides the connections 

between a Java application and the native GUI of the computer 

on which the application runs. Also called: AWT. 

A/B switch box n. A switch box with two outputs. By 

flipping the switch, the user can select which to use. See 

also switch (definition 1), switch box. 

AC n. See alternating current. 

AC adapter n. An external power supply that converts 

from a 110 VAC or 220 VAC domestic electric supply 

(“house current” or “main power”) to low-voltage DC, 

which is required to operate solid-state electronic equipment 

(such as a laptop computer) that does not include an 

internal power supply. 

Accelerated Graphics Port n. See AGP. 

accelerator n. 1. In applications, a key or key combination 

used to perform a defined function. Also called: shortcut 

key. 2. In hardware, a device that speeds or enhances the 

operation of one or more subsystems, leading to improved 

program performance. See also accelerator card, Windows-based 

accelerator. 

accelerator board n. See accelerator card. 

accelerator card n. A printed circuit board that replaces 

or augments the computer’s main microprocessor, resulting 

in faster performance. Also called: accelerator board. 

See also expansion board, graphics accelerator. 

acceptable use policy n. A statement issued by an ISP 

(Internet service provider) or an online information service 

that indicates what activities users may or may not 

engage in while logged into the service. For example, 

some providers prohibit users from engaging in commercial 

activity on the network. Acronym: AUP.See also ISP, 

online information service. 

13 

acceptance test n. A formal evaluation of a hardware 

product performed by the customer, usually at the factory, 

to verify that the product is performing according to 

specifications. 

access1 n. 1. The act of reading data from or writing data 

to memory. 2. Connection to the Internet or other network 

or system. 

access2 vb. To gain entry to memory in order to read or 

write data. 

Access n. Microsoft’s relational database–management 

software for the Windows desktop platform. Part of the 

family of Microsoft Office products, Access in its most 

recent version (Access 2002) supports Web technology for 

building, managing, and sharing data. Access 2002 also 

includes new and improved tools for accessing and viewing 

information and offers integration with Microsoft’s 

BackOffice database product, SQL Server. See also 

Office. 

access arm n. A mechanical arm that moves the read/ 

write head(s) over the surface of a disk in a disk drive. See 

the illustration. Also called: head arm. 

f0agn02.eps 

Access arm. 

Access arm 

ACCESS.bus n. A bidirectional bus for connecting 

peripherals to a PC. The ACCESS.bus can connect up to 

125 low-speed peripherals, such as printers, modems, mice, 

and keyboards, to the system through a single, general-purpose 

port. Peripherals that support the ACCESS.bus provide 

a connector or port connection that is similar to a 

phone-jack connector and are daisy-chained together. 

However, the PC communicates directly with each peripheral 

and vice versa. Connecting an ACCESS.bus device 

(for example, a printer) to a system results in the system 

A

A access code accounting machine 

automatically identifying and configuring it for optimum 

performance. Peripherals can be connected while the computer 

is running (hot plugging) and are automatically 

assigned a unique address (auto-addressing). Developed 

from the l2 architecture designed jointly by Philips and 

Digital Equipment Corporation, the ACCESS.bus specification 

is controlled by the ACCESS.bus Industry Group 

and competes with Intel’s USB. See also bidirectional, 

bus, daisy chain1 , hot plugging, input/output port, peripheral. 

Compare USB. 

access code n. See password. 

access control n. The mechanisms for limiting access to 

certain items of information or to certain controls based on 

users’ identities and their membership in various predefined 

groups. Access control is typically used by system 

administrators for controlling user access to network 

resources, such as servers, directories, and files. See also 

access privileges, system administrator. 

access control list n. A list associated with a file or a 

resource that contains information about which users or 

groups have permission to access a resource or modify the 

file. Acronym: ACL. 

accessibility n. A quality of software, hardware, or a 

complete computer system that makes it usable by people 

with one or more physical disabilities, such as restricted 

mobility, blindness, or deafness. 

accessibility aids n. Utilities that make computers easier 

to use for people with disabilities. Examples of accessibility 

aids include screen readers, speech recognition programs, 

and on-screen keyboards. 

access key n. A key combination, such as ALT+F, that 

moves the focus to a menu, a command, or a control, without 

using the mouse. 

access mechanism n. 1. The disk drive components that 

move the read/write head(s) to the proper track of a magnetic 

disk or optical disc. See also disk controller. 2. A circuit 

that allows one part of a computer system to send 

signals to another part. 3. In programming, the means by 

which an application can read from or write to a resource. 

Also called: access method. 

access method n. See access mechanism. 

access number n. The telephone number used by a subscriber 

to gain access to an online service. 

accessory n. See peripheral. 

14 

access path n. See search path. 

access permission n. See permission. 

access point n. In a wireless LAN (local area network), 

a transceiver that connects the LAN to a wired network. 

See also wireless LAN. 

access privileges n. The type of operations permitted a 

given user for a certain system resource on a network or a 

file server. A variety of operations, such as the ability to 

access a server, view the contents of a directory, open or 

transfer files, and create, modify, or delete files or directories, 

can be allowed or disallowed by the system administrator. 

Assigning access privileges to users helps the system 

administrator to maintain security on the system, as well as 

the privacy of confidential information, and to allocate system 

resources, such as disk space. Also called: access 

rights. See also file protection, file server, permission, system 

administrator, write access. 

access provider n. See ISP. 

access rights n. See access privileges. 

access speed n. See access time. 

access time n. 1. The amount of time it takes for data to 

be delivered from memory to the processor after the 

address for the data has been selected. 2. The time needed 

for a read/write head in a disk drive to locate a track on a 

disk. Access time is usually measured in milliseconds and 

is used as a performance measure for hard disks and CD- 

ROM drives. See also read/write head, seek time, settling 

time, wait state. Compare cycle time. 

account n. 1. A record-keeping arrangement used by the 

vendor of an online service to identify a subscriber and to 

maintain a record of customer usage for billing purposes. 

2. The record-keeping mechanism used by networks and 

multiuser operating systems for keeping track of authorized 

users. Network accounts are created by network administrators 

and are used both to validate users and to administer 

policies—for example, permissions—related to each user. 

accounting file n. A file generated by a printer controller 

that keeps track of the number of pages printed per job as 

well as the user that requested the print job. 

accounting machine n. 1. One of the earliest applications 

of automatic data processing, used in business 

accounting primarily during the 1940s and 1950s. The 

first accounting machines were nonelectronic and used 

punched cards and wires arranged in plugboard panels. 

2. A computer in which an accounting software package

account lockout Acrobat Reader 

starts up whenever the machine is turned on, the computer 

thus becoming a dedicated machine with accounting as its 

sole function. 

account lockout n. A security feature in Windows XP 

that locks a user account if a number of failed logon 

attempts occur within a specified amount of time, based 

on security policy lockout settings. Locked accounts cannot 

log on. 

account name n. The part of an e-mail address that identifies 

a user or an account on an e-mail system. An e-mail 

address on the Internet typically consists of an account 

name, followed by the @ (at) symbol, a host name, and a 

domain name. See also account (definition 2), domain 

name, e-mail address. 

account policy n. On local area networks and multi-user 

operating systems, a set of rules governing whether a new 

user is allowed access to the system and whether an existing 

user’s rights are expanded to include additional system 

resources. An account policy also generally states the 

rules with which the user must comply while using the 

system in order to maintain access privileges. 

ACCU n. See Association of C and C++ Users. 

accumulator n. A register used for logic or arithmetic, 

usually to count items or accumulate a sum. See also 

register. 

accuracy n. The degree to which the result of a calculation 

or measurement approximates the true value. Compare 

precision (definition 1). 

ACID n. Short for Atomicity, Consistency, Isolation, 

Durability. The four essential properties of an electronic 

transaction. Atomicity requires that a transaction be fully 

completed or else fully canceled. Consistency requires 

that resources used are transformed from one consistent 

state to another. Isolation requires all transactions to be 

independent of each other. Durability requires that the 

completed transaction be permanent, including survival 

through system failure. See also transaction. 

ACIS n. Acronym for Andy, Charles, Ian’s System. An 

object-oriented geometric modeling toolkit owned by Spatial 

Technology. Designed for use as a “geometry engine” 

within 3-D modeling applications, ACIS provides an open 

architecture framework for wire-frame, surface, and solid 

modeling from a common, unified data structure. ACIS is 

generally considered the de facto standard for solids modeling 

in the CAM/CAE industries. 

15 

ACK n. Short for acknowledgment. A message sent by the 

receiving unit to the sending station or computer indicating 

either that the unit is ready to receive transmission or 

that a transmission was received without error. Compare 

NAK. 

ACL n. See access control list. 

ACM n. See Association for Computing Machinery. 

acoustic coupler n. An archaic device once used in computer 

communications. The coupler was a cradle-like 

instrument into which the headset of a telephone was 

placed. Its function was somewhat similar to the job now 

done by modems. 

ACPI n. Acronym for Advanced Configuration and Power 

Interface. An open specification developed jointly by 

Microsoft, Intel, and Toshiba for managing power consumption 

on mobile, desktop, and server computers. 

Unlike earlier, BIOS-based management solutions, ACPI 

provides a means of integrating power management 

through all parts of a PC, including applications, hardware, 

and the operating system (OS). ACPI enables an OS to 

control a computer’s power state in response to input from 

the user, from an application, or from a device driver. For 

example, an ACPI-enabled OS could turn a CD-ROM 

drive, a printer, or even a television on or off as needed. 

ACPI is part of the industry-wide OnNow initiative that 

allows system manufacturers to deliver computers that start 

at the touch of a keyboard. See also plug and play, power 

management. Compare Advanced Power Management. 

Acrobat n. A program from Adobe Systems, Inc., that 

converts a fully formatted document created on a Windows, 

Macintosh, MS-DOS, or UNIX platform into a Portable 

Document Format (PDF) file that can be viewed on 

several different platforms. Acrobat enables users to send 

documents that contain distinctive typefaces, color, graphics, 

and photographs electronically to recipients, regardless 

of the application used to create the originals. 

Recipients need the Acrobat Reader, which is available 

free, to view the files. Depending on version and platform, 

it also includes tools such as Distiller (which creates PDF 

files from PostScript files), Exchange (which is used for 

links, annotations, and security-related matters), and PDF 

Writer (which creates PDF files from files created with 

business software). 

Acrobat Reader n. A free program produced and distributed 

by Adobe Systems, Inc., for displaying and printing 

documents that are in Portable Document Format (PDF). 

A

A ACSE Active Directory Services Interface 

ACSE n. See Association Control Service Element. 

action query n. In Microsoft Access, a query that copies 

or changes data. Action queries include append, delete, 

make-table, and update queries. They are identified by an 

exclamation point (!) next to their name in the Database 

window. 

action statement n. See statement. 

activation n. In Sun Microsystem’s J2EE network platform, 

the process of transferring an enterprise java bean 

(EJB) from secondary storage to memory. See also EJB, 

J2EE. Compare passivation. 

activation record n. A data structure that represents the 

state of some construct (such as a procedure, a function, a 

block, an expression, or a module) of a running program. 

An activation record is useful for the run-time management 

of both data and sequencing. See also data structure. 

active adj. Pertaining to the device, program, file, or portion 

of the screen that is currently operational or subject to 

command operations. Usually the cursor or a highlighted 

section shows the active element on the display screen. 

Active Accessibility n. A Microsoft initiative, introduced 

in 1997, that consists of program files and conventions 

that make it easier for software developers to 

integrate accessibility aids, such as screen magnifiers or 

text-to-voice converters, into their application’s user interface 

to make software easier for users with limited physical 

abilities to use. Active Accessibility is based on COM 

technologies and is supported by Windows 9x, Windows 

XP, Windows NT 4.0 and above, Internet Explorer 3 and 

above, and Office 2000 and above. Acronym: MSAA.Also 

called: Microsoft Active Accessibility. 

active cell n. The highlighted cell on a spreadsheet display 

that is the current focus of operation. Also called: 

current cell, selected cell. See also range. 

Active Channel n. A Web site described by a Channel 

Definition Format (CDF) file. Developers can use Active 

Channels to automatically download content to a user on a 

subscription basis, to send content to users on a regular 

schedule, to deliver personalized content to individual 

users, and to provide content to a Windows screen saver. 

Active Channels were introduced in Microsoft Internet 

Explorer 4 and can be used to deliver information through 

either the Internet or an intranet. See also pull, webcasting. 

16 

Active Client n. The client-side set of technologies in 

Microsoft’s Active Platform for Web-oriented, crossplatform 

distributed computing. The chief features of the 

Active Client include support for HTML and dynamic 

HTML, language-independent scripting, Java applets, 

and ActiveX objects. Active Client is operating system– 

independent, so it runs on multiple platforms, including 

Microsoft Windows, UNIX, and Apple Macintosh. See 

also Active Platform, Active Server. 

active content n. Material on a Web page that changes 

on the screen with time or in response to user action. 

Active content is implemented through ActiveX controls. 

See also ActiveX control. 

Active data object n. An application programming 

interface (API) developed by Microsoft for applications 

that access databases. ADO is an easy-to-use interface to 

OLE Database (OLE DB), an API that accesses the data 

directly from a database. Also called: ActiveX data object. 

Active Desktop n. The feature introduced with 

Microsoft’s Internet Explorer 4 that enables end users to 

display active—that is, updateable, customizable—HTML 

content on the Windows desktop. Active content includes 

such items as channels, Web pages, ActiveX controls, and 

Java applets. See also Active Channel, ActiveX, HTML, 

Internet Explorer, Java. 

Active Directory n. A Microsoft technology, part of the 

Active Platform, that is designed to enable applications to 

find, use, and manage directory resources (for example, 

user names, network printers, and permissions) in a distributed 

computing environment. Distributed environments 

are usually heterogeneous collections of networks 

that often run proprietary directory services from different 

providers. To simplify directory-related activities associated 

with locating and administering network users and 

resources, Active Directory presents applications with a 

single set of interfaces that eliminates the need to deal 

with differences between and among these proprietary services. 

Active Directory is a component of the Windows 

Open Services Architecture (WOSA). See also directory 

service, WOSA. 

Active Directory Services Interface n. An administrative 

tool known as a Microsoft Management Console 

(MMC) snap-in that allows administrators to manage 

objects in the domain. Acronym: ADSI.

active file ActiveStore 

active file n. The file affected by a current command— 

typically a data file. 

Active Framework for Data Warehousing n. A data 

warehousing solution developed by Microsoft and Texas 

Instruments that represents Microsoft’s standard for managing 

metadata. Acronym: AFDW.See also ActiveX, 

metadata. 

active hub n. 1. The central computer that regenerates 

and retransmits all signals in an active star network. See 

also active star. 2. A type of hub used on ARCnet networks 

that both regenerates (boosts) signals and passes 

them along. Compare intelligent hub, passive hub. 

active-matrix display n. A liquid crystal display (LCD) 

made from a large array of liquid crystal cells using 

active-matrix technology. The active matrix is a method of 

addressing an array of simple LC cells—one cell per pixel. 

In its simplest form there is one thin-film transistor (TFT) 

for each cell. Voltage applied selectively to these cells produces 

the viewable image. Active-matrix displays are 

often used in laptop and notebook computers because of 

their shallow depth and are notable for their high-quality 

color displays, which are viewable from wider angles than 

images produced by most passive-matrix displays. Also 

called: TFT, TFT display, TFT LCD. See also liquid crystal 

display, TFT. Compare passive-matrix display. 

ActiveMovie n. Former name for the DirectX component 

now known as DirectShow. Also called: DirectShow. See 

also DirectX. 

Active Platform n. A Microsoft development platform 

that offers a standardized approach to incorporating Internet 

and distributed computing technologies in client/server 

applications. Microsoft Windows 9x, Microsoft Windows 

NT, and Microsoft Internet Explorer 4.x (and later) provide 

the basis for the Active Platform. On the client side, 

users are given a consistent interface that enables them to 

easily access both local and remote information. On the 

server side, developers can take advantage of the tools and 

technologies that span the client and the server. Active 

Platform supports development of the modular object-oriented 

programs known as component software and allows 

creation of cross-platform applications that can run on 

multiple chips and operating systems. Active Platform 

includes support for HTML and the creation of small programs 

in several languages through client-side scripting. 

See also Active Desktop, Active Server, ActiveX. 

17 

active program n. The program currently in control of a 

microprocessor. 

Active Server n. The server-based component of 

Microsoft’s Active Platform. Comprised of a set of technologies 

that includes DCOM (distributed component 

object model), Active Server Pages, Microsoft Transaction 

Server, and message queues, Active Server provides support 

for developing component-based, scalable, high-performance 

Web applications on Microsoft Windows NT 

servers. Active Server is designed to allow developers to 

concentrate on creating Internet and intranet software in a 

variety of languages without having to focus on the intricacy 

of the network itself. See also Active Desktop, Active 

Platform, Active Server Pages, ActiveX. 

Active Server Pages n. A Web-oriented technology 

developed by Microsoft that is designed to enable serverside 

(as opposed to client-side) scripting. Active Server 

Pages are text files that can contain not only text and 

HTML tags as in standard Web documents, but also commands 

written in a scripting language (such as VBScript 

or JavaScript) that can be carried out on the server. This 

server-side work enables a Web author to add interactivity 

to a document or to customize the viewing or delivery of 

information to the client without worrying about the platform 

the client is running. All Active Server Pages are 

saved with an .asp extension and can be accessed like standard 

URLs through a Web browser, such as Microsoft 

Internet Explorer or Netscape Navigator. When an Active 

Server Page is requested by a browser, the server carries 

out any script commands embedded in the page, generates 

an HTML document, and sends the document back to the 

browser for display on the requesting (client) computer. 

Active Server Pages can also be enhanced and extended 

with ActiveX components. Acronym: ASP.See also Active 

Server, ActiveX. 

active star n. A form of the star network topology in 

which the central computer actively regenerates and 

retransmits all signals. See also star network. 

ActiveStore n. A Microsoft initiative, introduced in 1998, 

for supporting integration of applications used in retail 

environments regardless of the developing vendor. Active- 

Store provides a common user interface, base system services 

(such as security and crash recovery), common 

access to data across applications, and communication 

between applications. 

A

A ActiveSync adapter card 

ActiveSync n. A Microsoft program that manages synchronization 

of information, including e-mail, schedules, 

and application files, between a handheld PC and a desktop 

computer. 

active vision n. A branch of computer vision research 

that believes robotic vision problems can be solved by 

allowing a robot to collect and analyze a sequence of 

images dynamically from changing viewpoints. Not 

unlike human or animal vision, active vision uses the 

information derived from multiple viewpoints to gain a 

greater depth of perception, resolve haziness, and establish 

relationships between the visual representation of an 

action and the action itself. Active vision systems may be 

characterized by simple image-processing algorithms, little 

or no calibration, and fast real-time hardware. See also 

artificial intelligence, computer vision, robotics. 

active window n. In an environment capable of displaying 

multiple on-screen windows, the window containing 

the display or document that will be affected by current 

cursor movements, commands, and text entry. See also 

graphical user interface. Compare inactive window. 

ActiveX n. A set of technologies that enables software 

components to interact with one another in a networked 

environment, regardless of the language in which the components 

were created. ActiveX, which was developed by 

Microsoft in the mid 1990s and is currently administered 

by the Open Group, is built on Microsoft’s Component 

Object Model (COM). Currently, ActiveX is used primarily 

to develop interactive content for the World Wide 

Web, although it can be used in desktop applications and 

other programs. ActiveX controls can be embedded in 

Web pages to produce animation and other multimedia 

effects, interactive objects, and sophisticated applications. 

See also ActiveX control, COM. Compare applet, plug-in 


ActiveX control n. A reusable software component based 

on Microsoft’s ActiveX technology that is used to add 

interactivity and more functionality, such as animation or 

a popup menu, to a Web page, applications, and software 

development tools. An ActiveX control can be written in 

any of a number of languages, including Java, C++, and 

Visual Basic. See also ActiveX. Compare helper program. 

activity ratio n. The number of records in use compared 

with the total number of records in a database file. See 

also database, record1 . 

18 

ACTOR n. An object-oriented language developed by The 

Whitewater Group, Ltd., designed primarily to facilitate 

Microsoft Windows programming. See also object-oriented 

programming. 

actuator n. A disk drive mechanism for moving the read/ 

write head(s) to the location of the desired track on a disk. 

See the illustration. See also disk drive, stepper motor, 

voice coil. 

f0agn03.eps 

Actuator. 

Actuator 

Ada n. A high-level programming language designed 

under the direction of the U.S. Department of Defense 

(DoD) in the late 1970s and intended to be the primary 

language for DoD software development. Originally based 

on Pascal, Ada supports real-time operations and multitasking. 

The language was named after Augusta Ada 

Byron, who assisted Charles Babbage in developing programs 

for his Analytical Engine, the first mechanical computer, 

in the nineteenth century. See also multitasking, 

Pascal, real-time. 

adapter or adaptor n. A printed circuit board that 

enables a personal computer to use a peripheral device, 

such as a CD-ROM drive, modem, or joystick, for which it 

does not already have the necessary connections, ports, or 

circuit boards. Commonly, a single adapter card can have 

more than one adapter on it. Also called: interface card. 

See also controller, expansion board, network adapter, 

port1 , video adapter. 

adapter card or adaptor card n. See adapter.

adaptive answering address mask 

adaptive answering n. The ability of a modem to detect 

whether an incoming call is a fax or a data transmission 

and respond accordingly. See also modem. 

adaptive delta pulse code modulation n. A class of 

compression encoding and decoding algorithms used in 

audio compression and other data compression applications. 

These algorithms store digitally sampled signals as a 

series of changes in value, adapting the range of the 

change with each sample as needed, thus increasing the 

effective bit resolution of the data. Acronym: ADPCM.See 

also pulse code modulation. Compare adaptive differential 

pulse code modulation. 

adaptive differential pulse code modulation n. A digital 

audio compression algorithm that stores a sample as 

the difference between a linear combination of previous 

samples and the actual sample, rather than the measurement 

itself. The linear combination formula is modified 

every few samples to minimize the dynamic range of the 

output signal, resulting in efficient storage. See also pulse 

code modulation. Compare adaptive delta pulse code 

modulation. 

adaptive load balancing n. See load balancing. 

adaptive routing n. See dynamic routing. 

adaptive system n. An artificial intelligence system that 

is capable of altering its behavior based on certain features 

of its experience or environment. See also expert system. 

ADB n. See Apple Desktop Bus. 

ADC n. See analog-to-digital converter. 

A-D converter n. See analog-to-digital converter. 

adder n. 1. A component of the CPU (central processing 

unit) that adds two numbers sent to it by processing 

instructions. See also central processing unit. 2. A circuit 

that sums the amplitudes, or strength, of two input signals. 

See also full adder, half adder. 

add-in n. See add-on. 

addition record n. 1. A file that describes new record 

entries (such as a new customer, employee, or product) in 

a database so that they can later be scrutinized and posted. 

2. A record in a change file specifying a new entry. See 

also change file. 

add-on n. 1. A hardware device, such as an expansion 

board or chip, that can be added to a computer to expand 

its capabilities. Also called: add-in. See also open archi- 

19 

tecture (definition 2). 2. A supplemental program that can 

extend the capabilities of an application program. See also 

utility program. 

address1 n. 1. A number specifying a location in memory 

where data is stored. See also absolute address, address 

space, physical address, virtual address. 2. A name or 

token specifying a particular computer or site on the Internet 

or other network. 3. A code used to specify an e-mail 

destination. 

address2 vb. To reference a particular storage location. 

addressable cursor n. A cursor programmed so that it 

can be moved to any location on the screen, by means of 

the keyboard or a mouse. 

address book n. 1. In an e-mail program, a reference section 

listing e-mail addresses and individuals’ names. 2. As 

a Web page, an informal e-mail or URL phone book. 

address bus n. A bus consisting of 20 to 64 separate 

hardware lines that is used to carry the signals specifying 

memory locations for data. See also bus. 

address classes n. Predefined groupings of Internet 

addresses with each class defining networks of a certain 

size. The range of numbers that can be assigned for the 

first octet in the IP address is based on the address class. 

Class A networks (values 1 to 126) are the largest, with 

more than 16 million hosts per network. Class B networks 

(128 to 191) have up to 65,534 hosts per network, and 

Class C networks (192 to 223) can have up to 254 hosts 

per network. 

address decoder n. An electronic device that converts a 

numeric address to the electrical signals needed to select a 

specific memory location on one or more RAM chips. 

addressing n. The process of assigning or referring to an 

address. In programming, the address is typically a value 

specifying a memory location. See also address1 . 

address mapping table n. A table used by routers or 

DNS (Domain Name System) servers to obtain the corresponding 

IP (Internet Protocol) address of a text name of a 

computer resource, such as the name of a host computer 

on the Internet. Acronym: AMT.See also DNS server, IP 

address, router. 

address mark n. See index mark. 

address mask n. A number that, when compared by the 

computer with a network address number, will block out 

A

A address mode Advanced Digital Network 

all but the necessary information. For example, in a network 

that uses XXX.XXX.XXX.YYY and where all computers 

within the network use the same first address 

numbers, the mask will block out XXX.XXX.XXX and 

use only the significant numbers in the address, YYY. See 

also address1 (definition 2). 

address mode n. The method used to indicate an address 

in memory. See also absolute address, indexed address, 

paged address, relative address. 

address modification n. The process of updating an 

address of a location in memory during computation. 

address munging n. The practice of modifying an 

e-mail address in posts to newsgroups or other Internet 

forums to foil computer programs that gather e-mail 

addresses. The host name in an e-mail address is altered 

to create a fictitious address in such a way that a human 

can still easily determine the correct address. For example, 

a person with an e-mail address of Jane@myispoffersusersfreeemail.com 

could modify, or “mung,” her address 

to read Jane@remove-this-to-reply-myispoffersusersfreeemail.com. 

Address munging is generally used to prevent 

delivery of unsolicited junk e-mail or spam. Also 

called: munging. See also address1 (definition 2), host 

name, mung, spam. 

address register n. A register (a high-speed memory circuit) 

that holds an address where specific data can be 

found for the transfer of information. See also register. 

address resolution n. The identification of a computer’s 

IP (Internet Protocol) address by finding the corresponding 

match in an address mapping table. See also address 

mapping table. 

Address Resolution Protocol n. See ARP. 

address space n. The total range of memory locations 

addressable by a computer. 

address translation n. The process of converting one 

kind of address to another, such as a virtual address to a 

physical address. 

ad-hoc network n. A temporary network formed by communicating 

stations or computers in a wireless LAN. See 

also wireless LAN. 

ADJ n. Short for adjacent. A Boolean qualifier to indicate 

cases where two instances are adjacent to each other. In 

the case of a search string, “Microsoft ADJ Word” would 

20 

return only instances where “Microsoft” and “Word” are 

adjacent in the string. 

administrative alerts n. Alerts that relate to server and 

resource use. They notify users about problems in areas 

such as security and access, user sessions, server shutdown 

due to power loss (when an uninterruptible power 

supply is available), directory replication, and printing. 

When a computer generates an administrative alert, a message 

is sent to a predefined list of users and computers. 

See also Alerter service. 

ADN n. See Advanced Digital Network. 

ADO n. See Active data object. 

Adobe Type Manager n. Software from Adobe Systems, 

Inc., that manages PostScript fonts on a system. 

Acronym: ATM.See also PostScript. 

ADO.NET n. The suite of data access technologies 

included in the .NET Framework class libraries that provide 

access to relational data and XML. ADO.NET consists 

of classes that make up the DataSet (such as tables, 

rows, columns, relations, and so on), .NET Framework 

data providers, and custom type definitions (such as Sql- 

Types for SQL Server). 

ADP n. See data processing. 

ADPCM n. See adaptive delta pulse code modulation. 

ADSL n. Acronym for asymmetric digital subscriber line. 

Technology and equipment allowing high-speed digital 

communication, including video signals, across an ordinary 

twisted-pair copper phone line, with speeds up to 8 

Mbps (megabits per second) downstream (to the customer) 

and up to 640 Kbps (kilobits per second) upstream. 

ADSL access to the Internet is offered by some regional 

telephone companies, offering users faster connection 

times than those available through connections made over 

standard phone lines. Also called: asymmetric digital subscriber 

loop. Compare SDSL. 

Advanced Configuration and Power Interface n. See 

ACPI. 

Advanced Digital Network n. A dedicated line service 

capable of transmitting data, video, and other digital signals 

with exceptional reliability, offered as a premier service 

by communications companies. Usually Advanced 

Digital Network refers to speeds at or above 56 kilobits 

per second (Kbps). See also dedicated line.

Advanced Encryption Standard AFIPS 

Advanced Encryption Standard n. See AES. 

Advanced Interactive Executive n. See AIX. 

Advanced Mobile Phone Service n. See AMPS. 

Advanced Power Management n. An older power 

management technology used in mobile PCs before the 

implementation of Advanced Configuration and Power 

Interface (ACPI). Advanced Power Management is a software 

interface that functions between the BIOS powermanagement 

software that is specific to the hardware and 

a power-management policy driver that is run by the operating 

system. Acronym: APM. 

Advanced Program-to-Program Communication n. 

See APPC. 

Advanced Research Projects Agency Network n. See 

ARPANET. 

Advanced RISC n. Short for Advanced reduced instruction 

set computing. A specification for a RISC microchip 

architecture and system environment designed by MIPS 

Computer Systems to provide binary compatibility among 

software applications. See also RISC. 

Advanced RISC Computing Specification n. The minimum 

hardware requirements enabling a RISC-based system 

to comply with the Advanced Computing Environment 

standard. See also Advanced RISC. 

Advanced RISC Machines n. See ARM. 

Advanced SCSI Programming Interface n. An interface 

specification developed by Adaptec, Inc., for sending 

commands to SCSI host adapters. The interface provides 

an abstraction layer that insulates the programmer from 

considerations of the particular host adapter used. 

Acronym: ASPI.See also adapter, SCSI. 

Advanced Streaming Format n. An open file format 

specification for streaming multimedia files containing 

text, graphics, sound, video, and animation. Advanced 

Streaming Format (ASF) does not define the format for 

any media streams within the file. Rather, it defines a standardized, 

extensible file “container” that is not dependent 

on a particular operating system or communication protocol, 

or on a particular method (such as HTML or MPEG-4) 

used to compose the data stream in the file. An ASF file 

consists of three objects: a Header object containing information 

about the file itself, a Data object containing the 

media streams, and an optional Index object that can help 

support random access to data within the file. The ASF 

21 

specification has been submitted to the ISO (International 

Organization for Standardization) for consideration. 

Acronym: ASF.See also streaming. 

adventure game n. A role-playing computer game in 

which the player becomes a character in a narrative. In 

order to complete the game, the player must solve problems 

and avoid or overcome attacks and other forms of 

interference from the game’s environment and other characters. 

The first adventure game was called “Adventure.” 

It was developed in 1976 by Will Crowther of Bolt, 

Baranek & Newman. See also arcade game, computer 

game, role-playing game. 

AE n. Acronym for application entity. In the ISO/OSI 

reference model, one of the two software parties 

involved in a communications session. See also ISO/OSI 

reference model. 

A/E/C SYSTEMS conference n. Annual conference of 

the architecture, engineering, and construction industry. 

The conference promotes the exchange of information on 

new techniques and technologies used by these industries. 

.aero n. One of seven new top-level domain names 

approved in 2000 by the Internet Corporation for Assigned 

Names and Numbers (ICANN). .aero is meant for use 

with air-transport industry-related Web sites. The seven 

new domain names became available for use in the spring 

of 2001. 

AES n. Acronym for Advanced Encryption Standard. A 

cryptographic algorithm specified by the National Institute 

of Standards and Technology (NIST) to protect sensitive 

information. AES is specified in three key sizes: 128, 192, 

and 256 bits. AES replaces the 56-bit key Data Encryption 

Standard (DES), which was adopted in 1976. See also DES. 

AFC n. See Application Foundation Classes. 

AFDW n. See Active Framework for Data Warehousing. 

affinity n. For Network Load Balancing, the method used 

to associate client requests to cluster hosts. When no affinity 

is specified, all network requests are load balanced 

across the cluster without respect to their source. Affinity 

is implemented by directing all client requests from the 

same IP address to the same cluster host. See also client 

request, IP address. 

AFIPS n. Acronym for American Federation of Information 

Processing Societies. An organization formed in 1961 

for the advancement of computing and information-related 

A

A AFK AIX 

concerns. The U.S. representative of the International Federation 

of Information Processing, AFIPS was replaced by 

the Federation on Computing in the United States (FOCUS) 

in 1990. 

AFK adv. Acronym for away from keyboard. A phrase 

occasionally seen in live chat services on the Internet and 

online information services as an indication that one is 

momentarily unable to answer. See also chat1 (definition 1). 

AFP n. Acronym for AppleTalk Filing Protocol. A remote 

filing system protocol that provides a standard means for a 

workstation on an AppleTalk network to access and 

manipulate files on an AFP-implemented server. Also 

called: AppleShare File Server. 

AFS n. Acronym for Andrew File System. A distributed 

file system that allows clients and servers to share 

resources through local-area and wide-area networks. AFS 

is based on a distributed file system developed at Carnegie- 

Mellon University, and is named for the university’s 

founders—Andrew Carnegie and Andrew Mellon. AFS is 

now maintained and supplied by Transarc Corporation. See 

also distributed file system. 

agent n. 1. A program that performs a background task 

for a user and reports to the user when the task is done or 

some expected event has taken place. 2. A program that 

searches through archives or other repositories of information 

on a topic specified by the user. Agents of this sort are 

used most often on the Internet and are generally dedicated 

to searching a single type of information repository, 

such as postings on Usenet groups. Spiders are a type of 

agent used on the Internet. Also called: intelligent agent. 

See also spider. 3. In client/server applications, a process 

that mediates between the client and the server. 4. In Simple 

Network Management Protocol (SNMP), a program 

that monitors network traffic. See also SNMP. 

aggregated links n. See link aggregation. 

aggregation of links n. See link aggregation. 

AGP n. Acronym for Accelerated Graphics Port. A highperformance 

bus specification designed for fast, highquality 

display of 3-D and video images. Developed by 

Intel Corporation, AGP uses a dedicated point-to-point 

connection between the graphics controller and main system 

memory. This connection enables AGP-capable display 

adapters and compatible chip sets to transfer video 

data directly between system memory and adapter memory, 

to display images more quickly and smoothly than they can 

be displayed when the information must be transferred over 

22 

the system’s primary (PCI) bus. AGP also allows for storing 

complex image elements such as texture maps in system 

memory and thus reduces the need for large amounts 

of memory on the adapter itself. AGP runs at 66 MHz— 

twice as fast as the PCI bus—and can support data transfer 

speeds of up to 533 Mbps. See also PCI local bus. 

AH n. Authentication Header. A form of IP packet authentication 

included in the IPSec security standard. AH 

attaches a header to the packet with authentication information 

but does not encrypt the packet data, which allows 

its use in cases where encryption is not allowed. See also 

ESP, IPSec. 

AI n. See artificial intelligence. 

.aiff n. The file extension that identifies audio files in the 

sound format originally used on Apple and Silicon Graphics 

(SGI) computers. 

AIFF n. The sound format originally used on Apple and 

Silicon Graphics (SGI) computers. AIFF stores waveform 

files in an 8-bit monaural format. See also waveform. 

AIM n. Acronym for America Online Instant Messenger. 

A popular instant-messaging service provided for free by 

America Online. With the AIM service, instant messages 

can be sent over an Internet connection using the AIM software 

or directly from a Web browser using AIM Express. 

See also America Online, instant messaging. Compare 

ICQ, .NET Messenger Service, Yahoo! Messenger. 

AirPort n. A wireless connectivity option introduced by 

Apple in 1999. AirPort provides wireless network and 

Internet communications to all AirPort card–equipped 

Macintosh computers within 150 feet of an AirPort base 

station. AirPort was developed around the IEEE 802.11 

Direct Sequence Spectrum (DSSS) industry standard and 

is interoperable with other 802.11-based equipment. 

AirSnort n. A hacking tool used to gather and decrypt 

passwords in data sent over wireless networks. AirSnort 

monitors wireless transmissions and collects packets of 

data. When it has collected enough data, AirSnort is able 

to compute the encryption key used in the transmission. 

AirSnort takes advantage of security flaws in the Wired 

Equivalent Protocol (WEP) standard. See also password 

sniffing. 

AIX n. Acronym for Advanced Interactive Executive. A 

version of the UNIX operating system developed and 

maintained by IBM for its UNIX workstations and PCs.

alarm allocation 

alarm n. A visual or auditory signal from a computer 

alerting the user to an error or a hazardous situation. 

ALB n. See load balancing. 

alert n. 1. In many operating systems with GUIs (graphical 

user interfaces), an audible or visual alarm that signals 

an error or represents a warning of some sort. See also 

alert box. 2. In programming, an asynchronous notification 

sent by one thread to another. The alert interrupts the 

recipient thread at defined points in its execution and 

causes it to execute an asynchronous procedure call. See 

also asynchronous procedure call, thread (definition 1). 

alert box n. An on-screen box in a GUI (graphical user 

interface) that is used to deliver a message or warning. 

Compare dialog box. 

Alerter service n. A service used by the server and other 

services to notify selected users and computers of administrative 

alerts that occur on a computer. The Alerter service 

requires the Messenger service. See also administrative 

alerts, Messenger service, service. 

ALGOL n. Acronym for Algorithmic Language. The first 

structured procedural programming language, developed 

in the late 1950s and once widely used in Europe. 

algorithm n. A finite sequence of steps for solving a logical 

or mathematical problem or performing a task. 

algorithmic language n. A programming language, such 

as Ada, Basic, C, or Pascal, that uses algorithms for problem 

solving. 

Algorithmic Language n. See ALGOL. 

alias n. 1. An alternative label for some object, such as a 

file or data collection. 2. A name used to direct e-mail 

messages to a person or group of people on a network. 

3. A false signal that results from the digitization of an 

analog audio sample. 

aliasing n. In computer graphics, the jagged appearance 

of curves or diagonal lines on a display screen, which is 

caused by low screen resolution. See the illustration. 

f0agn04.eps 

Aliasing. The lower resolution of the image on the right 

reveals the aliasing effect. 

aliasing bug n. A class of subtle programming errors that 

can arise in code that performs dynamic allocation. If sev- 

23 

eral pointers address the same chunk of storage, the program 

may free the storage using one of the pointers but 

then attempt to use another one (an alias), which would no 

longer be pointing to the desired data. This bug is avoidable 

by the use of allocation strategies that never use more 

than one copy of a pointer to allocated core memory, or by 

the use of higher-level languages, such as LISP, which 

employ a garbage collection feature. Also called: stale 

pointer bug. See also alias, dynamic allocation, garbage 

collection. 

align vb. 1. In an application such as a word processor, to 

position lines of type relative to some point, such as the 

page margin. The most common types of alignment are 

left- and right-aligned and centered. See the illustration. 

2. To adjust some device to position it within specified tolerances, 

such as the read/write head relative to a track on a 

disk. 3. In data handling, to store multiple-byte data units 

so that the respective bytes fall in corresponding locations 

of memory. 

Left 

aligned 

to the 

left 

edge 

f0agn05.eps 

Align. 

Right 

aligned 

to the 

right 

edge 

Center 

centered 

around 

a 

midpoint 

Decimal 

.999 

10.99 

100.999 

10.999 

alignment n. The arrangement of objects in fixed or predetermined 

positions, rows, or columns. For example, the 

Macintosh Finder can do automatic alignment of icons in 

a folder or on the desktop. 

Allegro n. Ported to a number of operating systems, Allegro 

is a freeware library of functions for use in programming 

computer games and graphics programs. It is written 

for the DJGPP compiler in a mixture of C and assembly 

language. The most recent release version is 4.0.0. See 

also assembly language, DJGPP. 

allocate vb. To reserve a resource, such as sufficient 

memory, for use by a program. Compare deallocate. 

allocation n. In operating systems, the process of reserving 

memory for use by a program. 

A

A allocation block size alphanumeric sort 

allocation block size n. The size of an individual block 

on a storage medium, such as a hard drive, which is determined 

by factors such as total disk size and partitioning 

options. 

allocation unit n. See cluster. 

all points addressable n. The mode in computer graphics 

in which all pixels can be individually manipulated. 

Acronym: APA.See also graphics mode. 

ALOHA n. See ALOHAnet. 

ALOHAnet n. The first wireless packet-switched network 

and the first large network to be connected to the ARPA- 

NET. ALOHAnet was built in 1970 at the University of 

Hawaii by Norm Abramson and was funded by Larry 

Roberts. ALOHAnet enabled computers at seven campuses 

on four different islands to communicate bidirectionally 

with the central computer on Oahu using a 

network of radio transmitters. The ALOHA protocol was 

the basis for Ethernet. See also ARPANET, Ethernet, network. 

alpha1 adj. Of or pertaining to software that is ready for 

initial testing. 

alpha2 n. A software product that is under development 

and has enough functionality to begin testing. An alpha is 

usually unstable and does not have all the features or 

functionality that the released product is to have. Compare 

beta2 . 

Alpha n. 1. Digital Equipment Corporation’s (DEC) line 

of computers built on its 64-bit RISC-based microprocessor 

(Alphachip). 2. DEC’s internal name for a microprocessor 

product introduced in February 1992 as the 

DECchip 21064, which evolved into DEC’s current 

Alphachips. See also Alphachip, DECchip 21064. 

Alpha AXP adj. Of, pertaining to, or characteristic of 

Digital Equipment Corporation’s 64-bit RISC-based 

microprocessor technology implemented in its DECchip 

product. The designation AXP is used by DEC in its personal 

computer products to indicate that a product has a 

DECchip microprocessor. See also Alpha, DECchip 

21064, RISC. 

alphabet n. In communications and data processing, the 

subset of a complete character set, including letters, 

numerals, punctuation marks, and other common symbols 

as well as the codes used to represent them. See also 

ASCII, CCITT, character set, EBCDIC, ISO. 

24 

alpha blending n. In 3-D computer game rendering and 

other digital animation applications, a graphics technique 

for creating realistic transparent and semi-transparent 

images. Alpha blending combines a transparent source 

color with a translucent destination color to realistically 

simulate effects such as smoke, glass, and water. 

Alpha box n. A computer built around the DEC’s DECchip 

21064 processor (called Alpha internally at Digital 

Equipment Corporation). See also DECchip 21064. 

alpha channel n. The high-order 8 bits of a 32-bit graphics 

pixel used to manipulate the remaining 24 bits for purposes 

of coloring or masking. 

Alphachip n. A 64-bit RISC-based microprocessor from 

Digital Equipment Corporation. See also DECchip 21064, 

RISC. 

alphageometric adj. In reference to computer graphics, 

especially videotext and teletext systems, pertaining to or 

being a display method that uses codes for alphanumeric 

characters and creates graphics using geometric primitives. 

Shapes such as horizontal and vertical lines and corners 

are alphageometric. See also alphamosaic. 

alphamosaic adj. In reference to computer graphics, 

especially videotext and teletext systems, pertaining to or 

being a display technique that uses codes for alphanumeric 

characters and creates graphics using rectangular 

arrangements of elements to form a mosaic. See also 

alphageometric. 

alphanumeric adj. Consisting of letters or digits, or both, 

and sometimes including control characters, space characters, 

and other special characters. See also ASCII, character 

set, EBCDIC. 

alphanumeric display n. Electronic display on a wireless 

phone, pager, or handheld device capable of showing both 

text and numbers. 

alphanumeric display terminal n. A terminal capable of 

displaying characters but not graphics. 

alphanumeric messaging n. Ability to receive messages 

containing text and numbers on a pager or digital wireless 

phone. Also known as short message service (SMS). 

alphanumeric mode n. See text mode. 

alphanumeric sort n. A method of sorting data, such as a 

set of records, that typically uses the following order: 

punctuation marks, numerals, alphabetic characters (with

alpha test AMI BIOS 

capitals preceding lowercase letters), and any remaining 

symbols. 

alpha test n. The process of user testing that is carried 

out on a piece of alpha software. 

Altair 8800 n. A small computer introduced in 1975 by 

Micro Instrumentation Telemetry Systems (MITS) of New 

Mexico and sold primarily in kit form. The Altair was 

based on the 8-bit Intel 8080 microprocessor, had 256 

bytes of random access memory, received input through a 

bank of switches on the front panel, and displayed output 

via a row of light-emitting diodes. Although it was shortlived, 

the Altair is considered the first successful personal 

computer, which was then called a home computer. 

AltaVista n. A World Wide Web search site and portal 

hosted by Digital Equipment Corporation. See also portal. 

alternate circuit-switched voice/circuit-switched 

data n. A configuration option for ISDN B (bearer) channels 

that enables the digital transmission of either voice or 

data communications between two users for the duration 

of a call. Acronym: CSV/CSD.See also B channel, circuitswitched 

data, circuit-switched voice, ISDN. 

alternate key n. 1. Any candidate key in a database not 

designated as the primary key. 2. See Alt key. 

alternating current n. Electric current that reverses its 

direction of flow (polarity) periodically according to a frequency 

measured in hertz, or cycles per second. 

Acronym: AC.Compare direct current. 

Alt key n. A key included on PC and other standard keyboards 

that is used in conjunction with another key to produce 

some special feature or function and is typically 

marked with the letters Alt. 

alt. newsgroups n. Internet newsgroups that are part of 

the alt. (“alternative”) hierarchy and have the prefix alt. 

Unlike the seven Usenet newsgroup hierarchies (comp., 

misc., news., rec., sci., soc., talk.) that require formal votes 

among users in the hierarchy before official newsgroups 

can be established, anybody can create an alt. newsgroup. 

Therefore, newsgroups devoted to discussions of obscure 

or bizarre topics are generally part of the alt. hierarchy. 

ALU n. See arithmetic logic unit. 

always on n. An Internet connection that is maintained 

continuously, whether or not the computer user is on line. 

Always-on connections provide convenience to users who 

don’t need to dial in or log on to access the Internet, but 

25 

also provide more opportunities for hackers to attempt to 

access the system or use the computer to spread malicious 

programs. 

AM n. See amplitude modulation. 

AMD-K6 n. Family of x86-compatible processors introduced 

by Advanced Micro Devices, Inc. (AMD) in 1997. 

Comparable in performance to the Intel Pentium II, the 

AMD-K6 family is composed of Windows-compatible 

processors with MMX support that run 32-bit programs. 

They have 8.8 million transistors, include 64-KB (AMD- 

K6) L1 caches for faster execution, and are based on a 

technology known as RISC86 that converts x86 program 

instructions into RISC operations for execution. The 

AMD-K6 family ranges in speed from 166 to over 500 

MHz. See also MMX, Pentium, RISC. 

AMD-K7 n. See Athlon. 

American Federation of Information Processing 

Societies n. See AFIPS. 

American National Standards Institute n. See ANSI. 

American Registry for Internet Numbers n. See ARIN. 

American Standard Code for Information Interchange 

n. See ASCII. 

America Online n. An online information service, based 

in Vienna, Virginia, that provides e-mail, news, educational 

and entertainment services, and Internet access. 

America Online is one of the largest American ISPs 

(Internet service providers). In 2000 America Online 

merged with media giant Time Warner Inc. to become 

AOL Time Warner Inc. Intended for mass-market delivery 

of branded content and communication services, the 

merged companies form a communication and media conglomerate 

with the Internet’s largest user base and a wide 

range of entertainment, publishing, and cable properties. 

Acronym: AOL. 

America Online Instant Messenger n. See AIM. 

AMI BIOS n. A ROM BIOS developed and marketed by 

American Megatrends, Inc. (AMI), for use in IBM-compatible 

computers. A popular feature is that its configuration 

software is stored in the ROM chip along with the 

BIOS routines, so the user does not need a separate configuration 

disk to modify system settings, such as amount 

of memory installed and number and types of disk drives. 

See also BIOS, Phoenix BIOS, ROM BIOS. 

A

A Amiga analog display 

Amiga n. An operating system owned by Amiga, Inc. The 

Amiga model of desktop computer, which featured the 

Amiga operating system, was introduced by Commodore 

in 1985. The Amiga was especially strong in its ability to 

support sound and video, which made it popular among 

broadcast and multimedia producers, but it was overshadowed 

by the IBM Personal Computer (and its clones) and 

the Apple Macintosh. The ownership of the Amiga design 

has been through the hands of several companies in the 

United States and Germany. 

amp n. See ampere. 

ampere n. The basic unit of electric current. One ampere 

is equivalent to a flow of 1 coulomb per second. 

Abbreviation: a, A, amp. 

amplitude n. A measure of the strength of a signal, such 

as sound or voltage, determined by the distance from the 

baseline to the peak of the waveform. See also waveform. 

amplitude modulation n. A method of encoding information 

in a transmission, such as radio, using a carrier wave of 

constant frequency but of varying amplitude. See the illustration. 

Acronym: AM.Compare frequency modulation. 

Amplitude 

Encoding signal 

Carrier wave 

f0agn06.eps 

Amplitude modulation. 

26 

amplitude shift keying n. A form of amplitude modulation 

that uses two different wave heights to represent the 

binary values 1 and 0. See also amplitude modulation. 

AMPS n. Acronym for Advanced Mobile Phone Service. 

The standard for analog cellular phone service, widely used 

in the United States and many other countries around the 

world. AMPS was introduced by AT&T in 1983. It relies 

on frequency division multiple access (FDMA) to divide 

frequencies in the 800 MHz to 900 MHz range into 30 KHz 

channels for sending and receiving calls. A form of AMPS 

based on a narrower bandwidth is known as N-AMPS. The 

comparable standard for digital cellular phones is known as 

D-AMPS. See also D-AMPS, N-AMPS. 

AMPS/D-AMPS/N-AMPS n. See AMPS, D-AMPS, 

N-AMPS. 

AMT n. See address mapping table. 

Anaglyph n. A 3-D effect obtained by creating two overlapping 

images that appear as a single three dimensional 

image when viewed through special lenses. Anaglyph 3-D 

technologies are used on the Web to produce 3-D images 

for a variety of virtual reality, teaching, and research 

applications. 

analog adj. Pertaining to or being a device or signal that 

is continuously varying in strength or quantity, such as 

voltage or audio, rather than based on discrete units, such 

as the binary digits 1 and 0. A lighting dimmer switch is 

an analog device because it is not based on absolute settings. 

Compare digital (definition 2). 

analog channel n. A communications channel, such as a 

voice-grade telephone line, carrying signals that vary 

continuously and can assume any value within a specified 

range. 

analog computer n. A computer that measures data varying 

continuously in value, such as speed or temperature. 

analog data n. Data that is represented by continuous 

variations in some physical property, such as voltage, frequency, 

or pressure. Compare digital data transmission. 

analog display n. A video display capable of depicting a 

continuous range of colors or shades rather than discrete 

values. Compare digital display.

analog line ANN 

analog line n. A communications line, such as a standard 

telephone line, that carries continuously varying (analog) 

signals. 

analog modem n. See modem. 

analog signal generator n. A device that generates continuously 

variable signals and is sometimes used to activate 

an actuator in a disk drive. See also actuator. 

analog-to-digital converter n. A device that converts a 

continuously varying (analog) signal, such as sound or 

voltage, from a monitoring instrument to binary code for 

use by a computer. See the illustration. 

Acronym: ADC.Also called: A-D converter. See also 

modem. Compare digital-to-analog converter. 

Analog 

input 

ADC 

Digital 

output 

f0agn07.eps 

Analog-to-digital converter. 

analysis n. The evaluation of a situation or problem, 

including review from various aspects or points of view. 

In computing, analysis commonly involves such features 

as flow control, error control, and evaluation of efficiency. 

Often the overall problem is divided into smaller 

components that can be more easily dealt with. See also 

flow analysis, numerical analysis, systems analysis. Compare 

synthesis. 

analysis graphics n. See presentation graphics. 

Analytical Engine n. A mechanical calculating machine 

designed by British mathematician Charles Babbage in 

1833 but never completed. It was the first general-purpose 

digital computer. See also Difference Engine. 

anchor n. 1. A format code in a desktop publishing or 

word processing document that keeps an element in the 

document, such as a figure or a caption or a label associated 

with the figure, in a certain position in the document. 

The anchored object is generally attached to another element 

in the document such as a piece of text (often a paragraph), 

a graphic, or a particular place in the document. As 

text and other objects are added to the document, the 

anchored object moves relative to the object to which it is 

anchored or remains stationary. 2. A tag in an HTML document 

that defines a section of text, an icon, or other ele- 

27 

ment as a link to another element in the document or to 

another document or file. See also hyperlink. 

ancillary equipment n. See peripheral. 

AND n. A logical operation combining the values of two 

bits (0, 1) or two Boolean values (false, true) that returns a 

value of 1 (true) if both input values are 1 (true) and 

returns a 0 (false) otherwise. See the table. 

Table A.1 The Possible Combinations with a Boolean AND. 

a b a AND b 

0 0 0 

0 1 0 

1 0 0 

1 1 1 

AND gate n. A digital circuit whose output is a value of 1 

only when all input values are 1. See the illustration. See 

also truth table. 

Input 1 

Input 2 

f0agn08.eps 

AND gate. 

Andrew File System n. See AFS. 

angle bracket n. See . 

Output 

angstrom n. A unit of measure equal to one 10-billionth 

(10 –10 ) of a meter or one 250-millionth of an inch. Light 

wavelength, for example, is commonly measured in angstroms. 

Abbreviation: Å. 

animated cursors n. A Windows 95 and Windows NT 

feature that allows a series of frames, one after another, to 

appear at the mouse pointer location instead of a single 

image, thus producing a short loop of animation. The animated 

cursors feature is designated by the .ani suffix. 

animated GIF n. A series of graphic images in GIF format, 

displayed sequentially in a single location to give the 

appearance of a moving picture. See also GIF. 

animation n. The illusion of movement created by using 

a succession of static images. In computer graphics, the 

images can all be drawn separately, or starting and ending 

points can be drawn with the intervening images provided 

by software. See also 3-D graphic, surface modeling, 

tween, wire-frame model. 

ANN n. See artificial neural network. 

A

A annotation ANSI X3.30-1997 

annotation n. A note or comment attached to some part 

of a document to provide related information. Some applications 

support voice annotations or annotations accessible 

by icons. See also comment. 

annoybot n. A bot on an Internet Relay Chat (IRC) channel 

or a multiuser dungeon (MUD) that interacts with the 

user in an obnoxious manner. See also bot, IRC, MUD. 

anode n. In electronics, the positively charged terminal or 

electrode toward which electrons flow. Compare cathode. 

anonymity n. The ability to send an e-mail message or an 

article to a newsgroup without one’s identity becoming 

known. Ordinarily, the e-mail address of the sender 

appears automatically in a message’s header, which is created 

by the client software. To achieve anonymity, a message 

must be sent through an anonymous remailer— 

which, however, maintains a record of the sender’s identity 

to enable replies. See also anonymous remailer. 

anonymous n. On the Internet, the standard login name 

used to obtain access to a public FTP file archive. See also 

anonymous FTP. 

anonymous FTP n. The ability to access a remote computer 

system on which one does not have an account, via 

the Internet’s File Transfer Protocol (FTP). Users have 

restricted access rights with anonymous FTP and usually 

can only copy files to or from a public directory, often 

named /pub, on the remote system. Users can also typically 

use FTP commands, such as listing files and directories. 

When using anonymous FTP, the user accesses the 

remote computer system with an FTP program and generally 

uses anonymous or ftp as a logon name. The password 

is usually the user’s e-mail address, although a user can 

often skip giving a password or give a false e-mail 

address. In other cases, the password can be the word 

anonymous. Many FTP sites do not permit anonymous 

FTP access in order to maintain security. Those that do 

permit anonymous FTP sometimes restrict users to only 

downloading files for the same reason. See also FTP1 (definition 

1), logon, /pub. 

anonymous post n. A message in a newsgroup or mailing 

list that cannot be traced to its originator. Generally 

this is accomplished by using an anonymous server for 

newsgroup posts or an anonymous remailer for e-mail. See 

also anonymous remailer. 

28 

anonymous remailer n. An e-mail server that receives 

incoming messages, replaces the headers that identify the 

original sources of the messages, and sends the messages 

to their ultimate destinations. The purpose of an anonymous 

remailer is to hide the identities of the senders of the 

e-mail messages. 

anonymous server n. 1. The software used by an anonymous 

remailer. See also anonymous remailer. 2. Software 

that provides anonymous FTP service. See also anonymous 

FTP. 

ANSI n. 1. Acronym for American National Standards 

Institute. A voluntary, nonprofit organization of business 

and industry groups formed in 1918 for the development 

and adoption of trade and communication standards in the 

United States. ANSI is the American representative of ISO 

(the International Organization for Standardization). 

Among its many concerns, ANSI has developed recommendations 

for the use of programming languages including 

FORTRAN, C, and COBOL, and various networking 

technologies. See also ANSI C, ANSI.SYS, SCSI. 2. The 

Microsoft Windows ANSI character set. This set is 

includes ISO 8859/x plus additional characters. This set 

was originally based on an ANSI draft standard. The MS- 

DOS operating system uses the ANSI character set if 

ANSI.SYS is installed. 

ANSI C n. A version of the C programming language 

standardized by ANSI. See also ANSI, K&R C. 

ANSI/SPARC n. Acronym for American National Standards 

Institute Standards Planning and Requirements 

Committee. The ANSI committee that, in the 1970s, proposed 

a generalized, three-schema architecture that is used 

as the foundation for some database management systems. 

ANSI.SYS n. An installable device driver for MS-DOS 

computers that uses ANSI commands (escape sequences) 

to enhance the user’s control of the console. See also 

ANSI, driver, escape sequence, install. 

ANSI X3.30-1997 n. A standard entitled “Representation 

for Calendar Date and Ordinal Date for Information 

Interchange” from the American National Standards Institute 

(ANSI) that covers date formats. Many organizations, 

including the U.S. federal government, have standardized 

date formats using this standard to facilitate work on the 

Year 2000 problem.

answer mode Apache 

answer mode n. A setting that allows a modem to answer 

an incoming call automatically. It is used in all fax 

machines. Also called: auto answer. 

answer-only modem n. A modem that can receive but 

not originate calls. 

answer/originate modem n. A modem that can both 

send and receive calls—the most common type of modem 

in use. 

antialiasing n. A software technique for smoothing the 

jagged appearance of curved or diagonal lines caused by 

poor resolution on a display screen. Methods of anti-aliasing 

include surrounding pixels with intermediate shades 

and manipulating the size and horizontal alignment of 

pixels. See the illustration. See also dithering. Compare 

aliasing. 

f0agn09.eps 

Antialiasing. The image on the right shows the result of antialiasing 

through the use of higher resolution. 

antiglare or anti-glare adj. Pertaining to any measure 

taken to reduce reflections of external light on a monitor 

screen. The screen may be coated with a chemical (which 

may reduce its brightness), covered with a polarizing filter, 

or simply rotated so that external light is not reflected 

into the user’s eye. 

anti-replay n. An IP packet–level security feature that 

prevents packets that have been intercepted and changed 

from being inserted into the data stream. Anti-replay creates 

a security association between a source and destination 

computer, with each agreeing on a numbering 

sequence for transmitted packets. The anti-replay mechanism 

detects packets tagged with numbers that fall outside 

the accepted sequence, discards them, sends an error message, 

and logs the event. The anti-replay protocol is 

included as part of the IPSec standard. See also IPSec. 

antistatic device n. A device designed to minimize 

shocks caused by the buildup of static electricity, which 

can disrupt computer equipment or cause data loss. An 

antistatic device may take the form of a floor mat, a wristband 

with a wire attached to the workstation, a spray, a 

29 

lotion, or other special-purpose device. See also static2 , 

static electricity. 

antivirus program n. A computer program that scans a 

computer’s memory and mass storage to identify, isolate, 

and eliminate viruses, and that examines incoming files 

for viruses as the computer receives them. 

anti-worm n. See automatic patching, do-gooder virus. 

anycasting n. Communication between a single sender 

and the nearest receiver in a group. In IPv6, anycasting 

enables one host to initiate the updating of routing tables 

for a group of hosts. See also IPv6. Compare multicasting, 

unicast. 

any key n. Any random key on a computer keyboard. 

Some programs prompt the user to “press any key” to continue. 

It does not matter which key the user presses. There 

is no key on the keyboard called Any. 

any-to-any connectivity n. The property of an integrated 

computer network environment where it is possible to 

share data across multiple protocols, host types, and network 

topologies. 

AOL n. See America Online. 

AOL Instant Messenger n. See AIM. 

AOL NetFind n. Resident Web-finding tool of America 

Online (AOL) information service. Searches by keyword 

and concept. Using Intelligent Concept Extraction (ICE) 

and Excite technology, this tool finds relationships 

between words and ideas; for example, between “elderly 

people” and “senior citizen.” See also Excite, Intelligent 

Concept Extraction. 

APA n. See all points addressable. 

Apache n. A free open-source HTTP (Web) server introduced 

in 1995 by the Apache Group as an extension to, 

and improvement of, the National Center for Supercomputing 

Applications’ earlier HTTPd (version 1.3). Apache 

is popular on UNIX-based systems, including Linux, and 

also runs on Windows NT and other operating systems, 

such as BeOS. Because the server was based on existing 

code with a series of patches, it became known as “A 

Patchy server,” which led to the official name Apache. See 

also HTTPd. 

A

A Apache Group Apple Extended Keyboard 

Apache Group n. A non-profit organization of volunteers 

from around the world that operates and contributes to the 

Apache HTTP Server Project. 

Apache HTTP Server Project n. A collaborative effort 

by the members of the Apache Group to design, develop, 

and maintain the Apache HTTP (Web) server. See also 

Apache, Apache Group. 

Apache project n. See Apache HTTP Server Project. 

APC n. See asynchronous procedure call. 

aperture grill n. A type of CRT (cathode ray tube) used 

in computer monitors that uses thin, closely-spaced vertical 

wires to isolate the individual pixels. The first aperture 

grill CRT was the Sony Trinitron, but several other manufacturers 

also produce aperture grill CRTs. See also CRT. 

APEX n. Acronym for Assembly Process Exhibition and 

Conference. Exhibition and conference for members of 

the electronics manufacturing industry. APEX features 

product exhibits, speeches, technical conferences, and 

forums on issues that affect the industry. 

API n. See application programming interface. 

APL n. Acronym for A Programming Language. A highlevel 

language introduced in 1968 for scientific and mathematical 

applications. APL is a subprogram-based interpreted 

language that uses a large set of special characters 

and terse syntax and is available for use on PC-compatible 

machines. See also interpreted language. 

APM n. See Advanced Power Management. 

APNIC n. Acronym for Asian-Pacific Network Information 

Center, a nonprofit, voluntary membership organization 

covering the Asia/Pacific Rim region. APNIC, like its 

European counterpart RIPE and its American counterpart 

ARIN, devotes itself to matters related to the Internet, 

among them such tasks as registering new members, allocating 

IP addresses, and maintaining database information. 

See also ARIN, RIPE. 

app n. See application. 

APPC n. Acronym for Advanced Program-to-Program 

Communication. A specification developed as part of 

IBM’s SNA (Systems Network Architecture) model and 

30 

designed to enable applications programs running on different 

computers to communicate and exchange data 

directly. APPC extends SNA to include minicomputers 

and PCs. 

append vb. To place or insert as an attachment by adding 

data to the end of a file or database or extending a character 

string. See also file, string. Compare truncate. 

Apple II n. The second computer introduced by the Apple 

Computer Corporation, in April 1977. The Apple II featured 

4 K dynamic RAM, expandable to 48 K (with 16 K 

chips), and used the 6502 microprocessor. The Apple II 

was the first computer to offer a TV video adapter as an 

optional alternative to a color computer monitor. It also 

featured sound and eight expansion slots. See also 6502. 

Apple Desktop Bus n. A serial communications pathway 

built into Apple Macintosh and Apple IIGS computers. 

Typically a flexible cord, it enables low-speed input 

devices, such as a keyboard or mouse, to communicate 

with the computer. The bus functions like a simple local 

area network that can connect up to 16 devices, such as 

light pens, trackballs, and graphics tablets, to the computer. 

Although there are only two external ports, more 

than two devices can be linked in a series called a daisy 

chain. Acronym: ADB.See also bus, daisy chain2 , device 

driver, input/output port, serial communication. 

AppleDraw n. A shareware drawing application for Macintosh 

computers. 

Apple Events n. A feature added to Mac OS System 7 

that enables one application to send a command, such as 

save or open, to another application. See also Mac OS. 

Apple Extended Keyboard n. A 105-key keyboard that 

works with the Macintosh SE, Macintosh II, and Apple 

IIGS computers. This keyboard marks Apple’s first inclusion 

of function (F) keys, whose absence was long cited as 

a shortcoming of the Macintosh compared with IBM PCs 

and compatibles. This feature, along with other layout 

changes and the addition of new keys and lights, makes 

the Apple Extended Keyboard quite similar in form to the 

IBM enhanced keyboard. See the illustration. See also 

enhanced keyboard.

Apple Filing Protocol application binary interface 

f0agn10.eps 

Apple Extended Keyboard. 

Apple Filing Protocol n. See AFP. 

Apple key n. A key on Apple keyboards labeled with an 

outline of the Apple logo. On the Apple Extended Keyboard, 

this key is the same as the Command key, which 

functions similarly to the Control key on IBM and compatible 

keyboards. It is generally used in conjunction with 

a character key as a shortcut to making menu selections or 

starting a macro. 

Apple Macintosh n. See Macintosh. 

Apple Newton n. See Newton. 

AppleScript n. A script language developed by Apple 

Computer, Inc., for Macintosh computers running under 

the Mac OS to execute commands and automate functions. 

See also script. 

AppleShare n. A file server software developed by Apple 

Computer, Inc., that works with the Mac OS and allows 

one Macintosh computer to share files with another on the 

same network. See also file server, Mac OS. 

applet n. A program that can be downloaded over the 

Internet and executed on the recipient’s machine. Applets 

are often written in the Java programming language and 

run within browser software, and they are typically used to 

customize or add interactive elements to a Web page. 

AppleTalk n. An inexpensive local area network developed 

by Apple Computer, Inc., for Macintosh computers 

that can be used by Apple and non-Apple computers to 

communicate and share resources such as printers and file 

servers. Non-Apple computers must be equipped with 

AppleTalk hardware and suitable software. The network 

31 

uses a layered set of protocols similar to the ISO/OSI reference 

model and transfers information in the form of 

packets called frames. AppleTalk supports connections to 

other AppleTalk networks through devices known as 

bridges, and it supports connections to dissimilar networks 

through devices called gateways. See also bridge, frame 

(definition 2), gateway. 

AppleTalk Phase 2 n. The extended AppleTalk Internet 

model designed by Apple Computer, Inc., that supports 

multiple zones within a network and extended addressing 

capacity. 

AppleWorks n. A suite of productivity applications, formerly 

known as ClarisWorks, distributed by Apple Computer, 

Inc., and shipped on the iMac computer. AppleWorks/ 

ClarisWorks is an integrated product that includes support 

for word processing, spreadsheets, databases, drawing, 

painting, charting, and the Internet. 

appliance n. 1. See server appliance. 2. See information 

appliance. 3. A device with a single or limited purpose 

with functionality. This functionality is similar to a simple 

consumer appliance. 

appliance server n. 1. An inexpensive computing device 

used for specific tasks including Internet connectivity or 

file-and-print services. The server is usually easy to use 

but does not possess the capabilities or software of a typical 

server for general office use. 2. See server appliance. 

application n. A program designed to assist in the performance 

of a specific task, such as word processing, 

accounting, or inventory management. Compare utility. 

application binary interface n. A set of instructions that 

specifies how an executable file interacts with the hardware 

A

A application-centric application notification 

and how information is stored. Acronym: ABI.Compare 

application programming interface. 

application-centric adj. Of, pertaining to, or characteristic 

of an operating system in which a user invokes an 

application to open or create documents (such as word 

processing files or spreadsheets). Command-line interfaces 

and some graphical user interfaces such as the Windows 

3.x Program Manager are application-centric. 

Compare document-centric. 

application developer n. An individual who designs and 

analyzes the appearance and operation of an application 

program. 

application development environment n. An integrated 

suite of programs for use by software developers. 

Typical components of application development environments 

include a compiler, file browsing system, debugger, 

and text editor for use in creating programs. 

application development language n. A computer language 

designed for creating applications. The term is usually 

restricted to refer to languages with specific highlevel 

constructs geared toward record design, form layout, 

database retrieval and update, and similar tasks. See also 

4GL, application, application generator. 

application development system n. A programming 

environment designed for the development of an application, 

typically including a text editor, compiler, and linker, 

and often including a library of common software routines 

for use in the developed program. 

application entity n. See AE. 

application file n. See program file. 

Application Foundation Classes n. A set of Java class 

libraries developed by Microsoft that provides developers 

with user-interface controls and graphics tools for creating 

and manipulating elements such as text and fonts. The 

Application Foundation Classes extend the capabilities of 

Java’s Abstract Windowing Toolkit (AWT) and are used to 

facilitate and expedite the creation of Java applets and 

applications through the use of prebuilt, customizable 

development components. Acronym: AFC.See also Internet 

Foundation Classes, Java, Java Foundation Classes, 

Microsoft Foundation Classes. 

application gateway n. Software running on a machine 

that is intended to maintain security on a secluded network 

32 

yet allow certain traffic to go between the private network 

and the outside world. See also firewall. 

application generator n. Software for generating source 

or machine code for running an application based on a 

description of the desired functionality. Limited in scope, 

application generators are included with some database 

programs and use built-in instruction sets to generate program 

code. See also application. 

application heap n. A block of RAM used by an application 

to store its code, resources, records, document data, 

and other information. See also heap (definition 1), RAM. 

application layer n. The highest layer of standards in the 

Open Systems Interconnection (OSI) reference model. 

The application layer contains signals that perform useful 

work for the user, such as file transfer or remote access to 

a computer, as opposed to lower levels, which control the 

exchange of data between transmitter and receiver. See the 

illustration. See also ISO/OSI reference model. 

ISO/OSI Layer 

ISO/OSI MODEL 

Focus 

Application Program-to-program transfer 

(highest level) of information 

Presentation Text formatting and display, code 

conversion 

Session Establishing, maintaining, and 

coordinating communication 

Transport Accurate delivery, service quality 

Network Transport routes, message 

handling and transfer 

Data-link Coding, addressing, and 

transmitting information 

Physical Hardware connections 

f0agn11.eps 

Application layer. The highest layer in the ISO/OSI reference 

model. 

application notification n. An application notification 

starts an application at a specified time or when a system 

event occurs. When an application starts as the result of a 

notification, the system specifies a command-line parameter 

that identifies the event that has occurred. See also 

Class A IP address, Class B IP address, Class C IP 

address.

application processor archive1 archive 

application processor n. A processor dedicated to a single 

application. 

application program n. See application. 

application program interface. n. See application programming 

interface. 

application programming interface n. A set of routines 

used by an application program to direct the performance 

of procedures by the computer’s operating system. 

Acronym: API.Also called: application program interface. 

application server n. 1. A server program on a computer 

in a distributed network that handles the business logic 

between users and backend business applications or databases. 

Application servers also can provide transaction 

management, failover, and load balancing. An application 

server is often viewed as part of a three-tier application 

consisting of a front-end GUI server such as an HTTP 

server (first tier), an application server (middle tier), and a 

backend database and transaction server (third tier). Also 

called: appserver. Compare HTTP server (definition 1). 

2. Any machine on which an application-server program 

is running. Also called: appserver. 

application service provider n. A third-party company 

or organization that hosts applications or services for individuals 

or business customers. The customer connects to a 

data center maintained by the application service provider 

(ASP) through Internet or private lines to access applications 

that would otherwise need to be housed on the customer’s 

local servers or individual PCs. This arrangement 

allows the customer to free up disk space that would otherwise 

be taken by applications, as well as to access the 

most recent software updates. ASPs deliver solutions 

ranging from high-end applications to services for small 

and medium-sized businesses. Acronym: ASP. 

application shortcut key n. A key or combination of 

keys that when pressed will quickly perform an action 

within an application that would normally require several 

user actions, such as menu selections. Also called: keyboard 

shortcut. 

application software n. See application. 

application-specific integrated circuit n. See gate array. 

application suite n. See suite (definition 1). 

appserver n. See application server. 

33 

Aqua n. The graphical user interface (GUI) of Macintosh 

OS X. Aqua was designed to maintain familiarity and a 

comfort level for users of the earlier Macintosh system 

while allowing access to newer Macintosh OS X capabilities. 

The Aqua GUI features updated versions of Macintosh 

staples such as the Finder alongside new features like 

the Dock, a new type of organizational tool. See also 

Dock, Macintosh OS X. 

arbitration n. A set of rules for resolving competing 

demands for a machine resource by multiple users or processes. 

See also contention. 

.arc n. The file extension that identifies compressed 

archive files encoded using the Advanced RISC Computing 

Specification (ARC) format. See also compressed file. 

arcade game n. 1. A coin-operated computer game for 

one or more players that features high-quality screen 

graphics, sound, and rapid action. 2. Any computer game 

designed to mimic the style of a coin-operated arcade 

game, such as games marketed for the home computer. 

See also computer game. 

Archie n. An Internet utility for finding files in public 

archives obtainable by anonymous FTP. The master 

Archie server at McGill University in Montreal downloads 

FTP indexes from participating FTP servers, merges them 

into a master list, and sends updated copies of the master 

list to other Archie servers each day. Archie is a shortened 

form of archive. See also anonymous FTP, FTP1 (definition 

1). Compare Jughead, Veronica. 

Archie client n. See Archie. 

Archie server n. On the Internet, a server that contains 

Archie indexes to the names and addresses of files in public 

FTP archives. See also Archie, FTP1 (definition 1), 

server (definition 2). 

architecture n. 1. The physical construction or design of 

a computer system and its components. See also cache, 

CISC, closed architecture, network architecture, open 

architecture, pipelining, RISC. 2. The data-handling 

capacity of a microprocessor. 3. The design of application 

software incorporating protocols and the means for expansion 

and interfacing with other programs. 

archive1 n. 1. A tape or disk containing files copied from 

another storage device and used as backup storage. 2. A 

compressed file. 3. A file directory on the Internet that is 

A

A archive 

archive2 .arj 

available by File Transfer Protocol (FTP) or an Internet 

directory established for dissemination of stored files. 

archive2 vb. 1. To copy files onto a tape or disk for longterm 

storage. 2. To compress a file. 

archive bit n. A bit that is associated with a file and is 

used to indicate whether the file has been backed up. See 

also back up, bit. 

archive file n. A file that contains a set of files, such as a 

program with its documentation and example input files, 

or collected postings from a newsgroup. On UNIX systems, 

archive files can be created using the tar program; 

they can then be compressed using compress or gzip. 

PKZIP under MS-DOS and Windows and StuffIt under 

Mac OS create archive files that are already compressed. 

See also compress1 , gzip, PKZIP, StuffIt, tar1 . 

archive site n. A site on the Internet that stores files. The 

files are usually accessed through one of the following 

ways: downloaded through anonymous FTP, retrieved 

through Gopher, or viewed on the World Wide Web. See 

also anonymous FTP, Gopher. 

ARCnet n. Short for Attached Resource Computer Network. 

A form of token bus network architecture for PCbased 

LANs developed by Datapoint Corporation. ARCnet 

relies on a bus or star topology and can support up to 

255 nodes. Different versions run at speeds of 1.5 Mbps, 

20 Mbps (ARCnet Plus), and 100 Mbps. 

ARCnet Plus n. See ARCnet. 

area chart n. A graphical presentation, such as of quarterly 

sales figures, that uses shading or coloring to emphasize 

the difference between the line representing one set of 

data points and the line representing a separate but related 

set of data points. See the illustration. 

Sales 

$2500 

$2000 

$1500 

$1000 

$500 

$0 

Qtr 1 

f0agn12.eps 

Area chart. 

Quarterly Sales Summary 

Qtr 2 Qtr 3 Qtr 4 

Quarter 

34 

area search n. In information management, the examination 

of a group of documents for the purpose of identifying 

those that are relevant to a particular subject or 

category. 

arg n. See argument. 

argument n. An independent variable, used with an operator 

or passed to a subprogram that uses the argument to 

carry out specific operations. See also algorithm, operator 

(definition 1), parameter, subprogram. 

ARIN n. Acronym for American Registry for Internet 

Numbers. A nonprofit organization formed to register and 

administer Internet Protocol (IP) addresses in North and 

South America. The American Registry for Internet Numbers 

separates the allocation of IP addresses from the 

administration of top-level Internet domains, such as .com 

and .edu. Both of these tasks were previously managed by 

Network Solutions, Inc., as part of the InterNIC consortium. 

Its international counterparts are RIPE, in Europe, 

and APNIC, in Asia and the Pacific Rim. See also APNIC, 

InterNIC, IP address, RIPE. 

arithmetic1 adj. Pertaining to the mathematical operations 

of addition, subtraction, multiplication, and division. 

arithmetic2 n. The branch of mathematics dealing with 

the addition, subtraction, multiplication, and division of 

real numbers. 

arithmetic expression n. A series of elements, including 

data labels and constants as well as numbers, that are 

joined by arithmetic operators, such as + and –, and can be 

calculated to produce a value. 

arithmetic logic unit n. A component of a microprocessor 

chip used for arithmetic, comparative, and logical 

functions. Acronym: ALU.See also gate (definition 1). 

arithmetic operation n. Any of the standard calculations 

performed in arithmetic—addition, subtraction, multiplication, 

or division. The term is also used in reference to 

negative numbers and absolute values. 

arithmetic operator n. An operator that performs an 

arithmetic operation: +, –,*, or /. An arithmetic operator 

usually takes one or two arguments. See also argument, 

binary1 , logical operator, operator (definition 1), unary. 

.arj n. The MS-DOS file extension used with archive files 

created with the ARJ compression program.

ARM artificial intelligence 

ARM n. Short for Advanced RISC Machines. A name for 

any of a group of small, high-performance 32-bit RISCbased 

microprocessors licensed to various semiconductor 

manufacturers by designer ARM Limited. ARM chips are 

notable for their low cost and efficient use of power. They 

are used in a wide variety of products, including mobile 

phones, handheld computers, automotive and embedded 

solutions, and consumer electronics, including digital 

cameras and game systems. See also StrongARM. 

ARP n. Acronym for Address Resolution Protocol. A 

TCP/IP protocol for determining the hardware address (or 

physical address) of a node on a local area network connected 

to the Internet, when only the IP address (or logical 

address) is known. An ARP request is sent to the network, 

and the node that has the IP address responds with its hardware 

address. Although ARP technically refers only to 

finding the hardware address, and RARP (for Reverse 

ARP) refers to the reverse procedure, ARP is commonly 

used for both senses. See also IP address, TCP/IP. 

ARPANET n. A large wide area network created in the 

1960s by the U.S. Department of Defense Advanced 

Research Projects Agency (ARPA, renamed DARPA in 

the 1970s) for the free exchange of information between 

universities and research organizations, although the military 

also used this network for communications. In the 

1980s MILNET, a separate network, was spun off from 

ARPANET for use by the military. ARPANET was the 

network from which the Internet evolved. See also 

ALOHAnet, Internet, MILNET. 

ARP request n. Short for Address Resolution Protocol 

request. An ARP packet containing the Internet address of 

a host computer. The receiving computer responds with or 

passes along the corresponding Ethernet address. See also 

ARP, Ethernet, IP address, packet. 

array n. In programming, a list of data values, all of the 

same type, any element of which can be referenced by an 

expression consisting of the array name followed by an 

indexing expression. Arrays are part of the fundamentals 

of data structures, which, in turn, are a major fundamental 

of computer programming. See also array element, index1 , 

record1 , vector. 

array element n. A data value in an array. 

array processor n. A group of interconnected, identical 

processors operating synchronously, often under the control 

of a central processor. 

35 

arrow key n. Any of four keys labeled with arrows pointing 

up, down, left, and right, used to move the cursor vertically 

or horizontally on the display screen or, in some 

programs, to extend the highlight. See the illustration. 

Arrow Keys 

(when Num Lock is off) 

e 

ol 

Insert Home 

Delete 

End 

Page 

Up 

Page 

Down 

Num 

Lock 

7 

Home 

1 

End 

0 

Ins 

Arrow Keys 

/ * - 

8 9 

PgUp 

4 5 6 

2 3 

PgDn 

. 

Del 

f0agn13.eps 

Arrow key. When Num Lock is off, the arrow keys on the number 

keypad can be used. 

ART n. Acronym for Adaptive Resonance Theory. First 

introduced as a theory of human information processing 

by Stephen Grossberg, ART has evolved into several 

classes of self-organizing neural networks that use two 

layers of ideal cases to predict outcome. It is a form of 

cluster analysis where data is classified or matched to the 

previously stored pattern it most closely resembles. This 

data is said to resonate with the ideal case layer, which is 

then updated to reflect the new information. The constant 

recategorization of input results in a powerful autonomous 

neural network. See also artificial intelligence, cluster 

analysis, neural network. 

article n. A message that appears in an Internet newsgroup. 

Also called: post. See also newsgroup. 

articulation n. A series of adjustments applied by a synthesizer 

to the pitch, volume, and other parameters of an 

instrument sound to make it more realistic. 

artifact n. A visible imperfection or distortion in a digital 

image. Artifacts may be caused by hardware/software limitations 

or may be a byproduct of compression. 

artificial intelligence n. The branch of computer science 

concerned with enabling computers to simulate such 

aspects of human intelligence as speech recognition, 

deduction, inference, creative response, the ability to learn 

+ 

Enter 

A

A artificial life Asian-Pacific Network Information Center 

from experience, and the ability to make inferences given 

incomplete information. Two common areas of artificialintelligence 

research are expert systems and naturallanguage 

processing. Acronym: AI.See also expert system, 

natural-language processing. 

artificial life n. The study of computer systems that simulate 

some aspects of the behavior of living organisms. 

Artificial life includes systems in which programs 

intended to perform some particular task compete for survival 

and reproduction based on their performance; the 

offspring can combine pieces of code and undergo random 

variations, and the programs so modified compete in turn, 

until an optimal solution is found. 

artificial neural network n. A form of computer artificial 

intelligence that uses software based on concepts 

understood from biological neural networks to adaptively 

perform a task. Acronym: ANN. 

AS n. See autonomous system. 

.asc n. A file name extension most commonly indicating 

that the file contains ASCII text that can be processed by 

all types of word processing software, including MS-DOS 

Edit, Windows Notepad, Windows 9x or Windows NT 

WordPad, and Microsoft Word. Some systems may use 

this extension to indicate that a file contains image information. 

See also ASCII. 

ascender n. The portion of a lowercase letter that extends 

above the main body (x-height) of the letter. See the illustration. 

See also base line, x-height. Compare descender. 

Ascender 

xylem X-height 

f0agn14.eps 

Ascender. 

ascending order n. The arrangement of a sequence of 

items from lowest to highest, such as from 1 to 10 or from 

A to Z. The rules for determining ascending order in a particular 

application can be very complicated: capital letters 

before lowercase letters, extended ASCII characters in 

ASCII order, and so on. 

ascending sort n. A sort that results in the arrangement 

of items in ascending order. See also alphanumeric sort, 

ascending order. Compare descending sort. 

36 

ascii n. In an FTP client program, the command that 

instructs the FTP server to send or receive files as ASCII 

text. See also ASCII, FTP client. Compare binary2 . 

ASCII n. Acronym for American Standard Code for Information 

Interchange. A coding scheme using 7 or 8 bits 

that assigns numeric values to up to 256 characters, 

including letters, numerals, punctuation marks, control 

characters, and other symbols. ASCII was developed in 

1968 to standardize data transmission among disparate 

hardware and software systems and is built into most 

minicomputers and all PCs. ASCII is divided into two 

sets: 128 characters (standard ASCII) and an additional 

128 (extended ASCII). See also ASCII file, character, 

character code, control character, extended ASCII, standard 

ASCII. Compare EBCDIC. 

ASCII character set n. A standard 7-bit code for representing 

ASCII characters using binary values; code values 

range from 0 to 127. Most PC-based systems use an 8-bit 

extended ASCII code, with an extra 128 characters used to 

represent special symbols, foreign-language characters, 

and graphic symbols. See also ASCII, character, 

EBCDIC, extended ASCII, standard ASCII. 

ASCII EOL value n. The sequence of bytes that indicates 

the end of a line of text. For Windows and MS-DOS systems, 

this is the hexadecimal sequence 0D 0A or the decimal 

sequence 13 10. Data files imported from other kinds 

of computers might not display correctly if the software 

used is not capable of recognizing these differences and 

adjusting for them. See also ASCII, EOL. 

ASCII file n. A document file in ASCII format, containing 

characters, spaces, punctuation, carriage returns, and sometimes 

tabs and an end-of-file marker, but no formatting 

information. Also called: ASCII file, text file, text-only 

file. See also ASCII, text file. Compare binary file. 

ASCII transfer n. The preferred mode of electronic 

exchange for text files. In ASCII mode, character conversions 

to and from the network-standard character set are 

performed. See also ASCII. Compare binary transfer. 

ASCIIZ string n. In programming, an ASCII string terminated 

by the NULL character (a byte containing the character 

whose ASCII value is 0). Also called: nullterminated 

string. 

ASF n. See Advanced Streaming Format. 

Asian-Pacific Network Information Center n. See 

APNIC.

ASIC assembly language 

ASIC n. Acronym for application-specific integrated circuit. 

See also gate array. 

ASK n. See amplitude shift keying. 

ASN n. Acronym for autonomous-system number. See 

autonomous system. 

ASN.1 n. See Abstract Syntax Notation One. 

.asp n. A file extension that identifies a Web page as an 

Active Server Page. 

ASP n. 1. See Active Server Pages. 2. See application service 

provider. 

aspect ratio n. In computer displays and graphics, the 

ratio of the width of an image or image area to its height. 

An aspect ratio of 2:1, for example, indicates that the 

image is twice as wide as it is high. The aspect ratio is an 

important factor in maintaining correct proportions when 

an image is printed, rescaled, or incorporated into another 

document. 

ASPI n. See Advanced SCSI Programming Interface. 

ASP.NET n. A set of technologies in the Microsoft .NET 

Framework for building Web applications and XML Web 

services. ASP.NET pages execute on the server and generate 

markup (such as HTML, WML, or XML) that is sent 

to a desktop or mobile browser. ASP.NET pages use a 

compiled, event-driven programming model that improves 

performance and enables the separation of application 

logic and user interface. ASP.NET pages and XML Web 

services files created using ASP.NET contain server-side 

(rather than client-side) logic written in Visual Basic 

.NET, C# .NET, or any .NET-compatible language. Web 

applications and XML Web services take advantage of the 

features of the common language runtime, such as type 

safety, inheritance, language interoperability, versioning, 

and integrated security. 

ASP.NET server control n. A server-side component that 

encapsulates user-interface and related functionality. An 

ASP.NET server control derives directly or indirectly from 

the System.Web.UI.Control class. The superset of 

ASP.NET server controls includes Web server controls, 

HTML server controls, and mobile controls. The page 

syntax for an ASP.NET server control includes a 

runat="server” attribute on the control’s tag. See also Web 

server control, HTML server control, validation server 

controls. 

37 

ASP.NET Web application n. An application that processes 

HTTP requests (Web requests) and executes on top 

of the ASP.NET runtime. An ASP.NET application can 

include ASP.NET pages, XML Web services, HTTP handlers, 

and HTTP modules. 

ASR n. 1. See automatic system reconfiguration. 

2. Acronym for Automatic Speech Recognition. Technology 

which allows machines to recognize and respond to 

human voice commands. ASR systems may be used to 

control a computer or to operate word processing and similar 

applications. Many ASR products are designed for use 

by users with disabilities who might have difficulty using 

a keyboard or mouse. 

assemble vb. In programming, to convert an assembly 

language program to equivalent machine language instructions 

called object code. See also assembler, assembly language, 

linker, object code. 

assembler n. A program that converts assembly language 

programs, which are understandable by humans, into executable 

machine language. See also assemble, assembly 

language, assembly listing, compiler (definition 2), 

machine code. 

assembly n. A collection of one or more files that are 

versioned and deployed as a unit. An assembly is the primary 

building block of a .NET Framework application. 

All managed types and resources are contained within an 

assembly and are marked either as accessible only within 

the assembly or as accessible from code in other assemblies. 

Assemblies also play a key role in security. The code 

access security system uses information about the assembly 

to determine the set of permissions that code in the 

assembly is granted. 

assembly cache n. A machine-wide code cache used for 

side-by-side storage of assemblies. There are two parts to 

the cache: the global assembly cache contains assemblies 

that are explicitly installed to be shared among many 

applications on the computer; the download cache stores 

code downloaded from Internet or intranet sites, isolated 

to the application that triggered the download so that code 

downloaded on behalf of one application/page does not 

impact other applications. See also global assembly cache. 

assembly language n. A low-level programming language 

using abbreviations or mnemonic codes in which 

each statement corresponds to a single machine instruction. 

An assembly language is translated to machine language 

by the assembler and is specific to a given 

A

A assembly listing asynchronous operation 

processor. Advantages of using an assembly language 

include increased execution speed and direct programmer 

interaction with system hardware. See also assembler, 

compiler, high-level language, low-level language, 

machine code. 

assembly listing n. A file created by an assembler that 

includes the statements of an assembly language program, 

the machine language generated by the assembler, and a 

list of the symbols used in the program. See also assembler, 

assembly language. 

assertion n. A Boolean statement used in a program to 

test a condition that, if the program is operating correctly, 

should always evaluate as true; otherwise the program will 

typically terminate with an appropriate error message. 

Assertions are used for debugging programs and for documenting 

how a program should operate. 

assignment operator n. An operator used to assign a 

value to a variable or data structure. See also assignment 

statement, operator (definition 1). 

assignment statement n. A programming language 

statement used to assign a value to a variable. It usually 

consists of three elements: an expression to be assigned, 

an assignment operator (typically a symbol such as = or 

:=), and a destination variable. On execution of the assignment 

statement, the expression is evaluated and the resulting 

value is stored in the specified destination. See also 

assignment operator, expression, variable. 

associate vb. To inform the operating system that a particular 

file name extension is linked to a specific application. 

When a file is opened that has an extension 

associated with a given application, the operating system 

automatically starts the application and loads the file. 

Association Control Service Element n. An Open Systems 

Interconnection (OSI) method to establish a call 

between two applications by checking the identities and 

contexts of the application entities and performing an 

authentication security check. Acronym: ACSE.See also 

ISO/OSI reference model. 

Association for Computing Machinery n. A membership 

society founded in 1947 and devoted to the advancement 

of knowledge and technical proficiency of 

information processing professionals. Acronym: ACM. 

Association of C and C++ Users n. An organization of 

people interested in the programming language C and its 

variants. Members of the association include professional 

38 

programmers, manufacturers and vendors of compilers, 

and nonprofessional programming enthusiasts. 

Acronym: ACCU. 

associative storage n. A memory-based storage method 

in which data items are accessed not on the basis of a fixed 

address or location but by analysis of their content. Also 

called: content-addressed storage. 

associativity n. See operator associativity. 

asterisk n. See *. 

asymmetrical transmission n. A form of transmission 

used by high-speed modems, typically those that operate 

at rates of 9600 bps or more, that allows simultaneous 

incoming and outgoing transmission by dividing a telephone 

line bandwidth into two channels: one in the range 

of 300 to 450 bps and one at a speed of 9600 bps or more. 

asymmetric digital subscriber line n. See ADSL. 

asymmetric digital subscriber loop n. See ADSL. 

asymmetric modem n. A modem that transmits data to 

the telephone network and receives data from the network 

at different speeds. Most commonly, an asymmetric 

modem will have a maximum download speed substantially 

higher than its upload speed. See also modem. 

asynchronous adj. Pertaining to, being, or characteristic 

of something that is not dependent on timing. For example, 

asynchronous communications can start and stop at 

any time instead of having to match the timing governed 

by a clock. 

asynchronous chip n. A microprocessor chip that does 

not need to operate in sync with a system clock. Asynchronous 

chip operations do not need to be timed to clock 

speed and draw power only when operations are in 

progress. This allows asynchronous chips the potential for 

greater computational speed and lower power consumption 

than traditional chips. 

asynchronous communications n. Computer-tocomputer 

communications in which the sending and 

receiving computers do not rely on timing as a means of 

determining where transmissions begin and end. Compare 

synchronous communications. 

asynchronous device n. A device whose internal operations 

are not synchronized with the timing of any other 

part of the system. 

asynchronous operation n. An operation that proceeds 

independently of any timing mechanism, such as a clock.

asynchronous procedure call ATA/IDE hard disk drive 

For example, two modems communicating asynchronously 

rely upon each sending the other start and stop 

signals in order to pace the exchange of information. Compare 

synchronous operation. 

asynchronous procedure call n. A function call that 

executes separately from an executing program when a set 

of enabling conditions exist. After the conditions have 

been met, the operating system’s kernel issues a software 

interrupt and directs the executing program to execute the 

call. Acronym: APC.See also function call. 

Asynchronous Protocol Specification n. The X.445 

standard. See also X series. 

asynchronous static RAM n. A type of static RAM 

(SRAM) that is not synchronized with the system clock. 

Like static RAM in general, asynchronous static RAM, or 

async SRAM, is used in a computer’s L2 cache—the special 

portion of memory used for storing frequently accessed 

information. Because this type of static RAM is not synchronized 

with the clock, the CPU must wait for data 

requested from the L2 cache. Asynchronous static RAM is 

faster than main memory but not as fast as synchronous 

burst static RAM or pipeline burst static RAM. Also 

called: async SRAM. See also L2 cache, static RAM. Compare 

dynamic RAM, pipeline burst static RAM, synchronous 

burst static RAM. 

Asynchronous Transfer Mode n. See ATM (definition 1). 

asynchronous transmission n. In modem communication, 

a form of data transmission in which data is sent 

intermittently, one character at a time, rather than in a 

steady stream with characters separated by fixed time 

intervals. Asynchronous transmission relies on the use of a 

start bit and stop bit(s), in addition to the bits representing 

the character (and an optional parity bit), to distinguish 

separate characters. See the illustration. 

Start 

bit 

Data 

bits 

Parity bit 

(optional) 

f0agn15.eps 

Asynchronous transmission. The coding of a typical character 

sent in asynchronous transmission. 

async SRAM n. See asynchronous static RAM. 

AT&T System V n. See System V. 

Stop 

bit(s) 

39 

ATA n. Acronym for Advanced Technology Attachment. 

ANSI group X3T10’s official name for the disk drive 

interface standard for integrating drive controllers directly 

on disk drives. The original ATA standard is commonly 

known as Integrated Drive Electronics (IDE). Later ATA 

versions include ATA-2, ATA-3, and Ultra-ATA. See the 

table. Also called: AT attachment. See also direct memory 

access, EIDE, IDE, logical block addressing, PIO, 

SMART system. 

Table A.2 ATA Specifications. 

ATA 

Specification 

Also 

Called Features 

ATA IDE Supports PIO (Programmed 

Input/Output), 

which transfers data 

through the CPU. Data 

transfer rates are 3.3 

mbps, 5.2 mbps, and 8.3 

ATA-2 Fast ATA, 

Enhanced 

IDE (EIDE) 

mbps. 

Supports faster PIO rates 

and DMA (direct memory 

access), which 

bypasses the CPU. Data 

transfer rates are between 

4 mbps and 16.6 mbps. It 

also supports LBA (logical 

block addressing), 

which allows support for 

drives larger than 528 

MB. 

ATA-3 Revision of ATA-2 with 

SMART (self-monitoring 

analysis and reporting 

technology) for 

Ultra-ATA ATA-33, 

DMA-33, 

Ultra-DMA, 

UDMA 

greater reliability. 

Supports DMA burst 

mode (roughly, all-atonce) 

data transfers of 

33.3 mbps. 

ATA hard disk drive card n. Expansion card used to control 

and interface with an ATA hard disk drive. These 

cards are usually ISA cards. See also ATA, ISA. 

ATA/IDE hard disk drive n. ATA (Advanced Technology 

Attachment) and IDE (Integrated Drive Electronics—or 

numerous other interpretations) are one and the same 

thing: a disk drive implementation designed to integrate 

A

A ATAPI atomic transaction 

the controller onto the drive itself, thereby reducing interface 

costs and making firmware implementations easier. 

ATAPI n. The interface used by the IBM PC AT system for 

accessing CD-ROM devices. 

AT Attachment n. See ATA. 

AT bus n. The electric pathway used by IBM AT and 

compatible computers to connect the motherboard and 

peripheral devices. The AT bus supports 16 bits of data, 

whereas the original PC bus supports only 8 bits. Also 

called: expansion bus. See also EISA, ISA, Micro Channel 

Architecture. 

aTdHvAaNnKcSe n. See TIA. 

ATDP n. Acronym for Attention Dial Pulse, a command 

that initiates pulse (as opposed to touch-tone) dialing in 

Hayes and Hayes-compatible modems. Compare ATDT. 

ATDT n. Acronym for Attention Dial Tone, a command 

that initiates touch-tone (as opposed to pulse) dialing in 

Hayes and Hayes-compatible modems. Compare ATDP. 

Athlon n. Family of x86-compatible processors introduced 

by Advanced Micro Devices, Inc. (AMD) in 1999. 

Athlon, which was code-named AMD-K7, is a successor 

to the AMD-K6 family. Comparable to upper-end Intel 

Pentium III processors in performance, Athlon is distinguished 

by over 22 million transistors; a fully pipelined, 

superscalar floating-point engine, which enhances performance 

of graphics and multimedia programs, Internet 

streaming applications, and games; a 200-MHz system 

bus; and a 128-KB L1 cache. Although the L2 cache is 

512 KB in size, the Athlon can support L2 cache sizes up 

to 8 MB. The first Athlon releases featured clock speeds 

of 500 to 650 MHz; 800-MHz and faster versions are now 

available. Athlon, which runs 32-bit programs, is compatible 

with most PC operating systems, including Microsoft 

Windows, Linux, OS/2 Warp, and NetWare. See also 

AMD-K6. 

ATM n. 1. Acronym for Asynchronous Transfer Mode. A 

network technology capable of transmitting data, voice, 

audio, video, and frame relay traffic in real time. Data, 

including frame relay data, is broken into packets containing 

53 bytes each, which are switched between any two 

nodes in the system at rates ranging from 1.5 Mbps to 622 

Mbps (over fiber optic cable). The basic unit of ATM transmission 

is known as a cell, a packet consisting of 5 bytes 

routing information and a 48-byte payload (data). These 

40 

cells are transmitted to their destination, where they are 

reassembled into the original traffic. During transmission, 

cells from different users may be intermixed asynchronously 

to maximize utilization of network resources. ATM 

is defined in the broadband ISDN protocol at the levels corresponding 

to levels 1 and 2 of the ISO/OSI reference 

model. It is currently used in LANs (local area networks) 

involving workstations and personal computers, but it is 

expected to be adopted by the telephone companies, which 

will be able to charge customers for the data they transmit 

rather than for their connect time. See also broadband, 

ISDN, ISO/OSI reference model. 2. Acronym for automated 

teller machine. A special-purpose terminal that 

bank customers can use to make deposits, obtain cash, and 

perform other transactions. 3. See Adobe Type Manager. 

ATM Adaptation Layer n. The ATM layer that mediates 

between higher-level and lower-level services, converting 

different types of data (such as audio, video, and data 

frames) to the 48-byte payloads required by ATM. 

Acronym: AAL.See also ATM (definition 1). 

ATM Forum n. Forum created in 1991 and including more 

than 750 companies related to communications and computing, 

as well as government agencies and research groups. 

The forum aims to promote Asynchronous Transfer Mode 

for data communication. See also ATM (definition 1). 

Atomicity, Consistency, Isolation, Durability n. See 

ACID. 

atomic operation n. An operation considered or guaranteed 

to be indivisible (by analogy with an atom of matter, 

once thought to be indivisible). Either the operation is 

uninterruptible or, if it is aborted, a mechanism is provided 

that ensures the return of the system to its state prior to initiation 

of the operation. 

atomic transaction n. A set of operations that follow an 

“all or nothing” principle, in which either all of the operations 

are successfully executed or none of them is executed. 

Atomic transactions are appropriate for order entry 

and fulfillment or for money transfers to ensure that information 

is fully updated. For example, if funds are transferred 

between accounts on two databases, one account 

cannot be credited if the other is not debited by the same 

amount. An atomic transaction would involve both recording 

the credit in one database and recording the corresponding 

debit in the other. If any operation in the 

transaction fails, the transaction is aborted and any infor-

at sign audio output port 

mation changes are undone. See also Distributed Computing 

Environment, TP monitor, transaction processing. 

at sign n. See @. 

attach vb. To include an external document, a file, or an 

executable program with an e-mail message. 

attached document n. An ASCII text file or a binary 

file, such as a document created in a word processing system, 

that is included with an e-mail message as an attachment. 

See also ASCII, attachment, binary file, BinHex1 , 

MIME, uuencode. 

attached file n. See attachment. 

attached processor n. A secondary processor attached 

to a computer system, such as a keyboard or video subsystem 

processor. 

Attached Resource Computer Network n. See ARCnet. 

attachment n. A file that accompanies an e-mail message. 

As transmitted, an attached file is an exact copy of 

the original file located on the sender’s computer. The file 

can be a document, an executable program, or a compressed 

file containing more than one item, among other 

types of files. The file is not part of the actual e-mail message, 

and it is generally encoded using uuencoding, 

MIME, or BinHex. Most e-mail programs automatically 

encode an attached document for transmission with a message. 

The recipient of the message must have an e-mail 

program capable of decoding the attached document or 

use a separate utility to decode it in order to read the document. 

Some gateways prohibit transmission of files over a 

certain size. Most e-mail systems permit more than one 

file to be attached to an e-mail message at a time. 

attachment unit interface n. See AUI. 

attenuation n. The weakening of a transmitted signal, 

such as the distortion of a digital signal or the reduction in 

amplitude of an electrical signal, as it travels farther from 

its source. Attenuation is usually measured in decibels and 

is sometimes desirable, as when signal strength is reduced 

electronically, for example, by a radio volume control, to 

prevent overloading. 

atto- prefix Metric prefix meaning 10 –18 (one quintillionth). 

attract mode n. In commercial arcade games, when a 

coin-operated game is not in use, the screen will rotate 

through “attract mode.” The aim is to both tempt prospective 

players and demonstrate game play or rules. Also, by 

41 

constantly changing the screen image, attract mode avoids 

screen burn in. See also arcade game, burn in. 

attribute n. 1. In a database record, the name or structure 

of a field. For example, the files LASTNAME, FIRST- 

NAME, and PHONE would be attributes of each record in 

a PHONELIST database. The size of a field or the type of 

information it contains would also be attributes of a database 

record. 2. In screen displays, an element of additional 

information stored with each character in the video buffer 

of a video adapter running in character mode. Such 

attributes control the background and foreground colors of 

the character, underlining, and blinking. 3. In markup languages 

such as SGML and HTML, a name-value pair 

within a tagged element that modifies certain features of 

that element. See also HTML, SGML. 

attribution line n. In newsgroups, e-mail, and other 

Internet-based communications, an identification line 

added to material quoted from earlier postings. Some mail 

and messaging software will add an attribution line automatically, 

which might read something like “News King 

wrote:” and usually appears immediately before the 

quoted text. 

ATX n. A specification for PC motherboard architectures 

with built-in audio and video capabilities, introduced by 

Intel in 1995. ATX supports USB and full-length boards in 

all sockets. See also board, motherboard, specification, USB. 

audio adj. Relating to frequencies within the range of perception 

by the human ear—from about 15 to 20,000 hertz 

(cycles per second). See also audio response, synthesizer. 

audio board n. See sound card. 

audio card n. See sound card. 

audiocast n. The transmission of an audio signal using IP 

protocols. See also IP. 

audio compression n. A method of reducing the overall 

loudness of an audio signal. This is accomplished by limiting 

the amount of apparent distortion when the signal is 

played back through a speaker or transmitted through a 

communications link. 

audio output n. See audio response. 

audio output port n. A circuit consisting of a digital-toanalog 

converter that transforms signals from the computer 

to audible tones. It is used in conjunction with an amplifier 

and a speaker. See also digital-to-analog converter. 

A

A audio response author2 author 

audio response n. Any sound produced by a computer; 

specifically, spoken output produced by a computer in 

response to some specific type of input. Such output may 

be generated using a combination of words from a digitized 

vocabulary or through the synthesis of words from tables of 

phonemes. See also frequency response, phoneme. 

audiotex n. An application allowing users to send and 

receive information by telephone. Users typically call an 

audiotex system and are presented with a series of choices 

or a series of questions through a voice mail system. When 

users select choices by pressing the buttons on the phone 

(rotary dial phones cannot be used for audiotex) or by 

speaking aloud, a database host responds by sending information 

to the voice mail system, which then converts the 

data to a spoken message for the user, or it responds by 

receiving and storing the information entered by the user. 

Also called: audiotext. See also voice mail. 

audiotext n. See audiotex. 

Audio Video Interleaved n. See AVI. 

audiovisual adj. Relating to or being any material that uses 

a combination of sight and sound to present information. 

audit n. In reference to computing, an examination of 

equipment, programs, activities, and procedures to determine 

how efficiently the overall system is performing, 

especially in terms of ensuring the integrity and security 

of data. 

auditing n. The process an operating system uses to 

detect and record security-related events, such as an 

attempt to create, to access, or to delete objects such as 

files and directories. The records of such events are stored 

in a file known as a security log, whose contents are available 

only to those with the proper clearance. See also 

security log. 

audit policy n. A policy that determines the security 

events to be reported to the network administrator. 

audit trail n. In reference to computing, a means of tracing 

all activities affecting a piece of information, such as a 

data record, from the time it is entered into a system to the 

time it is removed. An audit trail makes it possible to document, 

for example, who made changes to a particular 

record and when. 

AUI n. 1. Acronym for attachment unit interface. A 15pin 

(DB-15) connector commonly used to connect a net- 

42 

work interface card to an Ethernet cable. 2. See aural user 

interface. 

AUI cable n. Short for Attachment Unit Interface cable. 

A transceiver cable used to connect a host adapter within a 

computer to an Ethernet (10base5 or 10BaseF) network. 

See also 10Base5, 10Base-F, Ethernet (definition 1), 

transceiver cable. 

AUP n. See acceptable use policy. 

aural user interface n. Voice-activated interface that 

allows users to issue spoken commands to electronic 

devices. The aural user interface is used with features such 

as voice recognition for computers and voice-activated 

dialing for wireless phones. Acronym: AUI. 

authentication n. In a multiuser or network operating 

system, the process by which the system validates a user’s 

logon information. A user’s name and password are compared 

against an authorized list, and if the system detects a 

match, access is granted to the extent specified in the permission 

list for that user. See also logon, password, permission, 

user account, user name. 

authentication center n. Secure database used to identify 

and prevent wireless phone fraud. Authentication centers 

verify whether a wireless phone is registered with a 

wireless carrier’s network. 

Authentication Header n. See AH. 

Authenticode n. A security feature of Microsoft Internet 

Explorer. Authenticode allows vendors of downloadable 

executable code (plug-ins or ActiveX controls, for example) 

to attach digital certificates to their products to assure 

end users that the code is from the original developer and 

has not been altered. Authenticode lets end users decide 

for themselves whether to accept or reject software components 

posted on the Internet before downloading begins. 

See also ActiveX control, Internet Explorer, security. 

author1 vb. 1. To create a product for implementation via 

computer technology. 2. To write a computer program. 

3. To assemble multimedia components, such as graphics, 

text, audio, and animation, in a publication or product, for 

delivery on a CD-ROM or DVD or on line, to be viewed 

on a computer. 4. To create Web pages. Traditionally, to 

author meant to write a literary work or journalistic piece; 

in the cyberworld, to write is “to provide content”; thus, to 

author in the traditional sense is to be a “content provider.” 

author2 n. See Web author.

authoring language autoloader 

authoring language n. A computer language or application 

development system designed primarily for creating 

programs, databases, and materials for computer-aided 

instruction (CAI). A familiar example in relation to microcomputers 

is PILOT, a language used to create lessons. 

See also CAI, PILOT. 

authoring software n. A type of computer program used 

for creating Web pages and other hypertext and multimedia 

applications. Authoring software provides a way to 

define relationships between different types of objects, 

including text, graphics, and sound, and to present them in 

a desired order. This type of program is sometimes known 

as authorware, although the latter name is generally associated 

with a specific product from Macromedia. Also 

called: authoring tool. 

authoring system n. Application software that enables 

the operator to create and format a document for a specific 

kind of computer environment. An authoring system, 

especially for multimedia work, often consists of several 

applications within the framework of a single, controlling 

application. See also authoring language. 

authority n. A DNS server responsible for resolving 

names and IP addresses of sites and resources on the Internet 

at a particular level of authority: top-level domain, second-level 

domain, or subdomain. 

authorization n. In reference to computing, especially 

remote computers on a network, the right granted an individual 

to use the system and the data stored on it. Authorization 

is typically set up by a system administrator and 

verified by the computer based on some form of user identification, 

such as a code number or password. Also 

called: access privileges, permission. See also network, 

system administrator. 

authorization code n. See password. 

autoanswer n. See answer mode. 

autoassociative adj. In data reduction or clustering, 

autoassociative models use the same set of variables as 

both predictors and targets. In autoassociative neural networks, 

each pattern presented serves as both the input and 

output pattern. Autoassociative networks are typically 

used for tasks involving pattern completion. See also artificial 

intelligence, cluster analysis, neural networks, operator 

associativity, pattern recognition. 

43 

autoattendant adj. A term used to describe a store-andforward 

computer system that replaces the traditional 

switchboard operator, directing telephone calls to their 

correct extensions or voice mail. Autoattendant systems 

may implement voice prompts, touch-tone menus, or 

voice recognition features to send calls to their proper destinations. 

Compare interactive voice response systems. 

AutoCorrect n. A function in Microsoft Word for Windows 

that automatically corrects errors and makes other 

substitutions as soon as a user types text. For example, 

AutoCorrect can be set up to fix misspellings, such as teh 

for the, or to change “straight” (" ") quotation marks to 

“smart” (“ ”) quotation marks. The user can select which 

AutoCorrect features to enable. See also smart quotes. 

autodial n. A feature enabling a modem to open a telephone 

line and initiate a call by transmitting a stored telephone 

number as a series of pulses or tones. 

AUTOEXEC.BAT n. A special-purpose batch file (set of 

commands) that is automatically carried out by the MS- 

DOS operating system when the computer is started or 

restarted. Created by the user or (in later versions of MS- 

DOS) by the operating system at system installation, the file 

contains basic startup commands that help configure the 

system to installed devices and to the user’s preferences. 

AutoIP n. Short for automatic Internet Protocol addressing. 

A technique used by a device to obtain a valid IP address 

without a DHCP server or other IP-configuration authority. 

With AutoIP, a device randomly chooses an IP address from 

a set of reserved addresses and queries the local network to 

determine whether another client already is using that 

address. The device repeats the steps of picking and verifying 

until an unused address is found. AutoIP, based on an 

Internet Engineering Task Force (IETF) Internet Draft, is 

used in Universal Plug and Play (UPnP) networking. See 

also UPnP networking. 

autokey n. See typematic. 

autoload vb. To make some type of resource available 

without it having to be specifically requested. A program, 

for example, might autoload fonts or files as they are 

needed. Similarly, a CD-ROM drive might autoload audio 

discs or automatically start a setup program on a software 

CD-ROM. See also AutoPlay. 

autoloader n. A device that automatically prepares a diskette, 

CD, or other storage medium for use. 

A

A automagic autonomous system 

automagic adj. Slang for a process performed in some 

unexplained (but not inexplicable) way by a computer. An 

automagic process might either be too complicated to 

explain (such as a complex spreadsheet calculation), or it 

might be a complex process made to appear simple to the 

user (such as clicking on a heading to arrange the items in 

a list in alphabetical or chronological order). Compare 

black box. 

automata theory n. 1. The study of computing processes 

and their capabilities and limitations; that is, how systems 

receive and process input and produce output. See also 

cellular automata. 2. The study of the relationship between 

behavioral theories and the operation of automated 

devices. 

automated home n. See smart home. 

automated office n. A broad term used to refer to an 

office where work is carried out with the aid of computers, 

telecommunications facilities, and other electronic 

devices. 

automated teller machine n. See ATM (definition 2). 

automatic answering n. See answer mode. 

automatic data processing n. See data processing. 

automatic dialing n. See auto dial. 

automatic error correction n. A process that, upon 

detection of an internal processing or data transmission 

error, invokes a routine designed to correct the error or 

retry the operation. 

automatic IP addressing n. See AutoIP. 

automatic patching n. A process in which vulnerabilities 

caused by a destructive computer virus infection are 

tracked down and corrected by a do-gooder virus or other 

anti-virus program. Automatic patching may be initiated 

by the user, or may be done by a virus entering a back door 

left by a malicious virus, without the consent of the user. 

See also anti-worm, do-gooder virus. 

Automatic Private IP Addressing n. A feature of Windows 

XP TCP/IP that automatically configures a unique 

IP address from the range 169.254.0.1 through 

169.254.255.254 and a subnet mask of 255.255.0.0 when 

the TCP/IP protocol is configured for dynamic addressing 

and Dynamic Host Configuration Protocol (DHCP) is 

not available. Acronym: APIPA.See also DHCP server, 

44 

Dynamic Host Configuration Protocol (DHCP), IP 

address, Transmission Control Protocol/Internet Protocol 

(TCP/IP). 

Automatic Sequence Controlled Calculator n. See 

Mark I. 

automatic speech recognition n. See ASR (definition 2). 

automatic system reconfiguration n. Automation of 

configuration by the system to accommodate some change 

in either the software or the hardware. Acronym: ASR. 

Automation n. 1. The implementation of a mechanical 

or electronic system or tool to automatically complete a 

task, thereby reducing or eliminating human intervention. 

2. Formerly known as OLE Automation, a 

Microsoft-designed technology that enables an application 

to expose objects and their properties for use by 

other applications. This allows a word processor to display 

and manipulate a spreadsheet program, for instance. 

The application that exposes an object for use is called 

the server; the application that manipulates the object is 

called the client. Automation can be either local or 

remote (on a computer elsewhere on a network). It is 

intended primarily for use by high-level languages such 

as Microsoft Visual Basic and Microsoft Visual C++. See 

also ActiveX control, OLE. 

automonitor n. A process or system feature capable of 

assessing the status of its own internal environment. 

autonomous agent n. A software or robotic entity that is 

capable of independent action in open, unpredictable environments. 

Often referred to as an intelligent agent, or simply 

agent, autonomous agents complete some kind of 

automatic process that can communicate with other agents 

or perform different kinds of directed tasks. Autonomous 

agents are currently being applied in areas as diverse as 

computer games, interactive cinema, information retrieval 

and filtering, user interface design, electronic commerce, 

auto piloting of vehicles and spacecraft, and industrial 

process control. Also called: intelligent agent. See also 

agent (definition 2). 

autonomous-system number n. See autonomous 

system. 

autonomous system n. A group of routers or networks 

controlled by a single administrative authority using a 

common Interior Gateway Protocol (IGP) for routing

Auto PC A/UX 

packets. Each autonomous system is assigned a globally 

unique number called an autonomous-system number 

(ASN). Acronym: AS. Also called: routing domain. See 

also IGP. 

Auto PC n. An information and entertainment system for 

use in automobiles. Developed by Microsoft and powered 

by Microsoft Windows CE (a Windows-compatible operating 

system designed for embedded applications), Auto 

PC implements speech-recognition technology to enable 

individuals to rely on hands-free, spoken commands for 

tasks such as accessing a contact database (names, 

addresses, numbers), calling up e-mail or traffic reports, 

controlling an audio system, or obtaining destination 

directions. The Auto PC fits into the dashboard, in the 

space normally occupied by a radio. See also voice recognition, 

Windows. 

AutoPlay n. A feature in Windows 9x and later that 

allows it to automatically operate a CD-ROM. When a CD 

is inserted into a CD-ROM drive, Windows looks for a file 

called AUTORUN.INF on the CD. If the file is found, 

Windows will open it and carry out its instructions, which 

are usually to set up an application from the CD-ROM on 

the computer’s hard disk or to start the application once it 

has been installed. If an audio CD is inserted into the 

drive, Windows will automatically launch the CD Player 

application and play it. 

autopolling n. The process of periodically determining 

the status of each device in a set so that the active program 

can process the events generated by each device, such as 

whether a mouse button was pressed or whether new data 

is available at a serial port. This can be contrasted with 

event-driven processing, in which the operating system 

alerts a program or routine to the occurrence of an event 

by means of an interrupt or message rather than having to 

check each device in turn. Also called: polling. Compare 

event-driven processing, interrupt-driven processing. 

autorepeat n. See typematic. 

autoresponder n. E-mail utility that replies automatically 

to an incoming e-mail. Typically, an autoresponder 

sends a standard, pre-written message confirming the 

receipt of the original e-mail. 

autorestart n. A process or system feature that can automatically 

restart the system after the occurrence of certain 

type of errors or a power system failure. 

45 

AUTORUN.INF n. A file that when present on removable 

media, such as CD-ROMs, triggers the AutoPlay feature 

in Windows 9x and Windows NT. The file, located in the 

root directory of the inserted medium, contains information 

on what action the operating system is to take on the 

CD-ROM—generally, an instruction to run an installation 

program. 

autosave n. A program feature that automatically saves 

an open file to a disk or other medium at defined intervals 

or after a certain number of keystrokes to ensure that 

changes to a document are periodically saved. 

autosizing n. The ability of a monitor to accept signals at 

one resolution and display the image at a different resolution. 

A monitor capable of autosizing maintains the aspect 

ratio of an image but enlarges or reduces the image to fit 

in the space available. See also monitor, resolution (definition 

1). 

autostart routine n. A process by which a system or 

device is automatically prepared for operation with the 

occurrence of powering up, or turning the system on, or some 

other predetermined event. See also AUTOEXEC.BAT, 

autorestart, boot2 , power up. 

autostereogram n. A computer-generated image, popularized 

in books and posters, that looks like an abstract 

design, but which emerges as a three-dimensional picture 

when the user looks beyond the image, without trying to 

focus on the hidden picture itself. Autostereograms in 

which the overlying design consists of a repetitive pattern 

are known as Single Image Stereograms (SIS). Those in 

which the design looks like a random pattern of colored 

dots are called Single Image Random Dot Stereograms, or 

SIRDS. Also called: stereogram. 

autotrace n. A drawing program feature that draws lines 

along the edges of a bitmapped image to convert the image 

to an object-oriented one. See also bitmapped graphics, 

object-oriented graphics. 

AUX n. The logical device name reserved by MS-DOS for 

an auxiliary device, or peripheral. AUX usually refers to a 

system’s first serial port, also known as COM1. 

A/UX n. A version of the multiuser, multitasking UNIX 

operating system provided by Apple Computer for various 

Macintosh computers and based on the AT&T System V, 

release 2.2 of UNIX with some enhancements. A/UX 

incorporates a number of Apple features, including support 

for the Macintosh Toolbox, so that applications can 

A

A auxiliary device axis 

provide users with the graphics-based interface characteristic 

of that computer. See also System V. 

auxiliary device n. See peripheral. 

auxiliary equipment n. See peripheral. 

auxiliary storage n. Any storage medium, such as disk 

or tape, not directly accessed by a computer’s microprocessor, 

as is random access memory (RAM). In current 

usage, such media are typically referred to as storage or 

permanent storage, and the RAM chips that the microprocessor 

uses directly for temporary storage are referred to 

as memory. 

availability n. 1. In processing, the accessibility of a computer 

system or resource, such as a printer, in terms of 

usage or of the percentage of the total amount of time the 

device is needed. 2. A measure of the fault tolerance of a 

computer and its programs. A highly available computer 

runs 24 hours a day, 7 days a week. See also fault tolerance. 

available time n. See uptime. 

avalanche ad n. One of several larger formats for online 

ads developed to replace traditional banner ads on the 

Internet. Avalanche ads are generally 120 x 800 pixels in 

size. See also skyscraper ad. 

avatar n. In virtual-reality environments such as certain 

types of Internet chat rooms, a graphical representation of 

a user. An avatar typically is a generic picture or animation 

of a human of either gender, a photograph or caricature 

of the user, a picture or animation of an animal, or an 

object chosen by the user to depict his or her virtual-reality 

“identity.” See superuser. 

46 

.avi n. The file extension that identifies an audiovisual 

interleaved data file in the Microsoft RIFF format. 

AVI n. Acronym for Audio Video Interleaved. A Windows 

multimedia file format for sound and moving pictures that 

uses the Microsoft RIFF (Resource Interchange File Format) 

specification. 

awk n. A UNIX-based language designed for file processing 

applications, awk is a part of the POSIX Command 

Language and Utilities standard. It is considered a subset 

of PERL. 

AWT n. See Abstract Window Toolkit. 

axis n. In a chart or other two-dimensional system using 

coordinates, the horizontal line (x-axis) or vertical line (yaxis) 

that serves as a reference for plotting points. In a 

three-dimensional coordinate system, a third line (z-axis) 

is used to represent depth. See the illustration. See also 

Cartesian coordinates. 

f0agn16.eps 

Axis. 

y-axis 

z-axis 

x-axis

1 adj. Short for binary. 

b 2 n. 1. Short for bit. 2. Short for baud. 

B n. Short for byte. 

B: or b: n. 1. Identifier for a second floppy disk drive on 

MS-DOS and other operating systems. 2. Identifier for a 

single disk drive when used as the secondary drive. 

B1FF n. Slang for a new online user who is prone to 

making mistakes in e-mail, newsgroup articles, or chats 

that show his or her inexperience. Examples of typical 

mistakes made by B1FFs include sentences ending with 

multiple exclamation points (!!!!) and messages typed in 

ALL CAPS. Although it’s spelled B-1(one)-F-F, the term 

is pronounced “bif.” 

B2B n. Short for business-to-business. The electronic 

exchange of products and services between businesses 

without the direct involvement of consumers. B2B’s 

effects on business include streamlining purchasing, 

accounting, and other administrative functions; lowering 

transaction costs; and simplifying the sale of excess 

inventory. Related businesses have collaborated on the 

creation of Internet-based supply-chain networks. 

B2C n. Short for business-to-consumer. The direct 

electronic exchange of products and services between 

businesses and consumers. B2C’s effects on business 

include improving the efficiency in delivering goods 

and services to consumers. 

backbone n. 1. A network of communication transmission 

that carries major traffic between smaller networks. 

The backbones of the Internet, including communications 

carriers such as Sprint and MCI, can span thousands of 

miles using microwave relays and dedicated lines. 2. The 

smaller networks (compared with the entire Internet) that 

perform the bulk of the packet switching of Internet communication. 

Today these smaller networks still consist of 

the networks that were originally developed to make up 

the Internet—the computer networks of the educational 

and research institutions of the United States—especially 

B 

47 

NSFnet, the computer network of the National Science 

Foundation in Oak Ridge, Tennessee. See also NSFnet, 

packet switching. 3. The wires that carry major communications 

traffic within a network. In a local area network, a 

backbone may be a bus. Also called: collapsed backbone. 

backbone cabal n. On the Internet, a term for the group 

of network administrators responsible for naming the hierarchy 

of Usenet newsgroups and devising the procedures 

for creating new newsgroups. The backbone cabal no 

longer exists. 

back door n. A means of gaining access to a program or 

system by bypassing its security controls. Programmers 

often build back doors into systems under development so 

that they can fix bugs. If the back door becomes known to 

anyone other than the programmer, or if it is not removed 

before the software is released, it becomes a security risk. 

Also called: trapdoor. 

back end n. 1. In a client/server application, the part of 

the program that runs on the server. See also client/server 

architecture. Compare front end. 2. In networking, a 

server computer or the processing that takes place on it. 

3. The part of a compiler that transforms source code 

(human-readable program statements) into object code 

(machine-readable code). See also compiler (definition 2), 

object code, source code. 

back-end processor n. 1. A slave processor that performs 

a specialized task such as providing rapid access to 

a database, freeing the main processor for other work. 

Such a task is considered “back-end” because it is subordinate 

to the computer’s main function. 2. A processor that 

manipulates data sent to it from another processor; for 

example, a high-speed graphics processor dedicated to 

painting images on a video display operates in response to 

commands passed “back” to it by the main processor. 

Compare coprocessor. 

background1 adj. In the context of processes or tasks that 

are part of an operating system or program, operating 

without interaction with the user while the user is working 

on another task. Background processes or tasks are 

B

ackground2 background 

Backspace key 

B assigned a lower priority in the microprocessor’s allotment 

of time than foreground tasks and generally remain invisible 

to the user unless the user requests an update or brings 

the task to the foreground. Generally, only multitasking 

operating systems are able to support background processing. 

However, some operating systems that do not support 

multitasking may be able to perform one or more types of 

background tasks. For example, in the Apple Macintosh 

operating system running with multitasking turned off, the 

Background Printing option can be used to print documents 

while the user is doing other work. See also multitasking. 

Compare foreground1 . 

background2 n.1. The color against which characters and 

graphics are displayed, such as a white background for 

black characters. Compare foreground2 (definition 1). 

2. The colors, textures, patterns, and pictures that comprise 

the surface of the desktop, upon which icons, buttons, 

menu bars, and toolbars are situated. See also 

wallpaper. 3. The colors, textures, patterns, and pictures 

that comprise the surface of a Web page, upon which text, 

icons, graphics, buttons, and other items are situated. See 

also wallpaper. 4. The condition of an open but currently 

inactive window in a windowing environment. See also 

inactive window. Compare foreground2 (definition 2). 

background noise n. The noise inherent in a line or circuit, 

independent of the presence of a signal. See also noise. 

background printing n. The process of sending a document 

to a printer at the same time that the computer is performing 

one or more other tasks. 

background processing n. The execution of certain 

operations by the operating system or a program during 

momentary lulls in the primary (foreground) task. An 

example of a background process is a word processor program 

printing a document during the time that occurs 

between the user’s keystrokes. See also background1 . 

background program n. A program that can run or is 

running in the background. See also background1 . 

background task n. See background1 . 

back-lit or backlit adj. Having a source of light, such as 

a lamp or LED behind a (usually translucent) viewing surface, 

in order to illuminate the surface. 

back-lit display or backlit display n. Something illuminated 

from behind, rather than by a light source above or 

to the front. 

BackOffice n. A suite of software developed by 

Microsoft that provides certain network services. 

48 

Designed to work with Windows NT and Windows 2000, 

BackOffice includes such services as e-mail (Exchange), 

intranet capabilities (Site Server), network management 

(Systems Management Server), and high-end database 

development (SQL Server), among others. 

Back Orifice n. A hostile application tool used by hackers 

to gain control of a remote computer. Back Orifice 

consists of client and server applications. The client application 

is used to control a computer running the server 

application. A target computer is taken over after an executable 

file, typically delivered by an e-mail attachment or 

a removable disk, is opened. Back Orifice then copies 

itself to the Windows System directory and transfers control 

to the machine running the client application. Back 

Orifice first appeared in the summer of 1998 and was 

quickly contained through updated security software. Its 

name is a play on words for the Microsoft BackOffice 

suite of servers. 

back panel n. The panel at the rear of a computer cabinet 

through which most of the connections to outside power 

sources and peripherals are made. See the illustration. 

F0Bgn01.eps 

Back panel. 

Back panel 

backplane n. A circuit board or framework that supports 

other circuit boards, devices, and the interconnections 

among devices, and provides power and data signals to 

supported devices. 

backslash n. See \. 

Backspace key n. 1. A key that, on IBM and compatible 

keyboards, moves the cursor to the left, one character at a 

time, usually erasing each character as it moves. 2. On 

Macintosh keyboards, a key (called the Delete key on 

some Macintosh keyboards) that erases currently selected 

text or, if no text is selected, erases the character to the left 

of the insertion point (cursor). See the illustration.

} 

] 

backtracking .bak 

Backspace 

F0Bgn02.eps 

Backspace key. 

Inse 

backtracking n. The ability of an expert system to try 

alternative solutions in an attempt to find an answer. The 

various alternatives can be viewed as branches on a tree: in 

backtracking, the program follows one branch and, if it 

reaches the end without finding what it seeks, backs up 

and tries another branch. 

back up vb. 1. To make a duplicate copy of a program, a 

disk, or data. See also backup. 2. To return to a previous 

stable state, such as one in which a database is known to 

be complete and consistent. 

backup n. A duplicate copy of a program, a disk, or data, 

made either for archiving purposes or for safeguarding 

valuable files from loss should the active copy be damaged 

or destroyed. A backup is an “insurance” copy. Some 

application programs automatically make backup copies 

of data files, maintaining both the current version and the 

preceding version on disk. Also called: backup copy, 

backup file. 

backup and recovery n. A strategy available in many 

database management systems that allows a database to be 

restored to the latest complete unit of work (transaction) 

after a software or hardware error has rendered the database 

unusable. The process starts with the latest backup 

copy of the database. The transaction log, or change file, 

for the database is read, and each logged transaction is 

recovered through the last checkpoint on the log. See also 

backup, checkpoint, log (definition 1). 

backup and restore n. The process of maintaining 

backup files and putting them back onto the source 

medium if necessary. 

backup copy n. See backup. 

backup file n. See backup. 

Backus-Naur form n. A metalanguage used for defining 

the syntax of formal languages, both for the developer of 

the language and for the user. A language is defined by a 

49 

set of statements, in each of which a language element 

known as a metavariable, written in angle brackets, is 

defined in terms of actual symbols (called terminals) and 

other metavariables (including itself if necessary). See the 

illustration. Acronym: BNF. See also metalanguage, normal 

form (definition 2). 

Del ::= 

 

::= 

 

::=0 1 2 3 4 5 6 7 8 9 

::=+ - 

F0Bgn03.eps 

Backus-Naur form. 

backward chaining n. In expert systems, a form of problem 

solving that starts with a statement and a set of rules 

leading to the statement and then works backward, matching 

the rules with information from a database of facts 

until the statement can be either verified or proved wrong. 

Compare forward chaining. 

bacterium n. A type of computer virus that repeatedly 

replicates itself, eventually taking over the entire system. 

See also virus. 

BAD adj. Acronym for broken as designed. Derogatory 

jargon for a product or device that consistently fails to work. 

bad block n. A faulty memory location. A bad block is 

identified by the computer’s memory controller in the selftest 

procedure when the computer is turned on or is rebooted. 

See bad sector. 

bad sector n. A disk sector that cannot be used for data 

storage, usually because of media damage or imperfections. 

Finding, marking, and avoiding bad sectors on a 

disk is one of the many tasks performed by a computer’s 

operating system. A disk-formatting utility can also find 

and mark the bad sectors on a disk. 

bad track n. A track on a hard disk or floppy disk that is 

identified as containing a faulty sector and consequently is 

bypassed by the operating system. See also bad sector. 

.bak n. An auxiliary file, created either automatically or 

upon command, that contains the second-most-recent version 

of a file and that bears the same file name, with the 

extension .bak. See also backup. 

B

alanced line bank 

B balanced line n. A transmission line, such as twisted-pair 

cabling, that contains two conductors capable of carrying 

equal voltages and currents of opposite polarity and direction. 

Balloon Help n. An on-screen help feature in the form of 

a cartoon dialog balloon on the Mac OS developed by 

Apple Computer, Inc. After activating this feature by 

clicking on the balloon icon on the toolbar, the user can 

position the cursor over an icon or other item, and a dialog 

balloon will appear that describes the function of the item. 

balloons n. In print layout view or Web layout view, 

markup balloons show markup elements, such as comments 

and tracked changes, in the margins of your document. 

Use these balloons to easily see and respond to 

reviewers’ changes and comments. 

ball printer n. An impact printer that uses a small ballshaped 

print head that bears fully formed characters in 

raised relief on its surface. The printer rotates and tilts the 

ball to line up characters and then strikes the ball against a 

ribbon. This method was used in the IBM Selectric typewriter. 

band n. 1. In printing graphics, a rectangular portion of a 

graphic sent by the computer to a printer. The technique of 

dividing a graphic into bands prevents a printer from having 

to reconstruct an entire image in memory before printing 

it. 2. In communications, a contiguous range of 

frequencies used for a particular purpose, such as radio or 

television broadcasts. 

bandpass filter n. An electronic circuit that passes signals 

that are within a certain frequency range (band) but 

blocks or attenuates signals above or below the band. See 

also attenuation. Compare highpass filter, lowpass filter. 

bandwidth n. 1. The difference between the highest and 

lowest frequencies that an analog communications system 

can pass as measured in Hertz (Hz) or cycles per second. 

For example, a telephone accommodates a bandwidth of 

3000 Hz: the difference between the lowest (300 Hz) and 

highest (3300 Hz) frequencies it can carry. 2. The data 

transfer capacity, or speed of transmission, of a digital communications 

system as measured in bits per second (bps). 

bandwidth allocation n. See bandwidth reservation. 

bandwidth brokerage n. See bandwidth trading. 

bandwidth exchange n. See bandwidth trading. 

50 

bandwidth management n. The analysis and control of 

traffic on WAN (wide area network) and Internet links to 

prioritize bandwidth and improve quality of service (QoS). 

See also quality of service (definition 2), traffic shaping. 

bandwidth on demand n. In telecommunications, the 

capability of increasing throughput, in increments, as 

required by the channel to be serviced. See also bandwidth, 

channel (definition 2), throughput. 

bandwidth reservation n. Process of assigning in 

advance a percentage of bandwidth to each user or application 

served by a network. Bandwidth reservation optimizes 

the use of available traffic by prioritizing time-critical 

packets. Also called: bandwidth allocation, custom queuing. 

See also bandwidth management, traffic shaping. 

bandwidth shaping n. See traffic shaping. 

bandwidth test n. A benchmark test that determines the 

speed of a network connection. Bandwidth tests estimate 

the downstream and upstream speeds by sending a series 

of packets over the network and measuring how many 

packets are received in a given amount of time. Also 

called: throughput test. See also benchmark1 , throughput 


bandwidth trading n. The exchange of excess bandwidth 

capacity. Although considered a possible commodity market, 

bandwidth trading currently lacks standardized contracts 

and instantaneous provisioning needed to simplify 

the trading process. Also called: bandwidth brokerage, 

bandwidth exchange. 

bang n. The pronunciation for an exclamation point, particularly 

when the exclamation point is used in a file name 

or in a path on UNIX systems. See also bang path. 

bang path n. Slang for an older form of e-mail address 

used in UUCP (UNIX-to-UNIX copy). A bang address 

supplies the path that the message needs to take to reach 

its destination, including the name of each host through 

which the message is to be passed. Exclamation points 

called “bangs” separate the elements of the e-mail address, 

such as the user account and host names. The address 

name!location, where “name” is the user account and 

“location” is the host name, would be spoken as “name 

bang location.” 

bank n.1. Any group of similar electrical devices connected 

together for use as a single device. For example, 

transistors may be connected in a row/column array inside

ank switching bare bones1 bones 

a chip to form memory, or several memory chips may be 

connected together to form a memory module such as a 

SIMM. See also SIMM. 2. A section of memory, usually 

of a size convenient for a CPU to address. For example, an 

8-bit processor can address 65,536 bytes of memory; 

therefore, a 64-kilobyte (64-KB) memory bank is the 

largest that the processor can address at once. To address 

another 64-KB bank of memory requires circuitry that 

fools the CPU into looking at a separate block of memory. 

See also bank switching, page (definition 2). 

bank switching n. A method of expanding a computer’s 

available random access memory (RAM) by switching 

between banks of RAM chips that share a range of memory 

addresses, which is set aside before switching begins. 

Only one bank is directly accessible at a time; when a 

bank is not active, it retains whatever is stored in it. Before 

another bank can be used, the operating system, driver, or 

program must explicitly issue a command to the hardware 

to make the switch. Because switching between banks 

takes time, memory-intensive operations take longer with 

bank-switched memory than with main memory. Bankswitched 

memory typically takes the form of an expansion 

card that plugs into a slot on the motherboard. 

banner n. A section of a Web page containing an advertisement 

that is usually an inch or less tall and spans the 

width of the Web page. The banner contains a link to the 

advertiser’s Web site. See also Web page, Web site. 

banner page n.1. The title page that may be added to 

printouts by most print spoolers. Such a page typically 

incorporates account ID information, job length, and print 

spooler information, and is used primarily to separate one 

print job from another. See also print spooler. 2. In software, 

an initial screen used to identify a product and credit 

its producers. 

bar chart n. A type of graphic in which data items are 

shown as rectangular bars. The bars may be displayed 

either vertically or horizontally and may be distinguished 

from one another by color or by some type of shading or 

pattern. Positive and negative values may be shown in 

relation to a zero baseline. Two types of bar charts are 

common: a standard bar chart, in which each value is represented 

by a separate bar, and a stacked bar chart, in 

which several data points are “stacked” to produce a single 

bar. See the illustration. Also called: bar graph. 

51 

Sales 

Quarter 

$1400 

$1200 

$1000 

$800 

$600 

$400 

$200 

$0 

Qtr 4 

Qtr 3 

Qtr 2 

Qtr 1 

$0 


Qtr 1 Qtr 2 Qtr 3 Qtr 4 

$200 

Quarter 

Vertical bar chart 


$400 $600 $800 $1,000 $1,200 $1,400 

Sales 

Stacked bar chart 

F0Bgn04.eps 

Bar chart. Two common types of bar chart. 

bar code n. The special identification code printed as a set 

of vertical bars of differing widths on books, grocery products, 

and other merchandise. Used for rapid, error-free input 

in such facilities as libraries, hospitals, and grocery stores, 

bar codes represent binary information that can be read by 

an optical scanner. The coding can include numbers, letters, 

or a combination of the two; some codes include built-in 

error checking and can be read in either direction. 

bar code reader n. See bar code scanner. 

bar code scanner n. An optical device that uses a laser 

beam to read and interpret bar codes, such as the Universal 

Product Codes found on grocery products and other retail 

items. See also bar code, Universal Product Code. 

bare board n. A circuit board with no chips on it; most commonly, 

a memory board not populated with memory chips. 

bare bones1 adj. Purely functional; stripped or otherwise 

clean of features. Bare bones applications provide only the 

most basic functions necessary to perform a given task. By 

B

are bones2 bones 

base RAM 

B the same token, a bare bones computer provides a minimal 

amount of hardware or is sold at retail with no peripherals 

and just the operating system (and no other software). 

bare bones2 n. 1. An application that provides only the 

most basic functions necessary to perform a given task. 

2. A computer consisting only of motherboard (equipped 

with CPU and RAM), cabinet, power supply, floppy disk 

drive, and keyboard, to which the user must add hard disk, 

video adapter, monitor, and any other peripherals. See also 

motherboard, peripheral. 

bar graph n. See bar chart. 

base n. 1. In mathematics, a number that is raised to the 

power specified by an exponent. For example, in 23 = 2 x 2 

x 2 = 8, the base is 2. 2. In mathematics, the number of 

digits in a particular numbering system. With microcomputers, 

four numbering systems are commonly used or 

referred to—binary, octal, decimal, and hexadecimal— 

and each is based on a different number of digits. The 

binary, or base-2, numbering system, which is used to discuss 

the states of a computer’s logic, has two digits, 0 and 

1. Octal, or base-8, has eight digits, 0 through 7. The 

familiar decimal, or base-10, numbering system has ten 

digits, 0 through 9. Hexadecimal, or base-16, has sixteen 

digits, 0 through 9 and A through F. When numbers are 

written in a particular base, the base is often subscripted 

and enclosed in parentheses after the number, as in 

24AE(16) = 9,390. Also called: radix. See also binary1 , 

decimal, hexadecimal, octal. 3. One of three terminals 

(emitter, base, and collector) in a bipolar transistor. The 

current through the base controls the current between the 

emitter and the collector. See also transistor. 4. The insulating 

foundation of a printed circuit board. See also circuit 

board. 

base 10 adj. See decimal. 

base 16 adj. See hexadecimal. 

base 2 adj. See binary1 . 

base 8 adj. See octal. 

base address n. The part of a two-part memory address 

that remains constant and provides a reference point from 

which the location of a byte of data can be calculated. A 

base address is accompanied by an offset value that is 

added to the base to determine the exact location (the 

absolute address) of the information. The concept is similar 

to a street address system. For example, “2010 Main 

Street” consists of a base (the 2000 block of Main Street) 

plus an offset (10 from the beginning of the block). Base 

addresses are known as segment addresses in IBM PCs 

52 

and compatibles; data in these computers is identified by 

its position as a relative offset from the start of the segment. 

See also absolute address, offset, relative 

address, segment. 

baseband adj. Of or relating to communications systems 

in which the medium of transmission (such as a wire or 

fiber-optic cable) carries a single message at a time in digital 

form. Baseband communication is found in local area 

networks such as Ethernet and Token Ring. See also Ethernet, 

fiber optics, Token Ring network. Compare broadband. 

baseband network n. A type of local area network in 

which messages travel in digital form on a single transmission 

channel between machines connected by coaxial 

cable or twisted-pair wiring. Machines on a baseband network 

transmit only when the channel is not busy, although 

a technique called time-division multiplexing can enable 

channel sharing. Each message on a baseband network 

travels as a packet that contains information about the 

source and destination machines as well as message data. 

Baseband networks operate over short distances at speeds 

ranging from about 50 kilobits per second (50 Kbps) to 16 

megabits per second (16 Mbps). Receiving, verifying, and 

converting a message, however, add considerably to the 

actual time, reducing throughput. The maximum recommended 

distance for such a network is about 2 miles, or 

considerably less if the network is heavily used. See also 

coaxial cable, multiplexing, packet (definition 2), throughput, 

time-division multiplexing, twisted-pair cable. Compare 

broadband network. 

base class n. In C++, a class from which other classes 

have been or can be derived by inheritance. See also class, 

derived class, inheritance, object-oriented programming. 

base line or baseline n. In the printing and display of 

characters on the screen, an imaginary horizontal line 

with which the base of each character, excluding descenders, 

is aligned. See the illustration. See also ascender, 

descender, font. 

F0Bgn05.eps 

Base line. 

Descender Base line 

base memory n. See conventional memory. 

base RAM n. See conventional memory.

ase station baud 

base station n. Transmission tower for wireless phone 

signals. Commonly known as cell towers, base stations 

also encompass the radio antennas and electronics that 

handle wireless calls. Base stations relay conversations 

into and out of the wired phone network and between 

wireless phones. Each base station covers a limited area 

known as a cell. 

base style n. The underlying or original style on which 

other styles in a document are dependent. When you 

change a formatting element of the base style in a document, 

all other styles that originate from the base style will 

also reflect the change. 

Basic or BASIC n. Acronym for Beginner’s All-purpose 

Symbolic Instruction Code, a high-level programming 

language developed in the mid-1960s by John Kemeny 

and Thomas Kurtz at Dartmouth College. It is widely considered 

one of the easiest programming languages to learn. 

See also True BASIC, Visual BASIC. 

Basic Rate Interface n. See BRI. 

Basic Service Set n. The communicating stations, or 

nodes, on a wireless LAN. See also wireless LAN. 

bastion host n. A computer which provides security by 

serving as a gateway between an internal network and 

external systems. All outside traffic attempting to connect 

to the internal network is routed through the bastion host, 

which defends against potential attacks by intercepting 

and screening incoming packets. The bastion host may be 

part of a larger security system providing multiple layers 

of protection. 

.bat n. The file extension that identifies a batch program 

file. In MS-DOS, .bat files are executable files that contain 

calls to other program files. See also batch file. 

batch n. A group of documents or data records that are 

processed as a unit. See also batch job, batch processing. 

batch file n. An ASCII text file containing a sequence of 

operating-system commands, possibly including parameters 

and operators supported by the batch command language. 

When the user types a batch file name at the 

command prompt, the commands are processed sequentially. 

Also called: batch program. See also 

AUTOEXEC.BAT, .bat. 

batch file transmission n. The transmission of multiple 

files as the result of a single command. Acronym: BFT. 

batch job n. A program or set of commands that runs 

without user interaction. See also batch processing. 

53 

batch processing n. 1. Execution of a batch file. See 

also batch file. 2. The practice of acquiring programs and 

data sets from users, running them one or a few at a time, 

and then providing the results to the users. 3. The practice 

of storing transactions for a period of time before they are 

posted to a master file, typically in a separate operation 

undertaken at night. Compare transaction processing. 

batch program n. A program that executes without interacting 

with the user. See also batch file. Compare interactive 

program. 

batch system n. A system that processes data in discrete 

groups of previously scheduled operations rather than 

interactively or in real time. 

batch total n. A total calculated for an element common 

to a group (batch) of records, used as a control to verify 

that all information is accounted for and has been entered 

correctly. For example, the total of a day’s sales can be used 

as a batch total to verify the records of all individual sales. 

battery n. Two or more cells in a container that produce 

an electrical current when two electrodes within the container 

touch an electrolyte. In personal computers, batteries 

are used as an auxiliary source of power when the main 

power is shut off, as a power source for laptop and notebook 

computers (rechargeable batteries, such as nickel 

cadmium, nickel metal hydride, and lithium ion, are used), 

and as a method to keep the internal clock and the circuitry 

responsible for the part of RAM that stores important 

system information always powered up. See also lead 

ion battery, lithium ion battery, nickel cadmium battery, 

nickel metal hydride battery, RAM. 

battery backup n. 1. A battery-operated power supply 

used as an auxiliary source of electricity in the event of a 

power failure. 2. Any use of a battery to keep a circuit running 

when the main power is shut off, such as powering a 

computer’s clock/calendar and the special RAM that 

stores important system information between sessions. See 

also UPS. 

battery meter n. A device used to measure the current 

(capacity) of an electrical cell. 

baud n. One signal change per second, a measure of data 

transmission speed. Named after the French engineer and 

telegrapher Jean-Maurice-Emile Baudot and originally 

used to measure the transmission speed of telegraph 

equipment, the term now most commonly refers to the 

data transmission speed of a modem. See also baud rate. 

B

Baudot code BEDO DRAM 

B Baudot code n. A 5-bit coding scheme used principally 

for telex transmissions, originally developed for telegraphy 

by the French engineer and telegrapher Jean-Maurice-Emile 

Baudot. Sometimes it is equated, although inaccurately, 

with the International Alphabet Number 2 proposed by the 

Comité Consultatif Internationale Télégraphique et Téléphonique 

(CCITT). 

baud rate n. The speed at which a modem can transmit 

data. The baud rate is the number of events, or signal 

changes, that occur in one second—not the number of bits 

per second (bps) transmitted. In high-speed digital communications, 

one event can actually encode more than one 

bit, and modems are more accurately described in terms of 

bits per second than baud rate. For example, a so-called 

9600-baud modem actually operates at 2400 baud but 

transmits 9600 bits per second by encoding 4 bits per 

event (2400 x 4 = 9600) and thus is a 9600-bps modem. 

Compare bit rate, transfer rate. 

bay n. A shelf or opening used for the installation of electronic 

equipment—for example, the space reserved for 

additional disk drives, CD-ROM drives, or other equipment 

in the cabinets of microcomputers. See also drive bay. 

bayonet-Neill-Concelman n. See BNC. 

BBL n. Acronym for be back later. An expression used 

commonly on live chat services on the Internet and online 

information services to indicate that a participant is temporarily 

leaving the discussion forum but intends to return 

at a later time. See also chat1 (definition 1). 

BBS n. 1. Acronym for bulletin board system. A computer 

system equipped with one or more modems or other 

means of network access that serves as an information and 

message-passing center for remote users. Often BBSs are 

focused on special interests, such as science fiction, movies, 

Windows software, or Macintosh systems, and can 

have free or fee-based access, or a combination. Users dial 

into a BBS with their modems and post messages to other 

BBS users in special areas devoted to a particular topic, in 

a manner reminiscent of the posting of notes on a cork 

bulletin board. Many BBSs also allow users to chat online 

with other users, send e-mail, download and upload files 

that include freeware and shareware software, and access 

the Internet. Many software and hardware companies run 

proprietary BBSs for customers that include sales infor- 

54 

mation, technical support, and software upgrades and 

patches. 2. Acronym for be back soon. A shorthand 

expression often seen in Internet discussion groups by a 

participant leaving the group who wishes to bid a temporary 

farewell to the rest of the group. 

bcc n. Acronym for blind courtesy copy. A feature of email 

programs that allows a user to send a copy of an email 

message to a recipient without notifying other recipients 

that this was done. Generally, the recipient’s address 

is entered into a field called “bcc:” in the mail header. Also 

called: blind carbon copy. See also e-mail1 (definition 1), 

header (definition 1). Compare cc. 

BCD n. See binary-coded decimal. 

bCentral n. A Web site for small businesses that provides 

online subscription services for customer management, 

financial management, and e-commerce. BCentral is part 

of the Microsoft .NET initiative. See also MSN, .NET. 

B channel n. Short for bearer channel. One of the 64- 

Kbps communications channels that carry data on an 

ISDN circuit. A BRI (Basic Rate Interface) ISDN line has 

two B channels and one D (data) channel. A PRI (Primary 

Rate Interface) ISDN line has 23 B channels (in North 

America) or 30 B channels (in Europe) and one D channel. 

See also BRI, D channel, ISDN. 

BCNF n. Acronym for Boyce-Codd normal form. See 

normal form (definition 1). 

beacon n. On an FDDI network, a special frame generated 

and passed along when a node detects a problem. See 

also frame (definition 2). 

beam vb. To transfer information from one device to 

another through an infrared wireless connection. The term 

typically refers to data sharing using handheld devices such 

as Palm organizers, Pocket PCs, mobile phones, and pagers. 

bearer channel n. See B channel. 

BeBox n. A high-performance multiprocessor computer 

(RISC-based PowerPC) made by Be, Inc., and loaded with 

Be’s operating system, BeOS. Be discontinued production 

of the BeBox in January 1997 in order to focus on software 

(BeOS) development. See also BeOS, PowerPC, RISC. 

BEDO DRAM n. Acronym for Burst Extended Data Out 

Dynamic RAM. A type of EDO (extended-data-out) 

dynamic RAM (DRAM) that handles memory transfers in

Beginner’s All-purpose Symbolic Instruction Code Beowulf 

bursts of four items in order to speed the process of returning 

data to a computer’s CPU. BEDO DRAM takes advantage 

of the fact that memory requests typically refer to 

sequential addresses. BEDO DRAM does not function 

well with bus speeds above 66 MHz. However, once it has 

accessed the first memory address, it can process the 

remaining three items in the burst at 10 ns (nanoseconds) 

each. Also called: BEDO RAM. See also dynamic RAM, 

EDO DRAM. 

Beginner’s All-purpose Symbolic Instruction 

Code n. See Basic. 

beginning-of-file n. 1. A code placed by a program before 

the first byte in a file, used by the computer’s operating 

system to keep track of locations within a file with respect 

to the first byte (character) in it. 2. The starting location of 

a file on a disk relative to the first storage location on the 

disk. A data directory or catalog contains this location. 

Acronym: BOF. Compare end-of-file. 

Bell communications standards n. A series of data 

transmission standards originated by AT&T during the 

late 1970s and early 1980s that, through wide acceptance 

in North America, became de facto standards for modems. 

Bell 103, now mostly obsolete, governed transmission at 

300 bits per second (bps) with full-duplex, asynchronous 

communications over dial-up telephone lines using frequency-shift 

keying (FSK). Bell 212A governed modem 

operations at 1200 bps with full-duplex, asynchronous 

communications over dial-up telephone lines using phaseshift 

keying (PSK). An international set of transmission 

standards, known as the CCITT recommendations, has 

become generally accepted as the primary source of standardization, 

especially for communications at speeds 

greater than 1200 bps. See also CCITT V series, FSK, 

phase-shift keying. 

Bell-compatible modem n. A modem that operates 

according to the Bell communications standards. See also 

Bell communications standards. 

Bellman-Ford distance-vector routing algorithm n. 

An algorithm that helps to determine the shortest route 

between two nodes on a network. The Routing Information 

Protocol (RIP) is based on the Bellman-Ford distancevector 

routing algorithm. See also RIP (definition 2). 

bells and whistles n. Attractive features added to hardware 

or software beyond basic functionality, comparable 

to accessories such as electric door locks and air conditioning 

added to an automobile. Products, especially com- 

55 

puter systems, without such adornments are sometimes 

called “plain vanilla.” 

benchmark1 n. A test used to measure hardware or software 

performance. Benchmarks for hardware use programs 

that test the capabilities of the equipment—for 

example, the speed at which a CPU can execute instructions 

or handle floating-point numbers. Benchmarks for 

software determine the efficiency, accuracy, or speed of a 

program in performing a particular task, such as recalculating 

data in a spreadsheet. The same data is used with 

each program tested, so the resulting scores can be compared 

to see which programs perform well and in what 

areas. The design of fair benchmarks is something of an 

art, because various combinations of hardware and software 

can exhibit widely variable performance under different 

conditions. Often, after a benchmark has become a 

standard, developers try to optimize a product to run that 

benchmark faster than similar products run it in order to 

enhance sales. See also sieve of Eratosthenes. 

benchmark2 vb. To measure the performance of hardware 

or software. 

benign virus n. A program that exhibits properties of a 

virus, such as self-replication, but does not otherwise do 

harm to the computer systems that it infects. 

BeOS n. An operating system developed by Be, Inc., that 

runs on PowerPC systems and, until they were discontinued, 

the company’s original BeBox computers. Designed 

as a “media OS,” the BeOS was created to support the 

large file sizes and high-performance processing demands 

of digital media and the Internet. It is an object-oriented, 

multithreaded operating system and can be run on symmetric 

multiprocessing systems containing two or more 

processors. Like many other operating systems, the BeOS 

provides preemptive multitasking, virtual memory, and 

memory protection. It also provides high-performance 

input/output capabilities, a 64-bit file system that can support 

terabyte-sized files, and a number of Internet-related 

features including built-in mail and Web services. See 

also BeBox. 

Beowulf n. Name for a class of virtual supercomputer 

created by linking numerous PCs through network connections 

into a single high-performance unit based on 

inexpensive, x86-based hardware and publicly available 

software, such as some versions of UNIX. This clustering 

technique can provide performance comparable to a traditional 

supercomputer at approximately 10 percent of the 

B

Beowulf-class computing bias 

B cost. The first Beowulf cluster was assembled at NASA’s 

Goddard Space Flight Center in 1994. The origin of the 

name comes from Beowulf, the hero who fought and 

killed the monster Grendel in an eighth-century Old 

English saga. 

Beowulf-class computing n. See Beowulf. 

Berkeley Internet Name Domain n. See BIND. 

Berkeley Sockets API n. See sockets API. 

Bernoulli box n. A removable floppy disk drive for personal 

computers that uses a nonvolatile cartridge and has 

high storage capacity. Named after Daniel Bernoulli, an 

eighteenth-century physicist who first demonstrated the 

principle of aerodynamic lift, the Bernoulli box uses high 

speed to bend the flexible disk close to the read/write head 

in the disk drive. See also read/write head. 

Bernoulli distribution n. See binomial distribution. 

Bernoulli process n. A mathematical process involving 

the Bernoulli trial, a repetition of an experiment in which 

there are only two possible outcomes, such as success and 

failure. This process is used mostly in statistical analysis. 

See also Bernoulli sampling process, binomial distribution. 

Bernoulli sampling process n. In statistics, a sequence 

of n independent and identical trials of a random experiment, 

with each trial having one of two possible outcomes. 

See also Bernoulli process, binomial distribution. 

best of breed adj. A term used to describe a product that 

is the best in a particular category of products. 

beta1 adj. Of or relating to software or hardware that is a 

beta. See also beta2 . Compare alpha1 . 

beta2 n. A new software or hardware product, or one that 

is being updated, that is ready to be released to users for 

beta testing in real-world situations. Usually betas have 

most or all of the features and functionality implemented 

that the finished product is to have. See also beta test. 

Compare alpha2 . 

beta site n. An individual or an organization that tests 

software before it is released to the public. The company 

producing the software usually selects these beta sites 

from a pool of established customers or volunteers. Most 

beta sites perform this service free of charge, often to get a 

56 

first look at the software and to receive free copies of the 

software once it is released to the public. 

beta test n. A test of software that is still under development, 

accomplished by having people actually use the 

software. In a beta test, a software product is sent to 

selected potential customers and influential end users 

(known as beta sites), who test its functionality and report 

any operational or utilization errors (bugs) found. The beta 

test is usually one of the last steps a software developer 

takes before releasing the product to market; however, if 

the beta sites indicate that the software has operational difficulties 

or an extraordinary number of bugs, the developer 

may conduct more beta tests before the software is 

released to customers. 

betweening n. See tween. 

bezel n. In arcade games, the bezel refers to the glass 

located around the monitor. It is often silk-screened with 

artwork relating to the game. See also arcade game. 

Bézier curve n. A curve that is calculated mathematically 

to connect separate points into smooth, free-form curves 

and surfaces of the type needed for illustration programs 

and CAD models. Bézier curves need only a few points to 

define a large number of shapes—hence their usefulness 

over other mathematical methods for approximating a 

given shape. See the illustration. See also CAD. 

F0Bgn06.eps 

Bézier curve. 

BFT n. See batch file transmission, binary file transfer. 

BGP n. See Border Gateway Protocol. 

bias n. 1. A uniform or systematic deviation from a point 

of reference. 2. In mathematics, an indication of the 

amount by which the average of a group of values deviates 

from a reference value. 3. In electronics, a voltage applied 

to a transistor or other electronic device to establish a ref-

idirectional binary1 binary 

erence level for its operation. 4. In communications, a type 

of distortion in the length of transmitted bits, caused by a 

lag that occurs as voltage builds up or falls off each time 

the signal changes from 0 to 1 or vice versa. 

bidirectional adj. Operating in two directions. A bidirectional 

printer can print from left to right and from right to 

left; a bidirectional bus can transfer signals in both directions 

between two devices. 

bidirectional parallel port n. An interface that supports 

two-way parallel communication between a device, such 

as a printer, and a computer. See also interface (definition 

3), parallel port. 

bidirectional printing n. The ability of an impact or inkjet 

printer to print from left to right and from right to left. 

Bidirectional printing improves speed substantially 

because no time is wasted returning the print head to the 

beginning of the next line, but it may lower print quality. 

bi-endian adj. Of, pertaining to, or characteristic of processors 

and other chips that can be switched to work in big 

endian or little endian mode. The PowerPC chip has this 

ability, which allows it to run the little endian Windows 

NT or the big endian MacOS/PPC. See also big endian, 

little endian, PowerPC. 

BIFF n. Short for Binary Interchange File Format. The 

native file format used by Microsoft Excel. 

biff n. 1. A BSD utility that issues a signal when new mail 

has arrived. Biff was named after a University of California 

graduate student’s dog who had a habit of barking at the 

mailman at the time the utility was developed. 2. See B1FF. 

biff vb. To provide notification of new (incoming) e-mail. 

bifurcation n. A split that results in two possible outcomes, 

such as 1 and 0 or on and off. 

Big 5 n. Traditional Chinese encoding. 

Big Blue n. The International Business Machines (IBM) 

Corporation. This nickname comes from the corporate 

color used on IBM’s early mainframes and still used in the 

company logo. 

big endian adj. Storing numbers in such a way that the 

most significant byte is placed first. For example, given 

the hexadecimal number A02B, the big endian method 

would cause the number to be stored as A02B, and the little 

endian method would cause the number to be stored as 

57 

2BA0. The big endian method is used by Motorola microprocessors; 

Intel microprocessors use the little endian 

method. The term big endian is derived from Jonathan 

Swift’s Gulliver’s Travels, in which the Big-Endians were 

a group of people who opposed the emperor’s decree that 

eggs should be broken at the small end before they were 

eaten. Compare little endian. 

bigint data type n. In an Access project, a data type of 8 

bytes (64 bits) that stores whole numbers in the range of 

–2^63 (–9,223,372,036,854,775,808) through 2^63–1 

(9,223,372,036,854,775,807). 

big iron n. One or more large, fast, and expensive computers, 

such as a Cray supercomputer or a room-filling 

mainframe system. 

big red switch n. The power on/off switch of a computer, 

thought of as a kind of interrupt or last resort. On the original 

IBM PC and many other computers, it was indeed big 

and red. Using the switch is an interrupt of last resort 

because it deletes all the data in RAM and can also damage 

the hard drive. Acronym: BRS. 

billboard n. A primitive inserted into a 3-D scene that is 

oriented so that one face is toward the viewer. A texture, 

usually an animated sprite, is applied to the billboard to 

give the appearance of a 3-D object in the scene. 

billion n. 1. In American usage (as is usual with microcomputers), 

a thousand million, or 109 . Computer terminology 

uses the prefixes giga- for 1 billion and nano- for 1 

billionth. 2. In British usage, a million million, or 1012 , 

which is a trillion in American usage. 

billisecond n. See nanosecond. 

bimodal virus n. See multipartite virus. 

.bin n. A file name extension for a file encoded with Mac- 

Binary. See also MacBinary. 

binary1 adj. Having two components, alternatives, or outcomes. 

The binary number system has 2 as its base, so values 

are expressed as combinations of two digits, 0 and 1. 

These two digits can represent the logical values true and 

false as well as numerals, and they can be represented in 

an electronic device by the two states on and off, recognized 

as two voltage levels. Therefore, the binary number 

system is at the heart of digital computing. Although ideal 

for computers, binary numbers are usually difficult for 

people to interpret because they are repetitive strings of 1s 

B

inary2 binary 

binary tree 

B and 0s. To ease translation, programmers and others who 

habitually work with the computer’s internal processing abilities 

use hexadecimal (base-16) or octal (base-8) numbers. 

See Appendix E. See also base (definition 2), binary-coded 

decimal, binary number, bit, Boolean algebra, byte, cyclic 

binary code, digital computer, dyadic, logic circuit. Compare 

ASCII, decimal, hexadecimal, octal. 

binary2 n. In an FTP client program, the command that 

instructs the FTP server to send or receive files as binary 

data. See also FTP client, FTP server. Compare ascii. 

binary chop n. See binary search. 

binary-coded decimal n. A system for encoding decimal 

numbers in binary form to avoid rounding and conversion 

errors. In binary-coded decimal coding, each digit of a 

decimal number is coded separately as a binary numeral. 

Each of the decimal digits 0 through 9 is coded in 4 bits, 

and for ease of reading, each group of 4 bits is separated 

by a space. This format is also called 8-4-2-1, after the 

weights of the four bit positions, and uses the following 

codes: 0000 = 0; 0001 = 1; 0010 = 2; 0011 = 3; 0100 = 4; 

0101 = 5; 0110 = 6; 0111 = 7; 1000 = 8; 1001 = 9. Thus, 

the decimal number 12 is 0001 0010 in binary-coded decimal 

notation. Acronym: BCD. See also base (definition 

2), binary1 , binary number, decimal, EBCDIC, packed 

decimal, round. 

binary compatibility n. Portability of executable programs 

(binary files) from one platform, or flavor of operating 

system, to another. See also flavor, portable (definition 1). 

binary conversion n. The conversion of a number to or 

from the binary number system. See Appendix E. See also 

binary1 . 

binary device n. Any device that processes information 

as a series of on/off or high/low electrical states. See also 

binary1 . 

binary digit n. Either of the two digits in the binary number 

system, 0 and 1. See also bit. 

binary file n. A file consisting of a sequence of 8-bit data 

or executable code, as distinguished from files consisting 

of human-readable ASCII text. Binary files are usually in 

a form readable only by a program, often compressed or 

58 

structured in a way that is easy for a particular program to 

read. Compare ASCII file. 

binary file transfer n. Transfer of a file containing arbitrary 

bytes or words, as opposed to a text file containing 

only printable characters (for example, ASCII characters 

with codes 10, 13, and 32–126). On modern operating systems 

a text file is simply a binary file that happens to contain 

only printable characters, but some older systems 

distinguish the two file types, requiring programs to handle 

them differently. Acronym: BFT. 

binary format n. Any format that structures data in 8-bit 

form. Binary format is generally used to represent object 

code (program instructions translated into a machinereadable 

form) or data in a transmission stream. See also 

binary file. 

binary notation n. Representation of numbers using the 

binary digits, 0 and 1. Compare floating-point notation. 

binary number n. A number expressed in binary form, or 

base 2. Binary numbers are composed of zeros and ones. 

See Appendix E. See also binary1 . 

binary search n. A type of search algorithm that seeks an 

item, with a known name, in an ordered list by first comparing 

the sought item to the item at the middle of the 

list’s order. The search then divides the list in two, determines 

in which half of the order the item should be, and 

repeats this process until the sought item is found. Also 

called: binary chop, dichotomizing search. See also search 

algorithm. Compare hash search, linear search. 

binary synchronous protocol n. See BISYNC. 

binary transfer n. The preferred mode of electronic 

exchange for executable files, application data files, and 

encrypted files. Compare ASCII transfer. 

binary tree n. In programming, a specific type of tree 

data structure in which each node has at most two subtrees, 

one left and one right. Binary trees are often used for 

sorting information; each node of the binary search tree 

contains a key, with values less than that key added to one 

subtree and values greater than that key added to the other. 

See the illustration. See also binary search, tree.

inaural sound biometrics 

F0Bgn07.eps 

Binary tree. 

20 

12 24 

8 13 22 28 

2 9 21 23 26 

binaural sound n. See 3-D audio. 

bind vb. To associate two pieces of information with one 

another. The term is most often used with reference to 

associating a symbol (such as the name of a variable) with 

some descriptive information (such as a memory address, 

a data type, or an actual value). See also binding time, 

dynamic binding, static binding. 

BIND n. Acronym for Berkeley Internet Name Domain. A 

domain name server originally written for the BSD version 

of UNIX developed at the Berkeley campus of the 

University of California but now available for most versions 

of UNIX. As a domain name server, BIND translates 

between human-readable domain names and Internetfriendly, 

numeric IP addresses. It is widely used on Internet 

servers. See also DNS, DNS server, IP address. 

Binder n. A Microsoft Office program that you can use to 

organize related documents. You can check spelling, number 

pages consecutively across all documents in the 

binder, and print the documents. 

binding n. The process by which protocols are associated 

with one another and the network adapter to provide a 

complete set of protocols needed for handling data from 

the application layer to the physical layer. See also ISO/ 

OSI reference model. 

binding time n. The point in a program’s use at which 

binding of information occurs, usually in reference to program 

elements being bound to their storage locations and 

values. The most common binding times are during compilation 

(compile-time binding), during linking (link-time 

59 

binding), and during program execution (run-time binding). 

See also bind, compile-time binding, link-time binding, 

run-time binding. 

BinHex1 n. 1. Short for binary to hexadecimal. A format 

for converting binary data files into ASCII text so they can 

be transmitted via e-mail to another computer or in a 

newsgroup post. This method can be used when standard 

ASCII characters are needed for transmission, as they are 

on the Internet. BinHex is used most frequently by Mac 

users. See also MIME. 2. An Apple Macintosh program 

for converting binary data files into ASCII text and vice 

versa using the BinHex format. Compare uudecode1 , 

uuencode1 . 

BinHex2 vb. To convert a binary file into printable 7-bit 

ASCII text or to convert the resulting ASCII text file back 

to binary format using the BinHex program. Compare 

uudecode2 , uuencode2 . 

binomial distribution n. In statistics, a list or a function 

that describes the probabilities of the possible values of a 

random variable chosen by means of a Bernoulli sampling 

process. A Bernoulli process has three characteristics: 

each trial has only two possible outcomes—success or 

failure; each trial is independent of all other trials; and the 

probability of success for each trial is constant. A binomial 

distribution can be used to calculate the probability 

of getting a specified number of successes in a Bernoulli 

process. For example, the binomial distribution can be 

used to calculate the probability of getting a 7 three times 

in 20 rolls of a pair of dice. Also called: Bernoulli distribution. 

BioAPI n. An open system specification for use in biometric 

security and authentication technologies. BioAPI supports 

a wide range of biometric technology, from handheld 

devices to large-scale networks, and applications include 

fingerprint identification, facial recognition, speaker verification, 

dynamic signatures, and hand geometry. BioAPI 

was developed for the BioAPI Consortium, a group of 

organizations with ties to biometrics. BioAPI incorporates 

compatibility with existing biometric standards such as 

HA-API, which allows applications to operate BioAPIcompliant 

technologies without modification. 

biometrics n. Traditionally, the science of measuring and 

analyzing human biological characteristics. In computer 

technology, biometrics relates to authentication and secu- 

B

ionics BISYNC 

B rity techniques that rely on measurable, individual biological 

stamps to recognize or verify an individual’s identity. 

For example, fingerprints, handprints, or voice-recognition 

might be used to enable access to a computer, to a 

room, or to an electronic commerce account. Security 

schemes are generally categorized into three levels: level 1 

relies on something the person carries, such as an ID 

badge with a photo or a computer cardkey; level 2 relies 

on something the person knows, such as a password or a 

code number; and level 3, the highest level, relies on 

something that is a part of the person’s biological makeup 

or behavior, such as a fingerprint, the pattern of blood vessels 

in a retina, or a signature. See also fingerprint reader, 

handwriting recognition (definition 1), voice recognition. 

bionics n. The study of living organisms, their characteristics, 

and the ways they function, with a view toward creating 

hardware that can simulate or duplicate the activities 

of a biological system. See also cybernetics. 

BIOS n. Acronym for basic input/output system. On PCcompatible 

computers, the set of essential software routines 

that tests hardware at startup, starts the operating system, 

and supports the transfer of data among hardware 

devices, including the date and time. The operating system 

date is initialized from the BIOS or Real Time Clock date 

when the machine is booted. Many older PCs, particularly 

those dating before 1997, have BIOSs that store only 2digit 

years and thus may have suffered from Year 2000 

problems. The BIOS is stored in read-only memory (ROM) 

so that it can be executed when the computer is turned on. 

Although critical to performance, the BIOS is usually 

invisible to computer users. See also AMI BIOS, CMOS 

setup, Phoenix BIOS, ROM BIOS. Compare Toolbox. 

BIOS test n. A test to see if a PC will make the transition 

to the year 2000 and keep the correct date. The test can 

range from resetting the system time in the BIOS and 

Synchronizing 

characters 

Optional 

header 

STX 

F0Bgn08.eps 

BISYNC. The structure of a BISYNC frame. 

60 

rebooting to running a program or software routine specially 

designed to uncover Year 2000 problems. 

bipartite virus n. See multipartite virus. 

bipolar adj. 1. Having two opposite states, such as positive 

and negative. 2. In information transfer and processing, 

pertaining to or characteristic of a signal in which 

opposite voltage polarities represent on and off, true and 

false, or some other pair of values. See also nonreturn to 

zero. Compare unipolar. 3. In electronics, pertaining to or 

characteristic of a transistor having two types of charge 

carriers. See also transistor. 

BIS n. See business information system. 

BISDN n. See broadband ISDN. 

bistable adj. Of, pertaining to, or characteristic of a system 

or device that has two possible states, such as on and 

off. See also flip-flop. 

bistable circuit n. Any circuit that has only two stable 

states. The transition between them must be initiated from 

outside the circuit. A bistable circuit is capable of storing 

1 bit of information. 

bistable multivibrator n. See flip-flop. 

BISYNC n. Short for binary synchronous communications 

protocol. A communications standard developed by 

IBM. BISYNC transmissions are encoded in either ASCII 

or EBCDIC. Messages can be of any length and are sent in 

units called frames, optionally preceded by a message 

header. BISYNC uses synchronous transmission, in which 

message elements are separated by a specific time interval, 

so each frame is preceded and followed by special characters 

that enable the sending and receiving machines to synchronize 

their clocks. STX and ETX are control characters 

that mark the beginning and end of the message text; BCC 

is a set of characters used to verify the accuracy of transmission. 

See the illustration. Also called: BSC. 

Message 

ETX 

BCC 

Final 

synchronizing 

characters

it bitmapped font 

bit n. Short for binary digit. The smallest unit of information 

handled by a computer. One bit expresses a 1 or a 0 in 

a binary numeral, or a true or false logical condition, and 

is represented physically by an element such as a high or 

low voltage at one point in a circuit or a small spot on a 

disk magnetized one way or the other. A single bit conveys 

little information a human would consider meaningful. A 

group of 8 bits, however, makes up a byte, which can be 

used to represent many types of information, such as a letter 

of the alphabet, a decimal digit, or other character. See 

also ASCII, binary1 , byte. 

bit block n. In computer graphics and display, a rectangular 

group of pixels treated as a unit. Bit blocks are so 

named because they are, literally, blocks of bits describing 

the pixels’ display characteristics, such as color and intensity. 

Programmers use bit blocks and a technique called bit 

block transfer (bitblt) to display images rapidly on the 

screen and to animate them. See also bit block transfer. 

bit block transfer n. In graphics display and animation, a 

programming technique that manipulates blocks of bits in 

memory that represent the color and other attributes of a 

rectangular block of pixels forming a screen image. The 

image described can range in size from a cursor to a cartoon. 

Such a bit block is moved through a computer’s 

video RAM as a unit so that its pixels can be rapidly displayed 

in a desired location on the screen. The bits can 

also be altered; for example, light and dark portions of an 

image can be reversed. Successive displays can thus be 

used to change the appearance of an image or to move it 

around on the screen. Some computers contain special 

graphics hardware for manipulating bit blocks on the 

screen independently of the contents of the rest of the 

screen. This speeds the animation of small shapes, 

because a program need not constantly compare and 

redraw the background around the moving shape. Also 

called: bitblt. See also sprite. 

bitblt n. See bit block transfer. 

bit bucket n. An imaginary location into which data can 

be discarded. A bit bucket is a null input/output device 

from which no data is read and to which data can be written 

without effect. The NUL device recognized by MS- 

DOS is a bit bucket. A directory listing, for example, simply 

disappears when sent to NUL. 

61 

bit data type n. In an Access project, a data type that 

stores either a 1 or 0 value. Integer values other than 1 or 0 

are accepted, but are always interpreted as 1. 

bit density n. A measure of the amount of information 

per unit of linear distance or surface area in a storage 

medium or per unit of time in a communications pipeline. 

bit depth n. The number of bits per pixel allocated for 

storing indexed color information in a graphics file. 

bit flipping n. A process of inverting bits—changing 1s to 

0s and vice versa. For example, in a graphics program, to 

invert a black-and-white bitmapped image (to change 

black to white and vice versa), the program could simply 

flip the bits that compose the bit map. 

bit image n. A sequential collection of bits that represents 

in memory an image to be displayed on the screen, particularly 

in systems having a graphical user interface. Each 

bit in a bit image corresponds to one pixel (dot) on the 

screen. The screen itself, for example, represents a single 

bit image; similarly, the dot patterns for all the characters 

in a font represent a bit image of the font. In a black-andwhite 

display each pixel is either white or black, so it can 

be represented by a single bit. The “pattern” of 0s and 1s 

in the bit image then determines the pattern of white and 

black dots forming an image on the screen. In a color display 

the corresponding description of on-screen bits is 

called a pixel image because more than one bit is needed 

to represent each pixel. See also bitmap, pixel image. 

bit manipulation n. An action intended to change only 

one or more individual bits within a byte or word. Manipulation 

of the entire byte or word is much more common 

and generally simpler. See also mask. 

bitmap n. A data structure in memory that represents 

information in the form of a collection of individual bits. 

A bit map is used to represent a bit image. Another use of 

a bit map in some systems is the representation of the 

blocks of storage on a disk, indicating whether each block 

is free (0) or in use (1). See also bit image, pixel image. 

bitmapped font n. A set of characters in a particular size 

and style in which each character is described as a unique 

bit map (pattern of dots). Macintosh screen fonts are 

examples of bitmapped fonts. See the illustration. See also 

B

itmapped graphics bits per inch 

B downloadable font, outline font, TrueType. Compare Post- 

Script font, vector font. 

F0Bgn09.eps 

Bitmapped font. Each character is composed of a pattern 

of dots. 

bitmapped graphics n. Computer graphics represented 

as arrays of bits in memory that represent the attributes of 

the individual pixels in an image (one bit per pixel in a 

black-and-white display, multiple bits per pixel in a color 

or gray-scale display). Bitmapped graphics are typical of 

paint programs, which treat images as collections of dots 

rather than as shapes. See also bit image, bit map, pixel 

image. Compare object-oriented graphics. 

bit mask n. A value used with bit-wise operators (And, 

Eqv, Imp, Not, Or, and Xor) to test, set, or reset the state of 

individual bits in a bit-wise field value. 

BITNET n. Acronym for Because It’s Time Network. A 

WAN (wide area network) founded in 1981 and operated 

by the Corporation for Research and Educational Networking 

(CREN) in Washington, D.C. Now defunct, BIT- 

NET provided e-mail and file transfer services between 

mainframe computers at educational and research institutions 

in North America, Europe, and Japan. BITNET used 

the IBM Network Job Entry (NJE) protocol rather than 

TCP/IP, but it could exchange e-mail with the Internet. 

The listserv software for maintaining mailing lists was 

originated on BITNET. 

bit. newsgroups n. A hierarchy of Internet newsgroups 

that mirror the content of some BITNET mailing lists. See 

also BITNET. 

bit-oriented protocol n. A communications protocol in 

which data is transmitted as a steady stream of bits rather 

than as a string of characters. Because the bits transmitted 

have no inherent meaning in terms of a particular character 

set (such as ASCII), a bit-oriented protocol uses special 

sequences of bits rather than reserved characters for control 

purposes. The HDLC (high-level data link control) 

defined by ISO is a bit-oriented protocol. Compare byteoriented 

protocol. 

62 

bit parallel adj. Transmitting simultaneously all bits in a 

set (such as a byte) over separate wires in a cable. See also 

parallel transmission. 

bit pattern n. 1. A combination of bits, often used to 

indicate the possible unique combinations of a specific 

number of bits. For example, a 3-bit pattern allows 8 possible 

combinations and an 8-bit pattern allows 256 combinations. 

2. A pattern of black and white pixels in a 

computer system capable of supporting bitmapped graphics. 

See also pixel. 

bitplane n. 1. One of a set of bit maps that collectively 

make up a color image. Each bit plane contains the values 

for one bit of the set of bits that describe a pixel. One bit 

plane allows two colors (usually black and white) to be 

represented; two bit planes, four colors; three bit planes, 

eight colors; and so on. These sections of memory are 

called bit planes because they are treated as if they were 

separate layers that stack one upon another to form the 

complete image. By contrast, in a chunky pixel image, the 

bits describing a given pixel are stored contiguously 

within the same byte. The use of bit planes to represent 

colors is often associated with the use of a color look-up 

table, or color map, which is used to assign colors to particular 

bit patterns. Bit planes are used in the EGA and 

VGA in 16-color graphics modes; the four planes correspond 

to the 4 bits of the IRGB code. See also color lookup 

table, color map, EGA, IRGB, layering, VGA. Compare 

color bits. 2. Rarely, one level of a set of superimposed 

images (such as circuit diagrams) to be displayed on 

the screen. 

bit rate n. 1. The speed at which binary digits are transmitted. 

See also transfer rate. 2. The streaming speed of 

digital content on a network. Bit rate is usually measured 

in kilobits per second (Kbps). 

bit serial n. The transmission of bits in a byte one after 

another over a single wire. See also serial transmission. 

bit slice microprocessor n. A building block for microprocessors 

that are custom-developed for specialized uses. 

These chips can be programmed to handle the same tasks 

as other CPUs but they operate on short units of information, 

such as 2 or 4 bits. They are combined into processors 

that handle the longer words. 

bits per inch n. A measure of data storage capacity; the 

number of bits that fit into an inch of space on a disk or a 

tape. On a disk, bits per inch are measured based on inches 

of circumference of a given track. Acronym: BPI. See also 

packing density.

its per pixel blackout 

bits per pixel n. Also known as color depth or bit depth. 

The term refers to the number of bits (8, 16, 24, or 32) 

used to store and display the color data for a single pixel. 

The number of bits per pixel determines the range of color 

available to an image. Acronym: bpp. 

bits per second n. See bps. 

bit stream n. 1. A series of binary digits representing a 

flow of information transferred through a given medium. 

2. In synchronous communications, a continuous flow of 

data in which characters in the stream are separated from 

one another by the receiving station rather than by markers, 

such as start and stop bits, inserted into the data. 

bit stuffing n. The practice of inserting extra bits into a 

stream of transmitted data. Bit stuffing is used to ensure 

that a special sequence of bits appears only at desired 

locations. For example, in the HDLC, SDLC, and X.25 

communications protocols, six 1 bits in a row can appear 

only at the beginning and end of a frame (block) of data, 

so bit stuffing is used to insert a 0 bit into the rest of the 

stream whenever five 1 bits appear in a row. The inserted 0 

bits are removed by the receiving station to return the data 

to its original form. See also HDLC, SDLC, X.25. 

bit transfer rate n. See transfer rate. 

bit twiddler n. Slang for someone devoted to computers, 

particularly one who likes to program in assembly language. 

See also hacker. 

BIX n. Acronym for BYTE Information Exchange. An 

online service originated by BYTE magazine, now owned 

and operated by Delphi Internet Services Corporation. 

BIX offers e-mail, software downloads, and conferences 

relating to hardware and software. 

.biz n. One of seven new top-level domain names 


Names and Numbers (ICANN), .biz is meant for use in 

business-related Web sites. 

biz. news groups n. Usenet newsgroups that are part of 

the biz. hierarchy and have the prefix of biz. These newsgroups 

are devoted to discussions related to business. 

Unlike most other newsgroup hierarchies, biz. newsgroups 

permit users to post advertisement and other marketing 

material. See also newsgroup, traditional newsgroup 

hierarchy. 

63 

BizTalk Server n. An application developed by Microsoft 

Corporation to streamline business processes within a 

large company’s internal network and between business 

partners over the Internet. BizTalk Server enables the integration 

of business applications written in different computer 

languages and running on various operating systems. 

BlackBerry n. A wireless handheld device that allows 

mobile users to send and receive e-mail, as well as view 

appointment calendars and contact lists. The BlackBerry 

features a display screen and a built-in keyboard operated 

by pressing the keys with the thumbs. BlackBerry’s ease 

of use and its ability to send and receive messages silently 

have made it a popular device for wireless text messaging 

in a business environment. 

black box n. A unit of hardware or software whose internal 

structure is unknown but whose function is documented. 

The internal mechanics of the function do not 

matter to a designer who uses a black box to obtain that 

function. For example, a memory chip can be viewed as a 

black box. Many people use memory chips and design 

them into computers, but generally only memory chip 

designers need to understand their internal operation. 

black box testing n. An approach to testing software in 

which the tester treats the software as a black box—that is, 

the testing focuses on the program’s functionality rather 

than on its internal structure. Black box testing is thus user 

oriented, in that the primary concern is whether the program 

works, not how it is constructed. Black box testing is 

generally performed on software that is under development. 

Compare white box testing. 

black hat n. A hacker who operates with malicious or 

criminal intent. A black hat will break into a system to alter 

or damage data or to commit theft. Compare white hat. 

black hole n. A mysterious “place” on a computer network 

where messages, such as e-mail and news items, disappear 

without a trace. The usage is derived from stellar 

black holes, which have such strong gravitational fields 

that even light cannot escape them. The term is sometimes 

also used to refer to projects that consume vast amounts of 

time with no apparent product. 

blackout n. A condition in which the electricity level 

drops to zero; a complete loss of power. A number of factors 

cause a blackout, including natural disasters, such as a 

storm or an earthquake, or a failure in the power company’s 

B

lank1 blank 

block2 block 

B equipment, such as a transformer or a power line. A blackout 

might or might not damage a computer, depending on 

the state of the computer when the blackout occurs. As 

with switching a computer off before saving any data, a 

blackout will cause all unsaved data to be irretrievably lost. 

The most potentially damaging situation is one in which a 

blackout occurs while a disk drive is reading information 

from or writing information to a disk. The information 

being read or written will probably become corrupted, 

causing the loss of a small part of a file, an entire file, or the 

entire disk; the disk drive itself might suffer damage as a 

result of the sudden power loss. The only reliable means of 

preventing damage caused by a blackout is to use a batterybacked 

uninterruptible power supply (UPS). See also UPS. 

Compare brownout. 

blank1 n. The character entered by pressing the spacebar. 

See also space character. 

blank2 vb. To not show or not display an image on part or 

all of the screen. 

blanking n. The brief suppression of a display signal as 

the electron beam in a raster-scan video monitor is moved 

into position to display a new line. After tracing each scan 

line, the beam is at the right edge of the screen and must 

return to the left (horizontal retrace) to begin a new line. 

The display signal must be turned off during the time of 

the retrace (horizontal blanking interval) to avoid overwriting 

the line just displayed. Similarly, after tracing the 

bottom scan line, the electron beam moves to the top left 

corner (vertical retrace), and the beam must be turned off 

during the time of this retrace (vertical blanking interval) 

to avoid marking the screen with the retrace path. 

blast vb. See burn (definition 1). 

bleed n. In a printed document, any element that runs off 

the edge of the page or into the gutter. Bleeds are often 

used in books to mark important pages so they are easier 

to find. See also gutter. 

blend1 n. A photo or graphic created with a software 

blending process. 

blend2 vb. In illustration and other graphics software, to 

create a new combined graphic from two or more separate 

graphic elements. Photos, art, colors, shapes, and text may 

be blended together digitally. Graphic elements may be 

blended for artistic effect, or may be realistic enough to 

appear as a single photo or graphic. 

64 

blind carbon copy n. See bcc. 

blind courtesy copy n. See bcc. 

blind search n. A search for data in memory or on a storage 

device with no foreknowledge as to the data’s order or 

location. See also linear search. Compare binary search, 

indexed search. 

blink vb. To flash on and off. Cursors, insertion points, 

menu choices, warning messages, and other displays on a 

computer screen that are intended to catch the eye are 

often made to blink. The rate of blinking in a graphical 

user interface can sometimes be controlled by the user. 

blink speed n. The rate at which the cursor indicating the 

active insertion point in a text window, or other display 

element, flashes on and off. 

blip n. A small, optically sensed mark on a recording 

medium, such as microfilm, that is used for counting or 

other tracking purposes. 

blit vb. To render a glyph/bitmap to the display. Also 

called: blitting. See also bit block transfer. 

blitter n. A function that copies a bitmap from memory 

onto the screen. 

bloatware n. Software whose files occupy an extremely 

large amount of storage space on a user’s hard disk, especially 

in comparison with previous versions of the same 

product. 

block1 n. 1. Generally, a contiguous collection of similar 

things that are handled together as a whole. 2. A section of 

random access memory temporarily assigned (allocated) 

to a program by the operating system. 3. A group of statements 

in a program that are treated as a unit. For example, 

if a stated condition is true, all of the statements in the 

block are executed, but none are executed if the condition 

is false. 4. A unit of transmitted information consisting of 

identification codes, data, and error-checking codes. 5. A 

collection of consecutive bytes of data that are read from 

or written to a device (such as a disk) as a group. 6. A rectangular 

grid of pixels that are handled as a unit. 7. A segment 

of text that can be selected and acted upon as a 

whole in an application. 8. In the Java programming language, 

any code between matching braces constitutes a 

block. For example, { x = 1; }. See also code, Java. 

block2 vb. 1. To distribute a file over fixed-size blocks in 

storage. 2. To prevent a signal from being transmitted.

lock cipher blow up 

3. To select a segment of text, by using a mouse, menu 

selection, or cursor key, to be acted upon in some way, 

such as to format or to delete the segment. 

block cipher n. A private key encryption method that 

encrypts data in blocks of a fixed size (usually 64 bits). 

The encrypted data block contains the same number of 

bits as the original. See also encryption, private key. 

block cursor n. An on-screen cursor that has the same 

width and height in pixels as a text-mode character cell. A 

block cursor is used in text-based applications, especially 

as the mouse pointer when a mouse is installed in the system. 

See also character cell, cursor (definition 1), mouse 

pointer. 

block device n. A device, such as a disk drive, that 

moves information in blocks—groups of bytes—rather than 

one character (byte) at a time. Compare character device. 

block diagram n. A chart of a computer or other system 

in which labeled blocks represent principal components 

and lines and arrows between the blocks show the pathways 

and relationships among the components. A block 

diagram is an overall view of what a system consists of 

and how it works. To show the various components of 

such a system in more detail, different types of diagrams, 

such as flowcharts or schematics, are used. See the illustration. 

Compare bubble chart, flowchart. 

F0Bgn10.eps 

Block diagram. 

ROM RAM 

Keyboard Processor Screen 

Disk drive 

block gap n. The unused physical space that separates 

blocks of data or physical records on a tape or formatted 

sectors on a disk. Also called: IBG, interblock gap. 

block header n. Information that appears at the beginning 

of a block of data and serves such purposes as signaling 

the beginning of the block, identifying the block, 

providing error-checking information, and describing such 

characteristics as the block length and the type of data 

contained in the block. See also header (definition 2). 

65 

blocking factor n. 1. The size of the chunks in which 

data is transferred to or from a block device such as a disk. 

If fewer bytes are requested, the disk drive will still read 

the whole block. Common blocking factors on personal 

computers are 128, 256, and 512 bytes. 2. The number of 

file records in one disk block. If the record length for a file 

is 170 bytes, a block on the disk contains 512 bytes, and 

records do not span blocks, then the blocking factor is 3, 

and each block contains 510 (170 x 3) bytes of data and 2 

unused bytes. 

block length n. The length, usually in bytes, of a block of 

data. Block length typically ranges from 512 bytes 

through 4096 kilobytes (KB), depending on the purpose 

for which the block is used. 

block move n. Movement of a number of items of data 

together to a different location, as in reorganizing documents 

with a word processor or moving the contents of 

cell ranges in a spreadsheet. Most CPUs have instructions 

that easily support block moves. 

block size n. The declared size of a block of data transferred 

internally within a computer, via FTP, or by 

modem. The size is usually chosen to make the most efficient 

use of all the hardware devices involved. See also 

FTP1 (definition 1). 

block structure n. The organization of a program into 

groups of statements called blocks, which are treated as 

units. Programming languages such as Ada, C, and Pascal 

were designed around block structure. A block is a section 

of code surrounded by certain delimiters (such as BEGIN 

and END or { and }), which signify that the intervening 

code can be treated as a related group of statements. For 

example, in C, each function is a separate block. Block 

structure also limits the scope of constants, data types, and 

variables declared in a block to that block. See also function 

(definition 2), procedure, scope (definition 1). 

block transfer n. The movement of data in discrete 

blocks (groups of bytes). 

blog1 n. See weblog. 

blog2 vb. To create or maintain a weblog. 

blogger n. One who creates or maintains a weblog. 

blow vb. See burn (definition 1). 

blow up vb. To terminate abnormally, as when a program 

crosses some computational or storage boundary and cannot 

handle the situation on the other side, as in, “I tried to 

B

lue screen BOF 

B draw outside the window, and the graphics routines blew 

up.” See also abend, abort. 

blue screen n. A technique used in film matte special 

effects, in which one image is superimposed on another 

image. Action or objects are filmed against a blue screen. 

The desired background is filmed separately, and the shot 

containing the action or objects is superimposed onto the 

background. The result is one image where the blue screen 

disappears. 

Blue Screen of Death n. In a Microsoft Windows computer 

environment, a semi-humorous reference to the 

result of a fatal error in which the screen turns blue and the 

computer crashes. Recovery from a Blue Screen of Death 

error typically requires the user to reboot the computer. 

Acronym: BSOD. Also called: blue-screen error. See also 

fatal error. 

Bluetooth n. Technology protocol developed to wirelessly 

connect electronic devices such as wireless phones, 

personal digital assistants (PDAs), and computers. 

Devices equipped with Bluetooth chips can exchange 

information within about a 30-foot range via radio waves 

in the 2.45 gigahertz (GHz) spectrum. Bluetooth was 

developed by the Bluetooth Special Interest Group, a consortium 

of telecommunications, computing, consumer 

electronics, and related industry groups. 

Bluetooth Special Interest Group n. A group of companies 

from the telecommunications, computing, and networking 

industries that promotes the development and 

deployment of Bluetooth technology. See also Bluetooth. 

Bluetooth wireless technology n. A specification for 

radio links between mobile PCs, mobile phones, and other 

portable devices. These radio links are small-form factor, 

low cost, and short range. 

.bmp n. The file extension that identifies raster graphics 

stored in bit map file format. See also bit map. 

BNC n. Acronym for bayonet-Neill-Concelman. Named 

for Paul Neill of Bell Labs and Carl Concelman (affiliation 

unknown), who developed two earlier types of coaxial 

connectors known as the N connector and C connector, 

BNC is a type of connector used to join segments of coaxial 

cable. When one connector is inserted into another and 

rotated 90 degrees, they lock. BNC connectors are often 

used with closed-circuit television. The letters BNC are 

sometimes also considered an acronym for British Naval 

Connector. See the illustration. Also called: BNC connector. 

See also coaxial cable. 

66 

F0Bgn11.eps 

BNC connector. Male (left) and female (right) BNC connector. 

BNC connector n. See BNC. 

board n. An electronic module consisting of chips and 

other electronic components mounted on a flat, rigid substrate 

on which conductive paths are laid between the 

components. A personal computer contains a main board, 

called the motherboard, which usually has the microprocessor 

on it and slots into which other, smaller boards, 

called cards or adapters, can be plugged to expand the 

functionality of the main system, allowing connections to 

monitors, disk drives, or a network. See also adapter, card 

(definition 1), motherboard. 

board computer n. See single-board. 

board level n. A level of focus in troubleshooting and 

repair that involves tracking down a problem in a computer 

to a circuit board and replacing the board. This is in 

contrast to the component level, which involves repairing 

the board itself. In many cases board-level repairs are 

made in order to quickly restore the device to working 

condition; the boards replaced are then repaired and tested 

for use in later board-level repairs. See also circuit board. 

body n. 1. In e-mail and Internet newsgroups, the content 

of a message. The body of a message follows the header, 

which contains information about the sender, origin, and 

destination of the message. See also header (definition 1). 

2. In HTML, SGML, and XML, a section of a document 

that contains the content of the document, along with tags 

describing characteristics of the content—for example, 

format. 3. A segment of a data packet containing the 

actual data. 

body face n. A typeface suitable for the main text in a 

document rather than for headings and titles. Because of 

their readability, fonts having serifs, such as Times and 

Palatino, are good body faces, although sans serif faces 

can also be used as body text. See also sans serif, serif. 

Compare display face. 

BOF n. Acronym for birds of a feather. Meetings of special 

interest groups at trade shows, conferences, and conventions. 

BOF sessions provide an opportunity for people

oilerplate Boolean algebra 

working on the same technology at different companies or 

research institutions to meet and exchange their experiences. 

See beginning-of-file. 

boilerplate n. Recyclable text; a piece of writing or code, 

such as an organization’s mission statement or the graphics 

code that prints a software company’s logo, which can 

be used over and over in many different documents. The 

size of boilerplate text can range from a paragraph or two 

to many pages. It is, essentially, generic composition that 

can be written once, saved on disk, and merged, either verbatim 

or with slight modification, into whatever documents 

or programs later require it. 

boldface n. A type style that makes the text to which it is 

applied appear darker and heavier than the surrounding 

text. Some applications allow the user to apply a “Bold” 

command to selected text; other programs require that 

special codes be embedded in the text before and after 

words that are to be printed in boldface. This sentence 

appears in boldface. 

bomb1 n. A program planted surreptitiously, with intent 

to damage or destroy a system in some way—for example, 

to erase a hard disk or cause it to be unreadable to the 

operating system. See also Trojan horse, virus, worm. 

bomb2 vb. To fail abruptly and completely, without giving 

the user a chance to recover from the problem short of 

restarting the program or system. See also abend, bug 

(definition 1), crash2 (definition 1), hang. 

bonding n. 1. Acronym for Bandwidth On Demand 

Interoperability Group. 2. The process of combining two 

or more ISDN B (bearer) channels to form a single channel 

with a bandwidth greater than the standard B channel 

bandwidth of 64 Kbps. Bonding two B channels, for 

example, provides a bandwidth of 128 Kbps, which is four 

times faster than a 28.8 Kbps modem. Such high-speed 

channels are ideal for video conferencing, imaging, and 

transferring large-scale data. See also B channel, BRI, ISDN. 

bonding vb. See link aggregation. 

bookmark n. 1. A marker inserted at a specific point in a 

document to which the user may wish to return for later 

reference. 2. In Netscape Navigator, a link to a Web page 

67 

or other URL that a user has stored in a local file in order 

to return to it later. See also Favorites folder, hotlist, URL. 

bookmark file n. 1. A Netscape Navigator file containing 

the addresses of preferred Web sites. It is synonymous 

with the Favorites folder in Internet Explorer and the hotlist 

in Mosaic. See also Favorites folder, hotlist, Internet 

Explorer, Mosaic. 2. A rendering of such a file in HTML 

format, generally posted on a Web page for the benefit of 

other people. See also HTML. 

Boolean adj. Of, pertaining to, or characteristic of logical 

(true, false) values. Many languages directly support a 

Boolean data type, with predefined values for true and 

false; others use integer data types to implement Boolean 

values, usually (although not always) with 0 equaling false 

and “not 0” equaling true. See also Boolean algebra, Boolean 

operator. 

Boolean algebra n. An algebra, fundamental to computer 

operations but developed in the mid-nineteenth century 

by English mathematician George Boole, for 

determining whether logical propositions are true or false 

rather than for determining the values of numerical 

expressions. In Boolean algebra, variables must have one 

of only two possible values, true or false, and relationships 

between these variables are expressed with logical operators, 

such as AND, OR, and NOT. Given these two-state 

variables and the relationships they can have to one 

another, Boolean algebra produces such propositions as C 

= A AND B, which means that C is true if and only if both 

A is true and B is true; thus, it can be used to process 

information and to solve problems. Furthermore, Boolean 

logic can be readily applied to the electronic circuitry used 

in digital computing. Like the binary numbers 1 and 0, 

true and false are easily represented by two contrasting 

physical states of a circuit, such as voltages, and computer 

circuits known as logic gates control the flow of electricity 

(bits of data) so as to represent AND, OR, NOT, and other 

Boolean operators. Within a computer, these logic gates 

are combined, with the output from one becoming the 

input to another so that the final result (still nothing more 

than sets of 1s and 0s) is meaningful data, such as the sum 

of two numbers. See the illustration. See also adder (definition 

1), binary1 , Boolean operator, gate (definition 1), 

logic circuit, truth table. 

B

B 

Boolean expression Boolean logic 

Figure A 

0 AND 0 

Figure D 

0 

OR 

0 

EQUALS 0 

Boolean AND logic: 

0 AND 0 = 0 (Figure A) 

0 AND 1 = 0 

1 AND 0 = 0 (Figure B) 

1 AND 1 = 1 (Figure C) 

Figure B 

1 AND 0 

Boolean OR logic: 

0 OR 0 = 0 (Figure D) 

0 OR 1 = 1 (Figure E) 

1 OR 0 = 1 

1 OR 1 = 1 

EQUALS 0 

F0Bgn12.eps 

Boolean algebra. The ways in which circuits can simulate Boolean operations. The boxed tables show the possible results 

of various input combinations. 

Boolean expression n. An expression that yields a Boolean 

value (true or false). Such expressions can involve 

comparisons (testing values for equality or, for non- 

Boolean values, the < [less than] or > [greater than] relation) 

and logical combination (using Boolean operators 

68 

EQUALS 0 

Figure E 

Figure C 

1 AND 1 

Legend: Gate open: (input = 0) Gate closed: (input = 1) 

0 

OR 

1 

EQUALS 1 

EQUALS 1 

such as AND, OR, and XOR) of Boolean expressions. 

Also called: conditional expression, logical expression. 

See also Boolean, Boolean algebra, Boolean operator, 

relational operator. 

Boolean logic n. See Boolean algebra.

Boolean operator Bootstrap Protocol 

Boolean operator n. An operator designed to work with 

Boolean values. The four most common Boolean operators 

in programming use are AND (logical conjunction), 

OR (logical inclusion), XOR (exclusive OR), and NOT 

(logical negation). Boolean operators are often used as 

qualifiers in database searches—for example, find all 

records where DEPARTMENT = “marketing” OR 

DEPARTMENT = “sales” AND SKILL = “word processing”. 

Also called: logical operator. See also AND, exclusive 

OR, NOT, OR. 

Boolean search n. A database search that uses Boolean 

operators. See also Boolean operator. 

boost vb. To strengthen a network signal before it is 

transmitted further. 

boot1 n. The process of starting or resetting a computer. 

When first turned on (cold boot) or reset (warm boot), the 

computer executes the software that loads and starts the 

computer’s more complicated operating system and prepares 

it for use. Thus, the computer can be said to pull 

itself up by its own bootstraps. Also called: bootstrap. See 

also BIOS, bootstrap loader, cold boot, warm boot. 

boot2 vb. 1. To start or reset a computer by turning the 

power on, by pressing a reset button on the computer case, 

or by issuing a software command to restart. Also called: 

bootstrap, boot up. See also reboot. 2. To execute the 

bootstrap loader program. Also called: bootstrap. See also 

bootstrap loader. 

bootable adj. Containing the system files necessary for 

booting a PC and running it. See also boot2 . 

bootable disk n. See boot disk. 

boot block n. A portion of a disk that contains the operating-system 

loader and other basic information that enables 

a computer to start up. See also block1 (definition 5). 

boot disk n. A floppy disk that contains key system 

files from a PC-compatible operating system and that 

can boot, or start, the PC. A boot disk must be inserted 

in the primary floppy disk drive (usually drive A:) and 

is used when there is some problem with starting the PC 

from the hard disk, from which the computer generally 

boots. Also called: bootable disk. See also A:, boot2 , 

boot drive, hard disk. 

69 

boot drive n. In a PC-compatible computer, the disk drive 

that the BIOS uses to automatically load the operating system 

when the computer is turned on. Generally, the default 

boot drive is the primary floppy disk drive A: in PC-compatible 

computers with MS-DOS, Windows 3x, or Windows 

9x operating systems. If a floppy disk is not found in 

that drive, the BIOS will check the primary hard disk next, 

which is drive C:. The BIOS for these operating systems 

can be reconfigured to search drive C: first by 

using the BIOS setup program. See also A:, BIOS, disk 

drive, hard disk. 

boot failure n. The inability of a computer to locate or 

activate the operating system and thus boot, or start, the 

computer. See also boot2 . 

boot files n. The system files needed to start Microsoft 

Windows. The boot files include Ntldr and Ntdetect.com. 

See also partition boot sector. 

boot loader n. See bootstrap loader. 

BOOTP n. See Bootstrap Protocol. 

boot partition n. The partition on a hard disk that contains 

the operating system and support files that the system 

loads into memory when the computer is turned on or 

restarted. 

boot record n. The section of a disk that contains the 

operating system. 

boot sector n. The portion of a disk reserved for the 

bootstrap loader (the self-starting portion) of an operating 

system. The boot sector typically contains a short machine 

language program that loads the operating system. 

bootstrap1 n. See boot1 . 

bootstrap2 vb. See boot2 . 

bootstrap loader n. A program that is automatically run 

when a computer is switched on (booted). After first performing 

a few basic hardware tests, the bootstrap loader 

loads and passes control to a larger loader program, which 

typically then loads the operating system. The bootstrap 

loader typically resides in the computer’s read-only memory 

(ROM). 

Bootstrap Protocol n. A protocol used primarily on 

TCP/IP networks to configure diskless workstations. 

RFCs 951 and 1542 define this protocol. DHCP is a later 

boot configuration protocol that uses this protocol. The 

B

oot up box 

B Microsoft DGCP service provided limited support for 

BOOTP service. Acronym: BOOTP. Also called: Boot 

Protocol. See also boot2 , DHCP, RFC, TCP/IP. 

boot up vb. See boot2 . 

border n. 1. In programs and working environments that 

feature on-screen windows, the edge surrounding the 

user’s workspace. Window borders provide a visible frame 

around a document or graphic. Depending on the program 

and its requirements, they can also represent an area in 

which the cursor or a mouse pointer takes on special characteristics. 

For example, clicking the mouse on a window 

border can enable the user to resize the window or split the 

window in two. 2. In printing, a decorative line or pattern 

along one or more edges of a page or illustration. 

Border Gateway Protocol n. A protocol used by NSFnet 

that is based on the External Gateway Protocol. Acronym: 

BGP. See also External Gateway Protocol, NSFnet. 

boss screen n. A false display screen usually featuring 

business-related material that can be substituted for a 

game display when the boss walks by. Boss screens were 

popular with MS-DOS games, where it was difficult to 

switch to another application quickly. However, games 

designed for the Mac or Windows 9x generally don’t need 

them because it is easy to switch to a different screen or 

application to hide the fact that one is playing a game. 

bot n. 1. Short for robot. A displayed representation of a 

person or other entity whose actions are based on programming. 

2. A program that performs some task on a network, 

especially a task that is repetitive or time consuming. 3. On 

the Internet, a program that performs a repetitive or timeconsuming 

task, such as searching Web sites and newsgroups 

for information and indexing them in a database or 

other record-keeping system (called spiders); automatically 

posting one or more articles to multiple newsgroups 

(often used in spamming and called spambots); or keeping 

IRC channels open. Also called: Internet robot. See also 

IRC, newsgroup, spam, spambot, spider. 

bottom-up design n. A program development design 

methodology in which the lower-level tasks of a program 

are defined first; the design of the higher-level functions 

proceeds from the design of the lower-level ones. See also 

bottom-up programming, top-down programming. Compare 

top-down design. 

70 

bottom-up programming n. A programming technique 

in which lower-level functions are developed and tested 

first; higher-level functions are then built using the lowerlevel 

functions. Many program developers believe that the 

ideal combination is top-down design and bottom-up programming. 

See also top-down design. Compare objectoriented 

programming, top-down programming. 

bounce vb. To return to the sender, used in reference to 

undeliverable e-mail. 

BounceKeys n. A feature in Windows 9x that instructs 

the processor to ignore double strokes of the same key and 

other unintentional keystrokes. 

bound1 adj. Limited in performance or speed; for example, 

an input/output-bound system is limited by the speed 

of its input and output devices (keyboard, disk drives, and 

so on), even though the processor or program is capable of 

performing at a higher rate. 

bound2 n. The upper or lower limit in a permitted range 

of values. 

bounding box n. See graphic limits. 

Bourne shell n. The first major shell, or command interpreter, 

for UNIX and part of the AT&T System V release. 

The Bourne shell scripting language, developed at AT&T 

Bell Laboratories by Steve Bourne in 1979, was one of the 

original command languages for the UNIX operating system. 

While the Bourne shell lacks some features common 

in other UNIX shells, such as command-line editing and 

recall of previously issued commands, it is the one that the 

majority of shell scripts adhere to. Also called: sh. See 

also shell1 , shell script, System V, UNIX. Compare C 

shell, Korn shell. 

boutique reseller n. A type of VAR (value-added 

reseller) that specializes in providing customized software, 

hardware, and services to vertical, or niche, markets. 

In the VAR environment, boutique resellers are distinguished 

from master resellers, or systems integrators, 

which offer a much wider variety of products and services. 

See also value-added reseller. 

box n. 1. Container for a piece of electronic equipment. 

2. Slang term for a computer; more specifically the unit 

holding the central processing unit, or CPU, and other 

“guts” of the system, as in “bet that new high-performance 

box really screams.” See also central processing unit.

ox-top license breadboard 

3. An IBM front-end processor. 4. A rectangular—actually, 

diamond-shaped—symbol, usually called a decision 

box, used in flowcharting to represent a point at which a 

process branches into more than one possible outcome, as 

in a yes/no situation. See also decision box. 5. The boundary 

around a graphic image on screen. See also graphic 

limits. 

box-top license n. See shrinkwrap agreement. 

Boyce-Codd normal form n. See normal form 


bozo n. A slang term used frequently on the Internet, particularly 

in newsgroups, for a foolish or eccentric person. 

bozo filter n. On the Internet, slang for a feature in some 

e-mail clients and newsgroup readers or a separate utility 

that allows the user to block, or filter out, incoming e-mail 

messages or newsgroup articles from specified individuals. 

Generally these individuals are ones that the user does 

not want to hear from, such as bozos. Also called: kill file. 

See also bozo. 

BPI n. See bits per inch, bytes per inch. 

bpp n. See bits per pixel. 

bps n. Short for bits per second. The measure of transmission 

speed used in relation to networks and communication 

lines. Although bps represents the basic unit of 

measure, networks and communications devices, such as 

modems, are so fast that speeds are usually given in multiples 

of bps—Kbps (kilobits, or thousands of bits, per second), 

Mbps (megabits, or millions of bits, per second), and 

Gbps (gigabits, or billions of bits, per second). Speed in 

bps is not the same as the baud rate for a modem. See also 

baud rate. 

braindamaged adj. Performing in an erratic or destructive 

manner. A braindamaged application or utility program 

is characterized by some or all of the following 

traits: a mysterious and unintuitive user interface, failure 

to respond predictably to commands, failure to release 

unused memory, failure to close open files, and use of 

“reserved” elements of the operating system that can 

result in a fatal error in a program or the operating system. 

Braindamaged programs are also often responsible for causing 

problems across local area networks. Compare kludge. 

brain dump n. A large, unorganized mass of information, 

presented in response to a query via e-mail or a newsgroup 

article, that is difficult to digest or interpret. 

71 

branch n. 1. A node intermediate between the root and 

the leaves in some types of logical tree structure, such as 

the directory tree in Windows or a tape distribution organization. 

2. Any connection between two items such as 

blocks in a flowchart or nodes in a network. See branch 

instruction. 

branch instruction n. An assembly- or machine-level 

instruction that transfers control to another instruction, 

usually based on some condition (that is, it transfers if a 

specific condition is true or false). Branch instructions are 

most often relative transfers, jumping forward or backward 

by a certain number of bytes of code. See also 

GOTO statement, jump instruction. 

branchpoint n. The location at which a given branch 

instruction occurs if the attendant condition (if any) is 

true. See also branch instruction. 

branch prediction n. A technique used in some processors 

with an instruction called prefetch to guess whether 

or not a branch will be taken in a program, and to fetch 

executable code from the appropriate location. When a 

branch instruction is executed, it and the next instruction 

executed are stored in a buffer. This information is used to 

predict which way the instruction will branch the next 

time it is executed. When the prediction is correct (as it is 

over 90 percent of the time), executing a branch does not 

cause a pipeline break, so the system is not slowed down 

by the need to retrieve the next instruction. See also 

branch instruction, buffer1 , central processing unit, pipeline 

processing. 

BRB n. Acronym for (I’ll) be right back. An expression 

used commonly on live chat services on the Internet and 

online information services by participants signaling their 

temporary departure from the group. See also chat1 (definition 1). 

breadboard n. A blank, perforated board used to support 

prototype electronic circuits. Experimenters would put 

components on one side of the board and run the leads 

through the perforations to be connected by wires running 

along the underside. Today a circuit designer’s breadboard 

is made of plastic. Its holes are small and closely spaced to 

accommodate the pins of chips, and connections are made 

by metal strips plugged into the holes. See the illustration. 

Compare wire-wrapped circuits. 

B

B 

break1 break 

bridgeware 

F0Bgn13.eps 

Breadboard. 

break1 n. 1. Interruption of a program caused by the user 

pressing the Break key or its equivalent. 2. Interruption of 

a communications transmission that occurs when the 

receiving station interrupts and takes over control of the 

line or when the transmitting station prematurely halts 

transmission. 3. In the Java programming language, a keyword 

used to resume program execution at the next statement 

following the current statement. If the keyword is 

followed by a label, the program resumes at the indicated 

labeled statement. See also execute, statement. 

break2 vb. 1. To interrupt execution at a given spot, usually 

for the purpose of debugging. See also breakpoint. 

2. To cause a routine, module, or program that had previously 

worked to cease working correctly. 

Break key n. A key or combination of keys used to tell a 

computer to halt, or break out of, whatever it is doing. On 

IBM PCs and compatibles under DOS, pressing the Pause/ 

Break or Scroll Lock/Break key while holding down the 

Ctrl key issues the break command (as does Ctrl-C). On 

Macintosh computers, the key combination that sends a 

break code is Command-period. See the illustration. 

Scroll 

Lock 

Pause 

Page 

F0Bgn14.eps 

Break key. 

caps 

lock 

Num 

Break key 

72 

break mode n. A temporary suspension of program execution 

while in the development environment. In break 

mode, you can examine, debug, reset, step through, or 

continue program execution. 

breakout box n. A small hardware device that can be 

attached between two devices normally connected by a 

cable (such as a computer and a modem) to display and, if 

necessary, change the activity through individual wires of 

the cable. 

breakpoint n. A location in a program at which execution 

is halted so that a programmer can examine the program’s 

status, the contents of variables, and so on. A breakpoint is 

set and used within a debugger and is usually implemented 

by inserting at that point some kind of jump, call, 

or trap instruction that transfers control to the debugger. 

See also debug, debugger. 

BRI n. Acronym for Basic Rate Interface. An ISDN subscriber 

service that uses two B (64 Kbps) channels and 

one D (64 Kbps) channel to transmit voice, video, and 

data signals. See also ISDN. 

bridge n. In terms of the Year 2000 problem, a program, 

routine, or other conversion mechanism that converts date 

formats from 2-digit years to 4-digit years and vice versa. 

A bridge is used as a remedy for literally bridging the 2digit/4-digit 

format gap between programs or systems. 

bridge n. 1. A device that connects networks using the 

same communications protocols so that information can 

be passed from one to the other. Compare gateway. 2. A 

device that connects two LANs (local area networks), 

whether or not they use the same protocols, and allows 

information to flow between them. The bridge operates at 

the ISO/OSI data-link layer. Also called: layer switch. See 

also data-link layer. Compare router. 

bridge page n. See doorway page. 

bridge router n. A device that supports the functions of 

both a bridge and router. A bridge router links two segments 

of a local or wide area network, passing packets of 

data between the segments as necessary, and uses Level 2 

addresses for routing. Also called: Brouter. See also 

bridge (definition 2), router. 

bridgeware n. Hardware or software designed to convert 

application programs or data files to a form that can be 

used by a different computer.

Briefcase browse 

Briefcase n. A system folder in Windows 9x used for 

synchronizing files between two computers, usually 

between desktop and laptop computers. The Briefcase can 

be transferred to another computer via disk, cable, or network. 

When files are transferred back to the original computer, 

the Briefcase updates all files to the most recent 

version. 

brightness n. The perceived quality of radiance or luminosity 

of a visible object. Brightness is literally in the eye 

(and mind) of the beholder; a candle in the night appears 

brighter than the same candle under incandescent lights. 

Although its subjective value cannot be measured with 

physical instruments, brightness can be measured as luminance 

(radiant energy). The brightness component of a 

color is different from its color (the hue) and from the intensity 

of its color (the saturation). See also color model, HSB. 

British Naval Connector n. See BNC. 

broadband adj. Of or relating to communications systems 

in which the medium of transmission (such as a wire 

or fiber-optic cable) carries multiple messages at a time, 

each message modulated on its own carrier frequency by 

means of modems. Broadband communication is found in 

wide area networks. Compare baseband. 

broadband ISDN n. Next-generation ISDN based on 

ATM (Asynchronous Transfer Mode) technology. Broadband 

ISDN divides information into two categories: interactive 

services, which are controlled by the user, and 

distributed (or distribution) services that can be broadcast 

to the user. Acronym: BISDN. See also ATM (definition 

1), ISDN. 

broadband modem n. A modem for use on a broadband 

network. Broadband technology allows several networks 

to coexist on a single cable. Traffic from one network does 

not interfere with traffic from another, since the conversations 

happen on different frequencies, rather like the commercial 

radio system. See also broadband network. 

broadband network n. A local area network on which 

transmissions travel as radio-frequency signals over separate 

inbound and outbound channels. Stations on a broadband 

network are connected by coaxial or fiber-optic 

cable, which can carry data, voice, and video simultaneously 

over multiple transmission channels that are distinguished 

by frequency. A broadband network is capable 

of high-speed operation (20 megabits or more), but it is 

73 

more expensive than a baseband network and can be difficult 

to install. Such a network is based on the same technology 

used by cable television (CATV). Also called: 

wideband transmission. Compare baseband network. 

broadcast1 adj. Sent to more than one recipient. In communications 

and on networks, a broadcast message is one 

distributed to all stations. See also e-mail1 (definition 1). 

broadcast2 n. As in radio or television, a transmission 

sent to more than one recipient. 

broadcast publishing point n. A type of publishing 

point that streams content in such a way that the client 

cannot control (start, stop, pause, fast forward, or rewind) 

the content. Content streamed from a broadcast publishing 

point can be delivered as a multicast or unicast stream. 

Formerly called a station. 

broadcast storm n. A network broadcast that causes 

multiple hosts to respond simultaneously, overloading the 

network. A broadcast storm may occur when old TCP/IP 

routers are mixed with routers that support a new protocol. 

See also communications protocol, router, TCP/IP. 

broken as designed adj. See BAD. 

Brouter n. See bridge router. 

brownout n. A condition in which the electricity level is 

appreciably reduced for a sustained period of time. In contrast 

to a blackout, or total loss of power, a brownout continues 

the flow of electricity to all devices connected to 

electrical outlets, although at lower levels than the normally 

supplied levels (120 volts in the United States). A 

brownout can be extremely damaging to sensitive electronic 

devices, such as computers, because the reduced 

and often fluctuating voltage levels can cause components 

to operate for extended periods of time outside the range 

they were designed to work in. On a computer, a brownout 

is characterized by a smaller, dimmer, and somewhat fluctuating 

display area on the monitor and potentially erratic 

behavior by the system unit. The only reliable means of 

preventing damage caused by a brownout condition is to 

use a battery-backed uninterruptible power supply (UPS). 

See also UPS. Compare blackout. 

browse vb. To scan a database, a list of files, or the Internet, 

either for a particular item or for anything that seems 

to be of interest. Generally, browsing implies observing, 

rather than changing, information. In unauthorized computer 

hacking, browsing is a (presumably) nondestructive 

B

owser B-tree 

B means of finding out about an unknown computer after 

illegally gaining entry. 

browser n. See Web browser. 

browser box n. See WebTV. 

browser CLUT n. A color look-up table consisting of the 

216 colors deemed safe when viewed with most Web 

browsers on most computer operating systems. See also 

CLUT, Web safe palette. 

BRS n. See big red switch. 

brush n. A tool used in paint programs to sketch or fill in 

areas of a drawing with the color and pattern currently in 

use. Paint programs that offer a variety of brush shapes 

can produce brushstrokes of varying width and, in some 

cases, shadowing or calligraphic effects. 

brute force adj. In general, any process that essentially 

involves “doing it the hard way.” In computer technology, 

however, brute force typically refers to a programming 

style that relies on the computer’s processing power rather 

than on skill and planning to create or find a more elegant 

solution to a problem. Brute-force programming also 

ignores available information on how similar situations 

were handled in the past and might depend on outmoded 

design methodologies. For example, a program using 

brute force to crack passwords might try all the words in a 

dictionary (which would require huge amounts of computing 

power). Instead, more elegant programming would 

involve using special rules, history, statistics, and other 

available techniques or information to limit the number 

and types of words to try first. 

Simple 

index 

9 22 31 

F0Bgn15.eps 

B-tree. A B-tree index structure. 

31 71 

Root 

71 999 

Pointers to data records (rows) 

74 

BSC n. See BISYNC. 

BSD/OS n. A version of the UNIX operating system 

based on BSD UNIX and sold by Berkeley Software 

Design, Inc. See also BSD UNIX. 

BSD UNIX n. Acronym for Berkeley Software Distribution 

UNIX. A UNIX version developed at the University 

of California at Berkeley, providing additional capabilities 

such as networking, extra peripheral support, and use of 

extended filenames. BSD UNIX was instrumental in gaining 

widespread acceptance of UNIX and in getting academic 

institutions connected to the Internet. BSD UNIX is 

now being developed by Berkeley Software Design, Inc. 

Also called: Berkeley UNIX. See also BSD/OS, UNIX. 

BSOD n. See Blue Screen of Death. 

BSS n. See Basic Service Set. 

B-tree or btree n. A tree structure for storing database 

indexes. Each node in the tree contains a sorted list of key 

values and links that correspond to ranges of key values 

between the listed values. To find a specific data record 

given its key value, the program reads the first node, or 

root, from the disk and compares the desired key with the 

keys in the node to select a subrange of key values to 

search. It repeats the process with the node indicated by 

the corresponding link. At the lowest level, the links indicate 

the data records. The database system can thus rapidly 

skip down through the levels of the tree structure to 

find the simple index entries that contain the location of 

the desired records or rows. See the illustration. 

115 999 

42 52 71 

87 99 115 

140 

1 5 9 11 15 22 23 26 31 35 37 42 45 50 52 61 68 71 75 84 87 96 97 99 101 112 115 120 122 140

BTW bubble sort 

BTW or btw n. Acronym for by the way. An expression 

often used to preface remarks in e-mail and Internet newsgroup 

articles. 

bubble chart n. A chart in which annotated ovals (bubbles) 

representing categories, operations, or procedures 

are connected by lines or arrows that represent data flows 

or other relationships among the items represented by bubbles. 

In systems analysis, bubble charts, rather than block 

diagrams or flowcharts, are used to describe the connections 

between concepts or parts of a whole, without 

emphasizing a structural, sequential, or procedural relationship 

between the parts. See the illustration. Compare 

block diagram, flowchart. 

Bookman 

Old Style 

Symbol 

Garamond 

Other 

F0Bgn16.eps 

Bubble chart. 

Wingdings 

Times 

New Roman 

Serif 

TrueType 

fonts 

Arial 

Courier 

New 

Century 

Schoolbook 

Sans serif 

Univers 

bubble-jet printer n. A form of nonimpact printer that 

uses a mechanism similar to that used by an ink-jet printer 

to shoot ink from nozzles to form characters on paper. A 

bubble-jet printer uses special heating elements to prepare 

the ink, whereas an ink-jet printer uses piezoelectric crystals. 

See also ink-jet printer, nonimpact printer. Compare 

laser printer. 

75 

bubble memory n. Memory formed by a series of persistent 

magnetic “bubbles” in a thin film substrate. In contrast 

to ROM, information can be written to bubble 

memory. In contrast to RAM, data written to bubble memory 

remains there until it is changed, even when the computer 

is turned off. For this reason, bubble memory has 

had some application in environments in which a computer 

system must be able to recover with minimal data 

loss in the event of a power failure. The use of and demand 

for bubble memory has all but disappeared because of the 

introduction of flash memory, which is less expensive and 

easier to produce. See also flash memory, nonvolatile 

memory. 

bubble sort n. A sorting algorithm that starts at the end 

of a list with n elements and moves all the way through, 

testing the value of each adjacent pair of items and swapping 

them if they aren’t in the right order. The entire process 

is then repeated for the remaining n – 1 items in the 

list, and so on, until the list is completely sorted, with the 

largest value at the end of the list. A bubble sort is so 

named because the “lightest” item in a list (the smallest) 

will figuratively “bubble up” to the top of the list first; 

then the next-lightest item bubbles up to its position, and 

so on. See the illustration. Also called: exchange sort. See 

also algorithm, sort. Compare insertion sort, merge sort, 

quicksort. 

List to be sorted 

Compared last 

3 

4 

Compared second 

2 

5 

1 

Compared third 

Compared first 

List after 

first pass 

1 

3 

4 

2 

5 

F0Bgn17.eps 

Bubble sort. 

List after 

second pass 

1 

2 

3 

4 

5 

B

ubble storage bump mapping 

B bubble storage n. See bubble memory. 

bucket n. A region of memory that is addressable as an 

entity and can be used as a receptacle to hold data. See 

also bit bucket. 

bucket brigade attack n. See man-in-the-middle attack. 

buffer1 n. A region of memory reserved for use as an 

intermediate repository in which data is temporarily held 

while waiting to be transferred between two locations or 

devices. For instance, a buffer is used while transferring 

data from an application, such as a word processor, to an 

input/output device, such as a printer. 

buffer2 vb. To use a region of memory to hold data that is 

waiting to be transferred, especially to or from input/output 

(I/O) devices such as disk drives and serial ports. 

buffer pool n. A group of memory or storage-device locations 

that are allocated for temporary storage, especially 

during transfer operations. 

buffer storage n. 1. The use of a special area in memory 

to hold data temporarily for processing until a program or 

operating system is ready to deal with it. 2. An area of 

storage that is used to hold data to be passed between 

devices that are not synchronized or have different bit 

transfer rates. 

bug n. 1. An error in coding or logic that causes a program 

to malfunction or to produce incorrect results. Minor 

bugs, such as a cursor that does not behave as expected, 

can be inconvenient or frustrating, but do not damage 

information. More severe bugs can require the user to 

restart the program or the computer, losing whatever previous 

work had not been saved. Worse yet are bugs that 

damage saved data without alerting the user. All such 

errors must be found and corrected by the process known 

as debugging. Because of the potential risk to important 

data, commercial application programs are tested and 

debugged as completely as possible before release. After 

the program becomes available, further minor bugs are 

corrected in the next update. A more severe bug can sometimes 

be fixed with a piece of software called a patch, 

which circumvents the problem or in some other way alleviates 

its effects. See also beta test, bomb2 , crash2 (definition 

1), debug, debugger, hang, inherent error, logic error, 

semantic error, syntax error. 2. A recurring physical problem 

that prevents a system or set of components from 

working together properly. While the origin of this defini- 

76 

tion is in some dispute, computer folklore attributes the 

first use of bug in this sense to a problem in the Harvard 

Mark I or the Army/University of Pennsylvania ENIAC 

that was traced to a moth caught between the contacts of a 

relay in the machine (although a moth is not entomologically 

a true bug). 

buggy adj. Full of flaws, or bugs, in reference to software. 

See also bug (definition 1). 

building-block principle n. See modular design. 

built-in check n. See hardware check, power-on self test. 

built-in font n. See internal font. 

built-in groups n. The default groups provided with 

Microsoft Windows NT and Windows NT Advanced 

Server. A group defines a collection of rights and permissions 

for the user accounts that are its members. Built-in 

groups are therefore a convenient means of providing 

access to commonly used resources. See also group1 . 

bulk eraser n. A device for eliminating all information 

from a storage medium, such as a floppy disk or a tape, by 

generating a strong magnetic field that scrambles the 

alignment of the ferrous materials in the media that 

encode stored data. 

bulk storage n. Any medium capable of containing large 

quantities of information, such as tape, fixed disk, or optical 

disc. 

bullet n. A typographical symbol, such as a filled or 

empty circle, diamond, box, or asterisk, used to set off a 

small block of text or each item in a list. Round and square 

bullets are used to set off different levels of information. 

See also dingbat. 

bulletin board system n. See BBS. 

bulletproof adj. Capable of overcoming hardware problems 

that, in another system, could lead to interruption of 

the task in progress. 

bump mapping n. In 3D computer game rendering and 

other digital animation applications, a graphic technique 

in which a texture is added to the surface of an image to 

increase the perceived detail of the object. Bump mapping 

gives each pixel a texture, which is calculated by the computer’s 

video card to respond to changes in surroundings, 

allowing a more realistic interpretation of objects. See the 

illustration.

undle bus 

3-D–rendered 

sphere 

3-D–rendered sphere 

with bump mapping 

F0Bgn18.eps 

Bump mapping. A 3-D–rendered sphere showing bump 

mapping. 

bundle vb. To combine products for sale as a lot. Frequently, 

operating system software and some widely used 

applications are bundled with a computer system for sale. 

bundled software n. 1. Programs sold with a computer 

as part of a combined hardware/software package. 

2. Smaller programs sold with larger programs to increase 

the latter’s functionality or attractiveness. 

burn vb. 1. To write data electronically into a programmable 

read-only memory (PROM) chip by using a special 

programming device known variously as a PROM programmer, 

PROM blower, or PROM blaster. Also called: 

blast, blow. See also PROM. 2. To create read-only memory 

compact discs (CD-ROMs). 3. To write data electronically 

on a flash memory chip or a PC Card Type III. 

Unlike PROM chips or CD-ROM, flash memory media 

can be burned, or flashed, repeatedly with new information. 

Also called: flash. 

burn in vb. 1. To keep a new system or device running 

continuously so that any weak elements or components 

will fail early and can be found and corrected before the 

system becomes an integral part of the user’s work routine. 

Such a test is often performed at the factory before a 

device is shipped. 2. To make a permanent change in the 

phosphor coating on the inside of a monitor screen by leaving 

the monitor on and keeping a bright, unchanging image 

on the screen for extended periods. Such an image will 

remain visible after the monitor is turned off. Burning in 

was a danger with older PC monitors; it is no longer a concern 

with most new PC monitors. Also called: ghosting. 

burst1 n. Transfer of a block of data all at one time without 

a break. Certain microprocessors and certain buses 

have features that support various types of burst transfers. 

See also burst speed (definition 1). 

77 

burst2 vb. To break fanfold continuous-feed paper apart at 

its perforations, resulting in a stack of separate sheets. 

burster n. A device used to burst, or break apart at the 

perforations, fanfold continuous-feed paper. 

burst extended-data-out RAM n. See BEDO DRAM. 

burst mode n. A method of data transfer in which information 

is collected and sent as a unit in one high-speed 

transmission. In burst mode, an input/output device takes 

control of a multiplexer channel for the time required to 

send its data. In effect, the multiplexer, which normally 

merges input from several sources into a single high-speed 

data stream, becomes a channel dedicated to the needs of 

one device until the entire transmission has been sent. 

Burst mode is used both in communications and between 

devices in a computer system. See also burst1 . 

burst rate n. See burst speed (definition 1). 

burst speed n. 1. The fastest speed at which a device can 

operate without interruption. For example, various communications 

devices (as on networks) can send data in 

bursts, and the speed of such equipment is sometimes 

measured as the burst speed (the speed of data transfer 

while the burst is being executed). Also called: burst rate. 

2. The number of characters per second that a printer can 

print on one line without a carriage return or linefeed. 

Burst speed measures the actual speed of printing, without 

consideration of the time taken to advance paper or to 

move the print head back to the left margin. Almost 

always, the speed claimed by the manufacturer is the burst 

speed. By contrast, throughput is the number of characters 

per second when one or more entire pages of text are 

being printed and is a more practical measurement of 

printer speed in real-life situations. 

bursty adj. Transmitting data in spurts, or bursts, rather 

than in a continuous stream. 

bus n. A set of hardware lines (conductors) used for data 

transfer among the components of a computer system. A 

bus is essentially a shared highway that connects different 

parts of the system—including the processor, disk-drive 

controller, memory, and input/output ports—and enables 

them to transfer information. The bus consists of specialized 

groups of lines that carry different types of information. 

One group of lines carries data; another carries 

memory addresses (locations) where data items are to be 

found; yet another carries control signals. Buses are characterized 

by the number of bits they can transfer at a single 

B

us enumerator bus network 

B time, equivalent to the number of wires within the bus. A 

computer with a 32-bit address bus and a 16-bit data bus, 

for example, can transfer 16 bits of data at a time from any 

of 232 memory locations. Most PCs contain one or more 

expansion slots into which additional boards can be 

plugged to connect them to the bus. 

bus enumerator n. A device driver that identifies devices 

located on a specific bus and assigns a unique identification 

code to each device. The bus enumerator is responsible 

for loading information about the devices onto the 

hardware tree. See also bus, device driver, hardware tree. 

bus extender n. 1. A device that expands the capacity of 

a bus. For example, IBM PC/AT computers used a bus 

extender to add onto the earlier PC bus and allow the use 

of 16-bit expansion boards in addition to 8-bit boards. See 

also bus. 2. A special board used by engineers to raise an 

add-on board above the computer’s cabinet, making it easier 

to work on the circuit board. 

business graphics n. See presentation graphics. 

business information system n. A combination of 

computers, printers, communications equipment, and 

other devices designed to handle data. A completely automated 

business information system receives, processes, 

and stores data; transfers information as needed; and produces 

reports or printouts on demand. Acronym: BIS. See 

also management information system. 

business logic n. A set of rules and calculations built 

into a business information application. The application 

uses business logic to sort incoming information and 

respond accordingly. Business logic functions as a set of 

guidelines that ensure the application’s actions conform to 

the specific needs of a business. 

business software n. Any computer application 

designed primarily for use in business, as opposed to scientific 

use or entertainment. In addition to the well-known 

areas of word processing, spreadsheets, databases, and 

communications, business software for microcomputers 

also encompasses such applications as accounting, payroll, 

financial planning, project management, decision and 

support systems, personnel record maintenance, and office 

management. 

78 

Business Software Alliance n. International organization 

of computer software companies that promotes the 

interests of the software industry. This alliance focuses on 

educating the public on the importance of software, 

advancing free and open world trade, and supporting legislation 

opposing software piracy and Internet theft. The 

Business Software Alliance has offices in the United 

States, Europe, and Asia, with members in more than 60 

nations around the world. Acronym: BSA. 

business-to-business n. See B2B. 

business-to-consumer n. See B2C. 

bus mastering n. In modern bus architectures, the ability 

of a device controller card—a network adapter or a disk 

controller, for example—to bypass the CPU and work 

directly with other devices to transfer data into and out of 

memory. Enabling devices to take temporary control of 

the system bus for data transfer and bus mastering frees 

the CPU for other work. This in turn improves performance 

in tasks, such as video replay and multiple-user 

queries to large databases, that require simultaneous data 

access and intensive processing. The technology known as 

direct memory access (DMA) is a well-known example of 

bus mastering. See also bus, controller, direct memory 

access. Compare PIO. 

bus mouse n. A mouse that attaches to the computer’s 

bus through a special card or port rather than through a 

serial port. See also mouse. Compare serial mouse. 

bus network n. A topology (configuration) for a LAN 

(local area network) in which all nodes are connected to a 

main communications line (bus). On a bus network, each 

node monitors activity on the line. Messages are detected 

by all nodes but are accepted only by the node(s) to which 

they are addressed. A malfunctioning node ceases to communicate 

but does not disrupt operation (as it might on a 

ring network, in which messages are passed from one 

node to the next). To avoid collisions that occur when two 

or more nodes try to use the line at the same time, bus networks 

commonly rely on collision detection or token passing 

to regulate traffic. See the illustration. Also called: bus 

topology, linear bus. See also collision detection, contention, 

CSMA/CD, token bus network, token passing. Compare 

ring network, star network.

us system bytes per inch 

F0Bgn19.eps 

Bus network. A bus network configuration. 

bus system n. The interface circuitry that controls the 

operations of a bus and connects it with the rest of the 

computer system. See also bus. 

bus topology n. See bus network. 

button n. 1. A graphic element in a dialog box that, when 

activated, performs a specified function. The user activates 

a button by clicking on it with a mouse or, if the button has 

the focus, by hitting the Return or Enter key. 2. On a 

mouse, a movable piece that is pressed to activate some 

function. Older mouse models have only one button; 

newer models typically have two or more buttons. 

button bomb n. A button on Web pages with the image 

of a bomb. 

button help n. Help information displayed via the selection 

of buttons or icons. Applications such as the World 

Wide Web, multimedia kiosks, and computer-aided instruction 

often use button help icons to ease system navigation. 

bypass n. In telecommunications, the use of communication 

pathways other than the local telephone company, 

such as satellites and microwave systems. 

79 

byte n. Short for binary term. A unit of data, today almost 

always consisting of 8 bits. A byte can represent a single 

character, such as a letter, a digit, or a punctuation mark. 

Because a byte represents only a small amount of information, 

amounts of computer memory and storage are usually 

given in kilobytes (1024 bytes), megabytes (1,048,576 

bytes), or gigabytes (1,073,741,824 bytes). 

Abbreviation: B. See also bit, gigabyte, kilobyte, megabyte. 

Compare octet, word. 

bytecode n. An encoding of a computer program that a 

compiler produces when the original source code is processed. 

This encoding is in an abstract, processor-independent 

form that cannot be directly executed by most CPUs 

but is highly suitable for further analysis (for example, 

compiler optimization), for processing by interpreters (for 

example, executing Java applets within Web browsers), or 

for use in generation of binary instructions for the target 

computer’s CPU. Intermediate bytecode production is a 

feature of the compilers for the Pascal and Java programming 

languages. See also central processing unit, compiler 

(definition 2), interpreter, Java, Java applet, Pascal. 

BYTE Information Exchange n. See BIX. 

byte-oriented protocol n. A communications protocol in 

which data is transmitted as a string of characters in a particular 

character set, such as ASCII, rather than as a 

stream of bits as in a bit-oriented protocol. To express control 

information, a byte-oriented protocol relies on control 

characters, most of which are defined by the coding 

scheme used. The asynchronous communications protocols 

commonly used with modems and IBM’s BISYNC 

protocol are byte-oriented protocols. Compare bit-oriented 

protocol. 

bytes per inch n. The number of bytes that fit into an 

inch of length on a disk track or a tape. Acronym: BPI. 

B

C 

C n. A programming language developed by Dennis 

Ritchie at Bell Laboratories in 1972. It is so named 

because its immediate predecessor was the B programming 

language. Although C is considered by many to be 

more a machine-independent assembly language than a 

high-level language, its close association with the UNIX 

operating system, its enormous popularity, and its standardization 

by the American National Standards Institute 

(ANSI) have made it perhaps the closest thing to a standard 

programming language in the microcomputer/workstation 

marketplace. C is a compiled language that 

contains a small set of built-in functions that are machine 

dependent. The rest of the C functions are machine independent 

and are contained in libraries that can be accessed 

from C programs. C programs are composed of one or 

more functions defined by the programmer; thus C is a 

structured programming language. See also C++, compiled 

language, library, Objective-C, structured programming. 

C++ n. An object-oriented version of the C programming 

language, developed by Bjarne Stroustrup in the early 

1980s at Bell Laboratories and adopted by a number of 

vendors, including Apple Computer, Inc. and Sun Microsystems, 

Inc. See also C, Objective-C, object-oriented 

programming. 

C2 n. A security class of the U.S. Department of Defense 

Trusted Computer System Evaluation Criteria (DOD 

4200.28.STD). C2 is the lowest level of security in the 

U.S. National Computer Security Center’s hierarchy of 

criteria for trusted computer systems, requiring user logon 

with password and a mechanism for auditing. The C2 

level is outlined in the Orange Book. See also Orange 

Book (definition 1). 

CA n. See certificate authority. 

.cab n. File extension for cabinet files, which are multiple 

files compressed into one and extractable with the 

extract.exe utility. Such files are frequently found on 

Microsoft software (for example, Windows 9x) distribution 

disks. 

cabinet n. The box in which the main components of a 

computer (CPU, the hard drive, floppy and CD-ROM 

C 

80 

drives, and expansion slots for peripheral devices, such as 

monitors) are located. See also CPU, expansion slot. 

cable1 n. A collection of wires shielded within a protective 

tube, used to connect peripheral devices to a computer. 

A mouse, a keyboard, and a printer might all be 

connected to a computer with cables. Printer cables typically 

implement a serial or a parallel path for data to travel 

along. See the illustration. 

f0cgn01.eps 

Cable. 

cable2 adj. Pertaining to the cable television (CATV) distribution 

system. For example, a cable modem is a modem 

that sends and receives digital data through a connection 

to a cable TV system. Because cable TV is a broadband 

service, it can carry data (such as an Internet connection) 

at a very high speed. See also CATV. 

cable connector n. The connector on either end of a 

cable. See also DB connector, DIN connector, RS-232-C 

standard, RS-422/423/449. 

cable matcher n. A device that allows the use of a cable 

that has slightly different wire connections from those 

required by the devices to which it is attached. 

cable modem n. A modem that sends and receives data 

through a coaxial cable television network instead of telephone 

lines, as with a conventional modem. Cable 

modems, which have speeds of 500 kilobits per second 

(Kbps), can generally transmit data faster than current 

conventional modems. However, cable modems do not 

operate at the same rate upstream (when sending information) 

and downstream (when receiving information). 

Upstream rates vary from about 2 Mbps to 10 Mbps,

cable telephony CAE 

downstream rates from about 10 Mbps to 36 Mbps. See 

also coaxial cable, modem. 

cable telephony n. Telephone service provided over a 

cable TV connection rather than over traditional telephone 

lines. Although service is delivered over cable rather than 

telephone wire, the end user perceives no difference 

between cable telephony and normal telephone service. 

Proponents of cable telephony see it as part of the eventual 

integration of Internet, television, and telephone services 

into a single communication/entertainment unit. 

cable television n. See CATV. 

cabling diagram n. A plan that shows the path of cables 

that attach computer system components or peripherals. 

Cabling diagrams are particularly important for explaining 

the connection of disk drives to a disk controller. 

cache n. A special memory subsystem in which frequently 

used data values are duplicated for quick access. 

A memory cache stores the contents of frequently 

accessed RAM locations and the addresses where these 

data items are stored. When the processor references an 

address in memory, the cache checks to see whether it 

holds that address. If it does hold the address, the data is 

returned to the processor; if it does not, a regular memory 

access occurs. A cache is useful when RAM accesses are 

slow compared with the microprocessor speed because 

cache memory is always faster than main RAM memory. 

See also disk cache, wait state. 

cache card n. An expansion card that increases a system’s 

cache memory. See also cache, expansion board. 

Cache-Coherent Non-Uniform Memory Access n. See 

ccNUMA. 

cache farm n. A group of servers that save copies of Web 

pages to caches to fulfill successive requests without calling 

the pages up repeatedly from the Web server. In 

essence, the servers are dedicated to caching. By saving 

Web pages where they can be accessed without increasing 

traffic on the Web site, the cache farm allows higher-performance 

Web access for the end user and a reduction in 

network congestion and volume. See also cache. 

cache memory n. See cache. 

cache poisoning n. Deliberate corruption of Internet 

Domain Name System (DNS) information through alteration 

of data that equates host names with their IP 

81 

addresses. Misleading information of this type, when 

cached (saved) by one DNS server and later passed to 

another, exposes DNS servers to attacks in which data sent 

from one host to another can be accessed or corrupted. 

Cache poisoning has been used to redirect network 

requests from a legitimate server to an alternate Web site. 

See also DNS. 

CAD n. Acronym for computer-aided design. A system of 

programs and workstations used in designing engineering, 

architectural, and scientific models ranging from simple 

tools to buildings, aircraft, integrated circuits, and molecules. 

Various CAD applications create objects in two or 

three dimensions, presenting the results as wire-frame 

“skeletons,” as more substantial models with shaded surfaces, 

or as solid objects. Some programs can also rotate 

or resize models, show interior views, generate lists of 

materials required for construction, and perform other 

allied functions. CAD programs rely on mathematics, 

often requiring the computing power of a high-performance 

workstation. See also CAD/CAM, I-CASE. 

CAD/CAM n. Acronym for computer-aided design/computer-aided 

manufacturing. The use of computers in both 

the design and manufacture of a product. With CAD/ 

CAM, a product, such as a machine part, is designed with 

a CAD program and the finished design is translated into a 

set of instructions that can be transmitted to and used by 

the machines dedicated to fabrication, assembly, and process 

control. See also CAD, I-CASE. 

CADD n. A system of hardware and software similar to 

CAD but with additional features related to engineering 

conventions, including the ability to display dimension 

specifications and other notes. Acronym: CADD. See 

also CAD. 

caddy n. A plastic carrier that holds a CD-ROM and is 

inserted into a CD-ROM drive. Some PCs, especially 

older models, have CD-ROM drives that require the use 

of a caddy. Most current CD-ROM drives do not require 

a caddy. 

CAE n. Acronym for computer-aided engineering. An 

application that enables the user to perform engineering 

tests and analyses on designs created with a computer. In 

some instances, capabilities such as logic testing that are 

generally attributed to CAE applications are also part of 

CAD programs, so the distinction between CAD and CAE 

is not a hard-and-fast one. See also CAD, I-CASE. 

C

C 

CAI calling sequence 

CAI n. Acronym for computer-aided (or computer-assisted) 

instruction. An educational program designed to serve as a 

teaching tool. CAI programs typically use tutorials, drills, 

and question-and-answer sessions to present a topic and to 

test the student’s comprehension. CAI programs are excellent 

aids for presenting factual material and for allowing 

students to pace their learning speed. Subjects and complexity 

range from beginning arithmetic to advanced 

mathematics, science, history, computer studies, and specialized 

topics. Also called: CAL, CAT, computer-aided 

learning, computer-aided teaching, computer-assisted learning, 

computer-assisted teaching, computer-augmented 

learning. See also I-CASE. Compare CBT, CMI. 

CAL n. 1. Acronym for computer-assisted (or computeraugmented) 

learning. See CAI. 2. Acronym for Common 

Application Language. An object-oriented communications 

language for controlling home-networking products. 

CAL, originally part of the CEBus (Consumer Electronic 

Bus) standard for home automation, can be implemented 

with various communication protocols, home-networking 

standards, and home electronic products. See also CEBus, 

home automation. 

calculator n. Broadly, any device that performs arithmetic 

operations on numbers. Sophisticated calculators 

can be programmed for certain functions and can store 

values in memory, but they differ from computers in several 

ways: they have a fixed set of commands, they do not 

recognize text, they cannot retrieve values stored in a data 

file, and they cannot find and use values generated by a 

program such as a spreadsheet. 

calendar program n. An application program in the form 

of an electronic calendar, commonly used for highlighting 

dates and scheduling appointments. Some calendar programs 

resemble wall calendars, displaying dates in blocks 

labeled with the days of the week; others display dates day 

by day and enable the user to enter appointments, notes, 

and other memoranda. A day-of-the-week type of calendar 

program could, for example, be used to find out that 

Christmas 2003 will be on a Saturday. Depending on its 

capabilities, such a program might cover only the current 

century, or it might cover hundreds of years and even 

allow for the change (in 1582) from the Julian to the Gregorian 

calendar. A calendar/scheduler program might 

show blocks of dates or, like an appointment book, single 

days divided into hours or half hours, with room for notes. 

Some programs allow the user to set an alarm to go off at 

82 

an important point in the schedule. Other programs can 

coordinate the calendars of different people on the same 

network so that a person entering an appointment into his 

or her calendar also enters the appointment into a colleague’s 

calendar. 

call1 n. In a program, an instruction or statement that 

transfers program execution to some section of code, such 

as a subroutine, to perform a specific task. Once the task is 

performed, program execution resumes at the calling point 

in the program. See also calling sequence. 

call2 vb. 1. To establish a connection through a telecommunications 

network. 2. To transfer program execution to 

some section of code (usually a subroutine) while saving 

the necessary information to allow execution to resume at 

the calling point when the called section has completed 

execution. Some languages (such as FORTRAN) have an 

explicit CALL statement; others (such as C and Pascal) 

perform a call when the name of a procedure or function 

appears. In assembly language, there are various names 

for a CALL instruction. When a subroutine call occurs in 

any language, one or more values (known as arguments or 

parameters) are often passed to the subroutine, which can 

then use and sometimes modify these values. See also 

argument, parameter. 

callback or callback security n. A security feature used 

to authenticate users calling in to a network. During callback, 

the network validates the caller’s username and password, 

hangs up, and then returns the call, usually to a 

preauthorized number. This security measure usually prevents 

unauthorized access to an account even if an individual’s 

logon ID and password have been stolen. See also 

authentication, preset-to callback, remote access server. 

callback modem n. A modem that, instead of answering 

an incoming call, requires the caller to enter a touch-tone 

code and hang up so that the modem can return the call. 

When the modem receives the caller’s code, it checks the 

code against a stored set of phone numbers. If the code 

matches an authorized number, the modem dials the number 

and then opens a connection for the original caller. 

Callback modems are used when communications lines 

must be available to outside users but data must be protected 

from unauthorized intruders. 

calling sequence n. In a program when a subroutine call 

occurs, an agreement between the calling routine and the 

called routine on how arguments will be passed and in 

what order, how values will be returned, and which routine

CALL instruction canonical name 

will handle any necessary housekeeping (such as cleaning 

up the stack). The calling sequence becomes important 

when the calling and called routines were created with different 

compilers or if either was written in assembly language. 

Two common calling sequences are the C calling 

sequence and the Pascal calling sequence. In the C calling 

sequence, the calling routine pushes any arguments 

included in the call on the stack in reverse order (right to 

left) and performs any stack cleanup; this permits a varying 

number of arguments to be passed to a given routine. In 

the Pascal calling sequence, the calling routine pushes any 

included arguments on the stack in the order in which they 

appear (left to right), and the called routine is expected to 

clean up the stack. See also argument, call1 , stack. 

CALL instruction n. A type of programming instruction 

that diverts program execution to a new area in memory 

(sequence of directives) and also allows eventual return to 

the original sequence of directives. 

CALS n. Acronym for Computer-Aided Acquisition and 

Logistics Support. A U.S. Department of Defense standard 

for electronic exchange of data with commercial suppliers. 

CAM n. 1. Acronym for computer-aided manufacturing. 

The use of computers in automating the fabrication, 

assembly, and control aspects of manufacturing. CAM 

applies to the manufacture of products ranging from 

small-scale production to the use of robotics in full-scale 

assembly lines. CAM relates more to the use of specialized 

programs and equipment than it does to the use of 

microcomputers in a manufacturing environment. See also 

CAD/CAM, I-CASE. 2. See Common Access Method. 

camera-ready adj. In publishing, of or pertaining to the 

stage at which a document, with all typographic elements 

and graphics in place, is suitably prepared to be sent to a 

printing service. The printing service photographs the 

camera-ready copy and then uses the photograph to make 

plates for printing. Some applications are advertised as 

being able to bring documents to the camera-ready stage, 

eliminating the need for manual layout and pasteup of elements 

onto boards. 

campuswide information system n. Information and 

services distributed on a college or university campus 

through computer networks. Campuswide information 

system services typically include student and faculty 

directories, calendars of campus events, and access to 

databases. Acronym: CWIS. 

83 

cancel n. A control character used in communication 

with printers and other computers, commonly designated 

as CAN. It usually means that the line of text being sent 

should be canceled. In ASCII, which is the basis of character 

sets used by most microcomputers, this is represented 

internally as character code 24. 

cancelbot n. Short for cancel robot. A program that 

identifies articles in newsgroups based on a set of criteria 

and cancels the distribution of those articles. Although the 

criteria for cancellation is set by the owner of the cancelbot, 

most cancelbots exist to identify and eliminate spam 

messages posted to dozens or hundreds of newsgroups. 

See also spam. 

cancel message n. A message sent to Usenet news servers 

indicating that a certain article is to be canceled, or 

deleted, from the server. See also article, news server, 

Usenet. 

candidate key n. A unique identifier for a tuple (row) 

within a relation (database table). The candidate key may 

be either simple (a single attribute) or composite (two or 

more attributes). By definition, every relation must have at 

least one candidate key, but it is possible for a relation to 

have more than one candidate key. If there is only one candidate 

key, it automatically becomes the primary key for 

the relation. If there are multiple candidate keys, the 

designer must designate one as the primary key. Any candidate 

key that is not the designated primary key is an 

alternate key. See also key (definition 2), primary key. 

canned program n. See canned software. 

canned routine n. A previously written routine that is 

copied into a program and used as is, without modification. 

See also library routine. 

canned software n. Off-the-shelf software, such as word 

processors and spreadsheet programs. 

canonical form n. In mathematics and programming, 

the standard or prototypical form of an expression or a 

statement. 

canonical name n. An object’s distinguished name presented 

with the root first and without the LDAP attribute 

tags (such as: CN=, DC=). The segments of the name are 

delimited with forward slashes (/). For example, 

CN=MyDocuments,OU=MyOU,DC=Microsoft,DC=Com 

is presented as microsoft.com/MyOU/MyDocuments in 

canonical form. See also Lightweight Directory Access 

Protocol. 

C

C 

capacitance carder 

capacitance n. The ability to store an electric charge. 

Capacitance is measured in farads. A capacitance of 1 

farad will hold 1 coulomb of charge at a potential of 1 

volt. In practical use, a farad is an extremely large amount 

of capacitance; typical capacitors have values of microfarads 

(10-6 ) or picofarads (10-12 ). See also capacitor. 

capacitor n. A circuit component that provides a known 

amount of capacitance (ability to store an electric charge). 

A capacitor typically consists of two conductive plates 

separated by an insulating (dielectric) material. If other 

factors remain constant, capacitance increases as the 

plates are made larger or brought closer together. A capacitor 

blocks direct current but passes alternating current to 

an extent that depends on its capacitance and on the frequency 

of the current. See also capacitance. 

capacity n. The amount of information a computer or an 

attached device can process or store. See also computer. 

caps n. Short for capital letters. Compare lowercase. 

Caps Lock key n. A toggle key that, when on, shifts the 

alphabetic characters on the keyboard to uppercase. The 

Caps Lock key does not affect numbers, punctuation 

marks, or other symbols. See the illustration. 

Tab 

Caps 

Lock 

Q 

A 

Shift Z 

f0cgn02.eps 

Caps Lock key. 

capstan n. On a tape recorder, a polished metal post 

against which a turning rubber wheel (called a pinch 

roller) presses to move a length of magnetic tape placed 

between the wheel and the post. The capstan controls the 

speed of the tape as it moves past the recording head. See 

also pinch roller. 

capture vb. In communications, to transfer received data 

into a file for archiving or later analysis. 

capture board n. See video capture card. 

capture card n. See video capture card. 

Carbon n. Code name for the Application Program Interfaces 

(API) and shared libraries used to write applications 

for Macintosh OS X. Since Macintosh OS X is an entirely 

different system rather than an update of the previous 

84 

Macintosh OS, Carbon bridges the gap between the systems, 

allowing developers to rewrite their programs to OS 

X without rewriting the code for the entire application. 

Carbon allows OS X native applications to run under earlier 

versions of the Macintosh OS without modification 

but with OS X advantages. 

carbon copy n. See cc. 

carbonize vb. To update a Macintosh application for OS 

X. Although older versions of Macintosh applications will 

run under OS X, only those that have been carbonized will 

be able to use OS X–specific advantages. 

carbon ribbon n. A ribbon used with impact printers, 

especially daisy-wheel printers, and with typewriters for 

highest-quality output. A carbon ribbon is made of a thin 

strip of Mylar coated on one side with a carbon film. Characters 

printed with a carbon ribbon are extremely crisp 

and free from the fuzziness that can be associated with an 

inked cloth ribbon. Also called: film ribbon, Mylar ribbon. 

See also daisy-wheel printer. Compare cloth ribbon. 

card n. 1. A printed circuit board or adapter that can be 

plugged into a computer to provide added functionality or 

new capability. These cards provide specialized services, 

such as mouse support and modem capabilities, that are 

not built into the computer. See also adapter, board, 

printed circuit board. 2. In programs such as the Hyper- 

Card hypertext program, an on-screen representation of an 

index card on which information can be stored and “filed” 

(saved) for future reference. See also hypertext. 3. A 

manila card about 3 inches high by 7 inches long on which 

80 columns of data could be entered in the form of holes 

punched with a keypunch machine. The punched holes 

corresponded to numbers, letters, and other characters and 

could be read by a computer that used a punched-card 

reader. Also called: punched card. See also card reader 


card cage n. An enclosure area for holding printed circuit 

boards (cards). Most computers have an area with 

protective metal and mounting brackets where cards are 

installed. The term originally came from an external box 

that held rack-mounted cards or peripherals and resembled 

a cage. 

carder n. A person who engages in online credit card 

fraud. Specifically, a carder steals credit card numbers, 

either to purchase merchandise (often computer-related) 

from Web-based stores or to trade the stolen numbers with 

like-minded individuals—again, over the Internet. Carders

cardinal number carrier sense multiple access with collision detection 

generally obtain credit card numbers through conventional 

means, such as “trashing” (searching through trash) or 

calling individuals and posing as bank officers. See also 

hacker (definition 2). 

cardinal number n. A number that indicates how many 

items there are in a set—for example, “There are 27 names 

on that list.” Compare ordinal number. 

card punch n. See keypunch. 

card reader n. 1. An input device used chiefly for identification 

purposes that reads information that has been 

magnetically encoded, usually in two tracks, on a plastic 

card, such as a credit card or an employee badge. 2. A 

mechanical apparatus that reads computer data from 

punched cards. No longer in widespread use, card readers 

allow computer data to be created off line and then input 

to the computer for processing. This need for offline data 

creation was because of limited CPU resources. Reading 

batches of punched cards was a better use of CPU time 

than waiting for a human operator to key data directly into 

the computer’s memory. Also called: punched-card reader. 

caret n. The small, upward-pointing symbol (^) typically 

found over the 6 key on the top row of a microcomputer 

keyboard. In some programming languages, the caret is 

used as an exponentiation operator. For example, the 

expression 3 ^ 2 represents the number 3 raised to the second 

power. The caret is also used to represent the Control 

key on the keyboard. For example, ^Z means “hold the 

Control key down and press the Z key.” 

careware n. Software developed by an individual or a 

small group and distributed freely, with the proviso that 

users make a donation to a charity if they continue to use 

the software after trying it out. The charity is one usually 

designated by the software creator. 

Carnivore n. Digital wiretap technology developed by the 

U.S. Federal Bureau of Investigation. Carnivore’s purpose 

is to track and capture e-mail and other Internet-based 

communications sent from and received by a suspect. Carnivore 

copies all of an ISP’s network traffic into a collection 

system where a filter sifts through all communications, 

disregarding all data but that related to the suspect. 

carpal tunnel syndrome n. A form of repetitive strain 

injury to the wrist and hand. Making the same small 

motions over and over can cause swelling and scarring of 

the soft tissue of the wrist, which then compresses the 

main nerve leading to the hand. Symptoms of carpal tunnel 

syndrome include pain and tingling in the fingers, and 

in advanced cases, carpal tunnel syndrome can lead to loss 

85 

of functionality of the hands. Typing at a computer keyboard 

without proper wrist support is a common cause of 

carpal tunnel syndrome. Acronym: CTS. See also repetitive 

strain injury, wrist support. 

carriage n. The assembly that holds the platen of a typewriter 

or a typewriterlike printer. On a standard typewriter, 

the platen and carriage move past a fixed position within the 

typewriter housing, where the keys strike the paper; the 

platen rotates to advance the paper held in the carriage. On 

most impact printers for computers, however, the print head 

moves back and forth across a platen, which rotates but 

does not move horizontally; in such machines, the assembly 

that carries the print head is often called the print-head carriage 

assembly. See also carriage return, platen. 

carriage return n. A control character that tells a computer 

or printer to return to the beginning of the current 

line. A carriage return is similar to the return on a typewriter 

but does not automatically advance to the beginning 

of a new line. For example, a carriage-return character 

alone, received at the end of the words This is a sample 

line of text would cause the cursor or printer to return to 

the first letter of the word This. In the ASCII character set, 

the carriage-return character has the decimal value of 13 

(hexadecimal 0D). See the illustration. 

" 

' 

+ 

= 

} 

] 

Backspace 

Enter 

In 

D 

Carriage return 

f0cgn03.eps 

Carriage return. 

carrier n. 1. In communications, a specified frequency 

that can be modulated to convey information. 2. A company 

that provides telephone and other communications 

services to consumers. 

Carrier Detect n. See CD (definition 2). 

carrier frequency n. A radio-frequency signal, such as 

those used with modems and on networks, used to transmit 

information. A carrier frequency is a signal that 

vibrates at a fixed number of cycles per second, or hertz 

(Hz), and is modulated (changed) in either frequency or 

amplitude to enable it to carry intelligible information. 

carrier sense multiple access with collision 

detection n. See CSMA/CD. 

C

C 

carrier signal cascading menu 

carrier signal n. See carrier frequency. 

carrier system n. A communications method that uses 

different carrier frequencies to transfer information along 

multiple channels of a single path. Transmission involves 

modulating the signal on each frequency at the originating 

station and demodulating the signal at the receiving station. 

carry n. In arithmetic, the process of moving a digit to the 

next higher position when the sum of two numbers is 

greater than the largest digit in the number system being 

used. Computers, based on logic circuits, and often able to 

add all digits in two numbers simultaneously (do parallel 

addition), perform carries in several exotic ways. For 

example, they perform complete carries, in which one 

carry is allowed to propagate—that is, to generate other 

carries in other digit positions. They can also perform partial 

carries, in which carries resulting from parallel addition 

are stored temporarily. 

carry bit n. The bit, associated with an adder circuit, that 

indicates that an addition operation has produced a carry 

(as in 9 + 7). Also called: carry flag. 

carry flag n. See carry bit. 

Cartesian coordinates n. Points on a plane (two dimensions) 

or in space (three dimensions) that are located by 

their positions in relation to intersecting axes; named after 

the French mathematician René Descartes, who introduced 

the system in the seventeenth century. In two 

dimensions, points are described by their positions in relation 

to the two familiar axes, x (usually horizontal) and y 

(usually vertical). In three dimensions, a third axis, z, is 

added to the x- and y-axes. See the illustration. See also 

x-y-z coordinate system. Compare polar coordinates. 

(-1, 3) 

-3 -2 -1 1 2 3 

(-3, -1) 

-1 

-2 

Origin 

-3 

(2, -3) 

3 

2 

1 

f0cgn04.eps 


y 

(3, 1) 

x 

86 

Cartesian product n. See product (definition 1). 

cartridge n. Any of various container devices that usually 

consist of some form of plastic housing. See also disk cartridge, 

ink cartridge, memory cartridge, ribbon cartridge, 

ROM cartridge, tape cartridge, toner cartridge. 

cartridge font n. A font contained in a plug-in cartridge 

and used to add fonts to laser, ink-jet, or high-end dotmatrix 

printers. Cartridge fonts are distinguished both 

from internal fonts, which are contained in ROM in the 

printer and are always available, and from downloadable 

(soft) fonts, which reside on disk and which can be sent to 

the printer as needed. See also font cartridge. Compare 

internal font. 

cascade n. 1. Additional elements displayed by a menu 

item or list box from which the user can choose in order to 

interact with other screen elements. See the illustration. 

2. In newsgroup articles, the accumulation of quotation 

marks (often angle brackets) added by newsgroup readers 

each time an article is replied to. Most newsgroup readers 

will copy the original article in the body of the reply; after 

several replies, the original material will have several quotation 

marks. See also article, newsgroup, newsreader. 

f0cgn05.eps 

Cascade. 

cascade connection n. See pipe (definition 1). 

cascaded star topology n. A star network in which 

nodes connect to hubs and hubs connect to other hubs in a 

hierarchical (cascaded) parent/child relationship. This 

topology is characteristic of 100Base-VG networks. 

cascading hubs n. A network configuration in which 

hubs are connected to other hubs. See also hub. 

cascading menu n. A hierarchical graphical menu system 

in which a side menu of subcategories is displayed 

when the pointer is placed on the main category.

Cascading Style Sheet mechanism catch 

Cascading Style Sheet mechanism n. See cascading 

style sheets. 

cascading style sheets n. A Hypertext Markup Language 

(HTML) specification developed by The World 

Wide Web Consortium (W3C) that allows authors of 

HTML documents and users to attach style sheets to 

HTML documents. The style sheets include typographical 

information on how the page should appear, such as the 

font of the text in the page. This specification also directs 

the way in which the style sheets of the HTML document 

and the user’s style will blend. Cascading style sheets have 

been proposed for the HTML 3.2 standard. Acronym: 

CSS. Also called: Cascading Style Sheet mechanism, 

CSS1. See also HTML, style sheet (definition 2). 

cascading windows n. A sequence of successive, overlapping 

windows in a graphical user interface, displayed 

so that the title bar of each is visible. Also called: overlaid 

windows. 

case n. In text processing, an indication of whether one 

or more alphabetic characters are capitalized (uppercase) 

or not (lowercase). A case-sensitive program or routine 

distinguishes between uppercase and lowercase letters and 

treats the word cat as totally distinct from either Cat or 

CAT. A case-sensitive program that also separates capitalized 

and lowercased words would list Arkansas before 

aardvark or antimony, even though its alphabetic position 

follows both lowercased words. 

CASE n. Acronym for computer-aided software engineering. 

A comprehensive label for software designed to use 

computers in all phases of computer program development, 

from planning and modeling through coding and 

documentation. CASE represents a working environment 

consisting of programs and other development tools that 

help managers, systems analysts, programmers, and others 

to automate the design and implementation of programs 

and procedures for business, engineering, and scientific 

computer systems. 

case-sensitive search n. A search in a database in 

which capitalization of key words must exactly match the 

capitalization of words in the database. A case-sensitive 

search for “north and south” would fail to find a database 

entry for “North and South.” 

case sensitivity n. Discrimination between lowercase 

and uppercase characters in a program or a programming 

language. See also case. 

87 

case statement n. In programming languages such as 

Ada, Pascal, and C, a type of control statement that executes 

one of several sets of instructions based on some key 

value. Case statements are used in evaluating situations 

that can have a number of different results. “Case” in this 

sense refers to a refinement of a basic IF-THEN type of 

conditional statement (if A is true, then do B), but a case 

statement functions more like a series of nested IFs (if A, 

then do this; else if B, then do that; else . . .). In a case 

evaluation, a variable (such as a number or a string of 

characters) is compared against one after another of a 

series of constants assigned by the programmer. Each constant 

represents a different case and defines an action to be 

carried out. When the program finds a constant that 

matches the variable, it carries out whatever action is dictated 

by the case in which the match occurs. See also constant, 

control statement, variable. 

cassette n. The unit consisting of both the plastic case 

and the magnetic tape it contains. Cassette tapes are used 

for backing up large amounts of computer data. 

cassette tape n. 1. The tape within a cassette. 2. The 

unit consisting of both the plastic cassette case and the 

tape it contains. 

cast n. A programmer-specified data conversion from 

one type to another, such as a conversion from integer to 

floating point. Also called: coercion. See also data type. 

CAT n. 1. Acronym for computer-aided testing. A procedure 

used by engineers for checking or analyzing designs, 

especially those created with CAD programs. Computeraided 

testing is also used by software developers for automated 

regression testing. 2. Acronym for computerassisted 

teaching or computer-aided teaching. See CAI. 

3. Acronym for computerized axial tomography. A medical 

procedure in which a computer is used to generate a 

three-dimensional image of a body part from a series of Xrays 

taken as cross sections along a single axis. See CAI. 

catalog n. 1. In a computer, a list containing specific 

information, such as name, length, type, and location of 

files or of storage space. 2. In a database, the data dictionary. 

See also data dictionary. 

catch n. A keyword in the Java programming language 

used to declare a block of statements to be executed in the 

event that a Java exception or runtime error occurs in a 

preceding “try” block. See also block, exception, keyword, 

runtime, try. 

C

C 

Category 3 cable CCC 

Category 3 cable n. Network cable that supports frequencies 

up to 16 MHz and transmission speeds up to 10 

Mbps (standard Ethernet). Category 3 cable has four 

unshielded twisted pairs (UTPs) of copper wire and RJ-45 

connectors, and is used in voice and 10Base-T applications. 

Also called: Cat 3 cable. 


up to 20 MHz and transmission speeds up to 16 

Mbps. Category 4 cable has four unshielded twisted pairs 

(UTPs) of copper wire and RJ-45 connectors. Less popular 

than Category 3 and Category 5 cables, it is used primarily 

for token ring networks. Also called: Cat 4 cable. 


up to 100 MHz and transmission speeds up to 

100 Mbps (using two pairs) or 1000 Mbps (using four 

pairs and called gigabit over copper). Category 5 cable has 

four unshielded twisted pairs (UTPs) of copper wire and 

RJ-45 connectors, and is used for 10/100/1000 Base-T, 

ATM, and token ring networks. Also called: Cat 5 cable. 

Category 5e cable n. Network cable that supports frequencies 

up to 100 MHz and transmission speeds up to 

1000 Mbps (half-duplex mode) or 2000 Mbps (full-duplex 

mode). Category 5e cable has four unshielded twisted 

pairs (UTPs) of copper wire, RJ-45 connectors, and 

enhanced shielding to prevent signal degradation. Category 

5e cable can be used for 10/100/1000 Base-T, ATM, 

and token ring networks. Also called: Cat 5e cable. See 

also duplex2 (definition 1), half-duplex transmission. 

catena n. A series of items in a chained list—that is, a list 

in which one item points to the next in sequence. See also 

linked list. 

cathode n. 1. The terminal or electrode that is negatively 

charged and from which electrons flow. 2. The electronemitting 

electrode in a vacuum tube. 3. The negative terminal 

of a battery. Compare anode. 

cathode-ray oscilloscope n. See oscilloscope. 

cathode-ray tube n. See CRT. 

CATV n. Acronym for community antenna television or 

cable television. A television broadcasting system that 

uses coaxial or fiber-optic cable to distribute a broadband 

signal containing many separate television program channels. 

CATV systems are also increasingly being used to 

carry digital data—for example, Internet connections—to 

and from subscribers. 

88 

CatXML n. Acronym for Catalogue XML. An open standard 

for using XML in catalogue information exchanges 

over the Internet. CatXML uses a flexible XML schema 

with multiple profiles that can be adapted to meet the 

needs of individual businesses. CatXML supports existing 

information structures and provides distributed query 

information grid models and dynamic output formats. 

cavity virus n. A type of virus that overwrites and hides 

within a section of the file it has infected. A cavity virus 

overwrites only a part of the host file filled with a constant, 

allowing the file to continue to function. 

CBEMA n. Acronym for Computer and Business Equipment 

Manufacturers Association. An organization of 

hardware vendors and manufacturers in the United States 

involved in standardizing information processing and 

related equipment. 

CBL n. Acronym for computer-based learning. Applies to 

either computer-aided instruction (CAI), which focuses 

primarily on education, or computer-based training 

(CBT), which is application-specific or job-oriented 

teaching. See also CAI, CBT. 

CBT n. Acronym for computer-based training. The use of 

computers and specially developed tutorial programs for 

teaching. CBT uses color, graphics, and other attentiongetting 

aids to help maintain interest, and it has both simple 

and sophisticated applications. A software developer, 

for example, might include a series of CBT lessons with 

an application to give new users a hands-on feel for the 

program; a consultant might use a longer and more 

detailed CBT program as a tool in a management-training 

seminar. 

cc n. Acronym for courtesy copy. A directive to an e-mail 

program to send a complete copy of a given piece of mail 

to another individual. The use of cc mail addressing, as 

opposed to directly addressing the mail to a person, generally 

implies that the recipient is not required to take any 

action; the message is for informational purposes only. In 

a cc directive, the fact that this recipient received the mail 

is printed in the mail header and is thus known to all other 

recipients. Also called: carbon copy. See also e-mail1 (definition 

1), header. Compare bcc. 

CCC n. Acronym for Computer Controlled Character. 

CCC is generally used in role-playing computer games 

like MUD. It refers to a character that is not played by a

CCD CDFS 

human player but is actually a computer-generated character 

built into the game itself. See also computer game, 

MUD, role-playing game. 

CCD n. See charge-coupled device. 

CCI n. See Common Client Interface. 

CCITT n. Acronym for Comité Consultatif International 

Télégraphique et Téléphonique, now called the International 

Telecommunication Union-Telecommunication 

Standardization Sector (ITU-TSS, often abbreviated as 

ITU-T). CCITT was the organization that performed the 

standardization functions for the International Telecommunication 

Union (ITU). Following a reorganization of 

the ITU in 1992, CCITT ceased to exist as a separate 

body, although several standards are still known by the 

CCITT prefix. See also ITU. 

CCITT Groups 1–4 n. A set of four standards recommended 

by the Comité Consultatif International 

Télégraphique et Téléphonique (International Telegraph 

and Telephone Consultative Committee) for the encoding 

and transmission of images over fax machines. Groups 1 

and 2 relate to analog devices and are generally out of use. 

Groups 3 and 4, which deal with digital devices, are outlined 

below. Group 3 is a widespread standard that supports 

standard images of 203 horizontal dots per inch (dpi) 

by 98 vertical dpi and fine images of 203 horizontal dpi by 

198 vertical dpi; supports two methods of data compression, 

one (based on the Huffman code) reducing an image 

to 10 to 20 percent of the original, the second (READ, for 

relative element address designate) compressing images to 

6 to 12 percent of the original; and provides for password 

protection and for polling so that a receiving machine can 

request transmission as appropriate. Group 4, a newer standard, 

supports images of up to 400 dpi; supports data compression 

based on a beginning row of white pixels (dots), 

with each succeeding line encoded as a series of changes 

from the line before, compressing images to 3 to 10 percent 

of the original; does not include error-correction 

information in the transmission; and requires an Integrated 

Services Digital Network (ISDN) phone line rather than a 

dial-up line. 

CCITT V series n. See V series. 

CCITT X series n. See X series. 

cc:Mail n. An e-mail program originally introduced by 

cc:mail, Inc., and currently produced by the Lotus Development 

Corporation. Lotus cc:Mail runs on multiple net- 

89 

working platforms and the Internet and is closely 

integrated with Lotus Notes collaborative software. 

ccNUMA n. Acronym for Cache-Coherent Non-Uniform 

Memory Access. A technology that enables many 

symmetric multiprocessing systems to be connected by 

high-speed/wide-bandwidth interconnect hardware so 

that they function as one machine. See also symmetric 

multiprocessing. 

CCP n. Acronym for Certificate in Computer Programming. 

A senior-level programming credential awarded by 

the Institute for Certification of Computer Professionals to 

individuals who pass an extensive set of programming 

examinations. 

cd n. Acronym for change directory. In MS-DOS, UNIX, 

and FTP client programs, the command that changes the 

current directory to the directory whose path follows cd in 

the command. See also directory, path (definition 5). 

CD n. 1. An individual compact disc, such as a CD-ROM. 

See also CD-ROM, compact disc (definition 2). 2. Acronym 

for Carrier Detect, a signal sent from a modem to the 

attached computer to indicate that the modem is on line. 

See also DCD. 

CD burner n. See CD recorder. 

CD drive n. See CD-ROM drive. 

CD-E n. Acronym for compact disc-erasable. A technological 

improvement in CDs (compact discs) whereby 

information can be repeatedly changed on the CD. Contemporary 

CDs are “write once, read many,” in that the 

information originally written cannot be changed. 

cdev n. Short for control panel device. A Macintosh utility 

that allows basic system settings to be customized. In 

Macintosh computers running System 6, a cdev is a utility 

program placed in the system folder. Keyboard and mouse 

cdevs are preinstalled. Other cdevs are provided with software 

packages and utilities. In System 7, cdevs are called 

control panels. See also control panel, system folder. 

Compare INIT. 

CDF n. See Channel Definition Format. 

CDFS n. 1. Acronym for CD-ROM File System. A 32-bit 

protected-mode file system that controls access to the contents 

of CD-ROM drives in Windows 9x. See also protected 

mode. 2. A designation used with UNIX computers 

to indicate that a file system resides on a read-only removable 

medium (that is a CD-ROM). This usually implies 

C

C 

CD-I CD-ROM File System 

that the compact disc is compliant with the ISO 9660 standard. 

CDFS is also used as a part of commands that mount 

media (hard drives, tape drives, remote networked drives, 

and CD-ROMs) for use on a computer. See also CD-ROM, 

ISO 9660. 

CD-I n. Acronym for compact disc-interactive. A hardware 

and software standard for a form of optical disc technology 

that can combine audio, video, and text on highcapacity 

compact discs. CD-I includes such features as 

image display and resolution, animation, special effects, 

and audio. The standard covers methods of encoding, 

compressing, decompressing, and displaying stored information. 

See also CD-ROM. 

CDMA n. See Code Division Multiple Access. 

CDN n. Acronym for content delivery network. A service 

that caches the pages of a Web site on geographically dispersed 

servers to enable faster delivery of Web pages. When 

a page is requested at a URL that is content delivery– 

enabled, the content delivery network routes the user’s 

request to a cache server close to the user. See also content 

delivery. 

CDP n. Acronym for Certificate in Data Processing. A 

certificate awarded by the Institute for Certification of 

Computer Professionals to individuals who pass a set of 

examinations on computers and related areas, including 

programming, software, and systems analysis. 

CDPD n. See Cellular Digital Packet Data. 

CD player n. Short for compact disc player. A device that 

reads the information stored on a CD. A CD player contains 

the optical equipment necessary for reading a disc’s 

contents and the electronic circuitry for interpreting the 

data as it is read. 

CD Plus n. A compact disc encoding format that allows 

mixing of audio recordings and computer data on the same 

CD, without the possibility of audio equipment becoming 

damaged by attempting to play the data sections. 

CD-R n. Acronym for compact disc-recordable. A type of 

CD-ROM that can be written on a CD recorder and read 

on a CD-ROM drive. See also CD recorder, CD-ROM. 

CD-R/E adj. Acronym for compact disc-recordable and 

erasable. Of or pertaining to hardware and software for 

interfacing computers with both CD-R (compact discrecordable) 

and CD-E (compact disc-erasable) devices. 

See also CD-R. 

90 

CD recorder n. A device used to write CD-ROMs. 

Because a disc can be written only once on these machines, 

they are used most commonly to create CD-ROMs for data 

archives or to produce CD-ROM masters that can be duplicated 

for mass distribution. Also called: CD-R machine, 

CD-ROM burner. See also CD-ROM. 

CD-R machine n. See CD recorder. 

CD-ROM n. 1. Acronym for compact disc read-only 

memory. A form of storage characterized by high capacity 

(roughly 650 megabytes) and the use of laser optics rather 

than magnetic means for reading data. Although CD-ROM 

drives are strictly read-only, they are similar to CD-R 

drives (write once, read many), optical WORM devices, 

and optical read-write drives. See also CD-I, CD-R, 

WORM. 2. An individual CD (compact disc) designed for 

use with a computer and capable of storing up to 650 

megabytes of data. See also CD, disc. 

CD-ROM burner n. See CD recorder. 

CD-ROM drive n. An electromechancial device that reads 

data on CD-ROMs. Most CD-ROM drives have a SCSI 

interface, although some are connected to a PC via a controller 

for a disk drive. Data is read through a small laser 

that is focused on the surface of the CD-ROM through 

optical mirrors in the read/write head. A spindle and drive 

motor revolve the CD-ROM, so all data, which is stored in 

spirals from the center, can be read. CD-ROM drives vary 

in the access time to locate a track on the CD-ROM and the 

seek time to move the read/write head. See the illustration. 

Also called: CD drive. See also CD-ROM, compact disc. 

CD-ROM drive 

f0cgn06.eps 

CD-ROM drive. 

CD-ROM Extended Architecture n. See CD-ROM/XA. 

CD-ROM File System n. See CDFS (definition 1).

CD-ROM jukebox cellular automata 

CD-ROM jukebox n. A CD-ROM player that can contain 

up to 200 CD-ROMs and is connected to a CD-ROM drive 

in a personal computer or workstation. A user can request 

data from any of the CD-ROMs in the jukebox, and the 

device will locate and play the disk that contains the data. 

Although only one CD-ROM can be played at a time, if 

multiple CD-ROM jukeboxes are each connected to separate 

CD-ROM drives that are daisy-chained together to the 

computer, more than one CD-ROM can be used at a time. 

See also CD-ROM, CD-ROM drive, daisy chain. 

CD-ROM/XA n. Short for CD-ROM Extended Achitecture. 

An extended CD-ROM format developed by Philips, 

Sony, and Microsoft. CD-ROM/XA is consistent with the 

ISO 9660 (High Sierra) standard, with further specification 

of ADPCM (adaptive differential pulse code modulation) 

audio, images, and interleaved data. See also 

adaptive differential pulse code modulation, CD-ROM, 

High Sierra specification. 

CD-RW n. Acronym for compact disc-rewritable. The 

technology, equipment, software, and media used in the 

production of multiple-write CDs (compact discs). 

CDS n. See Circuit Data Services. 

CDV n. 1. Acronym for compressed digital video. The 

compression of video images for high-speed transmission. 

2. Acronym for compact disc video. A 5-inch videodisc. 

See also videodisc. 

CD Video n. See CDV (definition 2). 

CeBIT n. One of the world’s leading tradeshows for the 

information technology, telecommunications, and office 

automation industries. Held annually in Hannover, Germany, 

CeBIT attracts hundreds of thousands of visitors 

and exhibitors from more than 60 countries. 

CEBus n. Short for Consumer Electronic Bus. CEBus is 

an open architecture set of specification documents that 

define protocols for how to make products communicate 

through power line wires, low voltage twisted pairs, coax, 

infrared, RF, and fiber optics. Anyone, anywhere can get a 

copy of the plans and develop products that work with the 

CEBus standard. 

Celeron n. Intel’s family of budget-priced microprocessors 

introduced in 1998. Celeron chips are based on the 

same P6 microarchitecture as the Pentium II processor. 

They include an integrated 128-KB L2 cache and support 

91 

Intel’s MMX technology. Celeron chips have speeds of up 

to 1.3 GHz in early 2002. See also Pentium. 

cell n. 1. The intersection of a row and a column in a 

spreadsheet. Each row and column in a spreadsheet is 

unique, so each cell can be uniquely identified—for example, 

cell B17, at the intersection of column B and row 17. 

Each cell is displayed as a rectangular space that can hold 

text, a value, or a formula. 2. An addressable (named or 

numbered) storage unit for information. A binary cell, for 

example, is a storage unit that can hold 1 bit of information—that 

is, it can be either on or off. 3. A fixed-length 

packet, the basic transmission unit on high-speed networks, 

such as ATM. See also ATM. 4. Coverage area for 

wireless phones served by a single base station (cell 

tower), usually surrounded by six other cells. As a wireless 

phone moves across the boundary between cells, the 

conversation is handed from one cell to the next. Cells 

may be less than a half mile or more than 15 miles in 

radius, depending on the volume of wireless calls or the 

presence of large buildings or terrain that might interfere 

with signals. 

cell animation or cel animation n. A process performed 

by software that emulates traditional cell animation, which 

uses transparent celluloid sheets (“cells” or “cels” for 

short) to overlay active elements in an animation frame 

onto a static background. Computer cell animation is quite 

efficient because images can be quickly reproduced and 

manipulated. 

cell padding n. The space between the contents and the 

inside edges of a table cell. 

cell reference n. The set of coordinates that a cell occupies 

on a worksheet. For example, the reference of the cell 

that appears at the intersection of column B and row 3 is B3. 

cell relay n. A form of packet switching in which information 

is multiplexed onto a carrier and transferred in 

fixed-length packets (cells). 

cellular automata n. 1. In computer science, theoretical 

models of parallel computers. They enable the investigation 

of parallel computers without the need to actually 

build them. The cellular automaton is composed of a network 

of multiple cells, each representing a processor in 

the parallel computer. The cells must be identical, and 

they must have a finite amount of available memory. Each 

cell outputs a value calculated from the input values it 

C

C 

Cellular Digital Packet Data CERT 

receives from its neighboring cells, and all cells output 

their values simultaneously. 2. Systems in which rules are 

applied to multiple cells and their neighbors in a regular 

spatial lattice or grid that advances through time. Usually, 

each cell in a cellular automaton has any one state out of a 

finite number of states. The state changes discretely in 

time according to rules that depend on the condition of the 

individual cell and its neighbors. Thus, an individual cell 

in a cellular automaton takes a neighbor cell’s state as 

input before outputting its own state. Additionally, all the 

cells in the lattice are updated simultaneously, while the 

state of the entire lattice also advances discretely in time. 

Many computer simulations of cellular automata are demonstrated 

on Web sites; the best known Web example is 

J.H. Conway’s Game of Life. 

Cellular Digital Packet Data n. A wireless standard 

providing two-way, 19.2-Kbps packet data transmission 

over existing cellular telephone channels. Acronym: 

CDPD. See also packet, wireless. 

Cellular Telecommunications and Internet Association 

n. Association based in Washington, D.C. that represents 

the wireless telecommunications industry and its 

equipment manufacturers. Acronym: CTIA. 

censorship n. The action of preventing material that a 

party considers objectionable from circulating within a 

system of communication over which that party has some 

power. The Internet as a whole is not censored, but some 

parts of it come under varying degrees of control. A news 

server, for example, often is set to exclude any or all of the 

alt. newsgroups, such as alt.sex.* or alt.music.whitepower, 

which are unmoderated and tend to be controversial. 

A moderated newsgroup or mailing list might be considered 

to be “censored” because the moderator will 

usually delete highly controversial and obscene content or 

content that is on a different topic from that followed by 

the newsgroup. Online services have identifiable owners, 

who often take some share of responsibility for what 

reaches their users’ computer screens. In some countries, 

censorship of certain political or cultural Web sites is a 

matter of national policy. 

censorware n. Software that imposes restrictions on 

what Internet sites, newsgroups, or files may be accessed 

by the user. 

center vb. To align characters around a point located in 

the middle of a line, page, or other defined area; in effect, 

to place text an equal distance from each margin or border. 

See also align (definition 1). 

92 

centi- prefix 1. One hundred. 2. One hundredth, as in 

centimeter—one hundredth of a meter. 

centralized network n. A network in which nodes connect 

to and use resources on a single central computer, 

typically a mainframe. 

centralized processing n. The location of computer 

processing facilities and operations in a single (centralized) 

place. Compare decentralized processing, distributed 

processing. 

central office n. In communications, the switching center 

where interconnections between customers’ communications 

lines are made. 

central office exchange service n. See Centrex. 

central processing unit n. See CPU. 

Centrex n. An option offered by some phone companies 

in which up-to-date phone facilities are available to business 

customers, giving the customer access to a complete 

range of phone services without having to purchase or 

maintain the necessary equipment. Customers can purchase 

just the lines and services they will use. The name 

central office exchange refers to the fact that the phone 

facilities for Centrex services, particularly switching services, 

are generally maintained at the offices of the local 

or central phone company. Since Centrex offers a wider 

range of services, it is replacing PBX for businesses. See 

also switching. Compare PBX. 

Centronics parallel interface n. A de facto standard for 

parallel data exchange paths between computers and 

peripherals, originally developed by the printer manufacturer 

Centronics, Inc. The Centronics parallel interface 

provides eight parallel data lines plus additional lines for 

control and status information. See also parallel interface. 

CERN n. Acronym for Conseil Européen pour la Recherche 

Nucléaire (the European Laboratory for Particle Physics). 

CERN, a physics research center located in Geneva, Switzerland, 

is where the original development of the World 

Wide Web took place by Tim Berners-Lee in 1989 as a 

method to facilitate communication among members of 

the scientific community. See also NCSA (definition 1). 

CERN server n. One of the first Hypertext Transfer Protocol 

(HTTP) servers, developed at CERN by Tim Berners- 

Lee. The CERN server is still in wide use and is free of 

charge. See also CERN, HTTP server (definition 1). 

CERT n. Acronym for Computer Emergency Response 

Team. An organization that provides a round-the-clock

certificate CGI script 

security consultation service for Internet users and provides 

advisories whenever new virus programs and other 

computer security threats are discovered. 

certificate n. A certificate is sent when a message is digitally 

signed. The certificate proves the sender’s identity 

and supplies the recipient with a public key with which to 

decrypt the sender’s encrypted messages. Also called: 

digital certificate. 

certificate authority n. An issuer of digital certificates, 

the cyberspace equivalent of identity cards. A certificate 

authority may be an external issuing company (such as 

VeriSign) or an internal company authority that has 

installed its own server (such as the Microsoft Certificate 

Server) for issuing and verifying certificates. A certificate 

authority is responsible for providing and assigning the 

unique strings of numbers that make up the “keys” used in 

digital certificates for authentication and to encrypt and 

decrypt sensitive or confidential incoming and outgoing 

online information. Acronym: CA. See also digital certificate, 

encryption. 

Certificate in Computer Programming n. See CCP. 

Certificate in Data Processing n. See CDP. 

certificate revocation list n. A document maintained 

and published by a certification authority that lists certificates 

that have been revoked. Acronym: CRL. See also 

certificate, certification authority. 

certificate trust list n. A signed list of root certification 

authority certificates that an administrator considers reputable 

for designated purposes, such as client authentication 

or secure e-mail. Acronym: CTL. See also certificate, certificate 

authority, root certificate. 

certification n. 1. The act of awarding a document to 

demonstrate a computer professional’s competence in a 

particular field. Some hardware and software suppliers, 

such as Microsoft and Novell, offer certification in the use 

of their products; other organizations, such as the Institute 

for Certification of Computer Professionals (ICCP) and 

the Computing Technology Industry Association (Comp- 

TIA), offer more general certification. 2. The act of awarding 

a document to demonstrate that a hardware or software 

product meets some specification, such as being able to 

work with a certain other hardware or software product. 

3. The issuance of a notice that a user or site is trusted for 

the purpose of security and computer authentication. 

Often certification is used with Web sites. 

93 

certification authority n. An organization that assigns 

encryption keys. See also certificate authority. 

CFML n. Acronym for Cold Fusion Markup Language. A 

programming environment and proprietary, tag-based 

markup language for server-side processing. 

CGA n. Acronym for Color/Graphics Adapter. A video 

adapter board introduced by IBM in 1981. The CGA is 

capable of several character and graphics modes, including 

character modes of 40 or 80 horizontal characters (columns) 

by 25 vertical lines with 16 colors, and graphics 

modes of 640 horizontal pixels by 200 vertical pixels with 

2 colors, or 320 horizontal pixels by 200 vertical pixels 

with 4 colors. See also graphics adapter, video adapter. 

CGI n. 1. Acronym for Common Gateway Interface. The 

specification that defines communications between information 

servers (such as HTTP servers) and resources on 

the server’s host computer, such as databases and other 

programs. For example, when a user submits a form 

through a Web browser, the HTTP server executes a program 

(often called a CGI script) and passes the user’s 

input information to that program via CGI. The program 

then returns information to the server via CGI. Use of CGI 

can make a Web page much more dynamic and add interactivity 

for the user. See also CGI script, HTTP server 

(definition 1). 2. See Computer Graphics Interface. 

cgi-bin n. Short for Common Gateway Interface-binaries. 

A file directory that holds external applications to 

be executed by HTTP servers via CGI. See also CGI 


CGI program n. See CGI script. 

CGI script n. Short for Common Gateway Interface 

script. An external application that is executed by an 

HTTP server machine in response to a request by a client, 

such as a Web browser. Generally, the CGI script is invoked 

when the user clicks on some element in a Web page, such 

as a link or an image. Communication between the CGI 

script and the server is carried out via the CGI specification. 

CGI scripts can be written in many programming languages, 

including C, C++, and Visual Basic. However, the 

most commonly used language for CGI scripts is Perl 

because it is a small but robust language and it is common 

on UNIX, which is the platform on which the majority of 

Web sites run. CGI scripts don’t necessarily need to be 

scripts; they can also be batch programs or compiled programs. 

CGI scripts are used to provide interactivity on a 

C

C 

CGM channel hop 

Web page, including such features as providing a form that 

users can fill out, image maps that contain links to other 

Web pages or resources, and links that users can click on to 

send e-mail to a specified address. ActiveX controls and 

Java applets can provide much the same functionality as 

CGI scripts, through different means. See also CGI (definition 

1), cgi-bin, image map, Perl. Compare ActiveX control, 

Java applet. 

CGM n. See Computer Graphics Metafile. 

chad n. The paper removed when a hole is punched in a 

card, in a tape, or at the perforated edge of continuous-form 

paper—the computer equivalent of a doughnut hole. 

chaining n. 1. In computers, the linking of two or more 

entities so that they are dependent upon one another for 

operation. 2. In programming, the linking of two or more 

programs so that the first program causes the second program 

to begin executing. 3. In programming, linking program 

statements so that each statement, except for the 

first, relies on the previous statement for input. 4. With 

batch files, linking two or more batch files so that the 

completion of the first batch file causes the second batch 

file to begin executing. 5. With data storage, linking two 

or more individual units of storage. For example, a single 

file on a disk may actually be stored on several different 

sectors of the disk, each of which points to the next sector 

containing a piece of that file. These sectors are said to be 

chained together, or, more literally, to be a chain of clusters. 

6. See daisy chaining. 

chain printer n. See line printer. 

chalkware n. See vaporware. 

Challenge Handshake Authentication Protocol n. An 

authentication scheme used by PPP servers to validate the 

identity of the originator of a connection, upon connection 

or any time later. Acronym: CHAP. See also authentication, 

PPP. 

change directory n. See cd. 

change file n. A file that records transactional changes 

occurring in a database, providing a basis for updating a 

master file and establishing an audit trail. Also called: 

transaction log. See also addition record. 

change management n. 1. The process of tracking and 

controlling updates, revisions, and other changes to a 

hardware or software product or project. 2. The process of 

managing change during a company’s restructuring or 

reengineering. 

94 

channel n. 1. A path or link through which information 

passes between two devices. A channel can be either internal 

or external to a microcomputer. 2. In communications, 

a medium for transferring information. Depending on its 

type, a communications channel can carry information 

(data, sound, and/or video) in either analog or digital form. 

A communications channel can be a physical link, such as 

the cable connecting two stations in a network, or it can 

consist of some electromagnetic transmission on one or 

more frequencies within a bandwidth in the electromagnetic 

spectrum, as in radio and television, or in optical, 

microwave, or voice-grade communication. Also called: 

circuit, line. See also analog, band, bandwidth, digital, 

electromagnetic spectrum, frequency. 3. A single color 

within a digital color space. For example, the RGB color 

space contains three channels—red, green, and blue—and 

all colors within the RGB color space are created with a 

combination of one or more of those three color channels. 

In CMYK there are four channels—cyan, magenta, yellow, 

and black. Color management and graphics applications 

rely on control and manipulation of individual color 

channels. See also color space. 

channel access n. 1. A method used in networked systems 

to gain access to the data communication channel 

that links two or more computers. Common methods of 

channel access are contention, polling, and the token ring 

network. See also channel, contention, polling, token ring 

network. 2. In wireless technology, an access method such 

as CDMA (Code Division Multiple Access). See also 

Code Division Multiple Access. 

channel adapter n. A device that enables hardware 

using two different types of communications channels to 

communicate. 

channel aggregator n. See content aggregator. 

channel capacity n. The speed at which a communications 

channel can transfer information, measured in bits 

per second (bps) or in baud. 

Channel Definition Format n. A file format based on 

XML that describes a channel—a collection of Web 

pages—on a server. The Channel Definition Format is 

used with the Active Channel feature in Microsoft Internet 

Explorer to deliver selected, often personalized, information 

to individuals on a subscription basis. See also Active 

Channel, webcasting. 

channel hop vb. To switch repeatedly from one IRC 

channel to another. See also IRC.

channel op character-oriented protocol 

channel op n. Short for channel operator. A user on an 

IRC channel who has the privilege of expelling undesirable 

participants. See also IRC. 

channel operator n. See channel op. 

Channel Service Unit n. See DDS. 

CHAP n. See Challenge Handshake Authentication 

Protocol. 

character n. A letter, number, punctuation mark, or other 

symbol or control code that is represented to a computer 

by one unit—1 byte—of information. A character is not 

necessarily visible, either on the screen or on paper; a 

space, for example, is as much a character as is the letter a 

or any of the digits 0 through 9. Because computers must 

manage not only so-called printable characters but also the 

look (formatting) and transfer of electronically stored 

information, a character can additionally indicate a carriage 

return or a paragraph mark in a word-processed document. 

It can be a signal to sound a beep, begin a new 

page, or mark the end of a file. See also ASCII, control 

character, EBCDIC. 

character cell n. A rectangular block of pixels that represents 

the space in which a given character is drawn on 

the screen. Computer displays use different numbers of 

pixels as character cells. Character cells are not always the 

same size for a given font, however; for proportionally 

spaced fonts, such as those commonly displayed on the 

Apple Macintosh, the height within a given font remains 

the same, but the width varies with each character. 

character code n. A specific code that represents a particular 

character in a set, such as the ASCII character set. 

The character code for a given key depends on whether 

another key, such as Shift, is pressed at the same time. For 

example, pressing the A key alone normally generates the 

character code for a lowercase a. Pressing Shift plus the A 

key normally generates the character code for an uppercase 

A. Compare key code. 

character definition table n. A table of patterns that a 

computer can hold in memory and use as a reference for 

determining the arrangement of dots used to create and 

display bitmapped characters on the screen. See also bitmapped 

font. 

95 

character density n. In printing or screen display, a 

measure of the number of characters per unit of area or of 

linear distance. See also pitch (definition 1). 

character device n. 1. A computer device, such as a keyboard 

or printer, that receives or transmits information as a 

stream of characters, one character at a time. The characters 

can be transferred either bit by bit (serial transmission) 

or byte by byte (parallel transmission) but are not moved 

from place to place in blocks (groups of bytes). Compare 

block device. 2. In reference to video displays, a device 

that handles text but not graphics. See also text mode. 

character entity n. In HTML and SGML, the notation 

for a special character. A character entity begins with an & 

(ampersand), followed by either a string of letters or of 

numbers, and ends with a semicolon. The special characters 

represented by character entities include acute and 

grave accents, the tilde, and Greek letters, among others. 

Also called: named entity. 

character generator n. A program or a hardware device 

that translates a given character code, such as an ASCII 

code, into a matching pixel pattern for display on the 

screen. Such devices are typically limited in the number 

and range of styles of fonts they support, as compared to 

machines that support bitmapped characters. Compare bitmapped 

font. 

character image n. A set of bits arranged in the shape of 

a character. Each character image exists within a rectangular 

grid, or character rectangle, that defines its height and 

width. See also bitmapped font. 

characteristic n. In mathematics, the exponent of a 

floating-point number (the portion following the E that 

indicates the position of the decimal point) or the integer 

portion of a logarithm. See also floating-point notation, 

logarithm. 

character map n. In text-based computer graphics, a 

block of memory addresses that correspond to character 

spaces on a display screen. The memory allocated to each 

character space is used to hold the description of the character 

to be displayed in that space. See also alphageometric. 

character mode n. See text mode. 

character-oriented protocol n. See byte-oriented 

protocol. 

C

C 

character printer charge-coupled device 

character printer n. 1. A printer that operates by printing 

one character at a time, such as a standard dot-matrix 

printer or a daisy-wheel printer. Compare line printer, 

page printer. 2. A printer that cannot print graphics, such 

as a daisy-wheel printer or even a dot-matrix or laser 

printer that lacks a graphics mode. Such a printer simply 

receives character codes from the controlling system and 

prints the appropriate characters. Compare graphics 

printer. 

character recognition n. The process of applying pattern-matching 

methods to character shapes that have been 

read into a computer to determine which alphanumeric 

characters or punctuation marks the shapes represent. 

Because different typefaces and text treatments, such as 

bold and italic, can make big differences in the way characters 

are shaped, character recognition can be prone to 

error. Some systems work only with known typefaces and 

sizes, with no text treatments. These systems achieve very 

high accuracy levels, but they can work only with text specifically 

printed for them. Other systems use extremely 

sophisticated pattern-matching techniques to learn new 

typefaces and sizes, achieving fairly good accuracy. See 

also magnetic-ink character recognition, optical character 

recognition, pattern recognition (definition 1). 

character rectangle n. The space taken up by the graphical 

representation (bit map) of a character. See the illustration. 

See also bit map. 

f0cgn07.eps 

Character rectangle. 

character set n. A grouping of alphabetic, numeric, and 

other characters that have some relationship in common. 

For example, the standard ASCII character set includes 

letters, numbers, symbols, and control codes that make up 

the ASCII coding scheme. 

96 

characters per inch n. A measurement for the number 

of characters of a particular size and font that can fit into a 

line one inch long. This number is affected by two 

attributes of the type: its point size and the width of the 

letters in the particular font being measured. In monospace 

fonts, characters have a constant width; in proportional 

fonts, characters have varying widths. Thus, measurements 

of the number of characters per inch must be averaged. 

Acronym: cpi. See also monospace font, pitch 

(definition 1), proportional font. 

characters per second n. 1. A measure of the speed of a 

nonlaser printer, such as a dot-matrix or an ink-jet printer. 

2. A measure of the rate at which a device, such as a disk 

drive, can transfer data. In serial communications, the 

speed of a modem in bits per second can generally be 

divided by 10 for a rough determination of the number of 

characters per second transmitted. Acronym: CPS. 

character string n. A set of characters treated as a unit 

and interpreted by a computer as text rather than numbers. 

A character string can contain any sequence of elements 

from a given character set, such as letters, numbers, control 

characters, and extended ASCII characters. Also 

called: string. See also ASCII, control character, extended 

ASCII. 

character style n. Any attribute, such as boldface, italic, 

underline, or small caps, applied to a character. Depending 

on the operating system or program considered, the range 

of character styles of text might or might not include the 

font, which refers to the design of a group of characters in 

a given size. See also font family. 

character user interface n. A user interface that displays 

only text characters. Acronym: CUI. See also user 

interface. Compare graphical user interface. 

charge n. A property of subatomic particles, which can 

have either a negative charge or a positive charge. In electronics, 

a charge consists of either an excess of electrons 

(a negative charge) or a deficiency of electrons (a positive 

charge). The unit of charge is the coulomb, which corresponds 

to 6.26 x 1018 electrons. 

charge-coupled device n. A device in which individual 

semiconductor components are connected so that the electrical 

charge at the output of one device provides the input 

to the next. The light-detecting component of digital cameras 

and many video cameras is a charge-coupled device. 

Acronym: CCD.

chart chiclet keyboard 

chart n. A graphic or diagram that displays data or the 

relationships between sets of data in pictorial rather than 

numeric form. 

chassis n. A metal frame on which electronic components, 

such as printed circuit boards, fans, and power supplies, 

are mounted. See the illustration. 

f0cgn08.eps 

Chassis. 

chat1 n. 1. Real-time conversation via computer. When a 

participant types a line of text and then presses the Enter 

key, that participant’s words appear on the screens of the 

other participants, who can then respond in kind. Most 

online services support chat; on the Internet, IRC is the 

usual system. See also IRC. 2. An Internet utility program 

that supports chat. IRC has largely superseded it. 

chat2 vb. To carry on a real-time conversation with other 

users by computer. See also IRC. 

chat room n. The informal term for a data communication 

channel that links computers and permits users to 

“converse” by sending text messages to one another in real 

time. Similar to the channels provided by IRC (Internet 

Relay Chat), chat rooms are available through online services 

and some electronic bulletin board systems (BBSs). 

Chat rooms are often devoted to a particular subject or are 

conducted on a certain schedule. See also BBS, chat, IRC, 

room. 

Cheapernet n. See 10Base2. 

cheat code n. In computer games, a secret keyboard 

sequence or code that gives a player an advantage in the 

game. For example, cheat codes often confer more ammunition, 

lives, or the ability to fly or walk through obstacles. 

See also adventure games, computer games. 

check bit n. One of a set of bits that are added to a data 

message at its origin and scrutinized by the receiving process 

to determine whether an error has occurred during 

97 

transmission. The simplest example is a parity bit. See 

also data integrity, parity bit. 

check box n. An interactive control often found in graphical 

user interfaces. Check boxes are used to enable or disable 

one or more features or options from a set. When an 

option is selected, an x or a check mark appears in the box. 

See also control (definition 2). Compare radio button. 

check digit n. A digit added to an account number or 

other identifying key value and then recomputed when the 

number is used. This process determines whether an error 

occurred when the number was entered. See also checksum. 

checkpoint n. 1. A processing juncture at which the normal 

operation of a program or system is momentarily suspended 

in order to determine its environmental status. 2. A 

file containing information that describes the state of the 

system (the environment) at a particular time. 

checksum n. A calculated value that is used to test data 

for the presence of errors that can occur when data is 

transmitted or when it is written to disk. The checksum is 

calculated for a given chunk of data by sequentially combining 

all the bytes of data with a series of arithmetic or 

logical operations. After the data is transmitted or stored, a 

new checksum is calculated in the same way using the 

(possibly faulty) transmitted or stored data. If the two 

checksums do not match, an error has occurred and the 

data should be transmitted or stored again. Checksums 

cannot detect all errors, and they cannot be used to correct 

erroneous data. See also error-correction coding. 

Cheese worm n. An Internet worm that patches security 

holes created by the Lion worm. The Cheese worm 

searches out and infects Linux-based systems that were 

previously compromised by the Lion worm, repairing vulnerabilities 

and closing a back door left by the earlier 

infection. It then uses the healed computer to scan for 

other vulnerable computers connected to the Internet and 

sends itself to them. 

Chernobyl packet n. A form of network attack in which 

a data packet sent by a hacker activates every available 

option for the protocol in use on the receiving system. The 

Chernobyl packet will cause a packet storm that will 

eventually overload and crash the network. Also called: 

kamikaze packet. 

Chernobyl virus n. See CIH virus. 

chiclet keyboard n. A microcomputer keyboard used on 

the first version of the IBM PCjr home computer. Chiclet 

keys are small and square, resembling the chewing gum 

C

C 

child CIM 

pieces, and they act like pushbuttons, without the resistance 

and clear feedback of traditional keys. They are also 

much smaller and typically are spread out, so touch typing 

is more difficult than on a conventional keyboard. 

child n. 1. A process initiated by another process (the parent). 

This initiating action is frequently called a fork. The 

parent process often sleeps (is suspended) until the child 

process stops executing. 2. In a tree structure, the relationship 

of a node to its immediate predecessor. See also generation 

(definition 2), tree structure. 

child directory n. See subdirectory. 

child menu n. See submenu. 

child process n. See child (definition 1). 

Children’s Online Privacy Protection Act n. See 

COPPA. 

chimes of doom n. In Macintosh computers, a series of 

chimes that sound as a result of serious system failure. 

chip n. See integrated circuit. 

chip card n. See smart card. 

chip set or chipset n. A collection of chips designed to 

function as a unit in the performance of some common 

task. The term is most commonly used to refer to the set of 

integrated circuits, such as the programmable interrupt 

controller, that support a CPU together with the CPU 

itself. Often a chip set will fit on one chip. See also CPU, 

integrated circuit, programmable interrupt controller. 

choke n. See inductor. 

choose vb. To pick a command or an option from within 

a graphical user interface, as by clicking a button in a dialog 

box or pulling down a menu and then releasing the 

mouse button on one of its options. Although select is 

often used instead of choose to describe the same action, 

choose is the preferred term because select has specific 

connotations within computing. See also select. 

Chooser n. On the Apple Macintosh, a desk accessory 

that allows the user to select a printer or a device on a network, 

such as a file server or a printer. 

Chooser extension n. A program that adds items to the 

Macintosh Chooser desk accessory. At system startup, 

Chooser adds to its menu of options from the extensions 

available in the system extensions folder. For example, if 

you want to use a particular printer with your Mac OS, 

you must have the right Chooser extension for that printer 

98 

in the extensions folder when the computer is turned on. 

See also Chooser, extension (definition 4). 

chroma n. The quality of a color that combines hue and 

saturation. See also hue, saturation. 

CHRP n. See Common Hardware Reference Platform. 

churn rate n. The rate of customer subscription turnover. 

In beeper, cell phone, and online businesses, it is common 

for customers to drop their monthly subscriptions, creating 

a churn rate as high as 2 or 3 percent per month. High churn 

rates are costly to companies because attracting new subscribers 

through advertising and promotion is expensive. 

CIDR n. See classless interdomain routing. 

CIFS n. See Common Internet File System. 

CIH virus n. A highly destructive virus that first appeared 

in early 1998. When activated, the CIH virus code will 

attempt to overwrite the flash BIOS of infected machines, 

rendering the computer unbootable. The CIH virus is also 

known as the Chernobyl virus because in its original form 

it was set to activate on the anniversary of the Chernobyl 

nuclear accident. Although the CIH virus lacks stealth or 

sophisticated replication capabilities and is easily detected 

by current virus security programs, it continues to appear 

regularly. Also called: Chernobyl virus. See also virus. 

CIM n. 1. Acronym for Common Information Model. A 

conceptual specification supported by the Desktop Management 

Task Force (DMTF) for applying an object-oriented, 

Web-based model to describing management data in an 

enterprise network. Part of the DMTF’s Web-Based Enterprise 

Management initiative, CIM is a system-independent 

and application-independent common framework for 

describing and sharing management information. It is based 

on a three-tiered model based on schemas—sets of classes: 

the Core Schema covers all areas of management; Common 

Schemas cover specific management areas, such as networks, 

applications, and devices; and Extension Schemas 

cover specific technologies, such as operating systems and 

applications. CIM is supported by a number of industry 

vendors, including Sun, IBM, Microsoft, and Cisco. See 

also DMTF, WBEM. 2. Acronym for computer-integrated 

manufacturing. The use of computers, communication 

lines, and specialized software to automate both the managerial 

functions and the operational activities involved in 

the manufacturing process. A common database is used in 

all aspects of the process, from design through assembly, 

accounting, and resource management. Advanced CIM

CIP circuit-switched voice 

systems integrate computer-aided design and engineering 

(CAD/CAE), material requirements planning (MRP), and 

robotic assembly control to provide “paperless” management 

of the entire manufacturing process. 3. Acronym for 

computer-input microfilm. A process in which information 

stored on microfilm is scanned and the data (both text 

and graphics) converted into codes that can be used and 

manipulated by a computer. Computer-input microfilm is 

similar to processes such as optical character recognition, 

in which images on paper are scanned and converted to 

text or graphics. Compare COM (definition 4). 

CIP n. 1. Short for Commerce Interchange Pipeline. A 

Microsoft technology that provides for secure routing of 

business data between applications over a public network 

such as the Internet. CIP is independent of data format and 

supports encryption and digital signatures, as well as various 

transport protocols including SMTP, HTTP, DCOM, 

and EDI value-added networks. Typically, data such as 

invoices and purchase orders travel over a network 

through a transmit pipeline and are read from the network 

by a receive pipeline that decodes and prepares the data 

for the receiving application. 2. Short for Common Indexing 

Protocol. A protocol defined by the Internet Engineering 

Task Force (IETF) for enabling servers to share 

indexing information. CIP was developed to provide servers 

with a standard means of sharing information about the 

contents of their databases. With such sharing, a server 

unable to resolve a particular query would be able to route 

the query to other servers that might contain the desired 

information—for example, to find the e-mail address of a 

particular user on the Web. 

cipher n. 1. A code. 2. An encoded character. 3. A zero. 

ciphertext n. The scrambled or otherwise encoded text 

of an encrypted message. See also encryption. 

circuit n. 1. Any path that can carry electrical current. 

2. A combination of electrical components interconnected 

to perform a particular task. At one level, a computer consists 

of a single circuit; at another, it consists of hundreds 

of interconnected circuits. 

circuit analyzer n. Any device for measuring one or 

more characteristics of an electrical circuit. Voltage, current, 

and resistance are the characteristics most commonly 

measured. Oscilloscopes are circuit analyzers. 

circuit board n. A flat piece of insulating material, such 

as epoxy or phenolic resin, on which electrical components 

are mounted and interconnected to form a circuit. 

99 

Most modern circuit boards use patterns of copper foil to 

interconnect the components. The foil layers may be on 

one or both sides of the board and, in more advanced 

designs, in several layers within the board. A printed circuit 

board is one in which the pattern of copper foil is laid 

down by a printing process such as photolithography. See 

the illustration. See also board, printed circuit board. 

f0cgn09.eps 

Circuit board. 

circuit breaker n. A switch that opens and cuts off the 

flow of current when the current exceeds a certain level. 

Circuit breakers are placed at critical points in circuits to 

protect against damage that could result from excessive 

current flow, which is typically caused by component failure. 

Circuit breakers are often used in place of fuses 

because they need only to be reset rather than replaced. 

Compare surge protector. 

circuit card n. See circuit board. 

Circuit Data Services n. A GTE service that uses circuit 

switching technology to provide fast data transfer using a 

laptop computer and cellular telephone. Acronym: CDS. 

See also circuit switching. 

circuit-switched data n. An ISDN option that can be 

specified for B (bearer) channels that enables an ISDN 

user to transmit digital data over the channel at 64 Kbps 

along a point-to-point, dedicated connection for the duration 

of a call. Acronym: CSD. See also alternate circuitswitched 

voice/circuit-switched data, B channel, ISDN. 

Compare circuit-switched voice. 

circuit-switched voice n. An ISDN option that can be 

specified for B (bearer) channels that uses the channel to 

set up a point-to-point, dedicated connection for the digital 

transmission of voice communications for the duration of 

a call. Acronym: CSV. See also alternate circuit-switched 

C

C 

circuit switching Class A network 

voice/circuit-switched data, B channel, ISDN. Compare 

circuit-switched data. 

circuit switching n. A method of opening communications 

lines, as through the telephone system, by creating a 

physical link between the initiating and receiving parties. 

In circuit switching, the connection is made at a switching 

center, which physically connects the two parties and 

maintains an open line between them for as long as 

needed. Circuit switching is typically used on the dial-up 

telephone network, and it is also used on a smaller scale in 

privately maintained communications networks. Unlike 

other methods of transmission, such as packet switching, 

it requires the link to be established before any communication 

can take place. Compare message switching, packet 

switching. 

circular list n. A linked or chained list in which processing 

continues through all items, as in a ring, and returns to 

the starting point, no matter where that point is located in 

the list. See also linked list. 

CIS n. 1. Acronym for CompuServe Information Service 

See CompuServe. 2. Short for contact image sensor. A 

light-sensitive mechanism used in scanners and fax 

machines. A CIS scanner reflects light from a row of lightemitting 

diodes (LEDs) onto a document or other object 

and converts the reflected light to digital images. CIS sensors 

are smaller and lighter than the charge-coupled 

devices (CCDs) traditionally used in scanners, but the 

image quality they produce is not as good as the image 

quality produced by CCDs. See also light-emitting diode, 

scanner. Compare charge-coupled device. 

CISC n. Acronym for complex instruction set computing. 

The implementation of complex instructions in a microprocessor 

design so that they can be invoked at the assembly 

language level. The instructions can be very powerful, 

allowing for complicated and flexible ways of calculating 

such elements as memory addresses. All this complexity, 

however, usually requires many clock cycles to execute 

each instruction. Compare RISC. 

CIX n. See Commercial Internet Exchange. 

CKO n. Acronym for Chief Knowledge Officer. A corporate 

executive in charge of management and distribution of 

all the business and technical knowledge of a company. 

The CKO maximizes the value of stored knowledge by 

ensuring that employees have access, and by avoiding 

knowledge loss caused by technology-based changes and 

upgrades in databases and other storage. 

100 

ClariNet n. A commercial service that distributes news 

articles from United Press International (UPI) and other 

news agencies in newsgroups that are part of the clari. 

hierarchy. Unlike most other newsgroups, access to the 

clari. newsgroups is restricted to Internet service providers 

who pay a subscription fee to ClariNet. 

clari. newsgroups n. Internet newsgroups maintained by 

ClariNet Communications, Inc. ClariNet newsgroups contain 

news articles obtained from the Reuters and United 

Press International wire services, SportsTicker, Commerce 

Business Daily, and other sources. Unlike most other 

newsgroups, ClariNet groups are only accessible through 

Internet service providers who purchase the service. See 

also ClariNet, ISP, newsgroup. 

ClarisWorks n. See AppleWorks. 

class n. 1. In object-oriented programming, a generalized 

category that describes a group of more specific items, 

called objects, that can exist within it. A class is a descriptive 

tool used in a program to define a set of attributes or a 

set of services (actions available to other parts of the program) 

that characterize any member (object) of the class. 

Program classes are comparable in concept to the categories 

that people use to organize information about their 

world, such as animal, vegetable, and mineral, that define 

the types of entities they include and the ways those entities 

behave. The definition of classes in object-oriented 

programming is comparable to the definition of types in 

languages such as C and Pascal. See also object-oriented 

programming. 2. For hardware, the method for grouping 

particular types of devices and buses according to the 

basic ways that they can be installed and managed by the 

operating system. The hardware tree is organized by 

device class, and Windows uses class installers to install 

drivers for all hardware classes. 

Class A IP address n. A unicast IP address that ranges 

from 1.0.0.1 through 126.255.255.254. The first octet 

indicates the network, and the last three octets indicate the 

host on the network. See also Class B IP address, Class C 

IP address, IP address classes. 

Class A network n. An Internet network that can define 

a maximum of 16,777,215 hosts. Class A networks use the 

first byte of an IP address to designate the network, with 

the first (high-order) bit set to 0. The host is designated by 

the last 3 bytes. Class A addressing currently allows for a 

maximum of 128 networks. Class A networks are best 

suited for sites with few networks but numerous hosts and

Class B IP address CLEC 

are usually designated for use by large government or educational 

institutions. See also host, IP address. 

Class B IP address n. A unicast IP address that ranges 

from 128.0.0.1 through 191.255.255.254. The first two 

octets indicate the network, and the last two octets indicate 

the host on the network. See also Class A IP address, 

Class C IP address, IP address classes. 

Class C IP address n. A unicast IP address that ranges 

from 192.0.0.1 to 223.255.255.254. The first three octets 

indicate the network, and the last octet indicates the host 

on the network. See also Class A IP address, Class B IP 

address, IP address classes. 

classful IP addressing n. An IP addressing scheme 

where IP addresses are organized into classes: Class A, 

Class B, and Class C. See also IP address classes. 

Classic n. An environment within Mac OS X that allows a 

user to run legacy software. Classic emulates the earlier 

Macintosh operating system chosen by the user and provides 

support for programs that aren’t compatible with Mac 

OS X architecture. See also Carbon, Cocoa, Mac OS X. 

classless interdomain routing n. An address scheme 

that uses aggregation strategies to minimize the size of 

top-level Internet routing tables. Routes are grouped with 

the objective of minimizing the quantity of information 

carried by core routers. The main requirement for this 

scheme is the use of routing protocols that support it, such 

as Border Gateway Protocol (BGP) version 4 and RIP 

version 2. Acronym: CIDR. See also Border Gateway Protocol, 

communications protocol, RIP, router, supernetting. 

class library n. A collection of standard routines and 

sub-programs that a programmer can use in object-oriented 

programs. A typical class library for a graphical user interface 

might include routines for buttons and scroll bars; or a 

class library for a communications program might include 

a routine for dialing a telephone line through a modem. See 

also class, object-oriented programming. 

classpath n. In Java programming, a classpath is an environmental 

variable that tells the Java Virtual Machine 

(JVM) and Java programs where to find class libraries, 

including user-defined class libraries. See also class, class 

library, Java Virtual Machine. 

clean boot n. Booting or starting a computer using the 

minimum system files in the operating system. The clean 

boot is used as a troubleshooting method for isolating 

101 

problems associated with software that may be calling on 

the same system resources at the same time, causing conflicts 

that lower the performance of the system, make 

some programs inoperable, or crash the computer. See 

also boot1 , crash1 (definition 1), operating system. 

clean install n. Reinstallation of software in a manner 

that ensures that no application or system files from a previous 

installation will remain. The procedure prevents 

smart installer programs from skipping file installations 

where a file already exists, which could potentially keep a 

problem from being removed. 

clean interface n. A user interface with simple features 

and intuitive commands. See also user interface. 

clean room n. A room in which dust and other small particles 

are filtered from the air and in which protective 

clothing is worn to avoid contaminating electronic components 

and other delicate, sensitive equipment. 

Clear key n. A key in the upper left corner of the numeric 

keypad on some keyboards. In many applications, it clears 

the currently selected menu choice or deletes the current 

selection. See the illustration. 

Num 

Lock 

Clear 

/ 

7 8 

Clear key 

f0cgn10.eps 

Clear key. 

clear memory vb. A process that erases all data stored in 

RAM. 

Clear To Send n. See CTS. 

ClearType n. A Microsoft font technology that improves 

the resolution of text on LCD displays, such as those used 

on laptop computers. ClearType technology uses proprietary 

signal processing and the properties of LCD displays 

to produce clearer, more detailed characters and spacing, 

and thus significantly increase readability. 

CLEC n. Acronym for Competitive Local Exchange Carrier. 

A company that sells access to the public switched 

telephone network, or other last mile network connections, 

in competition with a traditional telephone company. See 

also ILEC, last mile. 

C

C 

click client-side image maps 

click vb. To press and release a mouse button once without 

moving the mouse. Clicking is usually performed to select 

or deselect an item or to activate a program or program feature. 

See also right click. Compare double-click, drag. 

clickable maps n. See image map. 

click rate n. See clickthrough rate. 

clicks and mortar n. A business that combines an online 

presence with traditional “bricks and mortar” outlets. 

click speed n. The maximum interval between the first 

and second time a user presses a button on a mouse or 

other pointing device that will still identify these actions 

as a double-click to the computer as opposed to two 

single-clicks. See also double-click, mouse, pointing 

device. 

clickstream n. The path a user takes while browsing a 

Web site. Each distinct selection made on a Web page 

adds one click to the stream. The further down the clickstream 

the user goes without finding the sought item, the 

more likely he or she is to depart to another Web site. 

Analysis of usage patterns helps Web site designers create 

user-friendly site structures, links, and search facilities. 

See also Web site. 

clickthrough n. The number of times that visitors to a 

Web site click on an advertising banner within a specified 

period of time. Clickthrough is one of the elements that 

Web site producers use to decide how much to charge 

advertisers. See also clickthrough rate. 

clickthrough rate n. The proportion of visitors to a Web 

site who click on a banner advertisement there, expressed 

as a percentage of total visitors to the Web site. Also 

called: click rate. See also clickthrough. 

clickwrap agreement n. A contract or license in software 

or on a Web site that sets forth conditions for use of 

the software or for goods and services distributed through 

the Web site. Users must agree to the terms in a clickwrap 

agreement—typically by clicking on a button that states “I 

Agree” or “Agree”—before they can install the software 

or utilize goods or services. A clickwrap agreement is an 

electronic version of an End-User License Agreement. 

Also called: clickwrap license. See also End-User License 

Agreement. Compare shrinkwrap agreement. 

clickwrap license n. See clickwrap agreement. 

client n. 1. In object-oriented programming, a member of 

a class (group) that uses the services of another class to 

which it is not related. See also inheritance (definition 1). 

2. A process, such as a program or task, that requests a 

102 

service provided by another program—for example, a 

word processor that calls on a sort routine built into 

another program. The client process uses the requested 

service without having to “know” any working details 

about the other program or the service itself. Compare 

child (definition 1), descendant (definition 2). 3. On a 

local area network or the Internet, a computer that 

accesses shared network resources provided by another 

computer (called a server). See also client/server architecture, 

server. 

client error n. A problem reported by the Hypertext 

Transfer Protocol (HTTP) client module as the result of 

difficulty in interpreting a command or the inability to 

connect properly to a remote host. 

client/server architecture n. An arrangement used on 

LANs (local area networks) that makes use of distributed 

intelligence to treat both the server and the individual 

workstations as intelligent, programmable devices, thus 

exploiting the full computing power of each. This is done 

by splitting the processing of an application between two 

distinct components: a “front-end” client and a “backend” 

server. The client component is a complete, standalone 

personal computer (not a “dumb” terminal), and it 

offers the user its full range of power and features for running 

applications. The server component can be a personal 

computer, a minicomputer, or a mainframe that provides 

the traditional strengths offered by minicomputers and 

mainframes in a time-sharing environment: data management, 

information sharing between clients, and sophisticated 

network administration and security features. The 

client and server machines work together to accomplish 

the processing of the application being used. Not only 

does this increase the processing power available over 

older architectures but it also uses that power more efficiently. 

The client portion of the application is typically 

optimized for user interaction, whereas the server portion 

provides the centralized, multiuser functionality. See also 

distributed intelligence. Compare peer-to-peer network. 

client/server network n. See client/server architecture. 

client-side image maps n. An image map that performs 

the processing completely within the client program (i.e., 

Web browser) itself. Early Web implementations of image 

maps (circa 1993) transmitted user mouse click coordinates 

to the Web server for processing. Generally clientside 

image maps improve the speed of response to the 

user. See also image map.

client-side program clock rate 

client-side program n. On the Internet, a program that is 

run on a client computer rather than on a server computer. 

clip vb. 1. To cut off the portion of a displayed image that 

lies beyond a certain boundary, such as the edge of a window. 

Certain graphics programs also support clipping as a 

means of masking everything but a certain object so that 

painting tools, for example, can be applied to the object 

alone. 2. To cut a photograph, drawing, or other illustration 

from a clip art collection—either in a book or on a 

disk. See also clip art. 3. To cut off the peaks of a signal in 

an electronic circuit. 

clip art n. A collection—either in a book or on a disk—of 

proprietary or public-domain photographs, diagrams, 

maps, drawings, and other such graphics that can be 

“clipped” from the collection and incorporated into other 

documents. 

clipboard n. 1. A special memory resource maintained by 

windowing operating systems. The clipboard stores a copy 

of the last information that was copied or cut. A paste 

operation passes data from the clipboard to the current 

program. A clipboard allows information to be transferred 

from one program to another, provided the second program 

can read data generated by the first. Data copied 

using the clipboard is static and will not reflect later 

changes. See also cut and paste, DDE. Compare scrap. 

2. A computer that uses a pen as the primary input device. 

See also clipboard computer, pen computer. 

clipboard computer n. A portable computer whose overall 

appearance and operation resembles that of a traditional 

clipboard. A clipboard computer has an LCD or 

similar flat display and has a pen for user input instead of 

a keyboard, mouse, or other input device; the user operates 

the computer by touching the pen to the display. Data 

entered in a clipboard computer is generally transferred to 

another computer via a cable or a modem. A clipboard 

computer is used as a traditional clipboard is used, as in 

field work, data collection, or meetings. See also pen computer, 

portable computer. 

Clipper Chip n. An integrated circuit that implements the 

SkipJack algorithm, an encryption algorithm created by 

the National Security Agency that encrypts 64-bit blocks 

of data with an 80-bit key. The Clipper Chip is manufactured 

by the U.S. government to encrypt telephone data. It 

has the added feature that it can be decrypted by the U.S. 

government, which has tried unsuccessfully to make the 

chip compulsory in the United States. See also encryption. 

103 

clipping path n. A polygon or curve that is used to mask 

an area in a document. Only what is inside the clipping 

path appears when the document is printed. See also 

PostScript. 

clip source tag n. Computer coding tag that locates a 

streaming digital media image for use on a Web page. The 

clip source tag includes the pathway to the image, which 

may be stored on a Web server, a Web site, or on the computer 

where the Web page is displayed. 

clobber vb. To destroy data, generally by inadvertently 

writing other data over it. 

clock n. 1. The electronic circuit in a computer that generates 

a steady stream of timing pulses—the digital signals 

that synchronize every operation. The system clock signal 

is precisely set by a quartz crystal, typically at a specific 

frequency between 1 and 50 megahertz. The clock rate of 

a computer is one of the prime determinants of its overall 

processing speed, and it can go as high as the other components 

of the computer allow. Also called: system clock. 

2. The battery-backed circuit that keeps track of the time 

and date in a computer—not the same as the system clock. 

Also called: clock/calendar. 

clock/calendar n. An independent timekeeping circuit 

used within a microcomputer to maintain the correct time 

and calendar date. A clock/calendar circuit is battery powered, 

so it continues running even when the computer is 

turned off. The time and date kept by the clock/calendar 

can be used by the operating system (for example, to 

“stamp” files with the date and time of creation or revision) 

and by application programs (for example, to insert 

the date or time in a document). Also called: clock, internal 

clock. 

clock doubling n. A technology employed by some Intel 

microprocessors that enables the chip to process data and 

instructions at twice the speed of the rest of the system. 

See also i486DX2. 

clocking n. See synchronization (definition 3). 

clockless chip n. See asynchronous chip. 

clock pulse n. An electronic pulse generated periodically 

by a crystal oscillator to synchronize the actions of a digital 

device. 

clock rate n. The speed at which the internal clock in an 

electronic device oscillates. In computers, each tick (oscillation) 

of the clock is called a cycle, and the clock rate is 

measured in megahertz, or millions of cycles per second. 

Also called clock speed, the clock rate determines how 

C

C 

clock speed cluster analysis 

quickly the CPU can execute basic instructions, such as 

adding two numbers, and it is used to synchronize the activities 

of various components in the system. Between 1981, 

when the IBM PC was released, and early 2002, typical 

clock rates for personal computers increased about 1000fold, 

from 4.77 MHz to 2 GHz and faster. Also called: clock 

speed, hertz time. See also clock (definition 1). 

clock speed n. See clock rate. 

clock tick n. See CPU cycle (definition 2). 

clone1 n. A copy; in microcomputer terminology, a lookalike, 

act-alike computer that contains the same microprocessor 

and runs the same programs as a better-known, 

more prestigious, and often more expensive machine. 

clone2 vb. To copy or replicate the entire contents of a 

hard disk drive, including the operating system, configuration 

settings, and programs, by creating an image of the 

hard disk drive. Hard disk drives are often cloned for batch 

installation on other computers, particularly those on a 

network, or for use as backups. 

close1 n. An FTP command that instructs the client to 

close the current connection with a server. See also FTP1 (definition 1), Web site. 

close2 vb. 1. To end an application’s relationship with an 

open file so that the application will no longer be able to 

access the file without opening it again. 2. To end a computer’s 

connection with another computer on a network. 

close box n. In the Macintosh graphical user interface, a 

small box in the left corner of a window’s title bar. Clicking 

on the box closes the window. Compare close button. 

close button n. In the graphical user interface for Windows 

9x, Windows NT, and the X Window System, a 

square button in the right corner (left corner in X Windows) 

of a window’s title bar with an x mark on it. Clicking 

on the button closes the window. Also called: X 

button. Compare close box. 

closed architecture n. 1. Any computer design whose 

specifications are not freely available. Such proprietary 

specifications make it difficult or impossible for thirdparty 

vendors to create ancillary devices that work correctly 

with a closed-architecture machine; usually only its 

original maker can build peripherals and add-ons for such 

a machine. Compare open architecture (definition 1). 2. A 

computer system that provides no expansion slots for adding 

new types of circuit boards within the system unit. The 

original Apple Macintosh was an example of a closed 

architecture. Compare open architecture (definition 2). 

104 

closed file n. A file not being used by an application. An 

application must open such a file before reading or writing 

to it and must close it afterward. Compare open file. 

closed shop n. A computer environment in which access 

to the computer is restricted to programmers and other 

specialists. Compare open shop. 

closed system n. See closed architecture (definition 2). 

cloth ribbon n. An inked ribbon generally used with 

impact printers and typewriters. The print element strikes 

the ribbon and drives it against the paper so as to transfer 

ink; then the ribbon advances slightly to make fresh ink 

available. A cloth ribbon is wrapped onto a spool or 

loaded into a cartridge that is made to fit the printer used. 

Cloth ribbon, although adequate for most tasks, is sometimes 

replaced by film ribbon when the crispest possible 

output is called for. However, a cloth ribbon, which reinks 

itself by capillary action, is usable for multiple 

impressions, unlike a film ribbon. Compare carbon ribbon. 

CLS n. Acronym for Common Language Specification. A 

subset of language features supported by the .NET common 

language runtime, comprised of features common to several 

object-oriented programming languages. CLS-compliant 

components and tools are guaranteed to interoperate with 

other CLS-compliant components and tools. 

cluster n. 1. An aggregation, such as a group of data 

points on a graph. 2. A communications computer and its 

associated terminals. 3. In data storage, a disk-storage unit 

consisting of a fixed number of sectors (storage segments 

on the disk) that the operating system uses to read or write 

information; typically, a cluster consists of two to eight 

sectors, each of which holds a certain number of bytes 

(characters). 4. A group of independent network servers 

that operate—and appear to clients—as if they were a single 

unit. A cluster network is designed to improve network 

capacity by, among other things, enabling the servers 

within a cluster to shift work in order to balance the load. 

By enabling one server to take over for another, a cluster 

network also enhances stability and minimizes or eliminates 

downtime caused by application or system failure. 

See also client/server architecture. 

cluster analysis n. A technique used in data mining and 

knowledge discovery to group observations by identifying 

and extracting like or similar group conditions. Cluster 

analysis aims to describe the structure of a complex data 

set. See also ART, data mining.

cluster controller coaxial cable 

cluster controller n. An intermediary device that is situated 

between a computer and a group (cluster) of subsidiary 

devices, such as terminals on a network, and is used to 

control the cluster. 

clustering n. The grouping of multiple servers in a way 

that allows them to appear to be a single unit to client 

computers on a network. Clustering is a means of increasing 

network capacity, providing live backup in case one of 

the servers fails, and improving data security. See also 

cluster (definition 4), server. 

cluster network n. See cluster (definition 4). 

cluster virus n. A type of virus that infects once but gives 

the appearance of infecting every application launched. A 

cluster virus modifies the file system so that it is loaded 

before any application that the user attempts to open. 

Because the virus is also run when running any program, it 

appears that every program on the disk is infected. 

CLUT n. Acronym for Color Look Up Table. In digital 

graphics applications, a specific set of colors used in the 

creation of graphics. When a graphic is created or edited, 

the user may specify a CLUT that corresponds with the 

needs of print, Web, or other destination media. In Web 

design, a specific CLUT of browser-safe colors is used to 

be certain graphics and designs will display consistently 

across different platforms and with different browsers. See 

also browser CLUT, websafe palette. 

CMI n. Acronym for computer-managed instruction. Any 

type of teaching that uses computers as educational tools. 

See also CAI, CBT. 

CMOS n. 1. Acronym for complementary metal-oxide 

semiconductor. A semiconductor technology in which 

pairs of metal-oxide semiconductor field-effect transistors 

(MOSFETs), one N-type and one P-type, are integrated on 

a single silicon chip. Generally used for RAM and switching 

applications, these devices have very high speed and 

extremely low power consumption. They are, however, 

easily damaged by static electricity. See also MOSFET, Ntype 

semiconductor, P-type semiconductor. 2. The battery-backed 

memory used to store parameter values 

needed to boot PCs, such as the type of disks and the 

amount of memory, as well as the clock/calendar time. 

CMOS RAM n. Short for random access memory made 

using complementary metal-oxide semiconductor technology. 

CMOS chips consume extremely little power and 

have high tolerance for noise from the power supply. 

These characteristics make CMOS chips, including 

105 

CMOS RAM chips, very useful in hardware components 

that are powered by batteries, such as most microcomputer 

clocks and certain types of scratchpad RAM that are maintained 

by the operating system. See also CMOS (definition 

1), parameter RAM, RAM. 

CMOS setup n. A system configuration utility, accessible 

at boot time, for setting up certain system options, such as 

the date and time, the kind of drives installed, and port 

configuration. See also CMOS (definition 2). 

CMS n. See color management system. 

CMY n. Acronym for cyan-magenta-yellow. A model for 

describing colors that are produced by absorbing light, as 

by ink on paper, rather than by emitting light, as on a video 

monitor. The three kinds of cone cells in the eye respond to 

red, green, and blue light, which are absorbed (removed 

from white light) by cyan, magenta, and yellow pigments, 

respectively. Percentages of pigments in these subtractive 

primary colors can therefore be mixed to get the appearance 

of any desired color. Absence of any pigment leaves 

white unchanged; adding 100 percent of all three pigments 

turns white to black. Compare CMYK, RGB. 

CMYK n. Acronym for cyan-magenta-yellow-black. A 

color model that is similar to the CMY color model but 

produces black with a separate black component rather 

than by adding 100 percent of cyan, magenta, and yellow. 

See also CMY. 

coaxial cable n. A round, flexible, two-conductor cable 

consisting of—from the center outwards—a copper wire, 

a layer of protective insulation, a braided metal mesh 

sleeve, and an outer shield, or jacket of PVC or fire-resistant 

material. The shield prevents signals transmitted on 

the center wire from affecting nearby components and prevents 

external interference from affecting the signal carried 

on the center wire. Coaxial cable is widely used in 

networks. It is the same type of wiring as that used for 

cable television. See the illustration. Compare fiberoptic 

cable, twisted-pair wiring. 

f0cgn11.eps 

Coaxial cable. 

Braided shield 

Outer insulating sheath 

Central wire 

Insulated material 

C

C 

COBOL Code Red worm 

COBOL n. Acronym for Common Business-Oriented 

Language. A verbose, English-like compiled programming 

language developed between 1959 and 1961 and still 

in widespread use today, especially in business applications 

typically run on mainframes. A COBOL program 

consists of an Identification Division, which specifies the 

name of the program and contains any other documentation 

the programmer wants to add; an Environment Division, 

which specifies the computers being used and the 

files used in the program for input and output; a Data Division, 

which describes the format of the data structures 

used in the program; and a Procedure Division, which 

contains the procedures that dictate the actions of the program. 

See also compiled language. 

cobweb site n. A Web site that is far out of date. See also 

Web site. 

Cocoa n. A set of object-oriented development tools and 

interfaces available on Mac OS X. Cocoa contains a set of 

frameworks, software components, and development tools 

used to construct applications for Mac OS X and provides 

programming interfaces in Java and Objective-C. Cocoa is 

based on NeXT’s OpenStep and is integrated with Apple 

technologies. 

CODASYL n. Acronym for Conference on Data Systems 

Languages. An organization founded by the U.S. Department 

of Defense. CODASYL is dedicated to the development 

of data-management systems and languages, among 

them the widely used COBOL. 

code1 n. 1. Program instructions. Source code consists of 

human-readable statements written by a programmer in a 

programming language. Machine code consists of numerical 

instructions that the computer can recognize and execute 

and that were converted from source code. See also data, 

program. 2. A system of symbols used to convert information 

from one form to another. A code for converting information 

in order to conceal it is often called a cipher. 3. One 

of a set of symbols used to represent information. 

code2 vb. To write program instructions in a programming 

language. See also program. 

code access security n. A mechanism provided by the 

runtime whereby managed code is granted permissions by 

security policy and these permissions are enforced, limiting 

what operations the code will be allowed to perform. 

To prevent unintended code paths from exposing a security 

vulnerability, all callers on the call stack must be 

106 

granted the necessary permissions (possibly subject to 

override by assertion or denial). 

codec n. 1. Short for coder/decoder. Hardware that can 

convert audio or video signals between analog and digital 

forms. 2. Short for compressor/decompressor. Hardware 

or software that can compress and uncompress audio or 

video data. See also compress2 , uncompress. 3. Hardware 

that combines the functions of definitions 1 and 2. 

code conversion n. 1. The process of translating program 

instructions from one form into another. Code may be converted 

at the source-language level (for example, from C to 

Pascal), at the hardware-platform level (for example, from 

working on the IBM PC to working on the Apple Macintosh), 

or at the language level (for example, from source 

code in C to machine code). See also code1 (definition 1). 

2. The process of transforming data from one representation 

to another, such as from ASCII to EBCDIC or from 

two’s complement to binary-coded decimal. 

Code Division Multiple Access n. A form of multiplexing 

in which the transmitter encodes the signal, using a 

pseudo-random sequence that the receiver also knows and 

can use to decode the received signal. Each different random 

sequence corresponds to a different communication 

channel. Motorola uses Code Division Multiple Access 

for digital cellular phones. Acronym: CDMA. Also called: 

spread spectrum. See also multiplexing, transmitter. 

code page n. In MS-DOS versions 3.3 and later, a table 

that relates the binary character codes used by a program 

to keys on the keyboard or to the appearance of characters 

on the display. Code pages are a means of providing support 

for character sets and keyboard layouts used in different 

countries. Devices such as the display and the 

keyboard can be configured to use a specific code page 

and to switch from one code page (such as United States) 

to another (such as Portugal) at the user’s request. 

code profiler n. A tool designed to aid developers in 

identifying and eliminating the code inefficiencies that 

cause bottlenecks and degrade performance in their applications. 

Code profilers analyze an executing application to 

determine both how long functions take to execute and 

how often they are called. Using a code profiler is a repetitive 

process in that the tool must be reused after each section 

of inefficient code has been found and corrected. 

coder n. See programmer. 

Code Red worm n. A fast-spreading and pernicious 

Internet worm first discovered in mid-2001. The Code Red

code segment collaborative filtering 

worm propagates quickly, and any machine that was 

infected once is potentially vulnerable to re-infection. The 

Code Red worm is time sensitive, spreading in propagation 

mode from the 1st to the 19th of each month, attacking 

in flood mode from the 20th to the 27th, and finally 

hiding in hibernation mode until the 1st of the next month 

when the cycle begins again. The worm maintains a list of 

all computers previously infected, and all these computers 

will be attacked each month by every newly infected 

machine. This makes total eradication of the worm difficult 

because a single machine remaining infected from 

earlier propagation/attack cycles can potentially re-infect 

every machine on the list, and each computer might be 

subject to multiple attacks. At least three versions of the 

Code Red worm are known to exist. The Code Red worm 

was named for a caffeinated soft drink by the security 

team that first tracked the worm. 

code segment n. 1. A memory segment containing program 

instructions. 2. A named and segregated portion of a 

program’s code typically performing a specific class of 

operations. Code segments in this sense are often loaded 

into memory as memory segments. The main program 

segment is kept in memory, and auxiliary segments are 

loaded only when they are required. 

code signing n. The process of adding a digital signature 

to additions and updates made to source code and applications 

published on the Internet. Code signing is intended 

to provide a level of security and trust to Internet software 

distribution. See also digital signature. 

code snippet n. 1. In a graphical user interface, programming 

instructions embedded in a menu option or button 

defined by the user. The snippet—consisting of one or 

more lines of source code—determines what the option or 

button does when chosen or clicked. 2. A small piece of 

programming code that is part of a larger program. Usually 

the code snippet performs a specific function or task. 

coding form n. A sheet of paper ruled with horizontal and 

vertical lines to aid in writing source code for older languages 

that have position-dependent syntax (such as FOR- 

TRAN). Most programmers now use graph paper if they 

use paper at all. 

coercion n. See cast. 

Coffee Pot Control Protocol n. See HTCPCP. 

coherence n. 1. In raster-scan technology, the assignment 

of the value of one pixel to the pixel next to it. 2. In optics, 

107 

the property of some electromagnetic waves of being in 

phase with one another, as in light from a laser. 

cold boot n. A startup process that begins with turning on 

the computer’s power. Typically, a cold boot involves 

some basic hardware checking by the system, after which 

the operating system is loaded from disk into memory. See 

also boot1 . Compare warm boot. 

cold fault n. A fatal error that occurs immediately upon 

or shortly after startup as a result of the misalignment of 

components in the system. The process of running and 

shutting down any computer induces a series of thermal 

expansions and contractions in its internal components. 

Over time, these changes in the dimensions of components 

can create a microscopic crack in a chip or loosen a pin in 

a socket; thus, the system crashes when cold, but the problem 

seems to disappear after the machine is warm. For this 

reason, some users leave the system unit (but not the monitor) 

of a computer running from day to day, rather than 

turn the machine on only when needed. 

cold link n. A link established upon a request for data. 

Once the request is filled, the link is broken. The next time 

data is required, a link from the client to the server must be 

reestablished. In a client/server architecture, cold links are 

useful when the linked item consists of a large amount of 

data. Dynamic Data Exchange (DDE), used in applications 

such as Microsoft Excel, uses cold links for data 

exchange. See also client/server architecture, DDE. Compare 

hot link. 

cold start n. See cold boot. 

collaboration data object n. Microsoft Exchange 

Server technology for creating messaging and collaboration 

applications. A collaboration data object consists of a 

scripting interface added to Microsoft Messaging Application 

Programming Interface (MAPI). Acronym: CDO. 

collaborative filtering n. A means of deriving information 

from the experiences and opinions of a number of 

people. The term was coined by Doug Terry at Xerox 

PARC, who first used the technique by allowing users to 

annotate documents as they read them and to choose 

which documents to read next based not only on their content 

but also on what others wrote about them. A common 

use of collaborative filtering is the creation of lists of 

World Wide Web pages of interest to particular people; by 

documenting the experiences of several people, a list of 

interesting Web sites can be “filtered.” Collaborative filtering 

is also used as a marketing research tool; by keeping a 

C

C 

collapsed backbone color cycling 

database of opinions and ratings regarding several products, 

researchers can predict which new products the people 

contributing to the database will like. 

collapsed backbone n. See backbone (definition 3). 

collate vb. In data handling, to merge items from two or 

more similar sets to create a combined set that maintains 

the order or sequence of items in the original sets. 

collating sort n. A sort that proceeds by continuous 

merging of two or more files to produce a certain sequence 

of records or data items. 

collation sequence n. The ordering relationship 

(sequence) among objects that is to be established by a 

collating sort. See also collating sort. 

collector n. The region of a bipolar transistor into which 

charge carriers flow under normal operating conditions. 

The output of the transistor is usually taken from the collector. 

With respect to the base and emitter, the collector is 

positive in an NPN transistor and negative in a PNP transistor. 

See also NPN transistor, PNP transistor. Compare 

base (definition 3), emitter. 

collision n. The result of two devices or network workstations 

trying to transmit signals at the exact same time 

on the same channel. The typical outcome is a garbled 

transmission. 

collision detection n. 1. The process by which a node on 

a local area network monitors the communications line to 

determine when a collision has occurred; that is, when two 

nodes have attempted to transmit at the same time. 

Although network stations usually avoid collisions by 

monitoring the line and waiting for it to clear before transmitting, 

the method is not foolproof. When a collision 

does occur, the two nodes involved usually wait a random 

amount of time before attempting to retransmit. See also 

contention, CSMA/CD. 2. The process by which a game 

or simulation program determines whether two objects on 

the screen are touching each other. This is a time-consuming, 

often complicated procedure; some computers optimized 

for graphics and games, such as the Amiga, have 

special hardware built in specifically to detect collisions. 

colocation or co-location n. The operation of a server, 

router, or other device in a facility that provides a dedicated 

Internet connection, physical space in a secured 

cage, and regulated power. Colocation services often 

include fire detection and extinguishing, backup power, 

technical support, and additional security measures to 

ensure high availability. 

108 

color n. In physics, the component of the human perception 

of light that depends on frequency. For light of a single 

frequency, color ranges from violet at the highfrequency 

end of the visible-light band (a small portion of 

the total electromagnetic spectrum) to red at the low-frequency 

end. In computer video, color is produced by a 

combination of hardware and software. Software manipulates 

combinations of bits that represent the distinct shades 

of color that are destined for particular positions on the 

screen (characters or individual dots, called pixels). The 

video adapter hardware translates these bits into electrical 

signals, which in turn control the brightnesses of differentcolored 

phosphors at the corresponding positions on the 

screen of the monitor CRT. The user’s eye unites the light 

from the phosphors to perceive a single color. See also 

color model, color monitor, CRT, HSB, monitor, RGB, 

video, video adapter. 

color bits n. A predetermined number of bits assigned to 

each displayable pixel that determine the pixel’s color when 

it is displayed on a monitor. For example, two color bits are 

required for four colors; eight color bits are required for 256 

colors. See also pixel image. Compare bit plane. 

color box n. In the Windows NT and Windows 9x Paint 

accessory, a graphic screen element in the form of a paint 

box that is used to select foreground and background colors. 

color burst n. A technique used to encode color in a composite 

video signal, originally developed so that blackand-white 

television monitors could display programs 

broadcast in color. The color burst consists of a combination 

of the red, green, and blue intensities (used by blackand-white 

displays) and two color-difference signals that 

determine separate red, green, and blue intensities (used 

by color displays). See also color look-up table. 

color cycling n. A technique used in computer graphics 

for changing the color of one or more pixels on the screen 

by changing the color palette used by the video adapter 

rather than by changing the color bits for each pixel. For 

example, to cause a red circle to fade away to a black 

background color, the program need only change the set of 

signal values corresponding to “red” in the video adapter’s 

color look-up table, periodically making it darker until it 

matches the black background. At each step, the apparent 

color of the whole circle changes instantly; it appears to 

fade rather than to be painted over and over. The speed at 

which and the degree to which the circle fades are entirely 

up to the programmer.

color depth color space 

color depth n. The number of color values that can be 

assigned to a single pixel in an image. Also known as bit 

depth, color depth can range from 1 bit (black and white) 

to 32 bits (over 16.7 million colors). See also bit depth. 

color gamut n. The particular range of colors that a 

device is able to produce. A device such as a scanner, 

monitor, or printer can produce a unique range of colors, 

which is determined by the characteristics of the device 

itself. See also rendering intent. 

Color/Graphics Adapter n. See CGA. 

colorimeter n. A device that evaluates and identifies colors 

in terms of a standard set of synthesized colors. 

color look-up table n. A table stored in a computer’s 

video adapter, containing the color signal values that correspond 

to the different colors that can be displayed on 

the computer’s monitor. When color is displayed indirectly, 

a small number of color bits are stored for each 

pixel and are used to select a set of signal values from 

the color look-up table. Also called: color map, color 

table, video look-up table. See also color bits, palette 

(definition 2), pixel. 

Color Look Up Table n. See CLUT. 

color management n. The process of producing or 

reproducing accurate, consistent color across any of a 

variety of color input, output, and display devices. Color 

management includes, but is not limited to, accurate conversion 

of RGB input from input devices such as a scanner 

or a camera or from display devices such as a monitor to 

CMYK output for an output device such as a printer. Color 

management also encompasses application of a device 

profile, which contains information on color behavior for 

the printer or other device on which the image will be 

reproduced, and allowance for environmental variations 

such as humidity and lighting. See also CMYK, RGB. 

color management system n. A technology designed to 

calibrate, characterize, and process color production and 

reproduction across a variety of color input, output, and 

display devices. See also color management. 

color map n. See color look-up table. 

color model n. Any method or convention for representing 

color in desktop publishing and graphic arts. In the 

graphic arts and printing fields, colors are often specified 

with the Pantone system. In computer graphics, colors can 

be described using any of several different color systems: 

HSB (hue, saturation, and brightness), CMY (cyan, 

109 

magenta, and yellow), and RGB (red, green, and blue). 

See also CMY, HSB, Pantone Matching System, process 

color, RGB, spot color. 

color monitor n. A video display device designed to 

work with a video card or an adapter to produce text or 

graphics images in color. A color monitor, unlike a monochrome 

display, has a screen coated internally with patterns 

of three phosphors that glow red, green, and blue 

when struck by an electron beam. To create colors such as 

yellow, pink, and orange, the three phosphors are lighted 

together in varying degrees. A video card that uses large 

groups of bits (6 or more) to describe colors and that generates 

analog (continuously variable) signals is capable of 

generating an enormous potential range of colors on a 

color monitor. See also color, color model, Cycolor. 

color palette n. See palette (definition 1). 

color plane n. See bit plane. 

color printer n. A computer printer that can print fullcolor 

output. Most color printers can also produce blackand-white 

output. 

color saturation n. The amount of a hue contained in a 

color; the more saturation, the more intense the color. See 

also color model, HSB. 

color scanner n. A scanner that converts images to a digitized 

format and is able to interpret color. Depth of color 

depends on the scanner’s bit depth—its ability to transform 

color into 8, 16, 24, or 32 bits. High-end color scanners, 

commonly used when output is to be printed, are 

able to encode information at a high resolution or number 

of dots per inch (dpi). Low-end color scanners encode 

information at a resolution of 72 dpi and are commonly 

used for computer screen images not intended for printing. 

See also resolution (definition 1), scanner. 

color separation n. 1. The process of printing the colors 

in a document as separate output files, each of which is to 

be printed using a different-colored ink. There are two 

types of color separation: spot color separation and process 

color separation. See also color model, process color, 

spot color. 2. One of the output files produced by a color 

document, to be printed in its own color of ink. 

color space n. A means of describing color in digital 

environments. RGB is the most common color space on 

the Web, and with other color, the most common color 

space viewed on computer displays, while CMYK is the 

main color space for desktop publishing and other digital 

print media. 

C

C 

color supertwist nematic display combinatorics 

color supertwist nematic display n. See supertwist 

display. 

color table n. See color look-up table. 

column n. 1. A series of items arranged vertically within 

some type of framework—for example, a continuous 

series of cells running from top to bottom in a spreadsheet, 

a set of lines of specified width on a printed page, a vertical 

line of pixels on a video screen, or a set of values 

aligned vertically in a table or matrix. Compare row. 2. In 

a relational database management system, the name for an 

attribute. The collection of column values that form the 

description of a particular entity is called a tuple or row. A 

column is equivalent to a field in a record in a nonrelational 

file system. See also entity, field (definition 1), row, 

table (definition 2). 

column chart n. A bar chart in which values are displayed 

and printed as vertical bars. See the illustration. 

See also bar chart. 

8.00 

7.00 

6.00 

5.00 

4.00 

3.00 

2.00 

1.00 

0.00 

1988 1989 1990 1991 

High 

Low 

Average 

f0cgn12.eps 

Column chart. 

.com n. 1. In the Internet’s Domain Name System, the 

top-level domain that identifies addresses operated by 

commercial organizations. The domain name .com 

appears as a suffix at the end of the address. See also DNS 

(definition 1), domain (definition 3). Compare .edu, .gov, 

.mil, .net, .org. 2. In MS-DOS, the file extension that identifies 

a command file. See also COM (definition 3). 

COM n. 1. A name reserved by the MS-DOS operating 

system for serial communications ports. For example, if a 

modem is connected to one serial port and a serial printer 

to another, the devices are identified as COM1 and COM2 

by the operating system. 2. Acronym for Component 

110 

Object Model. A specification developed by Microsoft for 

building software components that can be assembled into 

programs or add functionality to existing programs running 

on Microsoft Windows platforms. COM components 

can be written in a variety of languages, although most are 

written in C++, and can be unplugged from a program at 

runtime without having to recompile the program. COM is 

the foundation of the OLE (object linking and embedding), 

ActiveX, and DirectX specifications. See also 

ActiveX, component (definition 2), DirectX, OLE. 3. The 

extension reserved by MS-DOS for a type of executable 

binary (program) file limited to a single 64-kilobyte (KB) 

segment. COM files are often used for utility programs 

and short routines. They are not supported in OS/2. 

4. Acronym for computer-output microfilm. Microfilm 

that can record data from a computer. 

COM1 n. A serial communications port in Wintel systems. 

COM1 is usually specified by the I/O range 03F8H, 

is usually associated with interrupt request line IRQ4, and 

in many systems is used to connect an RS232 serial 

mouse. See also IRQ. 

COM2 n. A serial communications port in Wintel systems. 

COM2 is usually specified by the I/O range 02F8H, is usually 

associated with interrupt request line IRQ3, and in 

many systems is used to connect a modem. See also IRQ. 

COM3 n. A serial communications port in Wintel (Windows 

running on an Intel chip) systems. COM3 is usually 

specified by the I/O range 03E8H, is usually associated 

with interrupt request line IRQ4, and in many systems is 

used as an alternative to COM1 or COM2 if the latter is 

being used by some other peripheral. See also IRQ, port, 

Wintel. 

combinatorial explosion n. A condition inherent in certain 

types of mathematical problems in which small increases 

in the problem’s size (number of data items or parameters of 

the operation) lead to enormous increases in the time 

required to obtain a solution. See also combinatorics. 

combinatorics n. A branch of mathematics related to 

probability and statistics, involving the study of counting, 

grouping, and arrangement of finite sets of elements. Combinatorics 

involves the two concepts of combinations and 

permutations. A combination is the grouping of elements 

taken from a larger set without regard to the order of the 

elements in each group; for example, taking two elements 

at a time from a set of four objects (A, B, C, and D) creates 

six combinations of objects: AB, AC, AD, BC, BD, and

COM callable wrapper command prompt window 

CD. A permutation is a grouping of elements taken from a 

larger set with regard to the order of the elements. For 

example, in making permutations of two objects from the 

same set of four objects, there would be four candidates to 

choose from for the first selection (A), and three left over 

to choose from for the second selection (B), or 12 permutations 

in all: AB, AC, AD, BA, BC, BD, CA, CB, CD, DA, 

DB, DC. See also combinatorial explosion. 

COM callable wrapper n. A proxy object generated by 

the runtime so that existing COM applications can use 

managed classes, including .NET Framework classes, 

transparently. Acronym: CCW. 

COMDEX n. Any of a series of annual computer trade 

shows operated by Softbank COMDEX, Inc. One of these 

shows takes place in Las Vegas each November and is the 

largest computer trade show in the United States. 

Comité Consultatif International Télégraphique et 

Téléphonique n. See CCITT. 

comma-delimited file n. A data file consisting of fields 

and records, stored as text, in which the fields are separated 

from each other by commas. Use of comma-delimited files 

allows communication between database systems that use 

different formats. If the data in a field contains a comma, 

the field is further surrounded with quotation marks. 

command n. An instruction to a computer program that, 

when issued by the user, causes an action to be carried out. 

Commands are usually either typed at the keyboard or 

chosen from a menu. 

command buffer n. An area in memory in which commands 

entered by the user are kept. A command buffer can 

enable the user to repeat commands without retyping them 

completely, edit past commands to change some argument 

or correct a mistake, undo commands, or obtain a list of 

past commands. See also history, template (definition 4). 

command button n. A control shaped like a pushbutton 

in a dialog box in a graphical user interface. By clicking a 

command button, the user causes the computer to perform 

some action, such as opening a file that has just been 

selected using the other controls in the dialog box. 

COMMAND.COM n. The command interpreter for MS- 

DOS. See also command interpreter. 

111 

command-driven adj. Accepting commands in the form 

of code words or letters, which the user must learn. Compare 

menu-driven. 

command-driven system n. A system in which the user 

initiates operations by a command entered from the console. 

Compare graphical user interface. 

command interpreter n. A program, usually part of the 

operating system, that accepts typed commands from the 

keyboard and performs tasks as directed. The command 

interpreter is responsible for loading applications and 

directing the flow of information between applications. In 

OS/2 and MS-DOS, the command interpreter also handles 

simple functions, such as moving and copying files and 

displaying disk directory information. See also shell1 . 

Command key n. On the original Macintosh keyboard, a 

key labeled with the special symbol, sometimes called the 

propeller or puppy foot. This key is found on one or both 

sides of the Spacebar, depending on the version of the 

Apple keyboard. The key serves some of the same functions 

as the Control key on IBM keyboards. See also Control 

key. 

command language n. The set of keywords and expressions 

that are accepted as valid by the command interpreter. 

See also command interpreter. 

command line n. A string of text written in the command 

language and passed to the command interpreter for execution. 

See also command language. 

command-line interface n. A form of interface between 

the operating system and the user in which the user types 

commands, using a special command language. Although 

systems with command-line interfaces are usually considered 

more difficult to learn and use than those with graphical 

interfaces, command-based systems are usually 

programmable; this gives them flexibility unavailable in 

graphics-based systems that do not have a programming 

interface. Compare graphical user interface. 

command mode n. A mode of operation in which a program 

waits for a command to be issued. Compare edit 

mode, insert mode. 

command processing n. See command-driven system. 

command processor n. See command interpreter. 

command prompt window n. A window displayed on 

the desktop used to interface with the MS-DOS operating 

C

C 

command shell common language runtime host 

system. MS-DOS commands are typed at an entry point 

identified by a blinking cursor. See also MS-DOS. 

command shell n. See shell1 . 

command state n. The state in which a modem accepts 

commands, such as a command to dial a telephone number. 

Compare online state. 

comment n. Text embedded in a program for documentation 

purposes. Comments usually describe what the program 

does, who wrote it, why it was changed, and so on. 

Most programming languages have a syntax for creating 

comments so that they can be recognized and ignored by 

the compiler or assembler. Also called: remark. See also 

comment out. 

comment out vb. To disable one or more lines of code 

from a program temporarily by enclosing them within a 

comment statement. See also comment, conditional compilation, 

nest. 

Commerce Interchange Pipeline n. See CIP. 

commerce server n. An HTTP server designed for conducting 

online business transactions. Data is transferred 

between the server and Web browser in an encrypted form 

to keep information such as credit card numbers reasonably 

secure. Commerce servers are typically used by 

online stores and companies that are set up for mail order 

business. The wares or services offered by the store or 

company are described and displayed in photographs on 

the store or company Web site and users can order directly 

from the site using their Web browser. A number of companies 

market commerce servers, including Netscape, 

Microsoft, and Quarterdeck. See also HTTP server (definition 

1), Secure Sockets Layer, Web browser. 

commercial access provider n. See ISP. 

Commercial Internet Exchange n. A nonprofit trade 

organization of public Internet service providers. In addition 

to the usual representational and social activities, the 

organization also operates an Internet backbone router that 

is accessible to its members. Acronym: CIX. See also 

backbone (definition 1), ISP, router. 

commercial off-the-shelf board n. A hardware board or 

platform that is readily available in the industry for purchase 

and can be used for development or test purposes. 

Also called: COTS board. 

112 

Common Access Method n. A standard developed by 

Future Domain and other SCSI vendors allowing SCSI 

adapters to communicate with SCSI peripherals regardless 

of the particular hardware used. See also SCSI. 

Common Application Language n. See CAL. 

common carrier n. A communications company (e.g., a 

telephone company) that provides service to the public 

and is regulated by governmental organizations. 

Common Client Interface n. A control interface begun 

with the X Windows version of NCSA Mosaic whereby 

other programs can control the local copy of a Web 

browser. The X Windows and Windows versions of NCSA 

Mosaic can communicate with other programs via TCP/IP. 

The Windows version is also capable of OLE communication. 

Acronym: CCI. See also Mosaic, OLE, TCP/IP, X 

Window System. 

Common Gateway Interface n. See CGI (definition 1), 

CGI script. 

Common Hardware Reference Platform n. A specification 

describing a family of machines, based on the 

PowerPC processor, that are capable of booting multiple 

operating systems, including Mac OS, Windows NT, 

AIX, and Solaris. Acronym: CHRP. See also PowerPC. 

Common Indexing Protocol n. See CIP. 

Common Information Model n. See CIM (definition 1). 

Common Internet File System n. A standard proposed 

by Microsoft that would compete directly with Sun Microsystems’ 

Web Network File System. A system of file sharing 

of Internet or intranet files. Acronym: CIFS. 

common language runtime n. The engine at the core of 

managed code execution. The runtime supplies managed 

code with services such as cross-language integration, 

code access security, object lifetime management, and 

debugging and profiling support. 

common language runtime host n. An unmanaged 

application that uses a set of APIs, called the hosting interfaces, 

to integrate managed code into the application. 

Common language runtime hosts often require a high 

degree of customization over the runtime that is loaded 

into the process. The hosting interfaces allow common 

language runtime hosts to specify settings that configure 

the garbage collector, select the appropriate build for their

Common Language Specification communications program 

environment (server versus workstation), and so on. Common 

language runtime hosts often support an extensibility 

model that allows the end user to dynamically add new 

pieces of functionality, such as a new control or a userwritten 

function. These extensions are typically isolated 

from each other in the process using application domains 

and custom security settings. Examples of common language 

runtime hosts include ASP.NET, Microsoft Internet 

Explorer, and a host to run executables launched from the 

Windows Shell. 

Common Language Specification n. See CLS. 

Common LISP n. Short for Common List Processing. A 

formalized and standardized version of the LISP programming 

language. Because LISP is in the public domain, a 

number of different versions of the language have evolved, 

and Common LISP was made a standard to give programmers 

a definitive source for LISP. See also LISP, programming 

language, standard (definition 1). 

Common Object Request Broker Architecture n. See 

CORBA. 

common type system n. The specification that determines 

how the runtime defines, uses, and manages types. 

Common User Access n. A set of standards for management 

of user interfaces as part of IBM’s Systems Application 

Architecture (SAA). Common User Access is 

designed to facilitate development of applications that are 

compatible and consistent across different platforms. 

Acronym: CUA. See also standard (definition 1), user 

interface. 

communications n. The vast discipline encompassing 

the methods, mechanisms, and media involved in information 

transfer. In computer-related areas, communications 

involves data transfer from one computer to another 

through a communications medium, such as a telephone, 

microwave relay, satellite link, or physical cable. Two primary 

methods of computer communications exist: temporary 

connection of two computers through a switched 

network, such as the public telephone system, and permanent 

or semipermanent linking of multiple workstations or 

computers in a network. The line between the two is indistinct, 

however, because microcomputers equipped with 

modems are often used to access both privately owned and 

public-access network computers. See also asynchronous 

transmission, CCITT, channel (definition 2), communications 

protocol, IEEE, ISDN, ISO/OSI model, LAN, 

113 

modem, network, synchronous transmission. Compare 

data transmission, telecommunications, teleprocess. 

Communications Act of 1934 n. See FCC. 

Communication Satellite Corporation n. Corporation 

created by the U.S. government to provide international 

satellite services for telecommunications. Acronym: 

COMSAT. 

communications channel n. See channel (definition 2). 

communications controller n. A device used as an 

intermediary in transferring communications to and from 

the host computer to which it is connected. By relieving 

the host computer of the actual tasks of sending, receiving, 

deciphering, and checking transmissions for errors, a communications 

controller helps to make efficient use of the 

host computer’s processing time—time that might be better 

used for noncommunications tasks. A communications 

controller can be either a programmable machine in its 

own right or a nonprogrammable device designed to follow 

certain communications protocols. See also front-end 

processor (definition 2). 

communications link n. The connection between computers 

that enables data transfer. 

communications network n. See network. 

communications parameter n. Any of several settings 

required in order to enable computers to communicate. In 

asynchronous communications, for example, modem 

speed, number of data bits and stop bits, and type of parity 

are parameters that must be set correctly to establish communication 

between two modems. 

communications port n. See COM. 

communications program n. A software program that 

enables a computer to connect with another computer and 

to exchange information. For initiating communications, 

communications programs perform such tasks as maintaining 

communications parameters, storing and dialing 

phone numbers automatically, recording and executing 

logon procedures, and repeatedly dialing busy lines. Once 

a connection is made, communications programs can also 

be instructed to save incoming messages on disk or to find 

and transmit disk files. During communication, these 

types of programs perform the major, and usually invisible, 

tasks of encoding data, coordinating transmissions to 

and from the distant computer, and checking incoming 

data for transmission errors. 

C

C 

communications protocol CompactFlash Association 

communications protocol n. A set of rules or standards 

designed to enable computers to connect with one another 

and to exchange information with as little error as possible. 

The protocol generally accepted for standardizing overall 

computer communications is a seven-layer set of hardware 

and software guidelines known as the OSI (Open Systems 

Interconnection) model. A somewhat different standard, 

widely used before the OSI model was developed, is IBM’s 

SNA (Systems Network Architecture). The word protocol 

is often used, sometimes confusingly, in reference to a multitude 

of standards affecting different aspects of communication, 

such as file transfer (for example, XMODEM and 

ZMODEM), handshaking (for example, XON/XOFF), and 

network transmissions (for example, CSMA/CD). See also 

ISO/OSI model, SNA. 

communications satellite n. A satellite stationed in 

geosynchronous orbit that acts as a microwave relay station, 

receiving signals sent from a ground-based station 

(earth station), amplifying them, and retransmitting them 

on a different frequency to another ground-based station. 

Initially used for telephone and television signals, communications 

satellites can also be used for high-speed transmission 

of computer data. Two factors affecting the use of 

satellites with computers, however, are propagation delay 

(the time lag caused by the distance traveled by the signal) 

and security concerns. See also downlink, uplink. 

communications server n. A gateway that translates 

packets on a local area network (LAN) into asynchronous 

signals, such as those used on telephone lines or in RS- 

232-C serial communications, and allows all nodes on the 

LAN access to its modems or RS-232-C connections. See 

also gateway, RS-232-C standard. 

communications slot n. On many models of the Apple 

Macintosh, a dedicated expansion slot for network interface 

cards. Acronym: CS. 

communications software n. The software that controls 

the modem in response to user commands. Generally such 

software includes terminal emulation as well as file transfer 

facilities. See also modem, terminal emulation. 

communications system n. The combination of hardware, 

software, and data transfer links that make up a 

communications facility. 

Communications Terminal Protocol n. A terminal protocol 

that enables a user at a remote location to access a 

computer as if the remote computer were directly connected 

(hardwired) to the computer. Acronym: CTERM. 

114 

community antenna television n. See CATV. 

COMNET Conference & Expo n. Conference and exposition 

for the communications networking industry. The 

conference features educational sessions and exhibitions 

on technical and business issues affecting communications 

networks. 

compact disc n. 1. An optical storage medium for digital 

data, usually audio. A compact disc is a nonmagnetic, polished 

metal disc with a protective plastic coating that can 

hold up to 74 minutes of high-fidelity recorded sound. The 

disk is read by an optical scanning mechanism that uses a 

high-intensity light source, such as a laser, and mirrors. 

Also called: optical disc. 2. A technology that forms the 

basis of media such as CD-ROM, CD-ROM/XA, CD-I, 

CD-R, DVI, and PhotoCD. These media are all compact 

disc–based but store various types of digital information 

and have different read/write capabilities. Documentation 

for compact disc formats can be found in books designated 

by the color of their covers. For example, documentation 

for audio compact discs is found in the Red Book. 

See also CD-I, CD-R, CD-ROM, CD-ROM/XA, DVI, 

Green Book (definition 2), Orange Book (definition 2), 

PhotoCD, Red Book (definition 2). 3. See CD. 

compact disc-erasable n. See CD-E. 

compact disc-interactive n. See CD-I. 

compact disc player n. See CD player. 

compact disc-recordable n. See CD-R. 

compact disc-recordable and erasable adj. See CD- 

R/E. 

compact disc-rewritable n. See CD-RW. 

CompactFlash n. Plug-in memory devices designed by 

the CompactFlash Association for use in digital cameras 

and, eventually, other devices for storing and transporting 

digital data, sound, images, and video. CompactFlash 

devices are small cards 1.7 x 1.4 x 0.13 inches (43 x 36 x 

3.3 mm) in size. They are based on nonvolatile flash technology, 

so they do not rely on batteries or other power to 

retain information. See also digital camera. 

CompactFlash Association n. A nonprofit association 

that developed and promotes the CompactFlash specification. 

Founded in October 1995, it has a membership that 

includes 3COM, Eastman Kodak Company, Hewlett- 

Packard, IBM, and NEC, among other corporations. See 

also CompactFlash.

compaction compiled Basic 

compaction n. The process of gathering and packing the 

currently allocated regions of memory or auxiliary storage 

into as small a space as possible, so as to create as much 

continuous free space as possible. Compare dispersion, 

file fragmentation (definition 1). 

compact model n. A memory model of the Intel 80x86 

processor family. The compact model allows only 64 kilobytes 

(KB) for the code of a program but up to 1 megabyte 

(MB) for the program’s data. See also memory model. 

CompactPCI n. An open bus specification for industrial 

computing needs developed by the PCI Industrial Computer 

Manufacturers Group (PICMG). CompactPCI is 

based on the desktop-computing PCI bus but differs in a 

number of respects, including a pin-and-socket connector 

and a design that allows for front loading and removal of 

cards. CompactPCI is intended for applications such as 

industrial automation, military systems, and real-time data 

acquisition. It is suitable for high-speed communications 

devices, such as routers, and allows for hot-plugging. See 

also hot plugging, PCI local bus. 

comparator n. A device for comparing two items to 

determine whether they are equal. In electronics, for 

example, a comparator is a circuit that compares two input 

voltages and indicates which is higher. 

compare vb. To check two items, such as words, files, or 

numeric values, so as to determine whether they are the 

same or different. In a program, the outcome of a compare 

operation often determines which of two or more actions 

is taken next. 

comparison criteria n. A set of search conditions that is 

used to find data. Comparison criteria can be a series of 

characters that you want to match, such as “Northwind 

Traders”, or an expression, such as “>300”. 

compatibility n. 1. The degree to which a computer, an 

attached device, a data file, or a program can work with or 

understand the same commands, formats, or language as 

another. True compatibility means that any operational 

differences are invisible to people and programs alike. 

2. The extent to which two machines can work in harmony. 

Compatibility (or the lack thereof) between two 

machines indicates whether, and to what degree, the computers 

can communicate, share data, or run the same programs. 

For example, an Apple Macintosh and an IBM PC 

are generally incompatible because they cannot communicate 

freely or share data without the aid of hardware and/ 

or software that functions as an intermediary or a con- 

115 

verter. 3. The extent to which a piece of hardware conforms 

to an accepted standard (for example, IBMcompatible 

or Hayes-compatible). In this sense, compatibility 

means that the hardware ideally operates in all 

respects like the standard on which it is based. 4. In reference 

to software, harmony on a task-oriented level among 

computers and computer programs. Computers deemed 

software-compatible are those that can run programs originally 

designed for other makes or models. Software compatibility 

also refers to the extent to which programs can 

work together and share data. In another area, totally different 

programs, such as a word processor and a drawing 

program, are compatible with one another if each can 

incorporate images or files created using the other. All 

types of software compatibility become increasingly 

important as computer communications, networks, and 

program-to-program file transfers become near-essential 

aspects of microcomputer operation. See also downward 

compatibility, upward-compatible. 

compatibility box n. See DOS box (definition 1). 

compatibility mode n. A mode in which hardware or 

software in one system supports operations of software 

from another system. The term often refers to the ability of 

advanced operating systems designed for Intel microprocessors 

(for example, OS/2 and Windows NT) to run MS- 

DOS software or to the ability of some UNIX workstations 

and of some Apple Macintosh systems to run MS- 

DOS software. 

Competitive Local Exchange Carrier n. See CLEC. 

compile vb. To translate all the source code of a program 

from a high-level language into object code prior to execution 

of the program. Object code is executable machine 

code or a variation of machine code. More generally, compiling 

is sometimes used to describe translating any highlevel 

symbolic description into a lower-level symbolic or 

machine-readable format. A program that performs this 

task is known as a compiler. See also compiler (definition 

2), compile time, high-level language, machine code, 

source code. Compare interpret. 

compile-and-go adj. Of, pertaining to, or characteristic of 

a development environment that automatically runs a program 

after compiling it. See also compile, execute. 

compiled Basic n. Any version of Basic that is translated 

into machine code prior to execution by a compiler. Basic 

has traditionally been an interpreted language (translated 

and executed statement by statement); because compiled 

C

C 

compiled language component software 

Basic generally produces faster-executing programs, it is the 

technology of choice for professional Basic programmers. 

See also Basic, compiled language, interpreted language. 

compiled language n. A language that is translated into 

machine code prior to any execution, as opposed to an 

interpreted language, which is translated and executed 

statement by statement. See also compiler (definition 2). 

Compare interpreted language. 

compiler n. 1. Any program that transforms one set of 

symbols into another by following a set of syntactic and 

semantic rules. 2. A program that translates all the source 

code of a program written in a high-level language into 

object code prior to execution of the program. See also 

assembler, compile, high-level language, interpreted language, 

language processor, object code. 

compile time n. 1. The amount of time required to perform 

a compilation of a program. Compile time can range 

from a fraction of a second to many hours, depending on 

the size and complexity of the program, the speed of the 

compiler, and the performance of the hardware. See also 

compiler (definition 2). 2. The point at which a program is 

being compiled (i.e., most languages evaluate constant 

expressions at compile time but evaluate variable expressions 

at run time). See also link time, run time. 

compile-time binding n. Assignment of a meaning to an 

identifier (such as a function name or a constant) in a program 

at the time the program is compiled rather than at the 

time it is run. Compare run-time binding. 

complement n. Loosely, a number that can be thought of 

as the mirror image of another number written to the same 

base, such as base 10 or base 2. Complements are commonly 

used to represent negative numbers. Two types of 

complements are encountered in computer-related contexts: 

radix-minus-1 complements and true complements. 

A radix-minus-1 complement is known in the decimal system 

as a nine’s complement and in the binary system as a 

one’s complement. True complements are known in the 

decimal system as ten’s complement and in binary as 

two’s complement—a form commonly used to represent 

negative numbers in processing. See also complementary 

operation, nine’s complement, one’s complement, ten’s 

complement, two’s complement. 

complementary metal-oxide semiconductor n. See 

CMOS. 

complementary operation n. In Boolean logic, an operation 

that produces the opposite result from that of another 

116 

operation performed on the same data. For example, if A 

is true, NOT A (its complement) is false. See also Boolean 

algebra. 

completeness check n. A survey to determine that all 

data required in a record is present. Compare consistency 

check. 

complex instruction set computing n. See CISC. 

complex number n. A number of the form a + bi, where 

a and b are real numbers and i is the square root of -1, 

called the imaginary unit. Complex numbers can be plotted 

as points on a two-dimensional plane called the complex 

plane. The a number is plotted along the plane’s 

horizontal axis (the real axis), and the b number is plotted 

along the vertical axis (the imaginary axis). Compare real 

number. 

comp. newsgroups n. Usenet newsgroups that are part 

of the comp. hierarchy and have the prefix comp. These 

newsgroups are devoted to discussions of computer hardware, 

software, and other aspects of computer science. 

Comp. newsgroups are one of the seven original Usenet 

newsgroup hierarchies. The other six are misc., news., 

rec., sci., soc., and talk. See also newsgroup, traditional 

newsgroup hierarchy, Usenet. 

component n. 1. A discrete part of a larger system or 

structure. 2. An individual modular software routine that 

has been compiled and dynamically linked, and is ready to 

use with other components or programs. See also compile, 

component software, link (definition 1), program, routine. 

3. In Sun Microsystem’s J2EE network platform, an application-level 

software unit supported by a container. Components 

are configurable at deployment time. The J2EE 

platform defines four types of components: enterprise java 

beans, Web components, applets, and application clients. 

See also applet, container (definition 3), Enterprise Java- 

Beans, J2EE. 

Component Object Model n. See COM (definition 2). 

Component Pascal n. A Pascal derivative designed for 

programming software components for .NET and JVM 

platforms. See also Oberon, Pascal. 

component software n. Modular software routines, or 

components, that can be combined with other components 

to form an overall program. A programmer can use and 

reuse an existing component and not have to understand its 

inner workings, just how to have another program or component 

call it and pass data to and from it. Also called: 

componentware. See also component, program, routine.

componentware Compressed Read-Only File System 

componentware n. See component software. 

COM port or comm port n. Short for communications 

port, the logical address assigned by MS-DOS (versions 

3.3 and later) and Microsoft Windows (including Windows 

9x and Windows NT) to each of the four serial ports 

on an IBM Personal Computer or a PC compatible. COM 

ports also have come to be known as the actual serial ports 

on a PC’s CPU where peripherals, such as printers, scanners, 

and external modems, are plugged in. See the illustration. 

See also COM (definition 1), input/output port, 

serial port. 

COM port 

f0cgn13.eps 

COM port. 

composite display n. A display, characteristic of television 

monitors and some computer monitors, that is capable 

of extracting an image from a composite signal (also 

called an NTSC signal). A composite display signal carries 

on one wire not only the coded information required to 

form an image on the screen but also the pulses needed to 

synchronize horizontal and vertical scanning as the electron 

beam sweeps back and forth across the screen. Composite 

displays can be either monochrome or color. A 

composite color signal combines the three primary video 

colors (red, green, and blue) in a color burst component 

that determines the shade of color displayed on the screen. 

Composite color monitors are less readable than either 

monochrome monitors or the RGB color monitors that use 

separate signals (and wires) for the red, green, and blue 

components of the image. See also color burst, color monitor, 

monochrome display, NTSC, RGB monitor. 

composite key n. A key whose definition consists of two 

or more fields in a file, columns in a table, or attributes in 

a relation. 

composite video display n. A display that receives all 

encoded video information (including color, horizontal 

synchronization, and vertical synchronization) in one signal. 

A composite video signal under NTSC (National 

Television System Committee) standards is generally 

117 

required for television sets and videotape recorders. See 

also NTSC. Compare RGB monitor. 

compound document n. A document that contains different 

types of information, each type created with a different 

application; for example, a report containing both 

charts (created with a spreadsheet) and text (created with a 

word processor) is a compound document. Although a 

compound document is visually a single, seamless unit, it 

is actually formed of discrete objects (blocks of information) 

that are created in their own applications. These 

objects can either be physically embedded in the destination 

document, or they can be linked to it while remaining 

in the originating file. Both embedded and linked objects 

can be edited. Linked objects, however, can be updated to 

reflect changes made to the source file. See also ActiveX, 

OLE, OpenDoc. 

compound statement n. A single instruction composed 

of two or more individual instructions. 

compress1 n. A proprietary UNIX utility for reducing the 

size of data files. Files compressed with this utility have 

the extension .Z added to their names. 

compress2 vb. To reduce the size of a set of data, such as 

a file or a communications message, so that it can be 

stored in less space or transmitted with less bandwidth. 

Data can be compressed by removing repeated patterns of 

bits and replacing them with some form of summary that 

takes up less space; restoring the repeated patterns decompresses 

the data. Lossless compression methods must be 

used for text, code, and numeric data files; lossy compression 

may be used for video and sound files. See also lossless 

compression, lossy compression. 

compressed digital video n. See CDV (definition 1). 

compressed disk n. A hard disk or floppy disk whose 

apparent capacity to hold data has been increased through 

the use of a compression utility, such as Stacker or Double 

Space. See also data compression. 

compressed drive n. A hard disk whose apparent capacity 

has been increased through the use of a compression 

utility, such as Stacker or Double Space. See also compressed 

disk, data compression. 

compressed file n. A file whose contents have been 

compressed by a special utility program so that it occupies 

less space on a disk or other storage device than in its 

uncompressed (normal) state. See also installation program, 

LHARC, PKUNZIP, PKZIP, utility program. 

Compressed Read-Only File System n. See cramfs. 

C

C 

Compressed SLIP computer-aided design/computer-aided manufacturing 

Compressed SLIP n. Short for Compressed Serial Line 

Internet Protocol. A version of SLIP using compressed 

Internet address information, thereby making the protocol 

faster than SLIP. Acronym: CSLIP. See also SLIP. 

compression n. See data compression. 

compressor n. A device that limits some aspect of a 

transmitted signal, such as volume, in order to increase 

efficiency. 

CompuServe n. An online information service that is a 

subsidiary of America Online. CompuServe provides 

information and communications capabilities, including 

Internet access. It is primarily known for its technical support 

forums for commercial hardware and software products 

and for being one of the first large commercial online 

services. CompuServe also operates various private network 

services. 

computational intelligence n. The study of the design 

of intelligent agents whose reasoning is based on computational 

methods. The central scientific goal of computational 

intelligence is to understand the principles that 

make intelligent behavior possible, in natural or artificial 

systems. An intelligent agent is flexible to changing environments 

and changing goals—it learns from experience, 

and it makes appropriate choices given perceptual limitations 

and finite computation. The central engineering goal 

of computational intelligence is to specify methods for the 

design of useful, intelligent artifacts. See also agents (definition 

2), artificial intelligence, autonomous agent. 

computation-bound adj. Of, pertaining to, or characteristic 

of a situation in which the performance of a computer is 

limited by the number of arithmetic operations the microprocessor 

must perform. When a system is computation-bound, 

the microprocessor is overloaded with calculations. Also 

called: CPU-bound. 

compute vb. 1. To perform calculations. 2. To use a computer 

or cause it to do work. 

computer n. Any device capable of processing information 

to produce a desired result. No matter how large or 

small they are, computers typically perform their work in 

three well-defined steps: (1) accepting input, (2) processing 

the input according to predefined rules (programs), 

and (3) producing output. There are several ways to categorize 

computers, including class (ranging from microcomputers 

to supercomputers), generation (first through 

fifth generation), and mode of processing (analog versus 

digital). See the table. See also analog, digital (definition 

118 

2), integrated circuit, large-scale integration, very-largescale 

integration. 

Table C.1 Ways to Categorize Computers 

Class Computers can be classified as supercomputers, 

mainframes, superminicomputers, 

minicomputers, workstations, 

microcomputers, or PDAs. All other 

things (for example, the age of the 

machine) being equal, such a categorization 

provides some indication of the computer’s 

speed, size, cost, and abilities. 

Generation First-generation computers of historic 

significance, such as UNIVAC, introduced 

in the early 1950s, were based on 

vacuum tubes. Second-generation computers, 

appearing in the early 1960s, 

were those in which transistors replaced 

vacuum tubes. Third-generation computers, 

dating from the 1960s, were those in 

which integrated circuits replaced transistors. 

Fourth-generation computers, 

appearing in the mid-1970s, are those, 

such as microcomputers, in which largescale 

integration (LSI) enabled thousands 

of circuits to be incorporated on one 

chip. Fifth-generation computers are 

expected to combine very-large-scale 

integration (VLSI) with sophisticated 

approaches to computing, including artificial 

intelligence and true distributed 

processing. 

Mode of Computers are either analog or digital. 

processing Analog computers, generally used in scientific 

pursuits, represent values by continuously 

variable signals that can have 

any of an infinite number of values 

within a limited range at any particular 

time. Digital computers, the type most 

people think of as computers, represent 

values by discrete signals—the bits representing 

the binary digits 0 and 1. 

computer-aided design n. See CAD. 

computer-aided design and drafting n. See CADD. 

computer-aided design/computer-aided 

manufacturing n. See CAD/CAM.

computer-aided engineering Computer Graphics Metafile 

computer-aided engineering n. See CAE. 

computer-aided instruction n. See CAI. 

computer-aided learning n. See CAL. 

computer-aided manufacturing n. See CAM (definition 

1). 

computer-aided testing n. See CAT (definition 1). 

Computer and Business Equipment Manufacturers 

Association n. See CBEMA. 

computer art n. A broad term that can refer either to art 

created on a computer or to art generated by a computer, 

the difference being whether the artist is human or electronic. 

When created by human beings, computer art is 

done with painting programs that offer a range of linedrawing 

tools, brushes, shapes, patterns, and colors. Some 

programs also offer predrawn figures and animation capabilities. 

computer-assisted diagnosis n. The use of computers 

by physicians in diagnosing patient conditions. Medical 

application programs can help to determine the cause, 

symptoms, and treatment of a problem as well as to maintain 

a record of a patient’s medical history and test results. 

See also expert system. 

computer-assisted instruction n. See CAI. 

computer-assisted learning n. See CAL. 

computer-assisted teaching n. See CAI. 

computer-augmented learning n. See CAL. 

computer-based learning n. See CBL. 

computer-based training n. See CBT. 

computer center n. A centralized location that contains 

computers, such as mainframes or minicomputers, along 

with associated equipment for providing data processing 

services to a group of people. 

computer conferencing n. Person-to-person interaction 

through the use of computers located in different places 

but connected through communications facilities. 

computer control console n. See system console. 

computer crime n. The illegal use of a computer by an 

unauthorized individual, either for pleasure (as by a computer 

hacker) or for profit (as by a thief). See also hacker 


computer-dependent adj. See hardware-dependent. 

119 

Computer Emergency Response Team n. See CERT. 

computer engineering n. The discipline that involves 

the design and underlying philosophies involved in the 

development of computer hardware. 

computer family n. A term commonly used to indicate a 

group of computers that are built around the same microprocessor 

or around a series of related microprocessors 

and that share significant design features. For example, the 

Apple Macintosh computers, from the original Macintosh 

(introduced in 1984) to the Quadra, represent a family 

designed by Apple around the Motorola 68000, 68020, 

68030, and 68040 microprocessors. Computer families 

tend to parallel microprocessor families, but this is not 

always the case. For instance, Macintoshes are no longer 

made with 680x0 processors, and the Macintosh family 

has “extended” to another generation: the Power Macs, 

based on the PowerPC microprocessor. 

computer game n. A class of computer program in 

which one or more users interacts with the computer as a 

form of entertainment. Computer games run the gamut 

from simple alphabet games for toddlers to chess, treasure 

hunts, war games, and simulations of world events. The 

games are controlled from a keyboard or with a joystick or 

other device and are supplied on disks, on CD-ROMs, as 

game cartridges, on the Internet, or as arcade devices. 

computer graphics n. The display of “pictures,” as 

opposed to only alphabetic and numeric characters, on a 

computer screen. Computer graphics encompasses different 

methods of generating, displaying, and storing information. 

Thus, computer graphics can refer to the creation 

of business charts and diagrams; the display of drawings, 

italic characters, and mouse pointers on the screen; or the 

way images are generated and displayed on the screen. See 

also graphics mode, presentation graphics, raster graphics, 

vector graphics. 

Computer Graphics Interface n. A software standard 

applied to computer graphics devices, such as printers and 

plotters. Computer Graphics Interface is an offshoot of a 

widely recognized graphics standard called GKS (Graphical 

Kernel System), which provides applications programmers 

with standard methods of creating, manipulating, 

and displaying or printing computer graphics. Acronym: 

CGI. See also Graphical Kernel System. 

Computer Graphics Metafile n. A software standard 

related to the widely recognized GKS (Graphical Kernel 

C

C 

computer-independent language computer program 

System) that provides applications programmers with a 

standard means of describing a graphic as a set of instructions 

for re-creating it. A graphics metafile can be stored 

on disk or sent to an output device; Computer Graphics 

Metafile provides a common language for describing such 

files in relation to the GKS standard. Acronym: CGM. See 

also Graphical Kernel System. 

computer-independent language n. A computer language 

designed to be independent of any given hardware 

platform. Most high-level languages are intended to be 

computer-independent; actual implementations of the languages 

(in the form of compilers and interpreters) tend to 

have some hardware-specific features and aspects. See 

also computer language. 

computer-input microfilm n. See CIM (definition 2). 

computer instruction n. 1. An instruction that a computer 

can recognize and act on. See also machine instruction. 

2. The use of a computer in teaching. See also CAI. 

computer-integrated manufacturing n. See CIM (definition 

1). 

computer interface unit n. See interface (definition 3). 

computerized axial tomography n. See CAT (definition 

3). 

computerized mail n. See e-mail1 . 

computer language n. An artificial language that specifies 

instructions to be executed on a computer. The term 

covers a wide spectrum, from binary-coded machine language 

to high-level languages. See also assembly language, 

high-level language, machine code. 

computer letter n. See form letter. 

computer literacy n. Knowledge and an understanding 

of computers combined with the ability to use them effectively. 

On the least specialized level, computer literacy 

involves knowing how to turn on a computer, start and 

stop simple application programs, and save and print 

information. At higher levels, computer literacy becomes 

more detailed, involving the ability of power users to 

manipulate complex applications and, possibly, to program 

in languages such as Basic or C. At the highest levels, 

computer literacy leads to specialized technical 

knowledge of electronics and assembly language. See also 

power user. 

computer-managed instruction n. See CMI. 

120 

computer name n. In computer networking, a name that 

uniquely identifies a computer to the network. A computer’s 

name cannot be the same as any other computer or 

domain name on the network. It differs from a user name 

in that the computer name is used to identify a particular 

computer and all its shared resources to the rest of the system 

so that they can be accessed. Compare alias (definition 

2), user name. 

computer network n. See network. 

computer-output microfilm n. See COM (definition 4). 

computerphile n. A person who is immersed in the world 

of computing, who collects computers, or whose hobby 

involves computing. 

computer power n. The ability of a computer to perform 

work. If defined as the number of instructions the machine 

can carry out in a given time, computer power is measured 

in millions of instructions per second (MIPS) or millions 

of floating-point operations per second (MFLOPS). Power 

is measured in other ways too, depending on the needs or 

objectives of the person evaluating the machine. By users 

or purchasers of computers, power is often considered in 

terms of the machine’s amount of random access memory 

(RAM), the speed at which the processor works, or the 

number of bits (8, 16, 32, and so on) handled by the computer 

at one time. Other factors enter into such an evaluation, 

however; two of the most important are how well the 

components of the computer work together and how well 

they are matched to the tasks required of them. For example, 

no matter how fast or powerful the computer, its speed 

will be hampered during operations involving the hard 

disk if the hard disk is slow (for example, with an access 

time of 65 milliseconds or higher). See also access time 

(definition 2), benchmark1 , MFLOPS, MIPS. 

Computer Press Association n. A trade organization of 

journalists, broadcasters, and authors who write or report 

about computer technology and the computer industry. 

Computer Professionals for Social Responsibility n. 

See CPSR. 

computer program n. A set of instructions in some computer 

language intended to be executed on a computer so 

as to perform some task. The term usually implies a selfcontained 

entity, as opposed to a routine or a library. See 

also computer language. Compare library (definition 1), 

routine.

computer-readable CON 

computer-readable adj. Of, pertaining to, or characteristic 

of information that can be interpreted and acted on by a 

computer. Two types of information are referred to as 

computer-readable: bar codes, magnetic tape, magneticink 

characters, and other formats that can be scanned in 

some way and read as data by a computer; and machine 

code, the form in which instructions and data reach the 

computer’s microprocessor. 

computer revolution n. The societal and technological 

phenomenon involving the swift development and widespread 

use and acceptance of computers—specifically single-user 

personal computers. The impact of these 

machines is considered revolutionary for two reasons. 

First, their appearance and success were rapid. Second, 

and more important, their speed and accuracy produced a 

change in the ways in which information can be processed, 

stored, and transferred. 

computer science n. The study of computers, including 

their design, operation, and use in processing information. 

Computer science combines both theoretical and practical 

aspects of engineering, electronics, information theory, 

mathematics, logic, and human behavior. Aspects of computer 

science range from programming and computer 

architecture to artificial intelligence and robotics. 

computer security n. The steps taken to protect a computer 

and the information it contains. On large systems or 

those handling financial or confidential data, computer 

security requires professional supervision that combines 

legal and technical expertise. On a microcomputer, data 

protection can be achieved by backing up and storing copies 

of files in a separate location, and the integrity of data 

on the computer can be maintained by assigning passwords 

to files, marking files read-only to avoid changes to 

them, physically locking a hard disk, storing sensitive 

information on floppy disks kept in locked cabinets, and 

installing special programs to protect against viruses. On a 

computer that many people have access to, security can be 

maintained by requiring personnel to use passwords and 

by granting only approved users access to sensitive information. 

See also bacterium, encryption, virus. 

computer simulation n. See simulation. 

computer system n. The configuration that includes all 

functional components of a computer and its associated 

hardware. A basic microcomputer system includes a console, 

or system unit, with one or more disk drives, a monitor, 

and a keyboard. Additional hardware, called 

peripherals, can include such devices as a printer, a 

121 

modem, and a mouse. Software is usually not considered 

part of a computer system, although the operating system 

that runs the hardware is known as system software. 

computer telephone integration n. A process allowing 

computer applications to answer incoming calls, provide 

database information on-screen at the same time the call 

comes in, automatically route and reroute calls by dragand-drop, 

automatically dial and speed-dial outgoing calls 

from a computer-resident database, and identify incoming 

customer calls and transfer them to predetermined destinations. 

See also drag-and-drop. 

Computer Telephony Expo n. See CT Expo. 

computer typesetting n. Typesetting operations that are 

partially or totally controlled by computers. Partial control 

can involve the transmittal of text directly from the source 

to the typesetter, without a paste-up stage. Full computerization 

can include the digitization of all graphics, which 

would then also be transmitted directly to the typesetter 

and regenerated without paste-up. 

computer users’ group n. See user group. 

computer utility n. See utility. 

computer virus n. See virus. 

computer vision n. The processing of visual information 

by a computer. Computer vision is a form of artificial 

intelligence that creates a symbolic description of images 

that are generally input from a video camera or sensor in 

order to convert the images to digital form. Computer 

vision is often associated with robotics. Acronym: CV. See 

also artificial intelligence, robotics. 

Computer Vision Syndrome n. A change in a user’s 

vision caused by prolonged exposure to computer monitors. 

Symptoms of Computer Vision Syndrome (CVS) can 

include blurred vision, dry, burning eyes, focusing problems, 

and headaches. CVS may be controlled with regular 

breaks from the computer, use of monitor filters or color 

adjustments, or adjustments to eyeglass prescriptions. 

Acronym: CVS. 

COM recorder n. Short for computer output microfilm 

recorder. A device that records computer information on 

microfilm. 

COMSAT n. See Communication Satellite Corporation. 

CON n. The logical device name for console; reserved by 

the MS-DOS operating system for the keyboard and the 

screen. The input-only keyboard and the output-only 

C

C 

concatenate condition code 

screen together make up the console and represent the primary 

sources of input and output in an MS-DOS computer 

system. 

concatenate vb. To join sequentially (for example, to 

combine the two strings “hello” and “there” into the single 

string “hello there”). See also character string. 

concatenated data set n. A group of separate sets of 

related data treated as a single unit for processing. 

concentrator n. A communications device that combines 

signals from multiple sources, such as terminals on a network, 

into one or more signals before sending them to 

their destination. Compare multiplexer (definition 2). 

conceptual schema n. In a database model that supports 

a three-schema architecture (such as that described by 

ANSI/X3/SPARC), a description of the information contents 

and structure of a database. A conceptual schema 

(also known as a logical schema) provides a model of the 

total database, thus acting as an intermediary between the 

two other types of schemas (internal and external) that 

deal with storing information and presenting it to the user. 

Schemas are generally defined using commands from a 

DDL (data definition language) supported by the database 

system. See also internal schema, schema. 

concordance n. A list of words that appear in a document, 

along with the contexts of the appearances. 

concrete class n. In object-oriented programming, a 

class in which objects can be created. See also class (definition 

1). Compare abstract class. 

concurrent adj. Of, pertaining to, or characteristic of a 

computer operation in which two or more processes (programs) 

have access to the microprocessor’s time and are 

therefore carried out nearly simultaneously. Because a 

microprocessor can work with much smaller units of time 

than people can perceive, concurrent processes appear to 

be occurring simultaneously but in reality are not. 

concurrent execution n. The apparently simultaneous 

execution of two or more routines or programs. Concurrent 

execution can be accomplished on a single process or 

by using time-sharing techniques, such as dividing programs 

into different tasks or threads of execution, or by 

using multiple processors. Also called: parallel execution. 

See also parallel algorithm, processor, sequential execution, 

task, thread (definition 1), time-sharing. 

concurrent operation n. See concurrent. 

concurrent processing n. See concurrent. 

122 

concurrent program execution n. See concurrent. 

Concurrent Versions System n. See CVS (definition 2). 

condensed adj. Of, pertaining to, or characteristic of a 

font style, supported in some applications, that reduces the 

width of each character and then sets the characters closer 

together than their normal spacing. Many dot-matrix printers 

have a feature that causes the printer to reduce the 

width of each character and print them closer together, 

resulting in more characters fitting on a single line. Compare 

expanded. 

condition n. The state of an expression or a variable (for 

example, when a result can be either true or false, or equal 

or not equal). 

conditional adj. Of, pertaining to, or characteristic of an 

action or operation that takes place based on whether or 

not a certain condition is true. See also Boolean expression, 

conditional statement. 

conditional branch n. In a program, a branch instruction 

that occurs when a particular condition code is true or 

false. The term is normally used in relation to low-level 

languages. See also branch instruction, condition code. 

conditional compilation n. Selective compilation or 

translation of source code of a program based on certain 

conditions or flags; for example, sections of a program 

specified by the programmer might be compiled only if a 

DEBUG flag has been defined at compilation time. See 

also comment out. 

conditional expression n. See Boolean expression. 

conditional jump n. In a program, a jump instruction that 

occurs when a particular condition code is true or false. 

The term is normally used in relation to low-level languages. 

See also condition code, jump instruction. 

conditional statement n. A programming-language 

statement that selects an execution path based on whether 

some condition is true or false (for example, the IF statement). 

See also case statement, conditional, IF statement, 

statement. 

conditional transfer n. A transfer of the flow of execution 

to a given location in a program based on whether a 

particular condition is true. The term is usually used in 

relation to high-level languages. See also conditional 

statement. 

condition code n. One of a set of bits that are set on (1, or 

true) or off (0, or false) as the result of previous machine 

instructions. The term is used primarily in assembly or

conditioning connection pooling 

machine language situations. Condition codes are hardware-specific 

but usually include carry, overflow, zero 

result, and negative result codes. See also conditional 

branch. 

conditioning n. The use of special equipment to improve 

the ability of a communications line to transmit data. Conditioning 

controls or compensates for signal attenuation, 

noise, and distortion. It can be used only on leased lines, 

where the path from sending to receiving computer is 

known in advance. 

conductor n. A substance that conducts electricity well. 

Metals are good conductors, with silver and gold being 

among the best. The most commonly used conductor is 

copper. Compare insulator, semiconductor. 

Conference on Data Systems Languages n. See 

CODASYL. 

CONFIG.SYS n. A special text file that controls certain 

aspects of operating-system behavior in MS-DOS and 

OS/2. Commands in the CONFIG.SYS file enable or disable 

system features, set limits on resources (for example, 

the maximum number of open files), and extend the operating 

system by loading device drivers that control hardware 

specific to an individual computer system. 

configuration n. 1. In reference to a single microcomputer, 

the sum of a system’s internal and external components, 

including memory, disk drives, keyboard, video, 

and generally less critical add-on hardware, such as a 

mouse, modem, or printer. Software (the operating system 

and various device drivers), the user’s choices established 

through configuration files such as the AUTOEXEC.BAT 

and CONFIG.SYS files on IBM PCs and compatibles, and 

sometimes hardware (switches and jumpers) are needed to 

“configure the configuration” to work correctly. Although 

system configuration can be changed, as by adding more 

memory or disk capacity, the basic structure of the system—its 

architecture—remains the same. See also 

AUTOEXEC.BAT, CONFIG.SYS. 2. In relation to networks, 

the entire interconnected set of hardware, or the 

way in which a network is laid out—the manner in which 

elements are connected. 

configuration file n. A file that contains machine-readable 

operating specifications for a piece of hardware or 

software or that contains information on another file or on 

a specific user, such as the user’s logon ID. 

congestion n. The condition of a network when the current 

load approaches or exceeds the available resources 

and bandwidth designed to handle that load at a particular 

123 

location in the network. Packet loss and delays are associated 

with congestion. 

connect charge n. The amount of money a user must 

pay for connecting to a commercial communications system 

or service. Some services calculate the connect charge 

as a flat rate per billing period. Others charge a varying 

rate based on the type of service or the amount of information 

being accessed. Still others base their charges on the 

number of time units used, the time or distance involved 

per connection, the bandwidth of each connected session, 

or some combination of the preceding criteria. See also 

connect time. 

connection n. A physical link via wire, radio, fiberoptic 

cable, or other medium between two or more communications 

devices. 

connection-based session n. A communications session 

that requires a connection to be established between 

hosts prior to an exchange of data. 

connectionism n. A model in artificial intelligence that 

advocates using highly parallel, specialized processes that 

compute simultaneously and are massively connected. 

Thus, the connectionist approach would not use a single 

high-speed processor to compute an algorithm, but would 

break out many simple specialized processing elements 

that are highly connected. Neural networks are classic 

examples of connectionism in that each “neuron” in the 

network may be assigned to a single processor. See also 

algorithm, artificial intelligence, neural network. 

connectionless adj. In communications, of, pertaining 

to, or characteristic of a method of data transmission that 

does not require a direct connection between two nodes on 

one or more networks. Connectionless communication is 

achieved by passing, or routing, data packets, each of 

which contains a source and destination address, through 

the nodes until the destination is reached. See also node 

(definition 2), packet (definition 2). Compare connectionoriented. 

connectionless session n. A communications session 

that does not require a connection to be established 

between hosts prior to an exchange of data. 

connection-oriented adj. In communications, of, pertaining 

to, or characteristic of a method of data transmission 

that requires a direct connection between two nodes 

on one or more networks. Compare connectionless. 

connection pooling n. A resource optimization feature 

of ODBC (Open Database Connectivity) 3 that results in 

C

C 

connectivity constellation 

more efficient sharing of database connections and 

objects. Connection pooling maintains open collections 

(pools) of database connections that can be used and 

reused by applications without the need to open and close 

a connection for each request. This is particularly important 

for Web-based applications. Connection pooling 

enables sharing among different components, maximizes 

performance, and minimizes the number of idle connections. 

See also ODBC. 

connectivity n. 1. The nature of the connection between 

a user’s computer and another computer, such as a server 

or a host computer on the Internet or a network. This may 

describe the quality of the circuit or telephone line, the 

degree of freedom from noise, or the bandwidth of the 

communications devices. 2. The ability of hardware 

devices or software packages to transmit data between 

other devices or packages. 3. The ability of hardware 

devices, software packages, or a computer itself to work 

with network devices or with other hardware devices, software 

packages, or a computer over a network connection. 

connectoid n. In Windows 9x and Windows NT, an icon 

representing a dial-up networking connection that will 

also execute a script for logging onto the network dialed. 

connector n. 1. In hardware, a coupler used to join cables 

or to join a cable to a device (for example, an RS-232-C 

connector used to join a modem cable to a computer). 

Most connector types are available in one of two genders—male 

or female. A male connector is characterized 

by one or more exposed pins; a female connector is characterized 

by one or more receptacles—sockets or jacks— 

designed to accept the pins on the male connector. See 

also DB connector, DIN connector. 2. In programming, a 

circular symbol used in a flowchart to indicate a break, as 

to another page. 

connect time n. The amount of time during which a user 

is actively connected to a remote computer. On commercial 

systems, the connect time is one means of calculating 

how much money the user must pay for using the system. 

See also connect charge. 

consistency check n. A survey to verify that items of 

data conform to certain formats, bounds, and other parameters 

and are not internally contradictory. Compare completeness 

check. 

console n. 1. A control unit, such as a terminal, through 

which a user communicates with a computer. In microcomputers, 

the console is the cabinet that houses the main 

components and controls of the system, sometimes includ- 

124 

ing the screen, the keyboard, or both. With the MS-DOS 

operating system, the console is the primary input (keyboard) 

and primary output device (screen), as evidenced by 

the device name CON. See also CON, system console. 

2. See game console. 

console game n. A special-purpose computer system 

designed specifically for the home user to play video 

games. A game console typically includes a CPU, one or 

more game controllers, audio output, and a video output 

that connects to a television set. Individual games and 

memory cards are supplied on plug-in cartridges or compact 

discs. Many recent versions are 128-bit systems and 

also include a modem for online gaming over the Internet. 

Well-known console games include Microsoft Xbox, Sony 

PlayStation 2, Nintendo GameCube, and Sega Dreamcast. 

Also called: game console. Compare arcade game. See 

also computer game, Dreamcast, GameCube, PlayStation, 

Xbox. 

constant n. A named item that retains a consistent value 

throughout the execution of a program, as opposed to a 

variable, which can have its value changed during execution. 

Compare variable. 

constant expression n. An expression that is composed 

only of constants and, hence, whose value does not change 

during program execution. Compare variable expression. 

constellation n. In communications, a pattern representing 

the possible states of a carrier wave, each of 

which is associated with a particular bit combination. A 

constellation shows the number of states that can be recognized 

as unique changes in a communications signal 

and thus the maximum number of bits that can be 

encoded in a single change (equivalent to 1 baud, or one 

event). See the illustration. 

0111 0110 0010 0001 

0100 0101 0011 0000 

1100 1111 1001 1000 

1101 1110 1010 1011 

f0cgn14.eps 

Constellation.

constraint content provider 

constraint n. In programming, a restriction on the solutions 

that are acceptable for a problem. 

consultant n. A computer professional who deals with 

client firms as an independent contractor rather than as an 

employee. Consultants are often engaged to analyze user 

needs and develop system specifications. 

Consumer Electronics Show n. Annual tradeshow of 

the consumer electronics industry, held in Las Vegas, 

Nevada. CES features exhibits of the latest consumer electronics 

products and conference events that focus on consumer 

trends and business strategies. Acronym: CES. 

contact manager n. A type of specialized database that 

allows a user to maintain a record of personal communication 

with others. Contact managers are widely used by 

salespeople and others who want to keep track of conversations, 

e-mail, and other forms of communication with a 

large number of current and prospective customers or clients. 

See also database. 

container n. 1. In OLE terminology, a file containing 

linked or embedded objects. See also OLE. 2. In SGML, 

an element that has content as opposed to one consisting 

solely of the tag name and attributes. See also element, 

SGML, tag. 3. In Sun Microsystem’s J2EE network platform, 

an entity that provides life cycle management, security, 

deployment, and runtime services to components such 

as beans, Web components, applets, and application clients. 

Each type of container created (for example, EJB, 

Web, JSP, servlet, applet, and application client) also provides 

component-specific services. See also applet, component 

(definition 3), enterprise java bean, JSP, servlet. 

container object n. An object that can logically contain 

other objects. For example, a folder is a container object. 

See also noncontainer object, object. 

content n. 1. The data that appears between the starting 

and ending tags of an element in an SGML, XML, or 

HTML document. The content of an element may consist 

of plain text or other elements. See also element (definition 

2), HTML, SGML, tag (definition 3). 2. The message body 

of a newsgroup article or e-mail message. 3. The “meat” of 

a document, as opposed to its format or appearance. 

content-addressed storage n. See associative storage. 

content aggregator n. 1. Broadly, an organization or 

business that groups Internet-based information by topic 

or area of interest—for example, sports scores, business 

news, or online shopping—to provide users with a means 

of accessing that content from a single location. 2. In 

125 

terms of push technology and multicasting, a service business 

that mediates between subscribers (“customers”) and 

content providers by gathering and organizing information 

for broadcast over the Internet. Content aggregators supply 

subscribers with client software through which content 

providers broadcast (push) information via “channels” that 

allow users both to choose the kind of information they 

receive and to decide when they want it updated. Also 

called: channel aggregator. See also push, webcasting. 

Compare content provider. 

content caching n. See content delivery. 

content delivery n. The process of caching the pages of 

a Web site on geographically dispersed servers to enable 

faster delivery of Web pages. When a page is requested at 

a URL that is content-delivery enabled, the content-delivery 

network routes the user’s request to a cache server 

closer to the user. Content delivery frequently is used for 

high-traffic Web sites or for specific high-traffic events. 

Also called: content distribution, content caching. 

content distribution n. See content delivery. 

contention n. On a network, competition among nodes 

for the opportunity to use a communications line or network 

resource. In one sense, contention applies to a situation 

in which two or more devices attempt to transmit at 

the same time, thus causing a collision on the line. In a 

somewhat different sense, contention also applies to a 

free-for-all method of controlling access to a communications 

line, in which the right to transmit is awarded to the 

station that wins control of the line. See also CSMA/CD. 

Compare token passing. 

Content Management Server n. Automated software 

application developed by Microsoft Corporation to assist 

nontechnical users in creating, tracking, and publishing 

content for Web sites. A workflow system delineates the 

tasks each user can perform, assigns content to individuals 

or groups, and allows users to monitor the status of content 

with which they are associated. 

Content Protection for Recordable Media n. See 

CPRM. 

content provider n. 1. Broadly, an individual, group, or 

business that provides information for viewing or distribution 

on the Internet or on private or semiprivate intranets or 

extranets. Content in this sense includes not only information 

but also video, audio, software, listings of Web sites, 

and product-specific materials such as online catalogs. 

2. A service business that makes Internet information 

C

C 

Content Scrambling System contouring 

resources available to users. Content providers include 

online services such as America Online and CompuServe, 

Internet service providers (ISPs), and an increasing number 

of media companies representing television, long-distance 

telephone, and publishing industries. See also ISP, 

online information service. Compare content aggregator. 

Content Scrambling System n. See CSS. 

contents directory n. A series of queues that contain the 

descriptors and addresses of routines located within a 

region of memory. 

context-dependent adj. Of, pertaining to, or characteristic 

of a process or a set of data characters whose meaning 

depends on the surrounding environment. 

context-sensitive help n. A form of assistance in which 

a program that provides on-screen help shows information 

to the user concerning the current command or operation 

being attempted. 

context-sensitive menu n. A menu that highlights 

options as available or unavailable depending on the context 

in which the option is called. The menus on Windows’ 

menu bar, for example, are context sensitive; options such 

as copy are grayed out if nothing is selected. 

context switching n. A type of multitasking; the act of 

turning the central processor’s “attention” from one task to 

another, rather than allocating increments of time to each 

task in turn. See also multitasking, time slice. 

contextual search n. A search operation in which the 

user can direct a program to search specified files for a 

particular set of text characters. 

contiguous adj. Having a shared boundary; being immediately 

adjacent. For example, contiguous sectors on a 

disk are data-storage segments physically located next to 

one another. 

contiguous data structure n. A data structure, such as 

an array, that is stored in a consecutive set of memory 

locations. See also data structure. Compare noncontiguous 

data structure. 

continuous carrier n. In communications, a carrier signal 

that remains on throughout the transmission, whether 

or not it is carrying information. 

continuous-form paper n. Paper in which each sheet is 

connected to the sheets before and after it, for use with 

most impact and ink-jet printers and some other printing 

devices designed with an appropriate paper-feed mechanism. 

The paper usually has holes punched along each side 

126 

so that it can be pulled by a tractor-feed device. See the 

illustration. See also pin feed, sprocket feed, tractor feed. 

f0cgn15.eps 

Continuous-form paper. 

continuous processing n. The processing of transactions 

as they are input to the system. Compare batch processing 


continuous speech recognition n. A type of automatic 

speech recognition (ASR) technology that responds to 

strings of words. Continuous speech recognition allows a 

user to speak in a natural voice without the need to slow 

down and enunciate each word separately. Continuous 

speech recognition software takes advantage of context in 

recognizing words, and thus will not operate at full efficiency 

if each word is spoken with distinct separation. See 

also ASR (definition 2). 

continuous-tone image n. An image, such as a photograph, 

in which color or varying shades of gray are reproduced 

as gradients rather than as clustered or variably 

sized dots, as in traditional book or newspaper printing. 

Continuous-tone images can be viewed on an analog monitor 

(such as a television monitor), which accepts input as 

a continuously variable signal. They cannot be viewed on 

a digital monitor, which requires input broken into discrete 

units, nor can they be printed in books or newspapers, 

which represent illustrations as groups of dots. See also 

scan (definition 2), video digitizer. Compare halftone. 

continuous-tone printer n. A printer that produces an 

image using smoothly blended levels of continuous ink for 

gradations of gray or color. Compare dithering. 

contouring n. 1. In computer graphics, such as CAD 

models, the representation of the surface of an object—its 

bumps and crannies. See the illustration. 2. In image processing, 

the loss of detail that occurs in a shaded image 

when too few gradations of gray are used to reproduce a 

graphic, such as a photograph. In photography and graphic 

arts, this phenomenon is sometimes called posterization.

contrast Control key 

f0cgn16.eps 

Contouring. 

contrast n. 1. The degree of difference between light and 

dark extremes of color on a monitor or on printed output. 

2. The control knob by which the contrast of a monitor is 

changed. 

control n. 1. Management of a computer and its processing 

abilities so as to maintain order as tasks and activities 

are carried out. Control applies to measures designed to 

ensure error-free actions carried out at the right time and 

in the right order relative to other data-handling or hardware-based 

activities. In reference to hardware, control of 

system operations can reside in a data pathway called a 

control bus. In reference to software, control refers to program 

instructions that manage data-handling tasks. 2. In a 

graphical user interface, an object on the screen that can 

be manipulated by the user to perform an action. The most 

common controls are buttons, which allow the user to 

select options, and scroll bars, which allow the user to 

move through a document or position text in a window. 

control break n. A transition in control of the computer 

that typically gives control of the CPU (central processing 

unit) to the user console or to some other program. 

Control-Break n. See Break key. 

control bus n. The set of lines (conductors) within a 

computer that carry control signals between the CPU (central 

processing unit) and other devices. For example, a 

control bus line is used to indicate whether the CPU is 

attempting to read from memory or to write to it; another 

control bus line is used by memory to request an interrupt 

in case of a memory error. 

control character n. 1. Any of the first 32 characters in 

the ASCII character set (0 through 31 in decimal representation), 

each of which is defined as having a standard control 

function, such as carriage return, linefeed, or backspace. 

2. Any of the 26 characters Control-A through Control-Z 

(1 through 26 in decimal representation) that can be typed 

127 

at the keyboard by holding the Control key down and typing 

the appropriate letter. The six remaining characters 

with control functions, such as Escape (ASCII 27), cannot 

be typed using the Control key. Compare control code. 

control code n. One or more nonprinting characters used 

by a computer program to control the actions of a device, 

used in printing, communications, and management of display 

screens. Control codes are mainly employed by programmers 

or by users to control a printer when an 

application program does not support the printer or one of 

its specialized features. In video, control codes are sent 

from a computer to a display unit to manipulate the appearance 

of text or a cursor on the screen. Popular video control 

code sets are ANSI and VT-100. Also called: escape 

sequence, setup string. See also control character. 

control console n. See console. 

control data n. Data that consists of information about 

timing and switching, used to synchronize and route other 

data or to manage the operation of a device such as a bus 

or a port. 

control flow n. The tracing of all possible execution paths 

in a program, often represented in the form of a diagram. 


No input 

Read input 

Quit Open database 

No records 

Process errors 

Read records 

Send record to 

output 

f0cgn17.eps 

Control flow. 

Control key n. A key that, when pressed in combination 

with another key, gives the other key an alternative meaning. 

In many application programs, Control (labeled 

CTRL or Ctrl on a PC keyboard) plus another key is used 

as a command for special functions. See the illustration. 

See also control character (definition 2). 

C

C 

hift 

controller conversational language 

f0cgn18.eps 

Control key. 

\ 

Control 

controller n. A device that other devices rely on for 

access to a computer subsystem. A disk controller, for 

example, controls access to one or more disk drives, managing 

physical and logical access to the drive or drives. 

control logic n. The electronic circuitry that generates, 

interprets, and uses control data. 

control panel n. In Windows and Macintosh systems, a 

utility that allows the user to control aspects of the operating 

system or hardware, such as system time and date, 

keyboard characteristics, and networking parameters. 

control panel device n. See cdev. 

control sequence n. See control code. 

control signal n. An electronic signal used to control 

internal or external devices or processes. 

control statement n. A statement that affects the flow of 

execution through a program. Control statements include 

conditional statements (CASE, IF-THEN-ELSE), iterative 

statements (DO, FOR, REPEAT, WHILE), and transfer 

statements (GOTO). See also conditional statement, iterative 

statement, statement, transfer statement. 

control strip n. 1. An equipment calibration tool used to 

determine the corrections needed to restore accuracy by 

comparing recorded data against known values. 2. A utility 

that groups shortcuts to commonly used items or information, 

such as time, battery power level, desktop items, 

and programs, in an easily accessible place. See also 

shortcut. 

control structure n. A portion of a program defined by 

the relationship between the statements, used in structured 

programming. There are three basic control structures: 

sequence, where one statement simply follows another; 

selection, where program flow depends on which criteria 

are met; and iteration, where an action is repeated until 

some condition occurs. 

control unit n. A device or circuit that performs an arbitrating 

or regulating function. For example, a memory 

128 

controller chip controls access to a computer’s memory 

and is the control unit for that memory. 

control variable n. In programming, the variable in a 

control statement that dictates the flow of execution. For 

example, the index variable in a FOR loop controls the 

number of times a group of statements are executed. See 

also control statement. 

convenience adapter n. See port replicator. 

convention n. Any standard that is used more or less universally 

in a given situation. Many conventions are applied 

to microcomputers. In programming, for example, a language 

such as C relies on formally accepted symbols and 

abbreviations that must be used in programs. Less formally, 

programmers usually adopt the convention of indenting 

subordinate instructions in a routine so that the structure of 

the program is more easily visualized. National and international 

committees often discuss and arbitrate conventions 

for programming languages, data structures, communication 

standards, and device characteristics. See also CCITT, 

ISO, NTSC, standard (definition 1). 

conventional memory n. The amount of RAM addressable 

by an IBM PC or compatible machine operating in 

real mode. This is typically 640 kilobytes (KB). Without 

the use of special techniques, conventional memory is the 

only kind of RAM accessible to MS-DOS programs. See 

also protected mode, real mode. Compare expanded memory, 

extended memory. 

convergence n. A coming together. Convergence can 

occur between different disciplines and technologies, as 

when telephone communications and computing converge 

in the field of telecommunications. It can also occur within 

a program, such as a spreadsheet, when a circular set of 

formulas are repeatedly recalculated (iterated), with the 

results of each iteration coming closer to a true solution. 

conversational adj. Of, pertaining to, or characteristic of 

the mode of operation, typical of microcomputers, in which 

the computer user and the system engage in a dialogue of 

commands and system responses. See also interactive. 

conversational interaction n. Interaction in which two 

or more parties alternately transmit and receive messages 

from each other. See also interactive processing. 

conversational language n. Any programming language 

that allows the programmer to instruct the computer 

in a conversational mode, as opposed to more formal, 

structured languages. For example, in a COBOL program, 

in order to execute a procedure called CHECK 10 times, a

conversational mode coordinate 

program would use the following statement: PERFORM 

CHECK 10 TIMES. 

conversational mode n. See conversational. 

conversion n. The process of changing from one form or 

format to another; where information is concerned, a 

changeover that affects form but not substance. Types of 

conversion include data (changing the way information is 

represented), file (changing a file from one format to 

another), hardware (changing all or part of a computer 

system), media (transferring data from one storage media 

to another), software (changing a program designed for 

one platform so that it runs on another), and system 

(changing from one operating system to another). 

conversion table n. A table listing a set of characters or 

numbers and their equivalents in another coding scheme. 

Common examples of conversion tables include ASCII 

tables, which list characters and their ASCII values, and 

decimal-to-hexadecimal tables. Several conversion tables 

are in Appendixes A-E. 

converter n. Any device that changes electrical signals or 

computer data from one form to another. For example, an 

analog-to-digital converter translates analog signals to 

digital signals. 

converter box n. See converter. 

cookbook1 adj. Of, pertaining to, or characteristic of a 

book or manual that presents information using a step-bystep 

approach. For example, a cookbook approach to programming 

might present a series of sample programs that 

the reader could analyze and adapt to his or her own 

needs. 

cookbook2 n. A computer book or manual that presents 

information using a step-by-step approach. Most often, 

cookbook refers to a programming guide, but it can refer 

to a book that shows how to accomplish specialized tasks 

in an application. 

cooked mode n. One of two forms (the other being raw 

mode) in which an operating system such as UNIX or 

MS-DOS “sees” the handle, or identifier, for a characterbased 

device. If the handle is in cooked mode, the operating 

system stores each character in a buffer and gives 

special treatment to carriage returns, end-of-file markers, 

and linefeed and tab characters, sending a line of data to a 

device, such as the screen, only after it reads a carriagereturn 

or end-of-file character. In cooked mode, characters 

129 

read from standard input are often automatically echoed 

(displayed) on the screen. Compare raw mode. 

cookie n. 1. A block of data that a server returns to a client 

in response to a request from the client. 2. On the 

World Wide Web, a block of data that a Web server stores 

on a client system. When a user returns to the same Web 

site, the browser sends a copy of the cookie back to the 

server. Cookies are used to identify users, to instruct the 

server to send a customized version of the requested Web 

page, to submit account information for the user, and for 

other administrative purposes. 3. Originally an allusion to 

fortune cookie, a UNIX program that outputs a different 

message, or “fortune,” each time it is used. On some systems, 

the cookie program is run during user logon. 

cookie filtering tool n. A utility that prevents a cookie 

on a Web browser from relaying information about the 

user requesting access to a Web site. See also cookie (definition 

2). 

cookies policy n. A statement that describes a Web site’s 

policy regarding cookies. The policy usually defines a 

cookie, explains the types of cookies used by the Web site, 

and describes how the Web site uses the information 

stored in the cookies. 

.coop n. One of seven new top-level domain names 

approved in 2000 by the Internet Corporation for Assigned- 

Names and Numbers (ICANN), .coop is meant for use 

with the Web sites of nonprofit cooperatives. The seven 


of 2001. 

cooperative multitasking n. A type of multitasking in 

which one or more background tasks are given processing 

time during idle times in the foreground task only if the 

foreground task allows it. This is the primary mode of 

multitasking in the Macintosh operating system. See also 

background1 , context switching, foreground1 , multitasking, 

time slice. Compare preemptive multitasking. 

cooperative processing n. A mode of operation characteristic 

of distributed systems in which two or more computers, 

such as a mainframe and a microcomputer, can 

simultaneously carry out portions of the same program or 

work on the same data. Compare distributed processing. 

coordinate n. Any element in a group of references to a 

particular location, such as the intersection of a certain 

row and column. In computer graphics and displays, 

C

C 

coordinate dimensioning copyright 

coordinates specify such elements as points on a line, the 

corners of a square, or the location of a pixel on the 

screen. In other computer applications, coordinates specify 

cells on a spreadsheet, data points on a graph, locations 

in memory, and so on. See also Cartesian 

coordinates, polar coordinates. 

coordinate dimensioning n. A form of spatial positioning 

in which a point is described, relative to a fixed reference, 

in terms of its distance and direction along 

predefined axes. See also Cartesian coordinates, threedimensional 

model, two-dimensional model. 

coordinated universal time format n. See Universal 

Time Coordinate. 

coordinate pair n. A pair of values representing the xcoordinate 

and y-coordinate of a point that are stored in a 

two-dimensional array that can contain coordinates for 

many points. 

COPPA n. Acronym for Children’s Online Privacy Protection 

Act. A U.S. federal law enacted in April 2000 and 

designed to protect the online privacy of children under 

the age of 13. COPPA requires Web sites that collect personal 

information from children under 13 to receive permission 

from parents or guardians first, and to monitor 

and supervise children’s experiences with interactive Web 

elements such as chat rooms and e-mail. 

copper chip n. A microprocessor that uses copper (rather 

than the more common aluminum) to connect transistors 

in a computer chip. Copper chip technology, which was 

developed by IBM and introduced in 1997, can be 

expected to boost the speed of a microprocessor by as 

much as 33 percent. 

coprocessor n. A processor, distinct from the main 

microprocessor, that performs additional functions or 

assists the main microprocessor. The most common type 

of coprocessor is the floating-point coprocessor, also 

called a numeric or math coprocessor, which is designed 

to perform numeric calculations faster and better than the 

general-purpose microprocessors used in personal computers. 

See also floating-point processor. 

copy vb. To duplicate information and reproduce it in 

another part of a document, in a different file or memory 

location, or in a different medium. A copy operation can 

affect data ranging from a single character to large segments 

of text, a graphics image, or from one to many data 

130 

files. Text and graphics, for example, can be copied to 

another part of a document, to the computer’s memory (by 

means of a temporary storage facility such as the Windows 

or Macintosh Clipboard), or to a different file. Similarly, 

files can be copied from one disk or directory to another, 

and data can be copied from the screen to a printer or to a 

data file. In most cases, a copy procedure leaves the original 

information in place. Compare cut and paste, move. 

copy disk n. An MS-DOS command to duplicate the contents 

of a floppy disk on a second disk. See also floppy 

disk, MS-DOS. 

copy holder n. An inclined clipboard or other such device 

designed to hold printed material so that it can be easily 

viewed by someone working at a computer keyboard. 

copyleft n. See General Public License. 

copy program n. 1. A program designed to duplicate one 

or more files to another disk or directory. 2. A program 

that disables or circumvents the copy-protection device on 

a computer program so that the software can be copied, 

often illegally, to another disk. See also copy protection. 

copy protection n. A software lock placed on a computer 

program by its developer to prevent the product from being 

copied and distributed without approval or authorization. 

copyright n. A method of protecting the rights of an originator 

of a creative work, such as a text, a piece of music, a 

painting, or a computer program, through law. In many 

countries the originator of a work has copyright in the 

work as soon as it is fixed in a tangible medium (such as a 

piece of paper or a disk file); that rule applies in the 

United States for works created after 1977. Registration of 

a copyright, or the use of a copyright symbol, is not 

needed to create the copyright but does strengthen the 

originator’s legal powers. Unauthorized copying and distribution 

of copyrighted material can lead to severe penalties, 

whether done for profit or not. Copyrights affect the 

computer community in three ways: the copyright protection 

of software, the copyright status of material (such as 

song lyrics) distributed over a network such as the Internet, 

and the copyright status of original material distributed 

over a network (such as a newsgroup post). The latter 

two involve electronic media that are arguably not tangible, 

and legislation protecting the information disseminated 

through electronic media is still evolving. See also 

fair use, General Public License.

CORBA CP/M 

CORBA n. Acronym for Common Object Request Broker 

Architecture. A specification developed by the Object 

Management Group in 1992 in which pieces of programs 

(objects) communicate with other objects in other programs, 

even if the two programs are written in different 

programming languages and are running on different platforms. 

A program makes its request for objects through an 

object request broker, or ORB, and thus does not need to 

know the structure of the program from which the object 

comes. CORBA is designed to work in object-oriented 

environments. See also IIOP, object (definition 2), Object 

Management Group, object-oriented. 

core n. One of the types of memory built into computers 

before random access memory (RAM) was available or 

affordable. Some people still use the term to refer to the 

main memory of any computer system, as in the phrase 

core dump—a listing of the raw contents of main memory 

at the moment of a system crash. Compare RAM. 

core class n. In the Java programming language, a public 

class or interface that is a standard member of the language. 

Core classes, at minimum, are available on all 

operating systems where the Java platform runs. A program 

written entirely in the Java programming language 

relies only on core classes. See also class (definition 1), 

object, object-oriented programming. 

core program n. A program or program segment that is 

resident in random access memory (RAM). 

coresident adj. Of or pertaining to a condition in which 

two or more programs are loaded in memory at the same 

time. 

corona wire n. In laser printers, a wire though which high 

voltage is passed to ionize the air and transfer a uniform 

electrostatic charge to the photosensitive medium in preparation 

for the laser. 

coroutine n. A routine that is in memory at the same time 

as, and frequently executed concurrently with, another. 

corrective maintenance n. The process of diagnosing 

and correcting computer problems after they occur. Compare 

preventive maintenance. 

correspondence quality n. See print quality. 

corruption n. A process wherein data in memory or on 

disk is unintentionally changed, with its meaning thereby 

altered or obliterated. 

131 

cost-benefit analysis n. The comparison of benefits to 

costs for a particular item or action. Cost-benefit analysis 

is often used in MIS or IS departments to determine such 

things as whether purchasing a new computer system is a 

good investment or whether hiring more staff is necessary. 

See also IS, MIS. 

coulomb n. A unit of electrical charge equivalent to 

roughly 6.26 x 1018 electrons, with a negative charge 

being an excess of electrons and a positive charge being a 

deficiency of electrons. 

counter n. 1. In programming, a variable used to keep 

count of something. 2. In electronics, a circuit that counts 

a specified number of pulses before generating an output. 

3. A device that keeps track of the number of visitors to a 

World Wide Web site. 

counting loop n. In a program, a group of statements that 

are repeated, thereby incrementing a variable used as a 

counter (for example, a program might repeat a counting 

loop that adds 1 to its counter until the counter equals 10). 

See also loop1 (definition 1). 

country code n. See major geographic domain. 

country-specific adj. Of, pertaining to, or characteristic 

of hardware or software that uses characters or conventions 

unique to a particular country or group of countries. 

Country-specific does not necessarily refer to spoken languages, 

although it does allow for special characters (such 

as accent marks) that are language-specific. Generally, the 

features considered country-specific include keyboard layout 

(including special-character keys), time and date conventions, 

financial and monetary symbols, decimal 

notation (decimal point or comma), and alphabetic sorting 

order. Such features are handled either by a computer’s 

operating system (for example, by the Keyboard and 

Country commands in MS-DOS) or by application programs 

that offer options for tailoring documents to a particular 

set of national or international conventions. 

courseware n. Software dedicated to education or training. 

courtesy copy n. See cc. 

CPA n. See Computer Press Association. 

CPCP n. See HTCPCP. 

cpi n. See characters per inch. 

CP/M n. Acronym for Control Program/Monitor. A line 

of operating systems from Digital Research, Inc. (DRI), 

C

C 

CPM cracker 

for microcomputers based on Intel microprocessors. The 

first system, CP/M-80, was the most popular operating 

system for 8080- and Z80-based microcomputers. Digital 

Research also developed CP/M-86 for 8086/8088-based 

computers, CP/M-Z8000 for Zilog Z8000-based computers, 

and CP/M-68K for Motorola 68000-based computers. 

When the IBM PC and MS-DOS were introduced, common 

use of CP/M by end users dwindled. DRI continues to 

enhance the CP/M line, supporting multitasking with the 

Concurrent CP/M and MP/M products. See also MP/M. 

CPM n. See critical path method. 

CPRM n. Acronym for Content Protection for Recordable 

Media. Technology developed to control the use of 

copyrighted digital music and video material by blocking 

the transfer of protected files to portable media such as zip 

disks and smart cards. CPRM would be added to storage 

devices and provide data scrambling and identification 

codes to block the copying of copyrighted files. 

cps n. See characters per second. 

CPSR n. Acronym for Computer Professionals for Social 

Responsibility. A public advocacy organization of computer 

professionals. CPSR was originally formed out of 

concern over the use of computer technology for military 

purposes but has extended its interest to such issues as 

civil liberties and the effect of computers on workers. 

CPU n. Acronym for central processing unit. The computational 

and control unit of a computer. The CPU is the 

device that interprets and executes instructions. Mainframes 

and early minicomputers contained circuit boards 

full of integrated circuits that implemented the CPU. Single-chip 

central processing units, called microprocessors, 

made possible personal computers and workstations. 

Examples of single-chip CPUs are the Motorola 68000, 

68020, and 68030 chips and the Intel 8080, 8086, 80286, 

80386, and i486 chips. The CPU—or microprocessor, in 

the case of a microcomputer—has the ability to fetch, 

decode, and execute instructions and to transfer information 

to and from other resources over the computer’s main 

data-transfer path, the bus. By definition, the CPU is the 

chip that functions as the “brain” of a computer. In some 

instances, however, the term encompasses both the processor 

and the computer’s memory or, even more broadly, the 

main computer console (as opposed to peripheral equipment). 

See the illustration. See also microprocessor. 

132 

f0cgn19.eps 

CPU. 

CPU-bound adj. See computation-bound. 

CPU cache n. A section of fast memory linking the CPU 

(central processing unit) and main memory that temporarily 

stores data and instructions the CPU needs to execute 

upcoming commands and programs. Considerably 

faster than main memory, the CPU cache contains data 

that is transferred in blocks, thereby speeding execution. 

The system anticipates the data it will need through algorithms. 

Also called: cache memory, memory cache. See 

also cache, CPU, VCACHE. 

CPU cycle n. 1. The smallest unit of time recognized by 

the CPU (central processing unit)—typically a few hundred-millionths 

of a second. 2. The time required for the 

CPU to perform the simplest instruction, such as fetching 

the contents of a register or performing a no-operation 

instruction (NOP). Also called: clock tick. 

CPU fan n. An electric fan usually placed directly on a 

CPU (central processing unit) or on the CPU’s heat sink to 

help dissipate heat from the chip by circulating air around 

it. See also CPU, heat sink. 

CPU speed n. A relative measure of the data-processing 

capacity of a particular CPU (central processing unit), 

usually measured in megahertz. See also CPU. 

CPU time n. In multiprocessing, the amount of time during 

which a particular process has active control of the CPU 

(central processing unit). See also CPU, multiprocessing. 

CR n. See carriage return. 

crack vb. 1. To gain unauthorized access to a network by 

breaching its security. 2. To decipher encrypted information. 

cracker n. A person who overcomes the security measures 

of a computer system and gains unauthorized access. 

The goal of some crackers is to obtain information ille-

cradle critical path method 

gally from a computer system or use computer resources. 

However, the goal of the majority is only to break into the 

system. See also hacker (definition 2). 

cradle n. A receptacle used to recharge the batteries in 

some handheld or palm-size PCs or PDAs (personal digital 

assistants). Some cradles also serve as a means to connect 

these smaller devices with a desktop PC. Not all of 

these devices require a cradle to recharge or connect to a 

desktop system. Also called: dock, docking station. 

cramfs n. Short for Compressed Read-Only File System 

and cram a filesystem onto a small ROM. A filesystem 

feature available with Linux version 2.4 systems. Cramfs 

are used in handheld Linux devices to compress and write 

applications to ROM or Flash memory. 

crash1 n. The failure of either a program or a disk drive. 

A program crash results in the loss of all unsaved data and 

can leave the operating system unstable enough to require 

restarting the computer. A disk drive crash, sometimes 

called a disk crash, leaves the drive inoperable and can 

cause loss of data. See also abend, head crash. 

crash2 vb. 1. For a system or program, to fail to function 

correctly, resulting in the suspension of operation. See 

also abend. 2. For a magnetic head, to hit a recording 

medium, with possible damage to one or both. 

crash recovery n. The ability of a computer to resume 

operation after a disastrous failure, such as the failure of a 

hard drive. Ideally, recovery can occur without any loss of 

data, although usually some, if not all, data is lost. See 

also crash1 . 

crawl vb. To compile and organize entries for a search 

engine by reading Web pages and related information. 

Crawling is typically performed by programs called 

“spiders.” 

crawler n. See spider, Web browser. 

Cray-1 n. An early supercomputer developed in 1976 by 

Seymour Cray. Extremely powerful in its day, the 64-bit 

Cray-1 ran at 75 MHz and was capable of executing 160 

million floating-point operations per second. See also 

supercomputer. 

CRC n. Acronym for cyclical (or cyclic) redundancy 

check. A procedure used in checking for errors in data 

transmission. CRC error checking uses a complex calculation 

to generate a number based on the data transmitted. 

The sending device performs the calculation before transmission 

and includes it in the packet that it sends to the 

133 

receiving device. The receiving device repeats the same 

calculation after transmission. If both devices obtain the 

same result, it is assumed that the transmission was error 

free. The procedure is known as a redundancy check 

because each transmission includes not only data but extra 

(redundant) error-checking values. Communications protocols 

such as XMODEM and Kermit use cyclical redundancy 

checking. 

create method n. In Java programming, a method 

defined in the home interface and invoked by a client to 

create an enterprise java bean. See also enterprise java 

bean, method. 

creator n. On the Apple Macintosh, the program that creates 

a file. Files are linked to their creators by creator 

codes; this link enables the operating system to open the 

creator application when a document file is opened. 

credentials n. A set of information that includes identification 

and proof of identification that is used to gain 

access to local and network resources. Examples of credentials 

are user names and passwords, smart cards, and 

certificates. 

creeping featurism n. The process by which features are 

added to a new version of a program by software developers 

until the program becomes unduly cumbersome and 

difficult to use. Generally, creeping featurism occurs as 

developers attempt to enhance the competitiveness of the 

program with each new release by adding new features. 

crippled version n. A scaled-down or functionally 

reduced version of hardware or software, distributed for 

demonstration purposes. See also demo. 

critical error n. An error that suspends processing until 

the condition can be corrected either by software or by 

user intervention (for example, an attempt to read to a 

nonexistent disk, an out-of-paper condition on the printer, 

or a checksum fault in a data message). 

critical-error handler n. A software routine that attempts 

to correct or achieve a graceful exit from a critical or 

threatening error. See also critical error, graceful exit. 

critical path method n. A means of evaluating and managing 

a large project by isolating tasks, milestone events, 

and schedules and by showing interrelationships among 

them. The critical path for which this method is named is a 

line connecting crucial events, any of which, if delayed, 

affects subsequent events and, ultimately, completion of 

the project. Acronym: CPM. 

C

C 

crop cross-site scripting 

crop vb. In computer graphics, to cut off part of an image, 

such as unneeded sections of a graphic or extra white 

space around the borders. As in preparing photographs or 

illustrations for traditional printing, cropping is used to 

refine or clean up a graphic for placement in a document. 

crop marks n. 1. Lines drawn at the edges of pages to 

mark where the paper will be cut to form pages in the final 

document. See the illustration. See also registration marks. 

2. Lines drawn on photographs or illustrations to indicate 

where they will be cropped, or cut. See also crop. 

f0cgn20.eps 

Crop marks. 

cross-assembler n. An assembler that executes on one 

hardware platform but generates machine code for 

another. See also assembler, compiler, cross-compiler, 

cross development. 

cross-check vb. To check the accuracy of a calculation 

by using another method to verify the result. Compare 

cross-foot. 

cross-compiler n. A compiler that executes on one hardware 

platform but generates object code for another. See 

also assembler, compiler (definition 2), cross-assembler, 

cross development. 

cross development n. The use of one system to develop 

programs for a different type of system, often because the 

software development tools of the development system are 

superior to those of the target system. 

cross-foot vb. To check the accuracy of a total, as on a 

ledger sheet, by adding across columns and down rows, all 

figures contributing to the total. 

cross hairs n. Intersecting lines used by some computer 

input devices to locate a particular x-y-coordinate. 

134 

cross-hatching n. Shading made up of regularly spaced, 

intersecting lines. Cross-hatching is one of several methods 

for filling in areas of a graphic. See the illustration. 

f0cgn21.eps 

Cross-hatching. 

Cross-hatching 

cross-linked files n. In Windows 9x, Windows 3.x, and 

MS-DOS, a file-storage error occurring when one or more 

sections, or clusters, of the hard drive or a floppy disk 

have been erroneously allocated to more than one file in 

the file allocation table. Like lost clusters, cross-linked 

files can result from the ungraceful exit (messy or abrupt 

termination) of an application program. See also file allocation 

table, lost cluster. 

crossover cable n. A cable used to connect two computers 

together for file sharing and personal networking. 

Crossover cables may be connected to Ethernet or 

FireWire ports. 

cross-platform adj. Of, pertaining to, or characteristic of 

a software application or hardware device that can be run 

or operated on more than one system platform. 

cross-post vb. To copy a message or news article from 

one newsgroup, conference topic, e-mail system, or other 

communications channel to another—for example, from a 

Usenet newsgroup to a CompuServe forum or from e-mail 

to a newsgroup. 

cross-site scripting n. A security vulnerability of 

dynamic Web pages generated from a database in response 

to user input. With cross-site scripting, a malicious user 

introduces unwanted executable script or code into 

another user’s Web session. Once running, this script 

could allow others to monitor the user’s Web session, 

change what is displayed on the screen, or shut down the 

Web browser. Web sites that allow visitors to add comments 

or make other additions or changes to the pages are 

the most vulnerable to this flaw. Cross-site scripting is not 

restricted to the products of a particular vendor or a particular 

operating system. See also script.

crosstab query CSMA/CD 

crosstab query n. A query that calculates a sum, an average, 

a count, or other type of total on records, and then 

groups the result by two types of information—one down 

the left side of the datasheet and the other across the top. 

crosstalk n. Interference caused by a signal transferring 

from one circuit to another, as on a telephone line. 

CRT n. Acronym for cathode-ray tube. The basis of the 

television screen and the standard microcomputer display 

screen. A CRT display is built around a vacuum tube containing 

one or more electron guns whose electron beams 

rapidly sweep horizontally across the inside of the front 

surface of the tube, which is coated with a material that 

glows when irradiated. Each electron beam moves from 

left to right, top to bottom, one horizontal scan line at a 

time. To keep the screen image from flickering, the electron 

beam refreshes the screen 30 times or more per second. 

The clarity of the image is determined by the number 

of pixels on the screen. See the illustration. See also pixel, 

raster, resolution (definition 1). 

Yoke 

Electron 

beam 

Phosphor 

layer 

Electron 

gun 

f0cgn22.eps 

CRT. Cutaway view of a CRT. 

CRT controller n. The part of a video adapter board that 

generates the video signal, including the horizontal and 

vertical synchronization signals. See also video adapter. 

cruise vb. See surf. 

crunch vb. To process information. See also number 

crunching. 

cryoelectronic adj. Involving the use of superconducting 

electronics kept in a cryogenic environment at very low 

temperatures. 

crypto n. See cryptography. 

135 

cryptoanalysis n. The decoding of electronically 

encrypted information for the purpose of understanding 

encryption techniques. See also cryptography, encryption. 

CryptoAPI n. An application programming interface (API) 

that is provided as part of Microsoft Windows. CryptoAPI 

provides a set of functions that allows applications to 

encrypt or digitally sign data in a flexible manner while 

providing protection for the user’s sensitive private key 

data. Actual cryptographic operations are performed by 

independent modules known as cryptographic service providers 

(CSPs). See also application programming interface 

(API), cryptographic service provider, private key. 

cryptographic service provider n. An independent 

module that performs cryptographic operations, such as 

creating and destroying keys. A cryptographic service provider 

consists of, at a minimum, a DLL and a signature 

file. Acronym: CSP. 

cryptography n. The use of codes to convert data so that 

only a specific recipient will be able to read it using a key. 

The persistent problem of cryptography is that the key 

must be transmitted to the intended recipient and may be 

intercepted. Public key cryptography is a recent significant 

advance. Also called: crypto. See also code1 (definition 2), 

encryption, PGP, private key, public key. 

CSD n. See circuit-switched data. 

C shell n. One of the command-line interfaces available 

under UNIX. The C shell is very usable but is not on every 

system. Compare Bourne shell, Korn shell. 

CSLIP n. See Compressed SLIP. 

CSMA/CA n. Acronym for Carrier Sense Multiple 

Access with Collision Avoidance, a protocol for controlling 

network access similar to CSMA/CD, in that nodes 

(stations) listen to the network and transmit only when it is 

free. But in CSMA/CA, nodes avoid data collisions by signaling 

their intention with a brief Request to Send (RTS) 

signal and then waiting for acknowledgment before actually 

transmitting. 

CSMA/CD n. Acronym for Carrier Sense Multiple 

Access with Collision Detection. A network protocol for 

handling situations in which two or more nodes (stations) 

transmit at the same time, thus causing a collision. With 

CSMA/CD, each node on the network monitors the line 

and transmits when it senses that the line is not busy. If a 

collision occurs because another node is using the same 

C

C 

CSO CUA 

opportunity to transmit, both nodes stop transmitting. To 

avoid another collision, both then wait for differing random 

amounts of time before attempting to transmit again. 

Compare token passing. 

CSO n. Acronym for Computing Services Office. An 

Internet directory service that matches users’ own names 

with e-mail addresses, generally at colleges and universities. 

The CSO service, which can be reached through 

Gopher, was originally developed at the Computing Services 

Office at the University of Illinois. 

CSO name server n. A facility that provides e-mail directory 

information through the CSO system. See also CSO. 

CSR n. See continuous speech recognition. 

CSS n. 1. See cascading style sheets. 2. Acronym for 

Content Scrambling System. An encryption feature added 

to DVDs distributed with approval of the MPAA. CSS 

looks for a matching region code on the DVD and the 

playback device. If the codes do not match (such as for a 

DVD purchased in Japan and a DVD player purchased in 

the United States), CSS will not allow the DVD to play. 

CSS also will not allow a DVD to be played on playback 

equipment not approved by the MPAA. See also deCSS, 

region code. 

CSS1 n. See cascading style sheets. 

CSTN display n. See supertwist display. 

CSU n. See DDS. 

.csv n. The file extension for a comma-delimited text file. 

CSV n. 1. See circuit-switched voice. 2. See alternate 

circuit-switched voice/circuit-switched data. 3. Acronym 

for comma separated values. Filename extension assigned 

to text files containing tabular data of the sort stored in 

database fields. As the name indicates, individual data 

entries are separated by commas. Compare TSV. 

CTERM n. See Communications Terminal Protocol. 

CT Expo n. Acronym for Computer Telephony Expo. 

Annual exposition on data and communications issues 

involving the computer, telecommunications, and Internet 

industries. Held in Los Angeles, California, CT Expo features 

exhibits by hundreds of companies displaying their 

latest products and services, as well as conferences on a 

range of subjects affecting computer telephony. 

CTI n. Acronym for computer-telephony integration. The 

practice of using a computer to control one or more telephone 

and communications functions. 

136 

CTIA n. See Cellular Telecommunications and Internet 

Association. 

CTIA Wireless n. Annual conference of the wireless data, 

mobile Internet, and handheld computing industries. Sponsored 

by the Cellular Telecommunications and Internet 

Association, CTIA Wireless showcases products and technical 

developments in the field of wireless communications 

and data. 

CTL n. Short for control. See control character (definition 

2), Control key. 

CTO n. Acronym for Chief Technology Officer. A corporate 

executive in charge of managing a company’s information 

technology (IT) architecture and other technological 

assets. The CTO’s responsibilities may include oversight of 

IT centers, networks and intranet, applications, databases, 

Web presence, and other technological resources. 

CTRL or Ctrl n. Short for control. A designation used to 

label the Control key on computer keyboards. See also 

control character (definition 2), Control key. 

Ctrl+Alt+Delete n. A three-key combination used with 

IBM and compatible computers to restart (reboot) the 

machine. Pressing Ctrl+Alt+Delete (Control+Alternate+ 

Delete) causes a warm boot in MS-DOS—the computer 

restarts but does not go through all of the internal checks 

involved when power to the system is switched on (cold 

boot). In Windows 9x and Windows NT, Ctrl+Alt+Delete 

provides a dialog box from which the user may choose to 

shut down the computer or end any current tasks. 

Ctrl+C n. 1. In UNIX, the key combination used to break 

out of a running process. 2. The keyboard shortcut recognized 

by many programs (as in Windows) as an instruction 

to copy the currently selected item. 

Ctrl+S n. 1. On systems in which a software handshake is 

used between terminals and a central computer, the key 

combination used to suspend output. Ctrl+Q will resume 

output after a Ctrl-S suspension. See also software handshake, 

XON/XOFF. 2. A keyboard shortcut recognized by 

many programs as an instruction to save the current document 

or file. 

CTS n. Acronym for Clear To Send. In serial communications, 

a signal sent, as from a modem to its computer, to 

indicate that transmission can proceed. CTS is a hardware 

signal sent over line 5 in RS-232-C connections. Compare 

RTS. 

CUA n. See Common User Access.

cube cut and paste 

cube n. An OLAP data structure. A cube contains dimensions 

(like Country/Region/City) and data fields (like 

Sales Amount). Dimensions organize types of data into 

hierarchies with levels of detail, and data fields measure 

quantities. 

Cube n. A personal computer design introduced by Apple 

in 2000. The Cube featured a unique 8-by-8-by-8-inch 

transparent curved cube shape with the power supply outside 

the chassis to create a small and extremely quiet computer. 

The Cube offered the same G4 processor and 

features available on other Macintosh computers, but with 

fewer expansion options. Although the unique design 

drew notice for innovation, Apple discontinued manufacture 

of the Cube in 2001 after only one year of production. 

CUI n. See character user interface. 

CUL8R n. A fanciful shorthand notation meaning “See 

you later,” sometimes seen in Internet discussion groups as 

a farewell by a participant temporarily leaving the group. 

curly quotes n. See smart quotes. 

current n. The flow of electric charge through a conductor, 

or the amount of such flow. Current is measured in 

amperes. See also ampere, coulomb. Compare volt. 

current cell n. See active cell. 

current directory n. The disk directory at the end of the 

active directory path—the directory that is searched first 

for a requested file, and the one in which a new file is 

stored unless another directory is specified. See also path 


current drain n. 1. The current taken from a voltage 

source by its load (the object receiving the current). Also 

called: drain. 2. The load itself. For example, a flashlight 

bulb takes current from the battery; this current is the 

drain on the battery, and the bulb itself may also be called 

the drain. 

current location counter n. See program counter. 

current-mode logic n. A type of circuit design in which 

the transistors operate in unsaturated (amplifying) mode. 

cursor n. 1. A special on-screen indicator, such as a blinking 

underline or rectangle, that marks the place at which a 

keystroke will appear when typed. 2. In reference to digitizing 

tablets, the stylus (pointer or “pen”). 3. In applications 

and operating systems that use a mouse, the arrow or other 

on-screen icon that moves with movements of the mouse. 

137 

cursor blink speed n. The rate at which a cursor on a 

screen flashes on and off. See also cursor (definition 1). 

cursor control n. The ability of a computer user to move 

the cursor to a specified location on the screen. Keys dedicated 

to cursor control include the left, right, up, and down 

arrow keys and certain others, such as Backspace, Home, 

and End. Pointing devices such as the mouse can also control 

cursor movements, often helping the user move the 

cursor long distances from place to place in a document. 

cursor key n. See arrow key. 

CUSeeMe n. A video conferencing program developed at 

Cornell University. It was the first program to give Windows 

and Mac OS users the ability to engage in real-time 

video conferencing over the Internet, but it requires a lot of 

bandwidth (at least 128 Kbps speed) to function properly. 

custom control n. A control authored by a user or a 

third-party software vendor that does not belong to the 

.NET Framework class library. This is a generic term that 

includes user controls. A custom server control is used in 

Web Forms (ASP.NET pages). A custom client control is 

used in Windows Forms applications. 

customize vb. To modify or assemble hardware or software 

to suit the needs or preferences of the user. Traditionally, 

hardware customizing ranges from designing an 

electronic circuit for a particular customer to putting 

together a computer facility tailored to a customer’s special 

need. Software customizing usually means modifying 

or designing software for a specific customer. 

custom queuing n. A form of queuing on Cisco routers 

where the wide area network (WAN) link is divided into 

micropipes based on a percentage of the total bandwidth 

available on the pipe. See also bandwidth reservation. 

custom software n. Any type of program developed for 

a particular client or to address a special need. Certain 

products, such as dBASE and Lotus 1-2-3, are designed to 

provide the flexibility and tools required for producing tailor-made 

applications. See also CASE. 

cut vb. To remove part of a document, usually placing it 

temporarily in memory so that the cut portion can be 

inserted (pasted) elsewhere. Compare delete. 

cut and paste n. A procedure in which the computer acts 

as an electronic combination of scissors and glue for reorganizing 

a document or for compiling a document from different 

sources. In cut and paste, the portion of a document 

C

C 

cut-through switch cybersex 

to be moved is selected, removed to storage in memory or 

on disk, and then reinserted into the same or a different document. 

cut-through switch n. A network switch that routes 

packets immediately to the port associated with the 

packet’s recipient. See also packet. 

CV n. See computer vision. 

CVS n. 1. See Computer Vision Syndrome. 2. Acronym 

for Concurrent Versions System. An open-source network-transparent 

version control system which allows 

multiple developers to view and edit code simultaneously. 

Popular because the client-server function allows operation 

over the Internet. CVS maintains a single copy of the 

source code with a record of who initiated changes and 

when the changes were made. CVS was developed for the 

UNIX operating system and is commonly used by programmers 

working with Linux, Mac OS X, and other 

UNIX-based environments. 

CWIS n. See campuswide information system. 

cXML n. Acronym for commerce XML. A set of document 

definitions for Extensible Markup Language (XML) 

developed for use in business-to-business e-commerce. 

cXML defines standards for product listings, allows for 

electronic requests and responses between procurement 

applications and suppliers, and provides for secure financial 

transactions via the Internet. 

cyber- prefix A prefix attached to “everyday” words in 

order to give them a computer-based or online meaning, as 

in cyberlaw (the practice of law either in relation to or 

through the use of the Internet) and cyberspace (the virtual 

online world). The prefix is derived from the word cybernetics, 

which refers to the study of mechanisms used to 

control and regulate complex systems, either human or 

machine. 

cyberart n. The artwork of artists who use computers to 

create or distribute their efforts. 

cybercafe or cyber café n. 1. A coffee shop or restaurant 

that offers access to PCs or other terminals that are connected 

to the Internet, usually for a per-hour or per-minute 

fee. Users are encouraged to buy beverages or food to 

drink or eat while accessing the Internet. 2. A virtual café 

on the Internet, generally used for social purposes. Users 

interact with each other by means of a chat program or by 

posting messages to one another through a bulletin board 

system, such as in a newsgroup or on a Web site. 

138 

cybercash n. See e-money. 

cyberchat n. See IRC. 

cybercop n. A person who investigates criminal acts 

committed on line, especially fraud and harassment. 

cyberculture n. The behavior, beliefs, customs, and etiquette 

that characterize groups of individuals who communicate 

or socialize over computer networks, such as the 

Internet. The cyberculture of one group can be vastly different 

from the cyberculture of another. 

Cyberdog n. Apple’s Internet suite for Web browsing and 

e-mail, based on OpenDoc for easy integration with other 

applications. See also OpenDoc. 

cyberlawyer n. 1. An attorney whose practice involves 

the law related to computers and online communication, 

including elements of communications law, intellectual 

property rights, privacy and security issues, and other specialties. 

2. An attorney who advertises or distributes information 

over the Internet and the World Wide Web. 

cyberlife n. In the gaming world, a technology that mimics 

biological DNA. See also digital DNA. 

cybernaut n. One who spends copious time on line, 

exploring the Internet. Also called: Internaut. See also 

cyberspace. 

cybernetics n. The study of control systems, such as the 

nervous system, in living organisms and the development 

of equivalent systems in electronic and mechanical 

devices. Cybernetics compares similarities and differences 

between living and nonliving systems (whether those systems 

comprise individuals, groups, or societies) and is 

based on theories of communication and control that can 

be applied to either living or nonliving systems or both. 

See also bionics. 

cyberpunk n. 1. A genre of near-future science fiction in 

which conflict and action take place in virtual-reality environments 

maintained on global computer networks in a 

worldwide culture of dystopian alienation. The prototypical 

cyberpunk novel is William Gibson’s Neuromancer 

(1982). 2. A category of popular culture that resembles the 

ethos of cyberpunk fiction. 3. A person or fictional character 

who resembles the heroes of cyberpunk fiction. 

cybersex n. Communication via electronic means, such 

as e-mail, chat, or newsgroups, for the purpose of sexual 

stimulation or gratification. See also chat1 (definition 1), 

newsgroup.

cyberspace Cycolor 

cyberspace n. 1. The advanced shared virtual-reality network 

imagined by William Gibson in his novel Neuromancer 

(1982). 2. The universe of environments, such as 

the Internet, in which persons interact by means of connected 

computers. A defining characteristic of cyberspace 

is that communication is independent of physical distance. 

cyberspeak n. Terminology and language (often jargon, 

slang, and acronyms) relating to the Internet (computerconnected) 

environment, that is, cyberspace. See also 

cyberspace. 

cybersquatter n. A person who registers company names 

and other trademarks as Internet domain names in order to 

force the named companies or owners of the trademarks to 

buy them at an inflated price. 

cyberwidow n. The spouse of a person who spends inordinate 

amounts of time on the Internet. 

cybrarian n. Software used at some libraries that allows 

one to query a database through the use of an interactive 

search engine. 

cycle power vb. To turn the power to a machine off and 

back on in order to clear something out of memory or to 

reboot after a hung or crashed state. 

cycle time n. The amount of time between a random 

access memory (RAM) access and the earliest time a new 

access can occur. See also access time (definition 1). 

cyclical redundancy check n. See CRC. 

cyclic binary code n. A binary representation of numbers 

in which each number differs from the one that precedes 

it by one unit (bit), in one position. Cyclic binary 

numbers differ from “plain” binary numbers, even though 

both are based on two digits, 0 and 1. The numbers in the 

cyclic binary system represent a code, much like Morse 

code, whereas “plain” binary numbers represent actual values 

in the binary number system. Because sequential numbers 

differ by only 1 bit, cyclic binary is used to minimize 

errors in representing unit measurements. See the table. 

139 

Table C.2 Cyclic Binary Code Compared to Other 

Numeral Systems 

Cyclic binary “Plain” binary Decimal 

0000 0000 0 

0001 0001 1 

0011 0010 2 

0010 0011 3 

0110 0100 4 

0111 0101 5 

0101 0110 6 

0100 0111 7 

1100 1000 8 

1101 1001 9 

Cycolor n. A color printing process that uses a special 

film embedded with millions of capsules filled with cyan, 

magenta, and yellow dyes. When exposed to red, green, or 

blue light, the respective capsules become hard and 

unbreakable. The film is then pressed against specially 

treated paper, and the capsules that have not hardened in 

the previous process break, releasing their colors onto the 

paper. See also CMY. 

C

D 

DA n. See desk accessory. 

DAC n. See digital-to-analog converter. 

DACL n. See discretionary access control list. 

daemon n. A program associated with UNIX systems 

that performs a housekeeping or maintenance utility function 

without being called by the user. A daemon sits in the 

background and is activated only when needed, for example, 

to correct an error from which another program cannot 

recover. 

daisy chain1 n. A set of devices connected in series. In 

order to eliminate conflicting requests to use the channel 

(bus) to which all the devices are connected, each device is 

given a different priority. SCSI (Small Computer System 

Interface) and the newer USB (Universal Serial Bus) both 

support daisy-chained devices. See also SCSI, USB. 

daisy chain2 vb. To connect a series of devices, one to 

another, like daisies in a chain of flowers. 

daisy wheel n. A print element consisting of a set of 

formed characters with each character mounted on a separate 

type bar, all radiating from a center hub. See also 

daisy-wheel printer, thimble, thimble printer. 

daisy-wheel printer n. A printer that uses a daisy-wheel 

type element. Daisy-wheel output is crisp and slightly 

imprinted, with fully formed characters resembling typewriter 

quality. Daisy-wheel printers were standard for 

high-quality printing until being superseded by laser printers. 

See also daisy wheel, thimble, thimble printer. 

damping n. A technique for preventing overshoot 

(exceeding the desired limit) in the response of a circuit or 

device. 

D-AMPS n. Acronym for Digital Advanced Mobile Phone 

Service. The digital form of the analog AMPS cellular 

phone service. D-AMPS, sometimes spelled DAMPS, differs 

from AMPS in being digital and in tripling the number 

of available channels by using time division multiple access 

(TDMA) to divide each of the 30 AMPS channels into three 

separate channels. See also AMPS, FDMA, TDMA. 

DAO n. See Data Access Objects. 

D 

140 

DAP n. See Directory Access Protocol. 

DaratechSUMMIT n. Conference on emerging engineering 

and technology developments in the information technology 

industry. The DaratechSUMMIT focuses on how 

information technology affects business practices and 

assists in manufacturing and production. 

dark fiber n. Unused capacity in fiber-optic communications. 

Darlington circuit n. An amplifier circuit made of two 

transistors, often mounted in the same housing. The collectors 

of the two transistors are connected, and the emitter 

of the first is connected to the base of the second. 

Darlington circuits provide high-gain amplification. Also 

called: Darlington pair. 

Darlington pair n. See Darlington circuit. 

DARPA n. See Defense Advanced Research Projects 

Agency. 

DARPANET n. Short for Defense Advanced Research 

Projects Agency Network. See ARPANET. 

Darwin n. Apple Computer’s open-source operating system, 

which forms the core of Mac OS X. Darwin is a processor-independent 

BSD UNIX operating system based on 

FreeBSD and Mach 3.0 technologies. Darwin offers 

advanced networking, protected memory, preemptive multitasking, 

and support for Macintosh and UNIX file systems. 

Darwin can be run on both the Power PC Macintosh 

and Intel processor–based computers. See also Mac OS X. 

DAS n. See dual attachment station. 

DASD n. Acronym for direct access storage device. A 

data storage device by which information can be accessed 

directly, instead of by passing sequentially through all 

storage areas. For example, a disk drive is a DASD, but a 

tape unit is not, because, with a tape unit, the data is stored 

as a linear sequence. See also direct access. Compare 

sequential access. 

.dat n. A generic file extension for a data file. 

DAT n. See digital audio tape, dynamic address translation.

data data compaction 

data n. Plural of the Latin datum, meaning an item of information. 

In practice, data is often used for the singular as well 

as the plural form of the noun. See also datum. Compare 

information. 

Data Access Objects n. A data access interface that 

communicates with Microsoft Jet and ODBC-compliant 

data sources to connect to, retrieve, manipulate, and 

update data and the database structure. Acronym: DAO. 

data acquisition n. The process of obtaining data from 

another source, usually one outside a specific system. 

data aggregate n. A collection of data records. It usually 

includes a description of the placement of the data 

blocks and their relation to the entire set. 

data attribute n. Structural information about data that 

describes its context and meaning. 

data bank n. Any substantial collection of data. 

database n. A file composed of records, each containing 

fields together with a set of operations for searching, sorting, 

recombining, and other functions. Acronym: DB. 

database administrator n. One who manages a database. 

The administrator determines the content, internal 

structure, and access strategy for a database, defines security 

and integrity, and monitors performance. Acronym: 

DBA. Also called: database manager. 

database analyst n. One who provides the analytic 

functions needed to design and maintain applications 

requiring a database. 

database designer n. One who designs and implements 

functions required for applications that use a database. 

database engine n. The program module or modules 

that provide access to a database management system 

(DBMS). 

database machine n. 1. A peripheral that executes database 

tasks, thereby relieving the main computer from performing 

them. 2. A database server that performs only 

database tasks. 

database management system n. A software interface 

between the database and the user. A database management 

system handles user requests for database actions 

and allows for control of security and data integrity 

requirements. Acronym: DBMS. Also called: database 

manager. See also database engine. 

database manager n. See database administrator, database 

management system. 

141 

database publishing n. The use of desktop publishing or 

Internet technology to produce reports containing information 

obtained from a database. 

database server n. A network node, or station, dedicated 

to storing and providing access to a shared database. 

Also called: database machine. 

database structure n. A general description of the format 

of records in a database, including the number of 

fields, specifications regarding the type of data that can be 

entered in each field, and the field names used. 

data bit n. In asynchronous communications, one of a 

group of from 5 to 8 bits that represents a single character 

of data for transmission. Data bits are preceded by a start 

bit and followed by an optional parity bit and one or more 

stop bits. See also asynchronous transmission, bit, communications 

parameter. 

data buffer n. An area in memory where data is temporarily 

stored while being moved from one location to 

another. See also buffer1 . 

data bus n. See bus. 

data cable n. Fiber-optic or wire cable used to transfer 

data from one device to another. 

data capture n. 1. The collection of information at the 

time of a transaction. 2. The process of saving on a storage 

medium a record of interchanges between a user and a 

remote information utility. 

data carrier n. See carrier (definition 1). 

Data Carrier Detected n. See DCD (definition 1). 

data chaining n. The process of storing segments of data 

in noncontiguous locations while retaining the ability to 

reconnect them in the proper sequence. 

data channel n. See channel (definition 1). 

data closet n. See wiring closet. 

data collection n. 1. The process of acquiring source 

documents or data. 2. The grouping of data by means of 

classification, sorting, ordering, and other organizing 

methods. 

datacom n. Short for data communications. See 

communications. 

data communications n. See communications. 

data compaction n. See data compression. 

D

D 

data compression data file 

data compression n. A means of reducing the amount of 

space or bandwidth needed to store or transmit a block of 

data, used in data communications, facsimile transmission, 

file storage and transfer, and CD-ROM publishing. 

Also called: data compaction. 

data conferencing n. Simultaneous data communication 

among geographically separated participants in a 

meeting. Data conferencing involves whiteboards and 

other software that enable a single set of files at one location 

to be accessed and modified by all participants. See 

the illustration. See also desktop conferencing, whiteboard. 

Compare video conferencing. 

F0Dgn01.eps 

Data conferencing. 

data control n. The aspect of data management concerned 

with tracking how and by whom data is used, 

accessed, altered, owned, and reported on. 

data conversion n. Changing the way information is represented 

in a document or file—for instance, changing 

binary representation to decimal or hexadecimal. 

data corruption n. See corruption. 

data declaration n. A statement in a program that specifies 

the characteristics of a variable. The requirements for 

data declarations vary among different programming languages 

but can include such values as variable name, data 

type, initial value, and size specification. See also array, 

data type, record1 , variable. 

data definition language n. A language that defines all 

attributes and properties of a database, especially record 

layouts, field definitions, key fields, file locations, and 

storage strategy. Acronym: DDL. 

data description language n. A language designed specifically 

for declaring data structures and files. See also 

data definition language. 

142 

data dictionary n. A database containing data about all 

the databases in a database system. Data dictionaries store 

all the various schema and file specifications and their 

locations. They also contain information about which programs 

use which data and which users are interested in 

which reports. 

data directory n. See catalog, data dictionary. 

data-driven attack n. A form of attack in which malicious 

code is hidden in a program or other innocuous data. 

When the data is executed, the virus or other destructive 

code is activated. A data-driven attack is typically used to 

bypass a firewall or other security measures. 

data-driven processing n. A form of processing where 

the processor or program must wait for data to arrive 

before it can advance to the next step in a sequence. Compare: 

demand-driven processing. 

data element n. A single unit of data. Also called: data 

item. See also data field. 

data encapsulation n. A method of dealing with computers 

with Year 2000 problems that entailed modifying 

the input and output logic of a program, leaving the actual 

data unchanged as it was processed. The input logic was 

modified to reflect a date in the past that the computer 

could handle that paralleled the current calendar. When 

output was generated, the output logic changed the data to 

reflect the correct date. 

data encryption n. See encryption. 

data encryption key n. A sequence of secret information, 

such as a string of decimal numbers or binary digits, 

that is used to encrypt and decrypt data. Acronym: DEK. 

See also decryption, encryption, key (definition 3). 

data encryption standard n. See DES. 

data entry n. The process of writing new data to computer 

memory. 

data/fax modem n. A modem that can handle both 

serial data and facsimile images to either send or receive 

transmissions. 

data field n. A well-defined portion of a data record, such 

as a column in a database table. 

data field masking n. The process of filtering or selecting 

part of a data field to control the way it is returned and 

displayed. 

data file n. A file consisting of data in the form of text, 

numbers, or graphics, as distinct from a program file of 

commands and instructions. Compare program file.

data flow data management 

data flow or dataflow n. 1. The movement of data 

through a system, from entry to destination. 2. In parallel 

processing, a design in which a calculation is made either 

when all necessary data is available (data-driven processing) 

or when other processors request the data (demanddriven 

processing). See also parallel processing. 

data fork n. In Macintosh files, the part of a stored document 

that contains user-supplied information, such as the 

text of a word-processing document. A Macintosh file can 

have a data fork, a resource fork (which contains information 

such as program code, font data, digitized sound, or 

icons), and a header. All three parts are used by the operating 

system in file management and storage. See also 

resource (definition 2), resource fork. 

data format n. The structure applied to data by an application 

program to provide a context in which the data can 

be interpreted. 

data frame n. A packet of information transmitted as a 

unit on a network. Data frames are defined by the network’s 

data-link layer and exist only on the wire between network 

nodes. See also data-link layer, frame (definition 2). 

data glove n. A data input device or controller in the 

form of a glove fitted with sensors that convert movement 

of the hand and fingers into commands. See also virtual 

reality. 

datagram n. One packet, or unit, of information, along 

with relevant delivery information such as the destination 

address, that is sent through a packet-switching network. 

See also packet switching. 

data independence n. The separation of data in a database 

from the programs that manipulate it. Data independence 

makes stored data as accessible as possible. 

data integrity n. The accuracy of data and its conformity 

to its expected value, especially after being transmitted or 

processed. 

data interchange format n. A format consisting of 

ASCII codes in which database, spreadsheet, and similar 

documents can be structured to facilitate their use by and 

transfer to other programs. Acronym: DIF. See also ASCII. 

data item n. See data element. 

data library n. A cataloged collection of data files on disk 

or in another storage medium. 

data link n. A connection between any two devices 

capable of sending and receiving information, such as a 

143 

computer and a printer or a main computer and a terminal. 

Sometimes the term is extended to include equipment, 

such as a modem, that enables transmission and 

receiving. Such devices follow protocols that govern data 

transmission. See also communications protocol, datalink 

layer, DCE (definition 1), DTE. 

Data Link Connection Identifier n. A virtual circuit on 

frame relay networks that permanently identifies the path 

to a particular destination. See also frame relay, virtual 

circuit. 

Data Link Control n. See DLC. 

data link escape n. In data transmission, a control character 

that changes the meaning of the characters immediately 

following it. 

data-link layer n. The second of seven layers in the ISO/ 

OSI reference model for standardizing computer-to-computer 

communications. The data-link layer is one layer 

above the physical layer. Its concern is packaging and 

addressing data and managing the flow of transmissions. It 

is the lowest of the three layers (data-link, network, and 

transport) involved in actually moving data between devices. 

See the illustration. See also ISO/OSI reference model. 

ISO/OSI Layer 

ISO/OSI MODEL 

Focus 




conversion 









F0Dgn02.eps 

Data-link layer on ISO/OSI reference model. 

data management n. The control of data from acquisition 

and input through processing, output, and storage. In 

microcomputers, hardware manages data by gathering it, 

moving it, and following instructions to process it. The 

operating system manages the hardware and ensures that 

D

D 

data manipulation data sharing 

the parts of the system work in harmony so that data is 

stored safely and accurately. Application programs manage 

data by receiving and processing input according to 

the user’s commands, and sending results to an output 

device or to disk storage. The user also is responsible for 

data management by acquiring data, labeling and organizing 

disks, backing up data, archiving files, and removing 

unneeded material from the hard disk. 

data manipulation n. The processing of data by means of 

programs that accept user commands, offer ways to handle 

data, and tell the hardware what to do with the data. 

data manipulation language n. In database management 

systems, a language that is used to insert data in, 

update, and query a database. Data manipulation languages 

are often capable of performing mathematical and 

statistical calculations that facilitate generating reports. 

Acronym: DML. See also structured query language. 

data mart n. A scaled-down version of a data warehouse 

that is tailored to contain only information likely to be 

used by the target group. See also data warehouse. 

data medium n. The physical material on which computer 

data is stored. 

data migration n. 1. The process of moving data from one 

repository or source, such as a database, to another, usually 

via automated scripts or programs. Often data migration 

involves transferring data from one type of computer system 

to another. 2. In supercomputing applications, the process 

of storing large amounts of data off line while making 

them appear to be on line as disk-resident files. 

data mining n. The process of identifying commercially 

useful patterns, problems, or relationships in a database, a 

Web server, or other computer repository through the use 

of advanced statistical tools. Some Web sites use data 

mining to monitor the efficiency of site navigation and to 

determine changes in the Web site’s design based on how 

consumers are using the site. 

data model n. A collection of related object types, operators, 

and integrity rules that form the abstract entity supported 

by a database management system (DBMS). Thus, 

one speaks of a relational DBMS, a network DBMS, and 

so on, depending on the type of data model a DBMS 

supports. In general, a DBMS supports only one data 

model as a practical rather than a theoretical restriction. 

data network n. A network designed for transferring 

data encoded as digital signals, as opposed to a voice network, 

which transmits analog signals. 

144 

Data Over Cable Service Interface Specification n. 

See DOCSIS. 

data-overrun error n. An error that occurs when more 

data is being acquired than can be processed. See also bps. 

data packet n. See packet. 

data path n. The route that a signal follows as it travels 

through a computer network. 

data point n. Any pair of numeric values plotted on a 

chart. 

data processing n. 1. The general work performed by 

computers. 2. More specifically, the manipulation of data 

to transform it into some desired result. Acronym: DP. 

Also called: ADP, automatic data processing, EDP, electronic 

data processing. See also centralized processing, 

decentralized processing, distributed processing. 

Data Processing Management Association n. See 

DPMA. 

data projector n. A device, similar to a slide projector, 

that projects the video monitor output of a computer onto 

a screen. 

data protection n. The process of ensuring the preservation, 

integrity, and reliability of data. See also data integrity. 

data rate n. The speed at which a circuit or communications 

line can transfer information, usually measured in 

bits per second (bps). 

data record n. See record1 . 

data reduction n. The process of converting raw data to 

a more useful form by scaling, smoothing, ordering, or 

other editing procedures. 

data segment n. The portion of memory or auxiliary 

storage that contains the data used by a program. 

Data Service Unit n. See DDS. 

data set n. 1. A collection of related information made 

up of separate elements that can be treated as a unit in data 

handling. 2. In communications, a modem. See also 

modem. 

Data Set Ready n. See DSR. 

data sharing n. The use of a single file by more than one 

person or computer. Data sharing can be done by physically 

transferring a file from one computer to another, or, 

more commonly, by networking and computer-to-computer 

communications.

data signal date dependency 

data signal n. The information transmitted over a line or 

circuit. It consists of binary digits and can include actual 

information or messages and other elements such as control 

characters or error-checking codes. 

data sink n. 1. Any recording medium where data can be 

stored until needed. 2. In communications, the portion of a 

Data Terminal Equipment (DTE) device that receives 

transmitted data. 

data source n. 1. The originator of computer data, frequently 

an analog or digital data collection device. 2. In 

communications, the portion of a Data Terminal Equipment 

(DTE) device that sends data. 

data stream n. An undifferentiated, byte-by-byte flow of 

data. 

data structure n. An organizational scheme, such as a 

record or array, that can be applied to data to facilitate 

interpreting the data or performing operations on it. 

data switch n. A device in a computer system that routes 

incoming data to various locations. 

Data Terminal Equipment n. See DTE. 

Data Terminal Ready n. See DTR. 

data traffic n. The exchange of electronic messages— 

control and data—across a network. Traffic capacity is 

measured in bandwidth; traffic speed is measured in bits 

per unit of time. 

data transfer n. The movement of information from one 

location to another, either within a computer (as from a 

disk drive to memory), between a computer and an external 

device (as between a file server and a computer on a 

network), or between separate computers. 

data transfer rate n. See data rate. 

data transmission n. The electronic transfer of information 

from a sending device to a receiving device. 

data type n. In programming, a definition of a set of data 

that specifies the possible range of values of the set, the 

operations that can be performed on the values, and the 

way in which the values are stored in memory. Defining 

the data type allows a computer to manipulate the data 

appropriately. Data types are most often supported in 

high-level languages and often include types such as real, 

integer, floating point, character, Boolean, and pointer. 

How a language handles data typing is one of its major 

characteristics. See also cast, constant, enumerated data 

type, strong typing, type checking, user-defined data type, 

variable, weak typing. 

145 

data validation n. The process of testing the accuracy 

of data. 

data value n. The literal or interpreted meaning of a data 

item, such as an entry in a database, or a type, such as an 

integer, that can be used for a variable. 

data warehouse1 n. A database, frequently very large, 

that can access all of a company’s information. While the 

warehouse can be distributed over several computers and 

may contain several databases and information from 

numerous sources in a variety of formats, it should be 

accessible through a server. Thus, access to the warehouse 

is transparent to the user, who can use simple commands 

to retrieve and analyze all the information. The data warehouse 

also contains data about how the warehouse is organized, 

where the information can be found, and any 

connections between data. Frequently used for decision 

support within an organization, the data warehouse also 

allows the organization to organize its data, coordinate 

updates, and see relationships between information gathered 

from different parts of the organization. See also 

database, decision support system, server (definition 1), 

transparent (definition 1). 

data warehouse2 vb. To acquire, collect, manage, and 

disseminate information gathered from various sources into 

a single location; or to implement an informational database 

used to store sharable data. Data warehousing is a four-step 

process: gathering data; managing the data in a centralized 

location; providing access to the data along with tools for 

interpreting, analyzing, and reporting on the data; and producing 

reports on the data to be used for decision making. 

See also downflow, inflow, metaflow, upflow. 

date and time stamp n. See time stamp. 

date counter overflow n. A problem that may occur in 

systems or programs when the value in a date variable 

exceeds allowable values. A date counter overflow can 

occur when an incremental date produces a number that the 

system interprets as zero or a negative number. This is 

likely to cause the system or program to post an error message 

in turn or to revert to the original starting point. 

Although this was largely considered a Year 2000 problem, 

such an error is not necessarily confined to the year 2000. 

date dependency n. In terms of the Year 2000 problem, 

the need many programs have for date-related input or 

output data and the way dates are represented in that data. 

This dependency affects whether the program can run correctly 

when the turn of the century is reached. 

D

D 

date expansion DCD 

date expansion n. A method of dealing with programs 

with Year 2000 problems that entails changing data, data 

descriptions, and (if necessary) program logic that pertains 

to dates by expanding date fields from two digits to four 

digits—for example, from DDMMYY to DDMMYYYY. 

date format n. The manner in which dates are formatted 

in a computer system or program. While some organizations 

require that the same format be used throughout their 

systems and programs, many organizations have not, 

which can make tracking down potential date problems, 

such as the Year 2000 problem, difficult. In addition, date 

formats can vary widely from organization to organization, 

although many have opted to standardize on formats 

specified in ANSI X3.30-1997 or ISO8601:1988. 

date horizon n. A period of time that a program uses to 

determine the beginning or ending point in performing its 

functions. A program that tracks inventory may have one 

date horizon that trails the current date by two months (a 

trailing date horizon) to process returned merchandise and 

another that precedes it by another two months (a leading 

date horizon) for planning purposes. If the program logic 

doesn’t account for any date horizons it may have, for 

example, if the year was 1999, the program could experience 

Year 2000 problems when the leading date horizon 

enters January 1, 2000. See also event horizon. 

date-in-key problem n. A potential problem in computer 

systems that depend on indexed files using a two-digit 

date as part of the key, such as certain databases. If the 

files need to be in chronological order, the files beginning 

with the year 2000 will be out of sequence—for example, 

(19)99 would be interpreted as more recent than (20)00. 

date rollover n. See Year 2000 rollover. 

date stamp n. See time stamp. 

date stamping n. A software feature that automatically 

inserts the current date into a document. 

datum n. Singular of data; a single item of information. 

See also data. 

daughterboard n. A circuit board that attaches to 

another, such as the main system board (motherboard), to 

add extra capabilities. See also motherboard. 

DAV connector n. See digital audio/video connector. 

day-of-the-week problem n. A reference to an inaccuracy 

that may occur after the Year 2000 in computers that 

146 

calculate the day of the week based on the last two digits 

of the year, assuming that the dates they calculate fall in 

the 1900s. Because January 1, 1900 was a Monday, but 

January 1, 2000 will be a Saturday, those computers may 

not be able to correctly determine the day of the week. 

This is particularly problematic in computers that regulate 

timed systems based on the business week, such as a door 

or vault that unlocks during business hours. 

DB n. See database. 

dB n. See decibel. 

DBA n. See database administrator. 

DB connector n. Any of various connectors that facilitate 

parallel input and output. The initials DB (for data bus) are 

followed by a number that indicates the number of lines 

(wires) within the connector. For example, a DB-9 connector 

has nine pins and supports up to nine lines, each of 

which can connect to a pin on the connector. 

.dbf n. A file extension for a dBASE database file. 

DBMS n. See database management system. 

DBS n. See direct broadcast satellite. 

dbXML n. Acronym for database XML. A native XML 

database server designed to manage large collections of 

XML documents. dbXML may be embedded in custom 

applications or run as a stand-alone database. 

DC n. See direct current. 

DCA n. 1. Acronym for Document Content Architecture. 

A formatting guideline used in IBM’s Systems Network 

Architecture (SNA) that enables the exchange of text-only 

documents between differing types of computers. DCA 

provides for two types of document formatting: Revisable- 

Form-Text DCA (RFTDCA), which allows for modification 

of formatting, and Final-Form-Text DCA (FFTDCA), 

which cannot be modified. See also DIA, SNA. 

2. Acronym for Directory Client Agent. See DUA. 

DCD n. 1. Acronym for Data Carrier Detected. A signal in 

serial communications that is sent from a modem to its 

computer to indicate that the modem is ready for transmitting. 

Also called: RLSD. See also RS-232-C standard. 

2. Acronym for Document Content Description. A specification 

governing the rules for defining the structure and content 

of XML documents. The specification was created by 

IBM and Microsoft in 1998 and was submitted to the World 

Wide Web Consortium for approval. See also XML.

DCE DDS 

DCE n. 1. Acronym for Data Communications Equipment. 

The term used in RS-232 and X.25 specifications 

for a device, such as a modem, that provides another 

device (known as the Data Terminal Equipment or DTE) 

with access to a communications line. A DCE is an intermediary 

device that often transforms input from a DTE 

before sending it to a recipient. See also RS-232-C standard, 

X series. Compare DTE. 2. See Distributed Computing 

Environment. 

D channel n. Short for data channel. In the ISDN communications 

architecture, the channel dedicated to carrying 

control signals, such as packet-switching information; 

and user-related data, such as phone numbers. The basic 

ISDN connection, called the Basic Rate Interface (BRI), is 

composed of two B (bearer) channels, which carry as 

much as 64 Kbps of actual data each, and one D channel, 

which transmits at either 16 Kbps or 64 Kbps. The faster 

Primary Rate Interface (PRI) is composed of one 64-Kbps 

D channel and either 23 or 30 B channels operating at 64 

Kbps. See also B channel, BRI, ISDN. 

DCOM n. Acronym for Distributed Component Object 

Model. The version of Microsoft’s Component Object 

Model (COM) specification that stipulates how components 

communicate over Windows-based networks. It permits the 

distribution of different components for a single application 

across two or more networked computers, running an application 

distributed across a network so that the distribution 

of components is not apparent to the user, and remotely displaying 

an application. Also called: Distributed COM. See 

also COM (definition 2), component (definition 2). 

DCS n. Acronym for Desktop Color Separation. The primary 

format for preparing digital publication text and 

graphics for printing. DCS layouts consist of five files, one 

for each of the CMYK colors, and a master file which, 

includes the display version of the page and information 

on the other four files. See also OPI. 

DCTL n. See direct-coupled transistor logic. 

DDBMS n. See distributed database management system. 

DDC n. Acronym for Display Data Channel. A VESA 

standard that allows software control of graphical computer 

monitors. Under DDC, monitor characteristics are 

provided to the graphics subsystem, which uses the data to 

configure the display and provide a bidirectional communication 

channel between the monitor and computer. Also 

called: VESA DDC. See also VESA2 . 

147 

DDCP n. See direct digital color proof. 

DDE n. Acronym for Dynamic Data Exchange. An interprocess 

communication method featured in Microsoft Windows 

and OS/2. DDE allows two or more programs that are 

running simultaneously to exchange data and commands. In 

Windows 3.1, DDE was largely supplanted by OLE, which 

is an extension of DDE. In Windows 95 and Windows NT, 

OLE and ActiveX are more commonly used. See also 

ActiveX, interprocess communication, OLE. 

DDK n. Acronym for Driver Development Kit. A set of 

tools used to create software that enables an operating system 

to work with hardware devices. With a DDK, a software 

developer can build drivers to support network, 

storage, print, sound, video, input, and other devices. Also 

called: Device Driver Kit, Device Driver Developer Kit. 

See also driver. 

DDL n. See data definition language. 

DDoS n. Acronym for distributed denial of service attack. 

A form of denial of service attack (DoS) originating from 

several computers that seeks to disrupt Web access by 

overwhelming a target with connection requests that cannot 

be completed. A DDoS attack involves cracking into a 

number of computers and planting programs that lie dormant 

until sent a signal to attack. At that point the computers 

send a steady stream of data packets to the targeted 

Web site, overwhelming the ability of the Web server to 

respond. Because the attack is coming from many computers, 

security features that might otherwise recognize the 

attack and stop accepting data packets from a single 

source are unable to shut down connections to all the 

attackers. See also DoS, packet, zombie. 

DDR SDRAM n. Short for Double Data Rate Synchronous 

Dynamic RAM (SDRAM). A form of SDRAM that 

essentially doubles memory throughput to 200 megahertz 

or better. DDR SDRAM gets a boost in data transfer rates 

by producing output on both the rising and falling of the 

system clock—that is, twice for each clock cycle. See 

also SDRAM. 

DDS n. Acronym for digital data service, a dedicated 

communications line that provides transmission at speeds 

up to 56 Kbps. DDS lines use a device known as a CSU/ 

DSU rather than a modem for connecting two networks. 

The CSU, or Channel Service Unit, connects the network 

to the transmission line; the DSU, or Data Service Unit, 

converts data for transmission by the CSU and controls 

data flow. 

D

D 

dead code decibel 

dead code n. Program code that never gets executed, 

possibly because the programmer has eliminated all references 

to it, or possibly because the program is written in 

such a way that the instruction(s) will never be needed— 

for example, an ELSE statement would never be needed in 

an IF condition that always proved to be true. Dead code 

can slow program execution and increase the size of the 

program in memory. Also called: grunge, software rot. 

dead halt n. A machine stop with no hope of recovery by 

either the program or the operating system. The only 

choice after a dead halt is to reboot. Also called: dropdead 

halt. See also hang. Compare reboot. 

dead key n. A key used with another key to create an 

accented character. When pressed, a dead key produces no 

visible character (hence its name) but indicates that the 

accent mark it represents is to be combined with the next 

key pressed. See also key (definition 1). 

dead-letter box n. In e-mail or message systems, a file to 

which undeliverable messages are sent. 

deadlock n. 1. A situation that occurs when two programs 

or devices are each waiting for a response from the 

other before continuing. Also called: deadly embrace. 

2. In operating systems, a situation in which two or more 

processes are prevented from continuing while each waits 

for resources to be freed by the continuation of the other. 

3. In computer games, a deadlock occurs when the 

resources needed to continue the game become unavailable 

to the player. The deadlock condition could be intentional, 

such as a loss condition, or a design error on the 

part of the game developer. See also computer games. 

deadly embrace n. See deadlock. 

deallocate vb. To free previously allocated memory. See 

also pointer. Compare allocate. 

deblock vb. To remove one or more logical records (units 

of stored information) from a block. Application or database 

systems must often deblock information to make specific 

units of information available for processing. 

Compare block2 (definition 1). 

debounce algorithm n. A set of instructions that makes 

an assumption about how fast a user can press and release 

a switch and then ensures that only one press is registered 

in the time specified. 

148 

debug vb. To detect, locate, and correct logical or syntactical 

errors in a program or malfunctions in hardware. In 

hardware contexts, the term troubleshoot is the term more 

often used, especially when the problem is a major one. 

See also bug, debugger. 

debugger n. A program designed to aid in debugging 

another program by allowing the programmer to step 

through the program, examine the data, and monitor conditions 

such as the values of variables. See also bug (definition 

1), debug. 

deca- prefix Metric prefix meaning 10—that is, 10 to the 

first power, or 101 . 

decay n. A decrease in the amplitude of a signal over time. 

DECchip 21064 n. A Digital Equipment Corporation 

microprocessor introduced in February 1992. The DECchip 

21064 is a 64-bit, RISC-based, superscalar, superpipelined 

chip with 64-bit registers, a 64-bit data bus, a 

64-bit address bus, and a 128-bit data path between the 

microprocessor and memory. It also has a built-in 8-KB 

instruction cache, a built-in 8-KB data cache, and a floating-point 

processor. The DECchip 21064 contains 1.7 million 

transistors and operates at 3.3 volts. The 200-MHz 

version runs at a peak rate of 400 MPS. The chip’s architecture 

is SMP compliant, so that several chips can be 

used in a parallel (multiprocessor) configuration. See also 

floating-point processor, MIPS, pipelining (definition 1), 

RISC, superpipelining, superscalar. 

deceleration time n. The time required for an access 

arm to come to a stop as it approaches the desired portion 

of a disk. The faster the arm moves, the more momentum 

it gains and the greater the deceleration time. 

decentralized processing n. The distribution of computer 

processing facilities in more than one location. 

Decentralized processing is not the same as distributed 

processing, which assigns multiple computers to the same 

task to increase efficiency. 

deci- prefix Metric prefix meaning 10 –1 (one-tenth). 

decibel n. One tenth of a bel (named after Alexander 

Graham Bell), a unit used in electronics and other fields 

to measure the strength of a sound or signal. Decibel 

measurements fall on a logarithmic scale and compare 

the measured quantity against a known reference. The 

following formula gives the number of decibels between

decimal decoder 

two values: dB = n log (x/r) where x is the measured 

quantity, r is the reference quantity, and n is 10 for voltage 

and current measurements and 20 for power 

measurements. Abbreviation: dB. 

decimal n. The base-10 numbering system. See also base 


decision box n. A diamond-shaped flowchart symbol 

denoting a decision that results in a branching in the process 

being considered. See the illustration. 

Get keypress 

Did user 

press Y? 

Yes 

No 

F0Dgn03.eps 

Decision box. 

decision support system n. A set of programs and 

related data designed to help with analysis and decision 

making. A decision support system provides more help in 

formulating decisions than a management information 

system (MIS) or an executive information system (EIS). It 

includes a database, a body of knowledge about the subject 

area, a “language” used to formulate problems and 

questions, and a modeling program for testing alternative 

decisions. Acronym: DSS. Compare executive information 

system, management information system. 

decision table n. A tabular listing of possible conditions 

(inputs) and the desired result (output) corresponding to 

each condition. A decision table may be used in the preliminary 

analysis of program flow, or it may be converted 

and incorporated into the program itself. 

decision tree n. Similar to a decision table, an analysis 

instrument where possible outcomes of some condition are 

represented as branches, which may in turn generate other 

branches. See the illustration. See also branch, tree structure. 

149 

Keep current 

car 

No 

No 

Yes 

Can you afford a 

new car? 

Yes 

Are you satisfied with 

current car? 

F0Dgn04.eps 

Decision tree. 

deck n. A storage device, such as a tape deck, or a group 

of such devices. 

declaration n. A binding of an identifier to the information 

that relates to it. For example, to make a declaration 

of a constant means to bind the name of the constant with 

its value. Declaration usually occurs in a program’s source 

code; the actual binding can take place at compile time or 

run time. See also bind, constant, data declaration, data type, 

identifier, instruction, routine, type declaration, variable. 

declarative markup language n. In text processing, a 

system of text-formatting codes that indicates only that a 

unit of text is a certain part of a document. Document formatting 

is then done by another program, called a parser. 

SGML and HTML are examples of declarative markup 

languages. Acronym: DML. Also called: data manipulation 

language. See also HTML, SGML. 

declare vb. To specify the name and type of a variable 

that will be used in a program. In most high-level programming 

languages, variables are declared at the beginning 

of sections of code. See also variable. 

DECnet n. A hardware, software, and protocol stack 

designed by Digital Equipment Corporation for its Digital 

Network Architecture (DNA). 

decoder n. 1. A device or program routine that converts 

coded data back to its original form. This can mean changing 

unreadable or encrypted codes into readable text or 

changing one code to another, although the latter type of 

decoding is usually referred to as conversion. Compare 

conversion. 2. In electronics and hardware, a type of circuit 

that produces one or more selected output signals 

based on the combination of input signals it receives. 

No 

Is there a new car 

model that you like? 

Yes 

Buy new car 

D

D 

decollate deferral time 

decollate vb. To separate copies in a multipart continuous 

paper form. 

decompiler n. A program that attempts to generate highlevel 

source code from assembly language code or machine 

code. This can be a difficult task, as some assembly language 

code has no corresponding high-level source code. 

See also disassembler. Compare compiler (definition 2). 

decompress vb. See uncompress. 

decrement1 n. The amount by which a number is 

decreased. Compare increment1 . 

decrement2 vb. To decrease a number by a given amount. 

Compare increment2 . 

decryption n. The process of restoring encrypted data to 

its original form. See also data encryption key. Compare 

encryption. 

deCSS n. Decrypt CSS. A utility capable of cracking the 

CSS encryption system used on DVD discs. By decrypting 

the CSS code, DVD movies and other copyrighted material 

can be used with any DVD playback device without 

regard to license or region coding. The origin of deCSS 

can be traced to a number of individuals interested in creating 

a DVD player for the Linux OS. The term deCSS is 

sometimes used generically for any software capable of 

defeating CSS technology. See also CSS, region code. 

DECstation n. 1. A small computer system used primarily 

for word processing, introduced by Digital Equipment 

Corporation in 1978. 2. A personal computer, part of a 

series, introduced by Digital Equipment Corporation in 

1989. 3. A single-user UNIX workstation introduced by 

Digital Equipment Corporation in 1989 and based on 

RISC processors. See also RISC. 

dedicated adj. Of, pertaining to, or being a device, program, 

or procedure devoted to a single task or function. 

dedicated channel n. A communications link reserved 

for a particular use or a particular user. 

dedicated circuit n. See dedicated line. 

dedicated connection n. See dedicated line. 

dedicated line n. 1. A communications channel that permanently 

connects two or more locations. Dedicated lines 

are private or leased lines, rather than public ones. T1 

lines, which are used by many organizations for Internet 

connectivity, are examples of dedicated lines. Also 

called: dedicated connection, leased line, private line. 

Compare switched line. 2. A telephone line that is used for 

150 

one purpose only, such as to receive or send faxes or to 

serve as a modem line. 

dedicated server n. A computer—usually quite powerful—that 

is used solely as a network server. See also 

server. Compare nondedicated server. 

deep copy n. A copy of the contents of a data structure, 

including all its substructures. 

deep hack n. A state of total concentration on and preoccupation 

with a programming effort. Also called: deep 

hack mode. 

de facto standard n. A design, program, or language 

that has become so widely used and imitated that it has little 

competition, but whose status has not been officially 

recognized as standard by an organization such as the 

American National Standards Institute (ANSI) or the 

International Organization for Standardization (ISO). See 

also standard. Compare de jure standard. 

default1 n. A choice made by a program when the user 

does not specify an alternative. Defaults are built into a 

program when a value or option must be assumed for the 

program to function. 

default2 vb. In reference to programs, to make a choice 

when the user does not specify an alternative. 

default button n. The control that is automatically 

selected when a window is introduced by an application 

or operating system, typically activated by pressing the 

Enter key. 

default drive n. The disk drive that an operating system 

reads to and writes from when no alternative is specified. 

default home page n. On a Web server, the file that is 

returned when a directory is referenced without a specific 

filename. This is specified by the Web server software and 

is typically the file called index.html or index.htm. 

default printer n. The printer to which a computer sends 

documents for printing unless an alternative is specified. 

Defense Advanced Research Projects Agency n. The 

U.S. government agency that provided the original support 

for the development of the interconnected networks that 

later grew into the Internet. Acronym: DARPA. See also 

ARPANET. 

deferral time n. The length of time that nodes on a 

CSMA/CD network wait before trying to retransmit after a 

collision. See also CSMA/CD.

deferred address deletia 

deferred address n. An indirect address (memory location) 

whose calculation is delayed until a program is run. 

See also relative address. 

deferred processing n. Processing of data after it has 

been received and stored in blocks. Compare direct 

processing. 

deflection coils n. See yoke. 

deflection routing n. See hot potato routing. 

deformation n. In multimedia and computer-aided design 

applications, the process of altering a model via certain 

tools, such as stretch, shatter, bend, and twist. See also 

CAD, multimedia. 

defrag vb. Slang for defragment. To rearrange data on a 

disk drive so that whole files are stored in contiguous sectors 

and the drive heads do not have to travel to scattered 

locations on the disk in order to read or write portions of a 

particular file. See also defragmentation. 

defragger n. A software utility for reuniting parts of a file 

that have become fragmented through rewriting and 

updating. A defragger physically restores the file to contiguous 

sectors on a hard disk to speed up access as much 

as 75 percent. See also defragmentation, fragmentation, 

optimizer. 

defragmentation n. The process of rewriting parts of a 

file to contiguous sectors on a hard disk to increase the 

speed of access and retrieval. When files are updated, the 

computer tends to save these updates on the largest continuous 

space on the hard disk, which is often on a different 

sector than the other parts of the file. When files are thus 

“fragmented,” the computer must search the hard disk 

each time the file is accessed to find all of the file’s parts, 

which slows down response time. See also optimization 

(definition 1). Compare fragmentation. 

degausser n. A device used to remove magnetization 

from a video monitor or tape recorder head and to erase 

information from magnetic storage media, such as tapes 

and disks. 

degradation n. 1. In communications, a deterioration of 

signal quality, as from line interference. 2. In computer 

systems, a reduction in level of performance or service. 

Degradation in microcomputer performance is indicated 

by slow response times or frequent pauses for disk access 

because memory is insufficient to hold an entire program 

plus the data the program is using. 

151 

deinstall vb. See uninstall. 

deinterlace n. To combine two interlaced fields into a 

single frame that is not interlaced. Deinterlacing is done to 

remove artifacts and improve the quality of encoded 

video. 

dejagging n. Smoothing of the jagged, “stairstep” 

appearance of diagonal lines and curves in graphical 

images. Also called: anti-aliasing. Compare aliasing. 

de jure standard n. A standard for hardware or software 

development that has been issued or approved through a 

formal process by a standards organization. See also standard. 

Compare de facto standard. 

DEK n. See data encryption key. 

deka- prefix See deca-. 

delay distortion n. See envelope delay. 

delete vb. To eliminate text, a file, or part of a document 

with the intention of removing the information permanently. 

There are several ways to delete. On-screen characters 

and parts of documents can be deleted with the 

Delete key, the Backspace key, or with a program’s Delete 

command. Files can be deleted through a command to the 


Delete key n. 1. On IBM and PC-compatible computers, 

a key whose function changes depending on the application 

program. Usually it erases the character under the cursor, 

although in some applications it can erase selected 

text or graphics. See the illustration. Also called: Del key. 

2. On Apple Macintosh computers, a key on the ADB and 

Extended keyboards that erases the character preceding 

the insertion point or erases highlighted text or graphics. 

pace 

Insert Ho 

Delete 

E 

Delete key 

F0Dgn05.eps 

Delete key. 

deletia n. Omitted material. The term is used in responses 

to Usenet or mailing list messages to indicate that some 

unnecessary material has been excluded from the incorporated 

message being answered. 

D

D 

delimit depth queuing 

delimit vb. To set the limits of some entity, generally by 

using a special symbol called a delimiter. Programming languages 

typically delimit such variable-length elements as 

comments, strings, and program blocks. See also delimiter. 

delimiter n. A special character that sets off, or separates, 

individual items in a program or set of data. Special characters 

often used include commas, semi-colons, tabs, and 

paragraph marks. See also delimit, field (definition 1), 

record1 . 

Del key n. See Delete key. 

delta channel n. See ISDN. 

demand-driven processing n. The processing of data 

immediately as it becomes available or ready. Such realtime 

processing avoids the need to store data that has not 

been processed. Compare data-driven processing. 

demand paging n. The most common implementation of 

virtual memory, in which pages of data are read into main 

memory from an auxiliary storage device only in response 

to interrupts that result when software requests a memory 

location that the system has saved to auxiliary storage and 

reused for other purposes. See also paging, swap (definition 

2), virtual memory. 

demand priority n. A network access method in which 

hubs control network access; a feature of 100Base-VG 

Ethernet networks. With demand priority, nodes send 

requests to hubs and the hubs give permission to transmit 

based on priority levels assigned to the requests by the 

nodes. See also 100Base-VG. 

demand publishing n. Producing print copies of publications 

on an as-needed basis rather than in a single long 

press run. Demand publishing is a by-product of desktop 

publishing and advancements in printer capabilities. 

demo n. 1. Short for demonstration. A partial or limited 

version of a software package distributed free of charge 

for advertising purposes. Demos often consist of animated 

presentations that describe or demonstrate the program’s 

features. See also crippled version. 2. A computer in a 

store that is available for customers to test, to see if they 

wish to buy it. 

demodulation n. In communications, the means by 

which a modem converts data from modulated carrier frequencies 

(waves that have been modified in such a way 

that variations in amplitude and frequency represent 

meaningful information) over a telephone line. Data is 

converted to the digital form needed by a computer to 

152 

which the modem is attached, with as little distortion as 

possible. Compare modulation (definition 1). 

demon dialer n. See war dialer. 

demonstration program or demo program n. 1. A prototype 

that shows the on-screen look and sometimes the 

proposed capabilities of a program under development. 

See also prototyping. 2. A scaled-down version of a proprietary 

program offered as a marketing tool. 

denial of service attack n. See DoS. 

denizen n. A participant in a Usenet newsgroup. 

dense wavelength division multiplexing n. A data 

transmission technique in which multiple optical signals, 

each assigned to a separate color (wavelength frequency), 

are multiplexed onto a single strand of optical fiber. 

Because each signal travels separately in its own color 

band on the fiber, dense wavelength division multiplexing 

allows for the simultaneous transmission of different types 

of signals, such as SONET and ATM, each traveling at its 

own rate of speed. Dense wavelength division multiplexing 

can greatly increase the carrying capacity of a single 

optical fiber. Depending on the number, type, and rate of 

the signals involved, bandwidth can range from more than 

40 Gbps to projected highs of 200 Gbps or more. Acronym: 

DWDM. Also called: wave divisision multiplexing, 

WDM. Compare time division multiple access. 

dependence n. The state in which one entity relies upon 

specific hardware, software, or specific events for its own 

definition or functionality. See also context-dependent, 

dependent variable, device dependence, hardware-dependent, 

software-dependent. 

dependent variable n. A variable in a program whose 

value relies on the outcome of another operation. 

deployment descriptor n. In the Java J2EE network 

platform, a deployment descriptor is an XML file provided 

for each module or application describing how it 

should be deployed. The deployment descriptor directs a 

deployment tool to deploy a module or application with 

specific container options. It also describes the specific 

configuration requirements that an administrator must 

resolve when installing modules and J2EE applications 

into an operational environment. See also container, J2EE, 

module, XML. 

depth queuing vb. 1. In computer graphics and modeling, 

giving a two-dimensional object a three-dimensional 

appearance through such techniques as shading and hidden-

deque desk accessory 

line removal. 2. Drawing objects from background to foreground 

to ease in the task of hidden-line removal. 

deque n. Short for double-ended que. A form of the 

queue data structure that can have elements added to or 

removed from either end of the list. See also queue. 

dequeue vb. To remove from a queue. See also queue. 

dereference vb. In programming, to access information 

at the address contained by a pointer. The syntax for dereferencing 

varies among computer languages. See also double-dereference, 

handle (definition 1), pointer. 

derived class n. In object-oriented programming, a class 

created from another class, called the base class. A derived 

class inherits all the features of its base class. It can then 

add data elements and routines, redefine routines from the 

base class, and restrict access to base-class features. See 

also base class, class, inheritance (definition 1), objectoriented 

programming. 

derived font n. A font that has been scaled or modified 

from a previously existing font. For example, the Macintosh 

operating system can generate characters in font sizes 

other than the installed range of sizes. See also font. Compare 

intrinsic font. 

derived relation n. A relation produced as the result of 

one or more relational-algebra operations on other relations. 

See also relational algebra, view1 (definition 2). 

DES n. Acronym for Data Encryption Standard. A specification 

for encryption of computer data developed by 

IBM and adopted by the U.S. government as a standard 

in 1976. DES uses a 56-bit key. See also encryption, key 


descendant n. 1. In object-oriented programming, a 

class (group) that is a more specialized form of another, 

higher-level class. See also class, object-oriented programming. 

2. In computing, a process (roughly, a program 

or task) that is called by another process and inherits 

certain of the originator’s properties, such as open files. 

See also child (definition 1), inheritance (definition 2). 

Compare client (definition 2). 

descendent key n. All the subkeys that appear when a 

key in the registry is expanded. A descendent key is the 

same as a subkey. Also called: descendant key. See also 

key, subkey. 

descender n. The portion of a lowercase letter that falls 

below the baseline. See the illustration. See also baseline, 

x-height. Compare ascender. 

153 

xylem 

Descender 

F0Dgn06.eps 

Descender. 

Baseline 

descending sort n. A sort that arranges items in 

descending order—for example, with Z preceding A and 

higher numbers preceding lower ones. See also alphanumeric 

sort. Compare ascending sort. 

descriptor n. 1. In information retrieval, a word, similar 

to an index entry in a book, that identifies a significant 

topic or element in a stored document or group of documents. 

It is used as a key in rapid search and retrieval of 

information. See also keyword (definition 1). 2. In programming, 

a piece of stored information used to describe 

something else, often in terms of structure, content, or 

some other property. Compare identifier. 

deselect vb. To reverse the action of selecting an option, 

a range of text, a collection of graphical objects, and so on. 

Compare select. 

deserialize vb. To change from serial (by bit) to parallel 

(by byte); to convert a single (serial) stream of bits to parallel 

streams representing the same information. Compare 

serialize. 

Design by Contract n. An approach to building reusable 

systems where a software system is viewed as a set of 

communicating components whose interaction is based on 

precisely defined specifications of the mutual obligations, 

also known as contracts. 

design cycle n. All the phases involved in developing 

and producing new hardware or software, including product 

specification, creation of prototypes, testing, debugging, 

and documentation. 

desk accessory n. A type of small program on Macintosh 

computers and in windowing programs for IBM and 

PC-compatible machines that acts as the electronic equivalent 

of a clock, calendar, calculator, or other small appliance 

found on a typical desktop. Desk accessories are 

conveniences that can be activated when needed and then 

either put away or moved to a small part of the screen. A 

special type of desk accessory, a control panel, provides 

the user with the ability to change the date and time as 

D

D 

desktop development cycle 

well as to control screen colors, mouse movements, and 

other parameters. Acronym: DA. Also called: desktop 

accessory. See also control panel. 

desktop n. An on-screen work area that uses icons and 

menus to simulate the top of a desk. A desktop is characteristic 

of the Apple Macintosh and of windowing programs 

such as Microsoft Windows. Its intent is to make a 

computer easier to use by enabling users to move pictures 

of objects and to start and stop tasks in much the same 

way as they would if they were working on a physical 

desktop. See also graphical user interface. 

desktop accessory n. See desk accessory. 

Desktop Color Separation n. See DCS. 

desktop computer n. A computer that fits conveniently 

on the surface of a business desk. Most personal computers 

as well as some workstations can be considered desktop 

computers. Compare portable computer. 

desktop conferencing n. The use of computers for 

simultaneous communication among geographically separated 

participants in a meeting. This communication may 

include input to and display from application programs as 

well as audio and video communication. See also data 

conferencing, teleconferencing, video conferencing. 

desktop enhancer n. Software that adds functionality to 

a windows-based operating system such as Microsoft 

Windows or Mac OS—for example, an enhanced file 

browser, clipboard, or multimedia player. 

desktop environment n. The appearance and user interface 

of a computer operating system (OS). An OS may 

offer the user opportunities to customize the desktop environment, 

or sometimes a choice of alternate desktop environments, 

with the OS underneath remaining the same. 

Desktop file n. A hidden file maintained on a particular 

volume (roughly equivalent to a disk) by the Macintosh 

operating system for storing information about the files on 

it, such as version data, lists of icons, and file references. 

Desktop Management Interface n. See DMI. 

desktop publishing n. The use of a computer and specialized 

software to combine text and graphics to create a 

document that can be printed on either a laser printer or a 

typesetting machine. Desktop publishing is a multiple-step 

process involving various types of software and equipment. 

The original text and illustrations are generally produced 

with software such as word processors and drawing 

and painting programs and with photograph-scanning 

154 

equipment and digitizers. The finished product is then 

transferred to a page-makeup program, which is the software 

most people think of as the actual desktop publishing 

software. This type of program enables the user to lay out 

text and graphics on the screen and see what the results 

will be; for refining parts of the document, these programs 

often include word processing and graphics features in 

addition to layout capabilities. As a final step, the finished 

document is printed either on a laser printer or, for the best 

quality, by typesetting equipment. 

desktop video n. The use of a personal computer to display 

video images. The video images may be recorded on 

video tape or on a laser disc or may be live footage from a 

video camera. Live video images can be transmitted in 

digital form over a network in video conferencing. Acronym: 

DTV. 

destination n. The location (drive, folder, or directory) to 

which a file is copied or moved. Compare source. 

destructive read n. An attribute of certain memory systems, 

notably core systems. In a destructive read of a 

memory location, the data is passed on to the processor, 

but the copy in memory is destroyed by the process of 

reading. Destructive memory systems require special logic 

to rewrite data back to a memory location after it is read. 

Also called: destructive readout. See also core. Compare 

nondestructive readout. 

detail file n. See transaction file. 

detection n. Discovery of a certain condition that affects 

a computer system or the data with which it works. 

determinant n. In database design theory, any attribute or 

combination of attributes on which any other attribute or 

combination of attributes is functionally dependent. 

determinism n. In computing, the ability to predict an 

outcome or to know in advance how data will be manipulated 

by a processing system. A deterministic simulation, 

for example, is one in which a certain input always produces 

the same output. 

developer n. 1. One who designs and develops software. 

2. See programmer. 

developer’s toolkit n. A set of routines (usually in one or 

more libraries) designed to allow developers to more easily 

write programs for a given computer, operating system, or 

user interface. See also library (definition 1), toolbox. 

development cycle n. The process of application development 

from definition of requirements to finished product,

device Dhrystone 

including the following stages: analysis, design and prototyping, 

software coding and testing, and implementation. 

device n. A generic term for a computer subsystem. 

Printers, serial ports, and disk drives are often referred to 

as devices; such subsystems frequently require their own 

controlling software, called device drivers. See also 

device driver. 

device address n. A location within the address space of 

a computer’s random access memory (RAM) that can be 

altered either by the microprocessor or by an external 

device. Device addresses are different from other locations 

in RAM, which can be altered only by the microprocessor. 

See also device, input/output, RAM. 

device control character n. See control character. 

device controller n. See input/output controller. 

device dependence n. The requirement that a particular 

device be present or available for the use of a program, 

interface, or protocol. Device dependence in a program is 

often considered unfortunate because the program either is 

limited to one system or requires adjustments for every 

other type of system on which it is to run. Compare device 

independence. 

device driver n. A software component that permits a 

computer system to communicate with a device. In most 

cases, the driver also manipulates the hardware in order to 

transmit the data to the device. However, device drivers 

associated with application packages typically perform only 

the data translation; these higher-level drivers then rely on 

lower-level drivers to actually send the data to the device. 

Many devices, especially video adapters on PC-compatible 

computers, will not work properly—if at all—without the 

correct device drivers installed in the system. 

Device Driver Developer Kit n. See DDK. 

Device Driver Kit n. See DDK. 

device independence n. A characteristic of a program, 

interface, or protocol that supports software operations that 

produce similar results on a wide variety of hardware. For 

example, the PostScript language is a device-independent 

page description language because programs issuing Post- 

Script drawing and text commands need not be customized 

for each potential printer. Compare device dependence. 

device-independent bitmap n. See DIB. 

device manager n. A software utility that allows viewing 

and changing hardware configuration settings, such as 

155 

interrupts, base addresses, and serial communication 

parameters. 

Device Manager n. In Windows 95, a function within the 

System Properties utility that indicates device conflicts 

and other problems and allows a user to change the properties 

of the computer and each device attached to it. See 

also property, property sheet. 

device name n. The label by which a computer system 

component is identified by the operating system. MS- 

DOS, for example, uses the device name COM1 to identify 

the first serial communications port. 

device partnership n. A registry key, stored on the Windows 

CE device, that a desktop computer uses to identify 

that Windows CE device when it is connected to the desktop. 

The key defines values for synchronization, file conversions, 

and backup and restore information, which 

enable multiple Windows CE devices to connect to the 

same desktop computer. A device partnership is created 

the first time you connect a Windows CE device to a desktop 

computer. 

device resolution n. See resolution (definition 1). 

DFP n. See digital flat panel port. 

DFS n. See distributed file system. 

DGIS n. Acronym for Direct Graphics Interface Specification. 

An interface developed by Graphics Software Systems. 

DGIS is firmware (generally implemented in ROM 

on a video adapter) that allows a program to display 

graphics on a video display through an extension to the 

IBM BIOS Interrupt 10H interface. 

DHCP n. Acronym for Dynamic Host Configuration Protocol. 

A TCP/IP protocol that enables a network connected 

to the Internet to assign a temporary IP address to a 

host automatically when the host connects to the network. 

See also IP address, TCP/IP. Compare dynamic SLIP. 

Dhrystone n. A general-performance benchmarking test, 

originally developed by Rheinhold Weicker in 1984 to measure 

and compare computer performance. The test reports 

general system performance in dhrystones per second. It is 

intended to replace the older and less reliable Whetstone 

benchmark. The Dhrystone benchmark, like most benchmarks, 

consists of standard code revised periodically to 

minimize unfair advantages to certain combinations of 

hardware, compiler, and environment. Dhrystone concentrates 

on string handling and uses no floating-point operations. 

Like most benchmarking tests, it is heavily 

D

D 

DHTML difference 

influenced by hardware and software design, such as compiler 

and linker options, code optimizing, cache memory, 

wait states, and integer data types. See also benchmark2 . 

Compare sieve of Eratosthenes, Whetstone. 

DHTML n. See dynamic HTML. 

DIA n. Acronym for Document Interchange Architecture. 

A document exchange guideline used in IBM’s Systems 

Network Architecture (SNA). DIA specifies methods of 

organizing and addressing documents for transmission 

between computers of different sizes and models. DIA is 

supported by IBM’s Advanced Program-to-Program Communication 

(APPC) and by Logical Unit (LU) 6.2, which 

establish the capabilities and types of interactions possible 

in an SNA environment. See also DCA (definition 1), SNA. 

diacritical mark n. An accent mark above, below, or 

through a written character—for example, the acute (´) 

and grave (`) accents. 

dialect n. A variant of a language or protocol. For example, 

Transact-SQL is a dialect of structured query language 

(SQL). 

dialog n. 1. In computing, the exchange of human input 

and machine responses that forms a “conversation” 

between an interactive computer and the person using it. 

2. The exchange of signals by computers communicating 

on a network. 

dialog box n. In a graphical user interface, a special window 

displayed by the system or application to solicit a 

response from the user. See also windowing environment. 

Compare integrator. 

dial-up adj. Of, pertaining to, or being a connection that 

uses the public switched telephone network rather than a 

dedicated circuit or some other type of private network. 

dial-up access n. Connection to a data communications 

network through a public switched telecommunication 

network. 

dial-up boot loader n. A tool for upgrading a version of 

an operating system on a target device. Acronym: DUB. 

dial-up networking n. Connection to a remote network 

through use of a modem. Dial-up networking is typically 

used in reference to telecommuting, although the term is 

equally applicable to connecting to the Internet. 

dial-up service n. A telephone connection provider for a 

local or worldwide public switched telephone network that 

provides Internet or intranet access, advertisement via a 

156 

Web page, access to news services, or access to the stock 

market and other resources. 

DIB n. 1. Acronym for device-independent bitmap. A file 

format designed to ensure that bitmapped graphics created 

using one application can be loaded and displayed in 

another application exactly the way they appeared in the 

originating application. See also bitmapped graphics. 

2. Acronym for Directory Information Base. A directory 

of user and resource names in an X.500 system. The DIB 

is maintained by a Directory Server Agent (DSA). Also 

called: white pages. 

DIBengine n. Software, or a combination of hardware 

and software, that produces DIB files. See also DIB 


dibit n. A set of 2 bits representing one of four possible 

combinations: 00, 01, 10, and 11. In communications, a 

dibit is a kind of transmission unit made possible by the 

modulation technique known as differential phase-shift 

keying, which encodes data by using four different states 

(phase shifts) in the transmission line to represent each of 

the four dibit combinations. See also phase-shift keying. 

dichotomizing search n. See binary search. 

dictation software n. Computer programs that can recognize 

spoken words as input. Used as an alternative to keyboard 

input, dictation software cannot comprehend the 

spoken language; it can only convert and transmit the sounds 

to the computer. Speaker-dependent dictation software 

requires the user to “train” the computer to become familiar 

with his or her voice patterns and accent. First-generation 

discrete speech systems require the user to speak slowly and 

distinctly, with pauses between words. Next-generation continuous 

speech systems can interpret natural speech patterns 

and speeds. See also voice recognition. 

dictionary attack n. Originally a method of guessing a 

user’s password or PIN by trying every word in the dictionary 

until successful. Currently used to identify any attack 

that tries known words or alphanumeric character strings 

to break a simple password. 

dielectric n. Insulating material, such as rubber or plastic, 

that does not conduct electricity. 

DIF n. See data interchange format. 

difference n. 1. The amount by which two values differ. In 

electronics, differences in physical elements, such as waveforms 

or voltages, are used in the operation of circuits, 

amplifiers, multiplexers, communications equipment, and

Difference Engine digital broadcast satellite 

so on. 2. In database management, it is an operator in relational 

algebra that is used in sorting record sets (tuples). For 

example, given two relational tables, A and B, that are 

union-compatible (contain the same number of fields, with 

corresponding fields containing the same types of values), 

the statement DIFFERENCE A, B builds a third relation 

containing all those records that appear in A but not in B. 

See also relational algebra, tuple. Compare intersect, union. 

Difference Engine n. An early computerlike mechanical 

device designed by British mathematician and scientist 

Charles Babbage in the early 1820s. The Difference 

Engine was intended to be a machine with a 20-decimal 

capacity capable of solving mathematical problems. The 

concept of the Difference Engine was enhanced by Babbage 

in the 1830s in the design of his more famous Analytical 

Engine, a mechanical precursor of the electronic 

computer. See also Analytical Engine. 

differential adj. In electronics, a reference to a type of 

circuit that makes use of the difference between two signals 

rather than the difference between one signal and 

some reference voltage. 

differential backup n. A backup that copies files created 

or changed since the last normal or incremental backup. It 

does not mark files as having been backed up (in other 

words, the archive attribute is not cleared). If you are performing 

a combination of normal and differential backups, 

restoring files and folders requires that you have the last 

normal, as well as the last differential, backup. 

differential phase-shift keying n. See phase-shift keying. 

differentiator n. A circuit whose output is the differential 

(first derivative) of the input signal. The differential measures 

how fast a value is changing, so the output of a differentiator 

is proportional to the instantaneous rate of change 

of the input signal. See the illustration. Compare integrator. 

Amplitude 

Output 

F0Dgn07.eps 

Differentiator. 

Input 

Time 

Diffie-Hellman n. Diffie-Hellman key agreement protocol. 

A public-key cryptography method that allows two 

157 

hosts to create and share a secret key. Diffie-Hellman is 

used for key management by virtual private networks 

(VPNs) operating on the IPSec standard. See also IPSec. 

digerati n. Cyberspace populace that can be roughly 

compared to literati. Digerati are people renowned as or 

claiming to be knowledgeable about topics and issues 

related to the digital revolution; more specifically, they are 

people “in the know” about the Internet and online activities. 

See also guru, techie, wizard (definition 1). 

digest n. 1. An article in a moderated newsgroup that 

summarizes multiple posts submitted to the moderator. 

See also moderator, newsgroup. 2. A message in a mailing 

list that is sent to subscribers in place of the multiple individual 

posts that the digest contains. If the mailing list is 

moderated, the digest may be edited. See also moderated. 

digicash n. See e-money. 

digit n. One of the characters used to indicate a whole 

number (unit) in a numbering system. In any numbering 

system, the number of possible digits is equal to the base, 

or radix, used. For example, the decimal (base-10) system 

has 10 digits, 0 through 9; the binary (base-2) system has 

2 digits, 0 and 1; and the hexadecimal (base-16) system 

has 16 digits, 0 through 9 and A through F. 

digital adj. 1. A reference to something based on digits 

(numbers) or their representation. 2. In computing, analogous 

in use, though not in meaning, to binary because the 

computers familiar to most people process information 

coded as different combinations of the binary digits (bits) 

0 and 1. Compare analog. 

Digital Advanced Mobile Phone Service n. See D- 

AMPS. 

digital audio disc n. An optical storage medium for 

recording digitally encoded audio information. See also 

compact disc (definition 1). 

digital audio tape n. A magnetic tape storage medium 

for recording digitally encoded audio information. Acronym: 

DAT. 

digital audio/video connector n. An interface on some 

high-end video cards or TV tuner cards that allows the 

simultaneous transmission of digital audio and video signals. 

Also called: DAV connector. See also interface (definition 

3), video adapter. 

digital broadcast satellite n. See direct broadcast 

satellite. 

D

D 

digital camera Digital Micromirror Device 

digital camera n. A type of camera that stores photographed 

images electronically instead of on traditional 

film. A digital camera uses a CCD (charge-coupled 

device) element to capture the image through the lens 

when the operator releases the shutter in the camera; circuitry 

within the camera then stores the image captured by 

the CCD in a storage medium such as solid-state memory 

or a hard disk. After the image has been captured, it is 

downloaded by cable to the computer using software supplied 

with the camera. Once stored in the computer, the 

image can be manipulated and processed much like the 

image from a scanner or related input device. See also 

charge-coupled device, digital photography. 

digital cash n. See e-money. 

digital certificate n. 1. An assurance that software 

downloaded from the Internet comes from a reputable 

source. A digital certificate provides information about the 

software—such as the identity of the author and the date 

on which the software was registered with a certificate 

authority (CA), as well as a measure of tamper-resistance. 

2. A user identity card or “driver’s license” for cyberspace. 

Issued by a certificate authority (CA), a digital certificate 

is an electronic credential that authenticates a user on the 

Internet and intranets. Digital certificates ensure the legitimate 

online transfer of confidential information, money, 

or other sensitive materials by means of public encryption 

technology. A digital certificate holder has two keys 

(strings of numbers): a private key held only by the user, 

for “signing” outgoing messages and decrypting incoming 

messages; and a public key, for use by anyone, for 

encrypting data to send to a specific user. See also certificate 

authority, encryption, private key, public key. 

digital communications n. Exchange of communications 

in which all information is transmitted in binaryencoded 

(digital) form. 

digital computer n. A computer in which operations are 

based on two or more discrete states. Binary digital computers 

are based on two states, logical “on” and “off,” represented 

by two voltage levels, arrangements of which are 

used to represent all types of information—numbers, letters, 

graphics symbols, and program instructions. Within 

such a computer, the states of various circuit components 

change continuously to move, operate on, and save this 

information. Compare analog computer. 

Digital Darkroom n. A Macintosh program developed by 

Silicon Beach Software for enhancement of black-andwhite 

photographs or scanned images. 

158 

digital data service n. See DDS. 

digital data transmission n. The transfer of information 

encoded as a series of bits rather than as a fluctuating 

(analog) signal in a communications channel. 

digital display n. A video display capable of rendering 

only a fixed number of colors or gray shades. Examples of 

digital displays are IBM’s Monochrome Display, Color/ 

Graphics Display, and Enhanced Color Display. See also 

CGA, EGA, MDA. Compare analog display. 

digital divide n. The gap between those who have the 

opportunity to take advantage of the Internet and related 

information resources, and those who do not. Differences 

in income, education, and comfort levels with technology 

are contributing factors to the separation between those 

with access to technological resources and those without. 

digital DNA n. 1. Broadly, a reference to the bits that 

comprise digital information. 2. In the gaming world, a 

technology called “Cyberlife” that mimics biological 

DNA in the creation and development of trainable creatures 

known as Norns. Like real DNA, digital DNA is 

passed from parent to offspring and determines the artificial 

creature’s characteristics and adaptability. 

digital fingerprinting n. See digital watermark. 

digital flat panel port n. An interface designed to allow 

direct connection between a flat panel monitor and a computer 

without requiring an analog-to-digital conversion. 

Acronym: DFP. 

digital home n. See smart home. 

digital light processing projector n. See DLP. 

digital line n. A communications line that carries information 

only in binary-encoded (digital) form. To minimize 

distortion and noise interference, a digital line uses 

repeaters to regenerate the signal periodically during 

transmission. See also repeater. Compare analog line. 

digital linear tape n. A magnetic storage medium used 

to back up data. Digital linear tape allows for faster transfer 

of data compared with other tape technologies. Acronym: 

DLT. 

Digital Micromirror Device n. The circuit technology 

behind Texas Instruments’ Digital Light Processing, used in 

image projectors. A Digital Micromirror Device, or DMD, 

consists of an array of individually addressable, hinged mirrors 

on a chip. Each chip, which is less than 0.002 mm 

wide, rotates in response to a digital signal to reflect light

digital modem Digital Signature Standard 

into the lens of the projection system and thus create a 

bright, full-color display. Displays can be combined to create 

high-definition systems of 1920 × 1035 (1,987,200) pixels 

with 64 million colors. Acronym: DMD. 

digital modem n. 1. A communications device that acts as 

the intermediary between a digital device such as a computer 

or terminal and a digital communications channel, 

such as a high-speed network line, an ISDN circuit, or a 

cable TV system. Although a digital modem supports standard 

(analog) modem protocols, it is not a “typical” modem 

in the sense of being a device whose primary function is to 

modulate (convert digital to analog) before transmission 

and demodulate (convert analog to digital) after transmission. 

It uses advanced digital modulation techniques for 

changing data frames into a format suitable for transmission 

over a digital line. See also terminal adapter. Compare 

modem. 2. A 56 Kbps modem. Such a modem is not purely 

digital but does eliminate the traditional digital-to-analog 

conversion for downstream transmissions—that is, transmissions 

moving from the Internet to the end user. A 56 

Kbps modem is also digital in that it requires a digital connection, 

such as T1, between the telephone company and 

the user’s Internet Service Provider (ISP) in order to achieve 

its highest speed. See also 56-Kbps modem. 3. A term used 

to distinguish all-digital communications devices, such as 

ISDN and cable “modems” from the more traditional analog-to-digital, 

phone-based modems. 

Digital Network Architecture n. A multilayered architecture 

and set of protocol specifications for networks. 

Designed by the Digital Equipment Corporation, Digital 

Network Architecture is implemented in the set of products 

known by the name DECnet. Acronym: DNA. See 

also DECnet. 

digital photography n. Photography by means of a digital 

camera. Digital photography differs from conventional 

photography in that a digital camera does not use a silver 

halide–based film to capture an image. Instead, a digital 

camera captures and stores each image electronically. See 

also digital camera. 

digital picture frame n. Electronic device used in displaying 

digital photos and graphics while giving the outward 

appearance of a traditional picture frame. Digital 

picture frames allow users to rotate photos within the 

frame at specified intervals, display a series of photos as a 

slide show, or use an Internet connection to download photos, 

order prints, or send customized photo sets to others. 

Digital Print Order Format n. See DPOF. 

159 

digital proof n. See direct digital color proof. 

digital recording n. The storage of information in 

binary-encoded (digital) format. Digital recording converts 

information—text, graphics, sound, or pictures—to 

strings of 1s and 0s that can be physically represented on a 

storage medium. Digital recording media include computer 

disks and tapes, optical (or compact) discs, and 

ROM cartridges of the type used for some software and 

many computer games. 

Digital Rights Management n. See DRM. 

digital satellite system n. A high-powered satellite system 

with the capability to deliver high-quality transmissions 

of hundreds of channels directly to television 

receivers. A DSS broadcast begins as a digital signal sent 

from a service provider’s station to a satellite. From there, 

it is directed to a satellite dish (typically 18 inches) at the 

user’s premises. The dish next transmits the signal to a 

converter box, which changes it to an analog signal before 

sending it to the television set. Acronym: DSS. 

Digital Services n. See DS. 

digital signal n. A signal, such as one transmitted within 

or between computers, in which information is represented 

by discrete states—for example, high and low voltages— 

rather than by fluctuating levels in a continuous stream, as 

in an analog signal. 

Digital Signal n. See DS. 

digital signal processor n. An integrated circuit 

designed for high-speed data manipulation and used in 

audio, communications, image manipulation, and other data 

acquisition and data control applications. Acronym: DSP. 

digital signature n. A security mechanism used on the 

Internet that relies on two keys, one public and one private, 

that are used to encrypt messages before transmission 

and to decrypt them on receipt. 

Digital Signature Algorithm n. The U.S. government 

standard for digital signatures, as specified by the National 

Institute of Standards and Technology, in FIPS 186, Digital 

Signature Standard. DSA is based on signature encryption 

based on a public and a private key. Acronym: DSA. 

See also digital signature. 

Digital Signature Standard n. A public key cryptographic 

standard issued in 1994 by the United States 

National Institute of Standards and Technology (NIST) to 

authenticate electronic documents. The DSS uses a Digital 

Signature Algorithm (DSA) to generate and verify digital 

D

D 

Digital Simultaneous Voice and Data digiterati 

signatures based on a public key, which is not secret, and a 

private key, which is known or held only by the person 

generating the signature. A digital signature serves to 

authenticate both the identity of the signer and the integrity 

of the transmitted information. Acronym: DSS. See 

also public key encryption. 

Digital Simultaneous Voice and Data n. A modem 

technology by Multi-Tech Systems, Inc., that allows a single 

telephone line to be used for conversation together with data 

transfer. This is accomplished by switching to packet-mode 

communications when the need for voice transfer is 

detected; digitized voice packets are then transferred along 

with data and command packets. Acronym: DSVD. 

digital sort n. A type of ordering process in which record 

numbers or their key values are sorted digit by digit, 

beginning with the least significant (rightmost) digit. Also 

called: radix sort. 

digital speech n. See speech synthesis. 

digital subscriber line or Digital Subscriber Line 

n. See DSL. 

Digital Subscriber Line Access Multiplexer or Digital 

Subscriber Line Multiplexer n. See DSLAM. 

digital-to-analog converter n. A device that translates 

digital data to an analog signal. A digital-to-analog converter 

takes a succession of discrete digital values as input 

and creates an analog signal whose amplitude corresponds, 

moment by moment, to each digital value. See the 

illustration. Acronym: DAC. Compare analog-to-digital 

converter. 

Digital 

input 

DAC 

Analog 

output 

F0Dgn08.eps 

Digital-to-analog converter. 

digital versatile disc n. See digital video disc. 

digital video n. Video images and sound stored in a digital 

format. Acronym: DV. 

digital TV or digital television n. The transmission of 

television signals using digital rather than the conventional 

analog signals. A digital TV standard for the United States 

was approved by the FCC in 1996. Digital TV provides a 

better television experience and new information services. 

Digital signals produce higher quality pictures and CD- 

160 

quality sound, compared to the analog signals used with 

today's television. Digital TV can support interactive television, 

electronic program guides, and a variety of digital 

services, such as Internet channel broadcasting and data 

services. Acronym: DTV. Compare HDTV. 

digital video disc n. The next generation of optical disc 

storage technology. With digital video disc technology, 

video, audio, and computer data can be encoded onto a 

compact disc (CD). A digital video disc can store greater 

amounts of data than a traditional CD. A standard singlelayer, 

single-sided digital video disc can store 4.7 GB of 

data; a two-layer standard increases the single-sided disc 

capacity to 8.5 GB. Digital video discs can be doublesided 

with a maximum storage of 17 GB per disc. A digital 

video disc player is needed to read digital video discs; 

this player is equipped to read older optical storage technologies. 

Advocates of the digital video disc intend to 

replace current digital storage formats, such as laser disc, 

CD-ROM, and audio CD, with the single digital format of 

the digital video disc. Acronym: DVD. Also called: digital 

versatile disc. See also digital video disc–ROM. 

digital video disc–erasable n. A proposed extension to 

the digital video disc recording format to allow multiple 

re-recording by a consumer. Acronym: DVD-E. Also 

called: digital video disc–ROM. 

digital video disc–recordable n. A proposed extension 

to the digital video disc recording format to allow onetime 

recording by a consumer. Acronym: DVD-R. 

digital video disc–ROM n. A computer-readable version 

of a digital video disc containing either 4.7 or 8.5 GB 

of storage per side, the larger if 3M’s dual-layer “2P” technology 

is used. Acronym: DVD-ROM. Also called: digital 

video disc–erasable. See also digital video disc. 

Digital Video–Interactive n. A hardware/software system 

developed by RCA, General Electric, and Intel that 

implements compression of digital video and audio for 

microcomputer applications. Acronym: DV-I. 

Digital Video Interface n. See DVI. 

digital video recording n. See DVR. 

digital watermark n. A unique identifier embedded in a 

file to deter piracy and prove file ownership and quality. 

Digital watermarking is often used with graphics and 

audio files to identify the owner’s rights to these works. 

See also fingerprint (definition 2). 

digiterati n. See digerati.

digitize direct access 

digitize vb. To convert any continuously varying (analog) 

source of input, such as the lines in a drawing or a sound 

signal, to a series of discrete units represented in a computer 

by the binary digits 0 and 1. Analog-to-digital converters 

are commonly used to perform this translation. See 

also aliasing, analog-to-digital converter. 

digitizing tablet n. See graphics tablet. 

DikuMUD n. 1. Multiuser dungeon (MUD) software developed 

by five individuals at the Computer Science Institute at 

Copenhagen University (whose acronym in Danish is 

DIKU). DikuMUD uses multimedia and is object-oriented, 

but the classes are hard-coded. The software is covered by a 

license agreement that forbids its distribution for money. 

See also MUD, multimedia, object-oriented. 2. A game that 

uses the DikuMUD software. 

dimensioning n. In CAD programs, a means of specifying 

and possibly controlling the measurements and spatial 

relationships of elements in a modeled object, such as 

using lines, arrows, and text (that is, measurements) to 

indicate the length, height, and thickness of each of the 

walls in a modeled room or house. See also CAD. 

DIMM n. Acronym for dual inline memory module. A 

type of memory board comprised of RAM chips mounted 

on a circuit board, similar to the more commonly used 

SIMM (Single Inline Memory Module). DIMMs are characterized 

by a 64-bit data path and pins (connectors) on 

each side that are on different circuits and that respond to 

different signals. SIMMs, in contrast, have a 32-bit data 

path, and their connectors are on the same circuit and 

respond to the same signal. While SIMMs must be added 

in pairs, DIMMs can be added to a computer one at a time. 

See also memory chip. Compare SIMM. 

dimmed adj. Shown on the screen in gray characters 

instead of black characters on white or white characters on 

black. Menu options appear dimmed in a graphical user 

interface to indicate that under current circumstances they 

are not available—for example, “Cut” when no text has 

been highlighted or “Paste” when there is no text in the 

clipboard. 

DIN connector n. A multipin connector conforming to 

the specification of the German national standards organization 

(Deutsch Industrie Norm). DIN connectors are used 

to link various components in personal computers. 

dingbat n. A small graphical element used for decorative 

purposes in a document. Some fonts, such as Zapf Dingbats, 

are designed to present sets of dingbats. See also 

font. Compare bullet. 

161 

diode n. A device that passes current in only one direction. 

A diode is usually a semiconductor. See the illustration. 

See also semiconductor. 

F0Dgn09.eps 

Diode. The drawings (top) show two of the many types of 

diode packages. The band on the right end of each indicates 

polarity. At bottom is a schematic representation of a diode. 

diode-transistor logic n. A type of circuit design that 

employs diodes, transistors, and resistors to perform logic 

functions. Acronym: DTL. 

DIP n. Acronym for dual inline package. A standard for 

packaging integrated circuits in which the microminiature 

electronic circuits etched on a silicon wafer are enclosed in 

a rectangular housing of plastic or ceramic and connected to 

downward-pointing pins protruding from the longer sides of 

the chip. Designed to facilitate circuit board manufacturing, 

this design does not work well for modern chips requiring 

very large numbers of connections. See also document 

image processing. Compare leadless chip carrier, pin grid 

array, SIP, surface-mount technology. 

dipole n. A pair of opposite electric charges or magnetic 

poles of opposite sign separated by a small distance. 

DIP switch n. Short for Dual Inline Package switch. One 

or more small rocker- or sliding-type toggle switches contained 

in the plastic or ceramic housing of a dual inline 

package (DIP) connected to a circuit board. Each switch on 

a DIP switch can be set to one of two positions, closed or 

open, to control options on the circuit board. See also DIP. 

dir n. An MS-DOS command that instructs a computer to 

display a list of files and subdirectories in the current 

directory or folder. If the command is followed by a path, 

the computer displays a list of files and subdirectories in 

the specified directory or folder. See also command, MS- 

DOS, path (definition 2). 

Direct3D n. See DirectX. 

direct access n. The ability of a computer to find and go 

straight to a particular storage location in memory or on 

disk to retrieve or store an item of information. Note that 

direct access is not the same as direct memory access 

(DMA), which is the ability to transfer information 

D

D 

direct access storage device directory replication 

directly between an input/output channel and memory 

rather than taking the longer and more circuitous route of 

I/O channel to microprocessor to memory. See also random 

access. Compare direct memory access. 

direct access storage device n. See DASD. 

direct address n. See absolute address. 

DirectAnimation n. See DirectX. 

direct broadcast satellite n. A digital telecommunications 

service that delivers television programming via the 

Digital Satellite System (DSS). Direct broadcast satellite 

technology uses a geostationary orbit satellite (GEO) to 

receive digitized signals sent by ground-based uplink centers; 

the satellite then beams the signal across a wide 

swath on Earth. Subscribers within that swath use small 

(18-inch) satellite dishes to bring the signal into a set-top 

box decoder for playback. Although primarily used for television 

broadcasts, the technology is seen as having potential 

to also deliver high-quality, digital communications and 

multimedia content in the future. Acronym: DBS. Also 

called: digital broadcast satellite. See also digital satellite 

system, geostationary orbit satellite, webcasting. 

direct cable connection n. A link between the I/O ports 

of two computers that uses a single cable rather than a 

modem or other active interface device. In most cases, a 

direct cable connection requires a null modem cable. 

direct-connect modem n. A modem that uses standard 

telephone wire and connectors and that plugs directly into 

a telephone jack, eliminating the need for an intermediary 

telephone. Compare acoustic coupler. 

direct-coupled transistor logic n. A circuit design that 

uses transistors and resistors only, with the transistors 

directly connected to each other. This design was used in 

the earliest commercial integrated circuits. The switching 

speed and power consumption of such circuits are about 

average. Acronym: DCTL. 

direct current n. Electrical current whose direction of 

flow does not reverse. The current may stop or change 

amplitude, but it always flows in the same direction. Acronym: 

DC. Compare alternating current. 

direct digital color proof n. A test sheet produced by a 

lower-cost output device, such as a color laser printer, to 

serve as an approximation of what the final image will 

look like when produced on professional-quality printing 

equipment. A direct digital color proof does not involve 

color separation, as in traditional proofs. Instead, a direct 

digital color proof is printed in all colors at one time on a 

162 

single page, resulting in somewhat lower quality compared 

with traditional separation methods but having the 

advantages of increased speed and reduced cost. Acronym: 

DDCP. Also called: digital proof. See also color separation 


DirectDraw n. See DirectX. 

Direct Graphics Interface Specification n. See DGIS. 

DirectInput n. An API (application programming interface) 

developed by Microsoft for joysticks and similar 

pointing devices in Windows 9x. See also DirectX. 

direction key n. See arrow key. 

direct memory access n. Memory access that does not 

involve the microprocessor and is frequently used for data 

transfer directly between memory and an “intelligent” 

peripheral device, such as a disk drive. Acronym: DMA. 

Compare PIO. 

DirectMusic n. See DirectX. 

directory n. 1. A catalog for filenames and other directories 

stored on a disk. A directory is a way of organizing 

and grouping the files so that the user is not overwhelmed 

by a long list of them. The uppermost directory is called 

the root directory; the directories within a directory are 

called subdirectories. Depending on how an operating system 

supports directories, filenames in a directory can be 

viewed and ordered in various ways—for example, alphabetically, 

by date, by size, or as icons in a graphical user 

interface. What the user views as a directory is supported 

in the operating system by tables of data, stored on the 

disk, that indicate characteristics and the location of each 

file. In the Macintosh and Windows 9x operating systems, 

directories are called folders. 2. On a network, an index of 

names and pertinent information related to authorized 

users and network resources. 

Directory Access Protocol n. The protocol that governs 

communications between X.500 clients and servers. See 

also CCITT X series. 

Directory Client Agent n. See DUA. 

Directory Information Base n. See DIB (definition 2). 

Directory Mozilla n. See Open Directory Project. 

directory path n. See pathname. 

directory replication n. The copying of a master set of 

directories from a server (called an export server) to specified 

servers or workstations (called import computers) in 

the same or other domains. Replication simplifies the task 

of maintaining identical sets of directories and files on

Directory Server Agent DirectX 

multiple computers because only a single master copy of 

the data must be maintained. See also directory, server. 

Directory Server Agent n. See DSA. 

directory service n. A service on a network that returns 

mail addresses of other users or enables a user to locate 

hosts and services. 

Directory System Agent n. See DSA. 

directory tree n. A graphic display listing the directories 

and subdirectories on a hard disk in tree form, with subdirectories 

shown as branches of the main directory. See 

also branch (definition 1), directory, tree structure. 

Directory User Agent n. See DUA. 

DirectPlay n. See DirectX. 

direct processing n. Processing of data as it is received 

by the system, as opposed to deferred processing, in which 

data is stored in blocks before processing. Compare 

deferred processing. 

direct read after write n. See DRAW. 

direct read during write n. See DRDW. 

direct sequence n. In spread spectrum communication, 

a form of modulation in which a carrier is modulated by a 

series of binary pulses. See also modulation (definition 1), 

spread spectrum. 

DirectShow n. See DirectX. 

DirectSound n. See DirectX. 

direct view storage tube n. A type of cathode-ray tube 

(CRT) in which the screen can retain images for a long 

time and in which a beam of electrons from an electron 

gun can be moved arbitrarily across the screen surface (as 

opposed to a standard cathode-ray tube, in which the electron 

beam is moved in a specific pattern). This type of CRT 

is capable of displaying a precise, detailed image without 

requiring any screen refresh. However, once the image is 

drawn, it cannot be changed without a complete erasing of 

the screen. Acronym: DVST. Also called: storage tube. 

Compare CRT. 

DirectX n. A set of Microsoft technologies that provide 

developers with the tools needed to create sophisticated 

multimedia applications on Windows-based computers. 

DirectX consists of components making up two integrated 

layers. The Foundation layer provides low-level functions, 

such as support for input devices, designed to ensure that 

163 

applications can run on—and take full advantage of— 

Windows-based hardware. The Media layer, above the 

Foundation layer, provides high-level services, such as 

support for media streaming and animation, that are 

needed in creating applications incorporating such features 

as surround sound, video, and 3-D animation. Direct- 

Animation, DirectSound, and other similarly named 

application programming interfaces (APIs) are members 

of the DirectX family. See the table. See also application 

programming interface. 

Table D.1 ATA Specifications. 

DirectX 

Component Part Of Supports 

Direct3D 

Immediate 

Mode 

Direct3D 

Retained 

Mode 

Direct- 

Animation 

Foundation 

layer 

DirectDraw Foundation 

layer 

DirectInput Foundation 

layer 

Access to 3-D video 

hardware 

Media layer Creation and animation 

of onscreen 3-D 

worlds 

Media layer Interactive animation 

and integration of dif- 

ferent multimedia types 

Access to display 

memory and hardware 

capabilities 

Direct access to various 

input devices, including 

force-feedback 

joysticks 

Real-time music 

DirectMusic Foundation 

layer composition 

DirectPlay Foundation Multiplayer online 

layer gaming and other networked 

applications 

DirectShow Media layer Capture and playback of 

streaming multimedia 

DirectSound Foundation Direct access to sound 

layer cards; wave sound capture 

and playback 

Direct- Foundation 3-D sound positioning 

Sound3D layer 

DirectX Media layer Extensibility of the 

Transform 

DirectX platform to 

include value-added 

products 

D

D 

DirectX Transform disk buffer 

DirectX Transform n. See DirectX. 

dirty adj. Of, pertaining to, or characteristic of a communications 

line that is hampered by excessive noise, degrading 

the quality of the signal. See also noise (definition 2). 

dirty bit n. A bit used to mark modified data in a cache so 

that the modifications may be carried over to primary 

memory. See also bit, cache. 

dirty power n. A power source that can cause damage to 

electronic components, due to noise, voltage spikes, or 

incorrect voltage levels. 

dirty ROM n. Short for dirty read-only memory. In the 

earlier versions of the Macintosh (Mac II, IIx, SE/30, and 

IIcx), a memory system that simulates a 32-bit system but 

is not a true (clean) 32-bit system. Among other flaws, a 

dirty ROM machine can access only 8 megabytes of memory 

under Mac OS System 7. System extensions such as 

MODE32 and the 32-bit enabler are available to allow a 

dirty ROM machine to function like a true, 32-bit clean 

machine. 

disable vb. To suppress something or to prevent it from 

happening. Disabling is a method of controlling system 

functions by disallowing certain activities. For example, 

a program might temporarily disable nonessential interrupts 

(requests for service from system devices) to prevent 

interruptions during a critical point in processing. 

Compare enable. 

disabled folders n. In the Mac OS, several folders in the 

System folder that contain system extensions, control panels, 

and other items that have been removed from the system 

by the extension manager. Items currently in disabled 

folders will not be installed upon system startup; they 

may, however, later be moved back to their regular folders 

automatically by the extension manager. See also extension 

manager, System folder. 

disassembler n. A program that converts machine code 

to assembly language source code. Most debuggers have 

some kind of built-in disassembler that allows the programmer 

to view an executable program in terms of 

human-readable assembly language. See also decompiler. 

Compare assembler. 

disassociate vb. In Windows 95 and Windows NT, to 

remove an association between a file and some application. 

Compare associate. 

164 

disaster dump n. A dump (transfer of memory contents 

to a printer or other output device) made when a program 

fails without hope of recovery. 

disc n. A round, flat piece of nonmagnetic, shiny metal 

encased in a plastic coating, designed to be read from and 

written to by optical (laser) technology. It is now standard 

practice to use the spelling disc for optical discs and disk 

in all other computer contexts, such as floppy disk, hard 

disk, and RAM disk. See also compact disc. 

disconnect vb. To break a communications link. 

discrete adj. Separate; individual; identifiable as a unit. 

For example, bits are discrete elements of data processed 

by a computer. 

discrete multitone n. In telecommunications, a technology 

that uses digital signal processors to split available 

bandwidth into a number of subchannels, allowing over 6 

Mbps of data to be carried over one copper twisted-pair 

wire. Acronym: DMT. 

discrete speech recognition n. Computer speech recognition 

format in which each word is recognized as a distinct 

individual unit, requiring a pause between each word 

spoken. 

discretionary access control list n. The part of an 

object’s security descriptor that grants or denies specific 

users and groups permission to access the object. Only the 

owner of an object can change permissions granted or 

denied in a DACL; thus, access to the object is at the owner’s 

discretion. Acronym: DACL. See also distribution group. 

discretionary hyphen n. See hyphen. 

discussion group n. Any of a variety of online forums in 

which people communicate about subjects of common 

interest. Forums for discussion groups include electronic 

mailing lists, Internet newsgroups, and IRC channels. 

dish n. See satellite dish. 

disk n. 1. A round, flat piece of flexible plastic coated 

with a magnetic material that can be electrically influenced 

to hold information recorded in digital (binary) form and 

encased in a protective plastic jacket to protect the disk 

from damage and contamination. Also called: floppy, 

floppy disk, microfloppy disk. Compare compact disc, 

disc. 2. See hard drive. 

disk access time n. See access time (definition 2). 

disk buffer n. A small amount of memory set aside for 

the purpose of storing data read from, or soon to be written

disk cache disk mirroring 

to, a disk. Because disk devices are slow compared with 

the CPU, it is not efficient to access the disk for only one 

or two bytes of data. Instead, during a read, a large chunk 

of data is read and stored in the disk buffer. When the program 

wants information, it is copied from the buffer. 

Many requests for data can be satisfied by a single disk 

access. The same technique can be applied to disk writes. 

When the program has information to store, it writes it 

into the disk buffer area in memory. When the buffer has 

been filled, the entire contents of the buffer are written to 

the disk in a single operation. 

disk cache n. A portion of a computer’s random access 

memory (RAM) set aside for temporarily holding information 

read from disk. A disk cache does not hold entire 

files, as does a RAM disk (a portion of memory that acts 

as if it were a disk drive). Instead, a disk cache is used to 

hold information that either has recently been requested 

from disk or has previously been written to disk. If the 

required information remains in a disk cache, access time 

is considerably faster than if the program must wait for the 

disk drive mechanism to fetch the information from disk. 

See also cache. Compare disk buffer. 

disk cartridge n. A removable disk enclosed in a protective 

case. A disk cartridge can be used by certain types of 

hard disk drives and related devices, such as the external 

data storage units known as Bernoulli boxes. 

disk controller n. A special-purpose chip and associated 

circuitry that directs and controls reading from and writing 

to a computer’s disk drive. A disk controller handles such 

tasks as positioning the read/write head, mediating 

between the drive and the microprocessor, and controlling 

the transfer of information to and from memory. Disk controllers 

are used with floppy disk drives and hard disks and 

can either be built into the system or be part of a card that 

plugs into an expansion slot. 

disk copy n. The process of duplicating a source disk’s 

data and the data’s organizational structure onto a target 

disk. See also backup. 

disk crash n. The failure of a disk drive. See also crash1 . 

disk directory n. An index of the files on a disk, analogous 

to a card catalog. A disk directory includes information 

about the files, such as their names, sizes, dates of 

creation, and physical locations on the disk. See also 

directory. 

disk drive n. An electromechanical device that reads 

from and writes to disks. The main components of a disk 

165 

drive include a spindle on which the disk is mounted, a 

drive motor that spins the disk when the drive is in operation, 

one or more read/write heads, a second motor that 

positions the read/write heads over the disk, and controller 

circuitry that synchronizes read/write activities and transfers 

information to and from the computer. Two types of 

disk drives are in common use: floppy disk drives and hard 

disk drives. Floppy disk drives are designed to accept 

removable disks in either 5.25-inch or 3.5-inch format; 

hard disk drives are faster, high-capacity storage units that 

are completely enclosed in a protective case. 

disk driver n. A device driver that is added to a system to 

support a specific manufacturer’s disk device. See also 


disk duplexing n. See disk mirroring. 

disk envelope n. The paper container that holds a 5.25inch 

floppy disk and its attached jacket. The disk envelope 

protects exposed surfaces of the disk from dust and other 

foreign material that can scratch and otherwise damage 

the surface, resulting in the loss of recorded data. See also 

disk jacket. 

diskette n. See floppy disk. 

disk farm n. A number of disk drives in a single location 

used together to store or process vast quantities of information, 

such as scientific data, years’ worth of corporate 

sales figures, large numbers of graphic images, or telephone 

company billing records. Current disk farms consist 

of magnetic or optical disks and can hold terabytes of 

information. In older usage, disk farms were sometimes 

known as “Laundromats” because they contained large 

drives referred to in jargon as “washing machines.” See 

also server farm. 

disk interface n. 1. The circuitry that connects a disk 

drive to a computer system. 2. A standard for connecting 

disk drives and computers. For example, the ST506 standard 

for connecting hard disks to computers is a disk interface 

standard. 

disk jacket n. The protective plastic sheath that covers a 

floppy disk. 

diskless workstation n. A station on a computer network 

that is not equipped with a disk drive and that uses 

files stored in a file server. See also file server. 

disk memory n. See virtual memory. 

disk mirroring n. A technique in which all or part of a 

hard disk is duplicated onto one or more other hard disks, 

D

D 

disk operating system display face 

each of which ideally is attached to its own controller. 

With disk mirroring, any change made to the original disk 

is simultaneously made to the other disks so that if the 

original disk becomes damaged or corrupted, the mirror 

disks will contain a current, undamaged collection of the 

data from the original disk. Also called: disk duplexing. 

See also fault tolerance. 

disk operating system n. See DOS. 

disk pack n. A collection of disks in a protective container. 

Used primarily with minicomputers and mainframe 

computers, a disk pack is a removable medium, generally 

a stack of 14-inch disks in a plastic housing. 

disk partition n. A logical compartment on a physical 

disk drive. A single disk might have two or more logical 

disk partitions, each of which would be referenced with a 

different disk drive name. Multiple partitions are divided 

into a primary (boot) partition and one or more extended 

partitions. 

disk server n. A node on a local area network that acts 

as a remote disk drive shared by network users. Unlike a 

file server, which performs the more sophisticated tasks 

of managing network requests for files, a disk server 

functions as a storage medium on which users can read 

and write files. A disk server can be divided into sections 

(volumes), each of which appears to be a separate disk. 

Compare file server. 

disk striping n. The procedure of combining a set of 

same-size disk partitions that reside on separate disks 

(from 2 to 32 disks) into a single volume, forming a virtual 

stripe across the disks that the operating system recognizes 

as a single drive. Disk striping enables multiple I/O 

operations in the same volume to proceed concurrently, 

thus offering enhanced performance. See also disk striping 

with parity, input/output. 

disk striping with parity n. The technique of maintaining 

parity information across a disk stripe so that if one 

disk partition fails, the data on that disk can be re-created 

using the information stored across the remaining partitions 

in the disk stripe. See also disk striping, fault tolerance, 

parity. 

disk unit n. A disk drive or its housing. 

dispatcher n. In some multitasking operating systems, 

the set of routines responsible for allocating CPU (central 

processing unit) time to various applications. 

166 

dispatch table n. A table of identifiers and addresses for 

a certain class of routines such as interrupt handlers (routines 

carried out in response to certain signals or conditions). 

Also called: interrupt vector table, jump table, 

vector table. See also interrupt handler. 

disperse vb. To break up and place in more than one location—for 

example, to disperse results among several sets 

of data or to disperse items (such as fields in records) so 

that they appear in more than one place in the output. 

Compare distribute. 

dispersion n. The degree to which, at any given time, 

data in a distributed (interconnected) system of computers 

is stored at different locations or on different devices. 

display n. The visual output device of a computer, which 

is commonly a CRT-based video display. With portable 

and notebook computers, the display is usually an LCDbased 

or a gas plasma–based flat-panel display. See also 

flat-panel display, liquid crystal display, video adapter, 

video display. 

display adapter n. See video adapter. 

display attribute n. A quality assigned to a character or 

an image displayed on the screen. Display attributes include 

such features as color, intensity, and blinking. Users of 

applications can control display attributes when programs 

allow them to change color and other screen elements. 

display background n. In computer graphics, the portion 

of an on-screen image that remains static while other elements 

change; for example, window borders on a screen, 

or a palette of shapes or patterns in a drawing program. 

display board n. See video adapter. 

display card n. See video adapter. 

display cycle n. The complete set of events that must 

occur in order for a computer image to be displayed on 

the screen, including both the software creation of an 

image in a computer’s video memory and the hardware 

operations required for accurate on-screen display. See 

also refresh cycle. 

Display Data Channel n. See DDC. 

display device n. See display. 

display element n. See graphics primitive. 

display entity n. See entity, graphics primitive. 

display face n. A typeface suitable for headings and titles 

in documents, distinguished by its ability to stand out from

display frame distributed database 

other text on the page. Sans serif faces such as Helvetica 

and Avant Garde often work well as display faces. See 

also sans serif. Compare body face. 

display frame n. One image in an animation sequence. 

See also frame (definition 3). 

display image n. The collection of elements displayed 

together at a single time on a computer screen. 

display page n. One screenful of display information 

stored in a computer’s video memory. Computers can have 

enough video memory to hold more than one display page 

at a time. In such instances, programmers, especially those 

concerned with creating animation sequences, can update 

the screen rapidly by creating or modifying one display 

page while another is being viewed by the user. See also 

animation. 

display port n. An output port on a computer that provides 

a signal for a display device such as a video monitor. 

See the illustration. Also called: monitor port. 

Display port 

F0Dgn10.eps 

Display port. 

Display PostScript n. An extended version of the Post- 

Script language intended to provide a device-independent 

language for displaying images and text on bitmapped displays. 

See also PostScript. 

Display Power Management Signaling n. See DPMS. 

display screen n. The part of a video unit on which 

images are shown. See also CRT. 

display terminal n. See terminal (definition 1). 

distance learning n. Broadly, any educational or learning 

process or system in which the teacher/instructor is 

separated geographically or in time from his or her students, 

or in which students are separated from other students 

or educational resources. Contemporary distance 

learning is effected through the implementation of computer 

and electronics technology to connect teacher and 

student in either real or delayed time or on an as-needed 

basis. Content delivery may be achieved through a variety 

167 

of technologies, including satellites, computers, cable television, 

interactive video, electronic transmissions via telephone 

lines, the World Wide Web and other Internet 

technology, and others. Distance learning does not preclude 

traditional learning processes; frequently it is used 

in conjunction with in-person classroom or professional 

training procedures and practices. 

Distance Vector Multicast Routing Protocol n. An 

Internet routing protocol that provides an efficient mechanism 

for connectionless datagram delivery to a group of 

hosts across an Internet network. It is a distributed protocol 

that dynamically generates IP multicast delivery trees 

using a technique called Reverse Path Multicasting 

(RPM). Acronym: DVMRP. 

distance-vector routing algorithm n. See Bellman- 

Ford distance-vector routing algorithm. 

distortion n. An undesirable change in the waveform of a 

signal. Distortion can occur during signal transmission, as 

when a radio broadcast becomes garbled, or when a signal 

passes through a circuit, as when a stereo system is turned 

up too loud. Distortion often results in loss of information. 

It is mainly a problem in analog signals; digital signals are 

not affected by moderate distortion. 

distribute vb. To allocate among locations or facilities, as 

in a data-processing function that is performed by a collection 

of computers and other devices linked together by 

a network. 

distributed bulletin board n. A collection of newsgroups 

distributed to all computers in a wide area network. 

See also newsgroup, Usenet. 

Distributed COM n. See DCOM. 

Distributed Component Object Model n. See DCOM. 

distributed computing n. See distributed processing. 

Distributed Computing Environment n. A set of standards 

from the Open Group (formerly the Open Software 

Foundation) for development of distributed applications 

that can operate on more than one platform. Acronym: 

DCE. See also distributed processing. 

distributed database n. A database implemented on a 

network. The component partitions are distributed over 

various nodes (stations) of the network. Depending on the 

specific update and retrieval traffic, distributing the database 

can significantly enhance overall performance. See 

also partition (definition 2). 

D

D 

distributed database management system dithering 

distributed database management system n. A database 

management system capable of managing a distributed 

database. Acronym: DDBMS. See also distributed 

database. 

distributed denial of service attack n. See DDoS. 

distributed file system n. A file management system in 

which files may be located on multiple computers connected 

over a local or wide area network. Acronym: DFS. 

distributed intelligence n. A system in which processing 

ability (intelligence) is distributed among multiple 

computers and other devices, each of which can work 

independently to some degree but can also communicate 

with the other devices to function as part of the larger system. 

See also distributed processing. 

distributed network n. A network in which processing, 

storage, and other functions are handled by separate units 

(nodes) rather than by a single main computer. 

distributed processing n. A form of information processing 

in which work is performed by separate computers 

linked through a communications network. Distributed 

processing is usually categorized as either plain distributed 

processing or true distributed processing. Plain distributed 

processing shares the workload among computers 

that can communicate with one another. True distributed 

processing has separate computers perform different tasks 

in such a way that their combined work can contribute to a 

larger goal. The latter type of processing requires a highly 

structured environment that allows hardware and software 

to communicate, share resources, and exchange information 

freely. 

distributed services n. See BISDN. 

distributed system n. A noncentralized network consisting 

of numerous computers that can communicate with 

one another and that appear to users as parts of a single, 

large, accessible “storehouse” of shared hardware, software, 

and data. 

Distributed System Object Model n. IBM’s System 

Object Model (SOM) in a shared environment, where 

binary class libraries can be shared between applications 

on networked computers or between applications on a 

given system. The Distributed System Object Model complements 

existing object-oriented languages by allowing 

SOM class libraries to be shared among applications writ- 

168 

ten in different languages. Acronym: DSOM. See also 

SOM (definition 1). 

distributed transaction processing n. Transaction processing 

that is shared by one or more computers communicating 

over a network. Acronym: DTP. See also 

distributed processing, transaction processing. 

distributed workplace n. An environment other than the 

traditional office or factory, in which work is carried out 

on a regular basis. The flexibility afforded by the combination 

of communications and computing technologies 

enables many workers to conduct business anywhere the 

appropriate computer and data communications infrastructure 

has been set up. See also SOHO, telecommute. 

distribution group n. A group that is used solely for email 

distribution and that is not security-enabled. Distribution 

groups cannot be listed in discretionary access control 

lists (DACLs) used to define permissions on resources and 

objects. Distribution groups can be used only with e-mail 

applications (such as Microsoft Exchange) to send e-mail 

messages to collections of users. If you do not need a 

group for security purposes, create a distribution group 

instead of a security group. See also discretionary access 

control list, security group. 

distribution list n. A list of recipients on an e-mail mailing 

list. This can be in the form of either a mailing list program, 

such as LISTSERV, or an alias in an e-mail program 

for all recipients of an e-mail message. See also alias (definition 

2), LISTSERV, mailing list. 

distribution services n. See BISDN. 

distributive sort n. An ordering process in which a list is 

separated into parts and then reassembled in a particular 

order. See also sort algorithm. Compare bubble sort, insertion 

sort, merge sort, quicksort. 

distro1 n. 1. A distribution of software (usually a version 

of Linux), digital music, or an online magazine or e-zine. 

See also e-zine, Linux. 2. A company or individual that 

sells items, typically software, music CDs, or books, via 

the Web. 

distro2 vb. To distribute or sell software releases, digital 

music, or text items via the Web. 

dithering n. A technique used in computer graphics to 

create the illusion of varying shades of gray on a monochrome 

display or printer, or additional colors on a color 

display or printer. Dithering relies on treating areas of an

divergence DLS 

image as groups of dots that are colored in different patterns. 

Akin to the print images called halftones, dithering 

takes advantage of the eye’s tendency to blur spots of different 

colors by averaging their effects and merging them 

into a single perceived shade or color. Depending on the 

ratio of black dots to white dots within a given area, the 

overall effect is of a particular shade of gray. Dithering is 

used to add realism to computer graphics and to soften 

jagged edges in curves and diagonal lines at low resolutions. 

See the illustration. See also aliasing, halftone. 

Not dithered 

Dithered 

F0Dgn11.eps 

Dithering. A halftone image (left) and a dithered image 

(right) both at 72 cells per inch. 

divergence n. A moving apart or separation. On computer 

displays, divergence occurs when the red, green, and 

blue electron beams in a color monitor do not collectively 

light the same spot on the screen. Within a program, such 

as a spreadsheet, divergence can occur when a circular set 

of formulas is repeatedly recalculated (iterated), with the 

results of each iteration moving further from a stable solution. 

Compare convergence. 

divide overflow n. See overflow error. 

division by zero n. An error condition caused by an 

attempt to divide a number by zero, which is mathematically 

undefined, or by a number that is sufficiently near to 

zero that the result is too large to be expressed by the 

machine. Computers do not allow division by zero, and 

software must provide some means of protecting the user 

from program failure on such attempts. 

DIX n. Acronym for Digital Intel Xerox, the companies 

that developed the AUI connector for thicknet Ethernet 

cable. See also AUI. 

DJGPP n. A compiler and a set of tools used by some 

game programmers to produce 32-bit protected-mode programs 

that run on Windows operating systems. DJGPP is a 

complete 32-bit C/C++ development system for PCs running 

MS-DOS; it includes ports of many GNU develop- 

169 

ment utilities. In most cases, programs produced using 

DJGPP can be sold commercially without license or royalties. 

See also 32-bit, Allegro, GNU. 

djinn n. A group of devices, resources, and users joined 

by Sun Microsystem’s JINI technology. The group, controlled 

by the JINI technology infrastructure, agrees on 

basic specifications for administration, trust, identification, 

and policy. See also JINI. 

DLC n. Acronym for Data Link Control. An error-correction 

protocol in the Systems Network Architecture (SNA) 

responsible for transmission of data between two nodes 

over a physical link. Supported by Microsoft Windows NT 

and Windows 2000, DLC is designed to provide access to 

IBM mainframe computers and to Hewlett-Packard printers 

connected to the network. See also HDLC, SNA. 

DLCI n. See Data Link Connection Identifier. 

.dll n. A file extension for a dynamic-link library. See also 

dynamic-link library. 

DLL n. See dynamic-link library. 

DLL hell n. A problem occurring in versions of Microsoft 

Windows prior to Windows Me and Windows 2000 in 

which a newly installed application overwrites shared 

dynamic-link library (DLL) files with the (older or newer) 

versions it needs in order to run. If the replaced files are 

incompatible with those needed by other applications, 

those applications may exhibit buggy behavior or crash 

when they access the incompatible DLL files. The latest 

versions of the Windows operating system, Windows 2000 

and Windows XP, incorporate a feature called Windows 

File Protection that eliminates this situation by monitoring 

and correcting installation and replacement of DLL files. 

See also dynamic-link library. 

DLP n. Short for Digital Light Processing, a digital projection 

technology developed by Texas Instruments in 

which a signal sent from a computer to a DLP projector is 

projected onto a screen by means of light reflected from a 

Digital Micromirror Device, or DMD, that consists of 

thousands of tiny hinged mirrors, each representing one 

pixel, attached to a chip. The chip acts as a bank of 

switches, one switch per mirror. These switches, in turn, 

rotate the mirrors in response to the digital signal to reflect 

light through a projection lens to create the image. DLP 

projectors represent a newer technology than the LCD 

projectors also used to display images on screen. See also 

Digital Micromirror Device. 

DLS n. See Downloadable Sounds. 

D

D 

DLT docking station 

DLT n. See digital linear tape. 

DMA n. See direct memory access, document management 

system. 

DMD n. See Digital Micromirror Device. 

DMI n. Acronym for Desktop Management Interface. A 

system for managing the configurations and status of PCs 

on a network from a central computer. In DMI an agent 

program runs in the background on each machine and 

returns information or performs some action (as specified 

by a file on that machine) in response to a query received 

from the central computer. The actions to be performed by 

the agent might include watching for errors and reporting 

them to the central computer as they occur; for example, a 

printer might be set up to report to the central computer 

when paper runs out or jams. DMI was developed by the 

DMTF (Desktop Management Task Force), a consortium 

of computer equipment manufacturers, and competes with 

SNMP (although the two can coexist on the same system). 

See also agent (definition 1), DMTF. Compare SNMP. 

DML n. See data manipulation language, declarative 

markup language. 

DMOZ n. See Open Directory Project. 

DMQL n. Acronym for Data Mining Query Language. 

Any query language developed and used for data mining 

relational databases. DMQLs provide a syntax for specifying 

the kind of knowledge to be mined, pattern presentation 

and visualization, conceptual hierarchies, and task 

relevant data. See also data mining. Compare structured 

query language (SQL). 

DMS n. See document management system. 

DMT n. See discrete multitone. 

DMTF n. Acronym for Desktop Management Task Force. 

A consortium formed in 1992 to develop standards for PCbased 

stand-alone and networked systems based on user 

and industry needs. 

DNA n. See digital DNA, Digital Network Architecture, 

distributed network, Windows DNA. 

DNS n. 1. Acronym for Domain Name System. The hierarchical 

system by which hosts on the Internet have both 

domain name addresses (such as bluestem.prairienet.org) 

and IP addresses (such as 192.17.3.4). The domain name 

address is used by human users and is automatically translated 

into the numerical IP address, which is used by the 

packet-routing software. DNS names consist of a top-level 

domain (such as .com, .org, and .net), a second-level 

170 

domain (the site name of a business, an organization, or an 

individual), and possibly one or more subdomains (servers 

within a second-level domain). See also domain name 

address, IP address. 2. Acronym for Domain Name Service. 

The Internet utility that implements the Domain 

Name System. DNS servers, also called name servers, 

maintain databases containing the addresses and are 

accessed transparently to the user. See also Domain Name 

System (definition 1), DNS server. 

DNS name server n. See DNS server. 

DNS server n. Short for Domain Name System server, a 

computer that can answer Domain Name System (DNS) 

queries. The DNS server keeps a database of host computers 

and their corresponding IP addresses. Presented with 

the name apex.com, for example, the DNS server would 

return the IP address of the hypothetical company Apex. 

Also called: name server. See also DNS (definition 2), IP 

address. 

DNS zone transfer n. See zone transfer. 

.doc n. A file extension that identifies document files formatted 

for a word processor. This is the default file extension 

for Microsoft Word document files. 

dock vb. 1. To connect a laptop or notebook computer to a 

docking station. See also docking station, laptop, portable 

computer. 2. To move a toolbar to the edge of an application 

window so that it attaches to and becomes a feature of 

the application window. 

Dock n. An organizational feature of Mac OS X that 

keeps track of frequently used applications, documents, 

and windows. Users can drag icons to the dock for easy 

access or can minimize an active window to the Dock and 

still see the application running while working with other 

windows. The Dock can run along the bottom or either 

side of the screen. See also Mac OS X. 

docking mechanism n. The portion of a docking station 

that physically connects the portable computer with the 

station. See also docking station. 

docking station n. A unit for housing a laptop or notebook 

computer that contains a power connection, expansion 

slots, and connections to peripherals, such as a 

monitor, printer, full-sized keyboard, and mouse. The purpose 

of a docking station is to turn the laptop or notebook 

computer into a desktop machine and allow users the convenience 

of using such peripherals as a monitor and a fullsized 

keyboard. See the illustration. See also expansion 

slot, laptop, peripheral, portable computer.

DOCSIS Document Object Model 

F0Dgn12.eps 

Docking station. 

DOCSIS n. Acronym for Data Over Cable Service Interface 

Specification. The International Telecommunications 

Union standard (ITU Recommendation J.112) that specifies 

functions and internal and external interfaces for highspeed, 

bidirectional transfer of digital data between cable 

television networks and subscribers. DOCSIS-compliant 

equipment ensures interoperability between cable 

modems and the cable television infrastructure, regardless 

of manufacturer or provider. Initially developed by a 

group of cable television providers, including Time 

Warner and TCI, DOCSIS was designed to support data, 

video, and rapid Internet access. Data rates are 27 Mbps to 

36 Mbps downstream (from the cable network) and 320 

Kbps to 10 Mbps upstream (to the cable network). See 

also cable modem. Compare IEEE 802.14. 

doctype n. A declaration at the beginning of an SGML 

document that gives a public or system identifier for the 

document type definition (DTD) of the document. See 

also SGML. 

document1 n. Any self-contained piece of work created 

with an application program and, if saved on disk, given a 

unique filename by which it can be retrieved. Documents 

are generally thought of as word-processed materials only. 

To a computer, however, data is nothing more than a collection 

of characters, so a spreadsheet or a graphic is as 

much a document as is a letter or report. In the Macintosh 

environment in particular, a document is any user-created 

work named and saved as a separate file. 

document2 vb. To explain or annotate something, such as 

a program or a procedure. 

documentation n. The set of instructions shipped with a 

program or a piece of hardware. Documentation usually 

includes necessary information about the type of computer 

system required, setup instructions, and instructions on the 

use and maintenance of the product. 

171 

document-centric adj. Of, pertaining to, or characteristic 

of an operating system in which the user opens document 

files and thus automatically invokes the applications 

(such as word processors or spreadsheet programs) that 

process them. Many graphical user interfaces, such as the 

Macintosh Finder, as well as the World Wide Web, are 

document-centric. Compare application-centric. 

Document Content Architecture n. See DCA (definition 

1). 

Document Content Description n. See DCD (definition 

2). 

document file n. A user-created file that represents the 

output of a program. Also called: data file. Compare program 

file. 

document image processing n. A system for storing 

and retrieving information for an enterprise in the form of 

bitmapped images of paper documents input with a scanner 

rather than in the form of text and numeric files. Document 

image processing takes more memory than purely 

electronic data processing, but it more readily incorporates 

signatures, drawings, and photographs and can be more 

familiar to users without computer training. See also 

paperless office. 

Document Interchange Architecture n. See DIA. 

document management n. The full spectrum of electronic 

document creation and distribution within an 

organization. 

document management system n. A server-based network 

facility designed for the storage and handling of an 

organization’s documents. A document management system, 

or DMS, is built around a central library known as a 

repository and typically supports controlled access, version 

tracking, cataloging, search capabilities, and the ability 

to check documents in and out electronically. The open 

interface specification known as ODMA (Open Document 

Management API) enables desktop applications that support 

ODMA to interface with a DMS so that users can 

access and manage documents from within their client 

applications. Acronym: DMS. Also called: EDMS, electronic 

document management system. 

Document Object Model n. A World Wide Web Consortium 

specification that describes the structure of 

dynamic HTML and XML documents in a way that allows 

them to be manipulated through a Web browser. In the 

Document Object Model, or DOM, a document is presented 

as a logical structure rather than as a collection of 

D

D 

document processing Domain Naming System 

tagged words. In essence, DOM is a means of defining a 

document as a treelike hierarchy of nodes in which the 

document is an object containing other objects, such as 

images and forms. Through DOM, programs and scripts 

can access these objects in order to change aspects such as 

their appearance or behavior. DOM is a vehicle for adding 

depth and interactivity to what would otherwise be a static 

Web page. Acronym: DOM. 

document processing n. The act of retrieving and 

manipulating a document. In terms of the way a computer 

works, document processing involves three main steps: creating 

or retrieving a data file, using a program to manipulate 

the data in some way, and storing the modified file. 

document reader n. A device that scans printed text and 

uses character recognition to convert it to computer text 

files. See also character recognition. 

document retrieval n. A capability built into some application 

programs that enables the user to search for specific 

documents by specifying items of information, such as 

date, author, or previously assigned keywords. Document 

retrieval depends on an indexing scheme that the program 

maintains and uses. Depending on the program’s capabilities, 

document retrieval might allow the user to specify 

more than one condition to refine a search. 

document source n. The plain-text HTML form of a 

World Wide Web document, with all tags and other 

markup displayed as such rather than being formatted. 

Also called: source, source document. See also HTML. 

Document Style Semantics and Specification 

Language n. An ISO standard derived from SGML that 

addresses the semantics of high-quality composition in a 

manner independent of particular formatting systems or 

processes. Like CSS and XSL, it can be used to format 

XML documents. Acronym: DSSSL. See also ISO, SGML. 

document type definition n. See DTD. 

document window n. In windowing environments, such 

as the Apple Macintosh and Microsoft Windows, an onscreen 

window (enclosed work area) in which the user can 

create, view, or work on a document. 

DoD n. See U.S. Department of Defense. 

do-gooder virus n. A virus or worm that has been 

released with the intention of correcting problems caused 

by other, more malicious viruses. The do-gooder virus 

typically looks for computers that have been compromised 

172 

and then infects the system and fixes back doors and other 

vulnerabilities left behind by the malicious program. The 

do-gooder virus may then use the repaired computer as a 

platform to infect other computers. See also anti-worm, 

automatic patching. 

DO loop n. A control statement used in programs that executes 

a section of code a number of times until a specified 

condition is met. DO loops are found in FORTRAN and 

Basic, among other languages. See also iterative statement. 

Compare FOR loop. 

DOM n. See Document Object Model. 

domain n. 1. In database design and management, the set 

of valid values for a given attribute. For example, the 

domain for the attribute AREA-CODE might be the list of 

all valid three-digit numeric telephone area codes in the 

United States. See also attribute (definition 1). 2. For Windows 

NT Advanced Server, a collection of computers that 

share a common domain database and security policy. Each 

domain has a unique name. 3. In the Internet and other networks, 

the highest subdivision of a domain name in a network 

address, which identifies the type of entity owning the 

address (for example, .com for commercial users or .edu for 

educational institutions) or the geographical location of the 

address (for example, .fr for France or .sg for Singapore). 

The domain is the last part of the address (for example, 

www.acm.org). See also domain name. 

domain controller n. In Windows NT, the master server 

that holds the directory services database that identifies all 

network users and resources. 

domain name n. An address of a network connection that 

identifies the owner of that address in a hierarchical format: 

server.organization.type. For example, www.whitehouse.gov 

identifies the Web server at the White House, 

which is part of the U.S. government. 

domain name address n. The address of a device connected 

to the Internet or any other TCP/IP network, in 

the hierarchical system that uses words to identify servers, 

organizations, and types, such as www.logos.net. See 

also TCP/IP. 

Domain Name Server n. See DNS server. 

Domain Name Service n. See DNS (definition 2). 

Domain Name System n. See DNS (definition 1). 

Domain Naming System n. See DNS (definition 1).

domain slamming dot 

domain slamming n. The practice of transferring ownership 

of domain names from one customer to another without 

the permission of the first customer. 

Domino n. See Lotus Domino. 

dongle n. 1. See hardware key. 2. An adapter device or 

cable enabling a nonstandard interface between a computer 

and a peripheral device or between two disparate 

items of computer hardware. 

do-nothing instruction n. See no-operation instruction. 

doorway page n. A Web page that functions as a doorway 

into a Web site. Usually a doorway page contains keywords, 

which Internet search engines seek when they scan the 

Internet. Placing the correct keywords on a doorway page 

can increase the number of viewers visiting a site. 

dopant n. An impurity that is added in small quantities to 

semiconductor material during the manufacture of diodes, 

transistors, and integrated circuits. The resistance of a 

semiconductor falls between the resistance of a conductor 

and the resistance of an insulator (hence its name); 

dopants are added to the semiconductor to increase its 

conductivity. The type and amount of dopant determine 

whether the semiconductor will be N-type (in which current 

is conducted by free electrons) or P-type (in which 

current is conducted by electron vacancies, called holes). 

Common dopants include arsenic, antimony, bismuth, and 

phosphorus. See also N-type semiconductor, P-type semiconductor. 

DoS n. Acronym for denial of service attack. A computerized 

assault, usually planned, that seeks to disrupt Web 

access. A denial of service attack can occur in a number of 

forms. The most common form of attack is to overwhelm 

an Internet server with connection requests that cannot be 

completed. This causes the server to become so busy 

attempting to respond to the attack that it ignores legitimate 

requests for connections. One example of this type of 

attack, known as a SYN flood, inundates the server’s entry 

ports with false connection messages. Another, known as 

the Ping of Death, sends a ping command with an oversized 

IP packet that causes the server to freeze, crash, or 

restart. Other forms of denial of service attacks include the 

destruction or alteration of a server’s configuration data, 

such as router information; unauthorized access to physical 

components of a system; and the sending of large or 

invalid data that causes a system to crash or freeze. See 

also packet, Ping of Death, SYN flood. 

173 

DOS n. 1. Acronym for disk operating system. A generic 

term describing any operating system that is loaded from 

disk devices when the system is started or rebooted. The 

term originally differentiated between disk-based systems 

and primitive microcomputer operating systems that were 

memory-based or that supported only magnetic or paper 

tape. 2. See MS-DOS. 

DOS box n. 1. An OS/2 process that supports the execution 

of MS-DOS programs. Also called: compatibility 

box. 2. A computer that uses the MS-DOS or PC-DOS 

operating system, as opposed to one that runs some other 

operating system, such as UNIX. 

DOS extender n. A program designed to extend the 640 

KB of conventional memory available for use by DOS and 

DOS-based applications. A DOS extender works by 

claiming a portion of reserved memory (memory used by 

other parts of the system, such as the video adapter, the 

ROM BIOS, and the I/O ports). 

DOS prompt n. The visual indication from the MS-DOS 

command processor that the operating system is ready to 

accept a new command. The default DOS prompt is a path 

followed by a greater-than sign (for example, C:>); the 

user can also design a custom prompt with the PROMPT 

command. 

DOS Protected Mode Interface n. A software interface, 

originally developed for Microsoft Windows version 3, 

that enables MS-DOS-based application programs to run 

in the protected mode built into 80286 and later microprocessors. 

In protected mode, the microprocessor can support 

multitasking and use of memory beyond 1 MB— 

capabilities otherwise unavailable to programs designed to 

run under MS-DOS. See also protected mode, real mode, 

Virtual Control Program Interface. 

dot n. 1. In the UNIX, MS-DOS, OS/2, and other operating 

systems, the character that separates a filename from 

an extension as in TEXT.DOC (pronounced “text-dotdoc”). 

2. In computer graphics and printing, a small spot 

combined with others in a matrix of rows and columns to 

form a character or a graphic element in a drawing or 

design. The dots forming an image on the screen are called 

pixels. The resolution of a display or printing device is 

often expressed in dots per inch (dpi). Dots are not the 

same as spots, which are groups of dots used in the halftoning 

process. See also pixel, resolution (definition 1). 

Compare spot. 3. In an Internet address, the character that 

separates the different parts of the domain name, such as 

D

D 

dot address double-density disk 

the entity name from the domain. See also domain (definition 

3), domain name. 

dot address n. An IP address in dotted quad form. See 

also IP address. 

dot-addressable mode n. A mode of operation in which 

a computer program can address (“point to”) individual 

dots on the screen or in a printed character. See also all 

points addressable. 

dot-bomb n. An Internet-based company or organization 

that has failed or downsized significantly. See also dotcommed. 

dot-com n. A company doing business primarily or 

entirely on the Internet. The term is derived from the toplevel 

domain, .com, at the end of the Web addresses of 

commercial Web sites. 

dot command n. A formatting command typed into a 

document and preceded by a period (dot) to distinguish it 

from printable text. Text formatting programs such as the 

XENIX nroff editor and word processing programs such 

as WordStar use dot commands for formatting. 

dot-commed adj. Losing a job because of the downsizing 

or failure of an Internet-based company or organization. 

See also dot-bomb. 

dot file n. A file under UNIX whose name begins with a 

period. Dot files do not appear in ordinary listings of the 

files in a directory. Dot files are often used to store program 

setup information for the particular user; for example, 

.newsrc in a user’s account indicates to a newsreader 

which newsgroups the user subscribes to. 

dot-matrix1 adj. Referring to video and print hardware 

that forms character and graphic images as patterns of dots. 

dot matrix2 n. The rectangular grid, or matrix, of tiny 

“cells” in which dots are displayed or printed in the patterns 

required to form text characters, circles, squares, and 

other graphical images. Depending on the frame of reference, 

the size of a dot matrix varies from a few rows and 

columns to an invisible grid covering an entire display 

screen or printed page. See also dot-matrix printer, raster. 

dot-matrix printer n. Any printer that produces characters 

made up of dots using a wire-pin print head. The quality 

of output from a dot-matrix printer depends largely on 

the number of dots in the matrix, which might be low 

enough to show individual dots or might be high enough 

to approach the look of fully formed characters. Dotmatrix 

printers are often categorized by the number of pins 

174 

in the print head—typically 9, 18, or 24. Compare daisywheel 

printer, laser printer. 

dot pitch n. 1. In printers, the distance between dots in a 

dot-matrix. See also dot matrix2 . 2. In video displays or 

CRTs, a measure of image clarity. A video display’s dot 

pitch is the vertical distance, expressed in millimeters, 

between like-colored pixels. A smaller dot pitch generally 

means a crisper image, although the difference between 

two displays can vary because some manufacturers use 

different methods to determine the dot pitch of their products. 

A display’s dot pitch is an integral part of the product 

and so cannot be altered. See also CRT, display. 

dots per inch n. A measure of screen and printer resolution 

that is expressed as the number of dots that a device 

can print or display per linear inch. Acronym: dpi. 

dotted decimal notation n. The process of formatting 

an IP address as a 32-bit identifier made up of four groups 

of numbers, with each group separated by a period. For 

example, 123.432.154.12. 

double buffering n. The use of two temporary storage 

areas (buffers) rather than one to hold information coming 

from and going to a particular input/output device. 

Because one buffer can be filled while the other is being 

emptied, double buffering increases transfer speed. Also 

called: ping-pong buffer. 

double-byte characters n. A set of characters in which 

each character is represented by two bytes. Some languages, 

such as Japanese, Chinese, and Korean, require 

double-byte character sets. 

double-click vb. To press and release a mouse button 

twice without moving the mouse. Double-clicking is a 

means of rapidly selecting and activating a program or 

program feature. Compare click, drag. 

double dabble n. A method of converting binary numbers 

to decimals by a process of doubling sums and adding 

successive bits: doubling the bit farthest to the left, adding 

the next bit and doubling the sum, adding the next bit and 

doubling the sum, and so on until the rightmost bit has 

been included in the total. 

Double Data Rate SDRAM n. See DDR SDRAM. 

Double Data Rate Synchronous Dynamic RAM n. See 

DDR SDRAM. 

double-density disk n. A disk created to hold data at 

twice the density (bits per inch) of a previous generation 

of disks. Early IBM PC floppy disks held 180 KB of

double-dereference downstream1 

downstream 

data. Double-density disks increased that capacity to 360 

KB. Double-density disks use modified frequency modulation 

encoding for storing data. See also floppy disk, 

microfloppy disk, modified frequency modulation 

encoding. Compare high-density disk. 

double-dereference vb. To dereference a pointer that is 

pointed to by another pointer; in other words, to access the 

information pointed to by a handle. See also dereference, 

handle (definition 1), pointer (definition 1). 

double leap year n. The mistaken idea that the year 2000 

would have two leap days—February 29 and February 

30—instead of one. In actuality, there was a potential leap 

year problem in 2000, but it was based on three rules for 

calculating leap years: (1) A year is a leap year if it is 

divisible by 4, but (2) not if it is divisible by 100, unless (3) 

it is also divisible by 400. Thus, 1900 was not a leap year, 

but 2000 is, although systems based on incorrect algorithms 

may not recognize it as a leap year and so may have 

difficulties functioning correctly after February 28, 2000. 

double posting n. In newsgroup discussions, the practice 

of replying to one’s own posts. Because it may be seen as 

the digital equivalent to talking to one’s self, double posting 

is considered an undesirable practice. 

double-precision adj. Of, pertaining to, or characteristic 

of a number stored in twice the amount (two words—typically 

8 bytes) of computer memory that is required for 

storing a less precise (single-precision) number. Doubleprecision 

numbers are commonly handled by a computer 

in floating-point form. See also floating-point number. 

Compare single-precision. 

double-sided disk n. A floppy disk that can hold data on 

both its top and bottom surfaces. 

double slash n. See //. 

double-strike n. On an impact printer, such as a daisywheel 

printer, the process of printing twice over a word, producing 

text that appears darker and heavier, or bolder, than it 

normally appears. On dot-matrix printers, double striking 

with a slight offset can be used to fill in the space between 

the dots, producing smoother and darker characters. 

double supertwist nematic display n. See supertwist 

display. 

double word n. A unit of data consisting of two contiguous 

words (connected bytes, not text) that are handled 

together by a computer’s microprocessor. 

175 

doubly linked list n. A series of nodes (items representing 

discrete segments of information) in which each node 

refers to both the next node and the preceding node. 

Because of these two-way references, a doubly linked list 

can be traversed both forward and backward, rather than in 

a forward direction only, as with a singly linked list. 

down adj. Not functioning, in reference to computers, 

printers, communications lines on networks, and other 

such hardware. 

downflow n. One of the four stages of the data warehousing 

process, during which stored information is delivered 

and archived. See also data warehouse2 . Compare inflow, 

metaflow, upflow. 

downlink n. The transmission of data from a communications 

satellite to an earth station. 

download vb. 1. In communications, to transfer a copy of 

a file from a remote computer to the requesting computer 

by means of a modem or network. 2. To send a block of 

data, such as a PostScript file, to a dependent device, such 

as a PostScript printer. Compare upload. 

downloadable font n. A set of characters stored on disk 

and sent (downloaded) to a printer’s memory when needed 

for printing a document. Downloadable fonts are most 

commonly used with laser printers and other page printers, 

although many dot-matrix printers can accept some of 

them. Also called: soft font. 

Downloadable Sounds n. A standard for synthesizing 

wave sounds from digital samples stored in software. The 

DLS level 1 and level 2 standards are published by the 

MIDI Manufacturers Association. Acronym: DLS. 

downsample n. To decrease the number of audio samples 

or pixels, by applying an operation such as averaging. 

Popular internet music formats, such as MP3, use downsampling 

to reduce file size. 

downsizing n. In computing, the practice of moving from 

larger computer systems, such as mainframes and minicomputers, 

to smaller systems in an organization, generally 

to save costs and to update to newer software. The 

smaller systems are usually client/server systems composed 

of a combination of PCs, workstations, and some 

legacy system such as a mainframe, connected in one or 

more local area networks or wide area networks. See also 

client/server architecture, legacy system. 

downstream1 n. The direction in which information, 

such as a news feed for a newsgroup or data from an http 

D

D 

downstream2 downstream 

drawing program 

(Web) server, is passed from one server to the next. See 

also news feed, newsgroup, server. 

downstream2 adv. 1. The location of a client computer in 

relation to a server. 2. The direction in which data moves 

from the server to the client. 

downstream3 adj. Refers to data that moves from a 

remote network to an individual computer. In some Internet-related 

communications technologies, data flows more 

quickly downstream than upstream; cable modems, for 

example, can transfer data as fast as 30 Mbps downstream 

but support much slower rates, from 128 Kbps to around 2 

Mbps, upstream. Compare upstream. 

downtime n. The amount or percentage of time a computer 

system or associated hardware remains nonfunctional. 

Although downtime can occur because hardware fails unexpectedly, 

it can also be a scheduled event, as when a network 

is shut down to allow time for maintenance. 

downward compatibility n. The capability of source 

code or programs developed on a more advanced system 

or compiler version to be executed or compiled by a less 

advanced (older) version. Compare upward-compatible. 

DP n. See data processing. 

dpi n. See dots per inch. 

DPMA n. Acronym for Data Processing Management 

Association. A trade organization of information systems 

(IS) professionals. DPMA was founded in 1951 as the 

National Machine Accountants Association. 

DPMI n. See DOS Protected Mode Interface. 

DPMS n. Acronym for VESA Display Power Management 

Signaling. A VESA standard for signals that put a 

video monitor into “standby” or suspend mode to reduce 

power consumption. See also green PC, VESA2 . 

DPOF n. Short for Digital Print Order Format. A printing 

specification developed by Canon Computer Systems, 

Inc., Eastman Kodak Company, Fuji Photo Film Co., Ltd., 

and Matsushita Electric Industrial Co., Ltd. DPOF is 

intended to ease the process of printing images stored on 

digital camera memory cards by enabling users to select 

the images to print, as well as specify the number of copies 

desired, on the card. The images ordered can then be 

printed by a professional photofinishing service or on a 

home printer. 

DPSK n. Acronym for differential phase-shift keying. See 

phase-shift keying. 

176 

draft mode n. A high-speed, relatively low-quality print 

mode offered by most dot-matrix printers. See also dotmatrix 

printer, draft quality, print quality. 

draft quality n. A low grade of printing generated by the 

draft mode on dot-matrix printers. Draft quality varies 

among printers, ranging from suitable for most purposes 

to nearly useless. See also draft mode, print quality. 

drag vb. In graphical user interface environments, to 

move an image or a window from one place on the screen 

to another by “grabbing” it and pulling it to its new location 

using the mouse. The mouse pointer is positioned 

over the object, and the mouse button is pressed and held 

while the mouse is moved to the new location. 

drag-and-drop vb. 1. In general, to delve into something 

in increasing detail. 2. More specifically, to perform operations 

in a graphical user interface by dragging objects on 

the screen with the mouse. For example, to delete a document, 

a user can drag the document icon across the screen 

and drop it on the trashcan icon (Macintosh OS) or in the 

Recycle Bin (Windows). See also drag, graphical user 

interface. 

drain n. 1. In an FET, the electrode toward which charge 

carriers (electrons or holes) move from the source under 

control of the gate. See also FET, gate (definition 2), 

MOSFET, source (definition 2). 2. See current drain. 

DRAM n. See dynamic RAM. 

DRAW n. Acronym for direct read after write. A technique 

used with optical discs to verify the accuracy of 

information immediately after it has been recorded (written) 

on the disc. Compare DRDW. 

drawer n. In the Mac OS X Aqua interface, small child 

windows containing extra information that slide out of the 

side of main parent windows. Drawers are intended to 

reduce clutter on the computer desktop by enabling more 

information to be displayed without opening additional 

full-sized windows. Also called: Drop Drawer. 

drawing interchange format n. See DXF. 

drawing program n. A program for manipulating objectoriented 

graphics, as opposed to manipulating pixel 

images. In a drawing program, for example, the user can 

manipulate an element, such as a line, a circle, or a block 

of text, as an independent object simply by selecting the 

object and moving it. See also object-oriented graphics, 

pixel image, vector graphics.

DRDW drop-dead halt 

DRDW n. Acronym for direct read during write. A technique 

used with optical discs to verify the accuracy of 

information at the time it is being recorded on the disc. 

Compare DRAW. 

Dreamcast n. A console game system designed by the 

Sega corporation. It features a Hitachi 128-bit graphics 

engine with an on-board SH-4 RISC processor (operating 

frequency of 200 MHz 360 MIPS/1.4 GFLOPS) and a 

customized OS using Windows CE as its base (supporting 

DirectX). Game developers for the Dreamcast platform 

use an environment supported by Microsoft Visual Studio 

and refined Visual C++. See also computer game, console 

game, DirectX, gigaflops, MIPS, OS, RISC, Visual C++. 

Compare GameCube, PlayStation, Xbox. 

dribbleware n. Updates, patches, and new drivers for a 

software product that are released one at a time, as they 

become available, rather than being issued together in a 

new version of the product. A company using the dribbleware 

technique might distribute new and replacement files 

on diskette or CD-ROM, or make them available for 

download through the Internet or a private network. See 

also driver, patch1 . 

drift n. The movement of charge carriers in a semiconductor 

caused by an applied voltage. The term is also used to 

refer to any slow, unwanted change in a parameter; for 

example, the value of a resistor might change, or drift, 

slightly as the resistor warms or cools. 

drill down vb. To start at a top-level menu, directory, or 

Web page and pass through several intermediate menus, 

directories, or linked pages, until the file, page, menu 

command, or other item being sought is reached. Drilling 

down is common practice in searching for files or information 

on the Internet, where high-level Gopher menus 

and World Wide Web pages are frequently very general 

and become more specific at each lower level. See also 

Gopher, menu, Web page. 

drive n. See disk drive. 

drive bay n. A hollow, rectangular area in a computer 

chassis designed to hold a disk drive. A drive bay always 

has side walls, usually made of metal, that generally contain 

holes to facilitate installation of a disk drive. Some 

drive bays, such as those intended to hold hard disks, are 

not visible to the user. Most drives are located on the front 

of the chassis so that the user can interact with the drive. 

drive letter n. The naming convention for disk drives on 

IBM and compatible computers. Drives are named by letter, 

beginning with A, followed by a colon. 

177 

drive mapping n. The assignment of a letter or name to a 

disk drive so that the operating system or network server 

can identify and locate it. For example, in PCs, the primary 

drive mappings are A: and B: for floppy disk drives 

and C: for the hard disk. See also A:, disk drive, hard disk. 

drive number n. The naming convention for Macintosh 

disk drives. For example, a two-drive system calls its 

drives 0 and 1. 

driver n. A hardware device or a program that controls or 

regulates another device. A line driver, for example, boosts 

signals transmitted over a communications line. A software 

driver is a device-specific control program that enables a 

computer to work with a particular device, such as a printer 

or a disk drive. Because the driver handles device-specific 

features, the operating system is freed from the burden of 

having to understand—and support—the needs of individual 

hardware devices. See also device driver. 

Driver Development Kit n. See DDK. 

DRM n. Acronym for Digital Rights Management. A 

group of technologies developed to protect intellectual 

property from online piracy by controlling who can view 

protected content and in what form. A DRM package may 

allow the purchaser to view protected content, but prevent 

printing or forwarding. Content may also be set to expire 

after a set amount of time or if distributed to multiple 

users. DRM technology is meant to protect multiple forms 

of digital and analog content, and includes encryption, 

digital watermarking, and content tracking software. 

DRO n. Acronym for destructive read out. See destructive 

read. 

drop cable n. A cable, also known as a transceiver cable, 

that is used to connect a network interface card (NIC) to a 

Thick Ethernet network. 

drop cap n. A large capital letter at the beginning of a text 

block that occupies the vertical depth of two or more lines 

of regular text. See the illustration. 

sectetuer 

adipsicing 

elite in sed 

Anonummy 

utm diam 

nibh wisi 

tincidunt eusismond 

ut laoreet dolore 

F0Dgn13.eps 

Drop cap. 

drop-dead halt n. See dead halt. 

D

D 

drop-down menu DSR 

drop-down menu n. A menu that drops from the menu 

bar when requested and remains open without further 

action until the user closes it or chooses a menu item. 

Compare pull-down menu. 

drop in vb. To read a spurious signal during a data read/ 

write operation, producing erroneous data. 

droplet n. 1. An extension for Quark XPress that allows 

files to be dragged onto a page from the finder. 2. A feature 

from Frontier that allows scripts to be embedded 

within an application and run when the application is double-clicked. 

3. A general name for any AppleScript program 

that allows files to be dragged and dropped into it for 

processing. See also AppleScript. 

drop out vb. To lose the signal momentarily during a data 

read/write operation, thus producing erroneous data. 

drum n. A rotating cylinder used with some printers and 

plotters and (in the early days of mainframe computing) as 

a magnetic storage medium for data. In laser printers, a 

rotating drum is coated with a photoelectric material that 

retains a charge when struck by a laser beam. The electrically 

charged spots on the drum then attract toner particles 

that the drum transfers to the paper as the paper passes by. 

drum plotter n. A plotter in which paper is wrapped 

around a large revolving drum, with a pen that moves back 

and forth at the uppermost point on the drum. The paper is 

rolled with the drum to align the correct point on the paper 

with the pen. Drums take up a fraction of the space 

required by flatbed plotters that can handle the same paper 

size. They also effectively have no limit on the length of 

the paper they can handle, which can be an advantage in 

some applications. See also plotter. Compare flatbed plotter, 

pinch-roller plotter. 

drum scanner n. A type of scanner where the medium 

being scanned, such as a sheet of paper, is rotated around a 

stationary scan head. See also scanner. Compare feed 

scanner, flatbed scanner, handheld scanner. 

.drv n. The file extension for a driver file. See also driver. 

dry run n. Running a program intended to have a dramatic 

effect, such as formatting a disk or printing a book, with 

the effect disabled, thus avoiding formatting a disk with 

data on it or wasting paper. 

DS n. Acronym for Digital Services or Digital Signal, a 

category used in referencing the speed, number of channels, 

and transmission characteristics of T1, T2, T3, and 

T4 communications lines. The basic DS unit, or level, is 

178 

known as DS-0, which corresponds to the 64 Kbps speed 

of a single T1 channel. Higher levels are made up of multiple 

DS-0 levels. DS-1 represents a single T1 line that 

transmits at 1.544 Mbps. For higher rates, T1 lines are 

multiplexed to create DS-2 (a T2 line consisting of four T1 

channels that transmits at 6.312 Mbps), DS-3 (a T3 line 

consisting of 28 T1 channels that transmits at 44.736 

Mbps), and DS-4 (a T4 line consisting of 168 T1 channels 

that transmits at 274.176 Mbps). 

DSA n. 1. Acronym for Directory System Agent or Directory 

Server Agent. An X.500 server program that looks up 

the address of a user on the network when requested by a 

DUA (Directory User Agent). See also agent (definition 3), 

CCITT X series, DUA. 2. See Digital Signature Algorithm. 

DSL n. Acronym for Digital Subscriber Line, a recently 

developed (late 1990s) digital communications technology 

that can provide high-speed transmissions over standard 

copper telephone wiring. DSL is often referred to as 

xDSL, where the x stands for one or two characters that 

define variations of the basic DSL technology. Currently, 

ADSL (Asymmetric DSL) is the form most likely to be 

provided, but even it is, as yet, available only to limited 

groups of subscribers. See also ADSL, DSL Lite, HDSL, 

RADSL, SDSL, VDSL. 

DSLAM n. Acronym for Digital Subscriber Line Access 

Multiplexer. A device in a telephone company central office 

that splits DSL subscriber lines and connects them to Internet 

network hosts and to the public telephone network. The 

use of a DSLAM makes it possible to provide both voice 

and data service through a single pair of copper wires. 

DSL Lite n. Short for Digital Subscriber Line Lite. A 

variation of ADSL currently under development that simplifies 

installation but transmits more slowly, at 1.544 

Mbps. See also ADSL, DSL. 

DSO n. Acronym for Dynamic Shared Object. An 

Apache HTTP server module that supports all UNIXbased 

platforms. DSO uses a dynamically linked shared 

library of resources that are loaded and executed only at 

run time when necessary. DSO is most commonly used 

with Linux and is included in most Linux distributions. 

DSOM n. See Distributed System Object Model. 

DSP n. See digital signal processor. 

DSR n. Acronym for Data Set Ready. A signal used in 

serial communications sent, for example, by a modem to 

the computer to which it is attached, to indicate that it is

DSS dual-ring topology 

ready to operate. DSR is a hardware signal sent over line 6 

in RS-232-C connections. See also RS-232-C standard. 

Compare CTS. 

DSS n. See decision support system, digital satellite system, 

Digital Signature Standard. 

DSSSL n. See Document Style Semantics and Specification 

Language. 

DSTN display n. Acronym for double supertwist nematic 

display. See supertwist display. 

DSU n. See DDS. 

DSVD n. See Digital Simultaneous Voice and Data. 

DTD n. Acronym for document type definition. A separate 

document that contains formal definitions of all of the 

data elements in a particular type of HTML, SGML, or 

XML document, such as a report or a book. By consulting 

the DTD for a document, a program called a parser can 

work with the markup codes that the document contains. 

See also HTML, SGML. 

DTE n. Acronym for Data Terminal Equipment. In the 

RS-232-C and X.25 specifications, a device, such as a PC, 

that has the ability to transmit information in digital form 

over a cable or a communications line to a mediating 

device (known as the DCE). See also RS-232-C standard. 

Compare DCE (definition 1). 

DTL n. See diode-transistor logic. 

DTMF n. Acronym for Dual Tone Multiple Frequency. 

See touch tone dialing. 

DTP n. See desktop publishing, distributed transaction 

processing. 

DTR n. Acronym for Data Terminal Ready. A signal used 

in serial communications sent, for example, by a computer 

to its modem to indicate that the computer is ready to accept 

an incoming transmission. See also RS-232-C standard. 

DTV n. Acronym for desk top video. The use of digital 

cameras over a network for video conferencing. See also 

video conferencing. 

DUA n. Acronym for Directory User Agent. An X.500 client 

program that sends a request to a DSA for the address of 

a user on the network. Also called: DCA, Directory Client 

Agent. See also agent (definition 3), DSA. 

dual attachment station n. An FDDI node with two 

connections to the network—either through a node and a 

179 

concentrator or through two concentrators. Compare single 

attachment station. 

dual-band phone n. Wireless phone that broadcasts and 

receives signals on both 800-MHz (digital cellular) and 

1900-MHz (personal communications service, or PCS) 

networks. 

dual boot n. A computer configuration in which two different 

operating systems are installed and either can be 

loaded at start-up. A user might set up a dual boot system 

to take advantage of specific applications and functions in 

each operating system. A dual boot system might also be 

set up with each operating system in a different language. 

A dual boot system is not limited to only two operating 

systems, and when more than two are installed, it may be 

called a multi-boot system. See also boot1 . 

dual channel controller n. A circuit or device that governs 

signal access to two pathways. 

dual density adj. Of, pertaining to, or characteristic of 

floppy disk drives that can read from and write to disks in 

more than one density format. 

dual disk drive n. A computer that has two floppy disk 

drives. 

dual homing n. A form of fault tolerance used with critical 

network devices on FDDI networks, in which such 

devices are attached to both the primary and secondary 

(backup) rings through two concentrators to provide the 

maximum possible security in case the primary ring fails. 

dual inline memory module n. See DIMM. 

dual inline package or dual in-line package n. See 

DIP. 

dual-mode phone n. Wireless phone that broadcasts and 

receives signals on both analog and digital networks. Dualmode 

phones allow wireless phone users with digital service 

to send and receive calls on analog networks in areas 

where wireless carriers do not provide digital service. 

dual processors n. Two processors used in a computer to 

speed its operation—one processor to control memory and 

the bus, and another to manage input/output. Many personal 

computers use a second processor to perform floating-point 

mathematical operations. See also coprocessor, 

floating-point notation. 

dual-ring topology n. A token-passing ring topology 

implemented in FDDI networks that consists of two rings 

in which information travels in opposite directions. One 

D

D 

dual-scan display DVI 

ring, the primary ring, carries information; the second ring 

is used for backup. See also FDDI. 

dual-scan display n. A passive matrix LCD-type display 

used in laptop computers. The screen refresh rate is twice 

as fast in dual-scan displays as in standard passive matrix 

displays. Compared with active matrix displays, dual-scan 

displays are more economical in terms of power consumption 

but have less clarity and a smaller viewing angle. See 

also passive matrix display. 

dual-sided disk drive n. A disk drive that can read or 

write information to both the top and bottom sides of a 

double-sided disk. Dual-sided disk drives have two read/ 

write heads, one for each disk surface. 

Dual Tone Multiple Frequency n. See touch tone dialing. 

DUB n. See dial-up boot loader. 

dumb quotes n. Quotation marks that have the same 

appearance (usually upright like the apostrophe ' and quotation 

marks " on a typewriter) whether they stand before 

or after the material being quoted. Compare smart quotes. 

dumb terminal n. A terminal that does not contain an 

internal microprocessor. Dumb terminals are typically capable 

of displaying only characters and numbers and responding 

to simple control codes. Compare smart terminal. 

dummy n. A placeholder, usually a character, a record, or 

a variable, that is used to reserve space until the intended 

item is available. See also stub. 

dummy argument n. In programming, an argument that 

does not convey any information into or out of the called 

routine and is usually used to hold a place for an argument 

that will be used in a future revision of the routine. See 

also argument. 

dummy instruction n. See no-operation instruction. 

dummy module n. A module, or group of routines, that 

performs no function but will do so in some future revision—essentially, 

a collection of dummy routines. See 

also dummy routine. 

dummy routine n. A routine that performs no action but 

that can be rewritten to do so at some future time. Top-down 

program development usually involves the creation of 

dummy routines that are turned into functional routines as 

development proceeds. Also called: stub. See also dummy 

argument, dummy module, top-down programming. 

DUN n. See dial-up networking. 

180 

duplex1 adj. Capable of carrying information in both 

directions over a communications channel. A system is 

full-duplex if it can carry information in both directions at 

once; it is half-duplex if it can carry information in only 

one direction at a time. 

duplex2 n. 1. Simultaneous communications, in both 

directions, between the sender and receiver. Also 

called: duplex transmission, full-duplex transmission. See 

also half-duplex transmission. 2. Photographic paper on 

which an image can be printed on both sides. 

duplex channel n. A communications link that allows for 

duplex (two-way) transmission. 

duplex printer n. A printer capable of printing on both 

sides of the page. 

duplex system n. A system of two computers, one of 

which is active while the other remains on standby, ready 

to take over processing if the active machine malfunctions. 

duplex transmission n. See duplex2 (definition 1). 

duplicate key n. A value assigned to an indexed field in 

one record in a database that duplicates a value assigned to 

the same field in another record in the database. For example, 

a key (or index) composed of ZIP-CODE would necessarily 

contain duplicate values if the file contained a 

number of addresses from a single ZIP Code. A field in 

which duplicate values are permitted cannot serve as a primary 

key because the primary key must be unique, but it 

can serve as a component of a composite primary key. See 

also field (definition 1), key (definition 2), primary key. 

duplication check n. 1. A survey made to determine 

whether duplicate records or keys exist in a file. See also 

key. 2. The use of separate independent calculations to 

establish the accuracy of a result. 

DV n. See digital video. 

DVD n. See digital video disc. 

DVD decoder n. A hardware or software component that 

allows a digital video disc (DVD) drive to display movies 

on your computer screen. See also digital video disc. 

DVD-E n. See digital video disc–erasable. 

DVD-R n. See digital video disc–recordable. 

DVD-ROM n. See digital video disc–ROM. 

DVI n. Acronym for Digital Video Interface. A hardwarebased 

compression/decompression technique for storing

DV-I dynamic address translation 

full-motion video, audio, graphics, and other data on a 

computer or on a CD-ROM. DVI technology was developed 

by RCA in 1987 and acquired by Intel in 1988. Intel 

has since developed a software version of DVI, called 

Indeo. Also called: digital video–interactive. 

DV-I n. See digital video–interactive. 

DVMRP n. See Distance Vector Multicast Routing Protocol. 

Dvorak keyboard n. A keyboard layout developed by 

August Dvorak and William L. Dealey in 1936 as an alternative 

to the overwhelmingly popular QWERTY keyboard. 

The Dvorak keyboard was designed to speed typing 

by placing the characters on the keyboard for easiest 

access to the most frequently typed letters. In addition, 

pairs of letters that often occur sequentially were separated 

so that the hands could alternate typing them. See the 

illustration. See also ergonomic keyboard, keyboard. 

Compare QWERTY keyboard. 

7 5 3 1 9 0 2 4 6 8 < > 

" ' 

, 

. 

P 

Y 

F 

F0Dgn14.eps 

Dvorak keyboard. 

DVR n. Acronym for Digital Video Recording. Technology 

allowing broadcast television programming to be digitized 

and played back immediately. Television signals are 

routed through a hard drive, converted to a digital format 

and displayed in real-time or, at the viewer’s option, on a 

delayed basis. DVR technology can be used like a VCR to 

record favorite programs in advance, with the user picking 

the programs to be recorded from an online programming 

guide. DVR capabilities can also be added to products that 

have related digital technologies and components, such as 

set-top boxes and digital TV converters. 

DVST n. See direct view storage tube. 

DWDM n. See dense wavelength division multiplexing. 

G 

C 

R 

L 

A O E U I D H T N S 

Q J K X B M W V 

: ; 

+ = 

? / 

_ - 

Z 

181 

DXF n. Short for drawing interchange format. A computer-aided 

design file format originally developed by 

Autodesk; for use with the AutoCAD program to facilitate 

transfer of graphics files between different applications 

dyadic adj. Of, pertaining to, or characteristic of a pair— 

for example, a dyadic processor, which contains two processors 

controlled by the same operating system. The term 

is usually limited to describing a system with two microprocessors. 

Dyadic Boolean operations are those such as 

AND and OR in which the outcome depends on both values. 

See also Boolean algebra, operand. Compare unary. 

dye-diffusion printer n. See continuous-tone printer. 

dye-polymer recording n. A recording technology used 

with optical discs in which dye embedded in a plastic 

polymer coating on an optical disc is used to create minute 

bumps on the surface that can be read by a laser. Dyepolymer 

bumps can be flattened and re-created, thus making 

an optical disc rewritable. 

dye-sublimation printer n. See continuous-tone printer. 

Dylan n. Short for Dynamic Language. An object-oriented 

programming language developed by Apple Computer 

in the mid-1990s for application and systems 

development. It includes garbage collection, type-safety, 

error recovery, a module system, and programmer control 

over runtime extensibility of programs. 

dynalink n. Short for dynamic link. See dynamic-link 

library. 

Dynaload drivers n. Device drivers that are supported by 

Dynaload. Dynaload is a command that can be run from 

a DOS prompt under IBM’s PC DOS 7 and will load 

compliant device drivers without modification of the 

CONFIG.SYS file. See also CONFIG.SYS. 

dynamic adj. Occurring immediately and concurrently. 

The term is used in describing both hardware and software; 

in both cases it describes some action or event that 

occurs when and as needed. In dynamic memory management, 

a program is able to negotiate with the operating 

system when it needs more memory. 

dynamic address translation n. On-the-fly conversion 

of memory-location references from relative addresses 

(such as “three units from the beginning of X”) to absolute 

addresses (such as “location number 123”) when a program 

is run. Acronym: DAT. 

D

D 

dynamic allocation dynamic scheduling 

dynamic allocation n. The allocation of memory during 

program execution according to current needs. Dynamic 

allocation almost always implies that dynamic deallocation 

is possible too, so data structures can be created and 

destroyed as required. See also allocate, deallocate. 

Compare static allocation. 

dynamic binding n. Binding (converting symbolic 

addresses in the program to storage-related addresses) that 

occurs during program execution. The term often refers to 

object-oriented applications that determine, during run 

time, which software routines to call for particular data 

objects. Also called: late binding. Compare static binding. 

dynamic caching n. A technique for storing recently 

used data in memory where cache size is based on how 

much memory is available rather than how much memory 

is assigned to the application currently running. 

Dynamic Data Exchange n. See DDE. 

dynamic dump n. A listing, either stored on disk or sent 

to a printer, of memory contents generated at the time of a 

break in the execution of a program—a useful tool for programmers 

interested in knowing what is happening at a 

certain point in the execution of a program. 

Dynamic Host Configuration Protocol n. See DHCP. 

dynamic HTML n. A technology designed to add richness, 

interactivity, and graphical interest to Web pages by 

providing those pages with the ability to change and 

update themselves dynamically—that is, in response to 

user actions, without the need for repeated downloads 

from a server. This is done by enabling the interaction of 

HTML, cascading style sheets (CSS), and JavaScript. 

Examples of dynamic HTML actions include moving 

graphics on the page and displaying information, such as 

menus or tables, in response to mouse movements or 

clicks. Interoperability is governed by the World Wide 

Web Consortium (W3C) Document Object Model (DOM) 

specification, a platform- and language-neutral interface 

to ensure that programs and scripts can dynamically 

access and update the content, structure, and style of documents. 

Acronym: DHTML. 

dynamic keys n. An encryption technique in which messages 

are encrypted differently for each transmission 

based on different keys so that if a key is captured and 

decrypted, it would never be useful again. See also 

encryption, key (definition 3). 

182 

dynamic-link library n. A feature of the Microsoft Windows 

family of operating systems and OS/2 that allows 

executable routines to be stored separately as files with 

DLL extensions and to be loaded only when needed by a 

program. A dynamic-link library has several advantages. 

First, it does not consume any memory until it is used. 

Second, because a dynamic-link library is a separate file, a 

programmer can make corrections or improvements to 

only that module without affecting the operation of the 

calling program or any other dynamic-link library. Finally, 

a programmer can use the same dynamic-link library with 

other programs. Acronym: DLL. 

dynamic memory allocation n. The allocation of memory 

to a process or program at run time. Dynamic memory 

is allocated from the system heap by the operating system 

upon request from the program. 

dynamic page n. An HTML document that contains animated 

GIFs, Java applets, or ActiveX controls. See also 

ActiveX control, GIF, HTML, Java applet. 

dynamic RAM n. A form of semiconductor random 

access memory (RAM). Dynamic RAM stores information 

in integrated circuits containing capacitors. Because 

capacitors lose their charge over time, dynamic RAM 

boards must include logic to refresh (recharge) the RAM 

chips continuously. While a dynamic RAM is being 

refreshed, it cannot be read by the processor; if the processor 

must read the RAM while it is being refreshed, one or 

more wait states occur. Despite being slower, dynamic 

RAM is more commonly used than RAM because its circuitry 

is simpler and because it can hold up to four times 

as much data. Acronym: DRAM. See also RAM. Compare 

static RAM. 

dynamic random access memory n. See dynamic RAM. 

dynamic relocation n. The relocation in memory of data 

or of the code of a currently running program by an internal 

system routine. Dynamic relocation helps a computer 

use memory efficiently. 

dynamic routing n. Routing that adjusts automatically to 

the current conditions of a network. Dynamic routing typically 

uses one of several dynamic-routing protocols such 

as Routing Information Protocol (RIP) and Border Gateway 

Protocol (BGP). Compare static routing. 

dynamic scheduling n. The management of concurrently 

running processes (programs), usually by the operating 

system.

Dynamic Shared Object dynamic Web page 

Dynamic Shared Object n. See DSO. 

dynamic SLIP n. Short for dynamic Serial Line Internet 

Protocol. Internet access under SLIP in which the user’s 

IP address is not permanent but is reassigned from a pool 

each time the user connects. The number of IP addresses 

an Internet service provider needs to offer is reduced to the 

number of connections that can be in use at once, rather 

than the total number of subscribers. See also IP address, 

ISP, SLIP. Compare DHCP. 

dynamic storage n. 1. Information storage systems 

whose contents will be lost if power is removed from the 

183 

system. RAM (random access memory) systems are the 

most common form of dynamic storage, and both dynamic 

RAM (DRAM) and static RAM (SRAM) are considered 

forms of dynamic storage. See also dynamic RAM, static 

RAM. Compare permanent storage. 2. In programming, 

blocks of memory that can be allocated, deallocated, or 

freely changed in size. 

dynamic Web page n. A Web page that has fixed form 

but variable content, allowing it to be tailored to a customer’s 

search criteria. 

D

E 

e n. The symbol for the base of the natural logarithm 

2.71828. Introduced by Leonhard Euler in the mid-eighteenth 

century, e is a fundamental mathematical constant used in calculus, 

science, engineering, and programming languages, as 

in logarithmic and exponential functions in C and Basic. 

e- prefix Short for electronic. A prefix indicating that a 

word refers to the computer-based version of some traditionally 

nonelectronic term, as e-mail, e-commerce, and 

e-money. 

E- prefix See exa-. 

E3 n. Acronym for Electronic Entertainment Expo. A 

major convention where game industry developers, manufacturers, 

and publishers demonstrate their latest wares. 

EAI n. Acronym for Enterprise Application Integration. 

The process of coordinating the operation of the various 

programs, databases, and existing technologies of a business 

or enterprise so that they function as an efficient, 

business-wide system. 

early binding n. See static binding. 

EAROM n. Acronym for electrically alterable read-only 

memory. See EEPROM. 

Easter egg n. A hidden feature of a computer program. It 

may be a hidden command, an animation, a humorous 

message, or a list of credits for the people who developed 

the program. In order to display an Easter egg, a user often 

must enter an obscure series of keystrokes. 

eavesdropper n. See lurker. 

EBCDIC n. Acronym for Extended Binary Coded Decimal 

Interchange Code. An IBM code that uses 8 bits to 

represent 256 possible characters, including text, numbers, 

punctuation marks, and transmission control characters. It 

is used primarily in IBM mainframes and minicomputers. 

Compare ASCII. 

e-bomb n. Short for e-mail bomb. A technique used by 

some hackers in which a target is put on a large number of 

mailing lists so that network traffic and storage are tied up 

by e-mail sent by other mailing list subscribers to the lists’ 

recipients. 

E 

184 

e-book n. Format allowing books and other large texts to 

be downloaded from a Web site and viewed digitally. 

Typically, reading an e-book requires using a small computer 

appliance that is about the size of a paperback book 

and consists of a display screen and basic controls. Users 

can bookmark, highlight, or annotate text, but rights 

management features may prevent users from e-mailing, 

printing, or otherwise sharing e-book contents. Also 

called: electronic book. 

e-cash n. See e-money. 

ECC n. See error-correction coding. 

echo1 n. In communications, a signal transmitted back to 

the sender that is distinct from the original signal. Network 

connections can be tested by sending an echo back to 

the main computer. 

echo2 vb. To transmit a received signal back to the sender. 

Computer programs, such as MS-DOS and OS/2, can be 

commanded to echo input by displaying data on the screen 

as it is received from the keyboard. Data communications 

circuits may echo text back to the originating terminal to 

confirm that it has been received. 

echo cancellation n. A technique for eliminating 

unwanted incoming transmissions in a modem that are 

echoes of the modem’s own transmission. The modem 

sends a modified, reversed version of its transmission on 

its receiving path, thus erasing echoes while leaving 

incoming data intact. Echo cancellation is standard in V.32 

modems. 

echo check n. In communications, a method for verifying 

the accuracy of transmitted data by retransmitting it to 

the sender, which compares the echoed signal with the 

original. 

echo loop attack n. A form of denial of service (DoS) 

attack in which a connection is established between User 

Datagram Protocol (UDP) services on two or more host 

machines that bounce an increasing volume of packets 

back and forth. The echo loop attack ties up the host 

machines and causes network congestion.

echoplex editing keys 

echoplex n. In communications, a technique for error 

detection. The receiving station retransmits data back to 

the sender’s screen, where it can be displayed visually to 

check for accuracy. 

echo suppressor n. In communications, a method for preventing 

echoes in telephone lines. Echo suppressors inhibit 

signals from the listener to the speaker, creating a one-way 

channel. For modems that send and receive on the same frequency, 

the echo suppressor must be disabled to allow 

two-way transmission. This disabling produces the 

high-pitched tone heard in modem-to-modem connections. 

ECL n. See emitter-coupled logic. 

ECMA n. Acronym for European Computer Manufacturers 

Association. An organization based in Geneva, Switzerland, 

whose American counterpart is CBEMA 

(Computer and Business Equipment Manufacturers Association). 

Its standard, ECMA-101, is used for transmitting 

formatted text and graphical images while retaining their 

original formatting. 

ECMAScript n. A standardized, object-oriented scripting 

language specification defined by the European Computer 

Manufacturers Association (ECMA) 262 specification. 

This language was originally designed to perform computations 

and manipulate objects within a Web environment. 

Microsoft implements ECMAScript as JScript, and 

Netscape implements ECMAScript as JavaScript. 

ECML n. See Electronic Commerce Modeling Language. 

e-commerce n. Short for electronic commerce. Commercial 

activity that takes place by means of computers 

connected through a network. Electronic commerce can 

occur between a user and a vendor through the Internet, an 

online information service, or a bulletin board system 

(BBS), or between vendor and customer computers 

through electronic data interchange (EDI). Also 

called: e-tail. See also EDI. 

ECP n. Acronym for Enhanced Capabilities Port. A protocol, 

developed by Microsoft and Hewlett Packard, for 

bidirectional, high-speed communication between a computer 

and a printer or scanner. ECP is part of the IEEE 

1284 standard, which specifies enhanced parallel ports 

that are compatible with the older, de facto standard Centronics 

parallel ports. See also EPP, IEEE 1284. 

e-credit n. See electronic credit. 

185 

e-currency n. See e-money. 

edge n. 1. In graphics, a border joining two polygons. 

2. In data structures, a link between two nodes on a tree or 

graph. See also graph, node (definition 3), tree. 

EDGE n. Acronym for Enhanced Data Rates for Global 

Evolution or Enhanced Data Rates for GSM and TDMA 

Evolution. A third-generation enhancement to the Global 

System for Mobile Communications (GSM) wireless service, 

which allows data, multimedia services, and applications 

to be delivered on broadband at rates up to 384 Kbps. 

edge connector n. The set of wide, flat, metallic contacts 

on an expansion board that is inserted into a personal 

computer’s expansion slot or a ribbon cable’s connector. It 

connects the board with the system’s shared data pathway, 

or bus, by means of a series of printed lines that connect to 

the circuits on the board. The number and pattern of lines 

differ with the various types of connectors. See also 

expansion board, ribbon cable. 

EDI n. Acronym for Electronic Data Interchange. A standard 

for exchanging bundles of data between two companies 

via telephone lines or the Internet. EDI transmits 

much larger bundles of data than can be transmitted via 

e-mail. For EDI to be effective, users must agree on certain 

standards for formatting and exchanging information, 

such as the X.400 protocol. See also CCITT X series, standard 


edit1 n. A change made to a file or a document. 

edit2 vb. 1. To make a change to an existing file or document. 

Changes to the existing document are saved in 

memory or in a temporary file but are not added to the 

document until the program is instructed to save them. 

Editing programs typically provide safeguards against 

inadvertent changes, such as by requesting confirmation 

before saving under an existing filename, by allowing the 

user to assign a password to a file, or by giving the option 

of setting the file to read-only status. 2. To run software 

that makes extensive, predictable changes to a file automatically, 

such as a linker or a filter for graphics. 

editing keys n. A set of keys on some keyboards that 

assists in editing. Located between the main keyboard and 

the numeric keypad, editing keys consist of three pairs: 

Insert and Delete, Home and End, and Page Up and Page 

Down. 

E

E 

edit key EIA 

edit key n. In a software application, a predefined key or 

combination of keys that, when pressed, causes the application 

to enter edit mode. 

edit mode n. The mode of a program in which a user can 

make changes to a document, as by inserting or deleting 

data or text. Compare command mode. 

editor n. A program that creates files or makes changes to 

existing files. An editor is usually less powerful than a 

word processor, lacking the latter’s capability for text formatting, 

such as use of italics. Text or full-screen editors 

allow the user to move through the document using direction 

arrows. In contrast, line editors require the user to 

indicate the line number on which text is to be edited. See 

also Edlin. 

Edlin n. An outdated line-by-line text editor used in 

MS-DOS through version 5. Its OS/2 counterpart is SSE. 

See also editor. 

EDMS n. Acronym for electronic document management 

system. See document management system. 

EDO DRAM n. Acronym for extended data out dynamic 

random access memory. A type of memory that allows for 

faster read times than DRAM of comparable speed by 

allowing a new read cycle to begin while data is being read 

from a previous cycle. This allows for faster overall system 

performance. Compare dynamic RAM, EDO RAM. 

EDO RAM n. Acronym for extended data out random access 

memory. A type of dynamic RAM that keeps data available 

for the CPU while the next memory access is being initialized, 

resulting in increased speed. Pentium-class computers using 

Intel’s Triton chip set are designed to take advantage of EDO 

RAM. See also central processing unit, dynamic RAM. Compare 

EDO DRAM. 

EDP n. 1. Acronym for electronic data processing. See 

data processing. 2. Acronym for Enhanced Capabilities 

Port. A protocol, developed by Microsoft and Hewlett 

Packard, for bidirectional, high-speed communication 

between a computer and a printer or scanner. ECP is part 

of the IEEE 1284 standard, which specifies enhanced parallel 

ports that are compatible with the older, de facto standard 

Centronics parallel ports. See also EPP, IEEE 1284. 

.edu n. In the Internet’s Domain Name System, the 

top-level domain that identifies addresses operated by 

four-year, degreed educational institutions. The domain 

name .edu appears as a suffix at the end of the address. In 

the United States, schools that offer kindergarten through 

186 

high school classes use the top-level domain of .k12.us or 

just .us. See also DNS (definition 1), domain (definition 

3), .k12.us, .us. Compare .com, .gov, .mil, .net, .org. 

edutainment n. Multimedia content in software, on 

CD-ROM, or on a Web site that purports to educate the 

user as well as entertain. See also multimedia. 

EEMS n. Acronym for Enhanced Expanded Memory 

Specification. A superset of the original Expanded Memory 

Specification (EMS). Version 3.0 of EMS allowed 

only storage of data and supported 4-page frames. EEMS 

allowed up to 64 pages along with executable code to be 

stored in expanded memory. The features of EEMS were 

included in EMS version 4.0. See also EMS, page frame. 

EEPROM n. Acronym for electrically erasable programmable 

read-only memory. A type of EPROM that can be 

erased with an electrical signal. It is useful for stable storage 

for long periods without electricity while still allowing 

reprogramming. EEPROMs contain less memory than 

RAM, take longer to reprogram, and can be reprogrammed 

only a limited number of times before wearing 

out. See also EPROM, ROM. 

EFF n. See Electronic Frontier Foundation. 

e-form n. Short for electronic form. An online document 

that contains blank spaces for a user to fill in with 

requested information and that can be submitted through a 

network to the organization requesting the information. 

On the Web, e-forms are often coded in CGI script and 

secured via encryption. See also CGI (definition 1). 

EGA n. Acronym for Enhanced Graphics Adapter. An 

IBM video display standard introduced in 1984. It emulates 

the Color/Graphics Adapter (CGA) and the Monochrome 

Display Adapter (MDA) and provides 

medium-resolution text and graphics. It was superseded 

by Video Graphics Display (VGA). 

ego-surfing n. The practice of using a Web search engine 

to search for one’s own name on the Internet. 

EGP n. See exterior gateway protocol. 

e-home n. See smart home. 

EIA n. Acronym for Electronic Industries Association. An 

association based in Washington, D.C., with members 

from various electronics manufacturers. It sets standards 

for electronic components. RS-232-C, for example, is the 

EIA standard for connecting serial components. See also 

RS-232-C standard.

EIDE electromagnetic spectrum 

EIDE or E-IDE n. Acronym for Enhanced Integrated Drive 

Electronics. An extension of the IDE standard, EIDE is a 

hardware interface standard for disk drive designs that 

house control circuits in the drives themselves. It allows 

for standardized interfaces to the system bus while providing 

for advanced features, such as burst data transfer and 

direct data access. EIDE accommodates drives as large as 

8.4 gigabytes (IDE supports up to 528 megabytes). It supports 

the ATA-2 interface, which permits transfer rates up 

to 13.3 megabytes per second (IDE permits up to 3.3 

megabytes per second), and the ATAPI interface, which 

connects drives for CD-ROMs, optical discs and tapes, 

and multiple channels. Most PCs have EIDE drives, which 

are cheaper than SCSI drives and provide much of the 

same functionality. See also IDE, SCSI. 

Eiffel n. An advanced object-oriented programming language 

with a syntax similar to C, developed by Bertrand 

Meyer in 1988. Eiffel runs on MS-DOS, OS/2, and UNIX. 

Its major design features are the ability to use modules in 

multiple programs and software extensibility. 

Eiffel# n. Pronounced “Eiffel Sharp.” A subset language 

of Eiffel specifically designed to target the .NET Framework 

and embody the full extent of Design by Contract. 

See also Design by Contract. 

eight dot three n. See 8.3. 

EIP n. See enterprise information portal. 

EIS n. See executive information system. 

EISA n. Acronym for Extended Industry Standard Architecture. 

A bus standard for the connection of add-on cards 

to a PC motherboard, such as video cards, internal 

modems, sound cards, drive controllers, and cards that 

support other peripherals. EISA was introduced in 1988 

by a consortium of nine computer industry companies. 

The companies—AST Research, Compaq, Epson, 

Hewlett-Packard, NEC, Olivetti, Tandy, Wyse, and 

Zenith—were referred to collectively as “the Gang of 

Nine.” EISA maintains compatibility with the earlier 

Industry Standard Architecture (ISA) but provides for 

additional features introduced by IBM in its Micro Chan- 

187 

nel Architecture bus standard. EISA has a 32-bit data path, 

and it uses connectors that can accept ISA cards. However, 

EISA cards are compatible only with EISA systems. EISA 

can operate at much higher frequencies than the ISA bus 

and provides much faster data throughput than ISA. See 

also ISA, Micro Channel Architecture. 

EJB n. See Enterprise JavaBeans. 

electroluminescent adj. Giving off light when electric 

current is applied. Electroluminescent panels are used in 

portable computers to backlight the liquid crystal displays. 

A thin phosphor layer is sandwiched between two thin 

electrode panels, one of which is nearly transparent. See 

also liquid crystal display. 

electroluminescent display n. A type of flat-panel display 

used in laptops in which a thin phosphor layer is set 

between vertical and horizontal electrodes. These electrodes 

form xy-coordinates; when a vertical and a horizontal 

electrode are charged, the phosphor at their intersection 

emits light. Electroluminescent displays provide a sharp, 

clear image and a wide viewing angle. They were replaced 

by active matrix LCD screens. See also flat-panel display, 

liquid crystal display, passive-matrix display. Compare 

active-matrix display. 

electrolysis n. A process in which a chemical compound 

is broken down into its constituent parts by passing an 

electric current through it. 

electromagnet n. A device that creates a magnetic field 

when electric current passes through it. An electromagnet 

typically contains an iron or steel core with wire wrapped 

around it. Current is passed through the wire, producing a 

magnetic field. Electromagnets are used in disk drives to 

record data onto the disk surface. 

electromagnetic radiation n. The propagation of a 

magnetic field through space. Radio waves, light, and X 

rays are examples of electromagnetic radiation, all traveling 

at the speed of light. 

electromagnetic spectrum n. The range of frequencies 

of electromagnetic radiation. In theory, the spectrum’s 

range is infinite. See the illustration. 

E

E 

electromotive force electronic publishing 

Wavelength in meters 

10 -12 

10 -10 

10 -8 

10 -6 

10 -4 

10 -2 

10 

10 2 

10 4 

10 6 

Gamma rays 

X rays 

Visible light 

Microwaves 

F0Exx01.eps 

Electromagnetic spectrum. 

FM and TV broadcasts 

AM broadcasts 

60-Hz house voltage 

electromotive force n. The force that causes movement 

in charge carriers (the electrons) in a conductor. Acronym: 

EMF. Also called: potential, voltage. See also ampere, 

coulomb. 

electron beam n. A stream of electrons moving in one 

direction. An electron beam is used in a cathode-ray tube 

(CRT) to produce an image as it is passed across the phosphor 

coating inside the tube. See also CRT. 

electron gun n. A device that produces an electron beam, 

typically found in television or computer monitors. See 

also CRT. 

electronic bulletin board n. See BBS (definition 1). 

electronic cash n. See e-money. 

electronic circuit n. See circuit. 

electronic commerce n. See e-commerce. 

Electronic Commerce Modeling Language n. A computer 

language developed by leading e-commerce companies 

as a standard for inputting e-wallet information 

into the payment fields of Web sites. This allows for 

one-click transfer of e-wallet information at compatible 

Web sites. Acronym: ECML. 

electronic credit n. A form of electronic commerce 

involving credit card transactions carried out over the 

Internet. Also called: e-credit. See also e-commerce. 

electronic data interchange n. See EDI. 

electronic data processing n. See data processing. 

188 

electronic form n. See e-form. 

Electronic Frontier Foundation n. A public advocacy 

organization dedicated to the defense of civil liberties for 

computer users. The organization was founded in 1990 by 

Mitchell Kapor and John Perry Barlow as a response to 

U.S. Secret Service raids on hackers. Acronym: EFF. 

electronic funds transfer n. The transfer of money via 

automated teller machine, telephone lines, or Internet connection. 

Examples of electronic fund transfers include 

using a credit card to make purchases from an e-commerce 

site, or using an automated teller machine or automated 

telephone banking system to move funds between 

bank accounts. Acronym: EFT. 

Electronic Industries Association n. See EIA. 

electronic journal n. See journal. 

electronic mail n. See e-mail1 . 

electronic mail services n. Services that allow users, 

administrators, or daemons to send, receive, and process 

e-mail. See also daemon. 

electronic mall n. A virtual collection of online businesses 

that affiliate with the intention of increasing the 

exposure of each business through the fellow businesses. 

electronic money n. See e-money. 

electronic music n. Music created with computers and 

electronic devices. See also MIDI, synthesizer. 

electronic office n. A term used especially in the late 

1970s to mid-1980s to refer to a hypothetical paperless 

work environment to be brought about by the use of computers 

and communications devices. 

electronic paper n. Technology allowing a computer 

display to imitate the look and feel of traditional paper 

media. Electronic paper consists of thin, flexible sheets of 

plastic containing millions of small beads called microcapsules. 

Each microcapsule contains both a black and a 

white pigment and displays the proper color in response to 

an electrical charge. It retains this pattern until a new 

screen of text or images is requested. 

electronic photography n. See digital photography. 

Electronic Privacy Information Center n. See EPIC. 

electronic publishing n. A general term for distributing 

information via electronic media, such as communications 

networks or CD-ROM.

electronics elevator 

electronics n. The branch of physics dealing with electrons, 

electronic devices, and electrical circuits. 

Electronics Industries Association n. See EIA. 

electronic software distribution n. A means of directly 

distributing software to users on line over the Internet. 

Electronic software distribution is analogous to 

direct-mail ordering. Acronym: ESD. 

electronic spreadsheet n. See spreadsheet program. 

electronic storefront n. A business that displays its merchandise 

on the Internet and has provisions for contact or 

online sales. 

electronic text n. See e-text. 

electron tube n. A device for switching and amplifying 

electronic signals. It consists of a sealed glass container 

with electronic elements, such as metallic plates and grids, 

inside. In most applications, tubes have been replaced by 

transistors, although they are still used in cathode-ray tubes 

and in some radio frequency circuits and audio amplifiers. 

Also called: vacuum tube, valve. See also CRT. 

electrophotographic printers n. Printers in a category 

including laser, LED, LCD, and ion-deposition printers. In 

such a printer, a negative image is applied to an electrically 

charged, photosensitive drum. A photosensitive 

drum develops a pattern of electrostatic charge on its surface 

representing the photo negative of the image the drum 

will print. Powdered ink (toner) adheres to the charged 

areas of the drum, the drum presses the ink onto the paper, 

and then heat binds the toner to the paper. The printer 

types vary mainly in how they charge the drum. See also 

ion-deposition printer, laser printer, LCD printer, LED 

printer. 

electrophotography n. The production of photographic 

images using electrostatic charges. This method is used in 

photocopiers and laser printers. Also called: xerography. 

See also electrophotographic printers. 

electroplating n. The use of electrolysis for depositing a 

thin layer of one material onto another material. See also 

electrolysis. 

electrostatic adj. Of or relating to electric charges that 

are not flowing along a conducting path. Electrostatic 

charges are used in copiers and laser printers to hold toner 

189 

particles on a photoconducting drum and in flatbed plotters 

to hold the plot medium in place. 

electrostatic discharge n. The discharge of static electricity 

from an outside source, such as human hands, into 

an integrated circuit, often resulting in damage to the circuit. 

Acronym: ESD. 

electrostatic plotter n. A plotter that creates an image 

from a dot pattern on specially coated paper. The paper is 

electrostatically charged and exposed to toner, which 

adheres to the dots. Electrostatic plotters can be up to 50 

times faster than pen plotters but are more costly. Color 

models produce images through multiple passes with 

cyan, magenta, yellow, and black. See also plotter. Compare 

electrophotographic printers, pen plotter. 

electrostatic printer n. See electrostatic plotter. 

elegant adj. Combining simplicity, terseness, efficiency, 

and subtlety. On the academic side of computer science, 

elegant design (say, of programs, algorithms, or hardware) 

is a priority, but in the frenetic pace of the computer industry, 

elegant design may be sacrificed for the sake of speeding 

a product’s development, sometimes resulting in bugs 

that are difficult to correct. 

element n. 1. Any stand-alone item within a broader context. 

For example, a data element is an item of data with 

the characteristics or properties of a larger set; a picture 

element (pixel) is one single dot on a computer screen or 

in a computer graphic; a print element is the part of a 

daisy-wheel printer that contains the embossed characters. 

See also daisy-wheel printer, data element, graphics primitive, 

pixel, thimble. 2. In markup languages such as 

HTML and SGML, the combination of a set of tags, any 

content contained between the tags, and any attributes the 

tags may have. Elements can be nested, one within the 

other. See also attribute (definition 3), HTML, markup 

language, SGML. 

elevator n. The square box within a scroll bar that can be 

moved up and down to change the position of text or an 

image on the screen. See the illustration. Also called: scroll 

box, thumb. See also scroll bar. 

F0Exx02.eps 

Elevator. 

Elevator 

E

E 

elevator seeking embedded system 

elevator seeking n. A method of limiting hard disk 

access time in which multiple requests for data are prioritized 

based on the location of the data relative to the read/ 

write head. This serves to minimize head movement. See 

also access time (definition 2), hard disk, read/write head. 

elite n. 1. A size of fixed-width type that prints 12 characters 

to the inch. 2. A fixed-width font that may be available 

in various type sizes. See also monospace font. 

ELIZA n. A program, modeled on Rogerian psychotherapy, 

that conducts simulated conversations with humans 

by echoing responses and posing questions based on key 

words in earlier comments. It was created by Dr. Joseph 

Weizenbaum, who considered it a bit of a joke and was 

alarmed that people took it seriously. See also artificial 

intelligence, Turing test. 

ellipsis n. A set of three dots (...) used to convey incompleteness. 

In many windowing applications, selection of a 

command that is followed by an ellipsis will produce a 

submenu or a dialog box. In programming and software 

manuals, an ellipsis in a syntax line indicates the repetition 

of certain elements. See also dialog box, syntax. 

elm n. Short for electronic mail. A program for reading 

and composing e-mail on UNIX systems. The elm program 

has a full-screen editor, making it easier to use than 

the original mail program, but elm has largely been superseded 

by pine. See also e-mail1 . Compare Eudora, pine. 

e-mail1 or email or E-mail n. 1. Short for electronic mail. 

The exchange of text messages and computer files over a 

communications network, such as a local area network or 

the Internet, usually between computers or terminals. 

2. An electronic text message. 

e-mail2 or email or E-mail vb. To send an e-mail message. 

e-mail address n. A string that identifies a user so that 

the user can receive Internet e-mail. An e-mail address 

typically consists of a name that identifies the user to the 

mail server, followed by an at sign (@) and the host name 

and domain name of the mail server. For example, if Anne 

E. Oldhacker has an account on the machine called baz at 

Foo Enterprises, she might have an e-mail address 

aeo@baz.foo.com, which would be pronounced “A E O at 

baz dot foo dot com.” 

e-mail filter n. A feature in e-mail-reading software that 

automatically sorts incoming mail into different folders or 

mailboxes based on information contained in the message. 

190 

For example, all incoming mail from a user’s Uncle Joe 

might be placed in a folder labeled “Uncle Joe.” Filters 

may also be used either to block or accept e-mail from 

designated sources. 

e-mail management system n. An automated e-mail 

response system used by an Internet-based business to sort 

incoming e-mail messages into predetermined categories 

and either reply to the sender with an appropriate response 

or direct the e-mail to a customer service representative. 

Acronym: EMS. 

embed vb. To insert information created in one program, 

such as a chart or an equation, into another program. After 

the object is embedded, the information becomes part of 

the document. Any changes made to the object are 

reflected in the document. 

embedded adj. In software, pertaining to code or a command 

that is built into its carrier. For example, application 

programs insert embedded printing commands into a document 

to control printing and formatting. Low-level 

assembly language is embedded in higher-level languages, 

such as C, to provide more capabilities or better efficiency. 

embedded chip n. See embedded system. 

embedded command n. A command placed in a text, 

graphics, or other document file, often used for printing or 

page-layout instructions. Such commands often do not 

appear on screen but can be displayed if needed. In transferring 

documents from one program to another, embedded 

commands can cause problems if the programs are 

incompatible. 

embedded controller n. A processor-based controller 

circuit board that is built into the computer machinery. See 

also controller. 

embedded hyperlink n. A link to a resource that is 

embedded within text or is associated with an image or an 

image map. See also hyperlink, image map. 

embedded interface n. An interface built into a hardware 

device’s drive and controller board so that the device 

can be directly connected to the computer’s system bus. 

See also controller, interface (definition 3). Compare 

ESDI, SCSI, ST506 interface. 

embedded system n. Microprocessors used to control 

devices such as appliances, automobiles, and machines 

used in business and manufacturing. An embedded system 

is created to manage a limited number of specific tasks

em dash encapsulate 

within a larger device or system. An embedded system is 

often built onto a single chip or board and is used to control 

or monitor the host device—usually with little or no 

human intervention and often in real time. See also 

microprocessor. 

em dash n. A punctuation mark (—) used to indicate a 

break or interruption in a sentence. It is named for the em, 

a typographical unit of measure that in some fonts equals 

the width of a capital M. Compare en dash, hyphen. 

EMF n. See electromotive force. 

emitter n. In transistors, the region that serves as a source 

of charge carriers. Compare base (definition 3), collector. 

emitter-coupled logic n. A circuit design in which the 

emitters of two transistors are connected to a resistor so 

that only one of the transistors switches at a time. The 

advantage of this design is very high switching speed. Its 

drawbacks are the high number of components required 

and susceptibility to noise. Acronym: ECL. 

EMM n. See Expanded Memory Manager. 

e-money or emoney n. Short for electronic money. A 

generic name for the exchange of money through the 

Internet. Also called: cybercash, digicash, digital cash, 

e-cash, e-currency. 

emotag n. In an e-mail message or newsgroup article, a 

letter, word, or phrase that is encased in angle brackets and 

that, like an emoticon, indicates the attitude the writer 

takes toward what he or she has written. Often emotags 

have opening and closing tags, similar to HTML tags, that 

enclose a phrase or one or more sentences. For example: 

You didn’t think there would really be a joke here, 

did you?. Some emotags consist of a single tag, 

such as . See also emoticon, HTML. 

emoticon n. A string of text characters that, when viewed 

sideways, form a face expressing a particular emotion. An 

emoticon is often used in an e-mail message or newsgroup 

post as a comment on the text that precedes it. Common 

emoticons include :-) or :) (meaning “I’m smiling at the 

joke here”), ;-) (“I’m winking and grinning at the joke 

here”), :-( (“I’m sad about this”), :-7 (“I’m speaking with 

tongue in cheek”), :D or :-D (big smile; “I’m overjoyed”), 

and :-O (either a yawn of boredom or a mouth open in 

amazement). Compare emotag. 

EMS n. Acronym for Expanded Memory Specification. A 

technique for adding memory to PCs that allows for 

increasing memory beyond the Intel 80x86 microproces- 

191 

sor real-mode limit of 1 megabyte (MB). In earlier versions 

of microprocessors, EMS bypassed this memory 

board limit with a number of 16-kilobyte banks of RAM 

that could be accessed by software. In later versions of 

Intel microprocessors, including the 80386 and 80486 

models, EMS is converted from extended memory by software 

memory managers, such as EMM386 in MS-DOS 5. 

Now EMS is used mainly for older MS-DOS applications 

because Windows and other applications running in protected 

mode on 80386 and higher microprocessors are free 

of the 1-MB limit. Also called: LIM EMS. See also 

expanded memory, protected mode. Compare conventional 

memory, extended memory. 

em space n. A typographical unit of measure that is 

equal in width to the point size of a particular font. For 

many fonts, this is equal to the width of a capital M, from 

which the em space takes its name. Compare en space, 

fixed space, thin space. 

emulate vb. For a hardware or software system to 

behave in the same manner as another hardware or software 

system. In a network, for example, microcomputers 

might emulate terminals in order to communicate with 

mainframes. 

emulation n. The process of a computer, device, or program 

imitating the function of another computer, device, 

or program. 

emulator n. Hardware or software designed to make one 

type of computer or component act as if it were another. 

By means of an emulator, a computer can run software 

written for another machine. In a network, microcomputers 

might emulate terminals in order to communicate with 

mainframes. 

emulsion laser storage n. A method for recording data 

in film by selective heating with a laser beam. 

enable vb. To activate or turn on. Compare disable. 

encapsulate vb. 1. To treat a collection of structured 

information as a whole without affecting or taking notice 

of its internal structure. In communications, a message or 

packet constructed according to one protocol, such as a 

TCP/IP packet, may be taken with its formatting data as an 

undifferentiated stream of bits that is then broken up and 

packaged according to a lower-level protocol (for example, 

as ATM packets) to be sent over a particular network; 

at the destination, the lower-level packets are assembled, 

re-creating the message as formatted for the encapsulated 

protocol. See also ATM (definition 1). 2. In object-oriented 

E

E 

Encapsulated PostScript End key 

programming, to keep the implementation details of a class 

a separate file whose contents do not need to be known by 

a programmer using that class. See also object-oriented 

programming, TCP/IP. 

Encapsulated PostScript n. See EPS. 

encapsulated type n. See abstract data type. 

encapsulation n. 1. In object-oriented programming, the 

packaging of attributes (properties) and functionality 

(methods or behaviors) to create an object that is essentially 

a “black box”—one whose internal structure remains 

private and whose services can be accessed by other 

objects only through messages passed via a clearly defined 

interface (the programming equivalent of a mailbox or telephone 

line). Encapsulation ensures that the object providing 

service can prevent other objects from manipulating its 

data or procedures directly, and it enables the object 

requesting service to ignore the details of how that service 

is provided. See also information hiding. 2. In terms of the 

Year 2000 problem, a method of dealing with dates that 

entails shifting either program logic (data encapsulation) or 

input (program encapsulation) backward into the past, to a 

parallel year that allows the system to avoid Year 2000 

complications. Encapsulation thus allows processing to 

take place in a “time warp” created by shifting to an earlier 

time before processing and—for accuracy—shifting output 

forward by the same number of years to reflect the actual 

date. See data encapsulation, program encapsulation. 

encipher vb. See encrypt. 

encode vb. 1. See encrypt. 2. In programming, to put 

something into code, which frequently involves changing 

the form—for example, changing a decimal number to 

binary-coded form. See also binary-coded decimal, 

EBCDIC. 

encoder n. 1. In general, any hardware or software that 

encodes information—that is, converts the information to 

a particular form or format. For example, the Windows 

Media Encoder converts audio and video to a form that 

can be streamed to clients over a network. 2. In reference 

to MP3 digital audio in particular, technology that converts 

a WAV audio file into an MP3 file. An MP3 encoder 

compresses a sound file to a much smaller size, about 

one-twelfth as large as the original, without a perceptible 

drop in quality. Also called: MP3 encoder. See also MP3, 

WAV. Compare rip, ripper. 

192 

encoding n. 1. See Huffman coding. 2. A method of dealing 

with computers with Year 2000 problems that entails 

storing a four-digit year in date fields designed to hold 

only two digits in a program or system. This can be 

accomplished by using the bits associated with the date 

field more efficiently—for example, by converting the 

date field from ASCII to binary or from decimal to hexadecimal, 

both of which allow storage of larger values. 

encrypt vb. To encode (scramble) information in such a 

way that it is unreadable to all but those individuals possessing 

the key to the code. Encrypted information is 

known as cipher text. Also called: encipher, encode. 

encryption n. The process of encoding data to prevent 

unauthorized access, especially during transmission. 

Encryption is usually based on one or more keys, or codes, 

that are essential for decoding, or returning the data to 

readable form. The U.S. National Bureau of Standards 

created a complex encryption standard, Data Encryption 

Standard (DES), which is based on a 56-bit variable that 

provides for more than 70 quadrillion unique keys to 

encrypt documents. See also DES. 

encryption key n. A sequence of data that is used to 

encrypt other data and that, consequently, must be used for 

the data’s decryption. See also decryption, encryption. 

end-around carry n. A special type of end-around shift 

operation on a binary value that treats the carry bit as an 

extra bit; that is, the carry bit is moved from one end of the 

value to the other. See also carry, end-around shift, shift. 

end-around shift n. An operation performed on a binary 

value in which a bit is shifted out of one end and into the 

other end. For example, a right-end shift on the value 

00101001 yields 10010100. See also shift. 

en dash n. A punctuation mark (–) used to show ranges 

of dates and numbers, as in 1990–92, and in compound 

adjectives where one part is hyphenated or consists of two 

words, as in pre–Civil War. The en dash is named after a 

typographical unit of measure, the en space, which is half 

the width of an em space. See also em space. Compare em 

dash, hyphen. 

End key n. A cursor-control key that moves the cursor to 

a certain position, usually to the end of a line, the end of a 

screen, or the end of a file, depending on the program. See 

the illustration.

endless loop Enhanced Graphics Display 

F0Exx03.eps 

End key. 

Insert Home 

Delete 

End 

Page 

Up 

Page 

Down 

endless loop n. See infinite loop. 

Nu 

Loc 

end mark n. A symbol that designates the end of some 

entity, such as a file or word processing document. 

end-of-file n. 1. A code placed by a program after the last 

byte of a file to tell the computer’s operating system that no 

additional data follows. In ASCII, end-of-file is represented 

by the decimal value 26 (hexadecimal 1A) or the Ctrl+Z 

control character. Acronym: EOF. 2. An indicator of some 

sort in a computer program or database that indicates that 

the end of a file has been reached. If older systems that have 

the capacity to store only two-digit years in the date field 

also use end-of-file markers such as 99, they can be susceptible 

to date-related problems. See also 99 or 9999. 

end-of-text n. In data transmission, a character used to 

mark the end of a text file. End-of-text does not necessarily 

signify the end of transmission; other information, such 

as error-checking or transmission control characters, can 

be included at the end of the file. In ASCII, end-of-text is 

represented by the decimal value 3 (hexadecimal 03). 

Acronym: ETX. 

end-of-transmission n. A character representing the end 

of a transmission. In ASCII, the end-of-transmission 

character has the decimal value 4 (hexadecimal 04). 

Acronym: EOT. 

endpoint n. The beginning or end of a line segment. 

end-to-end delivery n. A communications process in networks 

in which packets are delivered and then acknowledged 

by the receiving system. 

end-to-end examination n. An inspection of all of the 

processes and systems in place at an organization that 

affect the computer systems. The examination begins 

with the data or information that flows into the system, 

continues with how the data is manipulated and stored, 

and ends with how the data is output. For example, 

end-to-end examination is one technique that was 

7 

Hom 

4 

1 

End key 

193 

employed to ferret out Year 2000 problems in computer 

systems of an organization. 

end user n. The ultimate user of a computer or computer 

application in its finished, marketable form. 

End-User License Agreement n. A legal agreement 

between a software manufacturer and the software’s purchaser 

with regard to terms of distribution, resale, and 

restricted use. Acronym: EULA. 

Energy Star n. A symbol affixed to systems and components 

that denotes lower power-consumption design. 

Energy Star is the name of an Environmental Protection 

Agency program that encourages PC manufacturers to 

build systems that are energy efficient. Requirements dictate 

that systems or monitors be capable of automatically 

entering a “sleep state” or lower power-consumption state 

while the unit is inactive, where the low-power state is 

defined as 30 watts or less. Systems and monitors that 

comply with these guidelines are marked with an Energy 

Star sticker. 

engine n. A processor or portion of a program that determines 

how the program manages and manipulates data. 

The term engine is most often used in relation to a specific 

use; for example, a database engine contains the tools for 

manipulating a database, and a Web search engine has the 

ability to search World Wide Web indexes for matches to 

one or more key words entered by the user. Compare 

back-end processor, front-end processor. 

Enhanced Capabilities Port n. See ECP. 

enhanced Category 5 cable n. See Cat 5e cable. 

Enhanced Data Rates for Global Evolution n. See 

EDGE. 

Enhanced Data Rates for GSM and TDMA 

Evolution n. See EDGE. 

Enhanced Expanded Memory Specification n. See 

EEMS. 

Enhanced Graphics Adapter n. See EGA. 

Enhanced Graphics Display n. A PC video display 

capable of producing graphic images with resolutions 

ranging from 320 x 200 through 640 x 400 pixels, in color 

or in black and white. Resolution and color depth depend 

on the vertical and horizontal scanning frequencies of the 

display, the capabilities of the video display controller 

card, and available video RAM. 

E

E 

Enhanced IDE entity 

Enhanced IDE n. See EIDE. 

Enhanced Integrated Device Electronics n. See EIDE. 

enhanced keyboard n. An IBM 101/102-key keyboard 

that replaced the PC and AT keyboards. It features 12 

function keys across the top (rather than 10 on the left 

side), extra Control and Alt keys, and a bank of cursor and 

editing keys between the main keyboard and number pad. 

It is similar to the Apple Extended Keyboard. 

Enhanced Parallel Port n. See EPP. 

enhanced serial port n. A connection port for peripheral 

devices, commonly used for mice and external modems. 

Enhanced serial ports utilize 16550-type or newer 

high-speed UART circuits for faster data throughput. 

Enhanced serial ports are capable of transferring data at 

speeds as high as 921.6 Kbps. Acronym: ESP. See also 

input/output port, UART. 

Enhanced Small Device Interface n. See ESDI. 

ENIAC n. An 1800-square-foot, 30-ton computer containing 

about 18,000 vacuum tubes and 6000 manual 

switches. Developed between 1942 and 1946 for the U.S. 

Army by J. Presper Eckert and John Mauchly at the University 

of Pennsylvania, ENIAC is considered to have 

been the first truly electronic computer. It remained in 

operation until 1955. 

enlarge vb. In Windows and other graphical user interfaces, 

to increase the size of a window. See also maximize. 

Compare minimize, reduce. 

E notation n. See floating-point notation. 

ENQ n. See enquiry character. 

enquiry character n. Abbreviated ENQ. In communications, 

a control code transmitted from one station to 

request a response from the receiving station. In ASCII, 

the enquiry character is designated by decimal value 5 

(hexadecimal 05). 

en space n. A typographical unit of measure that is equal 

in width to half the point size of a particular font. Compare 

em space, fixed space, thin space. 

Enter key n. The key that is used at the end of a line or 

command to instruct the computer to process the command 

or text. In word processing programs, the Enter key 

is used at the end of a paragraph. Also called: Return key. 

Enterprise Application Integration n. See EAI. 

enterprise computing n. In a large enterprise such as a 

corporation, the use of computers in a network or series of 

194 

interconnected networks that generally encompass a variety 

of different platforms, operating systems, protocols, 

and network architectures. Also called: enterprise networking. 

enterprise information portal n. A portal or gateway 

that allows internal and external users in a business or 

enterprise to access information from intranets, extranets, 

and the Internet for business needs. An enterprise information 

portal provides a simple Web interface that is 

designed to help users sift through large amounts of data 

quickly to find the information they need. By organizing 

all internal information from company servers, databases, 

e-mail, and legacy systems, the enterprise information 

portal exercises control over the company’s information 

availability and presentation. Acronym: EIP. See also portal. 

Enterprise JavaBeans n. An application programming 

interface (API) designed to extend the JavaBean component 

model to cross-platform, server-side applications that 

can run on the various systems usually present in an enterprise 

environment. Enterprise JavaBeans are defined in the 

Enterprise JavaBean specification released by Sun Microsystems, 

Inc. The goal of the API is to provide developers 

with a means of applying Java technology to the creation 

of reusable server components for business applications, 

such as transaction processing. Acronym: EJB. See also 

Java, JavaBean. 

enterprise network n. In a large enterprise such as a corporation, 

the network (or interconnected networks) of 

computer systems owned by the enterprise, which fills the 

enterprise’s various computing needs. This network can 

span diverse geographical locations and usually encompasses 

a range of platforms, operating systems, protocols, 

and network architectures. 

enterprise networking n. See enterprise computing. 

Enterprise Resource Planning n. An approach to business 

information management that relies on integrated 

application software to provide data on all aspects of the 

enterprise, such as manufacturing, finance, inventory, 

human resources, sales, and so on. The objective of Enterprise 

Resource Planning software is to provide data, when 

and as needed, to enable a business to monitor and control 

its overall operation. Acronym: ERP. Compare Material 

Requirements Planning. 

entity n. In computer-aided design and object-oriented 

design, an item that can be treated as a unit and, often, as a 

member of a particular category or type. See also CAD, 

object-oriented design.

entry .eps 

entry n. 1. A unit of information treated as a whole by a 

computer program. 2. The process of inputting information. 

entry point n. A place in a program where execution can 

begin. 

enumerated data type n. A data type consisting of a 

sequence of named values given in a particular order. 

envelope n. 1. In communications, a single unit of information 

that is grouped with other items, such as 

error-checking bits. 2. The shape of a sound wave, caused 

by changes in amplitude. See the illustration. 

Amplitude 

F0Exx04.eps 

Envelope. 

Time 

envelope delay n. In communications, the difference in 

travel times of different frequencies in a signal. If the frequencies 

reach their destination at different times, signal distortion 

and errors can result. Also called: delay distortion. 

environment n. 1. The configuration of resources available 

to the user. Environment refers to the hardware and 

the operating system running on it. For example, Windows 

and Macintosh are called windowing environments 

because they are based on screen regions called windows. 

2. In microcomputing, environment refers to a definition 

of the specifications, such as command path, that a program 

operates in. 

EOF n. See end-of-file (definition 1). 

EOL n. Acronym for end of line. A control (nonprinting) 

character that signals the end of a data line in a data file. 

EOT n. See end-of-transmission. 

EPIC n. 1. Short for Explicitly Parallel Instruction Computing. 

A technology developed jointly by Intel and 

Hewlett-Packard as the foundation of the 64-bit instruction 

set architecture incorporated in IA-64, the basis of the 

Merced chip. EPIC technology is designed to enable IA-64 

processors to execute instructions efficiently and extremely 

quickly. Core elements include explicit parallelism based 

on software identification of instructions that the processor 

195 

can execute concurrently; improved execution of branch 

paths; and earlier loads from memory. See also IA-64, 

Merced. 2. Short for Electronic Privacy Information Center. 

A public-interest research center based in Washington, 

D.C., dedicated to directing public attention toward civil 

liberties and online privacy related to electronic communication, 

cryptography, and related technologies. 

epitaxial layer n. In semiconductors, a layer that has the 

same crystal orientation as the underlying layer. 

EPP n. Acronym for Enhanced Parallel Port, a high-speed 

port for peripheral devices other than printers and scanners—that 

is, for devices such as external drives. Specified 

in the IEEE 1284 standard, EPP describes bidirectional 

parallel ports that provide data throughput of 1 Mbps or 

more, as opposed to the 100 Kbps to 300 Kbps typical of 

the older, de facto standard Centronics ports. See also 

IEEE 1284, input/output port. Compare ECP. 

EPP IEEE standard n. An IEEE standard relating to the 

Enhanced Parallel Port (EPP) protocol. This protocol was 

originally developed by Intel, Xircom, and Zenith Data 

Systems as a means to provide a high-performance parallel 

port link that would still be compatible with the standard 

parallel port. This protocol capability was 

implemented by Intel in the 386SL chip set (82360 I/O 

chip), prior to the establishment of the IEEE 1284 committee 

and the associated standards work. The EPP protocol 

offered many advantages to parallel port peripheral 

manufacturers and was quickly adopted by many as an 

optional data transfer method. A loose association of 

about 80 interested manufacturers was formed to develop 

and promote the EPP protocol. This association became 

the EPP Committee and was instrumental in helping to get 

this protocol adopted as one of the IEEE 1284 advanced 

modes. See also communications protocol, IEEE 1284, 

parallel port. 

EPROM n. Acronym for erasable programmable 

read-only memory. A nonvolatile memory chip that is 

programmed after it is manufactured. EPROMs can be 

reprogrammed by removing the protective cover from the 

top of the chip and exposing the chip to ultraviolet light. 

Though EPROMs are more expensive than PROM chips, 

they can be more cost-effective if many changes are 

required. Also called: reprogrammable read-only memory 

(RPROM). See also EEPROM, PROM, ROM. 

.eps n. The file extension that identifies Encapsulated 

PostScript files. See also EPS. 

E

E 

EPS error-correction coding 

EPS n. Acronym for Encapsulated PostScript. A Post- 

Script file format that can be used as an independent 

entity. The EPS image must be incorporated into the Post- 

Script output of an application such as a desktop publisher. 

Many high-quality clip-art packages consist of such 

images. See also PostScript. 

EPSF n. Acronym for Encapsulated PostScript file. 

See EPS. 

equality n. The property of being identical, used most 

often in reference to values and data structures. 

equalization n. A form of conditioning used to compensate 

for signal distortion and delay on a communication 

channel. Equalization attempts to maintain the amplitude 

and phase characteristics of a signal so that it remains true 

to the original when it reaches the receiving device. 

equation n. A mathematical statement that indicates 

equality with the use of an equal sign (=) between two 

expressions. In programming languages, assignment statements 

are written in equation form. See also assignment 

statement. 

erasable programmable read-only memory n. See 

EPROM. 

erasable storage n. Storage media that can be used 

repeatedly because the user has the ability to erase whatever 

data was previously there. Most forms of magnetic 

storage, such as tape and disk, are erasable. 

erase vb. To remove data permanently from a storage 

medium. This is usually done by replacing existing data 

with zeros or meaningless text or, in magnetic media, by 

disturbing the magnetic particles’ physical arrangement, 

either with the erase head or with a large magnet. Erase 

differs from delete in that delete merely tells the computer 

that data or a file is no longer needed; the data remains 

stored and is recoverable until the operating system reuses 

the space containing the deleted file. Erase, on the other 

hand, removes data permanently. See also erase head. 

Compare delete. 

erase head n. The device in a magnetic tape machine 

that erases previously recorded information. 

Eratosthenes’ sieve n. See sieve of Eratosthenes. 

ergonomic keyboard n. A keyboard designed to reduce 

the risk of wrist and hand injuries that result from prolonged 

use or repetitive movement. An ergonomic keyboard 

can include such features as alternative key layouts, 

palm rests, and shaping designed to minimize strain. See 

196 

also Dvorak keyboard, keyboard, Kinesis ergonomic 

keyboard. 

ergonomics n. The study of people (their physical characteristics 

and the ways they function) in relation to their 

working environment (the furnishings and machines they 

use). The goal of ergonomics is to incorporate comfort, 

efficiency, and safety into the design of keyboards, computer 

desks, chairs, and other items in the workplace. 

Erlang n. A concurrent functional programming language. 

Originally developed for controlling telephone 

exchanges, Erlang is a general-purpose language best 

suited for applications where rapid development of complex 

systems and robustness are essential. Erlang has 

built-in support for concurrency, distribution, and fault tolerance. 

The most widely implemented version of Erlang is 

the open source version. 

ERP n. See Enterprise Resource Planning. 

error n. A value or condition that is not consistent with 

the true, specified, or expected value or condition. In computers, 

an error results when an event does not occur as 

expected or when impossible or illegal maneuvers are 

attempted. In data communications, an error occurs when 

there is a discrepancy between the transmitted and 

received data. See also critical error, error message, error 

rate, error ratio, fatal error, hard error, inherent error, 

intermittent error, logic error, machine error, overflow 

error, parity error. Compare fault. 

error analysis n. The art and science of detecting errors 

in numeric calculations, especially in long and involved 

computations, where the possibility of errors increases. 

error checking n. A method for detecting discrepancies 

between transmitted and received data during file transfer. 

error control n. 1. The section of a program, procedure, 

or function that checks for errors such as type mismatches, 

overflows and underflows, dangling or illegal pointer references, 

and memory-use inconsistencies. 2. The process 

of anticipating program errors during software development. 

error-correcting code n. See error-correction coding. 

error-correction coding n. A method for encoding that 

allows for detection and correction of errors that occur during 

transmission. Data is encoded in such a way that transmission 

errors may be detected and corrected by 

examination of the encoded data on the receiving end. Most 

error-correction codes are characterized by the maximum 

number of errors they can detect and by the maximum number 

of errors they can correct. Error-correction coding is

error detection and correction ESRB 

used by most modems. Also called: error-correcting code. 

See also error detection and correction. Compare 

error-detection coding. 

error detection and correction n. A method for discovering 

and resolving errors during file transfer. Some 

programs only detect errors; others detect and attempt 

to fix them. 

error-detection coding n. A method of encoding data so 

that errors that occur during storage or transmission can be 

detected. Most error-detection codes are characterized by 

the maximum number of errors they can detect. See also 

checksum. Compare error-correction coding. 

error file n. A file that records the time and type of data 

processing and transmission errors. 

error handling n. The process of dealing with errors (or 

exceptions) as they arise during the running of a program. 

Some programming languages, such as C++, Ada, and 

Eiffel, have features that aid in error handling. See also 

bug (definition 1). 

error message n. A message from the system or program 

indicating that an error requiring resolution has occurred. 

error rate n. In communications, the ratio of the number 

of bits or other elements that arrive incorrectly during 

transmission. For a 1200-bps modem, a typical error rate 

would be 1 in every 200,000 bits. See also parity, parity 

bit, Xmodem, Ymodem. 

error ratio n. The ratio of errors to the number of units of 

data processed. See also error rate. 

error trapping n. 1. The process by which a program 

checks for errors during execution. 2. The process of writing 

a function, program, or procedure such that it is capable 

of continuing execution despite an error condition. 

escape character n. See ESC character. 

escape code n. A character or sequence of characters 

that indicates that a following character in a data stream is 

not to be processed in the ordinary way. In the C programming 

language, the escape code is the backslash \. 

Escape key n. A key on a computer keyboard that sends 

the escape (ESC) character to the computer. In many 

applications, the Escape key moves the user back one level 

in the menu structure or exits the program. See the illustration. 

See also Clear key. 

197 

~ 

` 

Esc 

F0Exx05.eps 

Escape key. 

! 

1 

F1 F2 

@ 

2 

# 

3 

Escape key 

escape sequence n. A sequence of characters that usually 

begins with the ESC character (ASCII 27, hexadecimal 

1B), which is followed by one or more additional 

characters. An escape sequence escapes from the normal 

sequence of characters (such as text) and issues an instruction 

or command to a device or program. 

ESC character n. One of the 32 control codes defined in 

the ASCII character set. It usually indicates the beginning 

of an escape sequence (a string of characters that give 

instructions to a device such as a printer). It is represented 

internally as character code 27 (hexadecimal 1B). Also 

called: escape character. 

Esc key n. See Escape key. 

ESD n. See electronic software distribution, electrostatic 

discharge. 

ESDI n. Acronym for Enhanced Small Device Interface. 

A device that allows disks to communicate with computers 

at high speeds. ESDI drives typically transfer data at 

about 10 megabits per second, but they are capable of doubling 

that speed. Although fast, ESDI has been superseded 

by interfaces such as SCSI and EIDE. See also EIDE, 

SCSI. 

ESP n. See enhanced serial port. 

ESP IEEE standard n. Short for Encapsulating Security 

Payload IEEE standard. A standard for providing integrity 

and confidentiality to IP (Internet Protocol) datagrams. 

In some circumstances, it can also provide 

authentication to IP datagrams. See also authentication, 

datagram, IEEE, IP. 

ESRB n. Acronym for Entertainment Software Rating 

Board. An independent, self-regulatory body providing ratings 

to the public and support to companies in the interactive 

software entertainment industry. The ESRB provides 

E

E 

e-tail event-driven processing 

ratings for computer games and other interactive products 

such as Web sites, online games, and interactive chat. 

e-tail n. See e-commerce. 

e-text n. Short for electronic text. A book or other 

text-based work that is available on line in an electronic 

media format. An e-text can be read online or downloaded 

to a user’s computer for offline reading. See also e-zine. 

Ethernet n. 1. The IEEE 802.3 standard for contention 

networks. Ethernet uses a bus or star topology and relies 

on the form of access known as Carrier Sense Multiple 

Access with Collision Detection (CSMA/CD) to regulate 

communication line traffic. Network nodes are linked by 

coaxial cable, by fiberoptic cable, or by twisted-pair wiring. 

Data is transmitted in variable-length frames containing 

delivery and control information and up to 1500 bytes 

of data. The Ethernet standard provides for baseband 

transmission at 10 megabits (10 million bits) per second 

and is available in various forms, including those known 

as Thin Ethernet, Thick Ethernet, 10Base2, 10Base5, 

10Base-F, and 10Base-T. The IEEE standard dubbed 

802.3z, or Gigabit Ethernet, operates at 10 times 100 

Mbps speed. See also ALOHAnet, baseband, bus network, 

coaxial cable, contention, CSMA/CD, Gigabit Ethernet, 

IEEE 802 standards, twisted-pair cable. 2. A widely used 

local area network system developed by Xerox in 1976, 

from which the IEEE 802.3 standard was developed. 

Ethernet/802.3 n. The IEEE standard for 10- or 

100-Mbps transmissions over an Ethernet network. Ethernet/802.3 

defines both hardware and data packet construction 

specifications. See also Ethernet. 

E-time n. See execution time. 

etiquette n. See netiquette. 

ETX n. See end-of-text. 

Eudora n. An e-mail client program originally developed 

as freeware for Macintosh computers by Steve Dorner at 

the University of Illinois, now maintained in both freeware 

and commercial versions for both Macintosh and Windows 

by Qualcomm, Inc. 

EULA n. See End-User License Agreement. 

Euphoria n. Acronym for End User Programming with 

Hierarchical Objects for Robust Interpreted Applications. 

An interpreted programming language intended for general 

application development and game programming on 

MS-DOS, Windows, and Linux platforms. 

198 

European Computer Manufacturers Association 

n. See ECMA. 

European Laboratory for Particle Physics n. See CERN. 

EUV lithography n. Acronym for Extreme UltraViolet 

lithography. Manufacturing process allowing smaller circuits 

to be etched onto chips than is possible with traditional 

lithographic techniques. With this process, it is 

possible to economically produce chips that are much 

faster than those that are created using traditional processes. 

In EUV lithography, the image of a map of circuits 

to appear on a chip is bounced off a series of mirrors that 

condense the image. The condensed image is projected 

onto wafers containing layers of metal, silicon, and photosensitive 

material. Because EUV light has a short wavelength, 

extremely intricate circuit patterns can be created 

on the wafers. 

evaluation n. The determination, by a program, of the 

value of an expression or the action that a program statement 

specifies. Evaluation can take place at compile time 

or at run time. 

even parity n. See parity. 

event n. An action or occurrence, often generated by the 

user, to which a program might respond—for example, 

key presses, button clicks, or mouse movements. See also 

event-driven programming. 

event-driven adj. Of, pertaining to, or being software that 

accomplishes its purpose by responding to externally 

caused events, such as the user pressing a key or clicking a 

button on a mouse. For example, an event-driven data 

entry form will allow the user to click on and edit any field 

at any time rather than forcing the user to step through a 

fixed sequence of prompts. 

event-driven processing n. A program feature belonging 

to more advanced operating-system architectures such 

as the Apple Macintosh operating system, Windows, and 

UNIX. In times past, programs were required to interrogate, 

and effectively anticipate, every device that was 

expected to interact with the program, such as the keyboard, 

mouse, printer, disk drive, and serial port. Often, 

unless sophisticated programming techniques were used, 

one of two events happening at the same instant would be 

lost. Event processing solves this problem through the creation 

and maintenance of an event queue. Most common 

events that occur are appended to the event queue for the 

program to process in turn; however, certain types of 

events can preempt others if they have a higher priority.

event-driven programming exclusive OR 

An event can be of several types, depending on the specific 

operating system considered: pressing a mouse button 

or keyboard key, inserting a disk, clicking on a 

window, or receiving information from a device driver (as 

for managing the transfer of data from the serial port or 

from a network connection). See also autopolling, event, 

interrupt. 

event-driven programming n. A type of programming in 

which the program constantly evaluates and responds to 

sets of events, such as key presses or mouse movements. 

Event-driven programs are typical of Apple Macintosh 

computers, although most graphical interfaces, such as 

Windows or the X Window System, also use such an 

approach. See also event. 

event handler n. 1. A method within a program that is 

called automatically whenever a particular event occurs. 

2. A core function in JavaScript that handles client-side 

events. It is the mechanism that causes a script to react to 

an event. For example, common JavaScript event handlers 

coded in Web pages include onClick, onMouseOver, and 

onLoad. When the user initiates the action, such as a 

mouse over, the event handler executes, or carries out, the 

desired outcome. 3. In Java applets, rather than having a 

specific starting point, the applet has a main loop where it 

waits for an event or series of events (keystroke, mouse 

click, and so on). Upon occurrence of the event, the event 

handler carries out the instructions specified. See also 

applet, client, JavaScript. 

event horizon n. The time at which hardware or software 

began to have the potential to encounter a Year 2000 problem. 

For instance, the event horizon in an accounting system 

in a company whose fiscal year ended on June 30, 

1999, would be six months dating from January 1, 1999. 

Also called: time horizon to failure. 

event log n. A file that contains information and error 

messages for all activities on the computer. 

event logging n. The process of recording an audit entry 

in the audit trail whenever certain events occur, such as 

starting and stopping, or users logging on and off and 

accessing resources. See also event, service. 

event procedure n. A procedure automatically executed 

in response to an event initiated by the user or program 

code, or triggered by the system. 

event property n. A characteristic or parameter of an 

object that you can use to respond to an associated event. 

199 

You can run a procedure or macro when an event occurs 

by setting the related event property. 

e-wallet n. A program used in e-commerce that stores a 

customer’s shipping and billing information to facilitate 

Web-based financial transactions. An e-wallet allows customers 

to instantly enter encrypted shipping and billing 

information when placing an order, rather than manually 

typing the information into a form on a Web page. 

exa- prefix A prefix meaning 1 quintillion (1018 ). In 

computing, which is based on the binary (base-2) numbering 

system, exa- has a literal value of 

1,152,921,504,606,846,976, which is the power of 2 (260 ) 

closest to one quintillion. Abbreviation: E. 

exabyte n. Roughly one quintillion bytes, or a billion billion 

bytes, or 1,152,921,504,606,846,976 bytes. 

Abbreviation: EB. 

Excel n. Microsoft’s spreadsheet software for Windows 

PCs and Macintosh computers. Excel is part of the family 

of Office products. The most recent version, part of 

Office XP, includes the ability to access and analyze 

live data from the Web by simply copying and pasting 

Web pages into Excel. The first version of Excel was 

introduced for the Macintosh in 1985. Excel for Windows 

was released in 1987. 

exception n. In programming, a problem or change in 

conditions that causes the microprocessor to stop what it 

is doing and handle the situation in a separate routine. 

An exception is similar to an interrupt; both refer the 

microprocessor to a separate set of instructions. See also 

interrupt. 

exception handling n. See error handling. 

exchangeable disk n. See removable disk. 

exchange sort n. See bubble sort. 

Excite n. A World Wide Web search engine developed by 

Excite, Inc. After conducting a search, Excite provides 

both a summary of each matching Web site it has located 

and a link to more information of the same type. 

exclusive NOR n. A two-state digital electronic circuit in 

which the output is driven high only if the inputs are all 

high or all low. 

exclusive OR n. A Boolean operation that yields “true” if 

and only if one of its operands is true and the other is false. 

See the table. Acronym: EOR. Also called: XOR. See also 

Boolean operator, truth table. Compare AND, OR. 

E

.exe expansion bus 

E 

.exe n. In MS-DOS, a filename extension that indicates 

that a file is an executable program. To run an executable 

program, the user types the filename without the .exe 

extension at the prompt and presses Enter. See also executable 

program. 

executable1 adj. Of, pertaining to, or being a program 

file that can be run. Executable files have extensions such 

as .bat, .com, and .exe. 

executable2 Table E.1 Exclusive OR. 

a b a XOR b 

0 0 0 

0 1 1 

1 0 1 

1 1 0 

n. A program file that can be run, such as 

file0.bat, file1.exe, or file2.com. 

executable program n. A program that can be run. The 

term usually applies to a compiled program translated into 

machine code in a format that can be loaded into memory 

and run by a computer’s processor. In interpreter languages, 

an executable program can be source code in the 

proper format. See also code (definition 1), compiler (definition 

2), computer program, interpreter, source code. 

execute vb. To perform an instruction. In programming, 

execution implies loading the machine code of the program 

into memory and then performing the instructions. 

execute in place n. The process of executing code 

directly from ROM, rather than loading it from RAM first. 

Executing the code in place, instead of copying the code 

into RAM for execution, saves system resources. Applications 

in other file systems, such as on a PC Card storage 

device, cannot be executed in this way. Acronym: XIP. 

execution time n. The time, measured in clock ticks 

(pulses of a computer’s internal timer), required by a 

microprocessor to decode and carry out an instruction 

after it is fetched from memory. Also called: E-time. See 

also instruction time. 

executive n. The set of kernel-mode components that 

form the base operating system for Microsoft Windows 

NT or later. See also operating system. 

executive information system n. A set of tools 

designed to organize information into categories and 

reports. Because it emphasizes information, an executive 

information system differs from a decision support system 

200 

(DSS), which is designed for analysis and decision making. 

Acronym: EIS. Compare decision support system. 

exerciser n. A program that exercises a piece of hardware 

or software by running it through a large set of operations. 

exit vb. In a program, to move from the called routine 

back to the calling routine. A routine can have more than 

one exit point, thus allowing termination based on various 

conditions. 

expanded adj. A font style that sets characters farther 

apart than the normal spacing. Compare condensed. 

expanded memory n. A type of memory, up to 8 MB, 

that can be added to IBM PCs. Its use is defined by the 

Expanded Memory Specification (EMS). Expanded memory 

is not accessible to programs in MS-DOS, so the 

Expanded Memory Manager (EMM) maps pages (blocks) 

of bytes from expanded memory into page frames in 

accessible memory areas. Expanded memory is not 

needed in Windows 9x, all versions of Windows NT, and 

Windows 2000. See also EEMS, EMS, Expanded Memory 

Manager, page frame. 

Expanded Memory Manager n. A driver that implements 

the software portion of the Expanded Memory 

Specification (EMS) to make expanded memory in IBM 

and compatible PCs accessible. Acronym: EMM. See also 

EMS, expanded memory, extended memory. 

Expanded Memory Specification n. See EMS. 

expansion n. A way of increasing a computer’s capabilities 

by adding hardware that performs tasks that are not 

part of the basic system. Expansion is usually achieved by 

plugging printed circuit boards (expansion boards) into 

openings (expansion slots) inside the computer. See also 

expansion board, expansion slot, open architecture (definition 

2), PC Card, PCMCIA slot. 

expansion board n. A circuit board that is plugged into a 

computer’s bus (main data transfer path) to add extra functions 

or resources to the computer. Typical expansion boards 

add memory, disk drive controllers, video support, parallel 

and serial ports, and internal modems. For laptops and other 

portable computers, expansion boards come in credit 

card-sized devices called PC Cards that plug into a slot in 

the side or back of the computer. Also called: expansion 

board, extender board. See also expansion slot, PC Card, 

PCMCIA slot. 

expansion bus n. A group of control lines that provide a 

buffered interface to devices. These devices can be located

expansion card exponent 

either on the system board or on cards that are plugged 

into expansion connectors. Common expansion buses 

included on the system board are USB, PC Card, and PCI. 

See also AT bus. 

expansion card n. See card (definition 1), expansion 

board. 

expansion slot n. A socket in a computer, designed to 

hold expansion boards and connect them to the system bus 

(data pathway). Expansion slots are a means of adding or 

enhancing the computer’s features and capabilities. In laptop 

and other portable computers, expansion slots come in 

the form of PCMCIA slots designed to accept PC Cards. 

See also expansion board, PC Card, PCMCIA slot. 

experience points n. Often used in role-playing games 

(RPGs), experience points are a way of measuring how 

much a player has experienced or learned. As a player 

moves through a game, additional benefits, often in the 

form of increased statistics or skills, are earned. These 

points are frequently spent or used by the player to 

increase his or her score. See also computer game, 

role-playing game. 

expert system n. An application program that makes 

decisions or solves problems in a particular field, such as 

finance or medicine, by using knowledge and analytical 

rules defined by experts in the field. It uses two components, 

a knowledge base and an inference engine, to form 

conclusions. Additional tools include user interfaces and 

explanation facilities, which enable the system to justify 

or explain its conclusions as well as allowing developers 

to run checks on the operating system. See also artificial 

intelligence, inference engine, intelligent database, knowledge 

base. 

expiration date n. The date on which a shareware, beta, 

or trial version of a program stops functioning, pending 

purchase of the full version or the entry of an access code. 

expire vb. To stop functioning in whole or in part. Beta 

versions of software are often programmed to expire when 

a new version is released. See also beta2 . 

Explicitly Parallel Instruction Computing n. See EPIC. 

exploded view n. A form of display that shows a structure 

with its parts separated but depicted in relation to 

each other. See the illustration. 

201 

F0Exx06.eps 

Exploded view. 

Shutter 

Top shell 

Woven liner 

Hub 

Magnetic disk 

Woven liner 

Write-protect tab 

Bottom shell 

Lifter presses 

liners against 

disk to trap dust 

Shutter spring 

Explorer n. See Internet Explorer, Windows Explorer. 

ExploreZip n. A destructive virus that attacks computers 

running Windows, where it first appears as an e-mail attachment 

named zipped_files.exe. ExploreZip affects local 

drives, mapped drives, and accessible network machines 

and destroys both document and source-code files by opening 

and immediately closing them, leaving a zero-byte file. 

Described as both a Trojan horse (because it requires the 

victim to open the attachment) and a worm (because it can 

propagate itself in certain instances), ExploreZip spreads by 

mailing itself to the return address of every unread e-mail in 

the inbox of the computer’s e-mail program, as well as by 

searching for—and copying itself to—the Windows directory 

on mapped drives and networked machines. See also 

Trojan horse, virus, worm. 

exponent n. In mathematics, a number that shows how 

many times a number is used as a factor in a calculation; 

in other words, an exponent shows that number’s power. 

Positive exponents, as in 23 , indicate multiplication (2 

times 2 times 2). Negative exponents, as in 2-3 , indicate 

division (1 divided by 23 ). Fractional exponents, as in 81/3 , 

indicate the root of a number (the cube root of 8). 

E

E 

exponential notation Extensible Hypertext Markup Language 

exponential notation n. See floating-point notation. 

exponentiation n. The operation in which a number is 

raised to a given power, as in 23 . In computer programs 

and programming languages, exponentiation is often 

shown by a caret (^), as in 2^3. 

export vb. To move information from one system or program 

to another. Files that consist only of text can be 

exported in ASCII (plain text format). For files with 

graphics, however, the receiving system or program must 

offer some support for the exported file’s format. See also 

EPS, PICT, TIFF. Compare import. 

export n. In NFS, a file or folder made available to 

other network computers using the NFS mount protocol. 

See also NFS. 

expression n. A combination of symbols—identifiers, 

values, and operators—that yields a result upon evaluation. 

The resulting value can then be assigned to a variable, 

passed as an argument, tested in a control statement, 

or used in another expression. 

extended ASCII n. Any set of characters assigned to 

ASCII values between decimal 128 and 255 (hexadecimal 

80 through FF). The specific characters assigned to the 

extended ASCII codes vary between computers and 

between programs, fonts, or graphics characters. Extended 

ASCII adds capability by allowing for 128 additional 

characters, such as accented letters, graphics characters, 

and special symbols. See also ASCII. 

Extended Binary Coded Decimal Interchange 

Code n. See EBCDIC. 

extended characters n. Any of the 128 additional characters 

in the extended ASCII (8-bit) character set. These 

characters include those used in several foreign languages, 

such as accent marks, and special symbols used for creating 

pictures. See also extended ASCII. 

extended data out random access memory n. See 

EDO RAM. 

Extended Edition n. A version of OS/2 with built-in 

database and communications facilities, developed by 

IBM. See also OS/2. 

eXtended Graphics Array n. An advanced standard for 

graphics controller and display mode design, introduced 

by IBM in 1990. This standard supports 640 x 480 resolution 

with 65,536 colors, or 1024 x 768 resolution with 256 

colors, and is used mainly on workstation-level systems. 

Acronym: XGA. 

202 

Extended Industry Standard Architecture n. See EISA. 

extended memory n. System memory beyond 1 megabyte 

in computers based on the Intel 80x86 processors. This 

memory is accessible only when an 80386 or higher-level 

processor is operating in protected mode or in emulation on 

the 80286. To use extended memory, MS-DOS programs 

need the aid of software that temporarily places the processor 

into protected mode or by the use of features in the 

80386 or higher-level processors to remap portions of 

extended memory into conventional memory. Extended 

memory is not an issue in Windows 9x, all versions of Windows 

NT, Windows 2000, and Windows XP. See also EMS, 

extended memory specification, protected mode. 

extended memory specification n. A specification 

developed by Lotus, Intel, Microsoft, and AST Research 

that defines a software interface allowing real-mode applications 

to use extended memory and areas of memory not 

managed by MS-DOS. Memory is managed by an installable 

device driver, the Expanded Memory Manager 

(EMM). The application must use the driver to access the 

additional memory. Acronym: XMS. See also Expanded 

Memory Manager, extended memory. 

extended VGA n. An enhanced set of Video Graphics 

Array (VGA) standards that is capable of displaying an 

image of from 800 x 600 pixels to 1600 x 1200 pixels and 

that can support a palette of up to 16.7 million (224 ) colors. 

This palette approaches the 19 million colors that a 

normal person can distinguish, so it is considered a digital 

standard for color realism that parallels analog television. 

Also called: Super VGA, SVGA. See also analog-to-digital 

converter, CRT, VGA. 

extender board n. See expansion board. 

eXtensible Firmware Interface n. In computers with 

the Intel Itanium processor, the interface between the 

operating system and the computer’s low-level booting 

and initialization firmware. The interface is made up of 

data tables that contain platform-related information, plus 

boot and run-time service calls that are available to the 

operating system and its loader to provide a standard environment 

for booting an operating system and running preboot 

applications. Acronym: EFI. 

Extensible Forms Description Language or eXtensible 

Forms Description Language n. See XFDL. 

Extensible Hypertext Markup Language n. See 

XHTML.

extensible language extranet 

extensible language n. A computer language that allows 

the user to extend or modify the syntax and semantics of the 

language. In the strict sense, the term relates to only a few 

of the languages actually used that allow the programmer to 

change the language itself, such as Forth. See also computer 

language, semantics (definition 1), syntax. 

Extensible Markup Language or eXtensible Markup 

Language n. See XML. 

extensible style language n. See XSL. 

eXtensible Stylesheet Language n. See XSL. 

eXtensible Stylesheet Language Formatting 

Objects n. See XSL-FO. 

Extensible Stylesheets Language-Transformations n. 

See XSLT. 

extension n. 1. A set of characters added to a filename 

that serves to extend or clarify its meaning or to identify a 

file as a member of a category. An extension may be 

assigned by the user or by a program, as, for example, 

.com or .exe for executable programs that MS-DOS can 

load and run. 2. A supplemental set of codes used to 

include additional characters in a particular character set. 

3. A program or program module that adds functionality 

to or extends the effectiveness of a program. 4. On the 

Macintosh, a program that alters or augments the functionality 

of the operating system. There are two types: system 

extensions, such as QuickTime, and Chooser extensions, 

such as printer drivers. When a Macintosh is turned on, the 

extensions in the Extensions folder within the System 

folder are loaded into memory. See also Chooser extension, 

QuickTime, System folder. 

Extension Manager n. A Macintosh utility developed by 

Apple that allows the user to determine which extensions 

are loaded when the computer is turned on. See also extension 


extent n. On a disk or other direct-access storage device, 

a continuous block of storage space reserved by the operating 

system for a particular file or program. 

exterior gateway protocol n. A protocol used by routers 

(gateways) on separate, independent networks for distributing 

routing information between and among themselves—for 

example, between hosts on the Internet. 

Acronym: EGP. Also called: external gateway protocol. 

Compare interior gateway protocol. 

external command n. A program included in an operating 

system such as MS-DOS that is loaded into memory 

203 

and executed only when its name is entered at the system 

prompt. Although an external command is a program in its 

own right, it is called a command because it is included 

with the operating system. See also XCMD. Compare 

internal command. 

external function n. See XFCN. 

External Gateway Protocol n. A protocol for distributing 

information regarding availability to the routers and 

gateways that interconnect networks. Acronym: EGP. See 

also gateway, router. 

external gateway protocol n. See exterior gateway 

protocol. 

external hard disk n. A free-standing hard disk with its 

own case and power supply, connected to the computer 

with a data cable and used mainly as a portable unit. See 

also hard disk. 

external interrupt n. A hardware interrupt generated by 

hardware elements external to the microprocessor. See 

also hardware interrupt, internal interrupt, interrupt. 

external modem n. A stand-alone modem that is connected 

via cable to a computer’s serial port. See also 

internal modem. 

external reference n. A reference in a program or routine 

to some identifier, such as code or data, that is not 

declared within that program or routine. The term usually 

refers to an identifier declared in code that is separately 

compiled. See also compile. 

external storage n. A storage medium for data, such as a 

disk or tape unit, that is external to a computer’s memory. 

external viewer n. A separate application used to view 

documents that are of a type that cannot be handled by the 

current application. See also helper program. 

extract vb. 1. To remove or duplicate items from a larger 

group in a systematic manner. 2. In programming, to 

derive one set of characters from another by using a mask 

(pattern) that determines which characters to remove. 

extra-high-density floppy disk n. A 3.5-inch floppy disk 

capable of holding 4 MB of data and requiring a special 

disk drive that has two heads rather than one. See also 

floppy disk. 

extranet n. An extension of a corporate intranet using 

World Wide Web technology to facilitate communication 

with the corporation’s suppliers and customers. An extranet 

allows customers and suppliers to gain limited access 

E

E 

extrinsic semiconductor e-zine 

to a company’s intranet in order to enhance the speed and 

efficiency of their business relationship. See also intranet. 

extrinsic semiconductor n. A semiconductor that conducts 

electricity due to a P-type or N-type impurity that 

allows electrons to flow under certain conditions, such as 

heat application, by forcing them to move out of their 

standard state to create a new band of electrons or electron 

gaps. See also N-type semiconductor, P-type semiconductor, 

semiconductor. 

204 

eyeballs n. The individuals or the number of individuals 

who view a Web site or its advertising. 

e-zine or ezine n. Short for electronic magazine. A digital 

publication available on the Internet, a bulletin board system 

(BBS), or other online service, often free of charge.

F n. See farad. 

F2F adv. Short for face-to-face. In person, rather than 

over the Internet. The term is used in e-mail. 

face n. 1. In geometry and computer graphics, one side of 

a solid object, such as a cube. 2. In printing and typography, 

short for typeface. 

face time n. Time spent dealing face-to-face with another 

person, rather than communicating electronically. 

facsimile n. See fax. 

factor n. In mathematics, an item that is multiplied in a 

multiplication problem; for example, 2 and 3 are factors in 

the problem 2 x 3. The prime factors of a number are a set 

of prime numbers that, when multiplied together, produce 

the number. 

factorial n. Expressed as n! (n factorial), the result of 

multiplying the successive integers from 1 through n; n! 

equals n x (n – 1) x (n – 2) x ... x 1. 

failback n. In a cluster network system (one with two or 

more interconnected servers), the process of restoring 

resources and services to their primary server after they 

have been temporarily relocated to a backup system while 

repairs were implemented on the original host. See also 

cluster, failover. 

failover vb. In a cluster network system (one with two or 

more interconnected servers), to relocate an overloaded or 

failed resource, such as a server, a disk drive, or a network, 

to its redundant, or backup, component. For example, 

when one server in a two-server system stops processing 

because of a power outage or other malfunction, the system 

automatically fails over to the second server, with little 

or no disruption to the users. See also cluster, failback. 

fail-safe system n. A computer system designed to continue 

operating without loss of or damage to programs and 

data when part of the system breaks down or seriously 

malfunctions. Compare fail-soft system. 

fail-soft system n. A computer system designed to fail 

gracefully over a period of time when an element of hard- 

F 

205 

ware or software malfunctions. A fail-soft system terminates 

nonessential functions and remains operating at a 

diminished capacity until the problem has been corrected. 

Compare fail-safe system. 

failure n. The inability of a computer system or related 

device to operate reliably or to operate at all. A common 

cause of system failure is loss of power, which can be minimized 

with a battery-powered backup source until all 

devices can be shut down. Within a system, electronic failures 

generally occur early in the life of a system or component 

and can often be produced by burning in the 

equipment (leaving it turned on constantly) for a few 

hours or days. Mechanical failures are difficult to predict 

but are most likely to affect devices, such as disk drives, 

that have moving parts. 

failure rate n. The number of failures in a specified time 

period. Failure rate is a means of measuring the reliability 

of a device, such as a hard disk. See also MTBF. 

fair queuing n. A technique used to improve quality of 

service that gives each session flow passing through a network 

device a fair share of network resources. With fair 

queuing, no prioritization occurs. Acronym: FQ. See 

also quality of service, queuing. Compare weighted fair 

queuing. 

fair use n. A legal doctrine describing the boundaries of 

legitimate use of copyrighted software or other published 

material. 

fallout n. Any failure of components that occurs while 

equipment is being burned in, especially when the test is 

done at the factory. See also burn in (definition 1). 

family n. A series of hardware or software products that 

have some properties in common, such as a series of personal 

computers from the same company, a series of CPU 

chips from the same manufacturer that all use the same 

instruction set, a set of 32-bit operating systems based on 

the same API (for example, Windows 95 and Windows 

98), or a set of fonts that are intended to be used together, 

such as Times New Roman. See also central processing 

unit, font, instruction set, operating system. 

F

F 

fan1 fan 

fatbits 

fan1 n. The cooling mechanism built into computer cabinets, 

laser printers, and other such devices to prevent malfunction 

due to heat buildup. Fans are the main source of 

the continuous humming associated with computers and 

other hardware. 

fan2 vb. To flip through a stack of printer paper to ensure 

that the pages are loose and will not stick together or jam 

the printer. 

fanfold paper n. Paper with pin-feed holes on both margins 

designed to be fed into the tractor-feed mechanism of 

a printer, page by page, in a continuous, unbroken stream. 

Also called: z-fold paper. 

fan-in n. The maximum number of signals that can be fed 

to a given electronic device, such as a logic gate, at one 

time without risking signal corruption. The fan-in rating of 

a device depends on its type and method of construction. 

Compare fan-out. 

fan-out n. The maximum number of electronic devices 

that can be fed by a given electronic device, such as a logic 

gate, at one time without the signal becoming too weak. 

The fan-out rating of a device depends on its type and 

method of construction. Compare fan-in. 

fanzine n. A magazine, distributed on line or by mail, that 

is produced by and devoted to fans of a particular group, 

person, or activity. See also ezine. 

FAQ n. Acronym for frequently asked questions. A document 

listing common questions and answers on a particular 

subject. FAQs are often posted on Internet newsgroups 

where new participants tend to ask the same questions that 

regular readers have answered many times. 

farad n. The unit of capacitance (the ability to hold a 

charge). A 1-farad capacitor holds a charge of 1 coulomb 

with a potential difference of 1 volt between its plates. In 

practical use, a farad is an extremely large amount of capacitance; 

capacitance is usually expressed in terms of microfarads 

(10 –6 ) or picofarads (10 –12 ). Abbreviation: F. 

FARNET n. See Federation of American Research Networks. 

Fast Ethernet n. See 100BaseX. 

fast Fourier transform n. A set of algorithms used to 

compute the discrete Fourier transform of a function, which 

in turn is used for solving series of equations, performing 

spectral analysis, and carrying out other signal-processing 

and signal-generation tasks. Acronym: FFT. See also Fourier 

transform. 

206 

fast infrared port n. See FIR port. 

fast packet n. A standard for high-speed network technology 

that utilizes fast switching of fixed-length cells 

or packets for real-time transmission of data. Also 

called: Asynchronous Transfer Mode, ATM. See also 

packet (definition 2), packet switching. 

fast packet switching adj. Of, describing, or pertaining 

to high-speed packet-switching networks that perform little 

or no error checking. The term is often, however, 

restricted to high-speed networking technologies, such as 

ATM, that transmit fixed-length cells rather than including 

those, such as frame relay, that transmit variable-length 

packets. 

fast page-mode RAM n. See page mode RAM. 

Fast SCSI n. A form of the SCSI-2 interface that can 

transfer data 8 bits at a time at up to 10 megabytes per second. 

The Fast SCSI connector has 50 pins. Also 

called: Fast SCSI-2. See also SCSI, SCSI-2. Compare 

Fast/Wide SCSI, Wide SCSI. 

Fast/Wide SCSI n. A form of the SCSI-2 interface that 

can transfer data 16 bits at a time at up to 20 megabytes 

per second. The Fast/Wide SCSI connector has 68 pins. 

Also called: Fast/Wide SCSI-2. See also SCSI, SCSI-2. 

Compare Fast SCSI, Wide SCSI. 

FAT n. See file allocation table. 

fatal error n. An error that causes the system or application 

program to crash—that is, to fail abruptly with no 

hope of recovery. 

fatal exception error n. A Windows message signaling 

that an unrecoverable error, one that causes the system to 

halt, has occurred. Data being processed when the error 

occurs is usually lost, and the computer must be rebooted. 

See also error handling. 

fat application n. An application that can be used on 

both PowerPC processor–based Macintosh computers and 

68K-based Macintosh computers. 

fat binary n. An application format that supports both 

PowerPC processor–based Macintosh computers and 

68K-based Macintosh computers. 

fatbits n. 1. Originally (as FatBits), a feature of the Apple 

MacPaint program in which a small portion of a drawing 

can be enlarged and modified one pixel (FatBit) at a time. 

2. A similar feature in any program that allows pixel-bypixel 

modification through a zoom feature.

fat client fax on demand 

fat client n. In a client/server architecture, a client 

machine that performs most or all of the processing, with 

little or none performed by the server. The client handles 

presentation and functions, and the server manages data 

and access to it. See also client (definition 3), client/server 

architecture, server (definition 2), thin server. Compare fat 

server, thin client. 

FAT file system n. The system used by MS-DOS to organize 

and manage files. The FAT (file allocation table) is a 

data structure that MS-DOS creates on the disk when the 

disk is formatted. When MS-DOS stores a file on a formatted 

disk, the operating system places information 

about the stored file in the FAT so that MS-DOS can 

retrieve the file later when requested. The FAT is the only 

file system MS-DOS can use; OS/2, Windows NT, and 

Windows 9x operating systems can use the FAT file system 

in addition to their own file systems (HPFS, NTFS, 

and VFAT, respectively). See also file allocation table, 

HPFS, NTFS, OS/2, VFAT, Windows. 

father n. See generation (definition 1). 

father file n. A file that is the last previously valid set of a 

changing set of data. The father file is immediately preceded 

by a grandfather file and immediately succeeded by 

its son. The pairs father and son, parent and child (or 

descendant), and independent and dependent are synonymous. 

See also generation (definition 1). 

fat server n. In a client/server architecture, a server 

machine that performs most of the processing, with little 

or none performed by the client. Applications logic and 

data reside on the server, and presentation services are 

handled by the client. See also client (definition 3), client/ 

server architecture, server (definition 2), thin client. Compare 

fat client, thin server. 

fatware n. Software that monopolizes hard disk space and 

power due to an overabundance of features or inefficient 

design. Also called: bloatware. 

fault n. 1. A physical defect, such as a loose connection, 

that prevents a system or device from operating as it 

should. 2. A programming error that can cause the software 

to fail. 3. As page fault, an attempt to access a page 

of virtual memory that is not mapped to a physical 

address. See also page fault. 

fault resilience n. See high availability. 

fault tolerance n. The ability of a computer or an operating 

system to respond to a catastrophic event or fault, such 

as a power outage or a hardware failure, in a way that 

ensures that no data is lost and any work in progress is not 

207 

corrupted. This can be accomplished with a batterybacked 

power supply, backup hardware, provisions in the 

operating system, or any combination of these. In a faulttolerant 

network, the system has the ability either to continue 

the system’s operation without loss of data or to shut 

the system down and restart it, recovering all processing 

that was in progress when the fault occurred. 

favorite n. In Microsoft Internet Explorer, a user-defined 

shortcut to a page on the World Wide Web, analogous to a 

bookmark in Netscape Navigator. See also Favorites 

folder, hotlist. Compare bookmark (definition 2). 

Favorites folder n. In Microsoft Internet Explorer, a collection 

of shortcuts to Web sites that a user has selected 

for future reference. Other Web browsers refer to this collection 

by other names, such as bookmarks or hotlists. See 

also bookmark file (definition 1), Internet Explorer, URL. 

Compare bookmark (definition 2), hotlist. 

fax n. Short for facsimile. The transmission of text or 

graphics over telephone lines in digitized form. Conventional 

fax machines scan an original document, transmit 

an image of the document as a bit map, and reproduce the 

received image on a printer. Resolution and encoding are 

standardized in the CCITT Groups 1–4 recommendations. 

Fax images can also be sent and received by microcomputers 

equipped with fax hardware and software. See also 

CCITT Groups 1–4. 

fax machine n. Short for facsimile machine. A device 

that scans pages, converts the images of those pages to a 

digital format consistent with the international facsimile 

standard, and transmits the image through a telephone 

line. A fax machine also receives such images and prints 

them on paper. See also scan (definition 2). 

fax modem n. A modem that sends (and possibly 

receives) data encoded in a fax format (typically CCITT 

fax format), which a fax machine or another modem 

decodes and converts to an image. The image must already 

have been encoded on the host computer. Text and graphic 

documents can be converted into fax format by special 

software usually provided with the modem; paper documents 

must first be scanned in. Fax modems may be internal 

or external and may combine fax and conventional 

modem capabilities. See also fax, modem. 

fax on demand n. An automated system that makes 

information available for request by telephone. When a 

request is made, the system faxes the information to the 

telephone number given in the request. Acronym: FOD. 

F

F 

fax program Federal Internet Exchange 

fax program n. A computer application that allows the 

user to send, receive, and print fax transmissions. See 

also fax. 

fax server n. A computer on a network capable of sending 

and receiving fax transmissions to and from other computers 

on the network. See also fax, server (definition 1). 

FCB n. See file control block. 

FCC n. Acronym for Federal Communications Commission. 

The U.S. agency created by the Communications 

Act of 1934, which regulates interstate and international 

wire, radio, and other broadcast transmissions, including 

telephone, telegraph, and telecommunications. 

F connector n. A coaxial connector, used primarily in 

video applications, that requires a screw-on attachment. 


F0Fxx01.eps 

F connector. 

FDDI n. Acronym for Fiber Distributed Data Interface. 

A standard developed by the American National Standards 

Institute (ANSI) for high-speed fiber-optic LANs 

(local area networks). FDDI provides specifications for 

transmission rates of 100 megabits (100 million bits) per 

second on networks based on the token ring standard. 

See also token ring network. 

FDDI II n. Acronym for Fiber Distributed Data Interface. 

An extension of the FDDI standard, FDDI II contains 

additional specifications for the real-time transmission of 

analog data in digitized form for high-speed fiber-optic 

LANs (local area networks). See also FDDI. 

FDHP n. Acronym for Full Duplex Handshaking Protocol. 

A protocol used by duplex modems to determine the 

source type of the transmission and match it. See also 

duplex1 , handshake. 

FDM n. Acronym for Frequency Division Multiplexing. 

A means of loading multiple transmission signals onto 

separate bands of a single communications channel so that 

all signals can be carried simultaneously. FDM is used in 

analog transmissions, as on a baseband network or in communications 

over a telephone line. In FDM the frequency 

208 

range of the channel is divided into narrower bands, each 

of which can carry a different transmission signal. For 

example, FDM might divide a voice channel with a frequency 

range of 1400 hertz (Hz) into four subchannels— 

820–990 Hz, 1230–1400 Hz, 1640–1810 Hz, and 2050– 

2220 Hz—with adjacent subchannels separated by a 240- 

Hz guard band to minimize interference. 

FDMA n. Acronym for Frequency Division Multiple 

Access. A method of multiplexing in which the set of frequencies 

assigned to cellular phone service is divided into 

30 separate channels, each of which can be used by a different 

caller. FDMA is the technology used in the AMPS 

phone service, which is widespread in North America and 

in other countries around the world. See also AMPS. 

Compare TDMA. 

fear, uncertainty, and doubt n. See FUD. 

feasibility study n. An evaluation of a prospective 

project for the purpose of determining whether or not the 

project should be undertaken. Feasibility studies normally 

consider the time, budget, and technology required for 

completion and are generally used in computing departments 

in large organizations. 

feature n. A unique, attractive, or desirable property of a 

program or of a computer or other hardware. 

feature extraction n. The selection of significant aspects 

of a computer image for use as guidelines in computerized 

pattern matching and image recognition. See also image 

processing. 

featuritis n. Jargon for a tendency to add new features to 

a program at the expense of its original compact size or 

elegance. Creeping featuritis describes the accretion of 

feature upon feature over time, eventually resulting in a 

large, unwieldy, generally inelegant program that is, or 

appears to be, a collection of ad-hoc additions. The result 

of featuritis is a program condition known as software 

bloat. Also called: creeping featuritis, creeping featurism, 

feeping creaturism. See also bloatware. 

February 30 n. See double leap year. 

Federal Communications Commission n. See FCC. 

Federal Information Processing Standards n. A system 

of standards, guidelines, and technical methods for 

information processing within the U.S. federal government. 

Acronym: FIPS. 

Federal Internet Exchange n. See FIX.

federated database FET 

federated database n. A database to which scientists 

contribute their findings and knowledge regarding a particular 

field or problem. A federated database is designed 

for scientific collaboration on problems of such scope that 

they are difficult or impossible for an individual to solve. 

See also database. 

Federation of American Research Networks n. A 

nonprofit association of internetworking technology companies 

in the United States that serves as a national advocate 

for internetworking, with a primary focus on the 

education, research, and related communities. Acronym: 

FARNET. See also internetwork. 

Federation on Computing in the United States n. The 

U.S. representative of the International Federation of 

Information Processing (IFIP). Acronym: FOCUS. See 

also IFIP. 

feed1 n. See news feed. 

feed2 vb. 1. To advance paper through a printer. 2. To supply 

media to a recording device, as by inserting disks into 

a disk drive. 

feedback n. The return of a portion of system output as 

input to the same system. Often feedback is deliberately 

designed into a system, but sometimes it is unwanted. In 

electronics, feedback is used in monitoring, controlling, 

and amplifying circuitry. 

feedback circuit n. Any circuit or system that returns 

(feeds back) a portion of its output to its input. A common 

example of a feedback system, although it is not completely 

electronic, is a thermostatically controlled household 

heating system. This self-limiting or self-correcting 

process is an example of negative feedback, in which 

changes in output are fed back to the source so that the 

change in the output is reversed. In positive feedback, an 

increase in output is fed back to the source, increasing the 

output further, which creates a snowballing effect. An 

example of unwanted positive feedback is the “screech” 

that occurs when the microphone of a public address system 

is brought too close to its loudspeaker. 

feed scanner n. See sheet-fed scanner. 

feeping creaturism n. See featuritis. 

female connector n. A connector that has one or more 

receptacles for the insertion of pins. Female connector part 

209 

numbers often include an F (female), an S (socket), a J 

(jack), or an R (receptacle). For example, a female DB-25 

connector might be labeled DB-25S or DB-25F. (Note that 

although the letter F can denote a female connector, it 

does not have that meaning in F connector, which is a type 

of coaxial cable connector.) See the illustration. Compare 

male connector. 

F0Fxx02.eps 

Female connector. 

femto- prefix Metric prefix meaning 10 –15 (one 

quadrillionth). 

femtosecond n. One quadrillionth (10 –15 ) of a second. 

Abbreviation: fs. 

FEP n. See front-end processor. 

ferric oxide n. The chemical substance Fe2O3, an oxide 

of iron used with a binding agent in the magnetic coating 

applied to disks and tapes for data storage. 

ferric RAM n. See FRAM. 

ferromagnetic domain n. See magnetic domain. 

ferromagnetic material n. A substance that can become 

highly magnetized. Ferrite and powdered iron are ferromagnetic 

materials commonly used in electronics, for 

example, as cores for inductors to increase their inductance, 

and as part of the coating on floppy and hard disks 

and magnetic tape. 

FET n. Acronym for field-effect transistor. A type of transistor 

in which the flow of current between the source and 

the drain is modulated by the electric field around the gate 

electrode. FETs are used as amplifiers, oscillators, and 

switches and are characterized by an extremely high input 

impedance (resistance) that makes them particularly suitable 

for amplification of very small signals. Types of FETs 

include the junction FET and the metal-oxide semiconductor 

FET (MOSFET). See the illustration. See also 

MOSFET. 

F

F 

fetch field 

Gate (-) 

Depletion 

region 

Drain (+) 

Channel 

Source 

N-type 

material 

P-type 

material 

F0Fxx03.eps 

FET. An N-channel junction field-effect transistor. 

fetch vb. To retrieve an instruction or an item of data from 

memory and store it in a register. Fetching is part of the 

execution cycle of a microprocessor; first an instruction or 

item of data must be fetched from memory and loaded into 

a register, after which it can be executed (if it is an instruction) 

or acted upon (if it is data). 

fetch time n. See instruction time. 

FF n. See form feed. 

FFT n. See fast Fourier transform. 

FFTDCA n. See Final-Form-Text DCA. 

Fiber Distributed Data Interface n. See FDDI. 

fiberoptic cable or fiber-optic cable n. A form of cable 

used in networks that transmits signals optically, rather 

than electrically as do coaxial and twisted-pair cable. The 

light-conducting heart of a fiberoptic cable is a fine glass 

or plastic fiber called the core. This core is surrounded by 

a refractive layer called the cladding that effectively traps 

the light and keeps it bouncing along the central fiber. 

Outside both the core and the cladding is a final layer of 

plastic or plastic-like material called the coat, or jacket. 

Fiberoptic cable can transmit clean signals at speeds as 

high as 2 Gbps. Because it transmits light, not electricity, 

it is also immune to eavesdropping. 

fiber optics n. A technology for the transmission of light 

beams along optical fibers. A light beam, such as that produced 

in a laser, can be modulated to carry information. 

210 

Because light has a higher frequency on the electromagnetic 

spectrum than other types of radiation, such as radio 

waves, a single fiber-optic channel can carry significantly 

more information than most other means of information 

transmission. Optical fibers are thin strands of glass or 

other transparent material, with dozens or hundreds of 

strands housed in a single cable. Optical fibers are essentially 

immune to electromagnetic interference. See also 

optical fiber. 

fiber to the curb n. See FTTC. 

fiber to the home n. See FTTH. 

Fibonacci numbers n. In mathematics, an infinite series 

in which each successive integer is the sum of the two 

integers that precede it—for example, 1, 1, 2, 3, 5, 8, 13, 

21, 34, . . . . Fibonacci numbers are named for the thirteenth-century 

mathematician Leonardo Fibonacci of Pisa. 

In computing, Fibonacci numbers are used to speed binary 

searches by repeatedly dividing a set of data into groups in 

accordance with successively smaller pairs of numbers in 

the Fibonacci sequence. For example, a data set of 34 

items would be divided into one group of 21 and another 

of 13. If the item being sought is in the group of 13, the 

group of 21 is discarded, and the group of 13 is divided 

into groups of 5 and 8; the search would continue until the 

item was located. The ratio of two successive terms in the 

Fibonacci sequence converges on the Golden Ratio, a 

“magic number” that seems to represent the proportions of 

an ideal rectangle. The number describes many things, 

from the curve of a nautilus shell to the proportions of 

playing cards or, intentionally, the Parthenon, in Athens, 

Greece. See also binary search. 

fiche n. See microfiche. 

Fidonet n. 1. A protocol for sending e-mail, newsgroup 

postings, and files over telephone lines. The protocol originated 

on the Fido BBS, initiated in 1984 by Tom Jennings, 

and maintaining low costs has been a factor in its 

subsequent development. Fidonet can exchange e-mail 

with the Internet. 2. The network of BBSs, private companies, 

NGOs (nongovernment organizations), and individuals 

that use the Fidonet protocol. 

field n. 1. A location in a record in which a particular type 

of data is stored. For example, EMPLOYEE-RECORD 

might contain fields to store Last-Name, First-Name, 

Address, City, State, Zip-Code, Hire-Date, Current-Salary, 

Title, Department, and so on. Individual fields are characterized 

by their maximum length and the type of data (for

field-effect transistor file fragmentation 

example, alphabetic, numeric, or financial) that can be 

placed in them. The facility for creating these specifications 

usually is contained in the data definition language 

(DDL). In relational database management systems, fields 

are called columns. 2. A space in an on-screen form where 

the user can enter a specific item of information. 

field-effect transistor n. See FET. 

field expansion n. See date expansion. 

Field Programmable Gate Array n. See FPGA. 

field-programmable logic array n. An integrated circuit 

containing an array of logic circuits in which the connections 

between the individual circuits, and thus the 

logic functions of the array, can be programmed after 

manufacture, typically at the time of installation in the 

field. Programming can be performed only once, typically 

by passing high current through fusible links on 

the chip. Acronym: FPLA. Also called: PLA, programmable 

logic array. 

field separator n. Any character that separates one field of 

data from another. See also delimiter, field (definition 1). 

FIFO n. See first in, first out. 

fifth-generation computer n. See computer. 

fifth normal form n. See normal form (definition 1). 

file n. A complete, named collection of information, such 

as a program, a set of data used by a program, or a usercreated 

document. A file is the basic unit of storage that 

enables a computer to distinguish one set of information 

from another. A file is the “glue” that binds a conglomeration 

of instructions, numbers, words, or images into a 

coherent unit that a user can retrieve, change, delete, save, 

or send to an output device. 

file allocation table n. A table or list maintained by 

some operating systems to manage disk space used for file 

storage. Files on a disk are stored, as space allows, in 

fixed-size groups of bytes (characters) rather than from 

beginning to end as contiguous strings of text or numbers. 

A single file can thus be scattered in pieces over many 

separate storage areas. A file allocation table maps available 

disk storage space so that it can mark flawed segments 

that should not be used and can find and link the 

pieces of a file. In MS-DOS, the file allocation table is 

commonly known as the FAT. See also FAT file system. 

file attribute n. A restrictive label attached to a file that 

describes and regulates its use—for example, hidden, sys- 

211 

tem, read-only, archive, and so forth. In MS-DOS, this 

information is stored as part of the file’s directory entry. 

file backup n. See backup. 

file compression n. The process of reducing the size of a 

file for transmission or storage. See also data compression. 

file control block n. A small block of memory temporarily 

assigned by a computer’s operating system to hold 

information about an opened file. A file control block typically 

contains such information as the file’s identification, 

its location on a disk, and a pointer that marks the user’s 

current (or last) position in the file. Acronym: FCB. 

file conversion n. The process of transforming the data in 

a file from one format to another without altering the 

data—for example, converting a file from a word processor’s 

format to its ASCII equivalent. In some cases, information 

about the data, such as formatting, may be lost. 

Another, more detailed, type of file conversion involves 

changing character coding from one standard to another, 

as in converting EBCDIC characters (which are used primarily 

with mainframe computers) to ASCII characters. 

See also ASCII, EBCDIC. 

file extension n. See extension (definition 1). 

file extent n. See extent. 

file format n. The structure of a file that defines the way 

it is stored and laid out on the screen or in print. The format 

can be fairly simple and common, as are files stored 

as “plain” ASCII text, or it can be quite complex and 

include various types of control instructions and codes 

used by programs, printers, and other devices. Examples 

include RTF (Rich Text Format), DCA (Document Content 

Architecture), PICT, DIF (Data Interchange Format), 

DXF (Data Exchange File), TIFF (Tagged Image File Format), 

and EPSF (Encapsulated PostScript Format). 

file fragmentation n. 1. The breaking apart of files as 

they are stored by the operating system into small, separate 

segments on disk. The condition is a natural consequence 

of enlarging files and saving them on a crowded 

disk that no longer contains contiguous blocks of free 

space large enough to hold them. File fragmentation is not 

an integrity problem, although it can eventually slow read 

and write access times if the disk is very full and storage is 

badly fragmented. Software products are available for 

redistributing (optimizing) file storage to reduce fragmentation. 

2. In a database, a situation in which records are not 

stored in their optimal access sequence because of accumulated 

additions and deletions of records. Most database 

F

F 

file gap file server 

systems offer or contain utility programs that resequence 

records to improve efficiency of access and to aggregate 

free space occupied by deleted records. 

file gap n. See block gap. 

file handle n. In MS-DOS, OS/2, and Windows, a token 

(number) that the system uses to identify or refer to an 

open file or, sometimes, to a device. 

file-handling routine n. Any routine designed to assist in 

creating, opening, accessing, and closing files. Most highlevel 

languages have built-in file-handling routines, 

although more sophisticated or complex file-handling routines 

in an application are often created by the programmer. 

file header n. See header (definition 2). 

file layout n. In data storage, the organization of records 

within a file. Frequently, descriptions of the record structure 

are also included within the file layout. 

file librarian n. A person or process responsible for maintaining, 

archiving, copying, and providing access to a collection 

of data. 

file maintenance n. Broadly, the process of changing 

information in a file, altering a file’s control information 

or structure, or copying and archiving files. A person 

using a terminal to enter data, the program accepting the 

data from the terminal and writing it to a data file, and a 

database administrator using a utility to alter the format of 

a database file are all forms of file maintenance. 

file management system n. The organizational structure 

that an operating system or program uses to order and 

track files. For example, a hierarchical file system uses 

directories in a so-called tree structure. All operating systems 

have built-in file management systems. Commercially 

available products implement additional features 

that provide more sophisticated means of navigating, finding, 

and organizing files. See also file system, hierarchical 

file system. 

file manager n. A module of an operating system or environment 

that controls the physical placement of and 

access to a group of program files. 

file name n. The set of letters, numbers, and allowable 

symbols assigned to a file to distinguish it from all other 

files in a particular directory on a disk. A file name is the 

label under which a computer user saves and requests a 

block of information. Both programs and data have file 

names and often extensions that further identify the type 

or purpose of the file. Naming conventions, such as maxi- 

212 

mum length and allowable characters of a file name, vary 

from one operating system to another. See also directory, 

path (definition 5). 

file name extension n. See extension (definition 1). 

filename globbing n. A Linux command-line feature, 

available on most FTP servers, which allows a user to 

refer to sets of files without individually listing each file 

name. Filename globbing can be used to select or delete 

all files in a working directory with a single command. At 

the discretion of the user, globbing can match all files, or 

only those with filenames containing a specific character 

or range of characters. See also wildcard character. 

file property n. A detail about a file that helps identify it, 

such as a descriptive title, the author name, the subject, or 

a keyword that identifies topics or other important information 

in the file. 

file protection n. A process or device by which the 

existence and integrity of a file are maintained. Methods 

of file protection range from allowing read-only 

access and assigning passwords to covering the writeprotect 

notch on a disk and locking away floppy disks 

holding sensitive files. 

file recovery n. The process of reconstructing lost or 

unreadable files on disk. Files are lost when they are inadvertently 

deleted, when on-disk information about their 

storage is damaged, or when the disk is damaged. File 

recovery involves the use of utility programs that attempt 

to rebuild on-disk information about the storage locations 

of deleted files. Because deletion makes the file’s disk 

space available but does not remove the data, data that has 

not yet been overwritten can be recovered. In the case of 

damaged files or disks, recovery programs read whatever 

raw data they can find, and save the data to a new disk or 

file in ASCII or numeric (binary or hexadecimal) form. In 

some instances, however, such reconstructed files contain 

so much extraneous or mixed information that they are 

unreadable. The best way to recover a file is to restore it 

from a backup copy. 

file retrieval n. The act of accessing a data file and transferring 

it from a storage location to the machine where it is 

to be used. 

file server n. A file-storage device on a local area network 

that is accessible to all users on the network. Unlike 

a disk server, which appears to the user as a remote disk 

drive, a file server is a sophisticated device that not only 

stores files but manages them and maintains order as net-

File Server for Macintosh filter 

work users request files and make changes to them. To 

deal with the tasks of handling multiple—sometimes 

simultaneous—requests for files, a file server contains a 

processor and controlling software as well as a disk drive 

for storage. On local area networks, a file server is often a 

computer with a large hard disk that is dedicated only to 

the task of managing shared files. Compare disk server. 

File Server for Macintosh n. An AppleTalk network integration 

service that allows Macintosh clients and personal 

computers clients to share files. Also called: MacFile. See 

also Print Server for Macintosh, Services for Macintosh. 

file sharing n. The use of computer files on networks, 

wherein files are stored on a central computer or a server 

and are requested, reviewed, and modified by more than 

one individual. When a file is used with different programs 

or different computers, file sharing can require conversion 

to a mutually acceptable format. When a single 

file is shared by many people, access can be regulated 

through such means as password protection, security 

clearances, or file locking to prohibit changes to a file by 

more than one person at a time. 

file size n. The length of a file, typically given in bytes. A 

computer file stored on disk actually has two file sizes, 

logical size and physical size. The logical file size corresponds 

to the file’s actual size—the number of bytes it 

contains. The physical size refers to the amount of storage 

space allotted to the file on disk. Because space is set aside 

for a file in blocks of bytes, the last characters in the file 

might not completely fill the block (allocation unit) 

reserved for them. When this happens, the physical size is 

larger than the logical size of the file. 

filespec n. See file specification (definition 1). 

file specification n. 1. The path to a file, from a disk 

drive through a chain of directory files to the file name 

that serves to locate a particular file. Abbreviated filespec. 

2. A file name containing wildcard characters that indicate 

which files among a group of similarly named files are 

requested. 3. A document that describes the organization 

of data within a file. 

file structure n. A description of a file or group of files 

that are to be treated together for some purpose. Such a 

description includes file layout and location for each file 

under consideration. 

file system n. In an operating system, the overall structure 

in which files are named, stored, and organized. A file 

system consists of files, directories, or folders, and the 

information needed to locate and access these items. The 

term can also refer to the portion of an operating system 

213 

that translates requests for file operations from an application 

program into low-level, sector-oriented tasks that can 

be understood by the drivers controlling the disk drives. 

See also driver. 

file transfer n. The process of moving or transmitting a 

file from one location to another, as between two programs 

or over a network. 

File Transfer Protocol n. See FTP1 (definition 1). 

file type n. A designation of the operational or structural 

characteristics of a file. A file’s type is often identified in 

the file name, usually in the file name extension. See also 

file format. 

fill1 n. In computer graphics, the colored or patterned 

“paint” inside an enclosed figure, such as a circle. The 

portion of the shape that can be colored or patterned is the 

fill area. Drawing programs commonly offer tools for creating 

filled or nonfilled shapes; the user can specify color 

or pattern. 

fill2 vb. To add color or a pattern to the enclosed portion of 

a circle or other shape. 

fill handle n. The small black square in the lower-right 

corner of a cell selection. When you point to the fill handle, 

the pointer changes to a black cross. 

film at 11 n. A phrase sometimes seen in newsgroups. 

An allusion to a brief newsbreak on TV that refers to a top 

news story that will be covered in full on the 11 o’clock 

news, it is used sarcastically to ridicule a previous article’s 

lack of timeliness or newsworthiness. See also newsgroup. 

film recorder n. A device for capturing on 35-mm film 

the images displayed on a computer screen. 

film ribbon n. See carbon ribbon. 

filter n. 1. A program or set of features within a program 

that reads its standard or designated input, transforms the 

input in some desired way, and then writes the output to its 

standard or designated output destination. A database filter, 

for example, might flag information of a certain age. 

2. In communications and electronics, hardware or software 

that selectively passes certain elements of a signal 

and eliminates or minimizes others. A filter on a communications 

network, for example, must be designed to transmit 

a certain frequency but attenuate (dampen) frequencies 

above it (a lowpass filter), those below it (a highpass filter), 

or those above and below it (a bandpass filter). 3. A pattern 

or mask through which data is passed to weed out specified 

items. For instance, a filter used in e-mail or in 

retrieving newsgroup messages can allow users to filter 

F

F 

filtering program firewall 

out messages from other users. See also e-mail filter, 

mask. 4. In computer graphics, a special effect or production 

effect that is applied to bitmapped images; for example, 

shifting pixels within an image, making elements of 

the image transparent, or distorting the image. Some filters 

are built into a graphics program, such as a paint program 

or an image editor. Others are separate software 

packages that plug into the graphics program. See also bitmapped 

graphics, image editor, paint program. 

filtering program n. A program that filters information 

and presents only results that match the qualifications 

defined in the program. 

FilterKeys n. A Windows 9x accessibility control panel 

feature that enables users with physical disabilities to use 

the keyboard. With FilterKeys, the system ignores brief 

and repeated keystrokes that result from slow or inaccurate 

finger movements. See also accessibility. Compare 

MouseKeys, ShowSounds, SoundSentry, StickyKeys, 

ToggleKeys. 

Final-Form-Text DCA n. A standard in Document Content 

Architecture (DCA) for storing documents in readyto-print 

form for interchange between dissimilar programs. 

A related standard is Revisable-Form-Text DCA 

(RFTDCA). Acronym: FFTDCA. See also DCA (definition 

1). Compare Revisable-Form-Text DCA. 

finally n. A keyword used in the Java programming language 

that executes a block of statements regardless of 

whether a Java exception, or run-time error, occurred in a 

previous block defined by the “try” keyword. See also 

block, exception, keyword, try. 

find vb. See search2 . 

Finder n. The standard interface to the Macintosh operating 

system. The Finder allows the user to view the contents 

of directories (folders); to move, copy, and delete 

files; and to launch applications. Items in the system are 

often represented as icons, and a mouse or similar pointing 

device is used to manipulate these items. The Finder was 

the first commercially successful graphical user interface, 

and it helped launch a wave of interest in icon-based systems. 

See also MultiFinder. 

finger1 n. An Internet utility, originally limited to UNIX 

but now available on many other platforms, that enables a 

user to obtain information on other users who may be at 

other sites (if those sites permit access by finger). Given 

an e-mail address, finger returns the user’s full name, an 

indication of whether or not the user is currently logged 

214 

on, and any other information the user has chosen to supply 

as a profile. Given a first or last name, finger returns 

the logon names of users whose first or last names match. 

finger2 vb. To obtain information on a user by means of 

the finger program. 

fingerprint1 vb. To scan a computer system to discover 

what operating system (OS) the computer is running. By 

detecting a computer’s OS through fingerprinting, a 

hacker is better able to specify attacks on system vulnerabilities 

and therefore better able to plan an attack on that 

system. A hacker may use several different fingerprinting 

schemes separately and in tandem to pinpoint the OS of a 

target computer. 

fingerprint2 n. Information embedded or attached to a file 

or image to uniquely identify it. Compare digital watermark. 

fingerprint reader n. A scanner that reads human fingerprints 

for comparison to a database of stored fingerprint 

images. 

fingerprint recognition n. A technology used to control 

access to a computer, network, or other device or to a 

secure area through a user’s fingerprints. The patterns of 

an individual’s fingers are scanned by a fingerprint reader 

or similar device and matched with stored images of fingerprints 

before access is granted. See also biometric. 

FIPS n. See Federal Information Processing Standards. 

FIPS 140-1 n. Acronym for Federal Information Processing 

Standard 140-1. A U.S. Government standard, 

issued by the National Institute of Standards and Technology 

(NIST), entitled Security Requirements for Cryptographic 

Modules. FIPS 140-1 defines four levels of 

security requirements related to cryptographic hardware 

and software modules within computer and telecommunications 

systems used for sensitive but unclassified data. 

The four security levels range from basic module design 

through increasingly stringent levels of physical security. 

The standard covers such security-related features as hardware 

and software security, cryptographic algorithms, and 

management of encryption keys. FIPS 140-1products can 

be validated for federal use in both the United States and 

Canada after independent testing under the Cryptographic 

Module Validation (CMV) Program, developed and 

jointly adopted by NIST and the Canadian Communication 

Security Establishment. See also cryptography. 

firewall n. A security system intended to protect an organization’s 

network against external threats, such as hackers, 

coming from another network, such as the Internet.

firewall sandwich fixed-width spacing 

Usually a combination of hardware and software, a firewall 

prevents computers in the organization’s network 

from communicating directly with computers external to 

the network and vice versa. Instead, all communication is 

routed through a proxy server outside of the organization’s 

network, and the proxy server decides whether it is safe to 

let a particular message or file pass through to the organization’s 

network. See also proxy server. 

firewall sandwich n. The use of load-balancing appliances 

on both sides of Internetworked firewalls to distribute 

both inbound and outbound traffic among the 

firewalls. The firewall sandwich architecture helps to prevent 

firewalls from degrading network performance and 

creating a single point of network failure. See also firewall, 

load balancing. 

FireWire n. A high-speed serial bus from Apple that 

implements the IEEE 1394 standard. See also IEEE 1394. 

firmware n. Software routines stored in read-only memory 

(ROM). Unlike random access memory (RAM), readonly 

memory stays intact even in the absence of electrical 

power. Startup routines and low-level input/output instructions 

are stored in firmware. It falls between software and 

hardware in terms of ease of modification. See also RAM, 

ROM. 

FIR port n. Short for fast infrared port. A wireless I/O 

port, most common on a portable computer, that 

exchanges data with an external device using infrared 

light. See also infrared, input/output port. 

FIRST n. Acronym for Forum of Incident Response and 

Security Teams. An organization within the Internet Society 

(ISOC) that coordinates with CERT in order to encourage 

information sharing and a unified response to security 

threats. See also CERT, Internet Society. 

first-generation computer n. See computer. 

first in, first out n. A method of processing a queue, in 

which items are removed in the same order in which they 

were added—the first in is the first out. Such an order is 

typical of a list of documents waiting to be printed. Acronym: 

FIFO. See also queue. Compare last in, first out. 

first normal n. See normal form (definition 1). 

fishbowl n. A secure area within a computer system in 

which intruders can be contained and monitored. A fishbowl 

is typically set up by a security administrator to 

impersonate important applications or information so that 

215 

the system administrator can learn more about hackers 

who have broken into the network without the hacker 

learning more about or damaging the system. See also 

honeypot. 

fitting n. The calculation of a curve or other line that most 

closely approximates a set of data points or measurements. 

See also regression analysis. 

five-nines availability n. The availability of a system 

99.999 percent of the time. See also high availability. 

FIX n. Acronym for Federal Internet Exchange. A connection 

point between the U.S. government’s various 

internets and the Internet. There are two Federal Internet 

Exchanges: FIX West, in Mountain View, California; and 

FIX East, in College Park, Maryland. Together, they link 

the backbones of MILNET, ESnet (the TCP/IP network of 

the Department of Energy), and NSInet (NASA Sciences 

Internet) with NSFnet. See also backbone (definition 1), 

MILNET, NSFnet, TCP/IP. 

fixed disk n. See hard disk. 

fixed-length field n. In a record or in data storage, a field 

whose size in bytes is predetermined and constant. A 

fixed-length field always takes up the same amount of 

space on a disk, even when the amount of data stored in 

the field is small. Compare variable-length field. 

fixed-pitch spacing n. See monospacing. 

fixed-point arithmetic n. Arithmetic performed on 

fixed-point numbers. See also fixed-point notation. 

fixed-point notation n. A numeric format in which the 

decimal point has a specified position. Fixed-point numbers 

are a compromise between integral formats, which are compact 

and efficient, and floating-point numeric formats, which 

have a great range of values. Like floating-point numbers, 

fixed-point numbers can have a fractional part, but operations 

on fixed-point numbers usually take less time than floatingpoint 

operations. See also floating-point notation, integer. 

fixed space n. A set amount of horizontal space used to 

separate characters in text—often, the width of a numeral 

in a given font. See also em space, en space, thin space. 

fixed spacing n. See monospacing. 

fixed storage n. Any nonremovable storage, such as a 

large disk that is sealed permanently in its drive. 

fixed-width font n. See monospace font. 

fixed-width spacing n. See monospacing. 

F

F 

fixed-word-length computer flatbed scanner 

fixed-word-length computer n. A description that 

applies to almost all computers and refers to the uniform 

size of the data units, or words, that are processed by the 

microprocessor and shuttled through the system over the 

hardware lines composing the main data bus. Fixed-wordlength 

computers, including IBM and Macintosh personal 

computers, commonly work with 2 or 4 bytes at a time. 

F keys n. See function key. 

flag n. 1. Broadly, a marker of some type used by a computer 

in processing or interpreting information; a signal 

indicating the existence or status of a particular condition. 

Flags are used in such areas as communications, programming, 

and information processing. Depending on its use, a 

flag can be a code, embedded in data, that identifies some 

condition, or it can be one or more bits set internally by 

hardware or software to indicate an event of some type, 

such as an error or the result of comparing two values. 

2. In the HDLC communications protocol, a flag is the 

unique series of bits 01111110, used to start and end a 

transmission frame (message unit). See also HDLC. 

flame1 n. An abusive or personally insulting e-mail message 

or newsgroup posting. 

flame2 vb. 1. To send an abusive or personally insulting email 

message or newsgroup posting. 2. To criticize personally 

by means of e-mail messages or newsgroup postings. 

flame bait n. A posting to a mailing list, newsgroup, or 

other online conference that is likely to provoke flames, often 

because it expresses a controversial opinion on a highly emotional 

topic. See also flame1 , flame war. Compare troll. 

flamefest n. A series of inflammatory messages or articles 

in a newsgroup or other online conference. 

flamer n. A person who sends or posts abusive messages 

via e-mail, in newsgroups and other online forums, and in 

online chats. See also chat1 (definition 1), newsgroup. 

flame war n. A discussion in a mailing list, newsgroup, or 

other online conference that has turned into a protracted 

exchange of flames. See also flame1 . 

Flash n. A vector graphics file format (extension .swf) 

developed by Macromedia to enable designers to add animation 

and interactivity to multimedia Web pages. Flash 

files can be played back with a downloadable Shockwave 

plug-in or a Java program. The file format has been released 

by Macromedia as an open standard for the Internet. 

216 

flash vb. See burn. 

flash memory n. A type of nonvolatile memory. Flash 

memory is similar to EEPROM memory in function but it 

must be erased in blocks, whereas EEPROM can be erased 

one byte at a time. Because of its block-oriented nature, 

flash memory is commonly used as a supplement to or 

replacement for hard disks in portable computers. In this 

context, flash memory either is built into the unit or, more 

commonly, is available as a PC Card that can be plugged 

into a PCMCIA slot. A disadvantage of the block-oriented 

nature of flash memory is that it cannot be practically used 

as main memory (RAM) because a computer needs to be 

able to write to memory in single-byte increments. See also 

EEPROM, nonvolatile memory, PC Card, PCMCIA slot. 

flash ROM n. See flash memory. 

flat address space n. An address space in which each 

location in memory is specified by a unique number. (Memory 

addresses start at 0 and increase sequentially by 1.) The 

Macintosh operating system, OS/2, and Windows NT use a 

flat address space. MS-DOS uses a segmented address 

space, in which a location must be accessed with a segment 

number and an offset number. See also segmentation. Compare 

segmented address space. 

flatbed plotter n. A plotter in which paper is held on a 

flat platform and a pen moves along both axes, traveling 

across the paper to draw an image. This method is slightly 

more accurate than that used by drum plotters, which 

move the paper under the pen, but requires more space. 

Flatbed plotters can also accept a wider variety of media, 

such as vellum and acetate, because the material does not 

need to be flexible. See also plotter. Compare drum plotter, 

pinch-roller plotter. 

flatbed scanner n. A scanner with a flat, transparent surface 

that holds the image to be scanned, generally a book 

or other paper document. A scan head below the surface 

moves across the image. Some flatbed scanners can also 

reproduce transparent media, such as slides. See the illustration. 

Compare drum scanner, handheld scanner, sheetfed 

scanner.

flat file flicker 

F0Fxx04.eps 

Flatbed scanner. 

flat file n. A file consisting of records of a single record 

type in which there is no embedded structure information 

that governs relationships between records. 

flat-file database n. A database that takes the form of a 

table, where only one table can be used for each database. 

A flat-file database can only work with one file at a time. 

Compare relational database. 

flat file directory n. A directory that cannot contain subdirectories 

but simply contains a list of file names. Compare 

hierarchical file system. 

flat file format n. An image file format in which individual 

objects cannot be edited. Files stored in JPEG, GIF, 

and BMP formats, for example, are all flat files. 

flat file system n. A filing system with no hierarchical 

order in which no two files on a disk may have the same 

name, even if they exist in different directories. Compare 

hierarchical file system. 

flat memory n. Memory that appears to a program as one 

large addressable space, whether consisting of RAM or 

virtual memory. The 68000 and VAX processors have flat 

memory; by contrast, 80x86 processors operating in real 

mode have segmented memory, although when these processors 

operate in protected mode, OS/2 and 32-bit versions 

of Windows access memory using a flat memory 

model. Also called: linear memory. 

flat pack n. An integrated circuit housed in a flat rectangular 

package with connecting leads along the edges of 

the package. The flat pack was a precursor of surfacemounted 

chip packaging. See also surface-mount technology. 

Compare DIP (definition 1). 

flat-panel display n. A video display with a shallow 

physical depth, based on technology other than the CRT 

(cathode-ray tube). Such displays are typically used in lap- 

217 

top computers. Common types of flat-panel displays are 

the electroluminescent display, the gas discharge display, 

and the LCD display. 

flat panel monitor n. A desktop computer monitor that 

uses a liquid crystal display (LCD) rather than a cathode 

ray tube (CRT) to display data. Flat panel monitors 

are not as deep as CRT monitors and so occupy much 

less physical space. 

flat screen n. See flat-panel display. 

flatten vb. In digital graphic creation and manipulation 

programs, to combine all layers of text, images, and other 

graphic elements into a single layer. Elements cannot be 

edited after the graphic is flattened, so a graphic is not 

usually flattened until the final step when all adjustments 

have been made to the individual layers. Flattening an 

image significantly reduces its file size and allows it to be 

saved in a wider range of formats. Flattening is similar to 

grouping in that both actions combine a set of objects. 

However, flattening is a permanent action, whereas a 

group of objects can be ungrouped. See also layering. 

flavor n. One of several varieties of a system, having its 

own details of operation. UNIX in particular is found in 

distinct flavors, such as BSD UNIX or AT&T UNIX 

System V. 

flex circuit n. A circuit printed on a thin sheet of flexible 

polymer film that can be used in applications requiring 

circuits to curve and bend. Flex circuits offer space and 

weight savings over traditional circuits, and are used 

extensively for medical, industrial, and telecommunications 

applications. 

flexible disk n. See floppy disk. 

flexible transistor n. See plastic transistor. 

flicker n. Rapid, visible fluctuation in a screen image, as 

on a television or computer monitor. Flicker occurs when 

the image is refreshed (updated) too infrequently or too 

slowly for the eye to perceive a steady level of brightness. 

In television and raster-scan displays, flicker is not noticeable 

when the refresh rate is 50 to 60 times per second. 

Interlaced displays, in which the odd-numbered scan lines 

are refreshed on one sweep and even-numbered lines on 

the other, achieve a flicker-free effective refresh rate of 50 

to 60 times per second because the lines appear to merge, 

even though each line is actually updated only 25 to 30 

times per second. 

F

F 

flies floppy disk 

flies n. In Web development and marketing, individuals 

who spend significant time on the Web and who are the 

targets of specific Web content or advertising. 

flight simulator n. A computer-generated recreation of 

the experience of flying. Sophisticated flight simulators 

costing hundreds of thousands of dollars can provide pilot 

training, simulating emergency situations without putting 

human crews and planes at risk. Flight simulator software 

running on personal computers simulates flight in a less 

realistic fashion; it provides entertainment and practice in 

navigation and instrument reading. 

flip-flop n. A circuit that alternates between two possible 

states when a pulse is received at the input. For example, if 

the output of a flip-flop is high and a pulse is received at 

the input, the output “flips” to low; a second input pulse 

“flops” the output back to high, and so on. Also 

called: bistable multivibrator. 

flippy-floppy n. An outmoded 5.25-inch floppy disk that 

uses both sides for storage but is used in an older drive that 

can read only one side at a time. Thus, to access the opposite 

side, the disk must be physically removed from the 

drive and flipped over. See also double-sided disk. 

float n. The data type name used in some programming 

languages, notably C, to declare variables that can store 

floating-point numbers. See also data type, floating-point 

number, variable. 

floating-point arithmetic n. Arithmetic performed on 

floating-point numbers. See also floating-point notation, 

floating-point number. 

floating-point constant n. A constant representing a 

real, or floating-point, value. See also constant, floatingpoint 

notation. 

floating-point notation n. A numeric format that can be 

used to represent very large real numbers and very small 

real numbers. Floating-point numbers are stored in two 

parts, a mantissa and an exponent. The mantissa specifies 

the digits in the number, and the exponent specifies the 

magnitude of the number (the position of the decimal 

point). For example, the numbers 314,600,000 and 

0.0000451 are expressed respectively as 3146E5 and 

451E-7 in floating-point notation. Most microprocessors 

do not directly support floating-point arithmetic; consequently, 

floating-point calculations are performed either 

by using software or with a special floating-point processor. 

Also called: exponential notation. See also fixed-point 

notation, floating-point processor, integer. 

218 

floating-point number n. A number represented by a 

mantissa and an exponent according to a given base. The 

mantissa is usually a value between 0 and 1. To find the 

value of a floating-point number, the base is raised to the 

power of the exponent, and the mantissa is multiplied by 

the result. Ordinary scientific notation uses floating-point 

numbers with 10 as the base. In a computer, the base for 

floating-point numbers is usually 2. 

floating-point operation n. An arithmetic operation performed 

on data stored in floating-point notation. Floatingpoint 

operations are used wherever numbers may have 

either fractional or irrational parts, as in spreadsheets and 

computer-aided design (CAD). Therefore, one measure of 

a computer’s power is how many millions of floatingpoint 

operations per second (MFLOPS or megaflops) it 

can perform. Acronym: FLOP. Also called: floating-point 

operation. See also floating-point notation, MFLOPS. 

floating-point processor n. A coprocessor for performing 

arithmetic on floating-point numbers. Adding a floating-point 

processor to a system can speed up the 

processing of math and graphics dramatically if the software 

is designed to recognize and use it. The i486DX and 

68040 and higher microprocessors have built-in floatingpoint 

processors. Also called: math coprocessor, numeric 

coprocessor. See also floating-point notation, floatingpoint 

number. 

floating-point register n. A register designed to store 

floating-point values. See also floating-point number, 

register. 

flooding n. The networking technique of forwarding a 

frame onto all ports of a switch except the port on which it 

arrived. Flooding can be used for robust data distribution 

and route establishment. Also called: flood routing. 

FLOP n. See floating-point operation. 

floppy disk n. A round piece of flexible plastic film 

coated with ferric oxide particles that can hold a magnetic 

field. When placed inside a disk drive, the floppy disk 

rotates to bring different areas, or sectors, of the disk surface 

under the drive’s read/write head, which can detect 

and alter the orientation of the particles’ magnetic fields to 

represent binary 1s and 0s. A floppy disk 5.25 inches in 

diameter is encased in a flexible plastic jacket and has a 

large hole in the center, which fits around a spindle in the 

disk drive; such a disk can hold from a few hundred thousand 

to over one million bytes of data. A 3.5-inch disk 

encased in rigid plastic is also called a floppy disk or a

floppy disk controller flow control 

microfloppy disk. In addition, 8-inch floppy disks were 

common in DEC and other minicomputer systems. See 

also microfloppy disk. 

floppy disk controller n. See disk controller. 

floppy disk drive n. An electromechanical device that 

reads data from and writes data to floppy or microfloppy 

disks. See the illustration. See also floppy disk. 

Floppy disk drive 

F0Fxx05.eps 

Floppy disk drive. 

FLOPS n. Acronym for floating-point operations per second. 

A measure of the speed at which a computer can perform 

floating-point operations. See also floating-point 

operation, MFLOPS. Compare MIPS. 

floptical adj. Using a combination of magnetic and optical 

technology to achieve a very high data density on special 

3.5-inch disks. Data is written to and read from the 

disk magnetically, but the read/write head is positioned 

optically by means of a laser and grooves on the disk. 

flow analysis n. A method of tracing the movement of different 

types of information through a computer system, 

especially with regard to security and the controls applied to 

ensure the integrity of the information. See also flowchart. 

flowchart n. A graphic map of the path of control or data 

through the operations in a program or an informationhandling 

system. Symbols such as squares, diamonds, and 

ovals represent various operations. These symbols are 

connected by lines and arrows to indicate the flow of data 

or control from one point to another. Flowcharts are used 

both as aids in showing the way a proposed program will 

work and as a means of understanding the operations of an 

existing program. See the illustration. 

219 

Device 

Signals request 

IRQ 

Any 

IRQs 

active 

? 

Yes 

Is this 

INT 

masked 

off? 

No 

INT 

being 

serviced 

? 

No 

F0Fxx06.eps 

Flowchart. 

8259A 

No 

Signal request 

Yes 

Yes 

Place INT number 

on data bus 

INTR 

INTA 

Data 

bus 

Microprocessor 

Process 

Yes 

INTR 

high? 

INTs 

enabled? 

Yes 

Push 

flags 

Disable 

INTs 

Push 

CS:IP 

Acknowledge 

INT 

Get INT 

number 

Calculate 

new CS:IP 

No 

No 

flow control n. The management of data flow in a network 

to ensure that the receiver can handle all the incoming 

data. Flow-control mechanisms, implemented in both 

hardware and software, prevent a sender of traffic from 

sending it faster than the receiver can receive it. 

F

F 

flush1 flush 

font number 

flush1 adj. Aligned in a certain way on the screen or on 

paper. Flush left, for example, means aligned on the left 

side; flush right means aligned on the right side. See also 

align (definition 1). 

flush2 vb. To clear a portion of memory. For example, to 

flush a disk file buffer is to save its contents on disk and 

then clear the buffer for filling again. 

flux n. 1. The total strength of a magnetic, electric, or 

radiation field over a given area. 2. A chemical used to aid 

the binding of solder to electrical conductors. 

flux reversal n. The change in orientation of the minute 

magnetic particles on the surface of a disk or tape toward 

one of two magnetic poles. The two different alignments 

are used to represent binary 1 and binary 0 for data storage: 

a flux reversal typically represents a binary 1, and no 

reversal represents a binary 0. 

fly swapping n. See swap-on-the-fly. 

FM n. See frequency modulation. 

FM encoding n. See frequency modulation encoding. 

focus vb. In television and raster-scan displays, to make 

an electron beam converge at a single point on the inner 

surface of the screen. 

FOCUS n. See Federation on Computing in the United 

States. 

FOD n. See fax on demand. 

folder n. In the Mac OS, 32-bit versions of Windows, and 

other operating systems, a container for programs and files 

in graphical user interfaces, symbolized on the screen by a 

graphical image (icon) of a file folder. This container is 

called a directory in other systems, such as MS-DOS and 

UNIX. A folder is a means of organizing programs and 

documents on a disk and can hold both files and additional 

folders. It first appeared commercially in Apple Computer’s 

Lisa in 1983 and in the Apple Macintosh in 1984. 

See also directory. 

folio n. A printed page number. 

follow-up n. A post to a newsgroup that replies to an article. 

The follow-up has the same subject line as the original 

article, with the prefix “Re:” attached. An article and all of 

its follow-ups, in the order they were received, constitute a 

thread, which a user can read together using a newsreader. 

font n. A set of characters of the same typeface (such as 

Garamond), style (such as italic), and weight (such as bold). 

220 

A font consists of all the characters available in a particular 

style and weight for a particular design; a typeface consists 

of the design itself. Fonts are used by computers for onscreen 

displays and by printers for hard-copy output. In 

both cases, the fonts are stored either as bit maps (patterns 

of dots) or as outlines (defined by a set of mathematical formulas). 

Even if the system cannot simulate different typefaces 

on the screen, application programs may be able to 

send information about typeface and style to a printer, 

which can then reproduce the font if a font description is 

available. See also bit map, font generator. 

font card n. See font cartridge, ROM card. 

font cartridge n. A plug-in unit available for some printers 

that contains fonts in several different styles and sizes. 

Font cartridges, like downloadable fonts, enable a printer 

to produce characters in sizes and styles other than those 

created by the fonts built into it. Also called: font card. See 

also ROM cartridge. 

Font/DA Mover n. An application for older Apple Macintosh 

systems that allows the user to install screen fonts 

and desk accessories. 

font editor n. A utility program that enables the user to 

modify existing fonts or to create and save new ones. Such 

an application commonly works with a screen representation 

of the font, with a representation that can be downloaded 

to a PostScript or other printer, or with both. See 

also PostScript font, screen font. 

font family n. The set of available fonts representing variations 

of a single typeface. For example, Times Roman 

and Times Roman Italic are members of the same font 

family. When the user indicates italic, the system selects 

the correct italic font for the font family, with its characteristic 

appearance. If there is no italic font in the family, 

the system simply slants, or “obliques,” the corresponding 

roman character. See also italic, roman. 

font generator n. A program that transforms built-in 

character outlines into bit maps (patterns of dots) of the 

style and size required for a printed document. Font generators 

work by scaling a character outline to size; often they 

can also expand or compress the characters they generate. 

Some font generators store the resultant characters on 

disk; others send them directly to the printer. 

font number n. The number by which an application or 

operating system internally identifies a given font. On the 

Apple Macintosh, for example, fonts can be identified by 

their exact names as well as their font numbers, and a font

font page formal language 

number can be changed if the font is installed in a system 

already having a font with that number. See also font. 

font page n. A portion of video memory reserved for holding 

programmer-specified character definition tables (sets 

of character patterns) used for displaying text on the screen 

on IBM Multi-Color Graphics Array video systems. 

font size n. The point size of a set of characters in a particular 

typeface. See also point1 (definition 1). 

font suitcase n. A file on Macintosh computers that contains 

one or more fonts or desk accessories. Such files are 

indicated in early versions of the operating system with the 

icon of a suitcase marked with a capital A. From System 7.0 

onward, this icon is used to denote individual fonts. 

foo n. A string used by programmers in place of more specific 

information. Variables or functions in code examples 

intended to demonstrate syntax, as well as temporary 

scratch files, may all appear with the name foo. Likewise, 

a programmer may type foo to test a string input handler. 

If a second placeholder string is needed, it will often be 

bar, suggesting that the origin of both is the U.S. Army 

phrase FUBAR (an acronym which, in discreet language, 

represents Fouled Up Beyond All Recognition/Repair). 

However, other origins have been claimed. Compare fred 


footer n. One or more identifying lines printed at the bottom 

of a page. A footer may contain a folio (page number), 

a date, the author’s name, and the document title. 

Also called: running foot. Compare header (definition 1). 

footprint n. The surface area occupied by a personal computer 

or other device. 

force vb. In programming, to perform a particular action 

that would normally not occur. The term is most often 

used in the context of forcing data to be within a particular 

range of values—for example, forcing a divisor to be nonzero. 

See also cast. 

force feedback n. A technology that generates push or 

resistance in an input/output device. Force feedback 

enables an input/output device, such as a joystick or a 

steering wheel, to react to the user’s action in appropriate 

response to events displayed on the screen. For example, 

force feedback can be used with a computer game to react 

to a plane rising in a steep ascent or a race car turning a 

tight corner. See also input/output device. 

foreground1 adj. Currently having control of the system 

and responding to commands issued by the user. See also 

multitasking. Compare background1 . 

221 

foreground2 n. 1. The color of displayed characters and 

graphics. Compare background2 (definition 1). 2. The 

condition of the program or document currently in control 

and affected by commands and data entry in a windowing 

environment. Compare background2 (definition 4). 

forest n. A collection of one or more domains in 

Microsoft Windows that share a common schema, configuration, 

and global catalog and are linked with two-way 

transitive trusts. See also domain, global catalog, schema, 

transitive trust, two-way trust. 

fork1 n. One of the two parts of a file recognized by the 

Mac OS. A Macintosh file has a data fork and a resource 

fork. Most or all of a typical user-produced document is in 

the data fork; the resource fork usually contains application-oriented 

information, such as fonts, dialog boxes, and 

menus. See also data fork, resource fork. 

fork2 vb. To initiate a child process in a multitasking system 

after a parent process has been started. See also multitasking. 

fork bomb n. In UNIX-based systems, a program or shell 

script that locks up the system by recursively spawning 

copies of itself using the Unix system call “fork(2)” until 

they occupy all the process table entries. Also called: logic 

bomb. 

FOR loop n. A control statement that executes a section of 

code a specified number of times. Actual syntax and usage 

vary from language to language. In most cases, the value 

of an index variable moves through a range of values, 

being assigned a different (and usually consecutive) value 

each time the program moves through the section of code. 

See also iterative statement, loop1 (definition 1). Compare 

DO loop. 

form n. 1. A structured document with spaces reserved for 

entering information and often containing special coding 

as well. 2. In some applications (especially databases), a 

structured window, box, or other self-contained presentation 

element with predefined areas for entering or changing 

information. A form is a visual filter for the underlying 

data it is presenting, generally offering the advantages of 

better data organization and greater ease of viewing. 3. In 

optical media, a data storage format used in compact disc 

technology. 4. In programming, a metalanguage (such as 

Backus-Naur form) used to describe the syntax of a language. 

See also Backus-Naur form. 

formal language n. A combination of syntax and semantics 

that completely defines a computer language. See also 

Backus-Naur form, semantics (definition 1), syntax. 

F

F 

formal logic Forth 

formal logic n. A study of the logical expressions, 

sequences, and overall construction of a valid argument, 

without regard to the truth of the argument. Formal logic 

is used in proving program correctness. 

format1 n. 1. In general, the structure or appearance of a 

unit of data. 2. The arrangement of data within a document 

file that typically permits the document to be read or written 

by a certain application. Many applications can store a 

file in a more generic format, such as plain ASCII text. 

3. The layout of data storage areas (tracks and sectors) on 

a disk. 4. The order and types of fields in a database. 5. The 

attributes of a cell in a spreadsheet, such as its being alphabetic 

or numeric, the number of digits, the use of commas, 

and the use of currency signs. 6. The specifications for the 

placement of text on a page or in a paragraph. 

format2 vb. 1. To change the appearance of selected text 

or the contents of a selected cell in a spreadsheet. 2. To 

prepare a disk for use by organizing its storage space into 

a collection of data “compartments,” each of which can be 

located by the operating system so that data can be sorted 

and retrieved. When a previously used disk is formatted, 

any preexisting information on it is lost. 

format bar n. A toolbar within an application used for 

modifying the format of the document being displayed, 

such as changing font size or type. 

formatting n. 1. The elements of style and presentation 

that are added to documents through the use of margins, 

indents, and different sizes, weights, and styles of type. 

2. The process of initializing a disk so that it can be used 

to store information. See also initialize. 

form control n. On a Web site, an individual box or button 

with which you enter information on an electronic form. 

form factor n. 1. The size, shape, and configuration of a 

piece of computer hardware. The term is often applied to 

subcomponents such as disk drives, circuit boards, and 

small devices, such as handheld PCs. It can also be used 

more broadly to include the arrangement and positioning 

of external switches, plugs, and other components of the 

device, or it can refer to the footprint of an entire computer. 

2. A term used in computer graphics, specifically 

with reference to a method of rendering known as radiosity, 

which divides an image into small patches for calculating 

illumination. The form factor is a calculated value that 

represents the amount of energy radiated by one surface 

and received by another, taking into account such conditions 

as the distance between the surfaces, their orientation 

with respect to one another, and the presence of obstructions 

between them. 3. When used to describe software, 

222 

refers to the amount of memory required, the size of the 

program, and so on. 

form feed n. A printer command that tells a printer to 

move to the top of the next page. In the ASCII character 

set, the form-feed character has the decimal value 12 

(hexadecimal 0C). Because its purpose is to begin printing 

on a new page, form feed is also known as the page-eject 

character. Acronym: FF. 

form letter n. A letter created for printing and distribution 

to a group of people whose names and addresses are 

taken from a database and inserted by a mail-merge program 

into a single basic document. See also mail merge. 

formula n. A mathematical statement that describes the 

actions to be performed on numeric values. A formula sets 

up a calculation without regard to the actual values it is to 

act upon, such as A + B, with A and B representing whatever 

values the user designates. Thus, a formula is unlike 

an arithmetic problem, such as 1 + 2, which includes values 

and must be restated if any value is changed. Through 

formulas, users of applications such as spreadsheets gain 

the power to perform “what-if” calculations simply by 

changing selected values and having the program recalculate 

the results. Sophisticated programs include many 

built-in formulas for performing standard business and 

mathematical calculations. 

Forte n. Sun Microsystems integrated development environment 

(IDE) for Java developers. See also integrated 

development environment. 

Fortezza n. A cryptographic technology developed by the 

United States National Security Agency (NSA) for 

enabling secure communication of sensitive information. 

Fortezza is based on encryption, authentication, and other 

technologies built into a personalized card known as the 

Fortezza Crypto Card that can be inserted into a PCMCIA 

slot on a computer. This card works with Fortezza-enabled 

hardware and software to secure applications such as email, 

Web browsing, e-commerce, and file encryption. An 

RS-232 token can also be used with legacy systems that do 

not have card-reading capability. The technology is supported 

by a number of commercial vendors. 

Forth n. A programming language originated by Charles 

Moore in the late 1960s. Moore chose the language’s 

name, a shortened version of the word fourth, because he 

believed it was a fourth-generation language and his operating 

system would allow him to use only five letters for a 

program name. Forth is an interpreted, structured language 

that uses threading, which lets programmers easily 

extend the language and enables Forth to fit a great deal of

FORTRAN fractal 

functionality into limited space. Unlike most other programming 

languages, Forth uses postfix notation for its 

mathematical expressions and requires the programmer to 

work with the program stack directly. See also 4GL, interpreted 

language, postfix notation, stack, threading. 

FORTRAN or Fortran n. Short for formula translation. 

The first high-level computer language (developed over 

the period 1954–58 by John Backus) and the progenitor of 

many key high-level concepts, such as variables, expressions, 

statements, iterative and conditional statements, 

separately compiled subroutines, and formatted input/output. 

FORTRAN is a compiled, structured language. The 

name indicates its roots in science and engineering, where 

it is still used heavily, although the language itself has 

been expanded and improved vastly over the last 35 years 

to become a language that is useful in any field. See also 

compiled language, structured programming. 

fortune cookie n. A proverb, prediction, joke, or other 

phrase chosen at random from a collection of such items 

and output to the screen by a program. Fortune cookies are 

sometimes displayed at logon and logoff times by UNIX 

systems. 

forum n. A medium provided by an online service or BBS 

for users to carry on written discussions of a particular 

topic by posting messages and replying to them. On the 

Internet, the most widespread forums are the newsgroups 

in Usenet. 

Forum of Incident Response and Security Teams 

n. See FIRST. 

forward vb. In e-mail, to send a received message, either 

modified or in its entirety, to a new recipient. 

forward chaining n. In expert systems, a form of problem 

solving that starts with a set of rules and a database of 

facts and works to a conclusion based on facts that match 

all the premises set forth in the rules. See also expert system. 

Compare backward chaining. 

forward error correction n. In communications, a means 

of controlling errors by inserting extra (redundant) bits 

into a stream of data transmitted to another device. The 

redundant bits are used by the receiving device in detecting 

and, where possible, correcting errors in the data. See 

also error-correction coding. 

forward pointer n. A pointer in a linked list that contains 

the address (location) of the next element in the list. 

FOSDIC n. Acronym for film optical sensing device for 

input to computers. A device used by the U.S. government 

223 

to read documents on microfilm and store them digitally 

on magnetic tape or on a disk that can be accessed by a 

computer. 

Fourier transform n. A mathematical method, developed 

by the French mathematician Jean-Baptiste-Joseph Fourier 

(1768–1830), for signal processing and signal generation 

tasks such as spectral analysis and image processing. 

The Fourier transform converts a signal value that is a 

function of time, space, or both into a function of frequency. 

The inverse Fourier transform converts a function 

of frequencies into a function of time, space, or both. See 

also fast Fourier transform. 

four-nines availability n. The availability of a system 

99.99 percent of the time. See high availability. 

fourth-generation computer n. See computer. 

fourth-generation language n. See 4GL. 

fourth normal form n. See normal form (definition 1). 

FPD n. See full-page display. 

FPGA n. Acronym for Field Programmable Gate Array. A 

type of programmable logic chip that can be configured 

for a wide range of specialized applications after manufacture 

and delivery. FPGAs can be reprogrammed to incorporate 

innovations and upgrades. Because of their 

flexibility and adaptability, FPGAs are used in devices 

from microwave ovens to supercomputers. 

FPLA n. See field-programmable logic array. 

FPM RAM n. See page mode RAM. 

FPU n. Acronym for floating-point unit. A circuit that 

performs floating-point calculations. See also circuit, 

floating-point operation. 

FQ n. See fair queuing. 

fractal n. A word coined by mathematician Benoit Mandelbrot 

in 1975 to describe a class of shapes characterized 

by irregularity, but in a way that evokes a pattern. Computer 

graphics technicians often use fractals to generate 

naturelike images such as landscapes, clouds, and forests. 

The distinguishing characteristic of fractals is that they are 

“self-similar”; any piece of a fractal, when magnified, has 

the same character as the whole. The standard analogy is 

that of a coastline, which has a similar structure whether 

viewed on a local or continental scale. Interestingly, it is 

often difficult to measure the length of the perimeter of 

such a shape exactly because the total distance measured 

depends on the size of the smallest element measured. For 

example, one could measure on a given coastline the 

F

F 

fractional T1 frame relay 

perimeter of every peninsula and inlet, or at a higher magnification 

the perimeter of every small promontory and 

jetty, and so on. In fact, a given fractal may have a finite 

area but an infinite perimeter; such shapes are considered 

to have a fractional dimension—for example, between 1 (a 

line) and 2 (a plane)—hence the name fractal. See the 

illustration. See also cellular automata, graftal. 

F0Fxx07.eps 

Fractal. 

fractional T1 n. A shared connection to a T1 line, in 

which only a fraction of the 24 T1 voice or data channels 

are used. Acronym: FT1. See also T1. 

FRAD n. See frame relay assembler/disassembler. 

fraggle attack n. See smurf attack. 

fragmentation n. The scattering of parts of the same disk 

file over different areas of the disk. Fragmentation occurs 

as files on a disk are deleted and new files are added. Such 

fragmentation slows disk access and degrades the overall 

performance of disk operations, although usually not 

severely. Utility programs are available for rearranging file 

storage on fragmented disks. 

FRAM n. Acronym for ferromagnetic random access 

memory. A form of data storage technology in which data 

is recorded semipermanently on small cards or strips of 

material coated with a ferric oxide (iron-based) magnetic 

film. As with tape or disk, the data persists without power; 

as with semiconductor RAM, a computer can access the 

data in any order. 

frame n. 1. In asynchronous serial communications, a unit 

of transmission that is sometimes measured in elapsed 

time and begins with the start bit that precedes a character 

and ends with the last stop bit that follows the character. 

2. In synchronous communications, a package of information 

transmitted as a single unit. Every frame follows the 

same basic organization and contains control information, 

such as synchronizing characters, station address, and an 

224 

error-checking value, as well as a variable amount of data. 

For example, a frame used in the widely accepted HDLC 

and related SDLC protocols begins and ends with a unique 

flag (01111110). See the illustration. See also HDLC, 

SDLC. 3. A single screen-sized image that can be displayed 

in sequence with other, slightly different, images to 

create animated drawings. 4. The storage required to hold 

one screen-sized image of text, graphics, or both. 5. A 

rectangular space containing, and defining the proportions 

of, a graphic. 6. The part of an on-screen window (title 

bar and other elements) that is controlled by the operating 

system rather than by the application running in the window. 

7. A rectangular section of the page displayed by a 

Web browser that is a separate HTML document from the 

rest of the page. Web pages can have multiple frames, 

each of which is a separate document. Associated with 

each frame are the same capabilities as for an unframed 

Web page, including scrolling and linking to another 

frame or Web site; these capabilities can be used independently 

of other frames on the page. Frames, which were 

introduced in Netscape Navigator 2.0, are often used as a 

table of contents for one or more HTML documents on a 

Web site. Most current Web browsers support frames, 

although older ones do not. See also HTML document, 

Web browser. 

Flag Address Control Data Flag 

Frame 

check 

sequence 

F0Fxx08.eps 

Frame. The fields in an HDLC-SDLC frame. 

frame buffer n. A portion of a computer’s display memory 

that holds the contents of a single screen image. See 

also video buffer. 

frame grabber n. See video digitizer. 

frame rate n. 1. The speed at which full, single-screen 

images are transmitted to and displayed by a raster-scan 

monitor. Frame rate is calculated as the number of times 

per second (hertz) the electron beam sweeps the screen. 

2. In animation, the number of times per second an image 

is updated. When the frame rate exceeds about 14 frames 

per second, animation seems to blend into smooth motion. 

See also animation. 

frame relay n. A packet-switching protocol for use on 

WANs (wide area networks). Frame relay transmits 

variable-length packets at up to 2 Mbps over predetermined, 

set paths known as PVCs (permanent virtual circuits). 

It is a variant of X.25 but dispenses with some of

frame relay access device frequency 

X.25’s error detection for the sake of speed. See also 

ATM (definition 1), X.25. 

frame relay access device n. See frame relay assembler/disassembler. 

frame relay assembler/disassembler n. A combination 

channel service unit/digital service unit (CSU/DSU) 

and router that connects an internal network to a frame 

relay connection. The device converts data (which may be 

in the form of IP packets or conform to some other network 

protocol) into packets for transmission over the 

frame relay network and converts such packets back to the 

original data. Since this type of connection is direct— 

without a firewall—other network protection is necessary. 

Acronym: FRAD. See also firewall, frame relay, IP. 

frame source n. In the HTML frames environment, a 

contents document that will look for the source document 

to display within a frame drawn by the local browser. See 

also HTML. 

frames page n. A Web page that divides a Web browser 

window into different scrollable areas that can independently 

display several Web pages. One window can 

remain unchanged, while the other windows change based 

on hyperlinks that the user selects. 

frames per second n. See frame rate. 

framework n. In object-oriented programming, a reusable 

basic design structure, consisting of abstract and concrete 

classes, that assists in building applications. See also 

abstract class, object-oriented programming. 

FRC n. See functional redundancy checking. 

fred n. 1. An interface utility for X.500. See also CCITT 

X series. 2. A placeholder string used by programmers in 

syntax examples to stand for a variable name. If a programmer 

has used fred, the next placeholder needed is 

likely to be barney. Compare foo. 

free block n. A region (block) of memory that is not currently 

being used. 

FreeBSD n. A freely distributed version of BSD UNIX 

(Berkeley Software Distribution UNIX) for IBM and 

IBM-compatible PCs. See also BSD UNIX. 

free-form language n. A language whose syntax is not 

constrained by the position of characters on a line. C and 

Pascal are free-form languages; FORTRAN is not. 

225 

freenet or free-net n. A community-based computer BBS 

and Internet service provider, usually operated by volunteers 

and providing free access to subscribers in the community or 

access for a very small fee. Many freenets are operated by 

public libraries or universities. See also ISP. 

free software n. Software, complete with source code, 

that is distributed freely to users who are in turn free to 

use, modify, and distribute it, provided that all alterations 

are clearly marked and that the name and copyright notice 

of the original author are not deleted or modified in any 

way. Unlike freeware, which a user might or might not 

have permission to modify, free software is protected by a 

license agreement. Free software is a concept pioneered 

by the Free Software Foundation in Cambridge, Massachusetts. 

Compare freeware, open source, public-domain 

software, shareware. 

Free Software Foundation n. An advocacy organization 

founded by Richard Stallman, dedicated to eliminating 

restrictions on people’s right to use, copy, modify, and 

redistribute computer programs for noncommercial purposes. 

The Free Software Foundation is the maintainer of 

GNU software, which is UNIX-like software that can be 

freely distributed. See also GNU. 

free space n. Space on a floppy disk or a hard drive not 

currently occupied by data. See also floppy disk, hard disk. 

freeware n. A computer program given away free of 

charge and often made available on the Internet or through 

user groups. An independent program developer might 

offer a product as freeware either for personal satisfaction 

or to assess its reception among interested users. Freeware 

developers often retain all rights to their software, and 

users are not necessarily free to copy or distribute it further. 

Compare free software, public-domain software, 

shareware. 

freeze-frame video n. Video in which the image changes 

only once every few seconds. Compare full-motion video. 

frequency n. The measure of how often a periodic event 

occurs, such as a signal going through a complete cycle. 

Frequency is usually measured in hertz (Hz), with 1 Hz 

equaling 1 occurrence (cycle) per second. In the United 

States, household electricity is alternating current with a 

frequency of 60 Hz. Frequency is also measured in kilohertz 

(kHz, or 1000 Hz), megahertz (MHz, or 1000 kHz), 

gigahertz (GHz, or 1000 MHz), or terahertz (THz, or 1000 

GHz). See the illustration. Compare wavelength. 

F

F 

frequency counter front-end processor 

Amplitude 

F0Fxx09.eps 

Frequency. 

frequency counter n. 1. An item of engineering test 

equipment that measures and displays the frequencies of 

electronic signals. 2. An electronic circuit, often found 

embedded in process-control computers, that counts the 

frequency of occurrence of an activity. 

Frequency Division Multiple Access n. See FDMA. 

frequency-division multiplexing n. See FDM. 

frequency hopping n. The switching of frequencies 

within a given bandwidth during a point-to-point transmission. 

Frequency hopping reduces the chance of unauthorized 

signal interception or the effects of single-frequency 

jamming. 

frequency modulation n. A way of encoding information 

in an electrical signal by varying its frequency. The 

FM radio band uses frequency modulation, as does the 

audio portion of broadcast television. See the illustration. 

Acronym: FM. Compare amplitude modulation. 

Amplitude 

0 

F0Fxx10.eps 

Frequency modulation. 

180 360 

Time 

Time 

frequency modulation encoding n. A method of storing 

information on a disk in which both data and additional synchronizing 

information, called clock pulses, are recorded on 

the surface. FM encoding is relatively inefficient because of 

the extra disk space required by the clock pulses. It has been 

generally superseded by a more efficient method called 

modified frequency modulation (MFM) encoding and by 

226 

the complex but extremely efficient technique called runlength 

limited (RLL) encoding. Abbreviation: FM encoding. 

Compare modified frequency modulation encoding, 

run-length limited encoding. 

frequency response n. The range of frequencies an 

audio device can reproduce from its input signals. See also 

frequency. 

frequency-shift keying n. See FSK. 

frequently asked questions n. See FAQ. 

friction feed n. A means of moving paper through a 

printer in which the paper is pinched either between the 

printer’s platen and pressure rollers or (in printers that do 

not have a platen) between two sets of rollers. Friction 

feed is available on most printers, for use with paper that 

does not have pin-feed holes. In printers that have tractor 

feed as well as friction feed, the friction-feed mechanism 

should be left disengaged when the tractor is being used, 

to avoid unnecessary stress on the tractor gears. See also 

platen. Compare pin feed, tractor feed. 

friendly adj. Referring to features built into hardware or 

software that make a computer or computer program easy 

to learn and easy to use. Friendliness is emphasized by 

most developers and sought after by most users. See also 

user-friendly. 

fringeware n. Freeware whose reliability and value are 

questionable. See also freeware. 

front end n. 1. In a client/server application, the part of 

the program that runs on the client. See also client/server 

architecture. Compare back end (definition 1). 2. In applications, 

software or a feature of software that provides an 

interface to another application or tool. Front ends are 

often used to supply a common interface for a range of 

tools produced by a software manufacturer. A front end 

generally offers a more user-friendly interface than that of 

the application running “behind” it. 3. In networking, a 

client computer or the processing that takes place on it. 

Compare back end (definition 2). 

front-end processor n. 1. Generally, a computer or processing 

unit that produces and manipulates data before 

another processor receives it. Compare back-end processor 

(definition 2). 2. In communications, a computer that 

is located between communications lines and a main 

(host) computer and is used to relieve the host of housekeeping 

chores related to communications; sometimes 

considered synonymous with communications controller.

front panel fuel cell 

A front-end processor is dedicated entirely to handling 

transmitted information, including error detection and 

control; receipt, transmission, and possibly encoding of 

messages; and management of the lines running to and 

from other devices. See also communications controller. 

front panel n. The faceplate of a computer cabinet 

through which the control knobs, switches, and lights are 

available to an operator. See also console. 

fry vb. To destroy a circuit board or another component of 

a computer by applying excessive voltage. Even when 

applied voltage is not excessive, an electronic component 

can become fried when it breaks down, conducting more 

current than its design permits. 

fs n. See femtosecond. 

FSK n. Acronym for frequency-shift keying. A simple 

form of modulation in which the digital values 0 and 1 are 

represented by two different frequencies. FSK was used 

by early modems running at 300 bits per second. 

FT1 n. See fractional T1. 

FTAM n. Acronym for File-Transfer Access and Management. 

A communications standard for transferring files 

between different makes and models of computer. 

FTP1 n. 1. Acronym for File Transfer Protocol, a fast, 

application-level protocol widely used for copying files to 

and from remote computer systems on a network using 

TCP/IP, such as the Internet. This protocol also allows 

users to use FTP commands to work with files, such as 

listing files and directories on the remote system. See also 

TCP/IP. 2. A common logon ID for anonymous FTP. 

FTP2 vb. To download files from or upload files to remote 

computer systems, via the Internet’s File Transfer Protocol. 

The user needs an FTP client to transfer files to and 

from the remote system, which must have an FTP server. 

Generally, the user also needs to establish an account on 

the remote system to FTP files, although many FTP sites 

permit the use of anonymous FTP. See also FTP client, 

FTP server. 

FTP client or ftp client n. A program that enables the 

user to upload and download files to and from an FTP site 

over a network, such as the Internet, using the File Transfer 

Protocol. See also FTP1 (definition 1). Compare FTP 

server. 

FTP commands n. Commands that are part of the File 

Transfer Protocol. See also FTP1 (definition 1). 

227 

FTP program or ftp program n. See FTP client. 

FTP server n. A file server that uses the File Transfer 

Protocol to permit users to upload or download files 

through the Internet or any other TCP/IP network. See 

also file server, FTP1 (definition 1), TCP/IP. Compare 

FTP client. 

FTP site n. The collection of files and programs residing 

on an FTP server. See also FTP1 (definition 1), FTP 

server. 

FTTC n. Acronym for fiber to the curb. The installation 

and use of fiber-optic cable from the central office (CO) to 

within a thousand feet of a user’s home or office. With 

FTTC, coaxial cable or another medium carries the signals 

from the curb into the home or office. FTTC is a replacement 

for Plain Old Telephone Service (POTS) that enables 

the distribution of telephony, cable TV, Internet access, 

multimedia, and other communications over one line. 

Compare FTTH, POTS. 

FTTH n. Acronym for fiber to the home. The installation 

and use of fiber-optic cable from the central office (CO) 

directly into a user’s home or office. FTTH is a replacement 

for Plain Old Telephone Service (POTS) that enables 

the distribution of telephony, cable TV, Internet access, 

multimedia, and other communications over one line. 

Compare FTTC, POTS. 

FUD n. Acronym for fear, uncertainty, and doubt. Derogatory 

slang used to express disagreement or displeasure 

with a vendor’s public statements, particularly when the 

vendor is speaking of a competitor’s products. If a vendor 

is perceived as implying that buying from a competitor is 

obviously the wrong choice, that vendor is said to be using 

FUD as a marketing technique. 

fuel cell n. An electrochemical device, similar to a battery 

in function, in which the chemical energy of a fuel, such 

as hydrogen, and an oxidant, usually oxygen, are converted 

directly into electrical energy. Unlike batteries, 

however, fuel cells do not store energy, and they never run 

down or need recharging as long as the fuel and oxidant 

are supplied continuously. The principle of fuel cell technology 

was discovered more than 100 years ago, but until 

recently it had found use only in laboratories and in space 

travel (the Apollo missions and the space shuttle). Today, 

large and small fuel cells are being developed that will 

power portable devices such as laptop computers and cellular 

phones, generate electricity and heat, and replace 

automotive combustion engines. 

F

F 

fulfillment functional design 

fulfillment n. The process of delivering goods and services 

ordered by a consumer. Fulfillment involves establishing 

a reliable procedure for tracking orders and 

delivering products. 

fulfillment service provider n. A company that provides 

fulfillment services for an e-commerce Web site by tracking, 

packing, and shipping goods ordered via the e-commerce 

site. A fulfillment service provider allows an ebusiness 

to save time, costs, and labor by outsourcing 

order processing. 

full adder n. A logic circuit used in a computer to add 

binary digits. A full adder accepts three digital inputs 

(bits): 2 bits to be added and a carry bit from another digit 

position. It produces two outputs: a sum and a carry bit. 

Full adders are combined with two-input circuits called 

half adders to enable computers to add 4 or more bits at a 

time. See also carry bit, half adder. 

full-duplex adj. See duplex1 . 

full-duplex transmission n. See duplex2 (definition 1). 

full justification n. In typesetting, word processing, and 

desktop publishing, the process of aligning text evenly 

along both the left and right margins of a column or page. 

See also justify (definition 2). 

full mode n. The default operational state of Windows 

Media Player in which all of its features are displayed. The 

Player can also appear in skin mode. See also skin mode. 

full-motion video n. Video reproduction at 30 frames per 

second (fps) for NTSC signals or 25 fps for PAL signals. 

Also called: continuous motion video. See also frame 

(definition 1). Compare freeze-frame video. 

full-motion video adapter n. An expansion card for a 

computer that can convert motion video from devices such 

as a video cassette recorder to a digital format that a computer 

can use, such as AVI, MPEG, or Motion JPEG. See 

also AVI, Motion JPEG, MPEG. 

full name n. A user’s complete name, usually consisting 

of last name, first name, and middle initial. The full name 

is often maintained by the operating system as part of the 

information that identifies and defines a user account. See 

also user account. 

full-page display n. A video display with sufficient size 

and resolution to show at least one 81 /2-by-11-inch image. 

Such displays are useful for desktop publishing applications. 

Acronym: FPD. See also portrait monitor. 

228 

full path n. In a hierarchical filing system, a pathname 

containing all the possible components of a pathname, 

including the network share or drive and root directory, as 

well as any subdirectories and the file or object name. For 

example, the MS-DOS full path c:\book\chapter 

\myfile.doc indicates that myfile.doc is located in a directory 

called chapter, which in turn is located in a directory 

called book in the root directory of the C: drive. Also 

called: full pathname. See also path (definition 2), root 

directory, subdirectory. Compare relative path. 

full pathname n. See full path. 

full-screen adj. Capable of using or being displayed on 

the full area of a display screen. Applications running in 

windowing environments, although they might use the 

entire area of the screen, commonly allocate different 

areas to different windows, any of which can be enlarged 

to fill the entire screen. 

full-text search n. A search for one or more documents, 

records, or strings based on all of the actual text data 

rather than on an index containing a limited set of keywords. 

For example, a full-text search can locate a document 

containing the words “albatrosses are clumsy on 

land” by searching files for just those words without the 

need of an index containing the keyword “albatross.” See 

also index. 

fully formed character n. A character formed by striking 

an inked ribbon with a molded or cast piece of type in the 

manner of a typewriter. Impact printers that produce fully 

formed characters use letters attached to wheels (daisy 

wheels), balls, thimbles, bands, or chains, rather than dotmatrix 

wires. See also daisy wheel, near-letter-quality, 

thimble. 

fully populated board n. A printed circuit board whose 

integrated circuit (IC) sockets are all occupied. Memory 

boards in particular may have fewer than the maximum 

possible number of memory chips, leaving some IC sockets 

empty. Such a board is said to be partially populated. 

function n. 1. The purpose of, or the action carried out by, 

a program or routine. 2. A general term for a subroutine. 

3. In some languages, such as Pascal, a subroutine that 

returns a value. See also function call, procedure, routine, 

subroutine. 

functional design n. The specification of the relationships 

between working parts of a computer system, 

including details of logical components and the way they 

work together. Functional design is shown graphically in a

functional programming fuzzy computing 

functional diagram, which uses special symbols to represent 

the elements of the system. 

functional programming n. A style of programming in 

which all facilities are provided as functions (subroutines), 

usually without side effects. Pure functional programming 

languages lack a traditional assignment statement; assignment 

is usually implemented by copy and modify operations. 

Functional programming is thought to offer 

advantages for parallel-processing computers. See also 

side effect. 

functional redundancy checking n. A method of preventing 

errors by having two processors execute the same 

instructions on the same data at the same time. If the 

results produced by the two processors do not agree, an 

error has occurred. The Intel Pentium and higher processors 

have built-in support for functional redundancy 

checking. Acronym: FRC. 

functional specification n. A description of the scope, 

objectives, and types of operations that are to be considered 

in the development of an information-handling system. 

function call n. A program’s request for the services of 

a particular function. A function call is coded as the 

name of the function along with any parameters needed 

for the function to perform its task. The function itself 

can be a part of the program, be stored in another file 

and brought into the program when the program is compiled, 

or be a part of the operating system. See also 

function (definition 2). 

function key n. Any of the 10 or more keys labeled F1, 

F2, F3, and so on, that are placed along the left side or 

across the top of a keyboard (or both) and are used for special 

tasks by different programs. The meaning of a function 

key is defined by a program or, in some instances, by 

the user. Function keys are used in application programs 

or the operating system to provide either a shortcut for a 

series of common instructions (such as calling up a program’s 

on-screen help facility) or a feature that is not otherwise 

available. See also key (definition 1). Compare 

Command key, Control key, Escape key. 

function library n. A collection of routines compiled 

together. See also function (definition 2), library (definition 

1), toolbox. 

function overloading n. The capability of having several 

routines in a program with the same name. The different 

functions are distinguished by their parameter types, 

return value types, or both; the compiler automatically 

229 

selects the correct version, based on parameter types and 

return types. For example, a program might have one trigonometric 

sine function that uses a floating-point parameter 

to represent an angle in radians, and another that uses 

an integer parameter to represent an angle in degrees. In 

such a program, sin(3.14159/2.0) would return the value 

1.0 (because the sine of p/2 radians is 1), but sin(30) 

would return the value 0.5 (because the sine of 30 degrees 

is 0.5). See also operator overloading. 

Function procedure n. A procedure that returns a value 

and that can be used in an expression. You declare a function 

with the Function statement and end it with the End 

Function statement. 

fuse n. A circuit element that burns out or breaks when 

the current passing through it exceeds a certain level. A 

fuse protects a circuit from damage caused by excess current. 

It performs the same function as a circuit breaker, but 

it cannot be reset, so it must be replaced if it breaks. A 

fuse consists of a short length of wire of a specific composition 

and thickness; the thicker the wire, the more current 

it can pass before the wire melts and breaks the circuit. 

fusible link n. A circuit component, often part of an integrated 

circuit, that is designed to break, or burn like a fuse, 

when a relatively high current is applied. Rather than protecting 

against excessive current flow, fusible links allow 

intentional circuit modification in the field. Fusible links 

were used in PROM chips, and they form the foundation 

of a kind of integrated circuit known as a field-programmable 

logic array. One can customize such a circuit “in the 

field,” after it has been made in the factory, by selectively 

programming high current through certain fusible links 

and breaking them. See also field-programmable logic 

array, PROM. 

fuzzy computing n. 1. A computing technique that deals 

with vague, incomplete, or ambiguous data in a precise 

mathematical way while providing solutions based on the 

human way of thinking. The term fuzzy relates to the type 

of data it processes, not to the technique itself, which is 

very exact. Fuzzy computing is also known as fuzzy set 

theory or fuzzy logic, and covers fuzzy control and fuzzy 

expert systems, for example. 2. A computing technology 

in which the computer interprets data by looking for patterns 

in problems while completing tasks. Using fuzzy 

computing, the computer is able to examine patterns in the 

data it receives and to make inferences based on that data, 

and act accordingly. 

F

F 

fuzzy logic FYI 

fuzzy logic n. A form of logic used in some expert systems 

and other artificial-intelligence applications in which variables 

can have degrees of truthfulness or falsehood represented 

by a range of values between 1 (true) and 0 (false). 

With fuzzy logic, the outcome of an operation can be 

expressed as a probability rather than as a certainty. For 

example, an outcome might be probably true, possibly true, 

possibly false, or probably false. See also expert system. 

fuzzy set n. A set constructed using the principles of 

fuzzy logic. It is used in artificial intelligence to deal with 

vague or continuous data that cannot be expressed by conventional 

set theory. In a fuzzy set, the membership function 

for the set of objects is not binary but continuous, 

such that an object may be a member of the set to a specific 

degree or arbitrary value. In computer programming, 

a fuzzy set is usually effectively represented by an array. 

See also array, artificial intelligence, fuzzy logic. 

230 

FWIW adv. Acronym for for what it’s worth. An expression 

used in e-mail and newsgroups. 

FYI n. 1. Acronym for for your information. An expression 

used in e-mail and newsgroups to introduce information 

that is thought to be useful to the reader. 2. An 

electronic document distributed through InterNIC like a 

request for comments (RFC), but intended to explain an 

Internet standard or feature for users rather than to define 

it for developers, as the RFC does. See also InterNIC. 

Compare RFC.

G prefix See giga-. 

G3 n. See PowerPC 750. 

G4 n. See Power Macintosh. 

GaAs n. See gallium arsenide. 

gain n. The increase in the amplitude of a signal, as of 

voltage, current, or power, that is produced by a circuit. 

Gain can be expressed as a factor or in decibels. See also 

decibel. 

gallium arsenide n. A semiconductor compound used in 

place of silicon to make devices that perform faster, 

require less power, and are more tolerant of temperature 

changes and radiation than those made with silicon. Also 

called: GaAs. 

game n. See computer game. 

Game Boy n. Nintendo Corporation’s popular batterypowered, 

portable handheld gaming system first introduced 

in 1990 and updated frequently. Games are supplied 

on cartridges. The latest Game Boy, Game Boy Advance, 

features a 32-bit ARM CPU with embedded memory and 

a 2.9-inch TFT reflective screen with 240x160 resolution. 

See also computer game, TFT. 

game card n. See ROM card. 

game cartridge n. See ROM cartridge. 

game console n. See console game. 

Game Control Adapter n. In IBM personal computers 

and compatibles, a circuit that processes input signals at a 

game port. Devices such as joysticks and game paddles 

use potentiometers to represent their positions as varying 

voltage levels; the Game Control Adapter converts these 

levels to numbers using an analog-to-digital converter 

(ADC). See also analog-to-digital converter, game port, 

potentiometer. 

GameCube n. Nintendo Corporation’s console gaming 

system. It features a developer-friendly format and introduces 

1T-RAM technology, which reduces delays to the 

main memory and the graphics LSI mixed memory. The 

G 

231 

microprocessor is a custom IBM Power PC “Gekko” featuring 

a secondary cache (Level One: Instruction 32 KB, 

Data 32 KB (8-way); Level Two: 256 KB (2-way)). 

Games are supplied on a GameCube game disc. See also 

computer game, console game. Compare Dreamcast, 

PlayStation, Xbox. 

game pad n. An action-control input device used with 

arcade-type games played on PCs and game consoles such 

as Microsoft’s Xbox, Nintendo’s GameCube, Sega’s 

Dreamcast, and Sony’s PlayStation. A game pad, unlike a 

joystick, is meant to be held in a player’s hands. Buttons 

on the game pad allow a player to control direction, speed, 

and other screen actions. Also called: joypad. Compare 

joystick. 

game port n. In IBM personal computers and compatibles, 

an I/O port for devices such as joysticks and game 

paddles. The game port is often included with other I/O 

ports on a single expansion card. See the illustration. See 

also Game Control Adapter. 

Game port 

F0G gn01.eps 

Game port. 

gamer n. Refers to a person who plays games, sometimes 

role-playing games or trading card games; often a person 

who plays computer, console, arcade, or online games as a 

primary hobby or avocation. 

game theory n. A mathematical theory, ascribed to John 

von Neumann, that considers strategy and probability in 

terms of competitive games in which all players have partial 

control and each seeks the most advantageous moves 

in relation to the others. 

G

G 

game tree gatored 

game tree n. A tree structure representing contingencies 

in a game and used by game developers for design purposes. 

Each node in a game tree represents a possible position 

(for example, the configuration of pieces on a 

chessboard) in the game, and each branching represents a 

possible move. See also computer game. 

gamut n. The complete range of colors a display or 

printer is capable of producing. If a color falls outside the 

gamut of a device, it cannot be accurately displayed or 

printed from that device. 

gamut alarm n. A feature in graphics programs that 

alerts the user if a chosen color will fall outside the currently 

selected gamut. See also gamut. 

Gantt chart n. A bar chart that shows individual parts of 

a project as bars against a horizontal time scale. Gantt 

charts are used as a project-planning tool for developing 

schedules. Most project-planning software can produce 

Gantt charts. 

gap n. See inter-record gap. 

garbage n. 1. Incorrect or corrupted data. 2. Gibberish 

displayed on screen, either due to faulty hardware or software 

or because a program is unable to display a file’s 

content. For example, an executable file is not meant to be 

displayed by a text editor and so is indecipherable on 

screen. 

garbage collection n. A process for automatic recovery 

of heap memory. Blocks of memory that had been allocated 

but are no longer in use are freed, and blocks of 

memory still in use may be moved to consolidate the free 

memory into larger blocks. Some programming languages 

require the programmer to handle garbage collection. Others, 

such as Java, perform this task for the programmer. 

See also heap (definition 1). 

garbage in, garbage out n. A computing axiom meaning 

that if the data put into a process is incorrect, the data 

output by the process will also be incorrect. Acronym: 

GIGO. 

gas-discharge display n. A type of flat-panel display, 

used on some portable computers, containing neon 

between a horizontal and a vertical set of electrodes. 

When one electrode in each set is charged, the neon glows 

(as in a neon lamp) where the two electrodes intersect, 

representing a pixel. Also called: gas-plasma display. See 

also flat-panel display, pixel. 

232 

gas-plasma display n. See gas-discharge display. 

gate n. 1. An electronic switch that is the elementary 

component of a digital circuit. It produces an electrical 

output signal that represents a binary 1 or 0 and is related 

to the states of one or more input signals by an operation 

of Boolean logic, such as AND, OR, or NOT. Also 

called: logic gate. See also gate array. 2. The input terminal 

of a field-effect transistor (FET). Also called: gate 

electrode. See also drain (definition 1), FET, MOSFET, 

source (definition 2). 3. A data structure used by 80386 

and higher microprocessors to control access to privileged 

functions, to change data segments, or to switch tasks. 

gate array n. A special type of chip that starts out as a 

nonspecific collection of logic gates. Late in the manufacturing 

process, a layer is added to connect the gates for a 

specific function. By changing the pattern of connections, 

the manufacturer can make the chip suitable for many 

needs. This process is very popular because it saves both 

design and manufacturing time. The drawback is that much 

of the chip goes unused. Also called: application-specific 

integrated circuit, logic array. 

gated adj. 1. Transmitted through a gate to a subsequent 

electronic logic element. 2. Transmitted through a gateway 

to a subsequent network or service. For example, a 

mailing list on BITNET may be gated to a newsgroup on 

the Internet. 

gate electrode n. See gate (definition 2). 

gateway n. A device that connects networks using different 

communications protocols so that information can be 

passed from one to the other. A gateway both transfers 

information and converts it to a form compatible with the 

protocols used by the receiving network. Compare bridge. 

gateway page n. See doorway page. 

gating circuit n. An electronic switch whose output is 

either on or off, depending on the state of two or more 

inputs. For example, a gating circuit may be used to pass 

or not pass an input signal, depending on the states of one 

or more control signals. A gating circuit can be constructed 

from one or more logic gates. See also gate (definition 

1). 

gatored vb. To have been the victim of a hijackware program 

that seized control of an Internet shopping or surfing 

experience and caused the victim’s browser to display ads 

and Web sites chosen by the program. Users may be

GB General-Purpose Interface Bus 

gatored when they have unknowingly installed a program 

or plug-in with a hidden marketing agenda, which intrudes 

on the user’s Web shopping to display ads or Web sites 

promoting competing products. The term gatored comes 

from the name of a plug-in that was one of the first hijackware 

products to be used by Web marketers. See also 

hijackware. 

GB n. See gigabyte. 

Gbps n. See gigabits per second. 

GDI n. Acronym for Graphical Device Interface. In Windows, 

a graphics display system used by applications to 

display or print bitmapped text (TrueType fonts), images, 

and other graphical elements. The GDI is responsible for 

drawing dialog boxes, buttons, and other elements in a 

consistent style on screen by calling the appropriate screen 

drivers and passing them the information on the item to be 

drawn. The GDI also works with GDI printers, which have 

limited ability to prepare a page for printing. Instead, the 

GDI handles that task by calling the appropriate printer 

drivers and moving the image or document directly to the 

printer, rather than reformatting the image or document in 

PostScript or another printer language. See also bitmapped 

font, dialog box, driver, PostScript. 

Gecko n. A cross-platform Web browsing engine introduced 

by Netscape in 1998, distributed and developed as 

open-source software through Mozilla.org. Designed to be 

small, fast, and modular, the Gecko engine supports Internet 

standards including HTML, cascading style sheets 

(CSS), XML, and the Document Object Model (DOM). 

Gecko is the layout engine in Netscape’s Communicator 

software. 

geek n. 1. Generally, a person who enjoys cerebral activities 

(such as wordplay or computer programming) more 

than the mainstream population does. Geeks in this sense 

increasingly claim the word with pride, but it may give 

offense when used by others, suggesting inadequacy in 

normal social relationships. 2. A computer expert or specialist. 

For issues of etiquette, see definition 1. Compare 

guru, techie, wizard. 

GENA n. Acronym for General Event Notification Architecture. 

An extension to HTTP defined by an Internet 

Engineering Task Force (IETF) Internet-Draft and used to 

communicate events over the Internet between HTTP 

resources. Universal Plug and Play (UPnP) services use 

GENA to send XML event messages to control points. 

gender bender n. See gender changer. 

233 

gender changer n. A device for joining two connectors 

that are either both male (having pins) or both female 

(having sockets). See the illustration. Also called: gender 

bender. 

RS-232-C 

GENDER CHANGER 

MALE TO MALE 

F0G gn02.eps 

Gender changer. 

General Event Notification Architecture n. See 

GENA. 

General Inter-ORB Protocol n. See IIOP. 

General Packet Radio Service n. See GPRS. 

General Protection Fault n. The error condition that 

occurs in an 80386 or higher processor running in protected 

mode (such as Windows 3.1) when an application 

attempts to access memory outside of its authorized memory 

space or when an invalid instruction is issued. Acronym: 

GPF. See also protected mode. 

General Public License n. The agreement under which 

software, such as the GNU (GNU’s Not UNIX) utilities, is 

distributed by the Free Software Foundation. Anyone who 

has a copy of such a program may redistribute it to another 

party and may charge for distribution and support services, 

but may not restrict the other party from doing the 

same. A user may modify the program, but if the modified 

version is distributed, it must be clearly identified as such 

and is also covered under the General Public License. A 

distributor must also either provide source code or indicate 

where source code can be obtained. Acronym: GPL. Also 

called: copyleft. See also free software, Free Software 

Foundation, GNU. 

general-purpose computer n. A computer that can perform 

any computational task for which software is available. 

A PC is a general-purpose computer. 

general-purpose controller n. A controller that is 

designed for multiple uses. See also controller. 

General-Purpose Interface Bus n. A bus developed for 

the exchange of information between computers and 

industrial automation equipment. The electrical definition 

G

G 

general-purpose language geostationary orbit satellite 

of this bus has been incorporated into an IEEE standard. 

Acronym: GPIB. See also IEEE 488. 

general-purpose language n. A programming language, 

such as Ada, Basic, C, or Pascal, designed for a variety of 

applications and uses. By contrast, SQL is a language 

designed to be used only with databases. 

general-purpose register n. 1. A register within a 

microprocessor that is available for any use rather than 

being reserved, like a segment selector or stack pointer, for 

a specific use by the processor design or operating system. 

2. Any digital circuit capable of storing binary data. 

generation n. 1. A concept used to distinguish stored versions 

of a set of files. The oldest is called the grandfather, 

the next oldest is the father, and the newest is the son. 2. A 

concept used to distinguish among a process, another process 

that it initiates (its child), and the process that initiated 

it (its parent or the child’s grandparent). See also 

process1 . 3. A category that distinguishes products, such 

as computers or programming languages, according to the 

technological advances they represent. See also computer. 

generic icon n. An icon on a Macintosh screen that identifies 

a file only as a document or an application. Ordinarily 

the icon for an application will be specific to that 

application, and the icon for a document will be specific to 

the application that opens it. If a generic icon appears 

instead, the information that the Macintosh Finder uses to 

identify the application has been damaged. See also 

Finder, icon, Macintosh. 

genetic algorithm n. A computational method for adapting 

problem solutions based on genetic aspects of evolution. 

Implementations typically use fixed-length text 

strings to represent information, together with a population 

of individuals that undergo crossover and mutation in 

order to find promising results. Genetic algorithms typically 

have three distinct stages: 1) Encoding of the potential 

solutions into bit strings that support the necessary 

variation, 2) mating and mutation algorithms that produce 

a new generation of individuals that recombine features of 

the parents, and 3) a fitness function that judges the results 

based on what is most appropriate for a potential solution 

to the problem. See also algorithm, genetic programming. 

genetic programming n. A paradigm in which the principle 

of natural selection (whereby a biological entity 

whose structure is more fit for its environment than its 

peers produces descendants better able to survive) is 

applied to the creation of computer programs. Thus, 

234 

genetic programming seeks to find and develop, from the 

set of all possible programs, code that is highly fit to solve 

problems, but not necessarily explicitly designed for a 

specific task. This inductive discovery method aims to 

mimic the natural selection process by developing computer 

code based on its adaptability and suitability. See 

also artificial intelligence. 

Genie n. An online information service originally developed 

by General Electric (GE) Information Services as 

GEnie (General Electric network for information 

exchange); currently owned and provided by IDT Corporation 

as Genie (lowercase e). Genie provides business 

information, forums, home shopping, and news and can 

exchange e-mail with the Internet. 

GEO n. See geostationary orbit satellite. 

geographic information system n. An application or 

suite of applications for viewing and creating maps. Generally, 

geographic information systems contain a viewing 

system (sometimes allowing users to view maps with a 

Web browser), an environment for creating maps, and a 

server for managing maps and data for real-time online 

viewing. Acronym: GIS. 

geometry n. The branch of mathematics that deals with 

the construction, properties, and relationships of points, 

lines, angles, curves, and shapes. Geometry is an essential 

part of computer-aided design and graphics programs. 

GeoPort n. A fast serial input/output port on a range of 

Macintosh computers, including Macintosh Centris 

660AV, Quadra 660AV, Quadra 840AV, or PowerMac. 

Any Macintosh-compatible serial device can be connected 

to a GeoPort, but with GeoPort-specific hardware and 

software the GeoPort can transmit data at up to 2 Mbps 

(megabits per second) and can handle voice, fax, data, and 

video transmission. 

GEOS n. An operating system developed by Geoworks Corporation, 

used in some handheld devices. GEOS is designed 

to provide broad functionality in resource-constrained environments 

that have limited storage or memory capability, 

such as enhanced phones, some Internet access devices, 

and PDAs and other handheld computers. 

geostationary adj. See geosynchronous. 

geostationary orbit satellite n. A communications satellite 

that rotates with the earth and thus appears to remain 

fixed, or stationary, over a particular location. This travels 

in orbit 22,282 miles above the equator, where its period

geosynchronous gigaPoP 

of rotation matches the earth’s rotation. The service area, 

or footprint, of the satellite is approximately one-third of 

the earth’s surface, so global satellite coverage can be 

achieved with three satellites in orbit. In a voice communication 

system, a round-trip to and from this satellite takes 

approximately 250 milliseconds. Satellite-based data communications 

are necessary for delivering high bandwidth 

options to rural areas. Acronym: GEO. 

geosynchronous adj. Completing one revolution in the 

same time that the earth completes one rotation, as a communications 

satellite. Also called: geostationary. 

germanium n. A semiconductor element (atomic number 

32) that is used in some transistors, diodes, and solar cells 

but has been replaced by silicon in most applications. Germanium 

has a lower bias voltage than silicon but is more 

sensitive to heat (as in soldering). 

get n. An FTP command that instructs the server to transfer 

a specified file to the client. See also FTP client, FTP 

commands, FTP server. 

GFLOP n. See gigaflops. 

GGA n. Acronym for Good Game All. GGA is often used 

in online and chat games at the conclusion of play. See 

also role-playing game. 

ghost1 n. 1. A dim, secondary image that is displaced 

slightly from the primary image on a video display (due to 

signal reflection in transmission) or on a printout (due to 

unstable printing elements). 2. An abandoned or no-longermaintained 

Web site that remains accessible to visitors. 

ghost2 vb. 1. To produce a duplicate, such as duplicating 

an application in memory. See also screen saver. 2. To 

display an option on a menu or on a submenu in faint type 

to show that it cannot be selected at the present time. 

ghosting n. See burn in (definition 2). 

giant magnetoresistive head n. A type of hard-disk 

head developed by IBM and based on a physical property 

known as the giant magnetoresistive effect. Discovered by 

European scientists in the late 1980s, the giant magnetoresistive 

effect, or GMR, produces large resistance changes 

in magnetic fields when various metallic materials are 

“sandwiched” together in thin, alternating layers. When 

incorporated into disk heads, GMR technology allows for 

very dense data storage—currently, as much as 11.6 billion 

235 

bits per square inch, or the equivalent of more than 700,000 

typewritten pages. Acronym: GMR. See also head. 

.gif n. The file extension that identifies GIF bit map 

images. See also GIF. 

GIF n. 1. Acronym for Graphics Interchange Format. A 

graphics file format developed by CompuServe and used 

for transmitting raster images on the Internet. An image 

may contain up to 256 colors, including a transparent 

color. The size of the file depends on the number of colors 

actually used. The LZW compression method is used to 

reduce the file size still further. See also LZW compression, 

raster graphics. 2. A graphic stored as a file in the 

GIF format. 

GIF animation n. A file containing a series of graphics 

that are displayed in rapid sequence in a Web browser to 

appear as though they are a moving picture. 

giga- prefix 1. One billion (1000 million, 109 ). 2. In data 

storage, 1024 × 1,048,576 (230 ) or 1000 × 1,048,576. See 

also gigabyte, gigaflops, gigahertz, kilo-, mega-. 

Gigabit Ethernet n. The IEEE standard dubbed 802.3z, 

which includes support for transmission rates of 1 Gbps 

(gigabit per second)—1000 Mbps (megabits per second)—over 

an Ethernet network. The usual Ethernet standard 

(802.3) supports only up to 100 Mbps. Compare 

Ethernet/802.3. 

gigabit over copper n. See Cat 5 cable. 

gigabits per second n. A measurement of data transfer 

speed, as on a network, in multiples of 1,073,741,824 (230 ) 

bits. Acronym: Gbps. 

gigabyte n. 1. 1024 megabytes (1024 x 1,048,576 [230 ] 

bytes). 2. One thousand megabytes (1000 x 1,048,576 

bytes). Acronym: GB. 

gigaflops n. A measure of computing performance: one 

billion (1000 million) floating-point operations per second. 

Acronym: GFLOP. See also floating-point operation. 

gigahertz n. A measure of frequency: one billion (1000 

million) cycles per second. Abbreviation: GHz. 

gigaPoP n. Short for gigabit Point of Presence. A point 

of access for Internet2 (and possibly other high-speed 

networks) that supports data transfer speeds of at least 1 

Gbps. Approximately 30 gigaPoPs are located at various 

points across the United States. 

G

G 

GIGO Gnutella 

GIGO n. See garbage in, garbage out. 

GIMP n. Acronym for GNU Image Manipulation Program. 

A free and expandable graphics program for image creation 

and photo manipulation. GIMP is available for various 

UNIX-related platforms, including Linux and Mac OS X. 

GIOP n. Short for General Inter-ORB Protocol. See IIOP. 

GIS n. See geographic information system. 

GKS n. See Graphical Kernel System. 

glare filter n. A transparent mask placed over the screen 

of a video monitor to reduce or eliminate light reflected 

from its glass surface. 

glitch n. 1. A problem, usually minor. 2. A brief surge in 

electrical power. 

global adj. Pertaining to an entire document, file, or program 

rather than to a restricted segment of it. Compare 

local, local variable. 

global assembly cache n. A machine-wide code cache, 

introduced with Microsoft’s .NET systems, that stores 

assemblies specifically installed to be shared by many 

applications on the computer. Applications deployed in 

the global assembly cache must have a strong name. Acronym: 

GAC. See also assembly cache, strong name. 

global catalog n. A directory Windows database that 

applications and clients can query to locate any object in a 

forest. The global catalog is hosted on one or more domain 

controllers in the forest. It contains a partial replica of 

every domain directory partition in the forest. These partial 

replicas include replicas of every object in the forest, 

as follows: the attributes most frequently used in search 

operations and the attributes required to locate a full replica 

of the object. See also Active Directory, attribute, 

domain controller, forest, replication. 

globally unique identifier n. In the Component Object 

Model (COM), a 16-byte code that identifies an interface 

to an object across all computers and networks. Such an 

identifier is unique because it contains a time stamp and a 

code based on the network address hardwired on the host 

computer’s LAN interface card. These identifiers are generated 

by a utility program. Acronym: GUID. 

global operation n. An operation, such as a search and 

replace, that affects an entire document, program, or other 

object such as a disk. 

Global Positioning System n. See GPS. 

236 

global search and replace n. A search-and-replace 

operation that finds and changes all instances of the 

selected string throughout a document. See also search 

and replace. 

Global System for Mobile Communications n. See 

GSM. 

global universal identification n. An identification 

scheme in which only one name is associated with a particular 

object; this name is accepted across platforms and 

applications. Acronym: GUID. See also globally unique 

identifier. 

global variable n. A variable whose value can be 

accessed and modified by any statement in a program, not 

merely within a single routine in which it is defined. See 

also global. Compare local variable. 

GMR n. See giant magnetoresistive head. 

GNOME n. Acronym for GNU Network Object Model 

Environment. A popular open-source desktop environment 

for UNIX and UNIX-based operating systems such 

as Linux. GNOME provides a GUI desktop interface and 

basic applications that correspond to those found with 

Microsoft Windows or the Macintosh operating system. 

By providing a mainstream environment and familiar 

desktop appearance GNOME is intended to make UNIX 

easier for users. Development of GNOME is overseen by 

the GNOME Foundation, an association of computer 

industry companies and organizations with interests in the 

UNIX operating system. GNOME and KDE are leading 

contenders for consideration as a Linux desktop standard. 

See also KDE. 

gnomon n. In computer graphics, a representation of the 

three-dimensional (x-y-z) axis system. 

GNU n. Acronym for GNU’s Not UNIX. A collection of 

software based on the UNIX operating system maintained 

by the Free Software Foundation. GNU is distributed 

under the GNU General Public License, which requires 

that anyone who distributes GNU or a program based on 

GNU may charge only for distribution and support and 

must allow the user to modify and redistribute the code on 

the same terms. See also Free Software Foundation, General 

Public License. Compare Linux. 

GNU Image Manipulation Program n. See GIMP. 

Gnutella n. A file-sharing protocol that forms the basis of 

a number of peer-to-peer networking products. Gnutella 

forms a loose decentralized network with each user able to

Godwin’s Law GPS 

see and access all shared files of other Gnutella users. 

Unlike Napster, Gnutella does not require a central server, 

and any file type can be exchanged. Gnutella was originally 

developed by researchers at America Online’s 

Nullsoft group but the original implementation of the protocol 

was never publicly released. An open-source Gnutella 

preview appeared that resulted in a number of 

variations becoming available. See also Napster. 

Godwin’s Law n. As originally proposed by Internet 

activist Michael Godwin, the theory that as an online discussion 

grows longer, a comparison involving Nazis or 

Hitler will inevitably be made. When a participant in an 

online discussion resorts to invoking such a comparison, 

other participants might cite Godwin’s Law to indicate 

both that the person has lost the argument and that the discussion 

has continued too long. 

Good Times virus n. A purported e-mail virus alluded to 

in a warning that has been propagated widely across the 

Internet, as well as by fax and standard mail. The letter 

claims that reading an e-mail message with the subject 

“Good Times” will cause damage to the user’s system. In 

fact, it is currently impossible to harm a system by reading 

an e-mail message, although it is possible to include a 

virus in a file that is attached to an e-mail message. Some 

consider the chain letter itself to be the “virus” that wastes 

Internet bandwidth and the reader’s time. Information on 

such hoaxes and on real viruses can be obtained from 

CERT (http://www.cert.org/). See also urban legend, virus. 

Gopher or gopher n. An Internet utility for finding textual 

information and presenting it to the user in the form of 

hierarchical menus, from which the user selects submenus 

or files that can be downloaded and displayed. One 

Gopher client may access all available Gopher servers, so 

the user accesses a common “Gopherspace.” The name of 

the program is a three-way pun: it is designed to go for 

desired information; it tunnels through the Internet and 

digs the information up; and it was developed at the University 

of Minnesota, whose athletic teams are named the 

Golden Gophers. Gopher is being subsumed by the World 

Wide Web. 

Gopher server n. The software that provides menus and 

files to a Gopher user. See also Gopher. 

Gopher site n. A computer on the Internet on which a 

Gopher server runs. See also Gopher, Gopher server. 

237 

Gopherspace n. The total set of information on the Internet 

that is accessible as menus and documents through 

Gopher. See also Gopher. 

GOSIP n. Acronym for Government Open Systems Interconnection 

Profile. A U.S. government requirement that 

all of its new network purchases comply with the ISO/OSI 

standards. GOSIP went into effect on August 15, 1990, 

but was never fully implemented and was replaced by 

POSIT. 

GOTO statement n. A control statement used in programs 

to transfer execution to some other statement; the 

high-level equivalent of a branch or jump instruction. Use 

of GOTO statements is generally discouraged because 

they make it difficult not only for a programmer to trace 

the logic of a program but also for a compiler to generate 

optimized code. See also branch instruction, jump instruction, 

spaghetti code. 

.gov n. In the Internet’s Domain Name System, the toplevel 

domain that identifies addresses operated by government 

agencies. The domain name .gov appears as a suffix 

at the end of the address. In the United States, only nonmilitary 

federal government agencies may use the .gov 

domain. State governments in the United States use the 

top-level domain of .state.us, with .us preceded by the 

two-letter abbreviation for the state, or just .us; other 

regional governments in the United States are registered 

under the .us domain. See also DNS (definition 1), domain 

(definition 3), .state.us, .us. Compare .com, .edu, .mil, 

.net, .org. 

Government Open Systems Interconnection 

Profile n. See GOSIP. 

GPF n. See General Protection Fault. 

GPIB n. See General-Purpose Interface Bus. 

GPL n. See General Public License. 

GPRS n. Acronym for General Packet Radio Service. A 

third-generation enhancement to the Global System for 

Mobile Communications (GSM), which supports nonvoice 

applications such as Web browsing and other servicing 

requiring transfer of data packets without limits in 

message size. Systems using the service can be immediately 

connected when needed and therefore seem to the 

users to be always on. See also GSM, TDMA. 

GPS n. Acronym for Global Positioning System. A radio 

navigation system developed by the U.S. Department of 

G

G 

GPS receiver graph 

Defense that uses a constellation of 24 earth satellites, 

which are monitored by ground-based control stations, to 

provide precise, continuous worldwide positioning and 

timing information. GPS offers two services: a public 

Standard Positioning Service that provides positioning 

data accurate to within 100 meters horizontally and 156 

meters vertically and time accurate to within 340 nanoseconds; 

and a Precise Positioning Service, principally for 

government and military use, with positioning data accurate 

to within 22 meters horizontally and 27.7 meters vertically 

and time accurate to within 100 nanoseconds. See 

also GPS receiver. 

GPS receiver n. A device that includes an antenna, a 

radio receiver, and a processor for use with the worldwide 

GPS (Global Positioning System). A GPS receiver uses 

position and time information from four GPS satellites to 

calculate precise information about its current location, its 

speed of travel, and the current time. A portable GPS 

receiver may be a stand-alone device or a plug-in unit for 

use with a portable computer. GPS receivers are used for 

scientific work, such as surveying, mapping, and studies 

of volcanoes, as well as for land, sea, and air navigation. 

On the consumer front, they are used in outdoor activities 

such as hiking and sailing and in cars to provide location, 

destination, and traffic information. See also GPS. 

grabber n. 1. A device for capturing graphical image data 

from a video camera or another full-motion video source 

and putting it into memory. Also called: frame grabber, 

video digitizer. 2. Any device for capturing data. 

3. Software that takes a snapshot of the currently displayed 

screen image by transferring a portion of video 

memory to a file on disk. 4. In some graphics-based applications, 

a special type of mouse pointer. 

graceful exit n. The methodical termination of a process, 

even under error conditions, that allows the operating system 

or parent process to regain normal control, leaving the 

system in a state of equilibrium. This is expected behavior. 

See also fail-soft system. 

grade n. In communications, the range of frequencies 

available for transmission on a single channel. For example, 

voice-grade telephone frequencies range from about 

300 hertz (Hz) through 3400 Hz. 

grade of service n. The probability that a user of a shared 

communications network, such as a public telephone system, 

will receive an “all channels busy” signal. The grade 

of service is used as a measure of the traffic-handling abil- 

238 

ity of the network and is usually applied to a specific 

period, such as the peak traffic hour. A grade of service of 

0.002, for example, assumes that a user has a 99.8 percent 

chance that a call made during the specified period will 

reach its intended destination. 

gradient n. A smooth progression of colors and shades, 

usually from one color to another color, or from one shade 

to another shade of the same color. 

Graffiti n. A software application developed by Palm to 

allow handwriting recognition on personal digital assistants 

(PDAs). Graffiti contains preprogrammed shapes for 

each letter, which users of the application must match as 

closely as possible when writing. Text is written directly 

onto the PDA’s display screen using a stylus. The Graffiti 

application then passes the translated letter to the PDA’s 

application. 

grafPort n. A structure used on the Apple Macintosh to 

define a graphics environment with its own pen size, font, 

fill patterns, and so on. Each window has a grafPort, and 

grafPorts can be used to send graphics to off-screen windows 

or files. 

graftal n. One of a family of geometric forms, similar to 

fractals but easier to compute. Graftals are often used in 

the special-effects industry to create synthetic images of 

structures such as trees and plants. See also fractal. 

grammar checker n. A software accessory that checks 

text for errors in grammatical construction. 

Grammar Specification Language n. See GSL. 

grandfather n. See generation (definition 1). 

grandfather/father/son adj. See generation (definition 

1). 

grandparent n. See generation (definition 2). 

granularity n. A description, from “coarse” to “fine,” of a 

computer activity or feature (such as screen resolution, 

searching and sorting, or time slice allocation) in terms of 

the size of the units it handles (pixels, sets of data, or time 

slices). The larger the pieces, the coarser the granularity. 

graph n. 1. In programming, a data structure consisting of 

zero or more nodes and zero or more edges, which connect 

pairs of nodes. If any two nodes in a graph can be connected 

by a path along edges, the graph is said to be connected. 

A subgraph is a subset of the nodes and edges 

within a graph. A graph is directed (a digraph) if each 

edge links two nodes together only in one direction. A

Graphical Device Interface graphics import component 

graph is weighted if each edge has some value associated 

with it. See also node (definition 3), tree. 2. See chart. 

Graphical Device Interface n. See GDI. 

graphical interface n. See graphical user interface. 

Graphical Kernel System n. A computer graphics standard, 

recognized by ANSI and ISO, that specifies methods 

of describing, manipulating, storing, and transferring 

graphical images. It functions at the application level 

rather than the hardware level and deals with logical workstations 

(combinations of input and output devices such as 

keyboard, mouse, and monitor) rather than with individual 

devices. Graphical Kernel System was developed in 1978 

to handle two-dimensional graphics; the later modification, 

GKS-3D, extended the standard to three-dimensional 

graphics. Acronym: GKS. See also ANSI, ISO. 

graphical user interface n. A visual computer environment 

that represents programs, files, and options with 

graphical images, such as icons, menus, and dialog boxes, 

on the screen. The user can select and activate these 

options by pointing and clicking with a mouse or, often, 

with the keyboard. A particular item (such as a scroll bar) 

works the same way for the user in all applications, 

because the graphical user interface provides standard software 

routines to handle these elements and report the 

user’s actions (such as a mouse click on a particular icon or 

at a particular location in text, or a key press); applications 

call these routines with specific parameters rather than 

attempting to reproduce them from scratch. Acronym: 

GUI. 

graphic character n. Any character that is represented 

by a visible symbol, such as an ASCII character. A 

graphic character is not the same as a graphics character. 

Compare graphics character. 

graphic limits n. On a computer screen, the boundary of 

a graphical image in a graphics software program, including 

all the area enclosed within the graphic. In some 

graphics environments the limits of a graphic consist of 

the smallest rectangle that can completely enclose it, 

called its bounding rectangle or bounding box. 

graphics accelerator n. A video adapter that contains a 

graphics coprocessor. A graphics accelerator can update 

the video display much more quickly than the CPU can, 

and it frees the CPU for other tasks. A graphics accelerator 

is a necessity for modern software such as graphical user 

interfaces and multimedia applications. See also graphics 

coprocessor, video adapter. 

239 

graphics adapter n. A video adapter capable of displaying 

graphics as well as alphanumeric characters. Almost 

all video adapters in common use today are graphics 

adapters. 

graphics card n. See video adapter. 

graphics character n. A character that can be combined 

with others to create simple graphics, such as lines, boxes, 

and shaded or solid blocks. See the illustration. Compare 

graphic character. 

F0G gn03.eps 

Graphics character. Box built up from line graphics characters. 

graphics controller n. The part of the EGA and VGA 

video adapters that allows the computer to access the 

video buffer. See also EGA, VGA. 

graphics coprocessor n. A specialized microprocessor, 

included in some video adapters, that can generate graphical 

images such as lines and filled areas in response to 

instructions from the CPU, freeing the CPU for other work. 

graphics data structure n. A data structure that is 

designed specifically for representing one or more elements 

of a graphical image. 

graphics engine n. 1. A display adapter that handles 

high-speed graphics-related processing, freeing the CPU 

for other tasks. Also called: graphics accelerator, video 

accelerator. 2. Software that, based on commands from an 

application, sends instructions for creating graphic images 

to the hardware that actually creates the images. Examples 

are Macintosh QuickDraw and Windows Graphics Device 

Interface (GDI). 

graphics export component n. A technology developed 

by Apple for creating, editing, publishing, and viewing 

multimedia content. The graphics export component provides 

an application programming interface that enables a 

QuickTime player to export still images into a variety of 

file formats. 

graphics import component n. A technology developed 

by Apple for creating, editing, publishing, and viewing 

multimedia content. The graphics import component provides 

an application programming interface that enables a 

QuickTime player to import still images from a variety of 

file formats. 

G

G 

Graphics Interchange Format greeking 

Graphics Interchange Format n. See GIF. 

graphics interface n. See graphical user interface. 

graphics mode n. 1. On computers such as the IBM PC, 

the display mode in which lines and characters on the 

screen are drawn pixel by pixel. Because graphics mode 

creates images from individual dots on the screen, programs 

have more flexibility in creating images than they 

do in text (or character) mode. Thus, the computer is able 

to display a mouse pointer as an arrowhead or other shape 

rather than as a blinking square or rectangle, and it can 

display character attributes, such as boldface and italics, as 

they will appear in print rather than using conventions 

such as highlighting, underlining, or alternate colors. 

Compare text mode. 2. A particular set of color and resolution 

values, often related to a particular video adapter, 

such as VGA color with 16 colors and 640 x 480 pixels on 

the screen. See also high resolution, low resolution, resolution 


graphics port n. See grafPort. 

graphics primitive n. A drawing element, such as a text 

character, an arc, or a polygon, that is drawn and manipulated 

as a single unit and is combined with other primitives 

to create an image. Compare entity. 

graphics printer n. A printer, such as a laser, ink-jet, or 

dot-matrix impact printer, that can produce graphics 

formed pixel by pixel and not merely text characters. 

Nearly all printers presently used with personal computers 

are graphics printers; daisy-wheel printers are the exception. 

Compare character printer. 

graphics processor n. See graphics coprocessor. 

graphics tablet n. A device used to input graphics position 

information in engineering, design, and illustration 

applications. A flat rectangular plastic board is equipped 

with a puck or a pen (also called a stylus) and sensing 

electronics that report the position of the puck or stylus to 

the computer, which translates that data into a cursor position 

on the screen. Also called: digitizing tablet. See also 

puck, stylus. 

graphics terminal n. A terminal capable of displaying 

graphics as well as text. Such terminals usually interpret 

graphics control commands rather than receiving streams 

of already-processed pixels. 

Graphite n. An alternate appearance option in Mac OS X 

that features a gray interface with more subtle highlights 

than the colorful standard Aqua appearance. See also Aqua. 

240 

Gray code n. See cyclic binary code. 

gray market n. Resellers and other sources for hardware 

and software that obtain their inventory from distributors 

other than those authorized by the manufacturer. Gray 

market transactions may involve items that wholesalers 

purchase at discount and resell at higher prices, or they 

may refer to purchases made when sudden spikes in 

demand cannot be satisfied through normal distribution 

channels. On a more unsavory front, gray market transactions 

can also illegally involve stolen or counterfeit hardware, 

such as CPU chips and software packages. 

gray scale n. A sequence of shades ranging from black 

through white, used in computer graphics to add detail to 

images or to represent a color image on a monochrome 

output device. Like the number of colors in a color image, 

the number of shades of gray depends on the number of 

bits stored per pixel. Grays may be represented by actual 

gray shades, by halftone dots, or by dithering. See also 

dithering, halftone. 

greater than adj. See relational operator. 

greater than or equal to adj. See relational operator. 

Great Plains n. Microsoft Corporation’s suite of business 

solution applications for finance, accounting, and management. 

Microsoft acquired the Great Plains applications in 

December 2000, when it purchased Great Plains Software, 

which had originally developed the suite of business 

accounting and management solutions. Great Plains Business 

Solutions include applications for accounting and 

finance, customer relations management, e-commerce, 

human resources, manufacturing, project accounting, and 

supply-chain management. 

Great Renaming n. The changeover to the current system 

of Usenet hierarchies throughout the Internet. Before 

the Great Renaming, which took place in 1985, nonlocal 

newsgroup names had the form net.*; for example, a 

group that carried source code, formerly named 

net.sources, was renamed comp.sources.misc. See also 

local newsgroups, newsgroup, traditional newsgroup hierarchy, 

Usenet. 

greeking n. 1. The use of gray bars or other graphics to 

represent lines of characters too small to be drawn legibly 

on a screen at the chosen resolution, such as when viewing 

the layout of a whole page or pair of facing pages. 2. The 

use of nonsense words to represent the text of a document 

in design samples. A garbled Latin text beginning “Lorem 

ipsum dolor sit amet” is traditionally used for this purpose.

greek text groupware 

Greeking does not involve substituting the Greek alphabet 

for the Roman one. 

greek text n. See greeking. 

Green Book n. A specifications book written by the Sony 

and Philips Corporations, covering the CD-I (compact 

disc-interactive) technology. See also CD-I. Compare 

Orange Book (definition 2), Red Book (definition 2). 

green PC n. A computer system designed to conserve 

energy. For example, some computers shut off power to 

nonessential systems when no input has been detected for 

a certain amount of time, a condition known as sleep 

mode. Green PCs may also be distinguished by the use of 

minimal packaging materials and replaceable components, 

such as toner cartridges, that are recyclable. 

Gregorian calendar n. The calendar used today in the 

Western world, introduced by Pope Gregory XIII in 1582 

to replace the Julian calendar. To approximate better the 

length of the astronomical year (365.2422 days), years 

divisible by 100 are leap years only if they are also divisible 

by 400 (thus, 2000 was a leap year, but 1900 was not). 

To correct the error accumulated since A.D. 1, 10 days 

were dropped from October 1582; however, Britain and 

the American colonies did not adopt the Gregorian calendar 

until 1752 and had to remove 11 days then. Because 

the Gregorian calendar uses several rules for calculating 

leap years, systems based on algorithms that did not correctly 

determine that the year 2000 was a leap year might 

have encountered difficulties after February 28, 2000. 

Compare Julian calendar. 

grep1 n. Acronym for global regular expression print. A 

UNIX command used to search a file or files by keyword. 

grep2 vb. To search text, especially with the UNIX grep 

utility. 

grid n. 1. Two sets of lines or linear elements at right 

angles to each other. 2. A spreadsheet is a grid of rows and 

columns; a graphics screen is a grid of horizontal and vertical 

lines of pixels. 3. In optical character recognition, a 

grid is used for measuring or specifying characters. See 

also Cartesian coordinates. 

gridlines n. 1. Lines across a page in a graphics program 

that correspond to intervals on a ruler. 2. In many wordprocessing 

and spreadsheet programs, thin lines that indicate 

the cell boundaries in a table. 3. Lines you can add to a 

chart that make it easier to view and evaluate data. Grid- 

241 

lines extend from the tick marks on an axis across the plot 

area. Gridlines do not print when you print a document. 

grok vb. To understand deeply and appreciatively. The 

term comes from Robert A. Heinlein’s novel Stranger in 

a Strange Land, where it is also a Martian word for “to 

drink” and implies the kind of devoted interest that a 

Martian—native of a dry planet—would have in water. 

Hackers often use it (for example, in Internet discussions) 

in reference to computer expertise. See also cyberpunk. 

ground n. A conducting path from an electric circuit to 

earth or to a conducting body serving in place of earth, 

usually used as a safety device. See also grounding. 

grounding n. The connection of sections of an electrical 

circuit to a common conductor, called the ground, which 

serves as the reference for the other voltages in the circuit. 

The ground conductor on installed circuit boards is usually 

connected to the chassis, or metal frame, holding the 

electronic parts; the chassis is in turn usually connected to 

the third (round) prong on the power plug, which connects 

to a ground circuit that is, in fact, connected to the earth. 

This is important to avoid creating a shock hazard. 

group1 n. A collection of elements that can be treated as a 

whole, such as a collection of records in a database report, 

or a collection of objects that can be moved and transformed 

as a single object in a drawing program. In various 

multiuser operating systems, a group is a set of user 

accounts, sometimes called members; privileges can be 

specified for the group, and each member will then have 

those privileges. See also built-in groups, local group, user 

account. 

group2 vb. In a drawing program, to transform a number 

of objects into a group. See also drawing program. 

Group Policy Object n. A collection of Group Policy settings 

that are essentially the documents created by the 

Group Policy snap-in, a utility in Microsoft Windows 

2000. These settings are stored at the domain level and 

affect users and computers contained in sites, domains, 

and organizational units. Acronym: GPO. 

groupware n. Software intended to enable a group of 

users on a network to collaborate on a particular project. 

Groupware may provide services for communication 

(such as e-mail), collaborative document development, 

scheduling, and tracking. Documents may include text, 

images, or other forms of information. 

G

G 

grovel gzip 

grovel vb. 1. To search or do other work at great length 

without apparent progress. Some programs grovel over a 

whole input file before they begin to produce output. A 

programmer may have to grovel through manuals in 

search of documentation on a particular command, or 

through code in search of a bug. 2. To post a plea for some 

favor to a newsgroup. 

grunge n. See dead code. 

GSL n. Acronym for Grammar Specification Language. A 

grammar description format used by VoiceXML applications 

and other speech recognition systems. GSL was 

developed by Nuance and supports a number of XMLbased 

speech editing and voice-browsing applications. 

GSM n. Acronym for Global System for Mobile Communications. 

A digital cellular phone technology first 

deployed in 1992. In 2000, GSM was the predominant 

phone technology in Europe, and was used by 250 million 

subscribers worldwide. GSM phones offer a removable 

smart card containing subscriber account information. 

This card can be transferred from phone to phone quickly 

and easily, allowing the user to access his account from 

any phone in the system. Various enhancements to the 

GSM system allow increased Web browsing and data 

transfer options. See also GPRS, TDMA. 

guest n. A common name for a login account that can be 

accessed without a password. BBSs and service providers 

often maintain such an account so that prospective subscribers 

can sample the services offered. 

guest account n. An account used to log onto a system 

or domain where the user does not have access. Generally, 

resources and access are severely limited. On Windows 

NT technology, this account is built in to all domains. See 

also domain. 

242 

GUI n. See graphical user interface. 

GUID n. See globally unique identifier, global universal 

identification. 

GUID partition table n. A disk-partitioning scheme that 

is used by the eXtensible Firmware Interface (EFI) in Itanium-based 

computers. A GUID partition table offers 

more advantages than master boot record (MBR) partitioning 

because it allows up to 128 partitions per disk, provides 

support for volumes up to 18 exabytes in size, allows 

primary and backup partition tables for redundancy, and 

supports unique disk and partition IDs (GUIDs). Acronym: 

GPT. See also eXtensible Firmware Interface, Itanium, 

master boot record. 

gunzip n. A GNU utility for decompressing files compressed 

with gzip. See also GNU, uncompress. Compare 

gzip. 

guru n. A technical expert who is available to help solve 

problems and to answer questions in an intelligible way. 

See also techie, wizard (definition 1). 

gutter n. The blank area between two or more columns of 

text or between two facing pages in a publication. 

gzip n. A GNU utility for compressing files. See also 

compress2 , GNU. Compare gunzip.

H n. See henry. 

H.320 n. An International Telecommunications Union 

(ITU) standard that enables interoperability among videoconferencing 

equipment from different manufacturers 

over circuit-switched services such as ISDN, thus making 

desktop video conferencing viable. H.320 establishes the 

common formats necessary to make audio and video 

inputs and outputs compatible and defines a protocol that 

makes it possible for a multimedia terminal to use audio/ 

visual communications links and synchronization. See 

also International Telecommunications Union, ISDN, 

video conferencing. 


(ITU) interoperability protocol enabling cross-communication 

of multimedia products and applications over 

packet-based networks. Under H.323, multimedia products 

offered by one vendor can work with those of another, 

regardless of hardware compatibility. For example, a PC 

can share audio and video streams over either an intranet 

or the Internet. Applications are thus network-, platform-, 

and application-independent. See also International Telecommunications 

Union, packet switching. 


(ITU) standard for simultaneously transmitting video, 

data, and voice over POTS (Plain Old Telephone Service) 

modem connections. See also POTS. 

hack1 n. 1. A modification to the code in a program, often 

made without taking the time to find an elegant solution. 

2. A sloppy job. See also kludge (definition 2), patch2 . 

hack2 vb. 1. To apply creative ingenuity to a programming 

problem or project. 2. To alter the behavior of an 

application or an operating system by modifying its code 

rather than by running the program and selecting options. 

hacker n. 1. A computerphile; a person who is totally 

engrossed in computer technology and computer programming 

or who likes to examine the code of operating systems 

and other programs to see how they work. 2. A 

person, more commonly considered a cracker, who uses 

computer expertise for illicit ends, such as by gaining 

access to computer systems without permission and tam- 

H 

243 

pering with programs and data. Also called: cracker. See 

also hacktivist. 

hacktivist n. An individual who furthers political or 

social agendas through hacking activity. Hacktivists may 

break into computer systems to disrupt traffic or cause 

confusion, and may alter Web pages or e-mail to display 

content sympathetic to a specific cause. See also hacker. 

HAGO n. Acronym for have a good one. An expression 

used to conclude e-mail messages or in signing off from 

IRC. 

HailStorm n. See .NET My Services. 

hairline n. The smallest amount of visible space or the 

narrowest line that is displayable on a printed page. The 

size of a hairline depends on the materials, hardware, and 

software used or on the organizations involved. The 

United States Postal Service defines a hairline as 1/2 point 

(roughly 0.007 inch), whereas the Graphic Arts Technical 

Foundation (GATF) defines a hairline as 0.003 inch. See 

also point1 (definition 1), rule (definition 1). 

HAL n. 1. See hardware abstraction layer. 2. In the 1968 

book and movie “2001: A Space Odyssey” by novelist 

Arthur C. Clarke, the intelligent but eventually psychotic 

computer, HAL 9000, that takes over a spaceship bound 

for Jupiter. The name HAL is an acronym for Heuristic/ 

ALgorithmic computer, but the letters H-A-L are also one 

letter removed from I-B-M in the alphabet. 

half adder n. A logic circuit that can add two input data 

bits and produce a sum bit and a carry bit as output. A half 

adder cannot accept a carry bit from a previous addition; 

to add two input bits and a carry bit, a full adder is 

required. To add two multibit binary numbers, a computer 

uses a half adder and one or more full adders. See also 

carry bit, full adder. 

half-card n. See short card. 

half-duplex1 adj. Of or pertaining to two-way communication 

that takes place in only one direction at a time. For 

example, transmission between half-duplex modems 

occurs when one modem waits to transmit until the other 

has finished sending. Compare duplex1 . 

H

H 

half-duplex2 half-duplex 

handle 

half-duplex 2 n. Two-way electronic communication that 

takes place in only one direction at a time. Also 

called: half-duplex transmission. Compare duplex 2 (definition 

1), simplex transmission. 

half-duplex transmission n. See half-duplex 2 . 

half-height drive n. Any of a generation of disk drives 

that are roughly one-half the height of the previous generation 

of drives. 

half router n. A device that connects a local area network 

(LAN) to a communications line (such as one to the Internet) 

using a modem and that controls the routing of data to 

individual stations on the LAN. 

halftone n. A printed reproduction of a photograph or 

other illustration, using evenly spaced spots of varying 

diameter to produce apparent shades of gray. The darker 

the shade at a particular point in the image, the larger the 

corresponding spot in the halftone. In traditional publishing, 

halftones are created by photographing an image 

through a screen. In desktop publishing, each halftone 

spot is represented by an area containing a number of dots 

printed by a laser printer or digital imagesetter. In both 

cases, the frequency of the halftone dots is measured in 

lines per inch. Higher printer resolution enables effective 

use of higher frequencies of halftone dots, enhancing 

image quality. See also dithering, gray scale, imagesetter, 

spot function. 

half-word n. Half the number of bits considered to be a 

word in a particular computer; if a word is 32 bits, a halfword 

will be 16 bits or 2 bytes. See also word. 

hammer n. The part of an impact printer that strikes or 

causes another component to strike the ribbon to print a 

character on the paper. In a dot-matrix printer, the pins or 

wires are the hammers; in a daisy-wheel printer, the hammer 

strikes the daisy wheel. 

Hamming code n. A family of error-correction codes 

named for R. W. Hamming of Bell Labs. In one of the 

simplest Hamming codes, every 4 data bits are followed 

by 3 check bits, each computed from the 4 data bits. If any 

one of the 7 bits becomes altered, a simple computation 

can detect the error and determine which bit is altered. See 

also error-correction coding, forward error correction. 

handheld computer n. A computer small enough to be 

held in one hand while being operated with the other hand. 

244 

Handheld computers are commonly used in transportation 

and other field service industries. They are usually built to 

perform specific tasks. They often have restricted specialized 

keyboards rather than the standard QWERTY layout, 

smaller displays, input devices such as bar code readers, 

and communications devices for sending their data to a 

central computer; they rarely have disk drives. Their software 

is usually proprietary and stored in ROM. See also 

QWERTY keyboard, ROM. Compare handheld PC, PDA. 

Handheld Device Markup Language n. See HDML. 

Handheld Device Transport Protocol n. See HDTP. 

handheld PC n. A computer that is small enough to fit in 

a jacket pocket and can run, for example, Windows CE (an 

operating system for handheld PCs and embedded systems) 

and applications made for that operating system. 

See the illustration. Acronym: HPC. Compare handheld 

computer, PDA. 

FOHgn01.eps 

Handheld PC. 

handheld scanner n. A type of scanner used as follows: 

the user passes the scan head, contained within a handheld 

unit, over the medium being scanned, such as a piece of 

paper. See also scan head, scanner. Compare drum scanner, 

feed scanner, flatbed scanner. 

handle n. 1. A pointer to a pointer; that is, a variable that 

contains the address of another variable, which in turn contains 

the address of the desired object. In certain operating 

systems, the handle points to a pointer stored in a fixed 

location in memory, whereas that pointer points to a movable 

block. If programs start from the handle whenever they 

access the block, the operating system can perform 

memory-management tasks such as garbage collection

handler hard 

without affecting the programs. See also pointer. 2. Any 

token that a program can use to identify and access an 

object such as a device, a file, a window, or a dialog box. 

3. One of several small squares displayed around a graphical 

object in a drawing program. The user can move or 

reshape the object by clicking on a handle and dragging. 

See the illustration. 4. In online communication, such as 

chats and bulletin boards, the name a person uses to identify 

himself or herself. A handle is comparable to an alias or a 

nickname and is like those used with CB radio. 5. A unique 

alphanumeric identifier of up to 10 characters assigned by 

InterNIC to the domain names, contacts, and network 

records in its domain name database. The NIC handle is 

used as a shorthand means of finding records and ensuring 

accuracy in the database. Also called: NIC handle. 

Handle 

F0Hgn02.eps 

Handle. A computer graphic’s handle. 

handler n. 1. A routine that manages a common and relatively 

simple condition or operation, such as error recovery 

or data movement. 2. In some object-oriented programming 

languages that support messages, a subroutine that processes 

a particular message for a particular class of objects. 

See also message, object-oriented programming. 

handoff n. The process of transferring a wireless telephone 

signal between cell towers as a caller travels from 

one cell to another. A caller will not notice a smooth handoff, 

but an abrupt handoff can interfere with reception, 

with results ranging from momentary static to a disconnected 

call. Also called: handover. See also cell. 

hands-free kit n. Wireless phone accessory that allows 

users to make calls without holding the phone. A basic kit 

includes a headset or an earpiece with a microphone. More 

elaborate sets for use in automobiles may include a power 

amplifier, dashboard microphone, phone cradle, and 

speakers. 

handshake n. A series of signals acknowledging that 

communication or the transfer of information can take 

place between computers or other devices. A hardware 

handshake is an exchange of signals over specific wires 

(other than the data wires) in which each device indicates 

its readiness to send or receive data. A software handshake 

consists of signals transmitted over the same wires used to 

transfer data, as in modem-to-modem communications 

over telephone lines. 

245 

hands-on adj. Involving interactive work with a computer 

or a computer program. A hands-on tutorial, for example, 

would teach a skill (such as the use of a program) by means 

of practice sessions and question-and-answer dialogues. 

handwriting input device n. A tool, such as a digital pen 

and tablet, used to enter text by writing instead of typing. 

Along with writing tablets, additional devices include 3-D 

drawing or computer-aided design (CAD) tablets, a tablet 

PC, or moving a mouse on the mouse pad. 

handwriting recognition n. 1. The ability of a computer 

to identify a user by recognizing features of handwriting, 

especially a signature. 2. The ability of a computer to 

translate handwritten text into character data for input. 

This technology is still under considerable development, 

and most handwriting recognition programs require users 

to form letters and words in a very consistent and clear 

manner to work adequately. The development of handwriting 

recognition programs has been spurred by PDAs, 

which frequently have keyboards that are too small for 

data entry, and software designed for Asian markets that 

have languages with numerous characters, which makes 

keyboards a cumbersome method for entering text. See 

also PDA. Compare optical character recognition. 

hang vb. To stop responding. A hung program or computer 

system does not respond to user input, but the screen 

looks as if everything is running normally. The program or 

system might be waiting for something—for example, 

information from a network—or it might have terminated 

abnormally. It might resume running normally on its own, 

or the user might need to terminate and restart the program 

or reboot the computer. A hung computer system is said to 

be locked up. See also crash2 (definition 1). 

hanging indent n. Placement of the beginning of the first 

line of a paragraph farther to the left than the subsequent 

lines. Also called: outdent. Compare indent. 

haptics n. The study of the sense of touch. This study has 

extended to the study of human interaction with computer 

technology through tactile means. Haptics technology is 

central to virtual reality gaming settings, in which computers 

could sense and respond to finger, hand, body, or head 

movements. The computer could also re-create the sense 

of touch by altering texture, increasing resistance, or other 

simulations appropriate to the user’s virtual reality experience. 

See also force feedback. 

hard adj. 1. Permanent, fixed, or physically defined; 

unchangeable by the ordinary operation of a computer 

system. See also hard copy, hard error, hard return, 

H

H 

hard card hardware check 

hard-sectored disk. Compare soft (definition 1). 2. 

Retaining magnetization even in the absence of an external 

magnetic field. Compare soft (definition 2). 

hard card n. A circuit board, carrying a hard disk and containing 

its controller, that plugs into an expansion slot and 

uses the expansion bus for power as well as for data and 

control signals. By contrast, a hard disk in a drive bay communicates 

with a separate controller card by a ribbon cable 

and has a direct cable to the computer’s main power supply. 

See also controller, drive bay, expansion slot, ribbon cable. 

hard-coded adj. 1. Designed to handle a specific situation 

only. 2. Depending on values embedded in the program 

code rather than on values that can be input and changed 

by the user. 

hard copy n. Printed output on paper, film, or other permanent 

medium. Compare soft copy. 

hard disk n. A device containing one or more inflexible 

platters coated with material in which data can be 

recorded magnetically, together with their read/write 

heads, the head-positioning mechanism, and the spindle 

motor in a sealed case that protects against outside contaminants. 

The protected environment allows the head to 

fly 10 to 25 millionths of an inch above the surface of a 

platter rotating typically at 3600 to 7200 rpm; therefore, 

much more data can be stored and accessed much more 

quickly than on a floppy disk. Most hard disks contain 

from two to eight platters. See the illustration. Also 

called: hard disk drive. Compare floppy disk. 

Read/write head 

Platter 

FOHgn03.eps 

Hard disk. The cover of this hard disk has been removed to 

reveal the components within. 

hard disk drive n. See hard disk. 

246 

hard disk type n. One or more numbers that inform a 

computer about the characteristics of a hard disk, such as 

the number of read/write heads and the number of cylinders 

the hard disk contains. The hard disk type numbers 

are usually marked on a label attached to the disk and 

must be input to the computer when the hard disk is 

installed, often by means of the computer’s CMOS setup 

program. See also CMOS setup. 

hard error n. 1. An error caused by a hardware failure or 

by accessing incompatible hardware. See also hard failure. 

Compare soft error. 2. An error that prevents a program 

from returning to normal operation. See also fatal error. 

hard failure n. A cessation of function from which no 

recovery is possible, usually requiring a call to a repair 

service to correct. Also called: hardware failure. 

hard hyphen n. See hyphen. 

hard return n. A character input by the user to indicate 

that the current line of text is to end and a new line is to 

begin. In word-processing programs that automatically 

break lines within the margins of a page, a hard return 

indicates the end of a paragraph. In text-entry programs 

that lack wordwrap, on the other hand, a hard return is 

required to end each line, and often two or more hard 

returns are needed to end a paragraph. See also wordwrap. 

Compare soft return. 

hard-sectored disk n. A floppy disk whose data sectors 

have been physically marked with punched holes that are 

detected by sensors in the drive to locate the beginning of 

each sector. Compare soft-sectored disk. 

hard space n. See nonbreaking space. 

hardware n. The physical components of a computer system, 

including any peripheral equipment such as printers, 

modems, and mouse devices. Compare firmware, software. 

hardware abstraction layer n. In advanced operating 

systems such as Windows NT, Windows 2000, and Windows 

XP a layer in which assembly language code is isolated. 

A hardware abstraction layer functions similarly to 

an application programming interface (API) and is used 

by programmers to write device-independent applications. 

Acronym: HAL. See also application programming 

interface, device independence. 

hardware address n. See physical address. 

hardware check n. 1. An automatic check performed by 

hardware to detect internal errors or problems. 2. On a PC, 

a check of system hardware performed by a PC’s BIOS

hardware conversion hash2 hash 

(Basic Input/Output System) during the POST (Power On 

Self Test) portion of the startup process. 

hardware conversion n. Changing all or part of a computer 

system to work with new or different devices. 

hardware cryptographic module n. Hardware designed 

to handle the cryptographic functions necessary for data 

security. For example, a hardware cryptographic module, or 

HCM, can be used in an SSL-enabled Web server to reduce 

CPU processing time and improve overall performance by 

working to secure data during online transactions. Using an 

HCM allows the Web server to continue processing customer 

requests. Acronym: HCM. See also SSL. 

hardware-dependent adj. Of or pertaining to programs, 

languages, or computer components and devices that are 

tied to a particular computer system or configuration. 

Assembly language, for example, is hardware-dependent 

because it is created for and works only with a particular 

make or model of microprocessor. 

hardware emulation layer n. In advanced operating systems 

such as Windows NT, Windows 2000, and Windows 

XP a layer in which software drivers duplicate hardware 

functionality. This allows software programs to use hardware 

features even if the hardware is not present. Acronym: 

HEL. Compare hardware abstraction layer. 

hardware failure n. A malfunction of a physical component 

in a computer system, such as a disk head crash or 

memory error. See also hard failure. 

hardware handshake n. See handshake. 

hardware interrupt n. A request for service from the 

central processing unit, generated either externally by a 

hardware device such as a disk drive or an input/output 

port, or internally by the CPU itself. External hardware 

interrupts are used for such situations as a character 

received from a port and needing to be processed, a disk 

drive ready to transfer a block of data, or a tick of the system 

timer. Internal hardware interrupts occur when a program 

attempts an impossible action such as accessing an 

unavailable address or dividing by zero. Hardware interrupts 

are assigned levels of importance or priority. The 

highest priority is given to a type of interrupt called a nonmaskable 

interrupt—one that indicates a serious error, 

such as a memory failure, that must be serviced immediately. 

See also external interrupt, interrupt. 

hardware key n. 1. A security device connected to an 

input/output port to permit the use of a particular software 

package on that computer. The use of the hardware key 

247 

permits backup copying of software but prevents its unlicensed 

use on additional computers. Also called: dongle. 

2. Any physical device used to secure a computer system 

from unauthorized access, such as the lock on the front of 

the cabinet of some personal computers. 

hardware monitor n. A separate board-level circuit used 

to oversee the performance of a hardware/software system. 

A hardware monitor can detect the cause of a fatal 

error such as a system crash, whereas a software monitor 

or debugger cannot. Compare debugger. 

hardware profile n. A set of data that describes the configuration 

and characteristics of a given piece of computer 

equipment. Such data is typically used to configure computers 

for use with peripheral devices. 

hardware tree n. In Windows 9x, a data structure containing 

information about the configuration and requirements 

of a system’s hardware devices. Consisting of nodes 

that point to active devices, the hardware tree is dynamic 

and is reconstructed every time the operating system is 

started or refreshed. The hardware tree facilitates the Plug 

and Play capability of Windows 9x. 

hardwired adj. 1. Built into a system using hardware such 

as logic circuits, rather than accomplished through programming. 

2. Physically connected to a system or a network, 

as by means of a network connector board and cable. 

Harvard architecture n. A processor architecture that 

uses separate address buses for code and for data. This 

increases throughput by allowing the system to fetch 

instructions at the same time that it reads and writes data. 

This architecture also allows optimization of memory system 

design because instructions tend to be fetched sequentially, 

whereas data reads and writes are more random. 

Harvard Mark I n. See Mark I. 

Harvest research project n. See ICP. 

hash1 n. In many FTP client programs, a command that 

instructs the FTP client to display a pound sign (#) each time 

it sends or receives a block of data. See also FTP client. 

hash2 vb. To be mapped to a numerical value by a transformation 

known as a hashing function. Hashing is used to 

convert an identifier or key, meaningful to a user, into a 

value for the location of the corresponding data in a structure, 

such as a table. For example, given the key MOUSE 

and a hashing function that added up the ASCII values of 

the characters, divided the total by 127, and took the remainder, 

MOUSE would hash to 12 and the data identified by 

H

H 

hash coding head 

MOUSE would be found among the items in entry 12 in 

the table. 

hash coding n. See hash2 . 

hashing algorithm n. A formula used to generate hash 

values and digital signatures. Also called: hash function. 

hash search n. A search algorithm that uses hashing to 

find an element of a list. Hash searches are highly efficient 

because the hashing enables direct or almost direct access 

to the target element. See also binary search, hash2 , linear 

search, search algorithm. 

hash total n. An error-checking value derived from the 

addition of a set of numbers taken from data (not necessarily 

numeric data) that is to be processed or manipulated in 

some way. After processing, the hash total is recalculated 

and compared with the original total. If the two do not 

match, the original data has been changed in some way. 

hash value n. A value used in creating digital signatures. 

This value is generated by imposing a hashing algorithm 

onto a message. This value is then transformed, or signed, 

by a private key to produce a digital signature. Also 

called: message digest. 

Haskell n. A functional programming language based on 

lambda calculus and suitable for the creation of applications 

that need to be highly modifiable. 

Hayes-compatible adj. Responding to the same set of 

commands as the modems manufactured by Hayes Microcomputer 

Products. This command set has become the de 

facto standard for microcomputer modems. 

HCM n. See hardware cryptographic module. 

HDBMS n. See hierarchical database management system. 

HDCP n. Acronym for High-bandwidth Digital Content 

Protection. An encryption and authentication specification 

created by Intel for Digital Video Interface (DVI) devices 

such as digital cameras, high-definition televisions, and 

video disk players. HDCP is designed to protect transmissions 

between DVI devices from being copied. 

HDF n. See Hierarchical Data Format. 

HDLC n. Acronym for High-level Data Link Control. A 

protocol for information transfer adopted by the ISO. 

HDLC is a bit-oriented, synchronous protocol that applies 

to the data-link (message-packaging) layer (layer 2 of the 

ISO/OSI reference model) for computer-to-microcomputer 

communications. Messages are transmitted in units called 

frames, which can contain differing amounts of data but 

248 

which must be organized in a particular way. See also 

frame (definition 1), ISO/OSI reference model. 

HDML n. Acronym for Handheld Device Markup Language. 

A simple, first-generation markup language used to 

define hypertext-like content and applications for wireless 

and other handheld devices with small displays. This language 

is used primarily to create Web sites viewed via 

wireless phones and personal digital assistants (PDAs). 

HDML provides content consisting mainly of text with 

limited graphics. See also WML. 

HDSL n. Acronym for High-bit-rate Digital Subscriber 

Line. A form of DSL, HDSL is a protocol for digital transmission 

of data over standard copper telecommunications 

lines (as opposed to fiber-optic lines) at rates of 1.544 

Mbps in both directions. Also called: High-data-rate Digital 

Subscriber Line. See also DSL. 

HDTP n. Acronym for Handheld Device Transport Protocol. 

Protocol that enables a handheld device, such as a 

wireless phone or personal digital assistant (PDA), to 

access the Internet. HDTP regulates the input and output 

of data interpreted by the device’s microbrowser. See also 

WAP. 

HDTV n. Acronym for High-Definition TeleVision. A 

new television display standard that doubles the existing 

screen resolution and increases the screen aspect ratio 

from 4:3 to 16:9. This aspect ratio creates a television 

screen that is shaped like a movie screen. 

HDTV-over-IP n. An Internet-based delivery option for 

High Definition Television (HDTV). HDTV-over-IP provides 

options for new and expanded services to ISPs, cable 

companies, telecommunications carriers, and business 

intranets, with its most extensive use in education. Universities 

use high-speed networks such as Internet2 to provide 

the intensive bandwidth demanded by HDTV-over-IP. 

Because HDTV-over-IP offers extreme image fidelity and 

sharpness, it is seen as ideal for delivery of distance education 

courses requiring precise visuals for which conventional 

video cannot provide sufficient resolution. Also 

called: iHDTV. 

head n. 1. The read/write mechanism in a disk or tape 

drive. It converts changes in the magnetic field of the 

material on the disk or tape surface to changing electrical 

signals and vice versa. Disk drives usually contain one 

head for each surface that can be read from and written to. 

2. In relation to software or documents, the top or beginning 

of something. 3. In HTML, a section of coding that 

precedes the body of a document and is used to describe

head arm heap 

the document itself (title, author, and so on) rather than the 

elements within the document. 

head arm n. See access arm. 

head-cleaning device n. An apparatus for applying a 

small amount of cleaning fluid to a magnetic head to 

remove accumulated debris. 

head crash n. A hard disk failure in which a read/write 

head, normally supported on a cushion of air only millionths 

of an inch thick, comes into contact with the platter, 

damaging the magnetic coating in which data is recorded. 

Still more damage occurs when the head picks up material 

gouged out of the surface and pushes it. A head crash can be 

caused by mechanical failure or by heavy shaking of the 

disk drive. If the crash occurs on a directory track, the 

whole disk may become instantly unreadable. 

header n. 1. In word processing or printing, text that is to 

appear at the top of pages. A header might be specified for 

the first page, all pages after the first, even pages, or odd 

pages. It usually includes the page number and may also 

show the date, the title, or other information about a document. 

Also called: heading, running head. Compare 

footer. 2. An information structure that precedes and identifies 

the information that follows, such as a block of bytes 

in communications, a file on a disk, a set of records in a 

database, or an executable program. 3. One or more lines 

in a program that identify and describe for human readers 

the program, function, or procedure that follows. 

header file n. A file that is identified to be included at the 

beginning of a program in a language such as C and that 

contains the definitions of data types and declarations of 

variables used by the functions in the program. 

header label n. An initial structure, such as an opening 

record, in the linear organization of a file or communication 

that describes the length, type, and structure of the 

data that follows. Compare trailer label (definition 1). 

header record n. The first record in a sequence of 

records. 

heading n. See header (definition 1). 

headless computer n. A computer system that does not 

have a keyboard, mouse, or video monitor during normal 

operation. 

head-mounted device n. A headset or helmet used with 

virtual reality systems ranging from gaming to military, 

medical, educational, and industrial applications. A headmounted 

device contains small screens that display images 

249 

in such a way that the headset allows the wearer to view 

and move about in a three-dimensional, virtual world. The 

simulated environment is generated by a controlling computer, 

which adjusts the images in accordance with the 

wearer’s head and body movements. A head-mounted device 

can include audio capability and is often used with an 

interactive input device, such as a joystick or glove. Acronym: 

HMD. See also virtual reality, wearable computer. 

head-per-track disk drive n. A disk drive that has one 

read/write head for every data track. Such a disk drive has 

a very low seek time because the heads do not have to 

move across the disk surface to the required track for reading 

and writing. Because read/write heads are expensive, 

this type of drive is uncommon. 

head positioning n. The process of moving the read/ 

write head of a disk drive to the proper track for reading 

and writing. 

head slot n. The oblong opening in the jacket of a floppy 

disk that provides access to the magnetic surface of the 

disk for the read/write head. See the illustration. 

2DD 

Double sided/ 

Double density 

Head slot 

FOHgn04.eps 

Head slot. 

head switching n. The process of electrically switching 

among multiple read/write heads in a disk drive. 

heap n. 1. A portion of memory reserved for a program 

to use for the temporary storage of data structures whose 

existence or size cannot be determined until the program 

is running. To build and use such elements, programming 

languages such as C and Pascal include functions and 

procedures for requesting free memory from the heap, 

H

H 

heap sort henry 

accessing it, and freeing it when it is no longer needed. In 

contrast to stack memory, heap memory blocks are not 

freed in reverse of the order in which they were allocated, 

so free blocks may be interspersed with blocks that are in 

use. As the program continues running, the blocks may 

have to be moved around so that small free blocks can be 

merged together into larger ones to meet the program’s 

needs. See also garbage collection. Compare stack. 2. A 

complete binary tree in which the value of any node is not 

exceeded by the value of either of its children. See also 

binary tree. 

heap sort or heapsort n. A space-efficient sorting 

method that first arranges the key fields into a heap structure; 

then repeatedly removes the root of the heap, which 

must, by definition, have the largest key; and re-forms the 

heap. See also heap (definition 1). 

heat pipe n. A cooling device consisting of a sealed 

metal tube containing a liquid and a wick. The liquid 

evaporates at the hot end; the vapor spreads along the tube 

to the cold end, where it condenses onto the wick; the liquid 

flows back along the wick to the hot end by capillary 

action. Heat pipes have been used in Pentium-based laptop 

computers, which have high cooling requirements and little 

room for conventional heat sinks. Compare heat sink. 

heat sink n. A device that absorbs and dissipates heat 

produced by an electrical component, such as an integrated 

circuit, to prevent overheating. Heat sinks are usually 

made of metal and often have fins that assist in 

transferring heat to the atmosphere. See the illustration. 

Compare heat pipe. 

Heat sink 

Computer chip 

FOHgn05.eps 

Heat sink. 

hecto- prefix Metric prefix meaning 102 (one hundred). 

HEL n. See hardware emulation layer. 

hello, world n. The output of the first program in Brian 

Kernighan and Dennis Ritchie’s The C Programming Language. 

The program is traditionally the first test a C programmer 

makes in a new environment. 

help n. 1. The capability of many programs and operating 

systems to display advice or instructions for using their 

250 

features when so requested by the user, as by a screen button 

or a menu item or a function key. The user can access 

help without interrupting work in progress or leafing 

through a manual. Some help facilities are context-sensitive, 

meaning that the user receives information specific to 

the task or command being attempted. Also called: online 

help. 2. In many applications, a command that displays an 

explanation of another command that follows it. For 

instance, in many FTP programs, the command help can 

be followed by other commands, such as cd (change directory) 

or ls (list files and directories), to discover the purpose 

of these other commands. 3. In versions 5 and 6 of 

MS-DOS, the command used to request information about 

MS-DOS commands, command parameters, and switches. 

Help n. An item on a menu bar in a graphical user interface 

that enables the user to access the help feature of the 

present application. See also graphical user interface, help 

(definition 1), menu bar. 

help desk n. 1. Technical support staff who help solve 

users’ problems with hardware or software systems or 

refer such problems to those who can solve them. Help 

desks are typically run by larger organizations, such as 

corporations, universities, or vendors to corporations, to 

assist users in the organization. 2. A software application 

for tracking problems with hardware and software and 

their solutions. 

helper n. See helper application. 

helper application n. An application intended to be 

launched by a Web browser when the browser downloads 

a file that it is not able to process itself. Examples of 

helper applications are sound and movie players. Helper 

applications generally must be obtained and installed by 

users; they usually are not included in the browser itself. 

Many current Web browsers no longer require helper 

applications for common multimedia file formats. Also 

called: helper program. Compare ActiveX controls, plugin 


helper program n. See helper application. 

Help key n. A key on the keyboard that the user can press 

to request help. See also function key, help (definition 1). 

help screen n. A screen of information that is displayed 

when the user requests help. See also help (definition 1). 

henry n. The unit of inductance. A current changing at a 

rate of one ampere per second will generate one volt 

across an inductance of one henry. In practice, a henry is a

Hercules Graphics Card hide 

very large unit; inductances measured in millihenries (mH 

= 10 –3 H), microhenries (H = 10 –6 H), or nanohenries 

(nH = 10 –9 H) are more commonly encountered. 

Abbreviated H. See also inductance. 

Hercules Graphics Card n. See HGC. 

hertz n. The unit of frequency measurement; one cycle 

(of a periodic event such as a waveform) per second. Frequencies 

of interest in computers and electronic devices 

are often measured in kilohertz (kHz = 1000 Hz = 103 Hz), 

megahertz (MHz = 1000 kHz = 106 Hz), gigahertz (GHz = 

1000 MHz = 109 Hz), or terahertz (THz = 1000 GHz = 

1012 Hz). Abbreviated Hz. 

hertz time n. See clock rate. 

heterogeneous environment n. A computing milieu, 

usually within an organization, in which hardware and 

software from two or more manufacturers are used. Compare 

homogeneous environment. 

heuristic n. An approach or algorithm that leads to a correct 

solution of a programming task by nonrigorous or 

self-learning means. One approach to programming is first 

to develop a heuristic and then to improve on it. The term 

comes from Greek heuriskein (“to discover, find out”) and 

is related to “eureka” (“I have found it”). 

Hewlett-Packard Graphics Language n. See HPGL. 

Hewlett-Packard Printer Control Language n. See 

Printer Control Language. 

hex n. See hexadecimal. 

hexadecimal adj. Using 16 rather than 10 as the base for 

representing numbers. The hexadecimal system uses the 

digits 0 through 9 and the letters A through F (uppercase 

or lowercase) to represent the decimal numbers 0 through 

15. One hexadecimal digit is equivalent to 4 bits, and 1 

byte can be expressed by two hexadecimal digits. For 

example, binary 0101 0011 corresponds to hexadecimal 

53. To prevent confusion with decimal numbers, hexadecimal 

numbers in programs or documentation are usually 

followed by H or preceded by &, $, or 0x. Thus, 10H = 

decimal 16; 100H = decimal 162 = decimal 256. Equivalents 

and conversion tables for binary, decimal, hexadecimal, 

and octal numbers are given in Appendix E. Also 

called: hex. 

hexadecimal conversion n. Conversion of a number to 

or from the hexadecimal system. See Appendix E. 

HFS n. See Hierarchical File System. 

251 

HFS+ n. Acronym for Hierarchal File System Plus. The 

primary file system format available on the Macintosh 

operating system. With Mac OS 8.1, HFS+ replaced the 

earlier HFS format, adding support for names longer than 

31 characters and Unicode representation of file and directory 

names. Also called: Mac OS Extended format. 

HGA n. Acronym for Hercules Graphics Adapter. See 

HGC. 

HGC n. Acronym for Hercules Graphics Card. A video 

adapter introduced in 1982 by Hercules Computer Technology 

for IBM personal computers and compatibles and 

now superseded by VGA and its successors. It offered a 

monochrome graphics mode with 720 x 348 pixels. See 

also VGA. 

HGC Plus n. A video adapter, introduced in 1986 by Hercules 

Computer Technology, that offered additional video 

buffer space to store 12 fonts of 256 characters each, 

which could be used for graphics characters. 

HHOK n. Acronym for ha, ha, only kidding. An indication 

of humor or facetiousness often used in e-mail and online 


hibernation n. A state in which a computer shuts down 

after saving everything in memory to the hard disk. When 

the computer is powered on, programs and documents that 

were open are restored to the desktop. See also standby. 

hidden file n. A file that, in order to protect it from deletion 

or modification, is not shown in the normal listing of 

the files contained in a directory. Such a file is often used 

to store code or data critical to the operating system. 

hidden line n. In any application, such as a CAD program, 

that represents solid three-dimensional objects, a 

line in a drawing that would (or should) be hidden if the 

object were perceived as a solid construction. The process 

of removing such lines in an application is called hiddenline 

removal. See also CAD, hidden surface. 

hidden surface n. A surface of a solid three-dimensional 

object, such as one represented in a CAD program, 

that would not be visible when the object is 

viewed from a particular angle—for example, the underside 

of the wing of an airplane when viewed from above. 

See also CAD, hidden line. 

hide vb. To temporarily remove the onscreen display of an 

application’s active window while leaving the application 

running. Windows that have been hidden are returned to 

active display by issuing the appropriate command to the 


H

H 

hierarchical high byte 

hierarchical adj. Of, relating to, or organized as a hierarchy. 

See also hierarchy. 

hierarchical computer network n. 1. A network in 

which one host computer controls a number of smaller 

computers, which may in turn act as hosts to a group of 

PC workstations. 2. A network in which control functions 

are organized according to a hierarchy and in which data 

processing tasks may be distributed. 

hierarchical database n. A database in which records 

are grouped in such a way that their relationships form a 

branching, treelike structure. This type of database structure, 

most commonly used with databases for large computers, 

is well suited for organizing information that 

breaks down logically into successively greater levels of 

detail. The organization of records in a hierarchical database 

should reflect the most common or the most timecritical 

types of access expected. 

hierarchical database management system n. A 

database management system that supports a hierarchical 

model. Acronym: HDBMS. See also hierarchical model. 

Hierarchical Data Format n. A file format for storing 

multiple types of graphical and numerical data and transferring 

them between different types of machines, together 

with a library of functions for handling such files in a uniform 

way. NCSA developed and supports the file function 

and library and has placed them in the public domain. 

Hierarchical Data Format files are supported on most 

common types of computers. The format can easily be 

extended to accommodate additional data models. The 

library functions have both FORTRAN and C interfaces. 

Acronym: HDF. See also NCSA (definition 1). 

hierarchical file system n. A system for organizing files 

on a disk in which files are contained in directories or 

folders, each of which can contain other directories as well 

as files. The main directory for the disk is called the root; 

the chain of directories from the root to a particular file is 

called the path. See also hierarchy, path (definition 2), 

root. Compare flat file system. 

Hierarchical File System n. A tree-structured file system 

used on the Apple Macintosh in which folders can be 

nested within other folders. Acronym: HFS. See also hierarchy, 

path (definition 2), root. Compare flat file system. 

252 

hierarchical menu n. A menu that has one or more submenus. 

Such a menu/submenu arrangement is hierarchical 

because each level subsumes the next. 

hierarchical model n. A model used in database management 

in which each record may be the “parent” of one 

or more child records, which may or may not have the 

same structure as the parent; a record can have no more 

than one parent. Conceptually, therefore, a hierarchical 

model can be, and usually is, regarded as a tree. The individual 

records are not necessarily contained in the same 

file. See also tree. 

Hierarchical Storage Management n. See HSM. 

hierarchy n. A type of organization that, like a tree, 

branches into more specific units, each of which is 

“owned” by the higher-level unit immediately above. 

Hierarchies are characteristic of several aspects of computing 

because they provide organizational frameworks 

that can reflect logical links, or relationships, between 

separate records, files, or pieces of equipment. For example, 

hierarchies are used in organizing related files on a 

disk, related records in a database, and related (interconnected) 

devices on a network. In applications such as 

spreadsheets, hierarchies of a sort are used to establish the 

order of precedence in which arithmetic operations are to 

be performed by the computer. See also hierarchical file 

system. 

high availability n. The ability of a system or device to 

be usable when it is needed. When expressed as a percentage, 

high availability is the actual service time 

divided by the required service time. Although high 

availability does not guarantee that a system will have no 

downtime, a network often is considered highly available 

if it achieves 99.999 percent network uptime. Also 

called: RAS (reliability/availability/serviceability), fault 

resilience. See also five-nines availability, four-nines 

availability, three-nines availability, two-nines availability. 

Compare fault tolerance. 

High-bit-rate Digital Subscriber Line n. See HDSL. 

high byte n. The byte containing the most significant bits 

(bits 8 through 15) in a 2-byte grouping representing a 16bit 

(bits 0 through 15) value. See the illustration. See also 

hexadecimal.

hierarchical high-capacity menu CD-ROM 

high resolution 

High byte 

15 14 13 12 11 10 9 8 

0 

1 

1 

0 

1 

1 

0 0 

Low byte 

6 C A 2 

Hexadecimal F0Hgn06.eps value 

High byte. The high byte is binary 01101100 or hexadecimal 6C or decimal 108. 

high-capacity CD-ROM n. See digital video disc. 

High Contrast n. An accessibility display feature in 

Microsoft Windows that instructs programs to use the 

color scheme specified in the Settings dialog box and to 

increase legibility whenever possible. 

High-data-rate Digital Subscriber Line n. See HDSL. 

High-Definition Television n. See HDTV. 

high-density disk n. 1. A 3.5-inch floppy disk that can 

hold 1.44 MB. Compare double-density disk. 2. A 5.25inch 

floppy disk that can hold 1.2 MB. Compare doubledensity 

disk. 

high DOS memory n. See high memory. 

high-end adj. A descriptive term for something that uses 

the latest technology to maximize performance. There is 

usually a direct correlation between high-end technology 

and higher prices. 

High-level Data Link Control n. See HDLC. 

high-level language n. A computer language that provides 

a level of abstraction from the underlying machine 

language. Statements in a high-level language generally 

use keywords similar to English and translate into more 

than one machine-language instruction. In practice, every 

computer language above assembly language is a highlevel 

language. Acronym: HLL. Also called: high-order 

language. Compare assembly language. 

highlight vb. To alter the appearance of displayed characters 

as a means of calling attention to them, as by displaying 

them in reverse video (light on dark rather than dark on light, 

and vice versa) or with greater intensity. Highlighting is used 

to indicate an item, such as an option on a menu or text in 

a word processor, that is to be acted on in some way. 

high memory n. 1. Memory locations addressed by the 

largest numbers. 2. In IBM PCs and compatibles, the 

range of addresses between 640 kilobytes and 1 megabyte, 

7 

1 

6 

0 

5 

1 

4 

0 

3 

0 

2 

0 

1 

1 

0 

0 

Bit position 

Bit value 

253 

used primarily for the ROM BIOS and control hardware 

such as the video adapter and input/output ports. Compare 

low memory. 

high memory area n. In IBM PCs and compatibles, the 

64-kilobyte range of addresses immediately above 1 

megabyte. By means of the file HIMEM.SYS, MS-DOS 

(versions 5 and later) can move portions of itself into the 

high memory area, thereby increasing the amount of conventional 

memory available for applications. Acronym: 

HMA. See also conventional memory, expanded memory. 

high-order adj. Having the most weight or significance. 

The high-order term usually appears first or leftmost in 

writing systems based on the Roman alphabet or Arabic 

numerals. For example, in the 2-byte hex value 6CA2, 

the high-order byte 6C has a value by itself of decimal 

108 but counts for 108 x 256 = 27,648 in the group, 

whereas the low-order byte A2 counts only for decimal 

162. Compare low-order. 

high-order language n. See high-level language. 

highpass filter n. An electronic circuit that passes all frequencies 

in a signal that are above a specified frequency. 

Compare bandpass filter, lowpass filter. 

High-Performance File System n. See HPFS. 

High-Performance Parallel Interface n. See HIPPI. 

High-Performance Serial Bus n. See IEEE 1394. 

high-persistence phosphor n. A phosphor that glows for 

a relatively long time after being struck by electrons. Highpersistence 

phosphors are used in direct view storage tubes, 

but most CRTs (cathode-ray tubes) use phosphors of relatively 

low persistence so that their images can be changed 

quickly without “ghosts” of earlier images remaining on the 

screen. See also CRT, direct view storage tube. 

high resolution n. The capability for reproducing text 

and graphics with relative clarity and fineness of detail. 

H

H 

High Sierra specification Hollerith tabulating/recording machine 

High resolution is achieved by using a large number of 

pixels (dots) to create an image in a given area. For screen 

displays, the resolution is stated in terms of the total number 

of pixels in the horizontal and vertical dimensions. For 

example, the VGA video adapter has a resolution of 640 by 

480 pixels. In printing, resolution refers to the number of 

dots per inch (dpi) produced by the printer, such as 300 to 

600 dpi for a desktop laser or ink-jet printer or 1000 to 2000 

dpi for a production-quality imagesetter. Also called: hi-res. 

High Sierra specification n. An industry-wide format 

specification for the logical structure, file structure, and 

record structures on a CD-ROM. The specification is 

named after a meeting on CD-ROM held near Lake Tahoe 

in November 1985. It served as the basis for the international 

standard, ISO 9660. 

high tech n. 1. Cutting-edge applied science and engineering, 

usually involving computers and electronics. 

2. Sophisticated, often complex, specialized technical 

innovation. 

hijackware n. Software that appears to be a useful plugin 

or utility, but which will take over a user’s Internet surfing 

or shopping activity by creating pop-up advertisements 

for competing products or redirecting the user to 

competitor’s Web sites. Typically users will download and 

install a hijackware product believing it to be free browser 

enhancement software. Businesses pay the makers of 

hijackware products to push their shopping sites and product 

advertising onto Internet users, sometimes to the point 

of denying the user access to competing Web sites. See 

also gatored. 

Hijiri calendar n. The lunar calendar used in Islamic 

countries. Compare Gregorian calendar, Julian calendar. 

HIPPI n. Acronym for High-Performance Parallel Interface. 

An ANSI communications standard used with 

supercomputers. 

hi-res n. See high resolution. 

histogram n. A chart consisting of horizontal or vertical 

bars, the widths or heights of which represent the values of 

certain data. 

history n. A list of the user’s actions within a program, 

such as commands entered in an operating system shell, 

menus passed through using Gopher, or links followed 

using a Web browser. 

hit n. 1. A successful retrieval of data from a cache rather 

than from the slower hard disk or RAM. See also cache, 

254 

hard disk, RAM. 2. A successful retrieval of a record 

matching a query in a database. See also query (definition 

1), record1 . 3. Retrieval of a file from a Web site. Each 

separate file accessed on a Web page, including HTML 

documents and graphics, counts as a hit. 4. In computer 

war and other games, when a character is successfully 

fired on, attacked, or otherwise taken out. 

hit points n. Used in most computer and console war 

games to refer to the amount of times a player can be damaged 

before his or her character passes out or dies. 

hive n. One of the top-level sets of keys, subkeys, and values 

in Windows 9x, Windows NT, Windows 2000, and 

Windows CE Registries. The term was created by a 

Microsoft programmer who thought the structure of the Registry 

resembled a beehive. Each hive is a permanent part of 

the Registry and is associated with a set of files containing 

information related to the configuration (applications, user 

preferences, devices, and so on) of the computer on which 

the operating system is installed. Registry hives include 

HKEY_LOCAL_MACHINE, HKEY_CURRENT_USER, 

and HKEY_CURRENT_CONFIG. See also Registry. 

HKEY n. Short for hkey handle. In Windows 9x, Windows 

NT, and Windows 2000, a handle to a Registry key in which 

configuration information is stored. Each key leads to subkeys 

containing configuration information that, in earlier 

versions of Windows, was stored in .ini files. For example, 

the handle key HKEY_CURRENT_USERControl Panel 

leads to the subkey for the Windows Desktop. See also handle 


HLL n. See high-level language. 

HLS n. Acronym for hue-lightness-saturation. See HSB. 

HMA n. See high memory area. 

HMD n. See head-mounted device. 

Hollerith tabulating/recording machine n. An electromechanical 

machine invented by Herman Hollerith in 

the late 1800s for processing data supplied in the form of 

holes punched at predetermined locations in cards. Contacts 

made through the holes completed electrical circuits, 

allowing signals to be passed to counting and 

tabulating devices. This machine is considered to have 

reduced the time required to finish the 1890 U.S. census 

by two-thirds. Such machines were manufactured in the 

early 1900s by Hollerith’s Tabulating Machine Company, 

which eventually became the International Business 

Machines Corporation (IBM).

hologram homogeneous environment 

hologram n. A three-dimensional image record created 

by holography. The hologram consists of a light interference 

pattern preserved in a medium such as photographic 

film. When suitably illuminated, it produces an image that 

changes its appearance as the viewer changes viewing 

angle. See also holography. 

holography n. A method of reproducing three-dimensional 

visual images by recording light interference patterns 

on a medium such as photographic film, creating a 

hologram. See also hologram. 

holy war n. 1. A widespread and acrimonious debate 

among computer professionals over some aspect of the 

computer field, such as the debate over use of the GOTO 

statement in programming or that over big-endian versus 

little-endian data storage. 2. An argument in a mailing list, 

newsgroup, or other forum over some emotional and controversial 

topic, such as abortion or Northern Ireland. 

Introducing a holy war that is off the purported topic of the 

forum is considered a violation of netiquette. 

home n. A beginning position, such as the upper left corner 

of a character-based display, the left end of a line of 

text, cell A1 of a spreadsheet, or the top of a document. 

home automation n. The process of programmatically 

controlling appliances, lighting, heating and cooling systems, 

and other devices in a home network. See also home 

network (definition 1). 

homebrew n. Hardware or software developed by an individual 

at home or by a company for its own use rather than 

as a commercial product, such as hardware developed by 

electronics hobbyists when microcomputers first appeared 

in the 1970s. 

home computer n. A personal computer designed and 

priced for use in the home. 

home controller n. A software or hardware interface 

used to control the systems in a home network for home 

automation. 

home directory n. A directory associated with a user 

account under UNIX. The home directory is the current 

directory when the user first logs in, and the user can 

return to it by entering the command cd (change directory) 

without a pathname. The user’s files will ordinarily be 

stored in the home directory and its descendants. 

homegrown software n. Software developed by an individual 

at home rather than in a professional environment. 

255 

Most public-domain and shareware programs are created 

this way. 

Home key n. A key, found on most keyboards, whose 

function usually involves sending the cursor to some type 

of home position in an application. See also home. 

home network n. 1. A communications network in a 

home or building used for home automation. Home networks 

can use wiring (existing or new) or wireless connections. 

See also home automation, home controller. 

2. Two or more computers in a home that are interconnected 

to form a local area network (LAN). 

home office n. 1. An office set up within a residence. 

2. The main headquarters of a company. 

home page n. 1. A document intended to serve as a starting 

point in a hypertext system, especially the World Wide 

Web. A home page is called a start page in Microsoft 

Internet Explorer. 2. An entry page for a set of Web pages 

and other files in a Web site. 3. A personal Web page, usually 

for an individual. 

Home Phoneline Networking Alliance n. See 

HomePNA. 

HomePNA n. Short for Home Phoneline Networking 

Alliance. An association of more than 100 companies 

working toward the adoption of a unified technology for 

setting up home networks over existing telephone wiring. 

Phoneline networking allows multiple PCs, printers, and 

peripheral devices to be connected for such purposes as 

multiplayer gaming, sharing printers and other peripherals, 

and rapid downloads over the Internet. The alliance 

was founded by a number of companies including IBM, 

Intel, AT&T, and Lucent Technologies. 

Home Radio Frequency n. See HomeRF. 

home record n. See header record. 

HomeRF n. Acronym for Home Radio Frequency. A 

wireless home-networking specification that uses the 

2.4-GHz frequency band to communicate between computers, 

peripherals, cordless phones, and other devices. 

HomeRF is supported by Siemens, Compaq, Motorola, 

National Semiconductor, Proxim, and other companies. 

homogeneous environment n. A computing milieu, 

usually within an organization, in which only one manufacturer’s 

hardware and one manufacturer’s software are 

used. Compare heterogeneous environment. 

H

H 

homogeneous network Host Integration Server 

homogeneous network n. A network on which all the 

hosts are similar and only one protocol is used. 

Honeynet Project n. A nonprofit security research group 

created to collect and analyze data on hacking tools and 

methods by maintaining a decoy network of computers 

that is potentially attractive to hackers. The Honeynet 

Project sets up entire networks of computers in different 

combinations of operating systems and security to realistically 

simulate those used in businesses and organizations. 

Hackers are lured to the network where all inbound and 

outbound data is captured and contained to help researchers 

learn about hacker tactics and motives. 

honeypot n. A security program designed to lure and distract 

a network attacker with decoy data. The honeypot 

appears to be a system that the intruder would like to crack 

but which, in reality, is safely separated from the actual 

network. This allows network administrators to observe 

attackers and study their activities without the intruders 

knowing they are being monitored. Honeypot programs 

get their name from the “like a bear to honey” metaphor. 

honker n. A slang term for a hacker, the term originated 

in China. The Honker Union of China is an active group of 

Chinese hackers with nationalistic or hacktivist aims. The 

Honker Union of China has claimed patriotic motivation 

for defacing Japanese and U.S. Web sites, hacking U.S. 

networks, and releasing the Lion worm and other malicious 

programs. See also hacktivist, Lion worm. 

hook n. A location in a routine or program in which the 

programmer can connect or insert other routines for the 

purpose of debugging or enhancing functionality. 

hop n. In data communications, one segment of the path 

between routers on a geographically dispersed network. A 

hop is comparable to one “leg” of a journey that includes 

intervening stops between the starting point and the destination. 

The distance between each of those stops (routers) 

would be a communications hop. 

horizontal blanking interval n. See blanking, horizontal 

retrace. 

horizontal flyback n. See horizontal retrace. 

horizontal market n. A broad category of business activity, 

such as accounting or inventory control, that carries 

across many types of business. Compare vertical market. 

horizontal market software n. Application programs, 

such as word processors, that can be used in all types of 

business, as opposed to those geared for a certain industry. 

256 

horizontal retrace n. The movement of the electron 

beam in a raster-scan video display from the right end of 

one scan line to the left end (the beginning) of the next. 

During horizontal retrace, the electron beam is turned off, 

so the time required for the beam to move is called the 

horizontal blanking interval. See also blanking. Compare 

vertical retrace. 

horizontal scrolling n. A feature of programs such as 

word processors and spreadsheets that enables the user to 

scroll left and right to display information beyond the 

horizontal limits of the screen (or window, in a graphical 

user interface). 

horizontal synchronization n. On raster displays, the 

timing produced by a signal that controls the sweep of the 

display’s electron beam as it moves from left to right and 

back again to form an image line by line. The horizontal 

synchronization signal is usually controlled by a circuit 

known as a phase-locked loop, which maintains a constant 

precise frequency so that a clear image is formed. 

host1 n. 1. The main computer in a mainframe or minicomputer 

environment—that is, the computer to which 

terminals are connected. 2. In PC-based networks, a computer 

that provides access to other computers. 3. On the 

Internet or other large networks, a server computer that 

has access to other computers on the network. A host computer 

provides services, such as news, mail, or data, to 

computers that connect to it. 

host2 vb. To provide services to client computers that connect 

from remote locations—for example, to offer Internet 

access or to be the source for a news or mail service. 

host adapter n. A device for connecting a peripheral to 

the main computer, typically in the form of an expansion 

card. Also called: controller, host bus adapter. 

hosting n. The practice of providing computer and communication 

facilities to businesses or individuals, especially 

for use in creating Web and electronic commerce sites. A 

hosting service can provide high-speed access to the Internet, 

redundant power and data storage, and 24-hour maintenance 

at lower cost than implementing the same services 

independently. See also host2 , virtual hosting. 

Host Integration Server n. A software application from 

Microsoft Corporation to allow businesses to integrate 

existing application, data, and network assets with new 

business applications and technologies. Host Integration 

Server preserves a company’s existing legacy infrastructure 

and investments, while providing out-of-the-box

host language hot spot 

development tools that enable integration with client/ 

server and Web networks. 

host language n. 1. The machine language of a CPU. 

2. A high-level language that is specifically supported by 

an operating system with its toolbox routines and native 

development systems. 

host name n. The name of a specific server on a specific 

network within the Internet, leftmost in the complete host 

specification. For example, www.microsoft.com indicates 

the server called “www” within the network at Microsoft 

Corporation. 

host not responding n. An error message issued by an 

Internet client indicating that the computer to which a 

request has been sent is refusing the connection or is otherwise 

unavailable to respond to the request. 

host replacement n. See rehosting. 

host timed out n. An error condition that occurs when a 

remote system fails to respond within a reasonable amount 

of time (a few minutes) during an exchange of data over a 

TCP connection. This condition may mean that the remote 

system has crashed or been disconnected from the network. 

The error message the user sees may or may not be 

phrased in this manner. See also TCP. Compare host not 

responding. 

host unreachable n. An error condition that occurs 

when the particular computer to which the user wishes to 

connect over a TCP/IP network cannot be accessed on its 

LAN because it is either down or disconnected from the 

network. The error message the user sees may or may not 

be phrased in this manner. See also TCP/IP. 

hot adj. Of special or urgent interest, or deemed popular. 

HotBot n. An Internet search engine developed by Inktomi 

Corporation and HotWired, Inc. Using Slurp, a Web 

robot, this tool maintains a database of documents that can 

be matched to key words entered by the user, in a fashion 

similar to other search engines. HotBot incorporates many 

workstations in parallel to search and index Web pages. 

See also spider. 

hot carrier diode n. See Schottky diode. 

hot docking n. The process of attaching a laptop computer 

to a docking station while the computer is running, and 

automatically activating the docking station’s video display 

and other functions. See also docking station, laptop. 

hot insertion n. The insertion of a device or card while 

there is power to the system. Many newer laptops allow 

257 

for hot insertion of PCMCIA cards. High-end servers may 

also allow hot insertion to reduce downtimes. 

HotJava n. A Web browser developed by Sun Microsystems, 

Inc., that is optimized to run Java applications and 

applets embedded in Web pages. See also applet, Java, 

Java applet. 

hot key1 n. A keystroke or combination of keystrokes that 

switches the user to a different program, often a terminateand-stay-resident 

(TSR) program or the operating system 

user interface. See also TSR. 

hot key2 vb. To transfer to a different program by pressing 

a hot key. 

hot link n. A connection between two programs that 

instructs the second program to make changes to data 

when changes occur in the first program. For example, a 

word processor or desktop publishing program could 

update a document based on information obtained from a 

database through a hot link. See hyperlink. 

hotlist n. A list of frequently accessed items, such as Web 

pages in a Web browser, from which the user can select 

one. The hotlist of Web pages is called the bookmark list 

in Netscape Navigator and Lynx and is called the Favorites 

folder in Microsoft Internet Explorer. 

Hotmail n. A Web-based e-mail service launched in 

1996 and owned and operated by Microsoft since 

December 1997. Hotmail provides free e-mail accounts 

and can be used by anyone with Internet access and Web 

browsing software. 

hot plugging n. A feature that allows equipment to be 

connected to an active device, such as a computer, while 

the device is powered on. 

hot-potato routing n. A packet routing scheme that 

relies on keeping data moving, even if it may temporarily 

move away from its final destination. Also called: 

deflection routing. 

hot spare n. In RAID (redundant array of independent 

disks) systems, a spare drive in the array that is configured 

as a backup on which data can be rebuilt in the 

event that another drive fails. Hot spares are kept on line 

and do not require operator intervention to be activated. 

See also RAID. 

hot spot n. The position in a mouse pointer, such as the 

position at the tip of an arrow or the intersection of the 

lines in a cross, that marks the exact location that will be 

affected by a mouse action, such as a button press. 

H

H 

hot swapping HTML 

hot swapping n. See hot plugging. 

HotSync n. Software application from Palm that permits 

data synchronization between a Palm handheld computing 

device and another computing device, such as a laptop or 

personal computer. The synchronization occurs via a cable 

connection or wirelessly (for example, via infrared signals). 

HotWired n. A Web site affiliated with Wired magazine 

that contains news, gossip, and other information about 

the culture of the Internet. 

housekeeping n. Any of various routines, such as updating 

the clock or performing garbage collection, designed 

to keep the system, the environment within which a program 

runs, or the data structures within a program in good 

working order. 

hover button n. Text or an image on a Web page, usually 

in the form of a button, that changes appearance 

when a cursor passes over it. The hover button may 

change color, blink, display a pop-up with additional 

information, or produce other similar effects. Hover buttons 

are usually implemented through ActiveX objects 

and scripting, although hover behavior can also be set 

through HTML attributes. 

HPC n. See handheld PC. 

HPFS n. Acronym for High Performance File System. A 

file system available with OS/2 versions 1.2 and later. See 

also FAT file system, NTFS. 

HPGL n. Acronym for Hewlett-Packard Graphics Language. 

A language originally developed for images destined 

for plotters. An HPGL file consists of instructions 

that a program can use to reconstruct a graphical image. 

HPIB n. Acronym for Hewlett-Packard Interface Bus. See 

general-purpose interface bus. 

HPPCL n. Acronym for Hewlett-Packard Printer Control 

Language. See Printer Control Language. 

HP/UX or HP-UX n. Acronym for Hewlett-Packard 

UNIX. A version of the UNIX operating system specifically 

designed to be run on Hewlett-Packard’s workstations. 

See also UNIX. 

.hqx n. A file extension for a file encoded with BinHex. 

See also BinHex. 

HREF n. Short for hypertext reference. An attribute in an 

HTML document that defines a link to another document 

on the Web. See also HTML. 

258 

HSB n. Acronym for hue-saturation-brightness. A color 

model in which hue is the color itself as placed on a color 

wheel, where 0° is red, 60° is yellow, 120° is green, 180° 

is cyan, 240° is blue, and 300° is magenta; saturation is 

the percentage of the specified hue in the color; and 

brightness is the percentage of white in the color. Also 

called: HLS, HSV, hue. See also color model. Compare 

CMY, RGB. 

HSM n. Short for Hierarchical Storage Management. A 

technology for managing online data and data storage in 

which the medium on which the information resides is 

linked to the frequency with which the information is 

accessed. By migrating data to and from primary (rapidly 

accessed but expensive) and secondary (slower but less 

expensive) storage, HSM maintains often-used information 

on primary storage media and less frequently used 

data on secondary storage such as tape or an optical jukebox. 

Although information resides on different storage 

media, all of it appears to be on line and remains accessible 

to the user. When users request data residing on secondary 

storage, HSM moves the information back to the 

primary storage medium. 

HSV n. Acronym for hue-saturation-value. See HSB. 

H-sync n. See horizontal synchronization. 

HTCPCP n. Acronym for Hyper Text Coffee Pot Control 

Protocol. A protocol defined in jest as an April Fools’ 

Day spoof of open Internet standards. HTCPCP/1.0 was 

proposed in RFC 2324 on April 1, 1998 by Larry Masinter 

of Xerox PARC. In this RFC, Masinter described a protocol 

for controlling, monitoring, and diagnosing coffee pots. 

.htm n. The MS-DOS/Windows 3.x file extension that 

identifies Hypertext Markup Language (HTML) files, 

most commonly used as Web pages. Because MS-DOS 

and Windows 3.x cannot recognize file extensions longer 

than three letters, the .html extension is truncated to three 

letters in those environments. See also HTML. 

.html n. The file extension that identifies Hypertext 

Markup Language (HTML) files, most commonly used as 

Web pages. See also HTML. 

HTML n. Acronym for Hypertext Markup Language. The 

markup language used for documents on the World Wide 

Web. A tag-based notation language used to format documents 

that can then be interpreted and rendered by an 

Internet browser. HTML is an application of SGML (Standard 

Generalized Markup Language) that uses tags to 

mark elements, such as text and graphics, in a document to

HTML attribute HTTPS 

indicate how Web browsers should display these elements 

to the user and should respond to user actions such as activation 

of a link by means of a key press or mouse click. 

HTML 2, defined by the Internet Engineering Task Force 

(IETF), included features of HTML common to all Web 

browsers as of 1994 and was the first version of HTML 

widely used on the World Wide Web. HTML+ was proposed 

for extending HTML 2 in 1994, but it was never 

implemented. HTML 3, which also was never standardized 

or fully implemented by a major browser developer, 

introduced tables. HTML 3.2 incorporated features widely 

implemented as of early 1996, including tables, applets, 

and the ability to flow text around images. HTML 4, the 

latest specification, supports style sheets and scripting languages 

and includes internationalization and accessibility 

features. Future HTML development will be carried out by 

the World Wide Web Consortium (W3C). Most Web 

browsers, notably Netscape Navigator and Internet 

Explorer, recognize HTML tags beyond those included in 

the present standard. See also .htm, .html, SGML, tag 

(definition 3), Web browser. 

HTML attribute n. A value within an HTML tag that 

assigns additional properties to the object being defined. 

Some HTML editing software assigns some attributes 

automatically when you create an object such as a paragraph 

or table. 

HTML code fragment n. HTML code that you add to a 

Web page to create features such as a script, a counter, or a 

scrolling marquee. Often used in the context of webrings 

to add a link and standard graphics or automation to an 

individual page to indicate membership. 

HTML document n. A hypertext document that has been 

coded with HTML. See Web page. 

HTML editor n. A software program used to create and 

modify HTML documents (Web pages). Most HTML editors 

include a method for inserting HTML tags without 

actually having to type out each tag. A number of HTML 

editors will also automatically reformat a document with 

HTML tags, based on formatting codes used by the word 

processing program in which the document was created. 

See also tag (definition 3), Web page. 

HTML extensions n. A feature or setting that is an extension 

to the formal HTML specification. Extensions may 

not be supported by all Web browsers, but they may be 

used widely by Web authors. An example of an extension 

is marquee scrolling text. 

HTML page n. See Web page. 

259 

HTML server control n. An ASP.NET server control that 

belongs to the System.Web.UI.HtmlControls namespace. An 

HTML server control maps directly to an HTML element 

and is declared on an ASP.NET page as an HTML element 

marked by a runat=server attribute. In contrast to Web server 

controls, HTML server controls do not have an 

tag prefix. See also Web server control. 

HTML source n. See source (definition 2). 

HTML source file n. See source (definition 2). 

HTML tag n. See tag (definition 3). 

HTML validation service n. A service used to confirm 

that a Web page uses valid HTML according to the latest 

standard and/or that its hyperlinks are valid. An HTML 

validation service can catch small syntactical errors in 

HTML coding as well as deviations from the HTML standards. 

See also HTML. 

HTTP n. Acronym for Hypertext Transfer Protocol. The 

protocol used to carry requests from a browser to a Web 

server and to transport pages from Web servers back to the 

requesting browser. Although HTTP is almost universally 

used on the Web, it is not an especially secure protocol. 

HTTPd n. Acronym for Hypertext Transfer Protocol Daemon. 

A small, fast HTTP server that was available free 

from NCSA. HTTPd was the predecessor for Apache. 

Also called: HTTP Daemon. See also Apache, HTTP 

server, NCSA (definition 1). 

HTTP Daemon n. See HTTPd. 

HTTP Next Generation n. See HTTP-NG. 

HTTP-NG n. Acronym for Hypertext Transfer Protocol 

Next Generation. A standard under development by the 

World Wide Web Consortium (W3C) for improving performance 

and enabling the addition of features such as 

security. Whereas the current version of HTTP establishes 

a connection each time a request is made, HTTP-NG will 

set up one connection (which consists of separate channels 

for control information and data) for an entire session 

between a particular client and a particular server. 

HTTPS n. 1. Acronym for Hypertext Transfer Protocol 

Secure. A variation of HTTP that provides for encryption 

and transmission through a secure port. HTTPS was 

devised by Netscape and allows HTTP to run over a security 

mechanism known as SSL (Secure Sockets Layer). See 

also HTTP, SSL. 2. Web server software for Windows NT. 

Developed by the European Microsoft Windows NT Academic 

Centre (EMWAC) at the University of Edinburgh, 

H

H 

HTTP server hyperlink 

Scotland, it offers such features as WAIS search capability. 

See also HTTP server, WAIS. 

HTTP server n. 1. Server software that uses HTTP to 

serve up HTML documents and any associated files and 

scripts when requested by a client, such as a Web browser. 

The connection between client and server is usually broken 

after the requested document or file has been served. 

HTTP servers are used on Web and Intranet sites. Also 

called: Web server. See also HTML, HTTP, server (definition 

2). Compare application server. 2. Any machine on 

which an HTTP server program is running. 

HTTP status codes n. Three-digit codes sent by an 

HTTP server that indicate the results of a request for data. 

Codes beginning with 1 respond to requests that the client 

may not have finished sending; with 2, successful 

requests; with 3, further action that the client must take; 

with 4, requests that failed because of client error; and 

with 5, requests that failed because of server error. See 

also 400, 401, 402, 403, 404, HTTP. 

HTTP streaming n. The process of downloading streaming 

digital media using an HTTP server (a standard Internet 

server) rather than a server designed specifically to 

transmit streaming media. HTTP streaming downloads the 

media file onto a computer, which plays the downloaded 

file as it becomes available. See also real-time streaming. 

hub n. In a network, a device joining communication lines 

at a central location, providing a common connection to 

all devices on the network. The term is an analogy to the 

hub of a wheel. See also active hub, switching hub. 

hue n. In the HSB color model, one of the three characteristics 

used to describe a color. Hue is the attribute that 

most readily distinguishes one color from other colors. It 

depends on the frequency of a light wave in the visible 

spectrum. See also color model, HSB. Compare brightness, 

saturation (definition 2). 

Huffman coding n. A method of compressing a given set 

of data based on the relative frequency of the individual 

elements. The more often a given element, such as a letter, 

occurs, the shorter, in bits, is its corresponding code. It 

was one of the earliest data compression codes and, with 

modifications, remains one of the most widely used codes 

for a large variety of message types. 

human engineering n. The designing of machines and 

associated products to suit the needs of humans. See also 

ergonomics. 

260 

human-machine interface n. The boundary at which 

people make contact with and use machines; when applied 

to programs and operating systems, it is more widely 

known as the user interface. 

hung adj. See hang. 

hybrid circuit n. A circuit in which fundamentally different 

types of components are used to perform similar functions, 

such as a stereo amplifier that uses both tubes and 

transistors. 

hybrid computer n. A computer that contains both digital 

and analog circuits. 

hybrid microcircuit n. A microelectronic circuit that 

combines individual microminiaturized components and 

integrated components. 

hybrid network n. A network constructed of different 

topologies, such as ring and star. See also bus network, 

ring network, star network, Token-Ring network, topology. 

Hybris virus n. A slow-spreading but persistent selfupdating 

Internet worm first detected in late 2000. The 

Hybris virus is activated whenever an infected computer is 

connected to the Internet. It attaches itself to all outgoing 

e-mail messages, maintains a list of all e-mail addresses in 

the headers of incoming e-mail messages, and sends copies 

of itself to all e-mail addresses on the list. Hybris is 

difficult to eradicate because it updates itself regularly, 

accessing and downloading updates and plug-ins from 

anonymous postings to the alt.comp.virus newsgroup. 

Hybris incorporates downloaded extensions into its code, 

and it e-mails its modified form to additional potential 

victims. Hybris often includes a spiral plug-in which produces 

a spinning disk on top of any active windows on a 

user’s screen. 

HyperCard n. An information-management software tool, 

designed for the Apple Macintosh, that implements many 

hypertext concepts. A HyperCard document consists of a 

series of cards, collected into a stack. Each card can contain 

text, graphical images, sound, buttons that enable 

travel from card to card, and other controls. Programs and 

routines can be coded as scripts in an object-oriented language 

called HyperTalk or developed as external code 

resources (XCMDs and XFCNs). See also hypertext, 

object-oriented programming, XCMD, XFCN. 

hyperlink n. A connection between an element in a hypertext 

document, such as a word, a phrase, a symbol, or an 

image, and a different element in the document, another

hypermedia Hz 

document, a file, or a script. The user activates the link by 

clicking on the linked element, which is usually underlined 

or in a color different from the rest of the document 

to indicate that the element is linked. Hyperlinks are indicated 

in a hypertext document through tags in markup languages 

such as SGML and HTML. These tags are 

generally not visible to the user. Also called: hot link, 

hypertext link, link. See also anchor (definition 2), HTML, 

hypermedia, hypertext, URL. 

hypermedia n. The combination of text, video, graphic 

images, sound, hyperlinks, and other elements in the form 

typical of Web documents. Essentially, hypermedia is the 

modern extension of hypertext, the hyperlinked, textbased 

documents of the original Internet. Hypermedia 

attempts to offer a working and learning environment that 

parallels human thinking—that is, one in which the user 

can make associations between topics, rather than move 

sequentially from one to the next, as in an alphabetic list. 

For example, a hypermedia presentation on navigation 

might include links to astronomy, bird migration, geography, 

satellites, and radar. See also hypertext. 

hyperspace n. The set of all documents that can be 

accessed by following hyperlinks in the World Wide Web. 

Compare cyberspace (definition 2), Gopherspace. 

HyperTalk n. A programming language used to manipulate 

HyperCard stacks developed by Apple Computer, Inc. 

See also HyperCard. 

hypertext n. Text linked together in a complex, nonsequential 

web of associations in which the user can browse 

through related topics. For example, in an article with the 

word iron, traveling among the links to iron might lead the 

user to the periodic table of the elements or a map of the 

migration of metallurgy in Iron Age Europe. The term 

hypertext was coined in 1965 to describe documents presented 

by a computer that express the nonlinear structure 

of ideas as opposed to the linear format of books, film, and 

speech. The term hypermedia, more recently introduced, 

is nearly synonymous but emphasizes the nontextual element, 

such as animation, recorded sound, and video. See 

also HyperCard, hypermedia. 

Hyper Text Coffee Pot Control Protocol n. See 

HTCPCP. 

hypertext link n. See hyperlink. 

Hypertext Markup Language n. See HTML. 

Hypertext Transfer Protocol n. See HTTP. 

Hypertext Transfer Protocol Daemon n. See HTTPd. 

261 

Hypertext Transfer Protocol Next Generation n. See 

HTTP-NG. 

HyperWave n. A World Wide Web server that specializes 

in database manipulation and multimedia. 

hyphen n. A punctuation mark (-) used to break a word 

between syllables at the end of a line or to separate the 

parts of a compound word. Word processing programs 

with sophisticated hyphenation capabilities recognize 

three types of hyphens: normal, optional, and nonbreaking. 

Normal hyphens, also called required or hard 

hyphens, are part of a word’s spelling and are always 

visible, as in long-term. Optional hyphens, also called 

discretionary or soft hyphens, appear only when a word 

is broken between syllables at the end of a line; they are 

usually supplied by the word processing program itself. 

Nonbreaking hyphens are always visible, like normal 

hyphens, but they do not allow a line break. See also 

hyphenation program. 

hyphenation program n. A program (often included as 

part of a word processing application) that introduces 

optional hyphens at line breaks. A good hyphenation program 

will avoid ending more than three lines in a row with 

hyphens and will prompt the user for confirmation or tag 

ambiguous breaks, as in the word desert (did the army 

de-sert in the des-ert?). See also hyphen. 

hysteresis n. The tendency of a system, a device, or a circuit 

to behave differently depending on the direction of 

change of an input parameter. For example, a household 

thermostat might turn on at 68 degrees when the house is 

cooling down, but turn off at 72 degrees when the house is 

warming up. Hysteresis is important in many devices, 

especially those employing magnetic fields, such as transformers 

and read/write heads. 

HYTELNET n. A menu-driven index of Internet resources 

that are accessible via telnet, including library catalogs, 

databases and bibliographies, bulletin boards, and network 

information services. HYTELNET can operate through a 

client program on a computer connected to the Internet, or 

through the World Wide Web. 

HyTime n. Acronym for Hypermedia/Time-based Structuring 

Language. A markup language standard that 

describes links within and between documents and hypermedia 

objects. The standard defines structures and some 

semantic features, enabling description of traversal and 

presentation information of objects. 

Hz n. See hertz. 

H

I 

I 2 L n. See integrated injection logic. 

I2O n. Short for Intelligent Input/Output. A specification 

for I/O device driver architecture that is independent of 

both the device being controlled and the host operating 

system. See also driver, input/output device. 

i386 n. A family of 32-bit microprocessors developed by 

Intel. The i386 was introduced in 1985. See also 

80386DX. 

i486 n. A family of 32-bit microprocessors developed by 

Intel that extended and built upon the capabilities of the 

i386. The i486 was introduced in 1989. See also i486DX. 

i486DX n. An Intel microprocessor introduced in 1989. 

In addition to the features of the 80386 (32-bit registers, 

32-bit data bus, and 32-bit addressing), the i486DX has a 

built-in cache controller, a built-in floating-point coprocessor, 

provisions for multiprocessing, and a pipelined 

execution scheme. Also called: 486, 80486. See also pipelining 


i486DX2 n. An Intel microprocessor introduced in 1992 

as an upgrade to certain i486DX processors. The i486DX2 

processes data and instructions at twice the system clock 

frequency. The increased operating speed leads to the generation 

of much more heat than in an i486DX, so a heat 

sink is often installed on the chip. Also called: 486DX, 

80486. See also heat sink, i486DX, microprocessor. Compare 

OverDrive. 

i486SL n. A low-power-consumption version of Intel’s 

i486DX microprocessor designed primarily for laptop 

computers. The i486SL operates at a voltage of 3.3 volts 

rather than 5 volts, can shadow memory, and has a System 

Management Mode (SMM) in which the microprocessor 

can slow or halt some system components when the system 

is not performing CPU-intensive tasks, thus prolonging 

battery life. See also i486DX, shadow memory. 

i486SX n. An Intel microprocessor introduced in 1991 as 

a lower-cost alternative to the i486DX. It runs at slower 

clock speeds and has no floating-point processor. Also 

called: 486, 80486. See also 80386DX, 80386SX. Compare 

i486DX. 

I 

262 

IA-64 n. Short for Intel Architecture 64. Intel’s 64-bit 

microprocessor architecture based on EPIC (Explicitly 

Parallel Instruction Computing) technology. IA-64 is the 

foundation for the 64-bit Merced chip, as well as future 

chips to be based on the same architecture. Unlike architectures 

based on the sequential execution of instructions, 

IA-64 is designed to implement the parallel execution 

defined by EPIC technology. It also provides for numerous 

registers (128 general registers for integer and multimedia 

operations and 128 floating-point registers) and for grouping 

instructions in threes as 128-bit bundles. IA-64 architecture 

also features inherent scalability and compatibility 

with 32-bit software. See also EPIC, Merced. 

IAB n. See Internet Architecture Board. 

IAC n. Acronym for Information Analysis Center. One of 

several organizations chartered by the U.S. Department of 

Defense to facilitate the use of existing scientific and technical 

information. IACs establish and maintain comprehensive 

knowledge bases, including historical, technical, 

and scientific data, and also develop and maintain analytical 

tools and techniques for their use. 

IANA n. Acronym for Internet Assigned Numbers Authority. 

The organization historically responsible for assigning 

IP (Internet Protocol) addresses and overseeing technical 

parameters, such as protocol numbers and port numbers, 

related to the Internet protocol suite. Under the direction of 

the late Dr. Jon Postel, IANA operated as an arm of the 

Internet Architecture Board (IAB) of the Internet Society 

(ISOC) under contract with the U.S. government. However, 

given the international nature of the Internet, IANA’s 

functions, along with the domain name administration handled 

by U.S.-based Network Solutions, Inc. (NSI), were 

privatized in 1998 and turned over to a new, nonprofit 

organization known as ICANN (Internet Corporation for 

Assigned Names and Numbers). See also ICANN, NSI. 

I-beam n. A mouse cursor used by many applications, 

such as word processors, when in text-editing mode. The 

I-beam cursor indicates sections of the document where 

text can be inserted, deleted, changed, or moved. The cursor 

is named for its I shape. Also called: I-beam pointer. 

See also cursor (definition 3), mouse.

I-beam pointer icon 

I-beam pointer n. See I-beam. 

IBG n. Acronym for inter block gap. See inter-record gap. 

IBM AT n. A class of personal computers introduced in 

1984 and conforming to IBM’s PC/AT (Advanced Technology) 

specification. The first AT was based on the Intel 

80286 processor and dramatically outperformed its predecessor, 

the XT, in speed. See also 80286. 

IBM PC n. Short for IBM Personal Computer. A class of 

personal computers introduced in 1981 and conforming to 

IBM’s PC specification. The first PC was based on the 

Intel 8088 processor. For a number of years, the IBM PC 

was the de facto standard in the computing industry for 

PCs, and clones, or PCs that conformed to the IBM specification, 

have been called PC-compatible. See also PCcompatible, 

Wintel. 

IBM PC/XT n. A class of personal computers released by 

IBM in 1983. XT, short for eXtended Technology, 

enabled users to add a wider range of peripherals to their 

machines than was possible with the original IBM PC. 

Equipped with a 10-megabyte hard disk drive and one or 

two 51 /4-inch floppy drives, the PC/XT was expandable to 

256K of RAM on the motherboard and was loaded with 

MS-DOS v2.1, which supported directories and subdirectories. 

The popularity of this machine contributed to the 

production of what came to be known in the industry as 

“clones,” copies of its design by many manufacturers. See 

also IBM AT, IBM PC, XT. 

IBM PC-compatible adj. See PC-compatible. 

iBook n. A notebook computer introduced by Apple in 

July 1999. The iBook was intended as a portable version 

of the iMac and is easily distinguished by its rounded 

shape and the bright colors of its case. Initial iBook models 

were powered by a 300-MHz G3 (PowerPC 750) processor 

and had the capability for wireless networking. See 

also iMac, PowerPC 750. 

IC1 adj. Acronym for In Character. Used to refer to events 

going on within a role-playing game, such as MUD, as 

opposed to events in real life. It is also used in the context 

of online chat, e-mail, and newsgroup postings. See also 

MUD, role-playing game. 

IC2 n. See integrated circuit. 

ICANN n. Acronym for Internet Corporation for Assigned 

Names and Numbers. The private, nonprofit corporation 

to which the U.S. government in 1998 delegated authority 

for administering IP (Internet Protocol) addresses, domain 

263 

names, root servers, and Internet-related technical matters, 

such as management of protocol parameters (port numbers, 

protocol numbers, and so on). The successor to 

IANA (IP address administration) and NSI (domain name 

registration), ICANN was created to internationalize and 

privatize Internet management and administration. See 

also IANA, NSI. 

I-CASE n. Acronym for Integrated Computer-Aided Software 

Engineering. Software that performs a wide variety 

of software engineering functions, such as program 

design, coding, and testing parts or all of the completed 

program. 

ICE n. 1. Acronym for Information and Content 

Exchange. A protocol based on XML (Extensible Markup 

Language) designed to automate the distribution of syndicated 

content over the World Wide Web. Based on the 

concept of content syndicators (distributors) and subscribers 

(receivers), ICE defines the responsibilities of the parties 

involved, as well as the format and means of 

exchanging content so that data can easily be transferred 

and reused. The protocol has been submitted to the World 

Wide Web Consortium by Adobe Systems, Inc., CNET, 

Microsoft, Sun Microsystems, and Vignette Corporation. 

It is intended to help in both publishing and inter-business 

exchanges of content. 2. Acronym for in circuit emulator. 

A chip used as a stand-in for a microprocessor or a microcontroller. 

An in-circuit emulator is used to test and debug 

logic circuits. 3. Acronym for Intrusion Countermeasure 

Electronics. A fictional type of security software, popularized 

by science fiction novelist William Gibson, that 

responds to intruders by attempting to kill them. The origin 

of the term is attributed to a USENET subscriber, Tom 

Maddox. 4. See Intelligent Concept Extraction. 

ICM n. See image color matching. 

ICMP n. Acronym for Internet Control Message Protocol. 

A network-layer (ISO/OSI level 3) Internet protocol 

that provides error correction and other information relevant 

to IP packet processing. For example, it can let the IP 

software on one machine inform another machine about 

an unreachable destination. See also communications protocol, 

IP, ISO/OSI reference model, packet (definition 1). 

icon n. 1. A small image displayed on the screen to represent 

an object that can be manipulated by the user. By 

serving as visual mnemonics and allowing the user to control 

certain computer actions without having to remember 

commands or type them at the keyboard, icons contribute 

I

I 

iconic interface IDSL 

significantly to the user-friendliness of graphical user 

interfaces and to PCs in general. See also graphical user 

interface. 2. A high-level programming language designed 

to process non-numerical data structures and character 

strings using a Pascal-like syntax. 

iconic interface n. A user interface that is based on icons 

rather than on typed commands. See also graphical user 

interface, icon. 

icon parade n. The sequence of icons that appears during 

the boot-up of a Macintosh computer. 

ICP n. Acronym for Internet Cache Protocol. A networking 

protocol used by cache servers to locate specific Web 

objects in neighboring caches. Typically implemented 

over UDP, ICP also can be used for cache selection. ICP 

was developed for the Harvest research project at the University 

of Southern California. It has been implemented in 

SQUID and other Web proxy caches. 

ICQ n. A downloadable software program developed by 

Mirabilis, and now owned by AOL Time-Warner Inc., that 

notifies Internet users when friends, family, or other 

selected users are also on line and allows them to communicate 

with one another in real time. Through ICQ, users 

can chat, send e-mail, exchange messages on message 

boards, and transfer URLs and files, as well as launch 

third-party programs, such as games, in which multiple 

people can participate. Users compile a list of other users 

with whom they want to communicate. All users must register 

with the ICQ server and have ICQ software on their 

computer. The name is a reference to the phrase “I seek 

you.” See also instant messaging. 

ICSA n. Acronym for International Computer Security 

Association. An education and information organization 

concerned with Internet security issues. Known as the 

NCSA (National Computer Security Association) until 

1997, the ICSA provides security assurance systems and 

product certification; disseminates computer security 

information in white papers, books, pamphlets, videos, 

and other publications; organizes consortiums devoted to 

various security issues; and maintains a Web site that provides 

updated information on viruses and other computer 

security topics. Founded in 1987, the ICSA is currently 

located in Reston, VA. 

ID n. Acronym for intrusion detection. See IDS. 

264 

IDE n. 1. Acronym for Integrated Device Electronics. A 

type of disk-drive interface in which the controller electronics 

reside on the drive itself, eliminating the need for a 

separate adapter card. The IDE interface is compatible 

with the controller used by IBM in the PC/AT computer 

but offers advantages such as look-ahead caching. 2. See 

integrated development environment. 

identifier n. Any text string used as a label, such as the 

name of a procedure or a variable in a program or the 

name attached to a hard disk or floppy disk. Compare 

descriptor. 

IDL n. Acronym for Interface Definition Language. In 

object-oriented programming, a language that lets a program 

or object written in one language communicate with 

another program written in an unknown language. An 

IDL is used to define interfaces between client and server 

programs. For example, an IDL can provide interfaces to 

remote CORBA objects. See also CORBA, MIDL, objectoriented 

programming. 

idle adj. 1. Operational but not in use. 2. Waiting for a 

command. 

idle character n. In communications, a control character 

transmitted when no other information is available or 

ready to be sent. See also SYN. 

idle interrupt n. An interrupt that occurs when a device 

or process becomes idle. 

idle state n. The condition in which a device is operating 

but is not being used. 

IDS n. Acronym for intrusion-detection system. A type of 

security management system for computers and networks 

that gathers and analyzes information from various areas 

within a computer or a network to identify possible security 

breaches, both inside and outside the organization. An 

IDS can detect a wide range of hostile attack signatures, 

generate alarms, and, in some cases, cause routers to terminate 

communications from hostile sources. Also called: 

intrusion detection. Compare firewall. 

IDSL n. Acronym for Internet digital subscriber line. A 

high-speed digital communications service that provides 

Internet access as fast as 1.1 Mbps (megabits per second) 

over standard telephone lines. IDSL uses a hybrid of 

ISDN and digital subscriber line technology. See also digital 

subscriber line, ISDN.

IE IEEE 802.x 

IE n. Acronym for information engineering. A methodology 

for developing and maintaining information-processing 

systems, including computer systems and networks, 

within an organization. 

IEEE n. Acronym for Institute of Electrical and Electronics 

Engineers. A society of engineering and electronics professionals 

based in the United States but boasting membership 

from numerous other countries. The IEEE (pronounced 

“eye triple ee”) focuses on electrical, electronics, computer 

engineering, and science-related matters. 

IEEE 1284 n. The IEEE standard for high-speed signaling 

through a bidirectional parallel computer interface. A 

computer that is compliant with the IEEE 1284 standard 

can communicate through its parallel port in five modes: 

outbound data transfer to a printer or similar device (“Centronics” 

mode), inbound transfer 4 (nibble mode) or 8 

(byte mode) bits at a time, bidirectional Enhanced Parallel 

Ports (EPP) used by storage devices and other nonprinter 

peripherals, and Enhanced Capabilities Ports (ECP) used 

for bidirectional communication with a printer. See also 

Centronics parallel interface, ECP, enhanced parallel port. 

IEEE 1394 n. A nonproprietary, high-speed, serial bus 

input/output standard. IEEE 1394 provides a means of 

connecting digital devices, including personal computers 

and consumer electronics hardware. It is platform-independent, 

scalable (expandable), and flexible in supporting 

peer-to-peer (roughly, device-to-device) connections. 

IEEE 1394 preserves data integrity by eliminating the 

need to convert digital signals into analog signals. Created 

for desktop networks by Apple Computer and later developed 

by the IEEE 1394 working group, it is considered a 

low-cost interface for devices such as digital cameras, 

camcorders, and multimedia devices and is seen as a 

means of integrating personal computers and home electronics 

equipment. FireWire is the proprietary implementation 

of the standard by Apple Computer. See also analog 

data, IEEE. 

IEEE 1394 connector n. A type of connector that 

enables you to connect and disconnect high-speed serial 

devices. An IEEE 1394 connector is usually on the back of 

your computer near the serial port or the parallel port. The 

IEEE 1394 bus is used primarily to connect high-end digital 

video and audio devices to your computer; however, 

some hard disks, printers, scanners, and DVD drives can 

265 

also be connected to your computer using the IEEE 1394 

connector. 

IEEE 1394 port n. A 4- or 6-pin port that supports the 

IEEE 1394 standard and can provide direct connections 

between digital consumer electronics and computers. See 

also IEEE 1394. 

IEEE 488 n. The electrical definition of the General-Purpose 

Interface Bus (GPIB), specifying the data and control 

lines and the voltage and current levels for the bus. See 

also General-Purpose Interface Bus. 

IEEE 696/S-100 n. The electrical definition of the S-100 

bus, used in early personal computer systems that used 

microprocessors such as the 8080, Z-80, and 6800. The 

S-100 bus, based on the architecture of the Altair 8800, 

was extremely popular with early computer enthusiasts 

because it permitted installation of a wide range of expansion 

boards. See also Altair 8800, S-100 bus. 

IEEE 802.x n. A series of networking specifications 

developed by the IEEE. The x following 802 is a placeholder 

for individual specifications. The IEEE 802.x specifications 

correspond to the physical and data-link layers 

of the ISO/OSI reference model, but they divide the datalink 

layer into two sublayers. The logical link control 

(LLC) sublayer applies to all IEEE 802.x specifications 

and covers station-to-station connections, generation of 

message frames, and error control. The media access control 

(MAC) sublayer, dealing with network access and collision 

detection, differs from one IEEE 802 standard to 

another. IEEE 802.3 is used for bus networks that use 

CSMA/CD, both broadband and baseband, and the baseband 

version is based on the Ethernet standard. IEEE 

802.4 is used for bus networks that use token passing, and 

IEEE 802.5 is used for ring networks that use token passing 

(token ring networks). IEEE 802.6 is an emerging 

standard for metropolitan area networks, which transmit 

data, voice, and video over distances of more than 5 kilometers. 

IEEE 802.14 is designed for bidirectional transmission 

to and from cable television networks over optical 

fiber and coaxial cable through transmission of fixedlength 

ATM cells to support television, data, voice, and 

Internet access. See the illustration. See also bus network, 

ISO/OSI reference model, ring network, token passing, 

token ring network. 

I

I 

IEEE 802.11 illegal 

ISO/OSI model 

Application 

Presentation 

Session 

Transport 

Network 

Data-link 

Physical 

IEEE 802 LLC 

and MAC layers 

Logical link control 

Media access control 

F0Ign01.eps 

IEEE 802.x. ISO/OSI reference model with IEEE 802 LLC 

and MAC layers shown. 

IEEE 802.11 n. The Institute of Electrical and Electronics 

Engineers’ (IEEE) specifications for wireless networking. 

These specifications, which include 802.11, 802.11a, 

802.11b, and 802.11g, allow computers, printers, and 

other devices to communicate over a wireless local area 

network (LAN). 

IEEE printer cable n. A cable used to connect a printer to 

a PC’s parallel port that adheres to the IEEE 1284. See 

also IEEE 1284. 

IEPG n. Acronym for Internet Engineering and Planning 

Group. A collaborative group of Internet service providers 

whose goal is to promote the Internet and coordinate 

technical efforts on it. 

IESG n. See Internet Engineering Steering Group. 

IETF n. Acronym for Internet Engineering Task Force. A 

worldwide organization of individuals interested in networking 

and the Internet. Managed by the IESG (Internet 

Engineering Steering Group), the IETF is charged with 

studying technical problems facing the Internet and proposing 

solutions to the Internet Architecture Board (IAB). 

The work of the IETF is carried out by various Working 

Groups that concentrate on specific topics, such as routing 

and security. The IETF is the publisher of the specifications 

that led to the TCP/IP protocol standard. See also 

Internet Engineering Steering Group. 

IFC n. See Internet Foundation Classes. 

266 

.iff n. The file extension that identifies files in the IFF 

(Interchange File Format) format. IFF was most commonly 

used on the Amiga platform, where it constituted 

almost any kind of data. On other platforms, IFF is mostly 

used to store image and sound files. 

IFF n. Acronym for Interchange File Format. See .iff. 

IFIP n. Acronym for International Federation of Information 

Processing. An organization of societies, representing 

over 40 member nations, that serves information-processing 

professionals. The United States is represented by the 

Federation on Computing in the United States (FOCUS). 

See also AFIPS, FOCUS. 

IFS n. See Installable File System Manager. 

IF statement n. A control statement that executes a block 

of code if a Boolean expression evaluates to true. Most programming 

languages also support an ELSE clause, which 

specifies code that is to be executed only if the Boolean 

expression evaluates to false. See also conditional. 

IGES n. See Initial Graphics Exchange Specification. 

IGMP n. See Internet Group Membership Protocol. 

IGP n. See Interior Gateway Protocol. 

IGRP n. Acronym for Interior Gateway Routing Protocol. 

A protocol developed by Cisco Systems that allows coordination 

between the routing of a number of gateways. 

Goals of IGRP include stable routing in large networks, 

fast response to changes in network topology, and low 

overhead. See also communications protocol, gateway, 

topology. 

IIA n. See SIIA. 

IIL n. See integrated injection logic. 

IIOP n. Acronym for Internet Inter-ORB Protocol. A networking 

protocol that enables distributed programs written 

in different programming languages to communicate 

over the Internet. IIOP, a specialized mapping in the General 

Inter-ORB Protocol (GIOP) based on a client/server 

model, is a critical part of CORBA. See also CORBA. 

Compare DCOM. 

IIS n. See Internet Information Services. 

ILEC n. Acronym for Incumbent Local Exchange Carrier. 

A telephone company that provides local service to its 

customers. Compare CLEC. 

illegal adj. Not allowed, or leading to invalid results. For 

example, an illegal character in a word processing program 

would be one that the program cannot recognize; an

illuminance image editing 

illegal operation might be impossible for a program or 

system because of built-in constraints. Compare invalid. 

illuminance n. 1. The amount of light falling on, or illuminating, 

a surface area. 2. A measure of illumination 

(such as watts per square meter) used in reference to 

devices such as televisions and computer displays. Compare 

luminance. 

IM n. See instant messaging. 

iMac n. A family of Apple Macintosh computers introduced 

in 1998. Designed for nontechnical users, the iMac 

has a case that contains both the CPU and the monitor and 

is available in several bright colors. The “i” in iMac stands 

for Internet; the iMac was designed to make setting up an 

Internet connection extremely simple. The first version of 

the iMac included a 266-MHz PowerPC processor, a 66- 

MHz system bus, a hard drive, a CD-ROM drive, and a 15inch 

monitor, with a translucent blue case. Later iMacs 

came with faster processors and a choice of case colors. 

See the illustration. See also Macintosh. 

F0Ign02.eps 

iMac. 

.image n. A file extension for a Macintosh Disk Image, a 

storage type often used on Apple’s FTP software download 

sites. 

image n. 1. A stored description of a graphic picture, 

either as a set of brightness and color values of pixels or as 

a set of instructions for reproducing the picture. See also 

bit map, pixel map. 2. A duplicate, copy, or representation 

of all or part of a hard or floppy disk, a section of memory 

or hard drive, a file, a program, or data. For example, a 

RAM disk can hold an image of all or part of a disk in 

main memory; a virtual RAM program can create an 

267 

image of some portion of the computer’s main memory on 

disk. See also RAM disk. 

image-based rendering n. See immersive imaging. 

image color matching n. The process of image output 

correction to match the same colors that were scanned or 

input. 

image compression n. The use of a data compression 

technique on a graphical image. Uncompressed graphics 

files tend to use up large amounts of storage, so image 

compression is useful to conserve space. See also compressed 

file, data compression, video compression. 

image compression dialog component n. An application 

programming interface that sets parameters for compressing 

images and image sequences in QuickTime, a 

technology from Apple for creating, editing, publishing, 

and viewing multimedia content. The component displays a 

dialog box as a user interface, validates and stores the settings 

selected in the dialog box, and oversees the compression 

of the image or images based on the selected criteria. 

Image Compression Manager n. A major software 

component used in QuickTime, a technology from Apple 

for creating, editing, publishing, and viewing multimedia 

content. The Image Compression Manager is an interface 

that provides image-compression and image-decompression 

services to applications and other managers. Because the 

Image Compression Manager is independent of specific 

compression algorithms and drivers, it can present a common 

application interface for software-based compressors 

and hardware-based compressors and offer compression 

options so that it or its application can use the appropriate 

tool for a particular situation. See also QuickTime. 

image compressor component n. A software component 

used by the Image Compression Manager to compress 

image data in QuickTime, a technology from Apple for 

creating, editing, publishing, and viewing multimedia content. 

See also Image Compression Manager, QuickTime. 

image decompressor component n. A software component 

used by the Image Compression Manager to decompress 

image data in QuickTime, a technology from Apple 


content. See also Image Compression Manager, QuickTime. 

image editing n. The process of changing or modifying a 

bitmapped image, usually with an image editor. 

I

I 

image editor immersive imaging 

image editor n. An application program that allows users 

to modify the appearance of a bitmapped image, such as a 

scanned photo, by using filters and other functions. Creation 

of new images is generally accomplished in a paint 

or drawing program. See also bitmapped graphics, filter 

(definition 4), paint program. 

image enhancement n. The process of improving the 

quality of a graphic image, either automatically by software 

or manually by a user through a paint or drawing 

program. See also anti-aliasing, image processing. 

image map n. An image that contains more than one 

hyperlink on a Web page. Clicking different parts of the 

image links the user to other resources on another part of 

the Web page or a different Web page or in a file. Often an 

image map, which can be a photograph, drawing, or a 

composite of several different drawings or photographs, is 

used as a map to the resources found on a particular Web 

site. Older Web browsers support only server-side image 

maps, which are executed on a Web server through CGI 

script. However, most newer Web browsers (Netscape 

Navigator 2.0 and higher and Internet Explorer 3.0 and 

higher) support client-side image maps, which are executed 

in a user’s Web browser. Also called: clickable 

maps. See also CGI script, hyperlink, Web page. 

image processing n. The analysis, manipulation, storage, 

and display of graphical images from sources such as 

photographs, drawings, and video. Image processing 

spans a sequence of three steps. The input step (image 

capture and digitizing) converts the differences in coloring 

and shading in the picture into binary values that a computer 

can process. The processing step can include image 

enhancement and data compression. The output step consists 

of the display or printing of the processed image. 

Image processing is used in such applications as television 

and film, medicine, satellite weather mapping, machine 

vision, and computer-based pattern recognition. See also 

image enhancement, video digitizer. 

image sensor n. A light-sensitive integrated circuit or 

group of integrated circuits used in scanners, digital cameras, 

and video cameras. 

imagesetter n. A typesetting device that can transfer 

camera-ready text and artwork from computer files 

directly onto paper or film. Imagesetters print at high resolution 

(commonly above 1000 dpi) and are usually Post- 

Script-compatible. 

image transcoder component n. A component that 

transfers compressed images from one file format to 

268 

another in QuickTime, a technology developed by Apple 


content. 

imaginary number n. A number that must be expressed 

as the product of a real number and i, where i2 = –1. The 

sum of an imaginary number and a real number is a complex 

number. Although imaginary numbers are not 

directly encountered in the universe (as in “1.544 i megabits 

per second”), some pairs of quantities, especially in 

electrical engineering, behave mathematically like the real 

and imaginary parts of complex numbers. Compare complex 

number, real number. 

imaging n. The processes involved in the capture, storage, 

display, and printing of graphical images. 

IMAP4 n. Acronym for Internet Message Access Protocol 

4. The latest version of IMAP, a method for an e-mail 

program to gain access to e-mail and bulletin board messages 

stored on a mail server. Unlike POP3, a similar protocol, 

IMAP allows a user to retrieve messages efficiently 

from more than one computer. Compare POP3. 

IMC n. See Internet Mail Consortium. 

IMHO n. Acronym for in my humble opinion. IMHO, 

used in e-mail and in online forums, flags a statement that 

the writer wants to present as a personal opinion rather 

than as a statement of fact. See also IMO. 

Imitation Game n. See Turing test. 

immediate access n. See direct access, random access. 

immediate operand n. A data value, used in the execution 

of an assembly language instruction, that is contained 

in the instruction itself rather than pointed to by an address 

in the instruction. 

immediate printing n. A process in which text and printing 

commands are sent directly to the printer without 

being stored as a printing file and without the use of an 

intermediate page-composition procedure or a file containing 

printer setup commands. 

immersive imaging n. A method of presenting photographic 

images on a computer by using virtual reality 

techniques. A common immersive image technique puts 

the user in the center of the view. The user can pan 360 

degrees within the image and can zoom in and out. 

Another technique puts an object in the center of the view 

and allows the user to rotate around the object to examine 

it from any perspective. Immersive imaging techniques can 

be used to provide virtual reality experiences without equip-

IMO index2 index 

ment such as a headpiece and goggles. Also called: imagebased 

rendering. See also imaging, virtual reality. 

IMO n. Acronym for in my opinion. A shorthand phrase 

used often in e-mail and Internet news and discussion 

groups to indicate an author’s admission that a statement 

he or she has just made is a matter of judgment rather than 

fact. See also IMHO. 

impact printer n. A printer, such as a wire-pin dot-matrix 

printer or a daisy-wheel printer, that drives an inked ribbon 

mechanically against the paper to form marks. See 

also daisy-wheel printer, dot-matrix printer. Compare 

nonimpact printer. 

impedance n. Opposition to the flow of alternating current. 

Impedance has two aspects: resistance, which 

impedes both direct and alternating current and is always 

greater than zero; and reactance, which impedes alternating 

current only, varies with frequency, and can be positive 

or negative. See also resistance. 

implementor n. In role-playing games, the administrator, 

coder, or developer of the game. Also called: Imp. See 

also role-playing game. 

import vb. To bring information from one system or 

program into another. The system or program receiving 

the data must somehow support the internal format or 

structure of the data. Conventions such as the TIFF 

(Tagged Image File Format) and PICT formats (for 

graphics files) make importing easier. See also PICT, 

TIFF. Compare export. 

IMT-2000 n. See International Mobile Telecommunications 

for the Year 2000. 

inactive window n. In an environment capable of displaying 

multiple on-screen windows, any window other 

than the one currently being used for work. An inactive 

window can be partially or entirely hidden behind another 

window, and it remains inactive until the user selects it. 

Compare active window. 

in-band signaling n. Transmission within the voice or 

data-handling frequencies of a communication channel. 

in-betweening n. See tween. 

Inbox n. In many e-mail applications, the default mailbox 

where the program stores incoming messages. See 

also e-mail, mailbox. Compare Outbox. 

incident light n. The light that strikes a surface in computer 

graphics. See also illuminance. 

269 

in-circuit emulator n. See ICE (definition 2). 

INCLUDE directive n. A statement within a source-code 

file that causes another source-code file to be read in at 

that spot, either during compilation or during execution. It 

enables a programmer to break up a program into smaller 

files and enables multiple programs to use the same files. 

inclusive OR n. See OR. 

increment1 n. A scalar or unit amount by which the value 

of an object such as a number, a pointer within an array, or 

a screen position designation is increased. Compare 

decrement1 . 

increment2 vb. To increase a number by a given amount. 

For example, if a variable has the value 10 and is incremented 

successively by 2, it takes the values 12, 14, 16, 

18, and so on. Compare decrement2 . 

incumbent local exchange carrier n. See ILEC. 

indent1 n. 1. Displacement of the left or right edge of a 

block of text in relation to the margin or to other blocks of 

text. 2. Displacement of the beginning of the first line of a 

paragraph relative to the other lines in the paragraph. 

Compare hanging indent. 

indent2 vb. To displace the left or right edge of a text 

item, such as a block or a line, relative to the margin or to 

another text item. 

Indeo n. A codec technology developed by Intel for compressing 

digital video files. See also codec. Compare 

MPEG. 

independent content provider n. A business or organization 

that supplies information to an online information 

service, such as America Online, for resale to the information 

service’s customers. See also online information service. 

independent software vendor n. A third-party software 

developer; an individual or an organization that independently 

creates computer software. Acronym: ISV. 

index1 n. 1. A listing of keywords and associated data that 

point to the location of more comprehensive information, 

such as files and records on a disk or record keys in a database. 

2. In programming, a scalar value that allows direct 

access into a multi-element data structure such as an array 

without the need for a sequential search through the collection 

of elements. See also array, element (definition 1), 

hash, list. 

index2 vb. 1. In data storage and retrieval, to create and 

use a list or table that contains reference information 

I

I 

indexed address inference programming 

pointing to stored data. 2. In a database, to find data by 

using keys such as words or field names to locate records. 

3. In indexed file storage, to find files stored on disk by 

using an index of file locations (addresses). 4. In programming 

and information processing, to locate information 

stored in a table by adding an offset amount, called the 

index, to the base address of the table. 

indexed address n. The location in memory of a particular 

item of data within a collection of items, such as an 

entry in a table. An indexed address is calculated by starting 

with a base address and adding to it a value stored in a 

register called an index register. 

indexed search n. A search for an item of data that uses 

an index to reduce the amount of time required. 

indexed sequential access method n. A scheme for 

decreasing the time necessary to locate a data record 

within a large database, given a key value that identifies 

the record. A smaller index file is used to store the keys 

along with pointers that locate the corresponding records 

in the large main database file. Given a key, first the index 

file is searched for the key and then the associated pointer 

is used to access the remaining data of the record in the 

main file. Acronym: ISAM. 

index hole n. The small, round hole near the large, round 

spindle opening at the center of a 5.25-inch floppy disk. 

The index hole marks the location of the first data sector, 

enabling a computer to synchronize its read/write operations 

with the disk’s rotation. 

Indexing Service Query Language n. A query language 

available in addition to SQL for the Indexing Service in 

Windows 2000. Formerly known as Index Server, its original 

function was to index the content of Internet Information 

Services (IIS) Web servers. Indexing Service now 

creates indexed catalogs for the contents and properties of 

both file systems and virtual Webs. 

index mark n. 1. A magnetic indicator signal placed on a 

soft-sectored disk during formatting to mark the logical 

start of each track. 2. A visual information locator, such as 

a line, on a microfiche. 

indicator n. A dial or light that displays information 

about the status of a device, such as a light connected to a 

disk drive that glows when the disk is being accessed. 

indirect address n. See relative address. 

inductance n. The ability to store energy in the form of a 

magnetic field. Any length of wire has some inductance, 

and coiling the wire, especially around a ferromagnetic 

270 

core, increases the inductance. The unit of inductance is 

the henry. Compare capacitance, induction. 

induction n. The creation of a voltage or current in a 

material by means of electric or magnetic fields, as in the 

secondary winding of a transformer when exposed to the 

changing magnetic field caused by an alternating current 

in the primary winding. See also impedance. Compare 

inductance. 

inductor n. A component designed to have a specific 

amount of inductance. An inductor passes direct current 

but impedes alternating current to a degree dependent on 

its frequency. An inductor usually consists of a length of 

wire coiled in a cylindrical or toroidal (doughnut-shaped) 

form, sometimes with a ferromagnetic core. See the illustration. 

Also called: choke. 

F0Ign03.eps 

Inductor. One of several kinds of inductors. 

Industry Standard Architecture n. See ISA. 

INET n. 1. Short for Internet. 2. An annual conference 

held by the Internet Society. 

.inf n. The file extension for device information files, 

those files containing scripts used to control hardware 

operations. 

infection n. The presence of a virus or Trojan horse in a 

computer system. See also Trojan horse, virus, worm. 

infer vb. To formulate a conclusion based on specific 

information, either by applying the rules of formal logic or 

by generalizing from a set of observations. For example, 

from the facts that canaries are birds and birds have feathers, 

one can infer (draw the inference) that canaries have 

feathers. 

inference engine n. The processing portion of an expert 

system. It matches input propositions with facts and rules 

contained in a knowledge base and then derives a conclusion, 

on which the expert system then acts. 

inference programming n. A method of programming 

(as in Prolog) in which programs yield results based on

infinite loop information revolution 

logical inference from a set of facts and rules. See also 

Prolog. 

infinite loop n. 1. A loop that, because of semantic or 

logic errors, can never terminate through normal means. 

2. A loop that is intentionally written with no explicit termination 

condition but will terminate as a result of side 

effects or direct intervention. See also loop1 (definition 1), 

side effect. 

infix notation n. A notation, used for writing expressions, 

in which binary operators appear between their 

arguments, as in 2 + 4. Unary operators usually appear 

before their arguments, as in –1. See also operator precedence, 

postfix notation, prefix notation, unary operator. 

.info n. One of seven new top-level domain names 


Names and Numbers (ICANN). Unlike the other new 

domain names, which focus on specific types of Web sites, 

.info is meant for unrestricted use. 

infobahn n. The Internet. Infobahn is a mixture of the 

terms information and Autobahn, a German highway 

known for the high speeds at which drivers can legally 

travel. Also called: Information Highway, Information 

Superhighway, the Net. 

infomediary n. A term created from the phrase information 

intermediary. A service provider that positions itself 

between buyers and sellers, collecting, organizing, and 

distributing focused information that improves the interaction 

of consumer and online business. 

information n. The meaning of data as it is intended to be 

interpreted by people. Data consists of facts, which 

become information when they are seen in context and 

convey meaning to people. Computers process data without 

any understanding of what the data represents. 

Information Analysis Center n. See IAC. 

Information and Content Exchange n. See ICE 


information appliance n. A specialized computer 

designed to perform a limited number of functions and, 

especially, to provide access to the Internet. Although 

devices such as electronic address books or appointment 

calendars might be considered information appliances, the 

term is more typically used for devices that are less expensive 

and less capable than a fully functional personal computer. 

Set-top boxes are a current example; other devices, 

envisioned for the future, would include network-aware 

271 

microwaves, refrigerators, watches, and the like. Also 

called: appliance. 

information center n. 1. A large computer center and its 

associated offices; the hub of an information management 

and dispersal facility in an organization. 2. A specialized 

type of computer system dedicated to information retrieval 

and decision-support functions. The information in such a 

system is usually read-only and consists of data extracted 

or downloaded from other production systems. 

information engineering n. See IE (definition 1). 

information explosion n. 1. The current period in human 

history, in which the possession and dissemination of 

information has supplanted mechanization or industrialization 

as a driving force in society. 2. The rapid growth 

in the amount of information available today. Also 

called: information revolution. 

information hiding n. A design practice in which implementation 

details for both data structures and algorithms 

within a module or subroutine are hidden from routines using 

that module or subroutine, so as to ensure that those routines 

do not depend on some particular detail of the implementation. 

In theory, information hiding allows the module or subroutine 

to be changed without breaking the routines that use 

it. See also break, module, routine, subroutine. 

Information Highway or information highway n. See 

Information Superhighway. 

Information Industry Association n. See SIIA. 

information kiosk n. See kiosk. 

information management n. The process of defining, 

evaluating, safeguarding, and distributing data within an 

organization or a system. 

information packet n. See packet (definition 1). 

information processing n. The acquisition, storage, 

manipulation, and presentation of data, particularly by 

electronic means. 

information resource management n. The process of 

managing the resources for the collection, storage, and 

manipulation of data within an organization or system. 

information retrieval n. The process of finding, 

organizing, and displaying information, particularly 

by electronic means. 

information revolution n. See information explosion. 

I

I 

information science inheritance code 

information science n. The study of how information is 

collected, organized, handled, and communicated. See 

also information theory. 

Information Services n. The formal name for a company’s 

data processing department. Acronym: IS.Also 

called: Data Processing, Information Processing, Information 

Systems, Information Technology, Management 

Information Services, Management Information Systems. 

Information Superhighway n. The existing Internet and 

its general infrastructure, including private networks, 

online services, and so on. See also National Information 

Infrastructure. 

Information Systems n. See Information Services. 

Information Technology n. See Information Services. 

Information Technology Industry Council n. Trade 

organization of the information technology industry. The 

council promotes the interests of the information technology 

industry and compiles information on computers, 

software, telecommunications, business equipment, and 

other topics related to information technology. 

Acronym: ITIC. 

information theory n. A mathematical discipline 

founded in 1948 that deals with the characteristics and the 

transmission of information. Information theory was originally 

applied to communications engineering but has 

proved relevant to other fields, including computing. It 

focuses on such aspects of communication as amount of 

data, transmission rate, channel capacity, and accuracy of 

transmission, whether over cables or within society. 

information warehouse n. The total of an organization’s 

data resources on all computers. 

information warfare n. Attacks on the computer operations 

on which an enemy country’s economic life or safety 

depends. Possible examples of information warfare 

include crashing air traffic control systems or massively 

corrupting stock exchange records. 

Infoseek n. A Web search site that provides full-text 

results for user searches plus categorized lists of related 

sites. InfoSeek is powered by the Ultraseek search engine 

and searches Web pages, Usenet newsgroups, and FTP 

and Gopher sites. 

infrared adj. Having a frequency in the electromagnetic 

spectrum in the range just below that of red light. Objects 

radiate infrared in proportion to their temperature. Infrared 

radiation is traditionally divided into four somewhat arbi- 

272 

trary categories based on its wavelength. See the table. 

Acronym: IR. 

Table I.1 Infrared Radiation Categories. 

near infrared 750–1500 nanometers (nm) 

middle infrared 1500–6000 nm 

far infrared 6000–40,000 nm 

far-far infrared 40,000 nm–1 millimeter (mm) 

Infrared Data Association n. See IrDA. 

infrared device n. A computer, or a computer peripheral 

such as a printer, that can communicate by using infrared 

light. See also infrared. 

infrared file transfer n. Wireless file transfer between a 

computer and another computer or device using infrared 

light. See also infrared. 

infrared network connection n. A direct or incoming 

network connection to a remote access server using an 

infrared port. See also infrared port. 

infrared port n. An optical port on a computer for interfacing 

with an infrared-capable device. Communication is 

achieved without physical connection through cables. 

Infrared ports can be found on some laptops, notebooks, 

and printers. See also cable, infrared, port. 

inherent error n. An error in assumptions, design, logic, 

algorithms, or any combination thereof that causes a program 

to work improperly, regardless of how well written it 

is. For example, a serial communications program that is 

written to use a parallel port contains an inherent error. See 

also logic, semantics (definition 1), syntax. 

inherit vb. To acquire the characteristics of another class, 

in object-oriented programming. The inherited characteristics 

may be enhanced, restricted, or modified. See also 

class. 

inheritance n. 1. The transfer of the characteristics of a 

class in object-oriented programming to other classes 

derived from it. For example, if “vegetable” is a class, the 

classes “legume” and “root” can be derived from it, and 

each will inherit the properties of the “vegetable” class: 

name, growing season, and so on. See also class, objectoriented 

programming. 2. The transfer of certain properties, 

such as open files, from a parent program or process 

to another program or process that the parent causes to 

run. See also child (definition 1). 

inheritance code n. A set of structural and procedural 

attributes belonging to an object that has been passed on to

inhibit inline discussion 

it by the class or object from which it was derived. See 

also object-oriented programming. 

inhibit vb. To prevent an occurrence. For example, to 

inhibit interrupts from an external device means to prevent 

the external device from sending any interrupts. 

.ini n. In MS-DOS and Windows 3.x, the file extension 

that identifies an initialization file, which contains user 

preferences and startup information about an application 

program. 

ini file n. Short for initialization file, a text file containing 

information about the initial configuration of Windows 

and Windows-based applications, such as default settings 

for fonts, margins, and line spacing. Two ini files, win.ini 

and system.ini, are required to run the Windows operating 

system through version 3.1. In later versions of Windows, 

ini files are replaced by a database known as the registry. 

In addition to Windows itself, many older applications 

create their own ini files. Because they are composed only 

of text, ini files can be edited in any text editor or word 

processor to change information about the application or 

user preferences. All initialization files bear the extension 

.ini. See also configuration, configuration file, registry, 

system.ini, win.ini. 

INIT n. On older Macintosh computers, a system extension 

that is loaded into memory at startup time. See also 

extension (definition 4). Compare cdev. 

Initial Graphics Exchange Specification n. A standard 

file format for computer graphics, supported by the 

American National Standards Institute (ANSI), that is 

particularly suitable for describing models created with 

computer-aided design (CAD) programs. It includes a 

wide variety of basic geometric forms (primitives) and, in 

keeping with CAD objectives, offers methods for describing 

and annotating drawings and engineering diagrams. 

Acronym: IGES.See also ANSI. 

initialization n. The process of assigning initial values to 

variables and data structures in a program. 

initialization file n. See ini file. 

initialization string n. A sequence of commands sent to a 

device, especially a modem, to configure it and prepare it 

for use. In the case of a modem, the initialization string 

consists of a string of characters. 

initialize vb. 1. To prepare a storage medium, such as a 

disk or a tape, for use. This may involve testing the 

medium’s surface, writing startup information, and setting 

273 

up the file system’s index to storage locations. 2. To assign 

a beginning value to a variable. 3. To start up a computer. 

See also cold boot, startup. 

initializer n. An expression whose value is the first (initial) 

value of a variable. See also expression. 

initial program load n. The process of copying an operating 

system into memory when a system is booted. 

Acronym: IPL. See also boot, startup. 

initiator n. The device in a SCSI connection that issues 

commands. The device that receives the commands is the 

target. See also SCSI, target. 

ink cartridge n. A disposable module that contains ink 

and is typically used in an ink-jet printer. See also ink-jet 

printer. 

ink-jet printer or inkjet printer n. A nonimpact printer in 

which liquid ink is vibrated or heated into a mist and 

sprayed through tiny holes in the print head to form 

characters or graphics on the paper. Ink-jet printers are 

competitive with some laser printers in price and print 

quality if not in speed. However, the ink, which must be 

highly soluble to avoid clogging the nozzles in the print 

head, produces fuzzy-looking output on some papers and 

smears if touched or dampened shortly after printing. See 

also nonimpact printer, print head. 

inline adj. 1. In programming, referring to a function call 

replaced with an instance of the function’s body. Actual 

arguments are substituted for formal parameters. An inline 

function is usually done as a compile-time transformation 

to increase the efficiency of the program. Also 

called: unfold, unroll. 2. In HTML code, referring to 

graphics displayed along with HTML-formatted text. 

Inline images placed in the line of HTML text use the tag 

. Text within an inline image can be aligned to the 

top, bottom, or middle of a specific image. 

inline code n. Assembly language or machine language 

instructions embedded within high-level source code. The 

form it takes varies considerably from compiler to compiler, 

if it is supported at all. 

inline discussion n. Discussion comments that are associated 

with a document as a whole or with a particular 

paragraph, image, or table of a document. In Web browsers, 

inline discussions are displayed in the body of the 

document; in word-processing programs, they are usually 

displayed in a separate discussion or comments pane. 

I

I 

inline graphics input/output-bound 

inline graphics n. Graphics files that are embedded in an 

HTML document or Web page and viewable by a Web 

browser or other program that recognizes HTML. By 

avoiding the need for separate file opening operations, 

inline graphics can speed the access and loading of an 

HTML document. Also called: inline image. 

inline image n. An image that is embedded within the 

text of a document. Inline images are common on Web 

pages. See also inline graphics. 

inline processing n. Operation on a segment of low-level 

program code, called inline code, to optimize execution 

speed or storage requirements. See also inline code. 

inline stylesheet n. A stylesheet included within an 

HTML document. Because an inline stylesheet is directly 

associated with an individual document, any changes 

made to that document’s appearance will not affect the 

appearance of other Web site documents. Compare linked 

stylesheet. 

inline subroutine n. A subroutine whose code is copied 

at each place in a program at which it is called, rather than 

kept in one place to which execution is transferred. Inline 

subroutines improve execution speed, but they also 

increase code size. Inline subroutines obey the same 

syntactical and semantic rules as ordinary subroutines. 

Inmarsat n. Acronym for International Maritime Satellite. 

Organization based in London, England, that operates 

satellites for international mobile telecommunications services 

in more than 80 nations. Inmarsat provides services 

for maritime, aviation, and land use. 

inner join n. An operator in relational algebra, often 

implemented in database management. The inner join produces 

a relation (table) that contains all possible ordered 

concatenations (joinings) of records from two existing 

tables that meet certain specified criteria on the data values. 

It is thus equivalent to a product followed by a select 

applied to the resulting table. Compare outer join. 

inoculate vb. To protect a program against virus infection 

by recording characteristic information about it. For example, 

checksums on the code can be recomputed and compared 

with the stored original checksums each time the 

program is run; if any have changed, the program file is 

corrupt and may be infected. See also checksum, virus. 

input1 n. Information entered into a computer or program 

for processing, as from a keyboard or from a file stored on 

a disk drive. 

274 

input2 vb. To enter information into a computer for 

processing. 

input area n. See input buffer. 

input-bound adj. See input/output-bound. 

input buffer n. A portion of computer memory set aside 

for temporary storage of information arriving for processing. 

See also buffer1 . 

input channel n. See input/output channel. 

input device n. A peripheral device whose purpose is to 

allow the user to provide input to a computer system. 

Examples of input devices are keyboards, mice, joysticks, 

and styluses. See also peripheral. 

input driver n. See device driver. 

input language n. 1. A language to be inputted into the 

system through the keyboard, a speech-to-text converter, 

or an Input Method Editor (IME). 2. In Microsoft Windows 

XP, a Regional and Language Options setting that 

specifies the combination of the language being entered 

and the keyboard layout, IME, speech-to-text converter, or 

other device being used to enter it. This setting was formerly 

known as input locale. 

Input Method Editor n. Programs used to enter the thousands 

of different characters in written Asian languages 

with a standard 101-key keyboard. An IME consists of 

both an engine that converts keystrokes into phonetic and 

ideograph characters and a dictionary of commonly used 

ideographic words. As the user enters keystrokes, the IME 

engine attempts to identify which character or characters 

the keystrokes should be converted into. Acronym: IME. 

input/output n. The complementary tasks of gathering 

data for a computer or a program to work with, and of 

making the results of the computer’s activities available to 

the user or to other computer processes. Gathering data is 

usually done with input devices such as the keyboard and 

the mouse, while the output is usually made available to 

the user via the display and the printer. Other data 

resources, such as disk files and communications ports for 

the computer, can serve as either input or output devices. 

Acronym: I/O. 

input/output area n. See input/output buffer. 

input/output-bound adj. Characterized by the need to 

spend lengthy amounts of time waiting for input and output 

of data that is processed much more rapidly. For example, 

if the processor is capable of making rapid changes to 

a large database stored on a disk faster than the drive

input/output buffer insert mode 

mechanism can perform the read and write operations, the 

computer is input/output-bound. A computer may be just 

input-bound or just output-bound if only input or only output 

limits the speed at which the processor accepts and 

processes data. Also called: I/O-bound. 

input/output buffer n. A portion of computer memory 

reserved for temporary storage of incoming and outgoing 

data. Because input/output devices can often write to a 

buffer without intervention from the CPU, a program can 

continue execution while the buffer fills, thus speeding 

program execution. See also buffer1 . 

input/output bus n. A hardware path used inside a computer 

for transferring information to and from the processor 

and various input and output devices. See also bus. 

input/output channel n. A hardware path from the CPU 

to the input/output bus. See also bus. 

input/output controller n. Circuitry that monitors operations 

and performs tasks related to receiving input and 

transferring output at an input or output device or port, 

thus providing the processor with a consistent means of 

communication (input/output interface) with the device 

and also freeing the processor’s time for other work. For 

example, when a read or write operation is performed on a 

disk, the drive’s controller carries out the high-speed, electronically 

sophisticated tasks involved in positioning the 

read-write heads, locating specific storage areas on the 

spinning disk, reading from and writing to the disk surface, 

and even checking for errors. Most controllers 

require software that enables the computer to receive and 

process the data the controller makes available. Also 

called: device controller, I/O controller. 

input/output device n. A piece of hardware that can be 

used both for providing data to a computer and for receiving 

data from it, depending on the current situation. A disk 

drive is an example of an input/output device. Some 

devices, such as a keyboard or a mouse, can be used only 

for input and are thus called input (input-only) devices. 

Other devices, such as printers, can be used only for output 

and are thus called output (output-only) devices. Most 

devices require installation of software routines called 

device drivers to enable the computer to transmit and 

receive data to and from them. 

input/output interface n. See input/output controller. 

input/output port n. See port. 

275 

input/output processor n. Hardware designed to handle 

input and output operations to relieve the burden on 

the main processing unit. For example, a digital signal 

processor can perform time-intensive, complicated analysis 

and synthesis of sound patterns without CPU overhead. 

See also digital signal processor, front-end processor (definition 

1). 

input/output statement n. A program instruction that 

causes data to be transferred between memory and an 

input or output device. 

input port n. See port. 

input stream n. A flow of information used in a program 

as a sequence of bytes that are associated with a particular 

task or destination. Input streams include series of characters 

read from the keyboard to memory and blocks of data 

read from disk files. Compare output stream. 

inquiry n. A request for information. See also query. 

INS n. See WINS. 

insertion point n. A blinking vertical bar on the screen, 

such as in graphical user interfaces, that marks the location 

at which inserted text will appear. See also cursor 


insertion sort n. A list-sorting algorithm that starts with 

a list that contains one item and builds an ever-larger 

sorted list by inserting the items to be sorted one at a time 

into their correct positions on that list. Insertion sorts are 

inefficient when used with arrays, because of constant 

shuffling of items, but are ideally suited for sorting linked 

lists. See also linked list, sort algorithm. Compare bubble 

sort, quicksort. 

Insert key n. A key on the keyboard, labeled “Insert” or 

“Ins,” whose usual function is to toggle a program’s editing 

setting between an insert mode and an overwrite 

mode, although it may perform different functions in different 

applications. Also called: Ins key. 

insert mode n. A mode of operation in which a character 

typed into a document or at a command line pushes subsequent 

existing characters farther to the right on the screen 

rather than overwriting them. Insert mode is the opposite 

of overwrite mode, in which new characters replace subsequent 

existing characters. The key or key combination 

used to change from one mode to the other varies among 

programs, but the Insert key is most often used. Compare 

overwrite mode. 

I

I 

insider attack instruction set 

insider attack n. An attack on a network or system carried 

out by an individual associated with the hacked system. 

Insider attacks are typically the work of current or 

former employees of a company or organization who have 

knowledge of passwords and network vulnerabilities. 

Compare intruder attack. 

Ins key n. See Insert key. 

install vb. To set in place and prepare for operation. Operating 

systems and application programs commonly 

include a disk-based installation, or setup, program that 

does most of the work of preparing the program to work 

with the computer, printer, and other devices. Often such a 

program can check for devices attached to the system, 

request the user to choose from sets of options, create a 

place for the program on the hard disk, and modify system 

startup files as necessary. 

installable device driver n. A device driver that can be 

embedded within an operating system, usually in order to 

override an existing, less-functional service. 

Installable File System Manager n. In Windows 9x 

and Windows 2000, the part of the file system architecture 

responsible for arbitrating access to the different file system 

components. Acronym: IFS. 

installation program n. A program whose function is to 

install another program, either on a storage medium or in 

memory. An installation program, also called a setup program, 

might be used to guide a user through the often 

complex process of setting up an application for a particular 

combination of machine, printer, and monitor. 

Installer n. A program, provided with the Apple Macintosh 

operating system, that allows the user to install system 

upgrades and make bootable (system) disks. 

instance n. An object, in object-oriented programming, 

in relation to the class to which it belongs. For example, an 

object myList that belongs to a class List is an instance of 

the class List. See also class, instance variable, instantiate, 

object (definition 2). 

instance variable n. A variable associated with an 

instance of a class (an object). If a class defines a certain 

variable, each instance of the class has its own copy of that 

variable. See also class, instance, object (definition 2), 

object-oriented programming. 

instantiate vb. To create an instance of a class. See also 

class, instance, object (definition 2). 

276 

instant messaging n. A service that alerts users when 

friends or colleagues are on line and allows them to communicate 

with each other in real time through private 

online chat areas. With instant messaging, a user creates a 

list of other users with whom he or she wishes to communicate; 

when a user from his or her list is on line, the service 

alerts the user and enables immediate contact with the 

other user. While instant messaging has primarily been a 

proprietary service offered by Internet service providers 

such as AOL and MSN, businesses are starting to employ 

instant messaging to increase employee efficiency and 

make expertise more readily available to employees. 

Institute of Electrical and Electronics Engineers n. 

See IEEE. 

instruction n. An action statement in any computer language, 

most often in machine or assembly language. Most 

programs consist of two types of statements: declarations 

and instructions. See also declaration, statement. 

instruction code n. See operation code. 

instruction counter n. See instruction register. 

instruction cycle n. The cycle in which a processor 

retrieves an instruction from memory, decodes it, and carries 

it out. The time required for an instruction cycle is the 

sum of the instruction (fetch) time and the execution 

(translate and execute) time and is measured by the number 

of clock ticks (pulses of a processor’s internal timer) 

consumed. 

instruction mix n. The assortment of types of instructions 

contained in a program, such as assignment instructions, 

mathematical instructions (floating-point or 

integer), control instructions, and indexing instructions. 

Knowledge of instruction mixes is important to designers 

of CPUs because it tells them which instructions should be 

shortened to yield the greatest speed, and to designers of 

benchmarks because it enables them to make the benchmarks 

relevant to real tasks. 

instruction pointer n. See program counter. 

instruction register n. A register in a central processing 

unit that holds the address of the next instruction to be 

executed. 

instruction set n. The set of machine instructions that a 

processor recognizes and can execute. See also assembler, 

microcode.

instruction time integration 

instruction time n. The number of clock ticks (pulses of 

a computer’s internal timer) required to retrieve an instruction 

from memory. Instruction time is the first part of an 

instruction cycle; the second part is the execution (translate 

and execute) time. Also called: I-time. 

instruction word n. 1. The length of a machine language 

instruction. 2. A machine language instruction containing 

an operation code identifying the type of instruction, possibly 

one or more operands specifying data to be affected 

or its address, and possibly bits used for indexing or other 

purposes. See also assembler, machine code. 

insulator n. 1. Any material that is a very poor conductor 

of electricity, such as rubber, glass, or ceramic. Also 

called: nonconductor. Compare conductor, semiconductor. 

2. A device used to separate elements of electrical circuits 

and prevent current from taking unwanted paths, 

such as the stacks of ceramic disks that suspend highvoltage 

power lines from transmission towers. 

integer n. 1. A positive or negative “whole” number, such 

as 37, –50, or 764. 2. A data type representing whole 

numbers. Calculations involving only integers are much 

faster than calculations involving floating-point numbers, 

so integers are widely used in programming for 

counting and numbering purposes. Integers can be 

signed (positive or negative) or unsigned (positive). They 

can also be described as long or short, depending on the 

number of bytes needed to store them. Short integers, 

stored in 2 bytes, cover a smaller range of numbers (for 

example, –32,768 through 32,767) than do long integers 

(for example, –2,147,483,648 through 2,147,483,647), 

which are stored in 4 bytes. Also called: integral number. 

See also floating-point notation. 

integral modem n. A modem that is built into a computer, 

as opposed to an internal modem, which is a modem 

on an expansion card that can be removed. See also external 

modem, internal modem, modem. 

integral number n. See integer (definition 2). 

integrated circuit n. A device consisting of a number of 

connected circuit elements, such as transistors and resistors, 

fabricated on a single chip of silicon crystal or other 

semiconductor material. Integrated circuits are categorized 

by the number of elements they contain. See the 

table. Acronym: IC. Also called: chip. See also central 

processing unit. 

277 

Table I.2 Types of Integrated Circuits. 

Category Elements 

small-scale integration (SSI) in the 10s 

medium-scale integration (MSI) in the 100s 

large-scale integration (LSI) in the 1000s 

very-large-scale integration in the 100,000s 

(VLSI) 

ultra-large-scale integration 

(ULSI) 

1,000,000 or more 

integrated development environment n. A set of integrated 

tools for developing software. The tools are generally 

run from one user interface and consist of a compiler, 

an editor, and a debugger, among others. Acronym: IDE. 

Integrated Device Electronics n. See IDE (definition 1). 

integrated injection logic n. A type of circuit design 

that uses both NPN and PNP transistors and does not 

require other components, such as resistors. Such circuits 

are moderately fast, consume little power, and can be 

manufactured in very small sizes. Acronym: I2L, IIL. Also 

called: merged transistor logic. See also NPN transistor, 

PNP transistor. 

Integrated Services Digital Network n. See ISDN. 

Integrated Services LAN n. See isochronous network. 

integrated software n. A program that combines several 

applications, such as word processing, database 

management, and spreadsheets, in a single package. 

Such software is “integrated” in two ways: it can transfer 

data from one of its applications to another, helping 

users coordinate tasks and merge information created 

with the different software tools; and it provides the user 

with a consistent interface for choosing commands, 

managing files, and otherwise interacting with the programs 

so that the user will not have to master several, often 

very different, programs. The applications in an integrated 

software package are often not, however, designed to 

offer as much capability as single applications, nor does 

integrated software necessarily include all the applications 

needed in a particular environment. 

integration n. 1. In computing, the combining of different 

activities, programs, or hardware components into a functional 

unit. See also integral modem, integrated software, 

ISDN. 2. In electronics, the process of packing multiple 

electronic circuit elements on a single chip. See also integrated 

circuit. 3. In mathematics, specifically calculus, a 

procedure performed on an equation and related to finding 

I

I 

integrator Intelligent Transportation Infrastructure 

the area under a given curve or the volume within a given 

shape. 

integrator n. A circuit whose output represents the integral, 

with respect to time, of the input signal—that is, its 

total accumulated value over time. See the illustration. 

Compare differentiator. 

Amplitude 

Input Output 

Time 

F0Ign04.eps 

Integrator. An example of the action of an integrator circuit. 

integrity n. The completeness and accuracy of data stored 

in a computer, especially after it has been manipulated in 

some way. See also data integrity. 

Intel Architecture 64 n. See IA-64. 

intellectual property n. Content of the human intellect 

deemed to be unique and original and to have marketplace 

value—and thus to warrant protection under the law. Intellectual 

property includes but is not limited to ideas; inventions; 

literary works; chemical, business, or computer 

processes; and company or product names and logos. 

Intellectual property protections fall into four categories: 

copyright (for literary works, art, and music), trademarks 

(for company and product names and logos), patents (for 

inventions and processes), and trade secrets (for recipes, 

code, and processes). Concern over defining and protecting 

intellectual property in cyberspace has brought this 

area of the law under intense scrutiny. 

intelligence n. 1. The ability of hardware to process 

information. A device without intelligence is said to be 

dumb; for example, a dumb terminal connected to a computer 

can receive input and display output but cannot process 

information independently. 2. The ability of a 

program to monitor its environment and initiate appropriate 

actions to achieve a desired state. For example, a program 

waiting for data to be read from disk might switch to 

another task in the meantime. 3. The ability of a program 

to simulate human thought. See also artificial intelligence. 

4. The ability of a machine such as a robot to respond 

appropriately to changing stimuli (input). 

278 

intelligent adj. Of, pertaining to, or characteristic of a 

device partially or totally controlled by one or more 

processors integral to the device. 

intelligent agent n. See agent (definition 2). 

intelligent cable n. A cable that incorporates circuitry to 

do more than simply pass signals from one end of the 

cable to the other, such as to determine the characteristics 

of the connector into which it is plugged. Also called: smart 

cable. 

Intelligent Concept Extraction n. A technology owned 

by Excite, Inc., for searching indexed databases to retrieve 

documents from the World Wide Web. Intelligent Concept 

Extraction is like other search technologies in being able 

to locate indexed Web documents related to one or more 

key words entered by the user. Based on proprietary search 

technology, however, it also matches documents conceptually 

by finding relevant information even if the document 

found does not contain the key word or words specified by 

the user. Thus, the list of documents found by Intelligent 

Concept Extraction can include both documents containing 

the specified search term and those containing alternative 

words related to the search term. Acronym: ICE. 

intelligent database n. A database that manipulates 

stored information in a way that people find logical, natural, 

and easy to use. An intelligent database conducts 

searches relying not only on traditional data-finding routines 

but also on predetermined rules governing associations, 

relationships, and even inferences regarding the 

data. See also database. 

Intelligent hub n. A type of hub that, in addition to transmitting 

signals, has built-in capability for other network 

chores, such as monitoring or reporting on network status. 

Intelligent hubs are used in different types of networks, 

including ARCnet and 10Base-T Ethernet. See also hub. 

Intelligent Input/Output n. See I2O. 

intelligent terminal n. A terminal with its own memory, 

processor, and firmware that can perform certain functions 

independently of its host computer, most often the rerouting 

of incoming data to a printer or video screen. 

Intelligent Transportation Infrastructure n. A system 

of automated urban and suburban highway and mass 

transit control and management services proposed in 

1996 by U.S. Secretary of Transportation Federico Peña. 

Acronym: ITI.

IntelliSense interface 

IntelliSense n. A Microsoft technology used in various 

Microsoft products, including Internet Explorer, Visual 

Basic, Visual Basic C++, and Office that is designed to 

help users perform routine tasks. In Visual Basic, for 

example, information such as the properties and methods 

of an object is displayed as the developer types the name 

of the object in the Visual Basic code window. 

Intensity Red Green Blue n. See IRGB. 

interactive adj. Characterized by conversational 

exchange of input and output, as when a user enters a 

question or command and the system immediately 

responds. The interactivity of microcomputers is one of the 

features that makes them approachable and easy to use. 

interactive fiction n. A type of computer game in which 

the user participates in a story by giving commands to the 

system. The commands given by the user determine, to 

some extent, the events that occur during the story. Typically 

the story involves a goal that must be achieved, and 

the puzzle is to determine the correct sequence of actions 

that will lead to the accomplishment of that goal. See also 

adventure game. 

interactive graphics n. A form of user interface in 

which the user can change and control graphic displays, 

often with the help of a pointing device such as a mouse or 

a joystick. Interactive graphics interfaces occur in a range 

of computer products, from games to computer-aided 

design (CAD) systems. 

interactive processing n. Processing that involves the 

more or less continuous participation of the user. Such a 

command/response mode is characteristic of microcomputers. 

Compare batch processing (definition 2). 

interactive program n. A program that exchanges output 

and input with the user, who typically views a display of 

some sort and uses an input device, such as a keyboard, 

mouse, or joystick, to provide responses to the program. A 

computer game is an interactive program. Compare batch 

program. 

interactive services n. See BISDN. 

interactive session n. A processing session in which the 

user can more or less continuously intervene and control 

the activities of the computer. Compare batch processing 


interactive television n. A video technology in which a 

viewer interacts with the television programming. Typical 

uses of interactive television include Internet access, video 

279 

on demand, and video conferencing. See also video conferencing. 

interactive TV n. See iTV. 

interactive video n. The use of computer-controlled 

video, in the form of a CD-ROM or videodisc, for interactive 

education or entertainment. See also CD-ROM, interactive, 

interactive television, videodisc. 

interactive voice response n. A computer that operates 

through the telephone system, in which input commands 

and data are transmitted to the computer as spoken words 

and numbers or tones and dial pulses generated by a telephone 

instrument; and output instructions and data are 

received from the computer as prerecorded or synthesized 

speech. For example, a dial-in service that provides airline 

flight schedules when you press certain key codes on your 

telephone is an interactive voice response system. Also 

called: IVR. 

Interactive voice system n. See interactive voice 

response. 

interapplication communication n. The process of one 

program sending messages to another program. For 

example, some e-mail programs allow users to click on a 

URL within the message. After the user clicks on the 

URL, browser software will automatically launch and 

access the URL. 

interblock gap n. See inter-record gap. 

Interchange File Format n. See .iff. 

Interchange Format n. See Rich Text Format. 

interconnect n. 1. See System Area Network. 2. An 

electrical or mechanical connection. Interconnect is the 

physical connection and communication between two 

components in a computer system. 

interface n. 1. The point at which a connection is made 

between two elements so that they can work with each 

other or exchange information. 2. Software that enables a 

program to work with the user (the user interface, which 

can be a command-line interface, menu-driven interface, 

or a graphical user interface), with another program such 

as the operating system, or with the computer’s hardware. 

See also application programming interface, graphical 

user interface. 3. A card, plug, or other device that connects 

pieces of hardware with the computer so that information 

can be moved from place to place. For example, 

standardized interfaces such as RS-232-C standard and 

I

I 

interface adapter internal command 

SCSI enable communications between computers and 

printers or disks. See also RS-232-C standard, SCSI. 

interface adapter n. See network adapter. 

interface card n. See adapter. 

Interface Definition Language n. See IDL. 

interference n. 1. Noise or other external signals that 

affect the performance of a communications channel. 2. 

Electromagnetic signals that can disturb radio or television 

reception. The signals can be generated naturally, as in 

lightning, or by electronic devices, such as computers. 

Interior Gateway Protocol n. A protocol used for distributing 

routing information among routers (gateways) 

in an autonomous network—that is, a network under the 

control of one administrative body. The two most often 

used interior gateway protocols are RIP (Routing Information 

Protocol) and OSPF (Open Shortest Path First). 

Acronym: IGP. See also autonomous system, OSPF, RIP. 

Compare exterior gateway protocol. 

Interior Gateway Routing Protocol n. See IGRP. 

Interix n. A software application from Microsoft that 

allows businesses to run existing UNIX-based legacy 

applications while adding applications based on the 

Microsoft Windows operating system. Interix serves as a 

single enterprise platform from which to run UNIX-based, 

Internet-based, and Windows-based applications. 

interlaced adj. Pertaining to a display method on rasterscan 

monitors in which the electron beam refreshes or 

updates all odd-numbered scan lines in one vertical sweep 

of the screen and all even-numbered scan lines in the next 

sweep. Compare noninterlaced. 

interlaced GIF n. A picture in GIF format that is gradually 

displayed in a Web browser, showing increasingly detailed 

versions of the picture until the entire file has finished 

downloading. Users of slower modems have a perceived 

shorter wait time for the image to appear, and they can 

sometimes get enough information about the image to 

decide whether to proceed with the download or move on. 

Users with faster connections will notice little difference in 

effect between an interlaced GIF and a noninterlaced GIF. 

interlace scanning n. A display technique designed to 

reduce flicker and distortions in television transmissions; 

also used with some raster-scan monitors. In interlace 

scanning the electron beam in the television or monitor 

refreshes alternate sets of scan lines in successive top-tobottom 

sweeps, refreshing all even lines on one pass, and 

280 

all odd lines on the other. Because of the screen phosphor’s 

ability to maintain an image for a short time before 

fading and the tendency of the human eye to average or 

blend subtle differences in light intensity, the human 

viewer sees a complete display, but the amount of information 

carried by the display signal and the number of 

lines that must be displayed per sweep are halved. Interlaced 

images are not as clear as those produced by the progressive 

scanning typical of newer computer monitors. 

Interlace scanning is, however, the standard method of displaying 

analog broadcast television images. Also 

called: interlacing. Compare progressive scanning. 

interlacing n. See interlace scanning. 

interleave vb. To arrange the sectors on a hard disk in such 

a way that after one sector is read, the next sector in 

numeric sequence will arrive at the head when the computer 

is ready to accept it rather than before, which would make 

the computer wait a whole revolution of the platter for the 

sector to come back. Interleaving is set by the format utility 

that initializes a disk for use with a given computer. 

interleaved memory n. A method of organizing the 

addresses in RAM memory in order to reduce wait states. 

In interleaved memory, adjacent locations are stored in 

different rows of chips so that after accessing a byte, the 

processor does not have to wait an entire memory cycle 

before accessing the next byte. See also access time (definition 

1), wait state. 

interlock vb. To prevent a device from acting while the 

current operation is in progress. 

intermediate language n. 1. A computer language used 

as an intermediate step between the original source language, 

usually a high-level language, and the target language, 

usually machine code. Some high-level compilers 

use assembly language as an intermediate language. See 

also compiler (definition 2), object code. 2. See Microsoft 

intermediate language. 

intermittent adj. Pertaining to something, such as a signal 

or connection, that is not unbroken but occurs at periodic 

or occasional intervals. 

intermittent error n. An error that recurs at unpredictable 

times. 

internal clock n. See clock/calendar. 

internal command n. A routine that is loaded into memory 

along with the operating system and resides there for as 

long as the computer is on. Compare external command.

internal font Internet2 

internal font n. A font that is already loaded in a printer’s 

memory (ROM) when the printer is shipped. Compare 

downloadable font, font cartridge. 

internal interrupt n. An interrupt generated by the processor 

itself in response to certain predefined situations, 

such as an attempt to divide by zero or an arithmetic value 

exceeding the number of bits allowed for it. See also interrupt. 

Compare external interrupt. 

internal memory n. See primary storage. 

internal modem n. A modem constructed on an expansion 

card to be installed in one of the expansion slots inside 

a computer. Compare external modem, integral modem. 

internal schema n. A view of information about the 

physical files composing a database, including file names, 

file locations, accessing methodology, and actual or potential 

data derivations, in a database model such as that 

described by ANSI/X3/SPARC, that supports a threeschema 

architecture. The internal schema corresponds to 

the schema in systems based on CODASYL/DBTG. In a 

distributed database, there may be a different internal 

schema at each location. See also conceptual schema, 

schema. 

internal sort n. 1. A sorting operation that takes place on 

files completely or largely held in memory rather than on 

disk during the process. 2. A sorting procedure that produces 

sorted subgroups of records that will be subsequently 

merged into one list. 

International Computer Security Association n. See 

ICSA. 

International Federation of Information 

Processing n. See IFIP. 

International Maritime Satellite n. See Inmarsat. 

International Mobile Telecommunications for the 

Year 2000 n. Specifications set forth by the International 

Telecommunications Union (ITU) to establish third-generation 

wireless telecommunication network architecture. 

The specifications include faster data transmission speeds 

and improved voice quality. Acronym: IMT-2000. 

International Organization for Standardization n. See 

ISO. 

International Telecommunication Union n. See ITU. 

International Telecommunication Union-Telecommunication 

Standardization Sector n. See ITU-T. 

International Telegraph and Telephone Consultative 

Committee n. English-language form of the name for the 

281 

Comité Consultatif International Télégraphique et Téléphonique, 

a standards organization that became part of the 

International Telecommunication Union in 1992. See also 

CCITT, ITU-T. 

Internaut n. See cybernaut. 

internet n. Short for internetwork. A set of computer 

networks that may be dissimilar and are joined together by 

means of gateways that handle data transfer and conversion 

of messages from the sending networks’ protocols to 

those of the receiving network. 

Internet n. The worldwide collection of networks and 

gateways that use the TCP/IP suite of protocols to communicate 

with one another. At the heart of the Internet is a 

backbone of high-speed data communication lines 

between major nodes or host computers, consisting of 

thousands of commercial, government, educational, and 

other computer systems, that route data and messages. 

One or more Internet nodes can go off line without endangering 

the Internet as a whole or causing communications 

on the Internet to stop, because no single computer or network 

controls it. The genesis of the Internet was a decentralized 

network called ARPANET created by the U.S. 

Department of Defense in 1969 to facilitate communications 

in the event of a nuclear attack. Eventually other networks, 

including BITNET, Usenet, UUCP, and NSFnet, 

were connected to ARPANET. Currently the Internet 

offers a range of services to users, such as FTP, e-mail, the 

World Wide Web, Usenet news, Gopher, IRC, telnet, and 

others. Also called: the Net. See also BITNET, FTP1 (definition 

1), Gopher, IRC, NSFnet, telnet1 , Usenet, UUCP, 

World Wide Web. 

Internet2 n. A computer-network development project 

launched in 1996 by a collaborative group of 120 universities 

under the auspices of the University Corporation for 

Advanced Internet Development (UCAID). The consortium 

is now being led by over 190 universities working 

with industry and government. The goal of Internet2, 

whose high-speed, fiberoptic backbone was brought on 

line in early 1999, is the development of advanced Internet 

technologies and applications for use in research and education 

at the university level. Though not open for public 

use, Internet2 and the technologies and applications developed 

by its members are intended to eventually benefit 

users of the commercial Internet as well. Some of the new 

technologies Internet2 and its members are developing 

and testing include IPv6, multicasting, and quality of service 

(QoS). Internet2 and the Next Generation Internet 

I

I 

Internet access Internet Engineering Steering Group 

(NGI) are complementary initiatives. Compare Internet, 

Next Generation Internet. 

Internet access n. 1. The capability of a user to connect 

to the Internet. This is generally accomplished through 

one of two ways. The first is through a dialing up of an 

Internet service provider or an online information services 

provider via a modem connected to the user’s computer. 

This method is the one used by the majority of home computer 

users. The second way is through a dedicated line, 

such as a T1 carrier, that is connected to a local area network, 

to which, in turn, the user’s computer is connected. 

The dedicated line solution is used by larger organizations, 

such as corporations, which either have their own node on 

the Internet or connect to an Internet service provider that 

is a node. A third way that is emerging is for users to use 

set-top boxes with their TVs. Generally, however, this will 

give a user access only to documents on the World Wide 

Web. See also dedicated line (definition 1), ISP, LAN, 

modem, node (definition 2), set-top box. 2. The capability 

of an online information service to exchange data with the 

Internet, such as e-mail, or to offer Internet services to 

users, such as newsgroups, FTP, and the World Wide Web. 

Most online information services offer Internet access to 

their users. See also FTP1 (definition 1), online information 

service. 

Internet access device n. A communications and signal-routing 

mechanism, possibly incorporating usage 

tracking and billing features, for use in connecting multiple 

remote users to the Internet. 

Internet access provider n. See ISP. 

Internet account n. A generic term for a registered username 

at an Internet Service Provider (ISP). An Internet 

account is accessed via username and password. Services 

such as dial-in PPP Internet access and e-mail are provided 

by ISPs to Internet account owners. 

Internet address n. See domain name address, e-mail 

address, IP address. 

Internet appliance n. 1. See set-top box. 2. See server 

appliance. 

Internet Architecture Board n. The body of the Internet 

Society (ISOC) responsible for overall architectural considerations 

regarding the Internet. The IAB also serves to 

adjudicate disputes in the standards process. 

Acronym: IAB.See also Internet Society. 

Internet Assigned Numbers Authority n. See IANA, 

ICANN. 

282 

Internet backbone n. One of several high-speed networks 

connecting many local and regional networks, with 

at least one connection point where it exchanges packets 

with other Internet backbones. Historically, the NSFnet 

(predecessor to the modern Internet) was the backbone to 

the entire Internet in the United States. This backbone 

linked the supercomputing centers that the National Science 

Foundation (NSF) runs. Today, different providers 

have their own backbones so that the backbone for the 

supercomputing centers is independent of backbones for 

commercial Internet providers such as MCI and Sprint. 

See also backbone. 

Internet broadcasting n. Broadcasting of audio, or 

audio plus video, signals across the Internet. Internet 

broadcasting includes conventional over-the-air broadcast 

stations that transmit their signals into the Internet as well 

as Internet-only stations. Listeners use audio Internet software, 

such as RealAudio. One method of Internet broadcasting 

is MBONE. See also MBONE, RealAudio. 

Internet Cache Protocol n. See ICP. 

Internet Control Message Protocol n. See ICMP. 

Internet Corporation for Assigned Names and 

Numbers n. See ICANN. 

Internet cramming n. See Web cramming. 

Internet Directory n. 1. Online database of sites organized 

by category where you can search for files and information 

by subject, keyword, or other criteria. 2. Storage 

place for information such as names, Web addresses, organizations, 

departments, countries, and locations. Typically, 

Internet Directories are used to look up e-mail addresses 

that are not in a local address book or a corporate-wide 

directory. 

Internet Draft n. A document produced by the Internet 

Engineering Task Force (IETF) for purposes of discussing 

a possible change in standards that govern the Internet. 

An Internet Draft is subject to revision or 

replacement at any time; if not replaced or revised, the 

Internet Draft is valid for no more than six months. An 

Internet Draft, if accepted, may be developed into an 

RFC. See also IETF, RFC. 

Internet Engineering and Planning Group n. See 

IEPG. 

Internet Engineering Steering Group n. The group 

within the Internet Society (ISOC) that, along with the 

Internet Architecture Board (IAB), reviews the standards

Internet Engineering Task Force Internet robot 

proposed by the Internet Engineering Task Force (IETF). 

Acronym: IESG. 

Internet Engineering Task Force n. See IETF. 

Internet Explorer n. Microsoft’s Web browsing software. 

Introduced in October 1995, the latest versions of Internet 

Explorer include many features that allow you to customize 

your experience on the Web. Internet Explorer is also 

available for the Macintosh and UNIX platforms. See also 

ActiveX control, Java applet, Web browser. 

Internet Foundation Classes n. A Java class library 

developed by Netscape to facilitate the creation of fullfeature, 

mission-critical Java applications. Internet Foundation 

Classes (IFC) comprises user-interface objects and 

frameworks intended to extend Java’s Abstract Window 

Toolkit (AWT) and includes a multifont text editor; essential 

application controls; and drag-and-drop, drawing/ 

event, windowing, animation, object persistence, singlethread, 

and localization frameworks. See also Abstract 

Window Toolkit, Application Foundation Classes, Java 

Foundation Classes, Microsoft Foundation Classes. 

Internet gateway n. A device that provides the connection 

between the Internet backbone and another network, 

such as a LAN (local area network). Usually the device is 

a computer dedicated to the task or a router. The gateway 

generally performs protocol conversion between the Internet 

backbone and the network, data translation or conversion, 

and message handling. A gateway is considered a 

node on the Internet. See also gateway, Internet backbone, 

node (definition 2), router. 

Internet Group Membership Protocol n. A protocol 

used by IP hosts to report their host group memberships to 

any immediately neighboring multicast routers. 

Acronym: IGMP. 

Internet home n. See smart home. 

Internet Information Services n. Software services that 

support Web site creation, configuration, and management, 

along with other Internet functions. Internet Information 

Services include Network News Transfer Protocol 

(NNTP), File Transfer Protocol (FTP), and Simple Mail 

Transfer Protocol (SMTP). 

Internet Inter-ORB Protocol n. See IIOP. 

Internet Mail Consortium n. An international membership 

organization of businesses and vendors involved in 

283 

activities related to e-mail transmission over the Internet. 

The goals of the Internet Mail Consortium are related to 

the promotion and expansion of Internet mail. The group’s 

interests range from making Internet mail easier for new 

users to advancing new mail technologies and expanding 

the role played by Internet mail into areas such as electronic 

commerce and entertainment. For example, the 

Internet Mail Consortium supports two companion specifications, 

vCalendar and vCard, designed to facilitate electronic 

exchange of scheduling and personal information. 

Acronym: IMC. 

Internet Naming Service n. See WINS. 

Internet Printing Protocol n. A specification for transmission 

of documents to printers through the Internet. 

Development of the Internet Printing Protocol (IPP) was 

proposed in 1997 by members of the Internet Engineering 

Task Force (IETF). Intended to provide a standard protocol 

for Internet-based printing, IPP covers both printing 

and printer management (printer status, job cancellation, 

and so on). It is applicable to print servers and to networkcapable 

printers. 

Internet Protocol n. See IP. 

Internet Protocol address n. See IP address. 

Internet Protocol next generation n. See IPng. 

Internet Protocol number n. See IP address. 

Internet Protocol Security n. See IPSec. 

Internet Protocol version 4 n. See IPv4. 

Internet Protocol version 6 n. See IPv6. 

Internet reference model n. See TCP/IP reference 

model. 

Internet Relay Chat n. See IRC. 

Internet Research Steering Group n. The governing 

body of the Internet Research Task Force (IRTF). 

Acronym: IRSG. 

Internet Research Task Force n. A volunteer organization 

that is an arm of the Internet Society (ISOC) focused on 

making long-term recommendations concerning the Internet 

to the Internet Architecture Board (IAB). Acronym: IRTF. 

See also Internet Society. 

Internet robot n. See spider. 

I

I 

Internet security Internet Worm 

Internet security n. A broad topic dealing with all 

aspects of data authentication, privacy, integrity, and verification 

for transactions over the Internet. For example, 

credit card purchases made via a World Wide Web 

browser require attention to Internet security issues to 

ensure that the credit card number is not intercepted by an 

intruder or copied from the server where the number is 

stored, and to verify that the credit card number is actually 

sent by the person who claims to be sending it. 

Internet Security and Acceleration Server n. A software 

application from Microsoft Corporation to 

increase the security and performance of Internet 

access for businesses. Internet Security and Acceleration 

Server provides an enterprise firewall and high-performance 

Web cache server to securely manage the flow of information 

from the Internet through the enterprise’s internal network. 

Acronym: ISA Server. 

Internet Server Application Programming 

Interface n. See ISAPI. 

Internet service provider n. See ISP. 

Internet Society n. An international, nonprofit organization 

based in Reston, Virginia, comprising individuals, 

companies, foundations, and government agencies, that 

promotes the use, maintenance, and development of the 

Internet. The Internet Architecture Board (IAB) is a body 

within the Internet Society. In addition, the Internet Society 

publishes the Internet Society News and produces the 

annual INET conference. Acronym: ISOC.See also INET, 

Internet Architecture Board. 

Internet Software Consortium n. A nonprofit organization 

that develops software that is available for free, via 

the World Wide Web or FTP, and engages in development 

of Internet standards such as the Dynamic Host Configuration 

Protocol (DHCP). Acronym: ISC. See also DHCP. 

Internet SSE n. See SSE. 

Internet Streaming Media Alliance n. See ISMA. 

Internet synchronization n. 1. The process of synchronizing 

data between computing and communication 

devices that are connected to the Internet. 2. A feature in 

Microsoft Jet and Microsoft Access that allows replicated 

information to be synchronized in an environment in 

which an Internet server is configured with Microsoft 

Replication Manager, a tool included with Microsoft 

Office 2000 Developer. 

284 

Internet Talk Radio n. Audio programs similar to radio 

broadcasts but distributed over the Internet in the form of 

files that can be downloaded via FTP. Internet Talk Radio 

programs, prepared at the National Press Building in 

Washington, D.C., are 30 minutes to 1 hour in length; a 

30-minute program requires about 15 MB of disk space. 

Acronym: ITR. 

Internet telephone n. Point-to-point voice communication 

that uses the Internet instead of the public-switched telecommunications 

network to connect the calling and called 

parties. Both the sending and the receiving party need a 

computer, a modem, an Internet connection, and an Internet 

telephone software package to make and receive calls. 

Internet Telephony Service Provider n. See ITSP. 

Internet telephony n. See VoIP. 

Internet television n. The transmission of television 

audio and video signals over the Internet. 

Internet traffic distribution n. See ITM. 

Internet traffic management n. See ITM. 

internetwork1 adj. Of or pertaining to communications 

between connected networks. It is often used to refer to 

communication between one LAN (local area network) 

and another over the Internet or another WAN (wide-area 

network). See also LAN, WAN. 

internetwork2 n. A network made up of smaller, interconnected 

networks. 

Internetwork Packet Exchange n. See IPX. 

Internetwork Packet Exchange/Sequenced Packet 

Exchange n. See IPX/SPX. 

Internet World n. Series of international conferences and 

exhibitions on e-commerce and Internet technology sponsored 

by Internet World magazine. Major conferences 

include the world’s largest Internet conferences, Internet 

World Spring and Internet World Fall. 

Internet Worm n. A string of self-replicating computer 

code that was distributed through the Internet in November 

1988. In a single night, it overloaded and shut down a 

large portion of the computers connected to the Internet at 

that time by replicating itself over and over on each computer 

it accessed, exploiting a bug in UNIX systems. 

Intended as a prank, the Internet Worm was written by a 

student at Cornell University. See also back door, worm.

InterNIC interrupt handler 

InterNIC n. Short for NSFnet (Internet) Network Information 

Center. The organization that has traditionally registered 

domain names and IP addresses as well as 

distributed information about the Internet. InterNIC was 

formed in 1993 as a consortium involving the U.S. 

National Science Foundation, AT&T, General Atomics, 

and Network Solutions, Inc. (Herndon, Va.). The latter 

partner administers InterNIC Registration Services, which 

assigns Internet names and addresses. 

interoperability n. Referring to components of computer 

systems that are able to function in different environments. 

For example, Microsoft’s NT operating system is interoperable 

on Intel, DEC Alpha, and other CPUs. Another 

example is the SCSI standard for disk drives and other 

peripheral devices that allows them to interoperate with 

different operating systems. With software, interoperability 

occurs when programs are able to share data and 

resources. Microsoft Word, for example, is able to read 

files created by Microsoft Excel. 

interpolate vb. To estimate intermediate values between 

two known values in a sequence. 

interpret vb. 1. To translate a statement or instruction into 

executable form and then execute it. 2. To execute a program 

by translating one statement at a time into executable 

form and executing it before translating the next statement, 

rather than by translating the program completely 

into executable code (compiling it) before executing it 

separately. See also interpreter. Compare compile. 

interpreted language n. A language in which programs 

are translated into executable form and executed one statement 

at a time rather than being translated completely 

(compiled) before execution. Basic, LISP, and APL are 

generally interpreted languages, although Basic can also be 

compiled. See also compiler. Compare compiled language. 

interpreter n. A program that translates and then executes 

each statement in a program written in an interpreted 

language. See also compiler, interpreted language, language 

processor. 

interprocess communication n. The ability of one task 

or process to communicate with another in a multitasking 

operating system. Common methods include pipes, semaphores, 

shared memory, queues, signals, and mailboxes. 

Acronym: IPC. 

inter-record gap n. An unused space between data 

blocks stored on a disk or tape. Because the speed of disks 

285 

and tapes fluctuates slightly during operation of the drives, 

a new data block may not occupy the exact space occupied 

by the old block it overwrites. The inter-record gap prevents 

the new block from overwriting part of adjacent 

blocks in such a case. Acronym: IRG.Also called: gap, 

interblock gap. 

interrogate vb. To query with the expectation of an 

immediate response. For example, a computer may interrogate 

an attached terminal to determine the terminal’s 

status (readiness to transmit or receive). 

interrupt n. A signal from a device to a computer’s processor 

requesting attention from the processor. When the 

processor receives an interrupt, it suspends its current 

operations, saves the status of its work, and transfers control 

to a special routine known as an interrupt handler, 

which contains the instructions for dealing with the particular 

situation that caused the interrupt. Interrupts can be 

generated by various hardware devices to request service 

or report problems, or by the processor itself in response 

to program errors or requests for operating-system services. 

Interrupts are the processor’s way of communicating 

with the other elements that make up a computer 

system. A hierarchy of interrupt priorities determines 

which interrupt request will be handled first if more than 

one request is made. A program can temporarily disable 

some interrupts if it needs the full attention of the processor 

to complete a particular task. See also exception, external 

interrupt, hardware interrupt, internal interrupt, 

software interrupt. 

interrupt-driven processing n. Processing that takes 

place only when requested by means of an interrupt. After 

the required task has been completed, the CPU is free to 

perform other tasks until the next interrupt occurs. Interrupt-driven 

processing is usually employed for responding 

to events such as a key pressed by the user or a floppy disk 

drive that has become ready to transfer data. See also 

interrupt. Compare autopolling. 

interrupt handler n. A special routine that is executed 

when a specific interrupt occurs. Interrupts from different 

causes have different handlers to carry out the corresponding 

tasks, such as updating the system clock or reading the 

keyboard. A table stored in low memory contains pointers, 

sometimes called vectors, that direct the processor to the 

various interrupt handlers. Programmers can create interrupt 

handlers to replace or supplement existing handlers, 

I

I 

interrupt priority inverted file 

such as by making a clicking sound each time the keyboard 

is pressed. 

interrupt priority n. See interrupt. 

interrupt request line n. A hardware line over which a 

device such as an input/output port, the keyboard, or a disk 

drive can send interrupts (requests for service) to the CPU. 

Interrupt request lines are built into the computer’s internal 

hardware and are assigned different levels of priority 

so that the CPU can determine the sources and relative 

importance of incoming service requests. They are of concern 

mainly to programmers dealing with low-level operations 

close to the hardware. Acronym: IRQ. 

interrupt vector n. A memory location that contains the 

address of the interrupt handler routine that is to be called 

when a specific interrupt occurs. See also interrupt. 

interrupt vector table n. See dispatch table. 

intersect n. An operator in relational algebra, used in 

database management. Given two relations (tables), A and 

B, that have corresponding fields (columns) containing the 

same types of values (that is, they are union-compatible), 

then INTERSECT A, B builds a third relation containing 

only those tuples (rows) that appear in both A and B. See 

also tuple. 

interstitial n. An Internet ad format that appears in a popup 

window between Web pages. Interstitial ads download 

completely before appearing, usually while a Web page 

the user has chosen is loading. Because interstitial pop-up 

windows don’t appear until the entire ad has downloaded, 

they often use animated graphics, audio, and other attention-getting 

multimedia technology that require longer 

download time. 

in the wild adj. Currently affecting the computing public, 

particularly in regard to computer viruses. A virus that is 

not yet contained or controlled by antivirus software or 

that keeps reappearing despite virus detection measures is 

considered to be in the wild. See also virus. 

intranet n. A private network based on Internet protocols 

such as TCP/IP but designed for information management 

within a company or organization. Its uses include such 

services as document distribution, software distribution, 

access to databases, and training. An intranet is so called 

because it looks like a World Wide Web site and is based 

on the same technologies, yet is strictly internal to the 

organization and is not connected to the Internet proper. 

Some intranets also offer access to the Internet, but such 

286 

connections are directed through a firewall that protects 

the internal network from the external Web. Compare 

extranet. 

intrinsic font n. A font (type size and design) for which a 

bit image (an exact pattern) exists that can be used as is, 

without such modification as scaling. Compare derived font. 

intruder n. An unauthorized user or unauthorized program, 

generally considered to have malicious intent, on a 

computer or computer network. See also bacterium, 

cracker, Trojan horse, virus. 

intruder attack n. A form of hacker attack in which the 

hacker enters the system without prior knowledge or 

access to the system. The intruder will typically use a 

combination of probing tools and techniques to learn 

about the network to be hacked. Compare insider attack. 

Intrusion Countermeasure Electronics n. See ICE 


intrusion detection n. See IDS. 

intrusion-detection system n. See IDS. 

invalid adj. Erroneous or unrecognizable because of a 

flaw in reasoning or an error in input. Invalid results, for 

example, might occur if the logic in a program is faulty. 

Compare illegal. 

inverse video n. See reverse video. 

invert vb. 1. To reverse something or change it to its 

opposite. For example, to invert the colors on a monochrome 

display means to change light to dark and dark to 

light. See the illustration. 2. In a digital electrical signal, to 

replace a high level by a low level and vice versa. This 

type of operation is the electronic equivalent of a Boolean 

NOT operation. 

Normal Inverted 

F0Ign05.eps 

Invert. An example showing the effects of inverting the colors 

on a monochrome display. 

inverted file n. See inverted list.

inverted list IP address classes 

inverted list n. A method for creating alternative locators 

for sets of information. For example, in a file containing 

data about cars, records 3, 7, 19, 24, and 32 might contain 

the value “Red” in the field COLOR. An inverted list (or 

index) on the field COLOR would contain a record for 

“Red” followed by the locator numbers 3, 7, 19, 24, and 

32. See also field, record. Compare linked list. 

inverted-list database n. A database similar to a relational 

database but with several differences that make it 

much more difficult for the database management system 

to ensure data consistency, integrity, and security than 

with a relational system. The rows (records or tuples) of 

an inverted-list table are ordered in a specific physical 

sequence, independent of any orderings that may be 

imposed by means of indexes. The total database can also 

be ordered, with specified logical merge criteria being 

imposed between tables. Any number of search keys, either 

simple or composite, can be defined. Unlike the keys of a 

relational system, these search keys are arbitrary fields or 

combinations of fields. No integrity or uniqueness constraints 

are enforced; neither the indexes nor the tables are 

transparent to the user. Compare relational database. 

inverted structure n. A file structure in which record 

keys are stored and manipulated separately from the 

records themselves. 

inverter n. 1. A logic circuit that inverts (reverses) the 

signal input to it—for example, inverting a high input to a 

low output. 2. A device that converts direct current (DC) 

to alternating current (AC). 

invoke vb. To call or activate; used in reference to commands 

and subroutines. 

I/O n. See input/output. 

I/O-bound adj. See input/output-bound. 

I/O controller n. See input/output controller. 

I/O device n. See input/output device. 

ion-deposition printer n. A page printer in which the 

image is formed in electrostatic charges on a drum that 

picks up toner and transfers it to the paper, as in a laser, 

LED, or LCD printer, but the drum is charged using a 

beam of ions rather than light. These printers, used mainly 

in high-volume data-processing environments, typically 

operate at speeds from 30 to 90 pages per minute. In iondeposition 

printers, toner is typically fused to paper by a 

method that is fast and does not require heat but leaves the 

paper a little glossy, making it unsuitable for business cor- 

287 

respondence. In addition, ion-deposition printers tend to 

produce thick, slightly fuzzy characters; the technology is 

also more expensive than that of a laser printer. See also 

electrophotographic printers, nonimpact printer, page 

printer. Compare laser printer, LCD printer, LED printer. 

I/O port n. See port1 (definition 1). 

I/O processor n. See input/output processor. 

IO.SYS n. One of two hidden system files installed on an 

MS-DOS startup disk. IO.SYS in IBM releases of MS- 

DOS (called IBMBIO.COM) contains device drivers for 

peripherals such as the display, keyboard, floppy disk 

drive, hard disk drive, serial port, and real-time clock. See 

also MSDOS.SYS. 

IP n. Acronym for Internet Protocol. The protocol within 

TCP/IP that governs the breakup of data messages into 

packets, the routing of the packets from sender to destination 

network and station, and the reassembly of the packets 

into the original data messages at the destination. IP 

runs at the internetwork layer in the TCP/IP model— 

equivalent to the network layer in the ISO/OSI reference 

model. See also ISO/OSI reference model, TCP/IP. Compare 

TCP. 

IP address n. Short for Internet Protocol address. A 32bit 

(4-byte) binary number that uniquely identifies a host 

(computer) connected to the Internet to other Internet 

hosts, for the purposes of communication through the 

transfer of packets. An IP address is expressed in “dotted 

quad” format, consisting of the decimal values of its 4 

bytes, separated with periods; for example, 127.0.0.1. The 

first 1, 2, or 3 bytes of the IP address identify the network 

the host is connected to; the remaining bits identify the 

host itself. The 32 bits of all 4 bytes together can signify 

almost 232 , or roughly 4 billion, hosts. (A few small ranges 

within that set of numbers are not used.) Also 

called: Internet Protocol number, IP number. See also 

host, IANA, ICANN, InterNIC, IP, IP address classes, 

packet (definition 2). Compare domain name. 

IP address classes n. Short for Internet Protocol 

address classes. The classes into which IP addresses were 

divided to accommodate different network sizes. Each 

class is associated with a range of possible IP addresses 

and is limited to a specific number of networks per class 

and hosts per network. See the table. See also Class A IP 

address, Class B IP address, Class C IP address, IP 

address. 

I

I 

IP aliasing IP telephony 

Range of IP Networks 

Hosts per 

Network 

(maximum 

Address Class Addresses per Class number) 

Class A (/8) 1.x.x.x to 

126.x.x.x 

126 16,777,214 

Class B (/16) 128.0.x.x to 

191.255.x.x 

16,384 65,534 

Class C (/24) 192.0.0.x to 

223.255.255.x 

2,097,152 254 

IP address classes. Each x represents the host-number field 

assigned by the network administrator. 

IP aliasing n. See NAT. 

IPC n. See interprocess communication. 

ipchains n. See iptables. 

IP Filter n. Short for Internet Protocol Filter. A TCP/IP 

packet filter for UNIX, particularly BSD. Similar in functionality 

to netfilter and iptables in Linux, IP Filter can be 

used to provide network address translation (NAT) or firewall 

services. See also firewall. Compare netfilter, iptables. 

IPL n. See initial program load. 

IP masquerading n. See NAT. 

IP multicasting n. Short for Internet Protocol multicasting. 

The extension of local area network multicasting 

technology to a TCP/IP network. Hosts send and receive 

multicast datagrams, the destination fields of which specify 

IP host group addresses rather than individual IP 

addresses. A host indicates that it is a member of a group 

by means of the Internet Group Management Protocol. See 

also datagram, Internet Group Membership Protocol, IP, 

MBONE, multicasting. 

IPng n. Acronym for Internet Protocol next generation. A 

revised version of the Internet Protocol (IP) designed primarily 

to address growth on the Internet. IPng is compatible 

with, but an evolutionary successor to, the current 

version of IP, IPv4 (IP version 4), and was approved as a 

draft standard in 1998 by the IETF (Internet Engineering 

Task Force). It offers several improvements over IPv4 

including a quadrupled IP address size (from 32 bits to 

128 bits), expanded routing capabilities, simplified header 

formats, improved support for options, and support for 

quality of service, authentication, and privacy. Also 

called: IPv6. See also IETF, IP, IP address. 

288 

IP number n. See IP address. 

IPP n. See Internet Printing Protocol. 

IPSec n. Short for Internet Protocol Security. A security 

mechanism under development by the IETF (Internet 

Engineering Task Force) designed to ensure secure packet 

exchanges at the IP (Internet Protocol) layer. IPSec is 

based on two levels of security: AH (Authentication 

Header), which authenticates the sender and assures the 

recipient that the information has not been altered during 

transmission, and ESP (Encapsulating Security Protocol), 

which provides data encryption in addition to authentication 

and integrity assurance. IPSec protects all protocols in 

the TCP/IP protocol suite and Internet communications by 

using Layer Two Tunneling Protocol (L2TP) and is 

expected to ensure secure transmissions over virtual private 

networks (VPNs). See also anti-replay, communications 

protocol, Diffie-Hellman, ESP, IETF, IP, IPv6, 

Layer L2TP, TCP/IP, packet, virtual private network. 

IP Security n. See IPSec. 

IP/SoC Conference and Exhibition n. Acronym for 

Intellectual Property/System on a Chip Conference and 

Exhibition. Leading conference and exhibition for executives, 

architects, and engineers using intellectual property 

in the design and production of system-on-a-chip semiconductors. 

The event features product exhibits and forums 

for the exchange of information. 

IP splicing n. See IP spoofing. 

IP spoofing n. The act of inserting a false sender IP 

address into an Internet transmission in order to gain 

unauthorized access to a computer system. Also called: IP 

splicing. See also IP address, spoofing. 

IP switching n. A technology developed by Ipsilon Networks 

(Sunnyvale, Calif.) that enables a sequence of IP 

packets with a common destination to be transmitted over 

a high-speed, high-bandwidth Asynchronous Transfer 

Mode (ATM) connection. 

iptables n. A utility used to configure firewall settings 

and rules in Linux. Part of the netfilter framework in the 

Linux kernel, iptables replaces ipchains, a previous implementation. 

See also netfilter. Compare IP Filter. 

IP telephony n. Telephone service including voice and 

fax, provided through an Internet or network connection. 

IP telephony requires two steps: conversion of analog 

voice to digital format by a coding/uncoding device

IP tunneling IRQ 

(codec) and conversion of the digitized information to 

packets for IP transmission. Also called: Internet telephony, 

Voice over IP (VoIP). See also H.323, VoIP. 

IP tunneling n. A technique used to encapsulate data 

inside a TCP/IP packet for transmission between IP 

addresses. IP tunneling provides a secure means for data 

from different networks to be shared over the Internet. 

IPv4 n. Short for Internet Protocol version 4. The current 

version of the Internet Protocol (IP), as compared with the 

next-generation IP, which is known familiarly as IPng and 

more formally as IPv6 (IP version 6). See also IP. Compare 

IPng. 

IPv6 n. Short for Internet Protocol version 6. The nextgeneration 

Internet Protocol from the Internet Engineering 

Task Force (IETF), IPv6 is now included as part of IP support 

in many products and in the major operating systems. 

IPv6 offers several improvements from IPv4, most significantly 

an increase of available address space from 32 to 

128 bits, which makes the number of available addresses 

effectively unlimited. Usually called IPng (next generation), 

IPv6 also includes support for multicast and anycast 

addressing. See also anycasting, IP, IPng. 

ipvs n. Acronym for IP Virtual Server. See LVS. 

IPX n. Acronym for Internetwork Packet Exchange. The 

protocol in Novell NetWare that governs addressing and 

routing of packets within and between LANs. IPX packets 

can be encapsulated in Ethernet packets or Token Ring 

frames. IPX operates at ISO/OSI levels 3 and 4 but does 

not perform all the functions at those levels. In particular, 

IPX does not guarantee that a message will be complete 

(no lost packets); SPX has that job. See also Ethernet (definition 

1), packet, Token Ring network. Compare SPX 


IPX/SPX n. Acronym for Internetwork Packet Exchange/ 

Sequenced Packet Exchange. The network and transport 

level protocols used by Novell NetWare, which together 

correspond to the combination of TCP and IP in the TCP/ 

IP protocol suite. IPX is a connectionless protocol that 

handles addressing and routing of packets. SPX, which 

runs above IPX, ensures correct delivery. See also IPX, 

SPX (definition 1). 

IR n. See infrared. 

IRC n. Acronym for Internet Relay Chat. A service that 

enables an Internet user to participate in a conversation on 

line in real time with other users. An IRC channel, main- 

289 

tained by an IRC server, transmits the text typed by each 

user who has joined the channel to all other users who 

have joined the channel. Generally, a channel is dedicated 

to a particular topic, which may be reflected in the channel’s 

name. An IRC client shows the names of currently 

active channels, enables the user to join a channel, and 

then displays the other participants’ words on individual 

lines so that the user can respond. IRC was invented in 

1988 by Jarkko Oikarinen of Finland. See also channel 

(definition 2), server (definition 2). 

IrDA n. Acronym for Infrared Data Association. The 

industry organization of computer, component, and telecommunications 

vendors who have established the standards 

for infrared communication between computers and 

peripheral devices such as printers. 

IRE scale n. Short for Institute of Radio Engineers scale. 

Scale to determine video signal amplitudes as devised by 

the Institute of Radio Engineers, which is now part of the 

Institute of Electrical and Electronic Engineers (IEEE). 

The IRE scale includes a total of 140 units, with 100 up 

and 40 down from zero. 

IRG n. See inter-record gap. 

IRGB n. Acronym for Intensity Red Green Blue. A type 

of color encoding originally used in IBM’s Color/Graphics 

Adapter (CGA) and continued in the EGA (Enhanced 

Graphics Adapter) and VGA (Video Graphics Array). The 

standard 3-bit RGB color encoding (specifying eight colors) 

is supplemented by a fourth bit (called Intensity) that 

uniformly increases the intensity of the red, green, and 

blue signals, resulting in a total of 16 colors. See also RGB. 

IRL n. Acronym for in real life. An expression used by 

many online users to denote life outside the computer 

realm, especially in conjunction with virtual worlds such 

as online talkers, IRC, MUDs, and virtual reality. See also 

IRC, MUD, talker, virtual reality. 

IRQ n. Acronym for interrupt request. One of a set of possible 

hardware interrupts, identified by a number, on a 

Wintel computer. The number of the IRQ determines 

which interrupt handler will be used. In the AT bus, ISA, 

and EISA, 15 IRQs are available; in Micro Channel Architecture, 

255 IRQs are available. Each device’s IRQ is 

hardwired or set by a jumper or DIP switch. The VL bus 

and the PCI local bus have their own interrupt systems, 

which they translate to IRQ numbers. See also AT bus, 

DIP switch, EISA, interrupt, IRQ conflict, ISA, jumper, 

Micro Channel Architecture, PCI local bus, VL bus. 

I

I 

IRQ conflict ISO 

IRQ conflict n. The condition on a Wintel computer in 

which two different peripheral devices use the same IRQ 

to request service from the central processing unit (CPU). 

An IRQ conflict will prevent the system from working 

correctly; for example, the CPU may respond to an interrupt 

from a serial mouse by executing an interrupt handler 

for interrupts generated by a modem. IRQ conflicts can be 

prevented by the use of Plug and Play hardware and software. 

See also interrupt handler, IRQ, Plug and Play. 

irrational number n. A real number that cannot be 

expressed as the ratio of two integers. Examples of irrational 

numbers are the square root of 3, pi, and e. See also 

integer, real number. 

IRSG n. See Internet Research Steering Group. 

IRTF n. See Internet Research Task Force. 

IS n. See Information Services. 

ISA n. Acronym for Industry Standard Architecture. A 

bus design specification that allows components to be 

added as cards plugged into standard expansion slots in 

IBM Personal Computers and compatibles. Originally 

introduced in the IBM PC/XT with an 8-bit data path, ISA 

was expanded in 1984, when IBM introduced the PC/AT, 

to permit a 16-bit data path. A 16-bit ISA slot actually 

consists of two separate 8-bit slots mounted end-to-end so 

that a single 16-bit card plugs into both slots. An 8-bit 

expansion card can be inserted and used in a 16-bit slot (it 

occupies only one of the two slots), but a 16-bit expansion 

card cannot be used in an 8-bit slot. See also EISA, Micro 

Channel Architecture. 

ISAM n. See indexed sequential access method. 

ISAPI n. Acronym for Internet Server Application 

Programming Interface. An easy-to-use, high-performance 

interface for back-end applications for Microsoft’s 

Internet Information Server (IIS). ISAPI has its own 

dynamic-link library, which offers significant performance 

advantages over the CGI (Common Gateway Interface) 

specification. See also API, dynamic-link library, Internet 

Information Server. Compare CGI. 

ISAPI filter n. A DLL file used by Microsoft Internet 

Information Server (IIS) to verify and authenticate ISAPI 

requests received by the IIS. 

ISA Server n. See Internet Security and Acceleration 

Server. 

290 

ISA slot n. A connection socket for a peripheral designed 

according to the ISA (Industry Standard Architecture) 

standard, which applies to the bus developed for use in the 

80286 (IBM PC/AT) motherboard. See also ISA. 

ISC n. See Internet Software Consortium. 

ISDN n. Acronym for Integrated Services Digital Network. 

A high-speed digital communications network 

evolving from existing telephone services. The goal in 

developing ISDN was to replace the current telephone network, 

which requires digital-to-analog conversions, with 

facilities totally devoted to digital switching and transmission, 

yet advanced enough to replace traditionally analog 

forms of data, ranging from voice to computer transmissions, 

music, and video. ISDN is available in two forms, 

known as BRI (Basic Rate Interface) and PRI (Primary 

Rate Interface). BRI consists of two B (bearer) channels 

that carry data at 64 Kbps and one D (data) channel that 

carries control and signal information at 16 Kbps. In North 

America and Japan, PRI consists of 23 B channels and 1 D 

channel, all operating at 64 Kbps; elsewhere in the world, 

PRI consists of 30 B channels and 1 D channel. Computers 

and other devices connect to ISDN lines through simple, 

standardized interfaces. See also BRI, channel (definition 

2), PRI. 

ISDN terminal adapter n. The hardware interface 

between a computer and an ISDN line. See also ISDN. 

I seek you n. See ICQ. 

ISIS or IS-IS n. Acronym for Intelligent Scheduling and 

Information System. A toolkit designed to help prevent 

and eliminate faults in manufacturing systems. Developed 

in 1980 at Cornell University, ISIS is now available 

commercially. 

ISLAN n. See isochronous network. 

ISMA n. Acronym for Internet Streaming Media Alliance. 

A nonprofit organization promoting the adoption of open 

standards for the streaming of rich media over Internet Protocol 

(IP) networks. ISMA membership consists of a number 

of technology companies and groups including Apple 

Computer, Cisco Systems, IBM, Kasenna, Philips, and Sun 

Microsystems. See also Windows Metafile Format. 

ISO n. Short for International Organization for Standardization 

(often incorrectly identified as an acronym for 

International Standards Organization), an international 

association of 130 countries, each of which is represented

ISO 8601:1988 italic 

by its leading standard-setting organization—for example, 

ANSI (American National Standards Institute) for the 

United States. The ISO works to establish global standards 

for communications and information exchange. Primary 

among its accomplishments is the widely accepted ISO/OSI 

reference model, which defines standards for the interaction 

of computers connected by communications networks. 

ISO is not an acronym; rather, it is derived from the 

Greek word isos, which means “equal” and is the root of 

the prefix “iso-.” 

ISO 8601:1988 n. A standard entitled “Data elements 

and interchange formats” from the International Organization 

for Standardization (ISO) that covers a number of date 

formats. 

ISO 9660 n. An international format standard for CD- 

ROM adopted by the International Organization for Standardization 

(ISO) that follows the recommendations 

embodied in the High Sierra specification, with some 

modifications. See also High Sierra specification. 

ISOC n. See Internet Society. 

isochronous network n. A type of network defined in 

the IEEE 802.9 specification that combines ISDN and 

LAN technologies to enable networks to carry multimedia. 

Also called: Integrated Services LAN, ISLAN. 

isometric view n. A display method for three-dimensional 

objects in which every edge has the correct length 

for the scale of the drawing and in which all parallel lines 

appear parallel. An isometric view of a cube, for example, 

shows the faces in symmetrical relation to one another and 

the height and width of each face evenly proportioned; the 

faces do not appear to taper with distance as they do when 

the cube is drawn in perspective. See the illustration. 

Compare perspective view. 

Isometric 

view 

Perspective 

view 

F0Ign06.eps 

Isometric view. A cube in isometric view and in perspective 

view. 

ISO/OSI reference model n. Short for International 

Organization for Standardization Open Systems Interconnection 

reference model. A layered architecture (plan) 

291 

that standardizes levels of service and types of interaction 

for computers exchanging information through a communications 

network. The ISO/OSI reference model separates 

computer-to-computer communications into seven 

protocol layers, or levels, each building—and relying— 

upon the standards contained in the levels below it. The 

lowest of the seven layers deals solely with hardware 

links; the highest deals with software interactions at the 

application-program level. It is a fundamental blueprint 

designed to help guide the creation of networking hardware 

and software. See the illustration. Also called: OSI 

reference model. 

ISO/OSI Layer 

ISO/OSI MODEL 

Focus 




conversion 









F0Ign07.eps 


ISP n. Acronym for Internet service provider. A business 

that supplies Internet connectivity services to individuals, 

businesses, and other organizations. Some ISPs are large 

national or multinational corporations that offer access in 

many locations, while others are limited to a single city or 

region. Also called: access provider, service provider. 

ISSE n. See SSE. 

ISV n. See independent software vendor. 

IT n. Acronym for Information Technology. See Information 

Services. 

italic n. A type style in which the characters are evenly 

slanted toward the right. This sentence is in italics. Italics 

are commonly used for emphasis, foreign-language words 

and phrases, titles of literary and other works, technical 

terms, and citations. See also font family. Compare roman. 

I

I 

Itanium i-way 

Itanium n. An Intel microprocessor that uses explicitly 

parallel instruction set computing and 64-bit memory 

addressing. 

iterate vb. To execute one or more statements or instructions 

repeatedly. Statements or instructions so executed 

are said to be in a loop. See also iterative statement, loop. 

iterative statement n. A statement in a program that 

causes the program to repeat one or more statements. 

Examples of iterative statements in Basic are FOR, DO, 

REPEAT..UNTIL, and DO..WHILE. See also control 

statement. 

ITI n. See Intelligent Transportation Infrastructure. 

I-time n. See instruction time. 

ITM n. Short for Internet traffic management. The analysis 

and control of Internet traffic to improve efficiency and 

optimize for high availability. With ITM, Web traffic is 

distributed among multiple servers using load balancers 

and other devices. See also load balancing. 

ITR n. See Internet Talk Radio. 

ITSP n. Acronym for Internet Telephony Service Provider. 

A business that supplies PC-to-telephone calling 

capabilities to individuals, businesses, and organizations. 

Through an ITSP, calls initiated on a PC travel over the 

Internet to a gateway that, in turn, sends the call to the 

standard public switched phone network and, eventually, 

to the receiving telephone. See also ISP, telephony. 

ITU n. Acronym for International Telecommunication 

Union. An international organization based in Geneva, 

Switzerland, that is responsible for making recommendations 

and establishing standards governing telephone and 

data communications systems for public and private telecommunications 

organizations. Founded in 1865 under 

292 

the name International Telegraph Union, it was renamed 

the International Telecommunication Union in 1934 to 

signify the full scope of its responsibilities. ITU became 

an agency of the United Nations in 1947. A reorganization 

in 1992 aligned the ITU into three governing bodies: the 

Radiocommunication Sector, the Telecommunication 

Standardization Sector (ITU-TSS, ITU-T, for short; formerly 

the CCITT), and the Telecommunication Development 

Sector. See also ITU-T. 

ITU-T n. The standardization division of the International 

Telecommunication Union, formerly called Comité Consultatif 

International Télégraphique et Téléphonique 

(CCITT). The ITU-T develops communications recommendations 

for all analog and digital communications. 

Also called: ITU-TSS. See also CCITT Groups 1-4, ITU. 

ITU-TSS n. See ITU-T. 

ITU-T V series n. See V series. 

ITU-T X series n. See X series. 

iTV n. Acronym for Interactive television. A communications 

medium combining television with interactive services. 

iTV offers two-way communications between users 

and communications providers. From their televisions, 

users can order special programming, respond to programming 

options, and access the Internet and additional services 

such as instant messaging and telephone functions. 

IVR n. See interactive voice response. 

IVUE n. A proprietary image format (from Live Pictures) 

that allows files to be adjusted to screen resolution at any 

zoom level. 

i-way n. See Information Superhighway.

J2EE n. Acronym for Java 2 Platform Enterprise Edition. 

An application server framework from Sun Microsystems, 

Inc., for the development of distributed applications. It 

includes all the previous Java APIs targeted for multitiered 

distributed enterprise information systems. The 

J2EE platform consists of a set of services, application 

programming interfaces (APIs), and protocols that provide 

the functionality for developing multitiered, Web-based 

applications. See also application programming interface, 

Enterprise Java Beans, IDL, Java, JDBC, Jini, JMS, JNDI, 

JSP, JTA, JTS, RMI-IIOP. 

J n. A high-level programming language created by Kenneth 

Iverson, developer of APL, and Roger Hui. J is a successor 

language to APL that may be run on many 

platforms, including Windows 95, Windows NT, Macintosh, 

Linux, RS/6000, and Sun Sparc. Like APL, J is used 

primarily by mathematicians. See also APL. 

jabber n. A continuous stream of random data transmitted 

over a network as the result of some malfunction. 

Jabber n. An XML-based instant messaging system. Jabber 

software is available for most operating systems and 

allows user access to other instant messaging services. Jabber 

is an open source application overseen by Jabber.org. 

jack n. A connector designed to receive a plug. A jack is 

commonly used in making audio and video connections. 

jacket n. See disk jacket. 

jack in vb. 1. To log on to a computer. 2. To connect to a 

network or BBS, especially for purposes of entering an 

IRC or a virtual reality simulation, such as a MUD. (To 

leave is to jack out.) See also IRC, MUD. 

jack out vb. 1. To log off a computer. 2. To disconnect 

from a network or online bulletin board system. See also 

jack in, log on. 

Jacquard loom n. The first machine that used punched 

cards to control its operation. In this loom, developed in 

1801 by French inventor Joseph-Marie Jacquard, up to 

24,000 cards were placed on a rolling drum. Where a hole 

was punched on a card, one of a set of rods could pass 

J 

293 

through and select a particular thread to be woven into the 

pattern. Jacquard was awarded a medal by the Emperor 

Napoleon for his invention. Later in the nineteenth century, 

punched cards were used in Charles Babbage’s computerlike 

Analytical Engine and in Herman Hollerith’s 

statistical tabulating machine. See also Analytical Engine, 

Hollerith tabulating/recording machine. 

jaggies n. The “stairsteps” that appear in diagonal lines 

and curves drawn at low resolutions in computer graphics. 

Also called: aliasing. 

Janet n. Short for the Joint Academic Network. A wide 

area network in the United Kingdom that serves as the 

principal backbone for the Internet in that country. See 

also backbone (definition 1). 

.jar n. A file name extension that identifies a compressed 

JAR (Java Archive) file. Note: By changing the .jar extension 

to .zip, you can use popular extraction tools such as 

PKZIP or WINZIP to look at a .jar file’s contents. See also 

compressed file, JAR, PKZIP, .zip. 

JAR n. Acronym for Java Archive file. JAR files allow 

Java developers to efficiently deploy Java classes and their 

associated resources. The elements in a JAR file are compressed 

just as in a standard zip file. JAR files include a 

security mechanism and a special META-INF directory 

that contains administrative information about the contents 

of the files. Using a combination of a digital signature 

and the META-INF data, JAR files can be signed to 

ensure authenticity and security. See also .jar. 

Java n. An object-oriented programming language developed 

by Sun Microsystems, Inc. Similar to C++, Java is 

smaller, more portable, and easier to use than C++ because 

it is more robust and it manages memory on its own. Java 

was also designed to be secure and platform-neutral 

(meaning that it can be run on any platform) through the 

fact that Java programs are compiled into bytecode, which 

is not refined to the point of relying on platform-specific 

instructions and runs on a computer in a special software 

environment known as a virtual machine. This characteristic 

of Java makes it a useful language for programming 

J

J 

Java applet JavaMail 

Web applications, since users access the Web from many 

types of computers. Java is used in programming small 

applications, or applets, for the World Wide Web, as well 

as in creating distributed network applications. See also 

bytecode, Java applet, Jini, object-oriented programming. 

Java applet n. A Java class that is loaded and run by an 

already-running Java application such as a Web browser or 

an applet viewer. Java applets can be downloaded and run 

by any Web browser capable of interpreting Java, such as 

Internet Explorer, Netscape Navigator, and HotJava. Java 

applets are frequently used to add multimedia effects and 

interactivity to Web pages, such as background music, 

real-time video displays, animations, calculators, and 

interactive games. Applets can be activated automatically 

when a user views a page, or they may require some action 

on the part of the user, such as clicking on an icon in the 

Web page. See also applet, Java. 

JavaBean n. A Java component architecture defined in 

the JavaBeans specification developed by Sun Microsystems. 

A JavaBean, or Bean, is a reusable application component—an 

independent code segment—that can be 

combined with other JavaBean components to create a 

Java applet or application. The JavaBean concept emphasizes 

the platform-independence of the Java language, in 

which ideally a program, once written, can run on any 

computing platform. JavaBeans are similar to Microsoft’s 

ActiveX controls. ActiveX controls, however, can be 

developed in different programming languages but executed 

only on a Windows platform. JavaBeans can be 

developed only in the Java programming language but ideally 

can run on any platform. See also ActiveX, Java. 

Java Card n. An application programming interface 

(API) from Sun Microsystems, Inc., that allows Java 

applets and programs to run on smart cards and other 

devices with limited memory. Java Card uses a Java Card 

Virtual Machine designed for severely memory-constrained 

devices. See also applets, Java Card Virtual 

Machine, smart card (definition 2). 

Java Card Virtual Machine n. An ultra-small-footprint, 

highly optimized foundation of a runtime environment 

within the Java 2 Platform Micro Edition. Derived from the 

Java Virtual Machine (JVM), it is targeted at smart cards 

and other severely memory-constrained devices. The Java 

Card Virtual Machine can run in devices with memory as 

small as 24 KB of ROM, 16 KB of EEPROM, and 512 

bytes of RAM. See also EEPROM, Java Card, RAM, 

ROM. 

294 

Java chip n. An implementation on a single integrated 

circuit of the virtual machine specified for execution of the 

Java programming language. Such chips, which are being 

developed by Sun Microsystems, Inc., could be used in 

very small devices and as controllers for appliances. See 

also integrated circuit, Java, virtual machine. 

Java-compliant browser n. A Web browser with support 

for the Java programming language built into it. Most 

current Web browsers are Java-compliant. See also Java, 

Web browser. 

Java Developer’s Kit n. A set of software tools developed 

by Sun Microsystems, Inc., for writing Java applets 

or applications. The kit, which is distributed free, includes 

a Java compiler, interpreter, debugger, viewer for applets, 

and documentation. Acronym: JDK. See also applet, Java, 

Java applet. 

Java Foundation Classes n. A Java-based set of class 

libraries developed by Sun Microsystems, Inc. Encompassing 

fundamentals of the Internet Foundation Classes 

created by Netscape Communications Corp., the Java 

Foundation Classes extend the Java Abstract Window 

Toolkit (AWT) by providing graphical user interface 

components for use in developing commercial and 

Internet-related Java applications. See also Abstract Window 

Toolkit, Application Foundation Classes, Internet 

Foundation Classes, Java, JavaBean, Microsoft Foundation 

Classes. 

Java HotSpot n. A Java performance engine introduced 

by Sun Microsystems, Inc., in 1999 that is designed to run 

Java applications faster than just-in-time (JIT) compilers. 

The core of Java HotSpot, and the feature for which it is 

named, is its ability to perform adaptive optimization—the 

identification and optimization of “hot spots,” or sections 

of performance-critical code. Improved garbage collection 

(freeing of memory occupied by objects no longer in use) 

and better multithreading are additional features designed 

to contribute to increased performance. See also Java. 

Java IDL n. Short for Java Interface Definition Language. 

A Java technology that provides CORBA interoperability 

and connectivity capabilities for the Java platform. These 

capabilities enable Java applications to invoke operations 

on remote network services using the Object Management 

Group Interface Definition Language and Internet Inter- 

ORB Protocol. See also CORBA, IDL, J2EE, RMI-IIOP. 

JavaMail n. An API in the Sun Microsystems, Inc., Java 

platform for sending and receiving mail. A set of 

abstract APIs that model a mail system, JavaMail provides 

a platform-independent and protocol-independent

Java Management Application Programming Interface Jet SQL 

framework to build Java-based e-mail client applications. 

See also application programming interface, e-mail, J2EE. 

Java Management Application Programming 

Interface n. A set of application programming interface 

specifications, proposed by Sun Microsystems, 

Inc., to enable the Java language to be used for network 

management. Acronym: JMAPI. See also application 

programming interface, Java. 

JavaOS n. An operating system designed to run applications 

written in the Java programming language. JavaOS 

was created by JavaSoft, an operating company of Sun 

Microsystems, Inc., to run the Java Virtual Machine 

(JVM) directly on microprocessors, and thus eliminate the 

need for a resident operating system. JavaOS is small and 

designed for network computers, as well as devices ranging 

from game machines to pagers and cellular telephones. 

See also Java. 

JavaScript n. A scripting language developed by 

Netscape Communications and Sun Microsystems that is 

loosely related to Java. JavaScript, however, is not a true 

object-oriented language, and it is limited in performance 

compared with Java because it is not compiled. Basic 

online applications and functions can be added to Web 

pages with JavaScript, but the number and complexity of 

available application programming interface functions are 

fewer than those available with Java. JavaScript code, 

which is included in a Web page along with the HTML 

code, is generally considered easier to write than Java, 

especially for novice programmers. A JavaScript-compliant 

Web browser, such as Netscape Navigator or Internet 

Explorer, is necessary to run JavaScript code. See also 

application programming interface, HTML, scripting 

language. Compare Java. 

JavaServer Pages n. See JSP. 

Java Speech Grammar Format n. A platform-independent 

grammar description format developed for use with 

speech recognition systems. Java Speech Grammar Format 

is used extensively with Voice XML and can be used 

with most speech recognition systems and related applications. 

Acronym: JSGF. 

Java Virtual Machine n. The environment in which Java 

programs run. The Java Virtual Machine gives Java programs 

a software-based “computer” they can interact with. 

(Programs, even the most seemingly unchallenging ones 

designed for children or entertainment, must run within an 

environment from which they can use memory, display 

295 

information, gather input, and so on.) Because the Java 

Virtual Machine is not a real computer but exists in software, 

a Java program can run on any physical computing 

platform, such as a Windows 9x computer or a Macintosh, 

equipped with an interpreter—usually an Internet 

browser—that can carry out the program’s instructions 

and a Java Virtual Machine that provides the “hardware” 

on which the program can run. Acronym: JVM. 

JCL n. Acronym for Job Control Language. A command 

language used in IBM OS/360 mainframe systems. JCL is 

used to launch applications and specifies information on 

running time, program size, and the program files used for 

each application. See also command language. 

JDBC n. A Java API designed to provide access to relational 

databases and other tabular material, such as spreadsheets 

and flat files. Using JDBC, a developer can create a 

cross-platform Java application that can connect with, and 

send SQL statements to, a number of different relational 

databases. Although it is commonly thought to stand for 

Java Database Connectivity, JDBC is the name of the technology; 

it is not an acronym. 

JDK n. See Java Developer’s Kit. 

jDoc n. A cross-platform, interactive format for display, 

distribution, and interaction with live Web pages. jDoc 

documents are small in size and can be embedded in 

HTML documents to offer client-side interactivity. jDoc 

was created by EarthStones and is an extension to Sun’s 

Java platform. 

JetSend Protocol n. A platform-independent communications 

protocol developed by Hewlett-Packard to enable 

direct device-to-device communication. The JetSend protocol 

is designed to provide JetSend-enabled devices with 

the ability to exchange information and data without the 

need for device drivers or reliance on servers or user intervention. 

The protocol is intended for use with printers, 

scanners, fax machines, and other such information 

“appliances” and was developed to simplify and improve 

interoperability between and among a wide range of 

devices. 

Jet SQL n. A query language. Jet SQL is a dialect used by 

the Microsoft Access application, specifically by the 

Microsoft Jet database engine, to extract, manipulate, and 

structure data that resides in a relational database management 

system (RDBMS). Jet SQL is based largely on the 

ANSI SQL-92 standard, with additional extensions. 

J

J 

jewel box journaled file system 

jewel box n. A clear plastic container used to package 

and store a compact disc. Also called: jewel case. 

JFC n. See Java Foundation Classes. 

JFIF n. Acronym for JPEG File Interchange Format. A 

means of saving photographic images stored according to 

the Joint Photographic Experts Group image compression 

technique. JFIF represents a “common language” file format 

in that it is designed specifically to allow users to 

transfer JPEG images easily between different computers 

and applications. See also JPEG, TIFF JPEG. 

Jini n. A technical specification developed by Sun Microsystems 

that uses a small piece (48 KB) of Java code to 

allow any network device with a Java Virtual Machine 

(JVM) to announce its availability and provide its services 

to any other device connected to the same network. Jini is 

based on the concept of creating a “federation” of selfconfiguring 

devices capable of transparently exchanging 

code when necessary to simplify interactions between network 

devices. See also Java. 

JIT adj. See just-in-time. 

jitter n. 1. Small vibrations or fluctuations in a displayed 

video image caused by irregularities in the display signal. 

Jitter is often visible in the form of horizontal lines that are 

of the same thickness as scan lines. 2. A rough appearance 

in a fax caused by dots that are incorrectly recorded during 

the scanning process and thus wrongly positioned in the 

output. 3. In digital communication, distortion caused by 

lack of synchronization of signals. 

JMAPI n. See Java Management Application Programming 

Interface. 

JMS n. Acronym for Java Messaging Service. In the J2EE 

network platform, JMS is an API for using enterprise messaging 

systems such as IBM MQ Series, TIBCO Rendezvous, 

and others. See also application programming 

interface, J2EE. 

JNDI n. Acronym for Java Naming and Directory Interface. 

A set of APIs in the J2EE platform from Sun Microsystems, 

Inc., that assists with the interfacing to multiple 

naming and directory services. See also application programming 

interface, J2EE. 

job n. A specified amount of processing performed as a 

unit by a computer. On early mainframe computers, data 

was submitted in batches, often on punched cards, for processing 

by different programs; work was therefore scheduled 

and carried out in separate jobs, or operations. 

296 

Job Control Language n. See JCL. 

job processing n. A computing method in which a series 

of jobs, each consisting of one or more tasks grouped 

together as a computationally coherent whole, is processed 

sequentially. See also batch processing (definition 2). 

job queue n. A list of programs or tasks waiting for execution 

by a computer. Jobs in the queue are often ordered 

according to some basis of priority. See also queue. 

join n. 1. A database table operation that creates a resultant 

entry in another table for each entry in the one table 

whose key field matches that of an entry in the other. See 

also inner join. 2. A multiprocessing command that causes 

a child process to return control to its parent. See also 

child (definition 1), multiprocessing. 

join line n. In a database query, a line that connects fields 

between two tables and shows how the data is related. Generally, 

a join line starts with an arrow just beyond the boundary 

of the table window pointing at the field in one table and 

ends just beyond the boundary of another table with an 

arrow pointing at the related field. The type of join indicates 

which records are selected for the query’s result set. 

Joint Photographic Experts Group n. See JPEG (definition 

1). 

Joliet n. An extension to the ISO 9660 (1988) standard 

developed to include long filenames or filenames outside 

the 8.3 convention. This format is used in some new CD- 

ROMs for operating systems, such as Windows 9x, that 

can handle such filenames. See also 8.3, ISO 9660, long 

filenames. 

Josephson junction n. A cryoelectronic device that can 

attain extremely high circuit-switching speeds. In the 

Josephson effect, when two superconducting materials are 

in close proximity but are separated by an insulator, electric 

current can jump or tunnel through the gap. 

journal n. A computer-based log or record of transactions 

that takes place in a computer or across a network. A journal 

could be used, for example, to record message transfers 

on a communications network, to keep track of 

system activities that alter the contents of a database, or to 

maintain a record of files that have been archived for storage 

or deleted from the system. A journal is often kept as a 

means of reconstructing events or sets of data should they 

become lost or damaged. See also audit trail. 

journaled file system n. A fault-resilient file system 

that includes backup and recovery capabilities. When 

file server indexes are updated, all changes and related

joystick JTA 

information are recorded and stored in a separate log. If 

a system failure or other abnormal interruption occurs, 

the system will use stored backup files to repair files corrupted 

in the crash. Journaled file systems are widely used 

for business and intranet file servers. In 2001, IBM contributed 

journaled file system technology to the open 

source community to allow development of similar file 

systems for Linux servers. 

joystick n. A pointing device used mainly but not exclusively 

for computer games. A joystick has a base, on 

which control buttons can be mounted, and a vertical stem, 

which the user can move in any direction to control the 

movement of an object on the screen; the stem may also 

have control buttons. The buttons activate various software 

features, generally producing on-screen events. A joystick 

is usually used as a relative pointing device, moving an 

object on the screen when the stem is moved and stopping 

the movement when the stem is released. In industrial control 

applications, the joystick can also be used as an absolute 

pointing device, with each position of the stem 

mapped to a specific location on the screen. See the illustration. 

See also absolute pointing device, relative pointing 

device. Compare game pad. 

F0Jxx01.eps 

Joystick. 

.jpeg n. The file extension that identifies graphic image 

files in the JPEG format. See also JPEG. 

JPEG n. 1. Acronym for Joint Photographic Experts 

Group. An ISO/ITU standard for storing images in compressed 

form using a discrete cosine transform. JPEG 

trades off compression against loss; it can achieve a compression 

ratio of 100:1 with significant loss and possibly 

297 

20:1 with little noticeable loss. 2. A graphic stored as a file 

in the JPEG format. 

JPEG File Interchange Format n. See JFIF. 

.jpg n. The file extension that identifies graphic images 

encoded in the JPEG File Interchange Format, as originally 

specified by the Joint Photographic Experts Group 

(JPEG). Inline graphics on World Wide Web pages are 

often .jpg files, such as coolgraphic.jpg. See also JPEG 


JScript n. An interpreted, object-based scripting language 

that borrows from C, C++, and Java. It is Microsoft’s 

implementation of the ECMA 262 language specification 

(ECMAScript Edition 3). The latest versions of JavaScript 

and JScript are compliant with the European Computer 

Manufacturing Association’s ECMAScript Language 

Specification (ECMA 262 standard, for short). 

JSGF n. See Java Speech Grammar Format. 

JSP n. Short for JavaServer Pages. A technology created 

by Sun Microsystems to enable development of platformindependent 

Web-based applications. Using HTML and 

XML tags and Java scriptlets, JSP helps Web site developers 

create cross-platform programs. JSP scriptlets run on 

the server, not in a Web browser, and generate dynamic 

content on Web pages, with the ability to integrate content 

from a variety of data sources, such as databases, files, and 

JavaBean components. Web site developers can concentrate 

on design and display of a Web site without the need 

for application development expertise. See also Java, Java- 

Bean. Compare Active Server Pages. 

JSP container n. Short for JavaServer Pages container. 

In the J2EE platform, a JSP container provides the same 

services as a servlet container, such as providing network 

services over which requests and responses are sent, 

decoding requests, and formatting responses. All servlet 

containers must support HTTP as a protocol for requests 

and responses, but they may also support additional 

request-response protocols such as HTTPS. The JSP container 

is also an engine that interprets and processes JSP 

pages into a servlet. See also container, HTTP, HTTPS, 

J2EE, servlet, servlet container. 

JTA n. Acronym for Java Transaction API. In the J2EE 

platform, JTA specifies transactions, comments, and rollbacks 

used by EJBs (Enterprise JavaBeans). It is a highlevel, 

implementation-independent protocol API that 

allows applications and application servers to access transactions. 

See also application programming interface, 

J2EE, JTS, rollback. 

J

J 

JTS JVM 

JTS n. Acronym for Java Transaction Services. In the 

J2EE platform, JTS specifies the implementation of a 

transaction manager that supports JTA and implements the 

Java mapping of the OMG Object Transaction Service 

specification at a level below the API. JTS propagates 

transactions using the Internet Inter-ORB Protocol (IIOP). 

See also application programming interface, J2EE, JTA, 

rollback. 

JUG n. Acronym for Java User Group. A user group that 

meets to discuss the Java programming language and the 

Java platform. See also user group. 

Jughead n. Acronym for Jonzy’s Universal Gopher Hierarchy 

Excavation and Display. An Internet service that 

enables a user to locate directories in Gopherspace 

through a keyword search. A Jughead server indexes keywords 

appearing in directory titles in top-level Gopher 

menus but does not index the files within the directories. 

To access Jughead, users must point their Gopher clients 

to a Jughead server. See also Gopher, Gopherspace. Compare 

Archie, Veronica. 

jukebox n. Software that is designed to play a list of 

sound files in a user-specified order reminiscent of jukeboxes 

used to play vinyl records. See also CD-ROM 

jukebox. 

Julian calendar n. The calendar introduced by Julius 

Caesar in 46 B.C. to replace the lunar calendar. The Julian 

calendar provided for a year of 365 days with a leap year 

every 4 years, or an average year length of 365.25 days. 

Because the solar year is slightly shorter, the Julian calendar 

gradually moved out of phase with the seasons and 

was superseded by the Gregorian calendar, introduced by 

Pope Gregory XIII. Compare Gregorian calendar, Hijiri 

calendar. 

Julian date n. 1. A date expressed as the number of days 

elapsed since January 1, 4713 B.C. (on the Julian calendar)—for 

example, 2,450,000 for October 9, 1995 (Gregorian). 

Julian dates are useful for finding elapsed times 

between events that may be many years apart, as in astronomy. 

The starting point is the beginning of the Julian 

Period, defined in 1583 by Joseph Scaliger as the coincidence 

of several cycles based on the Julian calendar. See 

also Gregorian calendar, Julian calendar. 2. Often (but 

incorrectly), a date expressed as the year and the number 

of days elapsed since the beginning of the year—for 

example, 91.13 for January 13, 1991. Acronym: JD. 

298 

jumper n. A small plug or wire that can be connected 

between different points in an electronic circuit in order to 

alter an aspect of a hardware configuration. Compare DIP 

switch. 

jump instruction n. An instruction that transfers the flow 

of execution from one statement or instruction to another. 

See also GOTO statement, transfer statement. 

jump page n. See doorway page. 

jump table n. See dispatch table. 

Jump to .NET n. Acronym for Java User Migration Path 

to Microsoft .NET. A set of Microsoft technologies and 

services that enable Java programmers to preserve, 

enhance, and migrate Java language projects onto the 

Microsoft .NET platform. It includes tools for interoperability 

of existing code, Java language syntax support, and 

automated conversion of Java source code to C#. JUMP to 

.NET enables programmers using the Java language to 

move existing code to the Microsoft .NET platform. See 

also C#, .NET. 

junction n. 1. Any point at which two or more electrical 

components are connected. 2. The contact between two 

types of semiconductors, such as N-type and P-type semiconductors. 

See also N-type semiconductor, P-type semiconductor, 

semiconductor. 

justify vb. 1. To align vertically. 2. To align lines of text 

evenly along both the left and right margins of a column 

by inserting extra space between the words in each line. If 

the spacing is excessive, it can be reduced by rewriting or 

by hyphenating words at the ends of lines. See also align 

(definition 1). Compare rag. 

just-in-time adj. 1. Describing a system of inventory control 

and industrial production management based on the 

Japanese kanban system. Under a just-in-time system, 

workers receive materials from suppliers “just in time” for 

scheduled manufacturing to take place. Line workers generally 

signal that they require materials by means of a card 

or a computerized request system. 2. Describing an action 

that is taken only when it becomes necessary, such as justin-time 

compilation or just-in-time object activation. 

3. Describing a compiler that compiles Java on the fly. 

Acronym: JIT. See also Java, on the fly. 

JVM n. See Java Virtual Machine.

K 1 n. Short for kilobyte. 

K 2 prefix See kilo-. 

K&R C n. Short for (Brian W.) Kernighan and (Dennis 

M.) Ritchie C. The version of the C programming language, 

defined by those two authors, that was the informal 

C standard until a more formal standard was developed by 

an ANSI committee. See also C. 

Kalman filter n. An adaptive filter used to estimate the 

state of a system from measurements that contain random 

errors. This recursive adaptive filter determines the correct 

parameters of a process model. Each new measurement 

allows the parameters of a model to be predicted and 

adjusted, thus providing an estimate of error at each 

update. The Kalman filter’s computational structure and 

its ability to incorporate the effects of noise (from both 

measurement and modeling) recommends itself for use in 

computer vision tracking applications. See also active 

vision, distortion, modeling, noise. 

kamikaze packet n. See Chernobyl packet. 

kashidas n. Special characters that are used to extend the 

joiner between two Arabic characters. Kashidas are used 

to improve the appearance of justified text by visually 

lengthening words rather than increasing the spacing 

between words. See the illustration. 

F0Kgn01.eps 

Kashidas. 

Kb n. See kilobit. 

K 

299 

KB n. 1. See kilobyte. 2. Short for Knowledge Base. Primary 

source of product information for Microsoft support 

engineers and customers. This comprehensive collection 

of articles, updated daily, contains detailed how-to information, 

answers to technical-support questions, and 

known issues. Also called: Microsoft Knowledge Base. 

Kbit n. See kilobit. 

Kbps n. See kilobits per second. 

Kbyte n. See kilobyte. 

kc n. See kilocycle. 

KDE n. Acronym for K Desktop Environment. A popular 

open-source desktop environment originally intended for 

UNIX workstations and now developed for the Linux 

operating system. KDE provides a graphical user interface 

(GUI) and basic applications that correspond to those 

found with Microsoft Windows or the Macintosh operating 

system. By providing a mainstream environment and 

familiar desktop appearance, KDE is intended to make 

Linux easier for users. KDE and GNOME are leading contenders 

for consideration as a Linux desktop standard. See 

also GNOME, GUI. 

Kerberos n. A network authentication protocol developed 

by MIT. Kerberos authenticates the identity of users 

attempting to log on to a network and encrypts their 

communications through secret-key cryptography. A free 

implementation of Kerberos is available from MIT, 

although it is also available in many commercial products. 

Also called: Kerberos v5 authentication protocol. 

See also authentication, cryptography, IPSec. 

Kermit n. A file transfer protocol used in asynchronous 

communications between computers. Kermit is a very flexible 

protocol used in many software packages designed for 

communications over telephone lines. Compare Xmodem, 

Ymodem, Zmodem. 

K

K 

kern keyboard repeat 

kern vb. To alter selectively the distance between pairs of 

letters for readability and to make the type spacing more 

balanced and proportional. See the illustration. 

F0Kgn02.eps 

Kern. The first three letters of the second example are kerned. 

kernel n. The core of an operating system—the portion 

of the system that manages memory, files, and peripheral 

devices; maintains the time and date; launches applications; 

and allocates system resources. 

Kernel Extension n. See KEXT. 

kernel panic n. In Mac OS X and UNIX-based systems, 

a type of error that occurs when the core level of the operating 

system is unable to properly handle an instruction. A 

kernel panic appears to the user as a text screen containing 

information about the nature of the error, which often can 

be corrected with a system reboot. 

KEXT n. Acronym for Kernel Extension. In Mac OS X, an 

extension mechanism created to expand the functionality 

of the operating system kernel. KEXTs are modular and 

dynamic loading, and they may be created for any service 

that requires access to kernel internal interfaces. Creation 

of a KEXT allows the loading of pieces of code into the 

kernel without the need to recompile. 

key n. 1. On a keyboard, the combination of a plastic keycap, 

a tension mechanism that suspends the keycap but 

allows it to be pressed down, and an electronic mechanism 

that records the key press and key release. 2. In database 

management, an identifier for a record or group of records 

in a datafile. See also B-tree, hash2 , index1 (definition 1), 

inverted list, key field. 3. In encryption and digital signatures, 

a string of bits used for encrypting and decrypting 

information to be transmitted. Encryption commonly 

relies on two different types of keys, a public key known 

to more than one person (say, both the sender and the 

receiver) and a private key known only to one person (typically, 

the sender). 4. A metal object used with a physical 

lock to disable a computer system. 

key binary large object n. A key binary large object 

(BLOB) provides a way to store keys outside of the cryptographic 

service provider (CSP) and is used to transfer 

300 

keys securely from one CSP to another. A key BLOB consists 

of a standard header followed by data representing 

the key. Acronym: key BLOB. 

key BLOB n. See key binary large object. 

keyboard n. A hardware unit with a set of switches that 

resembles a typewriter keyboard and that conveys information 

from a user to a computer or data communications 

circuit. See also Alt key, Apple key, arrow key, Backspace 

key, Break key, Caps Lock key, character code, Clear key, 

Command key, control character, Control key, Delete key, 

Dvorak keyboard, End key, enhanced keyboard, Enter 

key, ergonomic keyboard, Escape key, function key, Help 

key, Home key, Insert key, keyboard buffer, keyboard 

controller, keyboard enhancer, keycap, key code, numeric 

keypad, Num Lock key, Option key, original Macintosh 

keyboard, Page Down key, Page Up key, Pause key, PC/ 

XT keyboard, Power-on key, Print Screen key, QWERTY 

keyboard, Return key, scan code, Scroll Lock key, Shift 

key, Sys Req key, Tab key. 

keyboard buffer n. A small amount of system memory 

that stores the most recently typed characters. This buffer 

is used to store typed characters that have not yet been 

processed. Also called: type-ahead buffer. 

keyboard controller n. A microprocessor installed in a 

keyboard whose primary function is to wait for and report 

on keystrokes. 

keyboard enhancer n. A program that monitors keystrokes 

as they are typed and that can be used to redefine 

the meaning of certain keys or key combinations. Keyboard 

enhancers are used to create and store macros— 

sets of keystrokes, mouse actions, menu selections, or 

other instructions—that are then assigned to keys. Also 

called: macro program. 

keyboard layout n. The key arrangement used for a particular 

keyboard, including such factors as the number of keys 

(101 is the current standard) and the configuration of the 

keys (QWERTY is the United States standard). Some proprietary 

systems use different layouts, and many allow you 

to map the keys to characters according to your preferences. 

keyboard port n. The connector on a computer that 

receives data from the keyboard. See also port1 (definition 

1). 

keyboard processor n. See keyboard controller. 

keyboard repeat n. See typematic.

keyboard shortcut kHz 

keyboard shortcut n. See application shortcut key. 

keyboard template n. A piece of plastic or heavy paper 

that fits over or around part of the keyboard, such as the 

function keys, and has information printed on it about the 

meanings of the keys. 

keycap n. The plastic piece identifying a key on a keyboard. 

key code n. A unique code number assigned to a particular 

key on a computer keyboard, used to tell the computer 

which key has been pressed or released. A key code is a 

special identifier for the key itself and is always the same 

for a particular key, regardless of the letter, number, or 

symbol on the key or the character generated by the key. 

Compare character code, scan code. 

key escrow n. An approach to key recovery in which an 

encryption key is provided to a third party approved by a 

government agency so that any encrypted message can, if 

necessary, be decrypted and read by the government. See 

also encryption, key recovery. 

key field n. A field in a record structure or an attribute of 

a relational table that has been designated to be part of a 

key. Any field can be keyed, or indexed, to improve or 

simplify the performance of retrieval and/or update operations. 

See also attribute (definition 1), field (definition 1), 

primary key. 

key-frame adj. Describing animation in which starting and 

ending positions of an object are given, and all frames in 

between are interpolated by a computer to produce smooth 

automated animation. Most ray-traced computer animation 

is created using this technique. See also ray tracing. 

key in vb. To enter information into a computer by typing 

it on the computer’s keyboard. 

keymaster n. A common host name assigned by network 

administrators to a gateway or router. Popularized 

in part by the Keymaster character in the 1984 movie 

“Ghostbusters.” See also gatekeeper. 

keypad n. See numeric keypad. 

key pair n. A widely used encryption scheme that allows 

secure use of digital certificate identification. A key pair 

consists of a public key and a private key. The public key 

is shared with other individuals; the private key is known 

only to its owner. The public and private key form an 

asymmetric pair, meaning the keys on either end of a 

transmission are different. A message encrypted with the 

public key can be decrypted only with the private key, and 

301 

a message encrypted with the private key can be decrypted 

only with the public key. 

keypunch n. An archaic keyboard-activated device used 

to punch holes in predetermined locations on paper cards 

roughly the size of a business envelope. It was used to provide 

programs and data to early computing systems. 

key recovery n. General term referring to the ability to 

retrieve a cryptographic key in order to decode encrypted 

information. Key recovery can be used to regain a lost key 

or, as has been publicized in recent years, can be used as a 

means of enabling government agencies to decode 

encrypted information. One method of providing for key 

recovery is known as key escrow. See also encryption, key 

escrow, private key. 

key sort n. See tag sort. 

keystroke n. The act of pressing a key on a keyboard to 

enter a character or initiate a command in a program. The 

efficiency and ease of use of certain applications is often 

measured in terms of how many keystrokes it takes to perform 

common operations. See also command, key (definition 

1), keyboard. 

keyword n. 1. A characteristic word, phrase, or code that 

is stored in a key field and is used to conduct sorting or 

searching operations on records in a database. See also 

key field. 2. Any of the set of words that composes a given 

programming language or set of operating-system routines. 

See also reserved word. 

keyword density n. A measurement of the keywords on a 

Web page as a percentage of total text. High keyword density 

can increase a Web site’s probability of being found 

by search engines, some of which use keyword density to 

rank a Web page’s relevance to an Internet search. See also 

keyword (definition 1). 

keyword-in-context n. An automatic search methodology 

that creates indexes of document text or titles. Each keyword 

is stored in the resulting index along with some surrounding 

text, usually the word or phrase that precedes or 

follows the keyword in the text or title. Acronym: KWIC. 

keyword stuffing vb. See spamdexter. 

Khornerstone n. A benchmark of floating-point calculation 

performance used to test UNIX workstations. See 

also benchmark1 , Dhrystone, floating-point operation, 

Whetstone. 

kHz n. See kilohertz. 

K

K 

kiddie script knowledge-based system 

kiddie script n. A simple and easy-to-use executable 

script used to hack into a computer or network. Unlike the 

traditional hacker’s techniques, which require detailed networking 

and programming knowledge, a kiddie script 

does not require any specialized skills or knowledge. See 

also script, script kiddie. 

kill vb. 1. To stop or abort a process in a program or operating 

system. 2. In file management, to erase a file, often 

without hope of reversing the action. 

killer app n. 1. An application of such popularity and 

widespread standardization that it fuels sales of the hardware 

platform or operating system for which it was written. 

See also application. 2. An application that supplants 

its competition. See also application. 

kill file n. See bozo filter. 

kilo- prefix 1. Metric prefix meaning 103 (one thousand). 

2. In computer-related terms, a prefix meaning 210 (1024). 

kilobaud n. A unit of measure of the transmission capacity 

of a communications channel, equal to 210 (1024) baud. 

See also baud. 

kilobit n. A data unit equal to 1024 bits. Abbreviated Kb 

or Kbit. 

kilobits per second n. Data transfer speed, as through a 

modem or on a network, measured in multiples of 1024 

bits per second. Abbreviated Kbps. 

kilobyte n. A data unit of 1024 bytes. Abbreviated K, KB, 

or Kbyte. See also kilo-. 

kilocycle n. A unit of measurement representing 1000 

cycles, generally meaning 1000 cycles per second. Abbreviated 

kc. See also kilohertz. 

kilohertz n. A measure of frequency equivalent to 1000 

hertz, or 1000 cycles per second. Abbreviated kHz. See 

also hertz. 

Kinesis ergonomic keyboard n. A keyboard designed 

ergonomically to eliminate repetitive strain injuries. See 

also ergonomic keyboard, repetitive strain injury. 

kiosk n. A freestanding computer or terminal that provides 

information to the public, usually through a multimedia 

display. 

kludge n. 1. A short-term or makeshift hardware construction. 

2. A program characterized by a lack of design 

or forethought, as if written in a hurry to satisfy an immediate 

need. A kludge basically operates properly, but its 

302 

construction or design is severely lacking in elegance or 

logical efficiency. See also braindamaged, hack1 (definition 

1), spaghetti code. 

knockout n. 1. In multicolor printing, the process of 

removing from one image the overlapping parts of a 

graphic or text that are to be printed in a different color so 

that ink colors will not mix. See the illustration. See also 

spot color. Compare overprint. 2. In hardware, a section of 

a panel that can be removed to make space for a switch or 

other component. 

Overprint 

Knockout 

F0Kgn03.eps 

Knockout. A knockout allows an overlapping image to print 

in the correct color. 

knowbot n. Short for knowledge robot. An artificialintelligence 

program that follows a set of predetermined 

rules to perform work, such as searching for files 

or looking for documents that contain specific pieces of 

information on a network, such as the Internet. See also 

bot (definition 2). 

knowledge acquisition n. The process of translating 

knowledge from one or more human experts into a form of 

representation usable by a computer, for the purpose of 

developing an expert system. See also expert system. 

knowledge base n. A form of database used in expert 

systems that contains the accumulated body of knowledge 

of human specialists in a particular field. The reasoning 

ability or problem-solving approach that a specialist 

would use is contained in the inference engine, which 

forms another crucial part of an expert system. See also 

expert system, inference engine. 

knowledge-based system n. See expert system.

knowledge domain KWIC 

knowledge domain n. The specific area of expertise to 

which an expert system is devoted. See also expert system. 

knowledge engineer n. A computer scientist who builds 

an expert system by acquiring the needed knowledge and 

translating it into a program. See also expert system. 

knowledge representation n. The methodology that 

forms the basis for the decision-making structure in an 

expert system, usually taking the form of if-then rules. See 

also expert system. 

knowledge worker n. Term invented by a management 

consultant, Peter Drucker, for an individual whose job 

centers on the collection, processing, and application of 

information, especially when meaningful value is added to 

purely factual information. A knowledge worker is someone 

with both formal education and the ability to apply 

303 

that education—knowledge—in a work situation. See also 

information explosion. 

Korn shell n. A command-line interface, available under 

UNIX, that combines features of the Bourne and C shells. 

The Korn shell is fully compatible with the Bourne shell 

but also offers the history and command-line editing capabilities 

of the C shell. See also command-line interface, 

shell1 , UNIX. Compare Bourne shell, C shell. 

KSR terminal n. Short for keyboard send/receive terminal. 

A type of terminal that accepts input from a keyboard 

only and uses an internal printer rather than a screen to 

display the keyboard input and the output received from 

the sending terminal. See also TTY. 

KWIC n. See keyword-in-context. 

K

L 

L1 cache n. A memory cache built into i486 and higherlevel 

processors to help improve processing speed. The L1 

cache, typically containing 8 KB, can be read in a single 

clock cycle, so it is tried first. The i486 contains one L1 

cache; the Pentium contains two, one for code and one for 

data. Also called: level 1 cache, on-chip cache. See also 

cache, i486DX, Pentium. Compare L2 cache. 

L2 cache n. A memory cache consisting of static RAM 

on a motherboard that uses an i486 or higher-level processor. 

The L2 cache, which typically contains 128 KB to 1 

MB, is faster than the system DRAM but slower than the 

L1 cache built into the CPU chip. Also called: level 2 

cache. See also cache, dynamic RAM, i486DX, static 

RAM. Compare L1 cache. 

L2TP n. See Layer Two Tunneling Protocol. 

L8R adv. Abbreviation for later, as in “See you later,” an 

expression often used in e-mail or Usenet groups as a closing 

remark. 

label n. An identifier. A label can be a physical item, such 

as a stick-on tag used to identify disks and other computer 

equipment, or an electronic label added to floppy disks or 

hard disks. It can also be a word, symbol, or other group of 

characters used to identify a file, a storage medium, an 

element defined in a computer program, or a specific item 

in a document such as a spreadsheet or a chart. See also 

identifier. 

label edge router n. See MPLS. 

label prefix n. In a spreadsheet, a character at the beginning 

of a cell entry that identifies the entry to the program 

as a label. 

label switching n. See MPLS. 

label switch path n. See MPLS. 

label switch router n. See MPLS. 

LACP n. Acronym for Link Aggregation Control Protocol. 

See link aggregation. 

lag n. The time difference between two events. In electronics, 

a lag is a delay between a change in input and a 

change in output. On computer displays, a lag is a fading 

L 

304 

brightness left on the phosphor coating of the screen after 

an image changes. See also persistence. 

LAN n. Acronym for local area network. A group of computers 

and other devices dispersed over a relatively limited 

area and connected by a communications link that enables 

any device to interact with any other on the network. 

LANs commonly include PCs and shared resources such 

as laser printers and large hard disks. The devices on a 

LAN are known as nodes, and the nodes are connected by 

cables through which messages are transmitted. See also 

baseband network, broadband network, bus network, client/server 

architecture, collision detection, communications 

protocol, contention, CSMA/CD, network, peer-topeer 

architecture, ring network, star network. Compare 

WAN. 

landscape mode n. A horizontal print orientation in 

which text or images are printed “sideways”—that is, the 

width of the image on the page is greater than the height. 

Compare portrait mode. 

landscape monitor n. A monitor that is wider than it is 

high. Landscape monitors are usually about 33 percent 

wider than they are high—roughly the same proportion as 

a television screen. Compare full-page display, portrait 

monitor. 

LANE n. Acronym for LAN Emulation. See ATM (definition 

1), communications protocol, LAN. 

LANGID n. See language identifier. 

language n. See programming language. 

language-description language n. See metalanguage. 

language identifier n. A standard international numeric 

abbreviation for a country or geographical region. A language 

identifier is a 16-bit value that consists of a primary 

language identifier and a secondary language identifier. 

Acronym: LANGID. See also locale identifier. 

language processor n. A hardware device or a software 

program designed to accept instructions written in a particular 

language and translate them into machine code. See 

also compiler (definition 2), interpreter.

language translation program last mile 

language translation program n. A program that translates 

statements written in one programming language 

into another programming language (usually from one 

high-level language into another). See also high-level 

language. 

LAN Manager n. An older LAN (local area network) 

technology developed by Microsoft and distributed by 

Microsoft, IBM (as IBM LAN Server), and other original 

equipment manufacturers. Superseded by TCP/IP networking 

protocols in Windows 9x, LAN Manager implemented 

the NetBEUI protocol and was notable for its 

small stack size. It was used to connect computers running 

the MS-DOS, OS/2, or UNIX operating systems to allow 

users to share files and system resources and to run distributed 

applications using a client/server architecture. See 

also client/server architecture, LAN, NetBEUI. 

LANtastic n. A network operating system from Artisoft 

designed to support both peer-to-peer and client/server 

networks consisting of PCs running a mix of MS-DOS 

and Windows operating systems. 

laptop n. A small, portable personal computer that runs 

on either batteries or AC power, designed for use during 

travel. Laptops have flat LCD or plasma screens and small 

keyboards. Most can run the same software as their desktop 

counterparts and can accept similar peripherals, such 

as sound cards, internal or external modems, floppy disks, 

and CD-ROM drives. Some laptops are designed to be 

plugged into a docking station, effectively making them 

desktop computers. Most have connectors for plugging in 

external keyboards and full-sized monitors. Older laptops 

weighed as much as 15 pounds; current laptops can weigh 

as little as 5 pounds without peripherals. While notebook 

is the current term for ultralight portable computers, these 

machines are also commonly referred to as laptops. See 

also portable computer. Compare subnotebook computer. 

large model n. A memory model of the Intel 80x86 processor 

family. The large model allows both code and data 

to exceed 64 kilobytes, but the total of both must generally 

be less than 1 megabyte. Each data structure must be less 

than 64 kilobytes in size. See also memory model. 

large-scale integration n. A term describing a chip on 

which circuit elements number in the thousands. Acronym: 

LSI. See also integrated circuit. Compare mediumscale 

integration, small-scale integration, super-largescale 

integration, ultra-large-scale integration, verylarge-scale 

integration. 

305 

laser or LASER n. Acronym for light amplification by 

stimulated emission of radiation. A device that uses certain 

quantum effects to produce coherent light, which travels 

with greater efficiency than noncoherent light because 

the beam diverges only slightly as it travels. Lasers are 

used in computer technology to transmit data through 

fiberoptic cables, to read and write data on CD-ROMs, 

and to place an image on a photosensitive drum in laser 

printers. 

laser engine n. See printer engine. 

laser printer n. An electrophotographic printer that is 

based on the technology used by photocopiers. A focused 

laser beam and a rotating mirror are used to draw an image 

of the desired page on a photosensitive drum. This image 

is converted on the drum into an electrostatic charge, 

which attracts and holds toner. A piece of electrostatically 

charged paper is rolled against the drum, which pulls the 

toner away from the drum and onto the paper. Heat is then 

applied to fuse the toner to the paper. Finally, the electrical 

charge is removed from the drum, and the excess toner is 

collected. By omitting the final step and repeating only the 

toner-application and paper-handling steps, the printer can 

make multiple copies. The only serious drawback of a 

laser printer is that it offers less paper-handling flexibility 

than do dot-matrix printers. Both multipart forms and 

wide-carriage printing, for example, are better handled by 

line printers or dot-matrix printers. See also electrophotographic 

printers, nonimpact printer, page printer. Compare 

dot-matrix printer, ion-deposition printer, LCD printer, 

LED printer. 

laser storage n. The use of optical read/write technology 

with metallic discs for information storage. See also compact 

disc. 

LaserWriter 35 n. The standard set of 35 PostScript fonts 

for the Apple LaserWriter family of laser printers. See 

also laser printer, PostScript font. 

last in, first out n. A method of processing a queue in 

which items are removed in inverse order relative to the 

order in which they were added—that is, the last in is the 

first out. Acronym: LIFO. See also stack. Compare first 

in, first out. 

last mile n. The connection (which may in fact be more 

or less than one mile) between an end user’s system and 

that of a service provider, such as a telephone company. 

The “last mile” connection historically has referred to the 

twisted-pair copper wires used between a home and the 

L

L 

latch layered interface 

telephone company. While this definition remains accurate, 

“last mile” is now often used more broadly to refer to 

the link between an end user’s system and the high-speed 

Internet access technology of a service provider, such as 

an ISP (Internet service provider). Thus, for modem users 

accessing the Internet through voice-grade lines, the last 

mile is still equivalent to the phone company’s twistedpair 

copper wiring. However, because standard modem 

transmission over voice-grade lines is sometimes frustratingly 

slow, other last mile solutions have been designed to 

provide greater speed and bandwidth. These include coaxial 

cable (used in cable TV), fiber optics, or a radio link 

(such as a cellular telephone or a point-to-point link). DSL 

and ISDN are methods for providing high-speed last-mile 

data service through twisted-pair copper wires. See also 

DSL, ISDN, twisted-pair wiring. Compare local loop. 

latch n. A circuit or circuit element used to maintain a 

particular state, such as on or off, or logical true or false. A 

latch changes state only in response to a particular input. 

See also flip-flop. 

late binding n. See dynamic binding. 

latency n. The time required for a signal to travel from 

one point on a network to another. See also ping1 (definition 

1). 

LaTeX1 or LATEX n. A document preparation system 

based on TeX, developed by Leslie Lamport. By using 

simple, intuitive commands for text elements such as 

headers, LaTeX lets the user focus more on document 

content than document appearance. See also header (definition 

1), TeX. 

LaTeX2 vb. To process a LaTeX file. See also LaTeX1 . 

launch vb. To activate an application program (especially 

on the Macintosh) from the operating system’s 

user interface. 

Launcher n. In Mac OS, a program that organizes frequently 

used applications and programs and that allows 

the user to execute them with a single mouse click. 

layer n. 1. The protocol or protocols operating at a particular 

level within a protocol suite, such as IP within the 

TCP/IP suite. Each layer is responsible for providing specific 

services or functions for computers exchanging information 

over a communications network (such as the layers 

in the ISO/OSI reference model) and information is 

306 

passed from one layer to the next. Although different 

suites have varying numbers of levels, generally the highest 

layer deals with software interactions at the application 

level, and the lowest governs hardware-level connections 

between different computers. See the table. See also ISO/ 

OSI reference model, protocol stack, TCP/IP. 2. In communications 

and distributed processing, a set of rules and 

standards that handles a particular class of events. 

Table L.1 Layers in the ISO/OSI reference model. 

ISO/OSI layer Focus 

Application (highest Program-to-program transfer of 

level) 

information 


conversion 




Network Transport routes, message handling 

and transfer 

Data-link Coding, addressing, and transmitting 

information 


layer 4 switching n. In Network Address Translation 

(NAT), a function that handles incoming packets and 

changes the IP address and destination port to transfer 

them to the proper server within the private network, and 

then readdresses return packets leaving the private network. 

Because layer 4 switching controls the address on 

packets moving in both directions, the internal network 

remains transparent to the client. See also LVS, NAT. 

layered architecture n. The division of a network model 

into multiple discrete layers, or levels, through which messages 

pass as they are prepared for transmission. In a layered 

architecture, protocols at each layer provide specific 

services or functions and rely on protocols in the layers 

above and below them for other needed services. See also 

protocol. 

layered interface n. In programming, one or more levels 

of routines lying between an application and the computing 

hardware and separating activities according to the 

type of task the activities are designed to carry out. Ultimately, 

such an interface makes it easier to adapt a program 

to different types of equipment. See the illustration.

layering leading 

Application 

program 

F0Lxx01.eps 

Layered interface. 

. . . 

System services 

File system 

Application 

program 

Memory and I/O device management 

Processor scheduling 

Hardware 

User mode 

Kernel mode 

layering n. In computer graphics, the grouping of logically 

related elements in a drawing. Layering enables a 

program user to view, and work on independently, portions 

of a graphic instead of the entire drawing. 

Layer Two Tunneling Protocol n. An industry-standard 

Internet tunneling protocol that provides encapsulation for 

sending Point-to-Point Protocol (PPP) frames across 

packet-oriented media. For IP networks, Layer Two Tunneling 

Protocol traffic is sent as User Datagram Protocol 

(UDP) messages. In Microsoft operating systems, this 

protocol is used in conjunction with Internet Protocol 

security (IPSec) as a virtual private network (VPN) technology 

to provide remote access or router-to-router VPN 

connections. Layer Two Tunneling Protocol is described 

in RFC 2661. Acronym: L2TP. See also IPSec, Point-to- 

Point Protocol, tunnel, User Datagram Protocol. 

layout n. 1. The overall plan or design of a document system. 

See also page layout. 2. In programming, the order 

and sequence of input and output. 3. In computer design, 

the arrangement of circuits and other components of the 

system. 

lazy evaluation n. A programming mechanism that 

allows an evaluation action to be performed only when 

needed and only to a certain extent. Lazy evaluation 

307 

allows a program to handle data objects such as extremely 

large tables and lists in a timely and effective manner. 

LBA n. See logical block addressing. 

LCC n. See leaded chip carrier, leadless chip carrier. 

lcd n. In some FTP clients, the command that changes the 

current directory on the local system. See also FTP client. 

LCD n. See liquid crystal display. 

LCD printer n. Short for liquid crystal display printer. 

An electrophotographic printer similar to a laser printer 

and often incorrectly labeled as one. LCD printers use a 

bright light source, typically a halogen lamp. Also 

called: liquid crystal shutter printer. See also electrophotographic 

printers, nonimpact printer, page printer. Compare 

ion-deposition printer, laser printer, LED printer. 

LCD projector n. Short for liquid crystal display projector. 

A type of data projector that uses electricity to turn 

the pixels representing a projected image off or on. Unlike 

the newer DLP projectors, LCD projectors are able to display 

shades of color (gray scale) by controlling the 

amount of electricity used to turn a particular pixel on or 

off. See also gray scale, liquid crystal display. Compare 

DLP projector. 

LCP n. See Point-to-Point Protocol. 

LDAP n. See Lightweight Directory Access Protocol. 

lead1 n. In electronics, the metallic connector of certain 

components such as resistors and capacitors. 

lead2 n. In typography, the amount of vertical space 

between two lines of text. 

leaded chip carrier n. A method of mounting chips on 

boards. A leaded chip carrier has leglike pins for connecting 

it to the board. The chip makes contact with the board 

through surface mount technology in which the leads are 

soldered to the surface rather than into predrilled holes. 

Somewhat confusingly, a leaded chip carrier goes by the 

same acronym (LCC) as a leadless chip carrier. Acronym: 

LCC. Compare leadless chip carrier. 

leader n. A row of dots, hyphens, or other such characters 

used to lead the eye across a printed page to related information. 

Leaders can be created by many word processors 

and other programs. 

leading n. The space, expressed in points, between lines 

of type, measured from the baseline (bottom) of one line 

to the baseline of the next. The term is derived from the 

traditional typesetting practice of inserting a thin bar of 

L

L 

leading edge legacy system 

lead between lines of metal type. See the illustration. See 

also point 1 . 

Leading 

A generous amount of space between 

lines of type is called open leading. 

Baselines 

F0Lxx02.eps 

Leading. Ordinary text is typically set with leading one or two 

points greater than the point size of the type. 

leading edge n. The initial part of an electronic signal. If 

a digital signal switches from off to on and then back to 

off, the transition from off to on is the leading edge of the 

signal. 

leading zero n. A zero that precedes the most significant 

(leftmost) digit of a number. One or more leading zeros 

may be used as fill characters in a field containing numeric 

input. Leading zeros have no significance in the value of a 

number. 

lead ion battery n. An energy storage device that is 

based on the conversion of chemical to electrical energy as 

ions flow from one terminal to another through an acid 

medium in which lead and copper are suspended. This 

type of battery is used in laptop and notebook computers. 

leadless chip carrier n. A method of mounting chips on 

boards. A leadless chip carrier has contacts, rather than 

leglike pins, for connecting it to the board. The chip simply 

rests in a socket that has contacts on its base for completing 

the connection, and the chip is clamped in place so 

that the contacts are secure. Acronym: LCC. See also 

PLCC. Compare DIP (definition 1), pin grid array. 

leaf n. Any node (location) in a tree structure that is at the 

farthest distance from the root (primary node), no matter 

which path is followed. Thus, in any tree, a leaf is a node 

at the end of a branch—one that has no descendants. See 

also root, subtree, tree. 

leapfrog attack n. A method used by hackers to make an 

attack difficult to trace back to the source. In a leapfrog 

attack the hacker uses a User ID stolen from another 

source or routes information through a series of hosts to 

hide their identity and obscure the origin of the attack. 

Also called: network weaving. 

leapfrog test n. A diagnostic routine, used for testing 

disk or tape storage, that repeatedly copies itself onto the 

storage medium. 

leap year n. A potential problem for some systems that 

follow an erroneous algorithm for calculating leap years. 

308 

There are three rules for calculating leap years: (1) A year 

is a leap year if it is divisible by 4, but (2) not if it is divisible 

by 100, unless (3) it is also divisible by 400. Thus, 

1900 was not a leap year, but 2000 was. 

leased line n. See dedicated line (definition 1). 

least significant bit n. In a sequence of one or more 

bytes, the low-order (usually rightmost) bit of a binary 

number. Acronym: LSB. See also low-order. Compare 

most significant bit. 

least significant character n. The low-order, or rightmost, 

character in a string. Acronym: LSC. See also loworder. 

Compare most significant character. 

least significant digit n. The low-order, or rightmost, 

digit in the normal representation of a number. Acronym: 

LSD. See also low-order. Compare most significant digit. 

LED n. See light-emitting diode. 

LED printer n. Short for light-emitting diode printer. An 

electrophotographic printer similar to LCD and laser 

printers. The significant difference between LED and laser 

or LCD printers is in the light source; LED printers use an 

array of light-emitting diodes. See also electrophotographic 

printers, light-emitting diode, nonimpact printer, 

page printer. Compare ion-deposition printer, laser 

printer, LCD printer. 

left justification n. In typesetting, word processing, and 

desktop publishing, the process of aligning text evenly 

along the left margin of a column or page. The right edge 

of the text is ragged. See also justify (definition 1), rag. 

Compare full justification, right justification. 

left-justify vb. To justify, as text, along the left. See also 

justify (definition 1), rag. Compare right-justify. 

legacy adj. Of or pertaining to documents, data, or hardware 

that existed prior to a certain time. The designation 

refers particularly to a change in process or technique that 

requires translating old data files to a new system. 

legacy data n. Data acquired by an organization that was 

compiled by another organization. The acquiring organization 

thus receives the existing information as a “legacy” 

from the information’s prior owner. 

legacy system n. A computer, software program, network, 

or other computer equipment that remains in use 

after a business or organization installs new systems. 

Compatibility with legacy systems is an important consideration 

when a new version is installed. For example, will

legend ligature 

a new spreadsheet software release be able to read the 

existing business records without expensive and time-consuming 

conversion to a new format? Legacy systems in 

many organizations are based on mainframe computers, 

which may be either augmented or slowly replaced by client/server 

architectures. See also mainframe computer. 

Compare client/server architecture. 

legend n. Text that describes or explains a graphic, usually 

printed below the graphic. On a graph or map, the legend 

is the key to the patterns or the symbols used. 

Lempel Ziv compression n. A data compression method 

designed by Abraham Lempel and Jakob Ziv in 1977 and 

1978. Lempel Ziv compression is based on the substitution 

of certain values for repeated data. It is implemented 

in two basic forms: LZ77, which is based on values that 

point to the positions of repeating data, and LZ78, which 

builds a dictionary and uses the dictionary index to point 

to repeating data. An enhanced version of LZ78, known as 

LZW, is implemented in well-known file formats, such as 

GIF and TIF. See also .lzh, LZW compression. 

length n. The number of linear units of storage space 

occupied by an object, such as a file on disk or a data 

structure in a program, typically measured in bits, bytes, 

or blocks. 

LEO n. See low-Earth-orbit satellite. 

LER n. See MPLS. 

less than adj. See relational operator. 

less than or equal to adj. See relational operator. 

letterbomb n. An e-mail message that is intended to 

impair the recipient’s computer use. Some sequences of 

control characters can lock up a terminal, files attached to 

the message may contain viruses or Trojan horses, and a 

sufficiently large message can overflow a mailbox or crash 

a system. See also control character, e-mail1 (definition 1), 

mailbox, Trojan horse, virus. 

letter quality adj. Pertaining to or being a level of print 

quality on dot-matrix printers that is better than draft quality. 

As the name implies, letter quality is supposed to be 

crisp and dark enough for use in business letters. See also 

print quality. Compare draft quality, near-letter-quality. 

letter-quality printer n. Any printer that produces output 

high enough in quality to be acceptable for business letters. 

See also daisy-wheel printer, laser printer. 

level 1 cache n. See L1 cache. 

309 

level 2 cache n. See L2 cache. 

lexicographic sort n. A sort that arranges items in the 

order in which they would appear if listed in a dictionary. 

A lexicographic sort puts numbers, for instance, where 

they would be if they were spelled out; for example, 567 

would fall in the Fs. Compare alphanumeric sort. 

lexicon n. 1. The words of a language and their definitions. 

2. In programming, the identifiers, keywords, constants, 

and other elements of a language that make up its 

“vocabulary.” The ways in which these vocabulary elements 

can be put together is the syntax of the language. 

Compare syntax. 

LF n. See linefeed. 

LHARC n. A freeware file-compression utility program 

developed by Haruyasu Yoshizaki and introduced in 1988. 

With LHARC, the contents of one or more files can be 

compressed into a singular, smaller file, with the extension 

.lha. A copy of the program is required to uncompress 

these files. LHARC can also embed a small program with 

the compressed information and save everything in a single 

file, called a self-extracting archive, with an .exe 

extension. As a result, the recipient of the compressed file 

does not need a separate utility program to uncompress the 

file. See also freeware, PKZIP, utility program. 

library n. 1. In programming, a collection of routines 

stored in a file. Each set of instructions in a library has a 

name, and each performs a different task. 2. A collection 

of software or data files. 

library routine n. In programming, a routine stored in a 

collection of routines (a library) that can be used by any 

program that can link into the library. See also function 

library, library (definition 1). 

license agreement n. A legal contract between a software 

provider and a user specifying the rights of the user 

regarding the software. Usually the license agreement is in 

effect with retail software once the user opens the software 

package. See also End-User License Agreement. 

licensing key n. A short character string that serves as a 

password during the installation of licensed commercial 

software. The use of licensing keys is a security device 

aimed at reducing illegal duplication of licensed software. 

LIFO n. See last in, first out. 

ligature n. In typography, a single character created 

from two joined letters that replaces the two separate letters. 

Because ligatures are not included with all digital 

L

L 

light-emitting diode linear memory 

fonts, their use may cause text problems in font substitution 

situations. 

light-emitting diode n. A semiconductor device that 

converts electrical energy into light, used, for example, for 

the activity lights on computer disk drives. Light-emitting 

diodes work on the principle of electroluminescence and 

are highly efficient, producing little heat for the amount of 

light output. Acronym: LED. 

light guide n. A structure, such as a fiberoptic filament, 

designed to transmit light over distances with minimal 

attenuation or loss. 

lightmap n. A basic lighting scheme used in 3D computer 

game rendering and other digital animation applications. 

A lightmap generates a precalculated 3D grid for lighting 

all objects in a game but cannot be adjusted for player-initiated 

changes within the scene. 

light pen n. An input device consisting of a stylus that is 

connected to a computer’s monitor. The user points at the 

screen with the stylus and selects items or chooses commands 

either by pressing a clip on the side of the light pen 

or by pressing the light pen against the surface of the 

screen (the equivalent of performing a mouse click). See 

also absolute pointing device. Compare touch screen. 

light source n. 1. The device that provides the luminescence 

(for example, a bulb or laser) in any technology 

based on the use and interpretation of light, such as a scanner 

or CRT. 2. In computer graphics, the imaginary location 

of a source of light, which determines the shading in 

an image. 

lightwave system n. A system that transmits information 

by means of light. 

Lightweight Directory Access Protocol n. A network 

protocol designed to work on TCP/IP stacks to extract 

information from a hierarchical directory such as X.500. 

This gives users a single tool to comb through data to find 

a particular piece of information, such as a user name, an 

e-mail address, a security certificate, or other contact 

information. Acronym: LDAP. See also CCITT X series. 

Lightweight Internet Person Schema n. In Lightweight 

Directory Access Protocol directories, a specification 

for the retrieval of such information as names and 

e-mail addresses. Acronym: LIPS. See also Lightweight 

Directory Access Protocol. 

LIM EMS n. Acronym for Lotus/Intel/Microsoft 

Expanded Memory Specification. See EMS. 

310 

limit check n. In programming, a test that checks specified 

information to verify that it is within acceptable limits. 

See also array. 

limiting operation n. Any routine or operation that constrains 

the performance of a larger process in which it is 

included; a bottleneck. 

line n. 1. Any wire or wires, such as power lines and telephone 

lines, used to transmit electrical power or signals. 

2. In communications, a connection, usually a physical 

wire or other cable, between sending and receiving (or 

calling and called) devices, including telephones, computers, 

and terminals. 3. In a SONET network, a segment that 

runs between two multiplexers. See also SONET. 4. In 

word processing, a string of characters displayed or 

printed in a single horizontal row. 5. In programming, a 

statement (instruction) that occupies one line of the program. 

In this context, the common reference is to a “program 

line” or a “line of code.” 

line adapter n. A device, such as a modem or network 

card, that connects a computer to a communications line and 

converts a signal to an acceptable form for transmission. 

line analyzer n. A monitoring device used to verify the 

integrity of a communications line and to assist in troubleshooting. 

linear adj. 1. Having the characteristics of a line. 

2. Proceeding sequentially. For example, a linear search is 

one that moves from A to B to C. 3. In mathematics and 

electronics, having a direct and proportional relationship 

among characteristics or variables. For example, the output 

of a linear amplifier is directly proportional to the 

input. See also linear programming. 

linear addressing architecture n. An architecture that 

allows a microprocessor to access any individual memory 

location by means of a single address value. Thus, each 

memory location within the entire range of addressable 

memory has a unique, specified address. See also flat 

address space, segmented address space. 

linear bus n. See bus network. 

linear inferences per second n. See LIPS (definition 2). 

linear list n. A simple ordered list of elements in which 

each element except the first immediately succeeds one 

other element, and each except the last immediately precedes 

one other. Compare linked list. 

linear memory n. See flat memory.

linear programming line load 

linear programming n. The process of creating programs 

that find optimal solutions for systems of equations (composed 

of linear functions) in which the terms given are not 

sufficient to derive a straightforward solution. 

linear search n. A simple, though inefficient, search 

algorithm that operates by sequentially examining each 

element in a list until the target element is found or the last 

item has been completely processed. Linear searches are 

primarily used for very short lists. Also called: sequential 

search. See also search algorithm. Compare binary search, 

hash search. 

linear structure n. A structure in which items are organized 

according to strict rules of precedence. In a linear 

structure, two conditions apply: if X precedes Y and Y 

precedes Z, then X precedes Z; and if X precedes Y and X 

precedes Z, then either Y precedes Z or Z precedes Y. 

line-based browser n. A Web browser whose display is 

based on text rather than graphics. A popular line-based 

browser is Lynx. See also Lynx, Web browser. 

line cap n. The way in which a line segment is terminated 

when the segment is printed, especially on a PostScriptcompatible 

printer. See the illustration. See also line join. 

F0Lxx03.eps 

Line cap. The dots represent the mathematical endpoints of a 

specified line. 

line chart n. A business graphic in which values from 

one or more sets of data are connected by lines. See the 

illustration. 

F0Lxx04.eps 

Line chart. 

Butt cap 

Square cap 

Round cap 

311 

line concentration n. The funneling of multiple input 

channels into a smaller number of output channels. See 

also concentrator. 

line conditioner n. A device for filtering electrical power 

to compensate for brownouts, suppress power surges, and 

act as a buffer between a power line and the computer (or 

other piece of equipment). Line conditioners contain 

transformers, capacitors, and other circuitry that help regulate 

the quality of power to ensure that electrical flow is 

constant. See also brownout, UPS. 

line conditioning n. See conditioning, line conditioner. 

line drawing n. A drawing made up of solid lines without 

shading or other features that suggest mass or contouring. 

line driver n. A device used to increase transmission distance 

by amplifying a signal before placing it on the line 

or passing it along the line. See also short-haul. 

line editor n. A text-editing program that numbers each 

line of text, working with the document on a line-by-line 

rather than on a word-by-word basis. See also editor. 

linefeed n. A control character that tells a computer or 

printer to advance one line below the current line without 

moving the position of the cursor or print head. 

Acronym: LF. 

line join n. The way in which two line segments are connected 

when they are printed, especially on a PostScriptcompatible 

printer. See the illustration. See also line cap. 

Miter join 

Round join 

Beveled join 

F0Lxx05.eps 

Line join. Three styles of line join. 

line level n. The strength of a communications signal at 

a given point on the line, measured in decibels (a multiple 

of the base-10 logarithm of the ratio between two values) 

or nepers (the natural logarithm of the ratio between 

two values). 

line load n. 1. In communications, a measure of the usage 

of a communications line expressed as a percentage of the 

L

L 

line noise linked list 

maximum capacity of the circuit. 2. In electronics, the 

amount of current carried by a line. 

line noise n. Spurious signals in a communications channel 

that interfere with the exchange of information. In an 

analog circuit, line noise may take the form of a pure 

audio tone, static, or signals leaked from another circuit. 

In a digital circuit, line noise is any signal that makes it 

difficult or impossible for the device at the receiving end 

of the circuit to interpret the transmitted signal accurately. 

See also channel. 

line number n. 1. A number assigned by a line editor to a 

line of text and used to refer to that line for purposes of 

viewing, editing, or printing. The line numbers are 

sequential. See also line editor. 2. In communications, an 

identifying number assigned to a communications channel. 

line printer n. Any printer that prints one line at a time as 

opposed to one character at a time (as with many dotmatrix 

printers) or one page at a time (as with some dotmatrix 

and most laser printers). Line printers typically 

produce the familiar 11-by-17-inch fanfold “computer” 

printouts. They are high-speed devices and are often used 

with mainframes, minicomputers, or networked machines 

rather than with single-user systems. 

line regulator n. See voltage regulator. 

line segment n. A portion of a line, defined by its beginning 

and ending points. 

lines of code n. A measure of program length. Depending 

on circumstances, a line of code can be each line in the program 

(including blank lines and comments), each line containing 

actual code, or each statement. See also statement. 

line spacing n. See leading. 

line speed n. See baud rate, data rate. 

lines per minute n. A measurement of printer speed, the 

number of lines of characters printed in one minute. Acronym: 

LPM. 

line style n. In desktop publishing, printing, and high-end 

word processing, the form and quality of a line, such as a 

dotted line, a double line, or a hairline. See also hairline. 

line surge n. A sudden, transient increase in the voltage 

or current carried by a line. A nearby lightning strike, for 

example, can cause a surge in power lines that can damage 

electrical equipment. Delicate types of equipment such as 

computers are often protected from line surges by surge 

suppressors placed in the power lines. 

312 

line voltage n. The voltage present in a power line. In 

North America, line voltage is approximately 115 volts 

alternating current (VAC). 

line width n. The length of a line of type measured from 

the left margin to the right margin on a piece of paper or 

on a computer screen. On a typewriter, line width is usually 

measured in terms of the number of monospace alphanumeric 

characters that can fit on the line; on a computer 

monitor or printer, line width is normally measured in 

inches, centimeters, points, or picas. See also pica (definition 

2), point1 (definition 1). 

linguistics n. The analytic study of human language. 

Close ties exist between linguistics and computer science 

because of the mutual interest in grammar, syntax, 

semantics, formal language theory, and natural-language 

processing. 

link1 vb. 1. To produce an executable program from compiled 

modules (programs, routines, or libraries) by merging 

the object code (assembly language object code, 

executable machine code, or a variation of machine code) 

of the program and resolving interconnecting references 

(such as a library routine called by a program). See also 

linker. 2. To connect two elements in a data structure by 

using index variables or pointer variables. See also index 

(definition 1), pointer (definition 1). 

link2 n. See hyperlink. 

linkage editor n. See linker. 

link aggregation n. A technique for combining two or 

more Ethernet connections into one logical link, or trunk, 

between two devices. It is used to increase the bandwidth 

capacity of connections and to make these connections 

more resilient. The IEEE 802.3ad specification standardizes 

this process among different vendors using the Link 

Aggregation Control Protocol (LACP). Also called: 

bonding, trunking. See also IEEE 802.x. 

Link Aggregation Control Protocol n. See link aggregation. 

Link Control Protocol n. See Point-to-Point Protocol. 

link edit vb. See link1 (definition 1). 

linked list n. In programming, a list of nodes or elements 

of a data structure connected by pointers. A singly linked 

list has one pointer in each node pointing to the next node 

in the list; a doubly linked list has two pointers in each 

node that point to the next and previous nodes. In a circular 

list, the first and last nodes of the list are linked

linked object LIPS 

together. See also array, key (definition 2), list, node (definition 

1), pointer (definition 1). Compare linear list. 

linked object n. An object that is inserted into a document 

but still exists in the source file. When information is 

linked, the new document is updated automatically if the 

information in the original document changes. If you want 

to edit the linked information, double-click it and the toolbars 

and menus from the original program appear, allowing 

you to edit it in its native format. If the original 

document is on your computer, changes that you make to 

the linked information will also appear in the original document. 

See also OLE, package, source document. 

linked stylesheet n. A stylesheet existing separately 

from the HTML documents to which it is linked. A linked 

stylesheet may be used for sets of Web pages or entire 

Web sites requiring a uniform appearance. Since the style 

is defined once and linked to associated Web pages, the 

entire site can be changed by modifying a single stylesheet 

file. Compare inline stylesheet. 

linker n. A program that links compiled modules and data 

files to create an executable program. A linker can also 

have other functions, such as creating libraries. See also 

library, link1 (definition 1), program creation. 

linkrot n. A condition affecting inadequately maintained 

Web pages that results in outdated, inoperative links to 

other Web pages. 

link time n. 1. The length of time required to link a program. 

See also link1 (definition 1). 2. The period during 

which a program is being linked. See also compile time 

(definition 2), link1 (definition 1), run time (definition 1). 

link-time binding n. Assignment of a meaning to an identifier 

(such as a subroutine label) in a program at the time 

that various files of compiled code are linked together to 

form an executable program, rather than when the source 

code is compiled or when the program is run. Compare 

compile-time binding, run-time binding. 

Linotronic n. Any in the series of high-quality typesetting 

devices known as Linotronic laser imagesetters, which can 

print at resolutions such as 1270 and 2540 dots per inch 

(dpi). These devices are commonly attached to PostScript 

raster image processors (RIPs) so that desktop publishing 

applications can typeset directly from a microcomputer. 

See also imagesetter, PostScript, raster image processor. 

Linpack n. A benchmarking routine that solves 100 simultaneous 

equations in a test of CPU, floating-point processor, 

313 

and memory access speeds. See also benchmark2 , central 

processing unit, floating-point processor. 

Linux n. A version of the UNIX System V Release 3.0 

kernel developed for PCs with 80386 and higher-level 

microprocessors. Developed by Linus Torvalds (for whom 

it is named) along with numerous collaborators worldwide, 

Linux is distributed free, and its source code is open 

to modification by anyone who chooses to work on it, 

although some companies distribute it as part of a commercial 

package with Linux-compatible utilities. The 

Linux kernel works with the GNU utilities developed by 

the Free Software Foundation, which did not produce a 

kernel. It is used by some as an operating system for network 

servers and in the 1998/1999 timeframe began to 

gain increased visibility through support from vendors 

such as IBM and Compaq. See also free software, GNU, 

kernel, UNIX. 

Linux Virtual Server n. See LVS. 

Linux World Expo n. The world’s largest trade show for 

designers, engineers, and businesses using the Linux operating 

system. 

Lion worm n. A UNIX shellscript worm first detected in 

early 2001 that infects Linux servers using Berkeley Internet 

Name Domain (BIND) tools. After it has used a BIND 

exploit to infect a machine, Lion steals password files and 

other critical information and transmits them to the hacker. 

Lion then installs hacking tools and replaces critical files, 

hiding itself and opening multiple back doors for further 

compromise. The Lion worm was apparently launched in 

early 2001 by a group of Chinese hackers with a specific 

political agenda. In references to this worm, “Lion” may 

also be spelled as “1i0n”. 

LIPS n. 1. Acronym for Language Independent Program 

Subtitling. A system developed by the GIST group (C-DAC, 

India) and used by Indian Television for nationwide 

broadcast of programs with multilingual subtitles in teletext 

mode. This system was judged the best design in the 

VLSI (Very Large Scale Integration) design contest in the 

VLSI ‘93 International Conference. Three versions of this 

application-specific integrated circuit (ASIC) with different 

features were implemented in Xilinx 3K and 4K series 

FPLAs (field programmable logic arrays). See also fieldprogrammable 

logic array, gate array, very-large-scale 

integration. 2. Acronym for linear inferences per second. 

A measure of speed for some types of artificial-intelligence 

L

L 

liquid crystal display liveware 

machines and expert systems. See also artificial intelligence, 

expert system. 3. See Lightweight Internet Person Schema. 

liquid crystal display n. A type of display that uses a liquid 

compound having a polar molecular structure, sandwiched 

between two transparent electrodes. When an 

electric field is applied, the molecules align with the field, 

forming a crystalline arrangement that polarizes the light 

passing through it. A polarized filter laminated over the 

electrodes blocks polarized light. In this way, a grid of 

electrodes can selectively “turn on” a cell, or a pixel, containing 

the liquid crystal material, turning it dark. In some 

types of liquid crystal displays, an electroluminescent 

panel is placed behind the screen to illuminate it. Other 

types of liquid crystal displays are capable of reproducing 

color. Acronym: LCD. See also supertwist display, twisted 

nematic display. 

liquid crystal display printer n. See LCD printer. 

liquid crystal shutter printer n. See LCD printer. 

LISP n. Short for List Processing. A list-oriented programming 

language developed in 1959–60 by John 

McCarthy and used primarily to manipulate lists of data. 

LISP is heavily used in research and academic circles 

and is considered the standard language for artificialintelligence 

research. See also artificial intelligence. 

Compare Prolog. 

list n. A multielement data structure that has a linear 

(first, second, third, . . .) organization but that allows elements 

to be added or removed in any order. Queues, 

deques, and stacks are simply lists with restrictions on 

adding and removing elements. See also deque, element 

(definition 1), linked list, queue, stack. 

list box n. A control in Windows that enables the user to 

choose one option from a list of possibilities. The list box 

appears as a box, displaying the currently selected option, 

next to a button marked with a down arrow. When the user 

clicks the button, the list appears. The list has a scroll bar if 

there are more options than the list has room to show. 

listing n. A printed copy of program source code. Some 

compilers and assemblers produce optional assembly listings 

during compilation or assembly. Such listings of code 

often have additional information such as line numbers, 

nested block depth, and cross-reference tables. See also 

assembly listing. 

list processing n. The maintenance and manipulation of 

multielement data structures. This involves adding and 

deleting elements, writing data into elements, and travers- 

314 

ing the list. List processing is the basis of the artificialintelligence 

programming language LISP. See also LISP, 

list, node (definition 1). 

LISTSERV n. One of the most popular commercial mailing 

list managers, marketed by L-SOFT International in 

versions for BITNET, UNIX, and Windows. See also 

mailing list, mailing list manager. 

literal n. A value, used in a program, that is expressed as 

itself rather than as a variable’s value or the result of an 

expression. Examples are the numbers 25 and 32.1, the 

character a, the string Hello, and the Boolean value 

TRUE. See also constant, variable. 

lithium ion battery n. An energy storage device based on 

the conversion of chemical to electrical energy in “dry” 

chemical cells. Despite the higher cost, the laptop industry 

is quickly adopting lithium ion batteries because of their 

increased storage capacity over both nickel cadmium and 

nickel metal hydride batteries, in response to the demand 

for greater power brought on by higher processor speeds 

and the use of devices such as CD-ROM drives. Compare 

nickel cadmium battery, nickel metal hydride battery. 

little endian adj. Of, pertaining to, or being a method of 

storing a number so that the least significant byte appears 

first in the number. For example, given the hexadecimal 

number A02B, the little endian method would cause the 

number to be stored as 2BA0. The little endian method is 

used by Intel microprocessors. Also called: reverse byte 

ordering. Compare big endian. 

live1 adj. 1. Of or relating to real-world data or a program 

working with it, as opposed to test data. 2. Of or relating 

to audio or video that is transmitted from one site to 

another as it is being produced, as opposed to being 

recorded before broadcast time. See also synchronous 

transmission. 3. Capable of being manipulated by a user to 

cause changes in a document or part of a document. 

live2 n. Used to identify a Web site that has been published 

to a Web server and can be browsed by site visitors. 

Also called: going live. 

Live3D n. A Netscape proprietary Virtual Reality Modeling 

Language (VRML) plug-in for Web browsers that 

allows users to view and interact with a virtual-reality 

world. See also VRML. 

liveware n. A slang term for people, to distinguish them 

from hardware, software, and firmware. Also called: 

wetware.

LLC locale identifier 

LLC n. Acronym for Logical Link Control. In the IEEE 

802.x specifications, the higher of two sublayers that make 

up the ISO/OSI data link layer. The LLC is responsible for 

managing communications links and handling frame traffic. 

See also IEEE 802.x, MAC. 

Lmhosts file n. A local text file that lists the names of 

network hosts (sometimes called NetBIOS names) to IP 

addresses for hosts that are not located on the local subnet. 

See also IP address, systemroot. 

load1 n. 1. The total computing burden a system carries 

at one time. 2. In electronics, the amount of current 

drawn by a device. 3. In communications, the amount of 

traffic on a line. 

load2 vb. To place information from storage into memory 

for processing, if it is data, or for execution, if it is program 

code. 

load-and-go adj. In reference to a routine, able to begin 

execution immediately, once loaded. The term is commonly 

used in reference to compilers and the machine 

code they generate. 

load balancing n. 1. In distributed processing, the distribution 

of activity across two or more servers in order to 

avoid overloading any one with too many requests from 

users. Load balancing can be either static or dynamic. In 

the former, the load is balanced ahead of time by assigning 

different groups of users to different servers. In the latter, 

software refers incoming requests at runtime to whichever 

server is most capable of handling them. 2. In client/server 

network administration, the process of reducing heavy 

traffic flows either by dividing a busy network segment 

into multiple smaller segments or by using software to distribute 

traffic among multiple network interface cards 

working simultaneously to transfer information to a 

server. 3. In communications, the process of routing traffic 

over two or more routes rather than one. Such load balancing 

results in faster, more reliable transmissions. 

loaded line n. A transmission cable fitted with loading 

coils, usually spaced about a mile apart, that reduce amplitude 

distortion in a signal by adding inductance (resistance 

to changes in current flow) to the line. Loaded lines minimize 

distortion within the range of frequencies affected by 

the loading coils, but the coils also reduce the bandwidth 

available for transmission. 

loader n. A utility that loads the executable code of a program 

into memory for execution. On most microcomputers, 

the loader is an invisible part of the operating system 

315 

and is automatically invoked when a program is run. See 

also loader routine, load module. 

loader routine n. A routine that loads executable code 

into memory and executes it. A loader routine can be part 

of an operating system or it can be part of the program 

itself. See also loader, overlay1 (definition 1). 

load module n. An executable unit of code loaded into 

memory by the loader. A program consists of one or more 

load modules, each of which can be loaded and executed 

independently. See also loader. 

load point n. The beginning of the valid data area on a 

magnetic tape. 

load sharing n. A method of managing one or more 

tasks, jobs, or processes by scheduling and simultaneously 

executing portions of them on two or more 

microprocessors. 

load shedding n. In electrical systems, the process of 

turning off power to some electronic equipment in order to 

maintain the integrity of the power supply to other connected 

devices. See also UPS. 

lobby page n. A page of information about the broadcast 

that is displayed in the viewer’s browser before the broadcast 

begins. It can contain a title, subject, host’s name, 

information about the broadcast, and a countdown to the 

time of the broadcast. 

local adj. 1. In general, close at hand or restricted to a 

particular area. 2. In communications, a device that can be 

accessed directly rather than by means of a communications 

line. 3. In information processing, an operation performed 

by the computer at hand rather than by a remote 

computer. 4. In programming, a variable that is restricted 

in scope, that is, used in only one part (subprogram, procedure, 

or function) of a program. Compare remote. 

local area network n. See LAN. 

local bus n. A PC architecture designed to speed up system 

performance by allowing some expansion boards to 

communicate directly with the microprocessor, bypassing 

the normal system bus entirely. See also PCI local 

bus, VL bus. 

local bypass n. A telephone connection used by some 

businesses that links separate buildings but bypasses the 

telephone company. 

locale identifier n. A 32-bit value that consists of a language 

identifier and a sort identifier. In code, a locale 

L

L 

localhost logarithm 

identifier (LCID) identifies the primary language and any 

secondary language of a specific locale. Acronym: LCID. 

See also language identifier. 

localhost n. The name that is used to represent the same 

computer on which a TCP/IP message originates. An IP 

packet sent to localhost has the IP address 127.0.0.1 and 

does not actually go out to the Internet. See also IP 

address, packet (definition 1), TCP/IP. 

localization n. The process of altering a program so that 

it is appropriate for the geographic area in which it is to be 

used. Localization involves the customization or translation 

of the separated data and resources required for a specific 

region or language. For example, the developers of a 

word processing program must localize the sorting tables 

in the program for different countries or languages 

because the correct order of characters in one language 

might be incorrect in another. L10N is a common abbreviation 

for Localization, where the “L” in Localization is 

followed by 10 letters and ends with the letter “N.” 

localized version n. A version of a program that has been 

translated into another language. Also called: international 

version. 

local loop n. The (end) portion of a telephone connection 

that runs from the subscriber to the local telephone 

exchange. See also last mile. 

local memory n. In multiprocessor systems, the memory 

on the same card or high-speed bus as a particular processor. 

Typically, memory that is local to one processor cannot 

be accessed by another without some form of 

permission. 

local newsgroups n. Newsgroups that are targeted 

toward a geographically limited area such as a city or educational 

institution. Posts to these newsgroups contain 

information that is specific to the area, concerning such 

topics as events, meetings, and sales. See also newsgroup. 

local reboot n. A reboot of the machine that one is 

directly working on, rather than of a remote host. See also 

reboot. 

LocalTalk n. An inexpensive cabling scheme used by 

AppleTalk networks to connect Apple Macintosh computers, 

printers, and other peripheral devices. See also 

AppleTalk. 

local user profile n. A user profile that is created automatically 

on the computer the first time a user logs on to a 

316 

computer. See also mandatory user profile, roaming user 

profile, user profile. 

local variable n. A program variable whose scope is limited 

to a given block of code, usually a subroutine. See 

also scope (definition 1). Compare global variable. 

location n. See address1 (definition 1). 

location-based service n. A service provided to a wireless 

mobile device based on the device’s location. Locationbased 

services can range from simple services, such as listing 

nearby restaurants, to more complex features, such as 

connecting to the Internet to monitor traffic conditions and 

find the least congested route to a destination. 

lock n. 1. A software security feature that requires a key 

or dongle in order for the application to run correctly. See 

also dongle. 2. A mechanical device on some removable 

storage medium (for example, the write-protect notch on a 

floppy disk) that prevents the contents from being overwritten. 

See also write-protect notch. 

locked file n. 1. A file on which one or more of the usual 

types of manipulative operation cannot be performed— 

typically, one that cannot be altered by additions or deletions. 

2. A file that cannot be deleted or moved or whose 

name cannot be changed. 

locked volume n. On the Apple Macintosh, a volume 

(storage device, such as a disk) that cannot be written to. 

The volume can be locked either physically or through 

software. 

lockout n. The act of denying access to a given resource 

(file, memory location, I/O port), usually to ensure that 

only one program at a time uses that resource. 

lock up n. A condition in which processing appears to be 

completely suspended and in which the program in control 

of the system will accept no input. See also crash1 . 

log n. A record of transactions or activities that take place 

on a computer system. See logarithm. 

logarithm n. Abbreviated log. In mathematics, the power 

to which a base must be raised to equal a given number. For 

example, for the base 10, the logarithm of 16 is (approximately) 

1.2041 because 101.2041 equals (approximately) 16. 

Both natural logarithms (to the base e, which is approximately 

2.71828) and common logarithms (to the base 10) 

are used in programming. Languages such as C and Basic 

include functions for calculating natural logarithms.

log files logic analyzer 

log files n. A computer file that records requests received 

by online applications or the number of hits a Web page 

receives. Log files are useful in analyzing the technical performance 

of a Web site, redesigning Web site navigation, 

and revising marketing strategies used by e-businesses. 

logic n. In programming, the assertions, assumptions, and 

operations that define what a given program does. Defining 

the logic of a program is often the first step in developing 

the program’s source code. See also formal logic. 

logical adj. 1. Based on true and false alternatives as 

opposed to arithmetic calculation of numeric values. For 

example, a logical expression is one that, when evaluated, 

has a single outcome, either true or false. See also Boolean 

algebra. Compare fuzzy logic. 2. Conceptually true to a 

particular design or idea—for example, network transmissions 

travel in a circle around a logical ring, even though 

the ring shape itself is not physically apparent. Compare 

physical. 

logical block addressing n. A technique in which the 

cylinder, head, and sector locations on a hard disk are converted 

to 24-bit addresses for data storage and retrieval. 

Logical block addressing is used with SCSI drives and is 

also a feature of Enhanced IDE (EIDE) disk drives, on 

which it breaks through the earlier 528-MB IDE limit and 

allows support for drives up to 8.4 GB in capacity if 24-bit 

logical address space is used. Address conversion is performed 

by an EIDE drive’s disk controller, but also 

requires support from the BIOS and the computer’s operating 

system. Acronym: LBA. See also EIDE, SCSI. 

logical decision n. Any decision that can have one of 

two outcomes (true/false, yes/no, and so on). Compare 

fuzzy logic. 

logical device n. A device named by the logic of a software 

system, regardless of its physical relationship to the 

system. For example, a single floppy disk drive can simultaneously 

be, to the MS-DOS operating system, both logical 

drive A and drive B. 

logical drive n. See logical device. 

logical error n. See logic error. 

logical expression n. See Boolean expression. 

logical file n. A file as seen from a conceptual standpoint, 

without reference to and as distinct from its physical realization 

in memory or storage. For example, a logical file 

might consist of a contiguous series of records, whereas 

the file might be physically stored in small pieces scat- 

317 

tered over the surface of a disk or even on several disks. A 

logical file might also consist of some subset of columns 

(fields) and rows (records) extracted from a database. In 

this case, the logical file (or view) is only that information 

required by a particular application program or user. 

Logical Link Control n. See LLC. 

logical memory n. A correlation between physical 

memory of the computer system and an address range 

that is accessible to devices. The hardware abstraction 

layer (HAL) provides this correlation (or mapping). See 

also map. 

logical network n. A way to describe the topology, or 

layout, of a computer network. Referring to a logical 

(rather than physical) topology describes the way information 

moves through the network—for example, in a 

straight line (bus topology) or in a circle (ring topology). 

The difference between describing a network as logical or 

physical is sometimes subtle because the physical network 

(the actual layout of hardware and cabling) doesn’t necessarily 

resemble the logical network (the path followed by 

transmissions). A logical ring, for example, might include 

groups of computers cabled octopus-like to hardware “collection 

points” which, in turn, are cabled to one another. In 

such a network, even though the physical layout of computers 

and connecting hardware might not visually resemble 

a ring, the logical layout followed by network 

transmissions would, indeed, be circular. See also bus network, 

ring network, star network, token ring network, 

topology. Compare physical network. 

logical operator n. An operator that manipulates binary 

values at the bit level. In some programming languages, 

logical operators are identical to Boolean operators, which 

manipulate true and false values. See also Boolean operator, 

mask. 

logical record n. Any unit of information that can be 

handled by an application program. A logical record can 

be a collection of distinct fields or columns from a database 

file or a single line in a text file. See also logical file. 

logical schema n. See conceptual schema. 

logic analyzer n. A hardware device that facilitates 

sophisticated low-level debugging of programs. Typical 

features include the ability to monitor bus signals during 

execution, to halt execution when a given memory location 

is read or written to, and to trace back through some 

number of instructions when execution is halted for any 

reason. See also debugger. 

L

L 

logic array LOL 

logic array n. See gate array. 

logic board n. Another name for motherboard or processor 

board. The term was used in conjunction with older 

computers to distinguish the video board (analog board) 

from the motherboard. See also motherboard. 

logic bomb n. 1. A logic error in a program that manifests 

itself only under certain conditions, usually when least 

expected or desired. The term bomb implies an error that 

causes the program to fail spectacularly. See also logic 

error. 2. A type of Trojan horse that executes when certain 

conditions are met, such as when a user performs a specific 

action. 3. See Year 2000 problem. 4. See fork bomb. 

logic chip n. An integrated circuit that processes information, 

as opposed to simply storing it. A logic chip is made 

up of logic circuits. 

logic circuit n. An electronic circuit that processes information 

by performing a logical operation on it. A logic 

circuit is a combination of logic gates. It produces output 

based on the rules of logic it is designed to follow for the 

electrical signals it receives as input. See also gate (definition 

1). 

logic diagram n. A schematic that shows the connections 

between computer logic circuits and specifies the expected 

outputs resulting from a specific set of inputs. 

logic error n. An error, such as a faulty algorithm, that 

causes a program to produce incorrect results but does not 

prevent the program from running. Consequently, a logic 

error is often very difficult to find. See also logic, semantics, 

syntax. 

logic gate n. See gate (definition 1). 

logic operation n. 1. An expression that uses logical values 

and operators. 2. A bit-level manipulation of binary 

values. See also Boolean operator. 

logic programming n. A style of programming, best 

exemplified by Prolog, in which a program consists of 

facts and relationships from which the programming language 

is expected to draw conclusions. See also Prolog. 

logic-seeking printer n. Any printer with built-in intelligence 

that lets it look ahead of the current print position 

and move the print head directly to the next area to be 

printed, thus saving time in printing pages that are filled 

with spaces. 

318 

logic symbol n. A symbol that represents a logical operator 

such as AND or OR. For example, the symbol + in 

Boolean algebra represents logical OR, as in A + B (read, 

“A or B,” not “A plus B”). 

logic tree n. A logic specification method that uses a 

branching representation. Each of the tree’s forks represents 

a decision point; the ends of the branches denote 

actions to be taken. 

login n. See logon. 

log in vb. See log on. 

Logo n. A programming language with features that are 

heavily drawn from LISP. Logo is often used to teach programming 

to children and was developed originally by 

Seymour Papert at MIT in 1968. Logo is considered an 

educational language, although some firms have sought to 

make it more widely accepted in the programming community. 

See also LISP, turtle, turtle graphics. 

logoff n. The process of terminating a session with a computer 

accessed through a communications line. Also 

called: logout. 

log off vb. To terminate a session with a computer 

accessed through a communications line—usually a computer 

that is both distant and open to many users. Also 

called: log out. Compare log on. 

logon n. The process of identifying oneself to a computer 

after connecting to it over a communications line. Also 

called: login. 

log on vb. To gain access to a specific computer, a program, 

or a network by identifying oneself with a username 

and a password. Also called: log in. Compare log off. 

logon script n. A file assigned to certain user accounts on 

a network system. A logon script runs automatically every 

time the user logs on. It can be used to configure a user’s 

working environment at every logon, and it allows an 

administrator to influence a user’s environment without 

managing all aspects of it. A logon script can be assigned 

to one or more user accounts. Also called: login script. See 

also user account. 

logout n. See logoff. 

log out vb. See log off. 

LOL n. Acronym for laughing out loud. An interjection 

used in e-mail, online forums, and chat services to express

Long data type Lotus 1-2-3 

appreciation of a joke or other humorous occurrence. See 

also ROFL. 

Long data type n. A fundamental data type that holds 

large integers. A Long variable is stored as a 32-bit number 

ranging in value from –2,147,483,648 to 

2,147,483,647. 

long filenames n. A feature of most current PC operating 

systems, including the Macintosh, Windows 9x, Windows 

NT, Windows 2000, and OS/2. Long filenames allow a 

user to assign a plain-text name to a file, rather than limiting 

possible names to just a few characters. Names can be 

over 200 characters long, include uppercase and lowercase 

letters, and have spaces between characters. Compare 8.3. 

long-haul adj. Of, pertaining to, or being a type of 

modem that is able to transmit over long distances. Compare 

short-haul. 

longitudinal redundancy check n. See LRC. 

LonWorks n. An open standard for network automation 

created by the Echelon Corporation and supported by the 

LonMark Interoperability Association. LonWorks, introduced 

in 1991, can be used in building, transportation, 

industrial, and home applications to implement a distributed 

control network. 

lookup n. A function, often built into spreadsheet programs, 

in which a previously constructed table of values 

called a lookup table is searched for a desired item of 

information. A lookup table consists of rows and columns 

of data. A lookup function examines the table either horizontally 

or vertically and then retrieves the data that corresponds 

to the argument specified as part of the lookup 

function. 

loop1 n. 1. A set of statements in a program executed 

repeatedly, either a fixed number of times or until some 

condition is true or false. See also DO loop, FOR loop, 

infinite loop, iterative statement. 2. A pair of wires that 

runs between a telephone central office and customer 

premises. 

loop2 vb. To execute a group of statements repeatedly. 

loop check n. See echo check. 

loop configuration n. A communications link in which 

multiple stations are joined to a communications line that 

runs in a closed loop. Generally, data sent by one station is 

received and retransmitted in turn by each station on the 

319 

loop. The process continues until the data reaches its final 

destination. See the illustration. See also ring network. 

Station 2 

Station 1 

Station 3 

Station 4 

F0Lxx06.eps 

Loop configuration. 

loophole n. In programming, a logical failure to account 

for all possible situations. See also bug (definition 1), 

logic error. 

loop invariant n. A condition that remains true while a 

loop iterates. 

loop structure n. See iterative statement. 

lo-res adj. See low resolution. 

loss balancing n. Amplification of a signal or value to 

compensate for loss during a transmission or translation of 

a value. 

lossless compression n. The process of compressing a 

file such that, after being compressed and decompressed, 

it matches its original format bit for bit. Text, code, and 

numeric data files must be compressed using a lossless 

method; such methods can typically reduce a file to 40 

percent of its original size. Compare lossy compression. 

lossy compression n. The process of compressing a file 

such that some data is lost after the file is compressed and 

decompressed. Video and sound files often contain more 

information than is apparent to the viewer or listener; a 

lossy compression method, which does not preserve that 

excess information, can reduce such data to as little as 5 

percent of its original size. Compare lossless compression. 

lost cluster n. A cluster (disk storage unit) marked by the 

operating system as being in use but not representing any 

part of any chain of stored segments of a file. A lost cluster 

usually represents debris resulting from incomplete data 

“housekeeping,” as might result from the ungraceful exit 

(messy or abrupt termination) of an application program. 

Lotus 1-2-3 n. An electronic spreadsheet product introduced 

in 1983 by Lotus Development Corporation. Notable 

L

L 

Lotus cc:Mail LS-120 

for its inclusion of graphing and data-management (database) 

capabilities in addition to spreadsheet functionality, 

Lotus 1-2-3 is important in the history of the personal computer 

because it was one of the first “killer apps” that convinced 

businesses to buy and use a PC. Lotus Development 

was purchased by IBM in 1995. See also killer app. 

Lotus cc:Mail n. See cc:Mail. 

Lotus Domino n. A groupware application that transforms 

Lotus Notes into an application and messaging 

server. See also Lotus Notes. 

Lotus Notes n. A groupware application introduced in 

1988 by Lotus Development Corporation and now owned 

by IBM. Lotus Notes combines e-mail, calendar management, 

group scheduling, contact and task management, 

newsgroup access, and Web browsing capability 

(through the integration of Microsoft Internet Explorer) 

in one client application. Lotus Notes also offers search 

capabilities across multiple formats and file types on a 

network or the Web. 

low-Earth-orbit satellite n. A communications satellite 

put into orbit no higher than 500 miles above the earth’s 

surface. A low-Earth-orbit satellite, or LEO, circles the 

planet in 90 minutes to 2 hours. LEOs allow for use of 

smaller dishes and handheld devices, so they are wellsuited 

for interactive conferencing. However, because a 

LEO remains above the local horizon for about only 20 

minutes, large numbers of these satellites, in several different 

orbits, are required to maintain service. Acronym: 

LEO. Compare geostationary orbit satellite. 

lowercase adj. In reference to letters, not capital—for 

example, a, b, c. Compare uppercase. 

low frequency n. The portion of the electromagnetic 

spectrum between 30 kilohertz (kHz) and 300 kHz. This 

range of frequencies is used for several types of radio 

communication, including the longwave broadcast band in 

Europe and Asia. 

low-level language n. A language that is machine dependent 

or that offers few control instructions and data types. 

Each statement in a program written in a low-level language 

usually corresponds to one machine instruction. See 

also assembly language. Compare high-level language. 

low memory n. On computers running MS-DOS, the first 

640 kilobytes of RAM. This RAM is shared by MS-DOS, 

device drivers, data, and application programs. Also 

called: conventional memory. Compare high memory. 

320 

low-order adj. Carrying the least weight or significance; 

typically, the rightmost element in a group. For example, 

the rightmost bit in a group of bits is the low-order bit. 

Compare high-order. 

lowpass filter n. An electronic circuit that allows all frequencies 

below a specified frequency to pass through it. 

Compare bandpass filter, highpass filter. 

low resolution adj. Abbreviated lo-res. Appearing in relatively 

coarse detail, used in reference to text and graphics 

in raster-oriented computer displays and printing. Lowresolution 

printing is comparable to draft-quality dotmatrix 

output printed at 125 dots per inch or less. See also 

resolution. Compare high resolution. 

LPM n. See lines per minute. 

LPMUD n. A type of multiuser dungeon (MUD), typically 

combat related, that contains its own object-oriented programming 

language for the creation of new areas and 

objects in the virtual world. See also MUD. 

LPT n. Logical device name for a line printer, a name 

reserved by the MS-DOS operating system for up to three 

parallel printer ports designated LPT1, LPT2, and LPT3. 

The first port, LPT1, is usually the same as the primary 

MS-DOS hard-copy output device PRN (the logical 

device name for the printer). The letters LPT were originally 

used to stand for line print terminal. 

LRC n. Acronym for longitudinal redundancy check. A 

procedure used to check the accuracy of data stored on 

magnetic tape or transmitted over a communications line. 

See also parity bit. Compare VRC. 

ls n. A UNIX command that instructs the server to return 

a list of files and subdirectories in the current directory or 

the directory specified in the command. Because many 

FTP sites are built on UNIX systems, this command can 

also be used on those sites. See also FTP site, UNIX. 

LS-120 n. Acronym for Laser Storage-120. A floppy 

disk drive developed by Imation Corporation that uses 

proprietary laser storage 120-megabyte (MB) media as 

well as standard 1.44 MB 3.5-inch floppy media. The LS- 

120 disk drive is capable of storing 120 MB of data on a 

single 3.5-inch floppy disk and is compatible with other 

floppy disk formats. LS-120 drives are ATAPI (AT Attachment 

Packet Interface) compliant so several different 

drives can use the same EIDE controller. Also called: 

Super Disk.

LSB LZW compression 

LSB n. 1. See least significant bit. 2. Acronym for Linux 

Standard Base. A standard developed to aid in Linux software 

development by providing a uniform foundation for 

all versions of the operating system. The Linux model provided 

by the LSB provides a stable platform for developers 

to create software that may be used with any version of 

the operating system, while leaving companies the ability 

to add other features on top of the base. 

LSC n. See least significant character. 

LSD n. See least significant digit. 

LSI n. See large-scale integration. 

LSP n. See MPLS. 

LSR n. See MPLS. 

LU n. Acronym for logical unit. In an IBM SNA network, 

a point denoting the beginning or end of a communications 

session. See also SNA. 

Luddite n. A person opposed to technological advances, 

especially those designed to replace human skill and experience 

with automated machinery. The first Luddites were 

bands of textile workers in Nottinghamshire, England, 

who protested the use of new large-scale machinery, 

which they blamed for low wages and high unemployment. 

The origin of the term has never been verified, but 

the most popular theory is that the name derives from Ned 

Ludd, an apprentice knitter who destroyed his knitting 

frame with a hammer to protest beatings by his master. See 

also technophobe. Compare technophile. 

LUG n. Acronym for Linux Users Group. See user group. 

luggable computer n. The first portable computers, produced 

in the early to mid-1980s. These early units, all of 

which had built-in CRT-based displays, weighed over 20 

pounds and were the size of a medium suitcase—hence 

their name. See also portable computer. 

luminance n. 1. A measure of the amount of light radiated 

by a given source, such as a computer display screen. 

2. The perceived brightness component of a given color, as 

opposed to its hue or its saturation. See also HSB. Compare 

illuminance. 

luminance decay n. See persistence. 

luminosity n. The brightness of a color based on a scale 

from black to white on your monitor. 

321 

Lunar calendar n. Predominant calendar type used in 

Israel among Hebrew speakers, in Islamic cultures, and in 

most of Asia. Lunar calendars calculate months based on 

lunar phases. 

lurk vb. To receive and read articles or messages in a 

newsgroup or other online conference without contributing 

to the ongoing exchange. 

lurker n. A person who lurks in a newsgroup or other 

online conference. See also lurk. Compare netizen. 

LVS n. Acronym for Linux Virtual Server. A highperformance 

open source server that handles connections 

from clients and passes them on to a cluster of real servers. 

LVS receives incoming packets and forwards them to the 

proper back-end server. LVS is typically used to build 

scalable Web, mail, or other network services. Also 

called: ipvs. See also layer 4 switching. 

Lycos n. A Web search engine and directory that provides 

summaries of pages matching search requests. In addition, 

the Lycos site offers categorized directories of sites, 

reviews of selected sites, and services for finding names, 

viewing maps, and so on. 

Lynx n. A text-only Web browser program for UNIX 

platforms. 

.lzh n. The file extension that identifies archive files compressed 

with the Lempel Ziv and Haruyasu algorithm. See 

also compressed file, Lempel Ziv compression, LHARC. 

LZW compression n. A compression algorithm named 

after Abraham Lempel and Jakob Ziv (creators of Lempel 

Ziv compression) and LZW designer Terry Welch 

that makes use of repeating strings of data in its compression 

of character streams into code streams. It is also 

the basis of GIF compression. See also GIF, Lempel Ziv 

compression. 

L

M 

m prefix See milli-. 

M prefix See mega-. 

Mac- prefix A prefix used to indicate a software product’s 

applicability for the Macintosh computer, as in MacDraw. 

Mac n. See Macintosh. 

MAC n. Acronym for Media Access Control. In the IEEE 

802.x specifications, the lower of two sublayers that make 

up the ISO/OSI data link layer. The MAC manages access 

to the physical network, delimits frames, and handles error 

control. See also IEEE 802.x, LLC. 

MacBinary n. A file transfer protocol used to preserve coding 

for Macintosh-produced files stored in non-Macintosh 

computers, containing the file’s resource fork, data fork, and 

Finder information block. See also data fork, Finder, 

resource fork. 

Mach n. A variant of the UNIX operating system developed 

at Carnegie-Mellon University. Mach was designed 

to support advanced features such as multitasking, multiprocessing, 

and distributed systems. See also UNIX. 

Mach 3.0 n. The microkernel forming the lowest level of 

the Mac OS X operating system. Mach 3.0 provides basic 

services such as memory management, thread-handling, 

virtual memory, and address space management to the 

operating system kernel. 

mach 3 kernel n. See Mach 3.0. 

machine address n. See absolute address. 

machine code n. The ultimate result of the compilation 

of assembly language or any high-level language such as 

C or Pascal: sequences of 1s and 0s that are loaded and 

executed by a microprocessor. Machine code is the only 

language computers understand; all other programming 

languages represent ways of structuring human language 

so that humans can get computers to perform specific 

tasks. Also called: machine language. See also compiler 


machine cycle n. 1. The time required for the fastest 

operation (usually a NOP, or no-op, which does nothing) a 

M 

322 

microprocessor can perform. 2. The steps taken for each 

machine instruction. These steps are, typically, fetch the 

instruction, decode it, execute it, and perform any necessary 

storing. 

machine-dependent adj. Of, pertaining to, or being a 

program or a piece of hardware that is linked to a particular 

type of computer because it makes use of specific or 

unique features of the equipment and that cannot easily be 

used with another computer, if at all. Compare machineindependent. 

machine error n. A hardware error. Probably the most 

common type of machine error involves media, such as an 

error in reading a hard disk. 

machine identification n. A code by which an executing 

program can determine the identity and characteristics of 

the computer and other devices with which it is operating. 

machine-independent adj. Of, pertaining to, or being a 

program or piece of hardware that can be used on more 

than one type of computer with little or no modification. 

Compare machine-dependent. 

machine instruction n. An instruction (action statement) 

in machine code that can be directly executed by a processor 

or microprocessor. See also instruction, statement. 

machine language n. See machine code. 

machine-readable adj. 1. Presented in a form that a computer 

can interpret and use as input. For example, bar 

codes that can be scanned and used directly as computer 

input contain machine-readable information. 2. Coded in 

the binary form used by computers and stored on a suitable 

medium such as magnetic tape. See also optical character 

recognition. 

machine translation n. The use of computer software to 

translate large amounts of text from one natural language 

into another. Machine translation is usually used by corporations, 

publishers, and government agencies that need 

large amounts of documentation, news stories, or business 

data translated quickly. See also natural-language 

processing.

Macintosh macro assembler 

Macintosh n. A popular series of personal computers 

introduced by the Apple Computer Corporation in January 

1984. The Macintosh was one of the earliest personal 

computers to incorporate a graphical user interface and the 

first to use 3.5-inch floppy disks. It was also the first to use 

the 32-bit Motorola 68000 microprocessor. Despite its 

user-friendly features, the Macintosh lost market share to 

PC-compatible computers during the 1990s, but it still 

enjoys widespread use in desktop publishing and graphics-related 

applications. In late 1998, both Apple Computer 

and Macintosh gained increased visibility with 

release of the home-oriented iMac computer. See the illustration. 

Also called: Mac. See also graphical user interface, 

iMac, PC-compatible. 

F0Mgn01.eps 

Macintosh. 

Macintosh Application Environment n. A system shell 

for open RISC-based systems that provides a Macintosh 

interface within an X Window System window. The Macintosh 

Application Environment is compatible with both 

Mac and UNIX and will support all off-the-shelf products 

for the Macintosh. Acronym: MAE. See also RISC, X 


Macintosh File System n. The early, flat file system 

used on the Macintosh before the Hierarchical File System 

was introduced. Acronym: MFS. See also flat file system. 

Compare Hierarchical File System. 

Mac OS n. Short for Macintosh operating system. The 

name given to the Macintosh operating system, beginning 

with version 7.5 in September 1994, when Apple started 

323 

licensing the software to other computer manufacturers. 

See also Macintosh. 

Mac OS X n. The first complete revision of the Macintosh 

operating system. Mac OS X is BSD 4.4 UNIXbased, 

uses the Mach 3.0 microkernel, and is built around 

Apple’s open-source Darwin. Mac OS X adds symmetric 

multiprocessing, multithreading, preemptive multitasking, 

advanced memory management, and protected memory 

to the Macintosh. The UNIX foundation of Mac OS X 

allows greater options for software development, networking, 

and update and expansion of the operating system. 

Mac OS X includes a graphical user interface and a command-line 

interface. 

macro n. 1. In applications, a set of keystrokes and 

instructions recorded and saved under a short key code or 

macro name. When the key code is typed or the macro 

name is used, the program carries out the instructions of 

the macro. Users can create a macro to save time by 

replacing an often-used, sometimes lengthy, series of 

strokes with a shorter version. 2. In programming languages, 

such as C or assembly language, a name that 

defines a set of instructions that are substituted for the 

macro name wherever the name appears in a program (a 

process called macro expansion) when the program is 

compiled or assembled. Macros are similar to functions in 

that they can take arguments and in that they are calls to 

lengthier sets of instructions. Unlike functions, macros are 

replaced by the actual instructions they represent when the 

program is prepared for execution; function instructions 

are copied into a program only once. Compare function 


macro assembler n. An assembler that can perform 

macro substitution and expansion. The programmer can 

define a macro that consists of several statements and then 

use the macro name later in the program, thus avoiding 

having to rewrite the statements. For example, a macro 

called swap exchanges the values of two variables: After 

defining swap, the programmer can then insert an instruction 

such as “swap a, b” in the assembly language program. 

While assembling, the assembler replaces the 

instruction with the statements within the macro that swap 

the values of the variables a and b. 

M

M 

macrocontent magnetic-ink character recognition 

macrocontent n. The primary text or other content of a 

Web page. Compare microcontent. 

macro expansion n. The act of replacing a macro with 

its defined equivalent. Also called: macro substitution. See 

also macro (definition 2), macro assembler, macro processor. 

macro instruction n. An instruction used to manage 

macro definitions. See also macro language. 

macro language n. The collection of macro instructions 

recognized by a given macro processor. See also macro 

instruction, macro processor. 

macro processor n. A program that performs macro 

expansion. All programs that support macros have some 

form of macro processor, but macro processors differ from 

program to program and in the macro language they support. 

See also macro (definition 2), macro expansion, 

macro instruction. 

macro program n. See keyboard enhancer. 

macro recorder n. A program that records and stores 

keyboard macros. See also macro (definition 1). 

macro substitution n. See macro expansion. 

macro virus n. A virus that is written in a macro language 

associated with an application. The macro virus is 

carried by a document file used with that application and 

executes when the document is opened. 

MacTCP n. A Macintosh extension that allows Macintosh 

computers to use TCP/IP. See also TCP/IP. 

MADCAP n. See multicast address dynamic client allocation 

protocol. 

MAE n. 1. See Macintosh Application Environment. 

2. Acronym for Metropolitan Area Exchange. One of the 

Internet exchange points operated by MCI WorldCom, 

through which Internet service providers (ISPs) connect in 

order to exchange data. The two largest MAEs, MAE East 

(outside Washington, D.C.) and MAE West (near San 

Jose, California) are major national and international network 

interconnect points; more than half of all traffic 

through the Internet travels through one or both of these 

points. MCI WorldCom also operates smaller, regional 

MAEs in Chicago, Dallas, Houston, Los Angeles, New 

York, Paris, and Frankfurt. See also backbone (definition 

1), ISP. 

Magellan n. A Web directory. Named for the Portuguese 

explorer, Magellan reviews and rates all Web sites it lists. 

324 

Published by the McKinley Group, Magellan is now 

owned by Excite, Inc. 

magic date n. A date or dates that in some computer systems 

resembles a reserved number or flag with a special 

significance. Examples are the numbers 00 and 99, which 

have been used in some systems or programs based on 

two-digit years. Magic dates indicate some special status— 

for example, that a system component or resource should 

never expire or should never be purged. Because 99 in particular 

has been used in this way in many systems, dates in 

the year 1999 had the potential to cause problems in those 

systems. 

magnetic bubble n. A movable magnetic domain in a 

thin-film substrate. In bubble memory, magnetic bubbles 

representing bits circulate past circuits that can read and 

write them. High costs and relatively long access times 

have relegated magnetic bubbles to specialized applications. 

See also bubble memory, magnetic domain. Compare 

core, RAM. 

magnetic disk n. A computer disk enclosed in a protective 

case (hard disk) or jacket (floppy disk) and coated 

with a magnetic material that enables data to be stored in 

the form of changes in magnetic polarity (with one polarity 

representing a binary 1 and the other a 0) on many 

small sections (magnetic domains) of the disk surface. 

Magnetic disks should be protected from exposure to 

sources of magnetism, which can damage or destroy the 

information they hold. See also disk, floppy disk, hard 

disk. Compare compact disc, magneto-optic disc. 

magnetic domain n. A region of a ferromagnetic material 

in which the individual atomic or molecular magnetic 

particles are aligned in the same direction. Also 

called: ferromagnetic domain. 

magnetic field n. The space around a magnetic object in 

which magnetic force acts. A magnetic field is conceived 

of as consisting of flux lines that originate at the north 

magnetic pole and terminate at the south magnetic pole. 

magnetic head n. See head. 

magnetic-ink character recognition n. A form of character 

recognition that reads text printed with magnetically 

charged ink, determining the shapes of characters by sensing 

the magnetic charge in the ink. Once the shapes have 

been determined, character recognition methods are used 

to translate the shapes into computer text. A familiar use 

of this form of character recognition is to identify bank 

checks. Acronym: MICR. See also character recognition. 

Compare optical character recognition.

magnetic oxide main body 

magnetic oxide n. See ferric oxide. 

magnetic storage n. A generic term for non-internalmemory 

computer data storage involving a magnetic 

medium, such as disk or tape. 

magnetic tape n. See tape (definition 1). 

magneto-optical recording n. A type of recording technology 

used with optical discs in which a laser beam heats 

a small portion of the magnetic material covering the disc. 

The heating enables a weak magnetic field to change the 

orientation of the portion, thus recording onto the disc. 

This technique can also be used to erase the disc, making 

the disc rewritable. 

magneto-optic disc n. An erasable or semi-erasable 

storage disc, similar to a CD-ROM disc and of very high 

capacity, in which a laser beam is used to heat the recording 

surface to a point at which tiny regions on the surface 

can be magnetically aligned to store bits of data. See also 

CD-ROM, magneto-optical recording. 

magnitude n. The size of a number, regardless of its sign 

(+ or –). For example, 16 and –16 have the same magnitude. 

See also absolute value. 

mailbomb1 n. An excessively large amount of e-mail data 

(a very large number of messages or one very large message) 

sent to a user’s e-mail address in an attempt to make 

the user’s mailer program crash or to prevent the user from 

receiving further legitimate messages. See also e-mail1 (definition 1). Compare letterbomb. 

mailbomb2 vb. To send a mailbomb to a user. One person 

might mailbomb a user with a single enormous message; a 

large number of users might mailbomb an unpopular person 

by simultaneously sending messages of normal size. 

mailbot n. A program that automatically responds to e-mail 

messages or performs actions based on commands within 

the messages. A mailing list manager is one example. See 

also mailing list manager. 

mailbox n. A disk storage area assigned to a network 

user for receipt of e-mail messages. See also e-mail1 (definition 1). 

mail digest n. See digest (definition 2). 

mailer-daemon n. A program used to transport e-mail 

between hosts on a network. See also daemon. 

mail filter n. See e-mail filter. 

325 

mail header n. A block of text at the top of an e-mail 

message containing such information as the addresses of 

the sender and recipients, the date and time sent, the 

address to which a reply is to be sent, and the subject. The 

mail header is used by an e-mail client or program. See 

also e-mail1 (definition 1). 

mailing list n. A list of names and e-mail addresses that 

are grouped under a single name. When a user places the 

name of the mailing list in a mail client’s To: field, the client 

sends the message to the machine where the mailing 

list resides, and that machine automatically sends the message 

to all the addresses on the list (possibly allowing a 

moderator to edit it first). See also LISTSERV, mailing list 

manager, Majordomo, moderator. 

mailing list manager n. Software that maintains an 

Internet or intranet mailing list. The mailing list manager 

accepts messages posted by subscribers; sends copies of 

the messages (which may be edited by a moderator) to all 

the subscribers; and accepts and processes user requests, 

such as to subscribe or to unsubscribe to the mailing list. 

The most commonly used mailing list managers are LIST- 

SERV and Majordomo. See also LISTSERV, mailing list, 

Majordomo, moderator. 

mail merge n. A mass-mail facility that takes names, 

addresses, and sometimes pertinent facts about recipients 

and merges the information into a form letter or another 

such basic document. 

mail reflector n. A newsgroup that consists simply of the 

messages posted to a mailing list translated into newsgroup 

format. 

mailto n. A protocol designator used in the HREF of a 

hyperlink that enables a user to send e-mail to someone. 

For instance, Anne E. Oldhacker has the e-mail address 

aeo@baz.foo.com and an HTML document contains the 

code E-mail 

Anne!. If a user clicks on the hyperlink “E-mail 

Anne!”, the user’s e-mail application is launched and 

the user can send e-mail to her without knowing her 

actual e-mail address. See also e-mail1 (definition 1), 

HTML, hyperlink. 

mainboard n. See motherboard. 

main body n. The set of statements in a computer program 

at which execution of the program begins and that 

invokes the subroutines of the program. 

M

M 

mainframe MAN 

mainframe n. A type of large computer system (in the 

past often water-cooled), the primary data processing 

resource for many large businesses and organizations. 

Some mainframe operating systems and solutions are over 

40 years old and have the capacity to store year values 

only as two digits. 

mainframe computer n. A high-level, typically large and 

expensive computer designed to handle intensive computational 

tasks. Mainframe computers are characterized by 

their ability to simultaneously support many users connected 

to the computer by terminals. The name is derived 

from “main frame,” the cabinet originally used to house 

the processing unit of such computers. See also computer, 

supercomputer. 

main function n. The main body of a program written in 

a computer language that uses sets of functions to create 

an entire program. For example, the C language requires 

each program to contain a function called main, which C 

uses as the starting point of execution. See also main body. 

main loop n. A loop in the main body of a program that 

performs the principal function of the program over and 

over until termination is somehow signaled. In eventdriven 

programs, this loop checks for events received from 

the operating system and handles them appropriately. See 

also event-driven programming, main body. 

main memory n. See primary storage. 

main segment n. On the Macintosh, the principal code 

segment of a program, which must remain loaded throughout 

the execution of the program. 

maintenance n. The process of taking measures to 

ensure that a hardware, software, or database system is 

functioning properly and is up to date. 

Majordomo n. The name of a popular software program 

that manages and supports Internet mailing lists. See also 

mailing list, mailing list manager. 

major geographic domain n. A two-character sequence 

in an Internet domain name address that indicates the 

country/region in which a host is located. The major geographic 

domain is the last part of the domain name 

address, following the subdomain and domain codes; for 

example, uiuc.edu.us indicates a host at the University of 

Illinois in the United States, whereas cam.ac.uk indicates a 

host at the University of Cambridge in the United Kingdom. 

The code .us, which indicates a domain in the United 

326 

States, is usually omitted. Also called: country code. See 

also DNS (definition 1), domain name address. 

major key n. See primary key. 

Make Changes n. The Macintosh-style permission that 

gives users the right to make changes to a folder’s contents; 

for example, modifying, renaming, moving, creating, 

and deleting files. When AppleTalk network 

integration translates access privileges into permissions, a 

user who has the Make Changes privilege is given Write 

and Delete permissions. See also permission. 

make-table query n. In Microsoft Office, an action query 

that moves the resulting data to a new table in either the 

current database or another database. 

male connector n. A type of connector that has pins for 

insertion into receptacles. Male connector part numbers 

often include an M (male) or P (plug). For example, a 

male DB-25 connector might be labeled DB-25M or DB- 

25P. See the illustration. Compare female connector. 

F0MgnF0Mgn02.eps 

Male connector. 

malicious mobile code n. A virus or other destructive 

program that takes advantage of security weaknesses in 

wireless transmission systems. Malicious mobile code 

may affect computers, PDAs, Internet-capable digital 

phones, and other wireless networking devices. 

malware n. Software created and distributed for malicious 

purposes, such as invading computer systems in the 

form of viruses, worms, or innocent-seeming plug-ins and 

extensions that mask other destructive capabilities. Also 

called: malicious software. 

MAME n. Acronym for Multiple Arcade Machine Emulator. 

MAME is software written in C that emulates the 

hardware and software of original arcade games, allowing 

them to run on PCs. See also arcade game, C. 

MAN n. Acronym for metropolitan area network. A highspeed 

network that can carry voice, data, and images at up 

to 200 Mbps or faster over distances of up to 75 km. Based 

on the network architecture, the transmission speed can be 

higher for shorter distances. A MAN, which can include

managed code mantissa 

one or more LANs as well as telecommunications equipment 

such as microwave and satellite relay stations, is 

smaller than a wide area network but generally operates at 

a higher speed. Compare LAN, WAN. 

managed code n. Code that is executed by the common 

language runtime environment rather than directly by the 

operating system. Managed code applications gain common 

language runtime services such as automatic garbage 

collection, runtime type checking and security support, 

and so on. These services provide uniform platform- and 

language-independent behavior of managed-code applications. 

See also unmanaged code. 

managed service provider n. A business that supplies 

remote access services to individuals and enterprises. 

Managed service providers offer remote connections, network 

management, user support, security, and applications 

hosting. Acronym: MSP. Compare ISP. 

Management and Monitoring Tools n. Software components 

that include utilities for network management and 

monitoring, along with services that support client dialing 

and the updating of client phone books. Also included is 

the Simple Network Management Protocol (SNMP). See 

also SNMP. 

Management Information Base n. A set of objects that 

represents various types of information about a device, 

used by a network management protocol (for example, 

SNMP) to manage the device. Because different network 

management services are used for different types of 

devices and protocols, each service has its own set of 

objects. Acronym: MIB. See also service, SNMP. 

Management Information Services n. See Information 

Services. 

management information system n. A computer-based 

system for processing and organizing information so as to 

provide various levels of management within an organization 

with accurate and timely information needed for 

supervising activities, tracking progress, making decisions, 

and isolating and solving problems. Acronym: MIS. 

Management Information Systems n. See Information 

Services. 

manager n. Any program that is designed to perform a 

certain set of housekeeping tasks related to computer 

operation, such as the maintenance of files. On the Macintosh, 

Manager (with a capital M) is used in the names of 

327 

various separate portions of the computer’s operating system 

that handle input, output, and internal functions (for 

example, File Manager and Memory Manager). 

Manchester coding n. A method of encoding data used 

in communications, such as on some LANs, that combines 

both data and timing signals in a stream of transmitted 

bits. See also phase encoding. 

mandatory user profile n. A user profile that is not 

updated when the user logs off. It is downloaded to the 

user’s desktop each time the user logs on, and it is created 

by an administrator and assigned to one or more users to 

create consistent or job-specific user profiles. See also 

local user profile, roaming user profile, user profile. 

Mandelbrot set n. See fractal. 

man-in-the-middle attack n. A form of attack in which 

the intruder intercepts messages between parties in a public 

key exchange. Each party’s messages are diverted to 

the intruder, who may alter them before sending them on. 

The parties on each end of the exchange remain unaware 

that their messages are being intercepted and modified. 

Also called: bucket brigade attack. 

man-machine interface n. The set of commands, displays, 

controls, and hardware devices enabling the human 

user and the computer system to exchange information. 

See also user interface. 

man pages n. 1. Online documentation for UNIX commands 

and programs and the UNIX library routines available 

for use in C programs. These documents, also found 

in the UNIX Programmer’s Manual, can be displayed on a 

user’s terminal or printed using the command man. 

2. Short for manual pages. A set of help files included 

with a Linux distribution. Man pages may come with the 

Linux distribution and be installed along with the operating 

system or may be available from online sources. 

mantissa n. 1. In calculations that have logarithms, the 

positive decimal fraction of a common (base-10) logarithm. 

For example, the common logarithm of 16 is 

1.2041; the characteristic, or whole-number portion, of 

the logarithm is 1 (the logarithm of 10); and the mantissa, 

or fractional portion, is .2041 (the logarithm of 

1.6). See also characteristic, logarithm. 2. In floatingpoint 

notation, the portion expressing the significant 

digits of a number. For example, the floating-point representation 

of 640,000 is 6.4E+05. The mantissa is 6.4; 

M

M 

manual link markup language 

the exponent (E+05) shows the power of 10 to which 6.4 

is raised. Also called: significand. See also floatingpoint 

notation. 

manual link n. A link that requires you to take action to 

update your data after the data in the source document 

changes. 

many-to-many relationship n. A complex association 

between two sets of parameters in which many parameters 

of each set can relate to many others in the second set. A 

many-to-many relationship is most commonly used to 

describe an association between two tables in which one 

record in either table can relate to many records in the 

other table. 

many-to-one relationship n. 1. A server configuration in 

which several small servers replicate the abilities of one 

larger, more powerful server. See also key pair. 2. In reference 

to asymmetric key encryption, the idea that many 

individuals in possession of the public key can decrypt the 

digital signature of one individual in possession of the private 

key. 

map1 n. Any representation of the structure of an object. 

For example, a memory map describes the layout of 

objects in an area of memory, and a symbol map lists the 

associations between symbol names and memory 

addresses in a program. See also image map. 

map2 vb. To translate one value into another. For example, 

in computer graphics one might map a three-dimensional 

image onto a sphere. In reference to virtual memory 

systems, a computer might translate (map) a virtual 

address into a physical address. See also virtual memory. 

MAPI n. Acronym for Messaging Application Programming 

Interface. The Microsoft interface specification that 

allows different messaging and workgroup applications 

(including e-mail, voice mail, and fax) to work through a 

single client, such as the Exchange client included with 

Windows 95 and Windows NT. See also application programming 

interface. 

mapped data field n. A field that represents commonly 

used information, such as “First Name.” If a data source 

contains a “First Name” field or variation, such as 

“FName,” the data source field automatically maps to the 

corresponding mapped data field. 

mapped drives n. 1. In the Windows environment, network 

drives that have been assigned local drive letters and 

are locally accessible. 2. Under UNIX, disk drives that 

have been defined to the system and can be made active. 

328 

MapPoint n. Business mapping software introduced by 

Microsoft as an Office-compatible product in 1999. 

Designed for use by business people, MapPoint consists of 

a database of United States maps showing detail down to 

the level of individual streets and demographic data broken 

out by state, county, zip code, and other regions. See 

also Office. 

margin n. In printing, those portions of a page—top, bottom, 

and sides—outside the main body of text. 

mark n. 1. In applications and data storage, a symbol or 

other device used to distinguish one item from others like 

it. 2. In digital transmission, the state of a communications 

line (positive or negative) corresponding to a binary 1. In 

asynchronous serial communications, a mark condition is 

the continuous transmission of binary 1s to indicate when 

the line is idle (not carrying information). In asynchronous 

error checking, setting the parity bit to 1 in each group of 

transmitted bits is known as mark parity. See also parity. 

Compare space. 3. In optical sensing, a pencil line, as on a 

voting form or an IQ test, that can be recognized by an 

optical reader. 

marker n. 1. Part of a data communications signal that 

enables the communications equipment to recognize the 

structure of the message. Examples are the start and stop 

bits that frame a byte in asynchronous serial communications. 

2. A symbol that indicates a particular location on a 

display surface. 

Mark I n. 1. An electromechanical calculating machine 

designed in the late 1930s and early 1940s by Howard 

Aiken of Harvard University and built by IBM. Also 

called: Automatic Sequence Controlled Calculator, Harvard 

Mark I. 2. The first fully electronic stored-program 

computer, designed and built at Manchester University in 

England. It successfully executed its first program in June 

1948. 3. The first commercial computer, which was based 

on the Manchester Mark I and released in 1951. 

markup n. Comments and tracked changes such as insertions, 

deletions, and formatting changes that you can view 

or print. 

markup language n. A set of codes in a text file that 

instructs a computer how to format the file on a printer or 

video display or how to index and link its contents. Examples 

of markup languages are Hypertext Markup Language 

(HTML) and Extensible Markup Language (XML), 

which are used in Web pages, and Standard Generalized 

Markup Language (SGML), which is used for typesetting

marquee master key 

and desktop publishing purposes and in electronic documents. 

Markup languages of this sort are designed to 

enable documents and other files to be platform-independent 

and highly portable between applications. See also 

HTML, SGML, XML. 

marquee n. A nonstandard HTML extension that causes 

scrolling text to appear as part of a Web page. Currently, 

marquees are viewable only with Internet Explorer. See 

also HTML, Internet Explorer, Web page. 

marquee component n. A region on a page that displays 

a horizontally scrolling text message. 

mask n. 1. A binary value used to selectively screen out 

or let through certain bits in a data value. Masking is performed 

by using a logical operator (AND, OR, XOR, or 

NOT) to combine the mask and the data value. For example, 

the mask 00111111, when used with the AND operator, 

removes (masks off) the two uppermost bits in a data 

value but does not affect the rest of the value. See the illustration. 

See also logical operator, mask bit. 2. In television 

and display technology, a thin perforated sheet of metal or 

a close-set series of metal strips on the surface of the 

screen that helps create a clear, sharp image by ensuring 

that the electron beam for a particular color (red, blue, or 

green) strikes only the phosphor it is intended to illuminate, 

while the phosphors for the other colors are shadowed 

by the mask. Three types of masks are in use: a 

shadow mask, with round perforations; an aperture grill, 

with vertical stripes; and a slot mask, with elliptical openings. 

See also aperture mask, shadow mask, slot mask. 

11010101 

AND 00111111 

00010101 

F0Mgn03.eps 

Mask. 

Data value 

Mask 

Resulting value 

maskable interrupt n. A hardware interrupt that can be 

temporarily disabled (masked) during periods when a program 

needs the full attention of the microprocessor. See 

also external interrupt, hardware interrupt, interrupt. Compare 

nonmaskable interrupt. 

mask bit n. A given bit within a binary mask whose function 

is to screen out or let through the corresponding bit in 

a data value when the mask is used in an expression with a 

logical operator. See also mask (definition 1). 

masking n. The process of using the mask operation to 

perform operations on bits, bytes, or words of data. See 

also mask (definition 1). 

329 

mask off vb. To use a mask to remove bits from a byte of 

data. See also mask (definition 1). 

massively parallel processing n. A computer architecture 

in which each of a large number of processors has its 

own RAM, which contains a copy of the operating system, 

a copy of the application code, and its own part of the data, 

on which that processor works independently of the others. 

Acronym: MPP. Compare SMP. 

massively parallel processor n. A computer designed 

to perform massively parallel processing. 

mass storage n. A generic term for disk, tape, or optical 

disc storage of computer data, so called for the large 

masses of data that can be stored in comparison with computer 

memory capacity. Compare memory. 

Master Boot Record n. The first sector of the first hard 

disk; a physically small but critical element in the startup 

process on an x86-based computer. When a computer is 

booted, it processes a series of self-tests and then reads the 

Master Boot Record, or MBR, into memory. The MBR 

contains instructions that locate the disk’s system (startup) 

partition, read the contents of the first sector of the system 

partition into memory, and then carry out the instructions 

contained in that sector. If the sector represents what is 

known as a Partition Boot Sector, the instructions found 

there begin the process of loading and starting the operating 

system. In other words, the startup process on an x86based 

computer is as follows: self-test to Master Boot 

Record; MBR to system partition and Partition Boot Sector; 

Partition Boot Sector to operating system; and, finally, 

a computer ready to go to work. Acronym: MBR. See also 

Partition Boot Sector. 

master file n. In a set of database files, the file containing 

more or less permanent descriptive information about the 

principal subjects of the database, summary data, and one 

or more critical key fields. For example, customers’ 

names, account numbers, addresses, and credit terms 

might be stored in a master file. See also master record. 

Compare transaction file. 

master key n. The server-based component of software 

or data protection. In some systems, data or applications 

are stored on a server and must be downloaded to the local 

machine for use. When a client requests the data, it presents 

a session key. If the session key supplied matches the 

master key, the key server sends the requested packet. See 

also client (definition 3), server (definition 2). 

M

M 

master record MC68000 

master record n. A record in a master file; typically, the 

descriptive and summary data related to the item that is the 

subject of the record. See also master file. 

master reseller n. A status assigned by computer equipment 

manufacturers to dealers and distributors who meet 

certain qualifications, usually related to the number of 

pieces the reseller expects to sell. 

master/slave arrangement n. A system in which one 

device, called the master, controls another device, called 

the slave. For example, a computer can control devices 

connected to it. 

matching n. The process of testing whether two data 

items are identical or of finding a data item that is identical 

to a key. See also pattern recognition. 

Material Requirements Planning n. An approach to 

information management in a manufacturing environment 

that makes use of software to help monitor and control processes 

related to manufacturing—for example, managing 

schedules and determining when and in what quantities to 

order materials. Acronym: MRP. Also called: Material 

Resource Planning. See also Enterprise Resource Planning. 

math coprocessor n. See floating-point processor. 

mathematical expression n. An expression that uses 

numeric values, such as integers, fixed-point numbers, 

and floating-point numbers, and operators, such as addition, 

subtraction, multiplication, and division. See also 

expression. 

mathematical function n. A function in a program that 

performs a set of mathematical operations on one or more 

values or expressions and that returns a numeric value. 

mathematical model n. The mathematical assumptions, 

expressions, and equations that underlie a given program. 

Mathematical models are used to model “real-world” physical 

systems such as planets in orbit around a star or resource 

production and consumption within a closed system. 

MathML n. Acronym for Mathematical Markup Language. 

An XML application for describing mathematical 

notation and capturing both its structure and content. The 

goal of MathML is to enable mathematics to be served, 

received, and processed on the Web, just as HTML has 

enabled this functionality for text. 

matrix n. An arrangement of rows and columns used for 

organizing related items, such as numbers, dots, spreadsheet 

330 

cells, or circuit elements. Matrices are used in mathematics 

for manipulating rectangular sets of numbers. In computing 

and computer applications, matrices are used for the similar 

purpose of arranging sets of data in table form, as in spreadsheets 

and lookup tables. In hardware, matrices of dots are 

used in creating characters on the screen as well as in print 

(as by dot-matrix printers). In electronics, matrices of 

diodes or transistors are used to create networks of logic circuits 

for such purposes as encoding, decoding, or converting 

information. See also grid. 

matrix line printer n. See line printer. 

MAU n. Acronym for Multistation Access Unit. A hub 

device in a token-ring network that connects computers in 

a physical hub-and-spokes arrangement but uses the logical 

ring required in token ring networks. Also called: 

MSAU. See also hub, token-ring network. 

maximize vb. In a graphical user interface, to cause a 

window to expand to fill all the space available within a 

larger window or on the screen. See also enlarge, graphical 

user interface, Maximize button, window. Compare 

minimize, reduce. 

Maximize button n. In Windows 3.x, Windows 9x, Windows 

NT, and Windows 2000, a button in the upper righthand 

corner of a window that, when clicked, maximizes a 

window to fill all the space available within a larger window 

or on the screen. See also graphical user interface, 

window. Compare Minimize button, zoom box. 

Maximum Transmission Unit n. See MTU. 

Mb n. See megabit. 

MB n. See megabyte. 

MBONE or Mbone n. Short for multicast backbone. A 

small set of Internet sites, each of which can transmit realtime 

audio and video simultaneously to all the others. 

MBONE sites are equipped with special software to send 

and receive packets at high speed using the IP one-tomany 

multicasting protocol. The MBONE has been used 

for video conferencing and even for a Rolling Stones concert 

in 1994. See also RealAudio. 

Mbps n. Short for mega bits per second. One million bits 

per second. 

MBR n. See Master Boot Record. 

MC n. See megacycle. 

MC68000 n. See 68000.

MC68020 mechanical mouse 

MC68020 n. See 68020. 

MC68030 n. See 68030. 

MC68040 n. See 68040. 

MC68881 n. See 68881. 

MCF n. See Meta-Content Format. 

MCGA n. Acronym for Multi-Color Graphics Array. An 

older video adapter included in the IBM PS/2 Models 25 

and 30. The MCGA was capable of emulating the CGA 

(Color/Graphics Adapter) and provided two additional 

graphics modes: the first mode had 640 horizontal pixels 

by 480 vertical pixels with 2 colors chosen from a palette 

of 262,144 colors; the second had 320 horizontal pixels by 

200 vertical pixels with 256 colors chosen from a palette 

of 262,144 colors. See also graphics mode (definition 2). 

MCI n. 1. Acronym for Media Control Interface. Part of 

the Windows application programming interface that 

enables a program to control multimedia devices. 2. A 

major long-distance telephone service carrier, originally 

Microwave Communications, Inc. 

m-commerce n. Short for mobile commerce. 

M-commerce involves the use of personal digital assistants 

(PDAs), digital phones, and other wireless handheld 

devices equipped with microbrowsers for the online buying 

and selling of goods. M-commerce is distinguished 

from other electronic commerce by the level of portability. 

Wireless Application Protocol (WAP) standards form the 

foundation of m-commerce technology, which takes 

advantage of smart phone capabilities with e-mail, fax, 

Internet, and phone in one mobile unit. See also microbrowser, 

Wireless Application Protocol. 

MCP n. Acronym for Microsoft Certified Professional. A 

basic certification from Microsoft that verifies an individual’s 

ability to successfully implement a Microsoft product 

or technology as part of a solution for an organization. 

The MCP certification is often used as a building block for 

acquiring additional certifications in specialized skill areas 

such as databases, programming languages, and Web 

development. 

MCSA n. Acronym for Microsoft Certified Systems 

Administrator. A certification from Microsoft that verifies 

an individual’s ability to implement, manage, and troubleshoot 

existing Microsoft Windows and Windows .NET 

network and system environments. See also MCP. 

331 

MCSD n. Acronym for Microsoft Certified Solution 

Developer. A certification from Microsoft that verifies an 

individual’s ability to use Microsoft development tools, 

technologies, and platforms to design and develop business 

solutions. See also MCP. 

MCSE n. Acronym for Microsoft Certified System Engineer. 

A certification from Microsoft that verifies an individual’s 

ability to analyze business requirements and then 

design and implement business solutions with Microsoft 

Windows platforms and server software. See also MCP. 

MD2 n. A hashing algorithm that creates a 128-bit hash 

value used to verify data integrity. MD2 is an earlier, 8bit 

version of the more common MD5. See also hashing 

algorithm. 

MD4 n. A hashing algorithm that creates a 128-bit hash 

value used to verify data integrity. Like the latest version, 

MD5, MD4 is optimized for 32-bit machines. See also 

hashing algorithm. 

MD5 n. An industry-standard, one-way, 128-bit hashing 

scheme, developed by MIT Laboratory for Computer Science 

and RSA Data Security, Inc., and used by various 

Point-to-Point Protocol (PPP) vendors for encrypted 

authentication. An extension of MD4, MD5 is slightly 

slower than the earlier version but offers improved data 

security. See also hashing algorithm. 

MDA n. Acronym for Monochrome Display Adapter. The 

video adapter introduced with the earliest model of the 

IBM PC in 1981. MDA was capable of only one video 

mode: a character mode with 25 lines of 80 characters 

each, with underlining, blinking, and high-intensity characters. 

IBM did not use the name Monochrome Display 

Adapter or the acronym MDA. 

MDI n. Acronym for multiple-document interface. A user 

interface in an application that allows the user to have 

more than one document open at the same time. See also 


MDIS n. See Metadata Interchange Specification. 

mean time between failures n. See MTBF. 

mean time to repair n. See MTTR. 

mechanical mouse n. A type of mouse in which the 

motion of a ball on the bottom of the mouse is translated 

into directional signals. As the user moves the mouse, the 

ball rolls, turning a pair of wheels mounted at right angles 

inside the mouse that have conductive markings on their 

M

M 

mechatronics Melissa 

surfaces. Because the markings permit an electric current 

to flow, a set of conductive brushes that ride on the surface 

of the conductive wheels can detect these conductive 

markings. The electronics in the mouse translate these 

electrical movement signals into mouse-movement information 

that can be used by the computer. See also mouse, 

trackball. Compare optical mouse, optomechanical 

mouse. 

mechatronics n. A term derived from the words mechanical 

and electronics to describe a field of engineering that 

applies mechanical, electrical, and electronic engineering 

concepts to product design and manufacture. A relatively 

new discipline, mechatronics is applicable to products in 

fields as diverse as medicine, robotics, manufacturing, and 

consumer electronics. 

media n. The physical material, such as paper, disk, and 

tape, used for storing computer-based information. Media 

is plural; medium is singular. 

Media Access Control n. See MAC. 

Media Control Interface n. See MCI (definition 1). 

media conversion n. Transferring data from one storage 

medium to another—for example, from disk to tape. 

media eraser n. A device that removes or obliterates data 

from a storage medium on a wholesale basis, usually by 

writing meaningless data (such as zeros) over it. See also 

bulk eraser. 

media filter n. 1. A device used with local area networks 

(LANs) as an adapter between two different types of 

media. For example, an RJ-45 connector might be used 

between coaxial cable and unshielded twisted pair (UTP) 

cables. Media filters are similar in function to transceivers. 

As with many components to LANs, manufacturers often 

choose different names for similar products, so a LAN 

expert is needed to decide which media filters are required 

for a particular LAN. See also coaxial cable, connector 

(definition 1), LAN, transceiver, UTP. 2. A device added 

to data networks to filter out electronic noise from the 

environment. For example, a media filter might be added 

to an Ethernet network based on coaxial cabling to prevent 

data loss from interference by nearby electronic equipment. 

See also coaxial cable, Ethernet (definition 1). 

media stream n. A continuous sequence of audio or 

audio-and-video through a network. 

medium1 adj. Of or relating to the middle part of a range 

of possible values. 

332 

medium2 n. A substance in which signals can be transmitted, 

such as a wire or fiber-optic cable. See media. 

medium model n. A memory model of the Intel 80x86 

processor family. The medium model allows only 64 kilobytes 

for data but generally up to 1 megabyte for code. See 

also memory model. 

medium-scale integration n. A concentration of circuit 

elements in the hundreds on a single chip. Acronym: MSI. 

See also integrated circuit. 

meg n. See megabyte. 

mega- prefix One million (106 ). In computing, which is 

based on the binary (base-2) numbering system, mega- has 

a literal value of 1,048,576, which is the power of 2 (220 ) 

closest to one million. Abbreviation: M. 

megabit n. Usually 1,048,576 bits (220 ); sometimes interpreted 

as 1 million bits. Abbreviation: Mb, Mbit. 

megabyte n. Usually 1,048,576 bytes (220 ); sometimes 

interpreted as 1 million bytes. Abbreviation: MB. 

megacycle n. A term for 1 million cycles—usually used 

to mean 1 million cycles per second. Abbreviation: MC. 

See also megahertz. 

megaflops n. See MFLOPS. 

megahertz n. A measure of frequency equivalent to 1 

million cycles per second. Abbreviation: MHz. 

megapel display n. See megapixel display. 

megapixel adj. A reference to image resolution of one 

million pixels or more. The term is used in reference to 

devices such as digital cameras, scanners, and computer 

monitors and display adapters. 

megapixel display n. A video display capable of displaying 

at least 1 million pixels. For example, a video display 

with a screen size of 1024 horizontal pixels and 1024 

vertical pixels is a megapixel display. Also 

called: megapel display. 

Melissa n. A macro virus that affects Word files in 

Microsoft Office 97 and Office 2000 and first appeared in 

the spring of 1999. Melissa is delivered as an attachment to 

an e-mail with the subject line “An Important Message 

From ,” a message beginning “Here is that 

document you asked for…,” or both. When the attachment 

is opened, the virus propagates (if Microsoft Outlook is 

installed) by sending itself to the first 50 e-mail addresses in 

the user’s Outlook address book. On the infected machine,

meltdown memory management 

the virus also changes the registry, infects the Normal.dot 

Word template (which, in turn, infects new documents), 

and, in Office 2000, disables the Word macro virus warning. 

Although the Melissa virus does not destroy data, it can 

affect e-mail performance through the increased volume of 

messages. If an infected document is open at a time when 

the day of the month is the same as the minute value of the 

current time, the virus inserts the text “Twenty-two points, 

plus triple-word-score, plus fifty points for using all my letters. 

Game’s over. I’m outta here” at the current location of 

the cursor. The virus was named after an acquaintance of 

the hacker who developed it. 

meltdown n. 1. The complete collapse of a computer network 

caused by a higher level of traffic than the network can 

support. The term refers, by analogy, to the accidental melting 

down of a nuclear reactor core. 2. Colloquially, the 

breakdown of a person, usually in a job situation, caused by 

overwork, stress, or failure. 

member n. 1. In object-oriented programming, a variable 

or routine that is part of a class. See also C++, class. 2. A 

value that is part of a set data structure. See also set2 (definition 

1). 

membrane keyboard n. A keyboard in which an unbroken 

plastic or rubber shell (a membrane) covers keys that 

have little or no travel (movement). Rather than use normal, 

full-travel keys, membrane keyboards use pressuresensitive 

areas that are sometimes, but not always, defined 

by small bumps under the membrane. 

memo field n. A field in a database file that can contain 

unstructured text. 

memo pad n. A note-taking feature offered by many personal 

digital assistants and other handheld computing 

devices. Memo pad allows for the entry of short notes via 

typing or handwriting recognition applications. The notes 

can be categorized, organized, and edited later. 

memory n. A device where information can be stored and 

retrieved. In the most general sense, memory can refer to 

external storage such as disk drives or tape drives; in common 

usage, it refers only to a computer’s main memory, 

the fast semiconductor storage (RAM) directly connected 

to the processor. See also core, EEPROM, EPROM, flash 

memory, PROM, RAM, ROM. Compare bubble memory, 

mass storage. 

333 

memory bank n. The physical location on a motherboard 

where a memory module can be inserted. See also bank 


memory board n. A plug-in printed circuit board that contains 

one or more memory chips. See also memory chip. 

memory cache n. See CPU cache. 

memory card n. A memory module that is used to extend 

RAM storage capacity or in place of a hard disk in a portable 

computer, such as a laptop, notebook, or handheld PC. 

The module is usually the size of a credit card and can be 

plugged into a PCMCIA-compliant portable computer. 

The module can be composed of EPROM, RAM, or ROM 

chips or flash memory. Also called: RAM card, ROM 

card. See also EPROM, flash memory, handheld PC, hard 

disk, memory cartridge, module (definition 2), PCMCIA, 

RAM, ROM. 

memory cartridge n. A plug-in module containing RAM 

(random access memory) chips that can be used to store 

data or programs. Memory cartridges are used primarily in 

portable computers as smaller, lighter (but more expensive) 

substitutes for disk drives. Memory cartridges typically 

use either a nonvolatile form of RAM, which does 

not lose its contents when power is turned off, or batterybacked 

RAM, which maintains its contents by drawing 

current from a rechargeable battery within the cartridge. 

Also called: RAM cartridge. See also memory card, 

RAM. Compare ROM cartridge. 

memory cell n. An electronic circuit that stores one bit of 

data. See also bit. 

memory chip n. An integrated circuit devoted to memory 

storage. The memory storage can be volatile and hold data 

temporarily, such as RAM, or nonvolatile and hold data 

permanently, such as ROM, EPROM, EEPROM, or 

PROM. See also EEPROM, EPROM, integrated circuit, 

memory board, nonvolatile memory, PROM, RAM, volatile 

memory. 

memory management n. 1. In operating systems for 

personal computers, procedures for optimizing the use of 

RAM (random access memory). These procedures include 

selectively storing data, monitoring it carefully, and freeing 

memory when the data is no longer needed. Most current 

operating systems optimize RAM usage on their own; 

some older operating systems, such as early versions of 

MS-DOS, required the use of third-party utilities to optimize 

RAM usage and necessitated that the user be more 

M

M 

memory management program menu item 

knowledgeable about how the operating system and applications 

used memory. See also memory management unit, 

RAM. 2. In programming, the process of ensuring that a 

program releases each chunk of memory when it is no 

longer needed. In some languages, such as C and C++, the 

programmer must keep track of memory usage by the program. 

Java, a newer language, automatically frees any 

chunk of memory that is not in use. See also C, C++, garbage 

collection, Java. 

memory management program n. 1. A program used to 

store data and programs in system memory, monitor their 

use, and reassign the freed space following their execution. 

2. A program that uses hard disk space as an extension 

of the random access memory (RAM). 

memory management unit n. The hardware that supports 

the mapping of virtual memory addresses to physical 

memory addresses. In some systems, such as those based 

on the 68020, the memory management unit is separate 

from the processor. In most modern microcomputers, 

however, the memory management unit is built into the 

CPU chip. In some systems, the memory management unit 

provides interfacing between the microprocessor and 

memory. This type of memory management unit is typically 

responsible for address multiplexing and, in the case 

of DRAMs, the refresh cycle. Acronym: MMU. See also 

physical address, refresh cycle, virtual address. 

memory model n. The approach used to address the code 

and the data that are used in a computer program. The 

memory model dictates how much memory can be used in 

a program for code and how much for data. Most computers 

with a flat address space support only a single memory 

model. Computers with a segmented address space usually 

support multiple memory models. See also compact 

model, flat address space, large model, medium model, 

segmented address space, small model, tiny model. 

memory module n. A removable circuit board, cartridge, 

or other carrier that contains one or more RAM memory 

chips. See also memory card, memory cartridge, RAM. 

memory-resident adj. Permanently located in a computer’s 

memory, rather than swapped in and out of memory 

as needed. See also memory, TSR. 

memory scrubbing n. 1. In mainframe computers, the 

process of a computer reading its own memory during idle 

periods in order to find and fix errors. 2. The process of 

334 

examining and correcting errors as data is transferred from 

memory to the CPU of a computer. 

memory size n. The memory capacity of a computer, usually 

measured in megabytes. See also megabyte, memory. 

memory typewriter n. An electric typewriter with internal 

memory and typically a one-line liquid crystal display 

for viewing the contents of that memory. Memory typewriters 

can usually hold one page of text at a time, to 

which small modifications can be made. Memory typewriters 

usually do not retain the contents of memory when 

power is turned off. 

MEMS n. Acronym for micro-electromechanical systems. 

A technology combining computers with extremely tiny 

mechanical devices. MEMS devices contain microcircuitry 

on a tiny silicon chip onto which a mechanical 

device such as a sensor or an actuator is attached. MEMS 

devices are used in switches, pacemakers, games, GPS 

tracking, data storage, and for accelerometers in air bags. 

Because MEMS devices have the potential to be manufactured 

in large quantities for little cost, many additional 

MEMS products are being planned or studied. 

menu n. A list of options from which a user can make a 

selection in order to perform a desired action, such as 

choosing a command or applying a particular format to 

part of a document. Many application programs, especially 

those that offer a graphical interface, use menus as a 

means of providing the user with an easily learned, easyto-use 

alternative to memorizing program commands and 

their appropriate usage. 

menu bar n. A rectangular bar displayed in an application 

program’s on-screen window, often at the top, from which 

menus can be selected by the user. Names of available 

menus are displayed in the menu bar; choosing one with 

the keyboard or with a mouse causes the list of options in 

that menu to be displayed. 

menu-driven adj. Using menus to present choices of 

commands and available options. Menu-driven programs 

are usually considered friendlier and easier to learn than 

programs with a command-line interface. Compare command-line 

interface. 

menu item n. A choice on a menu, selectable by either 

the keyboard or a mouse. In some instances, a menu item 

that is not available (that is, not appropriate) for a given

Merced message switching 

situation is “grayed” (dimmed in comparison to the valid 

menu choices). 

Merced n. Former code name for the next-generation 64bit 

microprocessor designed by Intel and Hewlett-Packard 

and released in 2000. Based on the IA-64 architecture, the 

64-bit microprocessor contains upwards of 10 million 

transistors and is used primarily in servers and high-performance 

workstations. See also IA-64. 

Mercury n. A logic/functional programming language 

that combines the clarity and expressiveness of declarative 

programming with advanced static analysis and errordetection 

features. 

merge vb. To combine two or more items, such as lists, in 

an ordered way and without changing the basic structure 

of either. Compare concatenate. 

merged transistor logic n. See integrated injection 

logic. 

merge sort n. A sorting technique that combines several 

sorted (input) lists into a single sorted (output) list. See 

also bubble sort, insertion sort, quicksort, sort algorithm. 

mesa n. An area of a germanium or silicon wafer that was 

protected during the etching process and is therefore 

higher than the surrounding etched areas. See also photolithography. 

mesh network n. A communications network having two 

or more paths to any node. 

message n. 1. In communications, a unit of information 

transmitted electronically from one device to another. A 

message can contain one or more blocks of text as well as 

beginning and ending characters, control characters, a 

software-generated header (destination address, type of 

message, and other such information), and error-checking 

or synchronizing information. A message can be routed 

directly from sender to receiver through a physical link, or 

it can be passed, either whole or in parts, through a switching 

system that routes it from one intermediate station to 

another. See also asynchronous transmission, block (definition 

4), control character (definition 1), frame (definition 

1), frame (definition 2), header (definition 2), message 

switching, network, packet (definition 1), packet switching, 

synchronous transmission. 2. In software, a piece of 

information passed from the application or operating system 

to the user to suggest an action, indicate a condition, 

or inform that an event has occurred. 3. In message-based 

335 

operating environments, such as Windows, a unit of information 

passed among running programs, certain devices 

in the system, and the operating environment itself. 

message header n. A sequence of bits or bytes at the 

beginning of a message that usually provides a timing 

sequence and specifies such aspects of the message structure 

as its length, data format, and block identification 

number. See also header (definition 2). 

message of the day n. A daily bulletin for users of a network, 

multiuser computer, or other shared system. In most 

cases, users are shown the message of the day when they 

log into the system. Acronym: MOTD. 

Message Passing Interface n. See MPI. 

message queue n. An ordered list of messages awaiting 

transmission, from which they are taken up on a first in, 

first out (FIFO) basis. 

Message Queuing n. A message queuing and routing 

system for Microsoft Windows that enables distributed 

applications running at different times to communicate 

across heterogeneous networks and with computers that 

may be off line. Message Queuing provides guaranteed 

message delivery, efficient routing, security, and prioritybased 

messaging. Message Queuing was formerly known 

as MSMQ. 

message reflection n. In object-oriented programming 

environments, such as Visual C++, OLE, and ActiveX, a 

function that allows a control to handle its own message. 

See also ActiveX controls, control (definition 2), OCX, 

VBX. 

Message Security Protocol n. A protocol for Internet 

messages that is based on the use of encryption and verification 

to ensure security. It also allows for permissions at 

the server level for delivery or rejection of e-mail. Acronym: 

MSP. 

message switching n. A technique used on some communications 

networks in which a message, with appropriate 

address information, is routed through one or more 

intermediate switching stations before being sent to its 

destination. On a typical message-switching network, a 

central computer receives messages, stores them (usually 

briefly), determines their destination addresses, and then 

delivers them. Message switching enables a network both 

to regulate traffic and to use communications lines efficiently. 

Compare circuit switching, packet switching. 

M

M 

message transfer agent metropolitan area network 

message transfer agent n. See MTA. 

messaging n. The use of computers and data communication 

equipment to convey messages from one person to 

another, as by e-mail, voice mail, or fax. 

messaging application n. An application that enables 

users to send messages (such as e-mail or fax) to each 

other. 

Messaging Application Programming Interface 

n. See MAPI. 

messaging client n. An application program that enables 

its user to send or receive messages (such as e-mail or fax) 

to and from other users with the help of a remote server. 

messaging-oriented middleware n. See MOM. 

meta- prefix Literally, a prefix that describes a process or 

characteristic beyond the normal meaning of the word 

without the prefix. For example, metaphysics is “beyond 

physics.” In computing, meta- is usually attached to a 

word to indicate that the “metaterm” describes, defines, or 

acts upon objects or concepts of the same type as itself. 

So, for example, metadata is data about data and a metatool 

is a tool for working on tools. 

metacharacter n. A character embedded in a program 

source or a data stream that conveys information about 

other characters, rather than itself representing a character. 

A simple example is the backslash (\) character, which, 

when used in strings in the C programming language, indicates 

that the letter following the backslash is part of an 

escape sequence that enables C to display a nongraphic 

character. See also escape character. 

metacompiler n. A compiler that produces compilers. 

The UNIX utility yacc (Yet Another Compiler-Compiler) 

is a metacompiler. If it is given a language specification, 

yacc produces a compiler for that language. See also compiler 


Meta-Content Format n. An open format for describing 

information about content of a structured body of data 

such as a Web page, a set of files on a Windows desktop, 

or a relational database. Meta-Content Format might be 

used for indexes, data dictionaries, or price lists. Acronym: 

MCF. 

metadata or meta data n.1. Data about data. For example, 

the title, subject, author, and size of a file constitute 

metadata about the file. See also data dictionary, repository. 

2. In the Microsoft .NET Framework, information 

that describes every element managed by the runtime: an 

336 

assembly, loadable file, type, method, and so on. This can 

include information required for debugging and garbage 

collection, as well as security attributes, marshaling data, 

extended class and member definitions, version binding, 

and other information required by the runtime. 

Metadata Interchange Specification n. A set of specifications 

dealing with the exchanging, sharing, and managing 

of metadata. Acronym: MDIS. See also metadata 


metafile n. A file that contains or defines other files. 

Many operating systems use metafiles to contain directory 

information about other files on a given storage device. 

metaflow n. One of the four stages of the data warehousing 

process, during which metadata (data about data) is 

tracked and managed; the business modeling stage. During 

metaflow, the operational environment is mapped to 

the data warehouse environment. See also data warehouse 

(definition 2), downflow, inflow, metadata (definition 1), 

upflow. 

metalanguage n. A language used to describe other languages. 

Backus-Naur form (BNF) is a metalanguage commonly 

used to define programming languages. Also 

called: language-description language. See also Backus- 

Naur form. 

metal-oxide semiconductor n. See MOS. 

metal-oxide semiconductor field-effect transistor 

n. See MOSFET. 

metaoperating system n. An operating system under 

which several other operating systems are active. Also 

called: supervisor. 

metatag or meta tag n. A tag in an HTML or XML 

document that allows a Web-page creator to include such 

information as the author’s name, keywords identifying 

content, and descriptive details (for example, non-text 

objects on the page). The information that is marked with 

metatags does not appear on the Web page when a user 

views it in a browser, but it can be viewed in the HTML or 

XML source. Metatags are included in the head of a document 

and are often used to assist search engines in indexing 

the page. See also HTML, source, tag, XML. 

method n. In object-oriented programming, a process 

performed by an object when it receives a message. See 

also object (definition 2), object-oriented programming. 

Metropolitan Area Exchange n. See MAE (definition 2). 

metropolitan area network n. See MAN.

MFC Microdrive 

MFC n. See Microsoft Foundation Classes. 

MFLOPS n. Acronym for million floating-point operations 

per second. A measure of computing speed. Also 

called: megaflops. 

MFM encoding n. See modified frequency modulation 

encoding. 

MFP n. See multifunction peripheral. 

MFS n. See Macintosh File System. 

mget n. Short for multiple get. A command in most FTP 

clients with which a user can request the transfer of several 

files at once. See also FTP1 (definition 1). 

MHTML n. Acronym for Multipurpose Internet Mail 

Extension Hypertext Markup Language, or MIME 

HTML. A standard method for sending an HTML document 

encapsulated with inline graphics, applets, linked 

documents, and other items referred to in the HTML document. 

See also HTML, MIME. 

MHz n. See megahertz. 

MI n. See multiple inheritance. 

MIB n. See Management Information Base. 

mickey n. A unit of measure for mouse movement. One 

mickey is typically equal to 1/200th of an inch. 

MICR n. See magnetic-ink character recognition. 

micro- prefix 1. In nonexact measurements, small or compact, 

as in microprocessor or microcomputer. 2. Metric 

prefix meaning 10 –6 (one millionth). 

microbrowser n. An application for mobile phones that 

allows users to access the Internet to send and receive e-mail 

and browse the Web. Microbrowsers don’t have the full 

functionality of a Web browser on a PC. For instance, microbrowsers 

are capable of loading only stripped-down text versions 

of Web pages. Most microbrowser products are built to 

utilize the Wireless Application Protocol (WAP) standard. 

See also Wireless Application Protocol. 

microcapsule n. In an electronic paper display, millions 

of tiny beads filled with dark dye and light pigment that, in 

response to an electrical charge, change color to create 

images and text. See also electronic paper. 

Micro Channel Architecture n. The design of the bus in 

IBM PS/2 cosmputers (except Models 25 and 30). The 

Micro Channel is electrically and physically incompatible 

with the IBM PC/AT bus. Unlike the PC/AT bus, the 

Micro Channel functions as either a 16-bit or a 32-bit bus. 

337 

The Micro Channel also can be driven independently by 

multiple bus master processors. 

microchip n. See integrated circuit. 

microcircuit n. A miniaturized electronic circuit etched 

on a semiconductor chip. A microcircuit is made up of 

interconnected transistors, resistors, and other components. 

However, it is fabricated as a unit, rather than as a 

set of vacuum tubes, discrete transistors, or other elements 

that have to be wired together. See also integrated circuit. 

microcode n. Very low-level code that defines how a processor 

operates. Microcode is even lower in level than 

machine code; it specifies what the processor does when it 

executes a machine-code instruction. See also machine 

code, microprogramming. 

microcomputer n. A computer built around a single-chip 

microprocessor. Less powerful than minicomputers and 

mainframes, microcomputers have nevertheless evolved 

into very powerful machines capable of complex tasks. 

Technology has progressed so quickly that state-of-the-art 

microcomputers—essentially, in today’s terms, a desktop 

PC—are as powerful as mainframe computers of only a 

few years ago, at a fraction of the cost. See also computer. 

microcontent n. Short pieces of text on a Web page that 

help provide an overview of the page’s contents. Microcontent 

introduces, summarizes, or enhances the macrocontent 

of a Web page, and includes headings, page titles, 

ALT text, links, and subheads. Compare macrocontent. 

microcontroller n. A special-purpose, single-chip computer 

designed and built to handle a particular, narrowly 

defined task. In addition to the central processing unit 

(CPU), a microcontroller usually contains its own memory, 

input/output channels (ports), and timers. When part 

of a larger piece of equipment, such as a car or a home 

appliance, a microcontroller is an embedded system. See 

also embedded system. 

microdisplay n. A tiny monitor screen that provides a 

full-size view when magnified. Microdisplays work by 

magnifying a screen as small as one-tenth of an inch to fill 

the user’s field of vision. Microdisplays may be used with 

computers, DVD players, or handheld devices, in headsets 

and viewfinders, or anywhere a full-size monitor is 

impractical or undesirable. 

Microdrive n. A 1-inch disk drive, introduced in 1998 by 

IBM. The Microdrive is designed for use in handheld 

M

M 

micro-electromechanical systems microprocessor 

computers and special-purpose devices such as digital 

cameras and cellular telephones. 

micro-electromechanical systems n. See MEMS. 

microelectronics n. The technology of constructing 

electronic circuits and devices in very small packages. The 

most significant advance in microelectronics technology 

has been the integrated circuit. Circuits that 40 years ago 

required a roomful of power-hungry vacuum tubes can 

now be fabricated on a silicon chip smaller than a postage 

stamp and require only a few milliwatts of power. See also 

integrated circuit. 

microfiche n. A small sheet of film, about 4 by 6 inches, 

used for recording photographically reduced images, such 

as document pages, in rows and columns forming a grid 

pattern. The resulting images are too small to read with the 

naked eye, and a microfiche reader is required to view the 

documents. Compare microfilm. 

microfilm n. A thin strip of film stored on a roll and used 

to record sequential data images. As with microfiche, a 

special device magnifies the images so that they can be 

read. See also CIM (definition 2), COM (definition 4). 

Compare microfiche. 

microfloppy disk n. A 3.5-inch floppy disk of the type 

used with the Macintosh and with IBM and compatible 

microcomputers. A microfloppy disk is a round piece of 

polyester film coated with ferric oxide and encased in a 

rigid plastic shell equipped with a sliding metal cover. On 

the Macintosh, a single-sided microfloppy disk can hold 

400 kilobytes (KB); a double-sided (standard) disk can 

hold 800 KB; and a double-sided high-density disk can 

hold 1.44 megabytes (MB). On IBM and compatible 

machines, a microfloppy can hold either 720 KB or 1.44 

MB of information. See also floppy disk. 

microfluidics n. Technology for control and manipulation 

of fluids on a microscopic scale using microscopic pumps 

and valves placed on a chip. Microfluidics devices have 

implications for a number of medical, pharmaceutical, 

genomics, and other biotechnology applications. 

microform n. The medium, such as microfilm or microfiche, 

on which a photographically reduced image, called 

a microimage, is stored. A microimage usually represents 

text, such as archived documents. See also microfiche, 

microfilm, micrographics. 

338 

micrographics n. The techniques and methods for 

recording data on microfilm. See also microform. 

microimage n. A photographically reduced image, usually 

stored on microfilm or microfiche, that is too small to 

be read without magnification. See also microform, micrographics. 

microinstruction n. An instruction that is part of the 

microcode. See also microcode. 

microjustification n. See microspace justification. 

microkernel n. 1. In programming, the strictly hardwaredependent 

part of an operating system that is intended to 

be portable from one type of computer to another. The 

microkernel provides a hardware-independent interface to 

the rest of the operating system, so only the microkernel 

needs to be rewritten to port the operating system to a different 

platform. See also kernel, operating system. 2. A 

kernel that has been designed with only the basic features 

and typically in a modular fashion. 

micrologic n. A set of instructions, stored in binary form, 

or a set of electronic logic circuits that defines and governs 

the operation within a microprocessor. 

microminiature n. An extremely small circuit or other 

electronic component, especially one that is a refinement 

of an already miniaturized element. 

microphone n. 1. A device that converts sound waves 

into analog electrical signals. Additional hardware can 

convert the microphone’s output into digital data that a 

computer can process; for example, to record multimedia 

documents or analyze the sound signal. 2. A communications 

program that runs on the Macintosh computer. 

microphotonics n. Technology for directing light on a 

microscopic scale. Microphotonics employs tiny mirrors 

or photonic crystals to reflect and transmit specific wavelengths 

of light, which can carry digital signals. Microphotonics 

technology has implications for optical 

networks under development for the telecommunications 

industry. See also MEMS, optical switching. 

microprocessor n. A central processing unit (CPU) on a 

single chip. A modern microprocessor can have several 

million transistors in an integrated-circuit package that 

can easily fit into the palm of one’s hand. Microprocessors 

are at the heart of all personal computers. When memory 

and power are added to a microprocessor, all the pieces, 

excluding peripherals, required for a computer are present.

microprogramming Microsoft Project 

The most popular lines of microprocessors today are the 

680x0 family from Motorola, which powers the Apple 

Macintosh line, and the 80x86 family from Intel, which is 

at the core of all IBM PC–compatible computers. See also 

6502, 65816, 6800, 68000, 68020, 68030, 68040, 80286, 

80386DX, 80386SX, 8080, 8086 

microprogramming n. The writing of microcode for a 

processor. Some systems, chiefly minicomputers and 

mainframes, allow modification of microcode for an 

installed processor. See also microcode. 

microsecond n. One millionth (10 –6 ) of a second. 

Abbreviation: µs. 

microsite n. 1. A small Web site targeted to a single message 

or topic and nested within a larger site. Microsites 

geared to promotional and sales of specific products and 

services may be integrated into popular Web sites by 

advertisers. 2. A small Web site with a single focus. Also 

called: minisite. 

Microsoft Access n. See Access. 

Microsoft Active Accessibility n. See Active Accessibility. 

Microsoft DOS n. See MS-DOS. 

Microsoft Excel n. See Excel. 

Microsoft Foundation Classes n. A C++ class library 

developed by Microsoft. The Microsoft Foundation Class 

library, or MFC, provides the framework and classes that 

make it easier and faster for programmers to build Windows 

applications. MFC supports ActiveX and is bundled 

with several C++ compilers, including Microsoft Visual 

C++, Borland C++, and Symantec C++. Acronym: MFC. 

See also ActiveX, C++. Compare Application Foundation 

Classes. 

Microsoft FrontPage n. A program you can use to create 

and manage Internet and intranet sites without programming; 

FrontPage is available as part of one of the 

Microsoft Office suites or as a stand-alone product. 

Microsoft intermediate language n. The CPUindependent 

instruction set into which .NET Framework 

programs are compiled. It contains instructions for loading, 

storing, initializing, and calling methods on objects. 

339 

Combined with metadata and the common type system, 

Microsoft intermediate language allows for true cross-language 

integration. Prior to execution, MSIL is converted 

to machine code. It is not interpreted. Acronym: MSIL. 

Microsoft Internet Explorer n. See Internet Explorer. 

Microsoft Knowledge Base n. See KB (definition 2). 

Microsoft Management Console n. See MMC. 

Microsoft MapPoint n. See MapPoint. 

Microsoft Money n. See Money. 

Microsoft MSN Explorer n. See MSN Explorer. 

Microsoft MSN Messenger Service n. See .NET Messenger 

Service. 

Microsoft .NET Messenger Service n. See .NET Messenger 

Service. 

Microsoft Network n. See MSN. 

Microsoft Office n. See Office. 

Microsoft Operations Manager n. A server and application 

management solution developed by Microsoft Corporation 

to deliver event and performance management for 

the Windows 2000–based environment and .NET Enterprise 

Server applications. Operations management features 

include enterprise event log reports from across the 

corporate network, proactive monitoring and alert messaging, 

and reporting and trend analysis for problem tracking. 

Microsoft Operations Manager provides flexibility 

through sophisticated management rules, which can be 

customized to meet the needs of individual businesses. 

Microsoft Operations Manager support for management 

technology standards permits easy integration with other 

enterprise management systems. 

Microsoft Outlook n. See Outlook. 

Microsoft PowerPoint n. See PowerPoint. 

Microsoft Project n. A software application developed 

by Microsoft Corporation to simplify the planning and 

management of projects. Microsoft Project includes features 

that help you build and manage projects, set schedules 

and milestones, and communicate and share ideas 

with team members. 

M

M 

Microsoft Reader midrange computer 

Microsoft Reader n. A software application developed 

by Microsoft for downloading electronic books and other 

publications onto any personal computer, laptop computer, 

or Pocket PC handheld device. Additional features allow 

users to bookmark pages, highlight text, write notes, and 

look up definitions. 

Microsoft Tech Ed n. An annual training conference 

held by Microsoft Corporation to educate engineers and 

businesses using Microsoft technology. The conference 

provides attendees with access to information, experts, 

and training labs on Microsoft’s latest technologies. 

Microsoft Visual InterDev n. See Visual InterDev. 

Microsoft Visual Studio n. See Visual Studio. 

Microsoft Visual Studio .NET n. A complete development 

environment for building on the Microsoft .NET 

technology. Using Visual Studio .NET, developers can 

create secure, scalable applications and Web services 

quickly in the language of their choice, leveraging existing 

systems and skills. 

Microsoft Windows n. See Windows. 

Microsoft Windows 2000 n. See Windows 2000. 



Microsoft Windows CE n. See Windows CE. 

Microsoft Windows Messenger n. See .NET Messenger 

Service. 

Microsoft Windows NT n. See Windows NT. 

Microsoft Word n. See Word. 

Microsoft XML n. See MSXML. 

microspace justification n. The addition of thin spaces 

between characters within words to fill out a line for justification, 

instead of relying only on adding space between 

words. Good microspace justification gives justified text a 

more polished, professional look; excessive microspace 

justification causes words to lose visual coherence. Also 

called: microjustification. See also justify (definition 2), 

microspacing. 

microspacing n. In printing, the process of adjusting 

character placement by very small increments. 

340 

microtransaction n. A business transaction that involves 

a very small amount of money, typically under about $5. 

See also millicent technology. 

microwave relay n. A communications link that uses 

point-to-point radio transmissions at frequencies higher 

than approximately 1 gigahertz (1000 megahertz). 

middleware n. 1. Software that sits between two or more 

types of software and translates information between 

them. Middleware can cover a broad spectrum of software 

and generally sits between an application and an operating 

system, a network operating system, or a database management 

system. Examples of middleware include 

CORBA and other object broker programs and network 

control programs. See also CORBA. 2. Software that provides 

a common application programming interface (API). 

Applications written using that API will run in the same 

computer systems as the middleware. An example of this 

type of middleware is ODBC, which has a common API 

for many types of databases. See also application programming 

interface, ODBC. 3. Software development 

tools that enable users to create simple programs by 

selecting existing services and linking them with a scripting 

language. See also scripting language. 

MIDI n. Acronym for Musical Instrument Digital Interface. 

A serial interface standard that allows for the connection 

of music synthesizers, musical instruments, and 

computers. The MIDI standard is based partly on hardware 

and partly on a description of the way in which 

music and sound are encoded and communicated between 

MIDI devices. The information transmitted between MIDI 

devices is in a form called a MIDI message, which 

encodes aspects of sound such as pitch and volume as 8bit 

bytes of digital information. MIDI devices can be used 

for creating, recording, and playing back music. Using 

MIDI, computers, synthesizers, and sequencers can communicate 

with each other, either keeping time or actually 

controlling the music created by other connected equipment. 

See also synthesizer. 

MIDL n. Acronym for Microsoft Interface Definition Language. 

Microsoft implementation and extension of the 

Interface Definition Language (IDL). See also IDL. 

midrange computer n. A medium-size computer. The 

term is used interchangeably with minicomputer, except 

midrange computers do not include single-user workstations. 

See also minicomputer.

migration minifloppy 

migration n. The process of making existing applications 

and data work on a different computer or operating system. 

.mil n. In the Internet’s Domain Name System, the toplevel 

domain that identifies addresses operated by U.S. 

military organizations. The designation .mil appears at the 

end of the address. See also DNS (definition 1), domain 

(definition 3). Compare .com, .edu, .gov, .net, .org. 

Military Network n. See MILNET. 

millennium bug n. See Year 2000 problem. 

millennium-compliant adj. See Year 2000-compliant. 

millennium computer bug n. See Year 2000 problem. 

millennium transition n. See Year 2000 rollover. 

milli- prefix Metric prefix meaning 10 –3 (one thousandth). 

Abbreviation: m. 

millicent technology n. A set of protocols for smallscale 

commercial transactions over the Internet, developed 

by Digital Equipment Corporation. Millicent technology 

is intended to handle purchases of items of information at 

prices less than a cent. 

millions of instructions per second n. See MIPS. 

millisecond n. One thousandth of a second. 

Abbreviation: ms or msec. 

millivolt n. One thousandth of a volt. Abbreviation: mV. 

MILNET n. Short for Military Network. A wide area network 

that represents the military side of the original 

ARPANET. MILNET carries nonclassified U.S. military 

traffic. See also ARPANET. Compare NSFnet. 

MIMD n. Acronym for multiple instruction, multiple data 

stream processing. A category of computer architecture 

engaged in parallel processing in which central processing 

units independently fetch instructions and operate on data. 

See also architecture (definition 1), central processing 

unit, instruction, parallel processing. Compare SIMD. 

MIME or mime n. Acronym for Multipurpose Internet 

Mail Extensions. A protocol widely used on the Internet 

that extends the SMTP (Simple Mail Transfer Protocol) to 

permit data, such as video, sound, and binary files, to be 

transmitted by Internet e-mail without having to be translated 

into ASCII format first. This is accomplished by the 

use of MIME types, which describe the contents of a document. 

A MIME-compliant application sending a file, 

such as some e-mail programs, assigns a MIME type to 

the file. The receiving application, which must also be 

341 

MIME-compliant, refers to a standardized list of documents 

that are organized into MIME types and subtypes to 

interpret the content of the file. For instance, one MIME 

type is text, and it has a number of subtypes, including 

plain and html. A MIME type of text/html refers to a file 

that contains text written in HTML. MIME is part of 

HTTP, and both Web browsers and HTTP servers use 

MIME to interpret e-mail files they send and receive. See 

also HTTP, HTTP server, Simple Mail Transfer Protocol, 

Web browser. Compare BinHex1 (definition 1). 

mindshare n. The presence and familiarity of a product, 

service, or company in the minds of users or consumers. 

Unlike market share, which is the percentage of the market 

won by a particular product, service, or company, 

mindshare is a less quantifiable but still important factor in 

engaging customer attention and generating sales. The 

term is used frequently by, but is not limited to, the computer 

industry. 

miniaturization n. In the development of integrated circuits, 

the process of reducing the size and increasing the 

density of transistors and other elements on a semiconductor 

chip. In addition to providing the benefits of small size, 

miniaturization of electronic circuits also lowers power 

requirements, reduces heat, and shortens delays in the 

propagation of signals from one circuit element to the 

next. See also integrated circuit, integration (definition 2). 

minicomputer n. A mid-level computer built to perform 

complex computations while dealing efficiently with a 

high level of input and output from users connected via 

terminals. Minicomputers also frequently connect to other 

minicomputers on a network and distribute processing 

among all the attached machines. Minicomputers are used 

heavily in transaction-processing applications and as interfaces 

between mainframe computer systems and wide area 

networks. See also computer, mainframe computer, 

microcomputer, supercomputer, wide area network. Compare 

midrange computer, workstation (definition 2). 

mini-driver architecture n. An architecture in Windows 

3.1, Windows 95, Windows 98, Windows NT, and Windows 

2000 that uses a relatively small and simple driver, 

containing any additional instructions needed by a specific 

hardware device, to interface with the universal driver for 

that class of devices. See also driver. 

minifloppy n. A 5.25-inch floppy disk. See also floppy 

disk. 

M

M 

minimize mirroring 

minimize vb. In a graphical user interface, to hide a window 

without shutting down the program responsible for 

the window. Usually an icon, a button, or a name for the 

window is placed on the desktop; when the user clicks on 

the button, icon, or name, the window is restored to its 

previous size. See also graphical user interface, Minimize 

button, taskbar, window. Compare maximize. 

Minimize button n. In Windows 3.x, Windows 9x, Windows 

NT, and Windows 2000, a button in the upper righthand 

corner of a window that when clicked hides the window. 

In Windows 3.x and Windows NT 3.5 and earlier, an 

icon appears on the desktop that represents the window; in 

Windows 95, Windows NT 4, and later versions, the name 

of the window appears on the taskbar at the bottom of the 

desktop screen. When the icon or the name is clicked, the 

window is restored to its previous size. See also graphical 

user interface, taskbar, window. 

mini-notebook n. A portable computer in a case smaller 

than that of a standard laptop computer. Most mini-notebook 

computers have small keyboards, LCD screens 

built into folding cases, Pentium processors, and built-in 

hard drives. They are designed to run on standard operating 

systems, such as Windows 98, rather than on the 

Windows CE operating system used by the even smaller 

handheld computers. 

miniport driver n. A kernel-mode driver that is specific to 

a device. A miniport driver is linked to a port driver that 

provides an interface between the port driver and the operating 

system. This is typically implemented as a dynamiclink 

library. 

minisite n. See microsite. 

342 

minitower n. A vertical floor-standing computer cabinet 

that is about half the height (13 inches) of a tower case (24 

inches). See also tower. 

minor key n. See alternate key (definition 1). 

MIP mapping n. Short for multum in parvo (Latin, 

“much in little”) mapping. A form of mapping in which 

the appearance of a bitmapped image is precalculated 

from a distance and used in a texture mapper. This allows 

for smoother texture-mapped images calculated in the distance, 

since pixel conversion may alter colors relative to 

human perception. 

MIPS n. Acronym for millions of instructions per second. 

A common measure of processor speed. See also central 

processing unit, MFLOPS. 

mirror image n. An image that is an exact duplicate of 

the original with the exception that one dimension is 

reversed. For example, a right-pointing arrow and a leftpointing 

arrow of the same size and shape are mirror 

images. 

mirroring n. 1. In computer graphics, the ability to display 

a mirror image of a graphic—a duplicate rotated or 

reflected relative to some reference such as an axis of 

symmetry. See the illustration. 2. In a network, a means of 

protecting data on a network by duplicating it, in its 

entirety, on a second disk. Mirroring is one strategy implemented 

in RAID security. 3. On the Internet, replicating a 

Web site or an FTP site on another server. A site is often 

mirrored if it is frequently visited by multiple users. This 

eases the network traffic to the site, making it easier for 

users to gain access to the information or files on it. A site 

may also be mirrored in different geographic locations to 

facilitate downloading by users in various areas. See also 

RAID. 

A B C D 

F0Mgn04.eps 

Mirroring. (A) twofold symmetry with vertical axis; (B) fourfold symmetry with vertical and horizontal axes; (C) twofold radial 

symmetry; (D) threefold radial symmetry.

mirror site mobile IP 

mirror site n. A file server that contains a duplicate set of 

files to the set on a popular server. Mirror sites exist to 

spread the distribution burden over more than one server 

or to eliminate the need to use high-demand international 

circuits. 

MIS n. See IS. 

misc. newsgroups n. Usenet newsgroups that are part of 

the misc. hierarchy and have the prefix misc. These newsgroups 

cover topics that do not fit into the other standard 

Usenet hierarchies (comp., news., rec., sci., soc., talk.). 

See also newsgroup, traditional newsgroup hierarchy, 

Usenet. 

mission critical adj. Pertaining to information, equipment, 

or other assets of a business or project that are 

essential to the successful operation of the organization. 

For example, accounting data and customer records are 

often considered mission critical information. 

misuse detection n. See IDS. 

mixed cell reference n. In spreadsheets, a cell reference 

(the address of a cell needed to solve a formula) in which 

either the row or the column is relative (automatically 

changed when the formula is copied or moved to another 

cell) and the other is absolute (not changed when the formula 

is copied or moved). See also cell (definition 1). 

MMC n. Acronym for Microsoft Management Console. 

A framework for hosting administrative tools called snapins. 

A console might contain tools, folders or other containers, 

World Wide Web pages, and other administrative 

items. These items are displayed in the left pane of the 

console, called a console tree. A console has one or more 

windows that can provide views of the console tree. The 

main MMC window provides commands and tools for 

authoring consoles. The authoring features of MMC and 

the console tree itself might be hidden when a console is 

in User Mode. See also snap-in. 

MMDS n. Short for multichannel multipoint distribution 

service. A fixed wireless service proposed for use as an 

alternative when DSL or cable modem options are not 

practical or desirable. The MMDS spectrum was originally 

used for distance learning and wireless cable video 

services before attracting interest for fixed broadband 

wireless services. See also broadband. 

MMU n. See memory management unit. 

MMX n. Short for Multimedia Extensions. An enhancement 

to the architecture of Intel Pentium processors that 

343 

improves the performance of multimedia and communications 

applications. 

mnemonic n. A word, rhyme, or other memory aid used 

to associate a complex or lengthy set of information with 

something that is simple and easy to remember. Mnemonics 

are widely used in computing. Programming languages 

other than machine language, for example, are known as 

symbolic languages because they use short mnemonics, 

such as ADD (for addition) and def (for define) to represent 

instructions and operations. Similarly, operating systems 

and applications based on typed commands use 

mnemonics to represent instructions to the program. MS- 

DOS, for example, uses dir (for directory) to request a list 

of files. 

MNP10 n. Short for Microcom Networking Protocol, 

Class 10. An industry-standard communication protocol 

used for modem connections over analog cellular telephone 

connections. The most recent version of MNP10 is 

MNP 10EC (EC stands for Enhanced Cellular). See also 

communications protocol. 

mobile computing n. The process of using a computer 

while traveling. Mobile computing usually requires a portable 

computer that is battery powered, rather than a desktop 

system. 

Mobile Explorer n. A modular wireless applications and 

services platform designed by Microsoft to power Webenabled 

wireless telephones. When connected to a wireless 

network, Mobile Explorer provides secure mobile 

access to corporate or personal e-mail, corporate networks, 

and the Internet. It includes a multimode microbrowser, 

which can display Web content coded in a variety 

of markup languages used for small, handheld devices, 

including cHTML, HTML, WAP 1.1, and WML. See also 

microbrowser. 

Mobile Information Server n. A software application 

developed by Microsoft to allow telecommunications carriers, 

enterprise customers, and business partners to 

securely extend Microsoft Exchange Server information, 

corporate intranet applications, and services to users of 

wireless handheld computing devices. Microsoft Information 

Server provides mobile users with access to personal 

services and data stored on the intranet, such as e-mail, 

document files, appointment calendars, and contacts. 

mobile IP n. Acronym for mobile Internet Protocol. An 

Internet protocol designed to support host mobility. 

Mobile IP enables a host to remain connected to the Internet 

with the same IP address (called the home address) 

M

M 

mobile telephone switching office modem ready 

while moving to different locations. Mobile IP tracks a 

moving host by registering the presence of the host with a 

foreign agent; the home agent then forwards packets to the 

remote network. See also IP. 

mobile telephone switching office n. Computer that 

controls wireless phone calls. The mobile telephone 

switching office controls the operation of wireless cell 

sites, tracks calls, and transfers signals between wireless 

networks and traditional wired telephone systems. Acronym: 

MTSO. 

mode n. The operational state of a computer or a program. 

For example, edit mode is the state in which a program 

accepts changes to a file. See also address mode, 

compatibility mode, safe mode, video mode, virtual real 

mode. 

modec n. In telecommunications, a device that generates 

analog modem signals digitally. The term modec is a combination 

of the terms modem and codec. See also codec 

(definition 1), modem (definition 2). 

model n. A mathematical or graphical representation of a 

real-world situation or object—for example, a mathematical 

model of the distribution of matter in the universe, a 

spreadsheet (numeric) model of business operations, or a 

graphical model of a molecule. Models can generally be 

changed or manipulated so that their creators can see how 

the real version might be affected by modifications or 

varying conditions. See also modeling, simulation. 

modeling n. 1. The use of computers to describe the 

behavior of a system. Spreadsheet programs, for example, 

can be used to manipulate financial data representing the 

health and activity of a company, to develop business 

plans and projections, or to evaluate the impact of proposed 

changes on the company’s operations and financial 

status. See also simulation, spreadsheet program. 2. The 

use of computers to describe physical objects and the spatial 

relationships among them mathematically. CAD programs, 

for example, are used to create on-screen 

representations of such physical objects as tools, office 

buildings, complex molecules, and automobiles. These 

models use equations to create lines, curves, and other 

shapes and to place those shapes accurately in relation to 

each other and to the two-dimensional or three-dimensional 

space in which they are drawn. See also CAD, rendering, 

solid model, surface modeling, three-dimensional 

model, two-dimensional model, wire-frame model. 

344 

modem n. 1. Short for modulator/demodulator. A communications 

device that converts between digital data 

from a computer or terminal and analog audio signals that 

can pass through a standard telephone line. Because the 

telephone system was designed to handle voice and other 

audio signals and a computer processes signals as discrete 

units of digital information, a modem is necessary at both 

ends of the telephone line to exchange data between computers. 

At the transmit end, the modem converts from digital 

to analog audio; at the receiving end, a second modem 

converts the analog audio back to its original digital form. 

In order to move a high volume of data, high-speed 

modems rely on sophisticated methods for “loading” 

information onto the audio carrier—for example, they 

may combine frequency shift keying, phase modulation, 

and amplitude modulation to enable a single change in the 

carrier’s state to represent multiple bits of data. In addition 

to the basic modulation and demodulation functions, most 

modems also include firmware that allows them to originate 

and answer telephone calls. International standards 

for modems are specified by the International Telecommunications 

Union, or ITU. Despite their capabilities, 

modems do require communications software in order to 

function. See also amplitude modulation, frequency modulation, 

quadrature amplitude modulation. Compare digital 

modem. 2. Any communications device that acts as an 

interface between a computer or terminal and a communications 

channel. Although such a device may not actually 

modulate or demodulate analog signals, it may be 

described as a modem because a modem is perceived by 

many users to be a black box that connects a computer to a 

communications line (such as a high-speed network or a 

cable TV system). See also digital modem. 

modem bank n. A collection of modems connected to a 

server maintained by an ISP or the operator of a BBS or 

remote-access LAN. Most modem banks are configured to 

allow a remote user to dial a single phone number that 

routes calls to an available phone number on the bank. See 

also BBS (definition 1), ISP, LAN. 

modem eliminator n. A device that enables two computers 

to communicate without modems. See also null 

modem. 

modem port n. A serial port used for connecting an 

external modem to a personal computer. See also modem 

(definition 1), serial port. 

modem ready n. See MR.

moderated modulate 

moderated adj. Subjected to review by a moderator, who 

may remove irrelevant or inflammatory articles or messages 

before redistributing them through a newsgroup, 

mailing list, or other messaging system. 

moderated discussion n. Communication taking place 

on a mailing list, newsgroup, or other online forum that is 

edited by a moderator. When a user submits a message to a 

moderated discussion, the moderator decides if the message 

is relevant to the discussion topic. If so, it is forwarded 

to the discussion group. The content of a 

moderated discussion is often perceived as more valuable 

than that of an unmoderated one because the information 

has been read and approved by a “gatekeeper,” who has 

(presumably) filtered out irrelevant submissions. Some 

moderators also filter submissions for obscene or pornographic 

material or material that is potentially offensive. 

See also mailing list, moderator, newsgroup. 

moderator n. In some Internet newsgroups and mailing 

lists, a person through whom all messages are filtered 

before they are distributed to the members of the newsgroup 

or list. The moderator discards or edits any messages 

that are not considered appropriate. See also mailing 

list, newsgroup. 

modified frequency modulation encoding n. An older 

method of storing data on disks. Modified frequency 

modulation encoding is based on an earlier technique 

called frequency modulation encoding but improves on its 

efficiency by reducing the need for synchronizing information 

and by basing the magnetic coding of each bit on 

the status of the previously recorded bit. This method of 

encoding stores more information on a disk than does 

frequency modulation encoding. It is not, however, as 

efficient a space saver as the technique known as runlength 

limited encoding, or RLL. Abbreviation: MFM 

encoding. Compare frequency modulation encoding, 


modifier key n. A key on the keyboard that, when held 

down while another key is pressed, changes the meaning 

of the keystroke. See also Alt key, Command key, Control 

key, Shift key. 

modify structure n. An operator available in some database 

management systems that permits fields (columns) to 

be added or deleted without the need to rebuild the entire 

database. 

MO disk n. See magneto-optic disc. 

MO disk drive n. See magneto-optic disc. 

345 

Modula-2 n. A modular high-level language designed in 

1980 by Niklaus Wirth. Derived from Pascal, Modula-2 is 

noted for its emphasis on modular programming, its early 

support for data abstraction, and its lack of standard functions 

and procedures. See also modular programming. 

modular design n. An approach to designing hardware or 

software in which a project is broken into smaller units, or 

modules, each of which can be developed, tested, and finished 

independently before being combined with the others 

in the final product. Each unit is designed to perform a 

particular task or function and can thus become part of a 

library of modules that can often be reused in other products 

having similar requirements. In programming, for 

example, one module might consist of instructions for 

moving the cursor in a window on the screen. Because it is 

deliberately designed as a stand-alone unit that can work 

with other sections of the program, the same module 

might be able to perform the same task in another program 

as well, thus saving time in development and testing. 

modular jack n. See phone connector. 

modular programming n. An approach to programming 

in which the program is broken into several independently 

compiled modules. Each module exports specified 

elements (such as constants, data types, variables, functions, 

and procedures); all other elements remain private 

to the module. Other modules can use only the exported 

elements. Modules clarify and regularize the interfaces 

among the major parts of a program. Thus, they facilitate 

group programming efforts and promote reliable programming 

practices. Modular programming is a precursor 

of object-oriented programming. See also module 

(definition 1), object-oriented programming. 

modular software n. A program created from multiple 

stand-alone software components. Modular components 

can work together to perform the work for which the larger 

program is designed while still remaining individually 

usable—and reusable—in other programs. Modular software 

is, in effect, made up of recyclable parts. Because each 

component is functionally autonomous and self-contained, 

other components can call on its services without having 

to “know” how it works. Thus, a programmer can change 

or modify the way one component performs its work without 

adversely affecting other components in the same program. 

See also component software, integrated software, 

modular design. 

modulate vb. To change some aspect of a signal intentionally, 

usually for the purpose of transmitting information. 

M

M 

modulation monochrome adapter 

modulation n. 1. The process of changing or regulating 

the characteristics of a carrier wave vibrating at a certain 

amplitude (height) and frequency (timing) so that the variations 

represent meaningful information. 2. In computer 

communications, the means by which a modem converts 

digital information sent by a computer to the audio form 

that it sends over a telephone line. 

modulation standards n. Protocols that determine how 

modems convert digital data into analog signals that can 

be transmitted over telephone lines. Initially, Bell created 

modulation standards used in the United States, and the 

CCITT created international recommendations. The ITU-T 

(formerly called the CCITT) now makes recommendations 

generally adopted by modem manufacturers both 

internationally and in the United States. The ITU-TV 

series recommendations (such as V.34 and V.90) define 

data communication over the telephone network. The suffixes 

-bis and -ter (for example, V.32bis) indicate later versions. 

See also V.34, V.90. 

module n. 1. In programming, a collection of routines and 

data structures that performs a particular task or implements 

a particular abstract data type. Modules usually 

consist of two parts: an interface, which lists the constants, 

data types, variables, and routines that can be accessed by 

other modules or routines; and an implementation, which 

is private (accessible only to the module) and which contains 

the source code that actually implements the routines 

in the module. See also abstract data type, information 

hiding, Modula-2, modular programming. 2. In hardware, 

a self-contained component that can provide a complete 

function to a system and can be interchanged with other 

modules that provide similar functions. See also memory 

card, SIMM. 

modulo n. An arithmetic operation whose result is the 

remainder of a division operation. For example, 17 modulo 

3 = 2 because 17 divided by 3 yields a remainder of 2. 

Modulo operations are used in programming. 

moiré n. A visible wavy distortion or flickering in an 

image that is displayed or printed with an inappropriate 

resolution. Several parameters affect moiré patterns, 

including the size and resolution of the image, resolution 

of the output device, and halftone screen angle. 

molecular beam epitaxy n. A process used in the fabrication 

of semiconductor devices, such as integrated circuits. 

A device employing molecular beam epitaxy creates thin 

346 

layers of semiconducting material by vaporizing the material 

and then directing a beam of molecules at the substrate 

on which the layer is to be formed. This technique allows 

very precise and very thin layers to be created. 

MOM n. Acronym for messaging-oriented middleware. A 

class of programs that translates data and messages 

between applications that use one format and communications 

services (such as NetBIOS and TCP/IP) that expect a 

different format. 

monadic adj. See unary. 

Money n. Microsoft’s Windows-based financial-management 

software for individuals, families, and small businesses. 

Money includes tools for managing bank accounts 

and investments, budgeting, tax estimating and financial 

planning, and paying bills. 

monitor n. The device on which images generated by the 

computer’s video adapter are displayed. The term monitor 

usually refers to a video display and its housing. The monitor 

is attached to the video adapter by a cable. See also 

CRT. 

monitoring software n. A program or set of programs 

used to oversee computer-based systems and networks for 

the purpose of tracking usage or identifying, reporting on, 

and solving problems at the earliest possible stage. Monitoring 

software is used in a variety of areas ranging from 

hardware platforms and their components to operating 

systems, databases, Internet/intranet access, and business 

applications. Typically, different tools are used to monitor 

individual system components, though the individual 

monitors might feed information to a higher-level monitor 

in order to encompass an entire computing environment. 

monitor port n. See display port. 

monochrome adj. Of, pertaining to, or being a monitor 

that displays images in only one color—black on white (as 

on early monochrome Macintosh screens) or amber or 

green on black (as on early IBM and other monochrome 

monitors). The term is also applied to a monitor that displays 

only variable levels of a single color, such as a grayscale 

monitor. 

monochrome adapter n. A video adapter capable of 

generating a video signal for one foreground color or 

sometimes for a range of intensities in a single color, as 

for a gray-scale monitor.

monochrome display MOSFET 

monochrome display n. 1. A video display capable of 

rendering only one color. The color displayed depends on 

the phosphor of the display (often green or amber). 2. A 

display capable of rendering a range of intensities in only 

one color, as in a gray-scale monitor. 

Monochrome Display Adapter n. See MDA. 

monochrome graphics adapter n. See HGC. 

monochrome monitor n. See monochrome display. 

monographics adapter n. Any video adapter that can 

display only monochrome text and graphics; any video 

adapter functionally compatible with the Hercules Graphics 

Card (HGC). See also HGC. 

monospace font n. A font (set of characters in a particular 

style and size), similar to that used on a typewriter, in 

which each character occupies the same amount of horizontal 

space regardless of its width—an i, for example, 

taking as much room as an m. See the illustration. Also 

called: fixed-width font. See also monospacing. Compare 

proportional font. 

Proportional 

F0Mgn05.eps 

Monospace font. Monospace font vs. proportional font. 

monospacing n. A form of print and display spacing in 

which each character occupies the same amount of horizontal 

space on the line, regardless of whether the character 

is wide (such as m) or narrow (such as I). Also 

called: fixed-pitch spacing, fixed spacing, fixed-width 

spacing. See also monospace font. Compare proportional 

spacing. 

Monte Carlo method n. A mathematical technique that 

uses repeated calculations and random numbers to find an 

approximate solution to a complex problem. The Monte 

Carlo method, named for its relationship to games of 

chance played in the casinos at Monte Carlo, Monaco, can 

be used in situations in which it is possible to calculate the 

probability of a particular event occurring but not to factor 

in the complex effects of many other contributing factors. 

MOO n. Short for MUD, object-oriented. A type of virtual 

environment on the Internet, similar to a game-oriented 

347 

MUD but based on an object-oriented language and generally 

focused more on programming than on games. See 

also MUD. 

Moore’s Law n. A prediction by Intel cofounder Gordon 

Moore in the early days of the computer revolution regarding 

the growth of semiconductor technology. Moore predicted 

that the number of transistors that could be put on a 

chip would double every year, and it did. Ten years later, 

Moore predicted that chip capacity would double every 

two years, and capacity has actually doubled every 18 

months since then. The doubling of capacity every 18 

months is popularly referred to as a “law.” 

.moov n. A file extension indicating a QuickTime MooV 

video file for a Macintosh computer. See also MooV. 

MooV n. The file format for QuickTime movies that 

stores synchronized tracks for control, video, audio, and 

text. See also QuickTime. 

morphing n. Short for metamorphosing. A process by 

which one image is gradually transformed into another, 

creating the illusion of a metamorphosis occurring in a 

short time. A common motion picture special-effects technique, 

morphing is available in many advanced computer 

animation packages. See also tween. 

MOS n. Acronym for metal-oxide semiconductor. An 

integrated-circuit technology in which field-effect transistors 

(FETs) are made with an insulating layer of silicon 

dioxide between a metal gate electrode and a semiconductor 

channel. MOS designs are widely used both in discrete 

components and in integrated circuits. MOS integrated 

circuits have the advantages of high component density, 

high speed, and low power consumption. MOS devices are 

easily damaged by static electricity, so before they are 

inserted in a circuit, they should be kept with their connectors 

embedded in conducting foam to prevent the buildup 

of static charges. See also FET, MOSFET. 

Mosaic n. The first popular graphical World Wide Web 

browser. Released on the Internet in early 1993 by the 

National Center for Supercomputing Applications (NCSA) 

at the University of Illinois at Urbana-Champaign, Mosaic is 

available as freeware and shareware for Windows, Macintosh, 

and X Window systems. Mosaic is distinguished from 

other early Web browsers by its ease of use and its addition 

of inline images to Web documents. Also called: NCSA 

Mosaic. 

MOSFET n. Acronym for metal-oxide semiconductor 

field-effect transistor. A common type of field-effect transistor 

in which a layer of silicon dioxide insulates the 

M

M 

most significant bit mouse pointer 

metal gate from the semiconductor current channel. MOS- 

FETs have extremely high input impedance and therefore 

require almost no driving power. They are used in many 

audio applications, including high-gain amplifier circuits. 

Like all metal-oxide semiconductor (MOS) devices, 

MOSFETs are easily damaged by static electricity. See the 

illustration. See also FET, MOS. 

Source 

F0Mgn06.eps 

MOSFET. 

Metal-oxide 

layer 

Gate 

Current channel 

Substrate material 

Drain 

most significant bit n. In a sequence of one or more 

bytes, the highest-order bit of a binary number, not including 

the sign bit. Acronym: MSB. See also high-order. 

Compare least significant bit. 

most significant character n. The high-order, or leftmost, 

character in a string. Acronym: MSC. See also highorder. 

Compare least significant character. 

most significant digit n. In a sequence of one or more 

digits, the highest-order digit, which is the leftmost digit. 

In 456.78, 4 is the most significant digit. Acronym: MSD. 

Compare least significant digit. 

MOTD n. See message of the day. 

motherboard n. The main circuit board containing the 

primary components of a computer system. This board 

contains the processor, main memory, support circuitry, 

and bus controller and connector. Other boards, including 

expansion memory and input/output boards, may attach to 

the motherboard via the bus connector. See also expansion 

slot. Compare daughterboard. 

Motion JPEG n. A standard for storing motion video, 

proposed by the Joint Photographic Experts Group 

(JPEG), that uses JPEG image compression for each 

frame. See also JPEG (definition 1). Compare MPEG 


motion path n. The path that a specified object or text 

will follow as part of an animation sequence for a slide. 

mount vb. To make a physical disk or tape accessible to a 

computer’s file system. The term is most commonly used 

to describe accessing disks in Macintosh and UNIX-based 

computers. 

348 

mount n. In NFS, a folder or file retrieved from elsewhere 

on the network and accessed locally. See also NFS. 

MOUS n. Acronym for Microsoft Office User Specialist. 

A certification from Microsoft that verifies an individual’s 

skills with the Microsoft Office desktop programs. See 

also MCP. 

mouse n. A common pointing device. The basic features 

of a mouse are a flat-bottomed casing designed to be 

gripped by one hand, one or more buttons on the top, a 

multidirectional detection device (usually a ball) on the 

bottom, and a cable connecting the mouse to the computer. 

By moving the mouse on a surface (such as a desk top), 

the user typically controls an on-screen cursor. A mouse is 

a relative pointing device because there are no defined 

limits to the mouse’s movement and because its placement 

on a surface does not map directly to a specific screen 

location. To select items or choose commands on the 

screen, the user presses one of the mouse’s buttons, producing 

a “mouse click.” See the illustration. See also bus 

mouse, mechanical mouse, optical mouse, optomechanical 

mouse, relative pointing device, serial mouse. Compare 

trackball. 

F0Mgn07.eps 

Mouse. Two types of mouse: for the Macintosh (left) and for 

the PC (right). 

MouseKeys n. A feature in Windows that allows a user to 

use the numeric keyboard to move the mouse pointer. 

MouseKeys is primarily intended for people who may 

have physical limitations that make it difficult to move a 

conventional mouse. See also mouse. 

mouse pad n. A surface on which a mouse can be moved, 

typically a rectangular rubber pad covered with fabric, 

providing more traction than a wooden or glass desktop or 

tabletop. See also mouse. 

mouse pointer n. An on-screen element whose location 

changes as the user moves the mouse. Depending on the 

location of the mouse pointer and the operation of the pro-

mouse port MP3 encoder 

gram with which it is working, the area of the screen 

where the mouse pointer appears serves as the target for an 

action when the user presses one of the mouse buttons. See 

also block cursor, cursor (definition 3). 

mouse port n. 1. In many PC-compatible computers, a 

dedicated connector where a mouse or other pointing 

device plugs into the computer. If a mouse port is not 

available, a serial port can be used to connect the mouse to 

the computer. See the illustration. See also connector, 

mouse, pointing device, serial port. 2. In a Macintosh, the 

Apple Desktop Bus port. See also Apple Desktop Bus. 

F0Mgn08.eps 

Mouse port. 

Mouse port 

mouse scaling n. See mouse sensitivity. 

mouse sensitivity n. The relationship of mouse movement 

to screen cursor movement. A more sensitive mouse 

signals to the computer more “mouse moves” per inch of 

physical mouse movement than does a less sensitive 

mouse. Increasing the sensitivity of the program or mouse 

driver can result in smaller cursor moves for a given 

mouse move, making it easier for the user to position the 

cursor precisely. High sensitivity is good for exacting 

work, such as CAD/CAM and graphic art; low sensitivity 

is good for tasks in which getting around the screen 

quickly is important and for applications such as Web 

browsers, word processors, and spreadsheets, in which the 

cursor is used mostly to select buttons or text. Also 

called: mouse scaling, mouse tracking. 

mouse tracking n. See mouse sensitivity. 

mouse trails n. The creation of a shadowlike trail following 

the mouse pointer on screen in order to make it easier 

to see. Mouse trails are useful for laptops and notebooks, 

particularly ones with passive matrix displays or older 

models with monochrome screens. The relatively low resolution 

and contrast of these screens made it easy to lose 

sight of a small mouse pointer. See also mouse pointer, 

submarining. 

349 

mousetrapping n. A practice employed by some Web 

sites in which the back and exit buttons of a visitor’s Web 

browser are disabled and attempts to leave the site are 

redirected to other pages on the site or to other sites 

against the visitor’s will. Mousetrapping is most often 

associated with adult-oriented Web sites. Compare pagejacking. 

.mov n. A filename extension for a movie file in Apple’s 

QuickTime format. See also QuickTime. 

move n. A command or an instruction to transfer information 

from one location to another. Depending on the operation 

involved, a move can affect data in a computer’s 

memory or it can affect text or a graphical image in a data 

file. In programming, for example, a move instruction 

might transfer a single value from one memory location to 

another. In applications, on the other hand, a move command 

might relocate a paragraph of text or all or part of a 

graphic from one place in a document to another. Unlike a 

copy procedure, which duplicates information, a move 

indicates that information either is or can be deleted from 

its original location. Compare copy. 

.movie n. See .mov. 

Moving Picture Experts Group n. See MPEG (definition 

1). 

Mozilla n. 1. A nickname for the Netscape Navigator (later, 

Netscape Communicator) Web browser, coined by the 

Netscape Corporation. See also Mosaic, Netscape Navigator. 

2. Since 1998, when the Communicator source code 

was released for free, for use by any interested parties, the 

name Mozilla has been extended as a generic reference to 

any Web browser based on Navigator source code. 

mozilla.org n. The name of the group charged by the 

Netscape Corporation to act as a clearinghouse for 

Mozilla-related matters, such as questions, changes to 

code, bug reporting, forums, and so on. 

MP3 n. Acronym for MPEG Audio Layer-3. A digital 

audio coding scheme used in distributing recorded music 

over the Internet. MP3 shrinks the size of an audio file by 

a factor of 10 to 12 without seriously degrading the quality 

(CD-recording level) of the sound. MP3 files are given the 

file extension .mp3. Although MP3 is part of the MPEG 

family, it is audio-only and is not the same as the nowdefunct 

MPEG-3 standard. See also MPEG-3. 

MP3 encoder n. See encoder. 

M

M 

MPC MSDN 

MPC n. See Multimedia PC. 

.mpeg n. The file extension that identifies video and 

sound files compressed in the MPEG format specified by 

the Moving Pictures Experts Group. See also MPEG. 

MPEG n. 1. Acronym for Moving Picture Experts Group. 

A set of standards for audio and video compression established 

by the Joint ISO/IEC Technical Committee on 

Information Technology. The MPEG standard has different 

types that have been designed to work in different situations. 

Compare Motion JPEG. 2. A video/audio file in 

the MPEG format. Such files generally have the extension 

.mpg. See also JPEG. Compare Motion JPEG. 

MPEG-1 n. The original MPEG standard for storing and 

retrieving video and audio information, designed for CD- 

ROM technology. MPEG-1 defines a medium bandwidth 

of up to 1.5 Mbps, two audio channels, and noninterlaced 

video. See also MPEG (definition 1). Compare MPEG-2, 

MPEG-3, MPEG-4. 

MPEG-2 n. An extension of the MPEG-1 standard 

designed for broadcast television, including HDTV. 

MPEG-2 defines a higher bandwidth of up to 40 Mbps, 

five audio channels, a wider range of frame sizes, and 

interlaced video. See also HDTV, MPEG (definition 1). 

Compare MPEG-1, MPEG-3, MPEG-4. 

MPEG-3 n. Initially an MPEG standard designed for 

HDTV (high-definition television), but it was found that 

MPEG-2 could be used instead. Therefore, this standard 

no longer exists. See also HDTV, MPEG (definition 1). 

Compare MP3, MPEG-1, MPEG-2, MPEG-4. 

MPEG-4 n. A standard currently under development 

designed for videophones and multimedia applications. 

MPEG-4 provides a lower bandwidth of up to 64 Kbps. 

See also MPEG (definition 1). Compare MPEG-1, 

MPEG-2, MPEG-3. 

.mpg n. See .mpeg. 

MPI n. Acronym for Message Passing Interface. A specification 

for message passing on workstation clusters and 

massively parallel processing (MPP) architectures. MPI 

was designed as a proposed standard by the MPI Forum, a 

committee of vendors and users. 

MPLS n. Acronym for Multiprotocol Label Switching. A 

standards-based technique used to manage and optimize 

traffic flow for large-scale networks. In an MPLS network, 

incoming packets are assigned a label by a label edge 

router (LER). Label switch routers (LSRs) use these labels 

350 

to forward the packets through the network along a label 

switch path (LSP). Each LSR removes the existing label 

and assigns a new one. MPLS combines the advantages of 

bridges (Layer 2 switching, which is used in ATM and 

frame relay) and routers (Layer 3 switching, which is used 

in IP). MPLS serves to create faster and more scalable networks 

to facilitate quality of service, class of service, and 

the use of VPNs. 

MP/M n. Acronym for Multitasking Program for Microcomputers. 

A multitasking, multiuser version of the CP/M 

operating system. See also CP/M. 

MPOA n. Acronym for Multi-Protocol Over ATM. A 

specification established by the ATM Forum (an industry 

group of Asynchronous Transfer Mode users and vendors) 

to integrate ATM into existing Ethernet, token ring, and 

TCP/IP networks. See also ATM (definition 1). 

MPP n. See massively parallel processing, massively parallel 

processor. 

MPPP n. See Multilink Point-to-Point Protocol. 

MPR II n. A standard for limiting magnetic and electric 

field emissions from video monitors, including VLF radiation. 

MPR II is a voluntary standard developed by the 

Swedish Board for Measurement and Testing in 1987 and 

updated in 1990. See also VLF radiation. 

mput n. In many FTP clients, the command that instructs 

the local client to transmit multiple files to the remote 

server. 

MR n. Acronym for modem ready. A light on the front 

panel of a modem indicating that the modem is ready. 

MRP n. See Material Requirements Planning. 

ms n. See millisecond. 

MSAA n. Short for Microsoft Active Accessibility. See 

Active Accessibility. 

MSAU n. See MAU. 

MS Audion. n. The code name, or working name, of Windows 

Media Audio, before the technology was released by 

Microsoft. See also Windows Media Audio. 

MSB n. See most significant bit. 

MSC n. See most significant character. 

MSD n. See most significant digit. 

MSDN n. Acronym for the Microsoft Developer Network. 

An online, print, and CD-DVD resource for developers

MS-DOS Multibus 

that features content and programs focused on development 

trends and Microsoft technologies. Some features of MSDN 

include technical articles and reference material; information 

on upcoming conferences and events; developer support 

through peer-to-peer interaction, information sharing, 

and direct interaction with Microsoft; and software subscription 

programs. 

MS-DOS n. Short for Microsoft Disk Operating System. 

A single-tasking, single-user operating system with a 

command-line interface, released in 1981, for IBM PCs 

and compatibles. MS-DOS, like other operating systems, 

oversees operations such as disk input and output, video 

support, keyboard control, and many internal functions 

related to program execution and file maintenance. 

MS-DOS mode n. A shell in which the MS-DOS environment 

is emulated in 32-bit systems such as Windows 95. 

See also MS-DOS, shell1 . 

MS-DOS shell n. A shell environment based on a command-line 

prompt that allows a user to interact with MS- 

DOS or an MS-DOS-emulating operating system. 

MSDOS.SYS n. One of two hidden system files installed 

on an MS-DOS startup disk. MSDOS.SYS, called IBM- 

DOS.SYS in IBM releases of MS-DOS, contains the software 

that makes up the heart (kernel) of the operating 

system. See also IO.SYS. 

msec n. See millisecond. 

MSI n. See medium-scale integration. 

MSIL n. See Microsoft intermediate language. 

MSN n. Acronym for Microsoft Network. An online service 

and Internet portal, launched with the introduction of 

Windows 95 in August 1995. 

MSN Explorer n. Microsoft software that integrates the 

functionality of Internet Explorer, Windows Media Player, 

Hotmail, MSN Messenger, MSN Communities, Music 

Central, and other MSN content and services. See also 

MSN. 

MSN Messenger Service n. See .NET Messenger Service. 

MSP n. See Message Security Protocol, managed service 

provider. 

MS-Windows n. See Windows. 

MSXML n. Acronym for Microsoft XML. A Java-based 

XML parser from Microsoft that provides support for 

World Wide Web Consortium (W3C) standards for XML 

documents and applications. 

351 

MTA n. Acronym for message transfer agent. An application 

process, as described in the X.400 message-handling 

system, responsible for delivering e-mail messages. After 

receiving a message, an MTA stores it temporarily and 

either delivers it or forwards it to another MTA. During 

this process, the MTA can change the message headers. 

See also X series. 

MTBF n. Acronym for mean time between failures. The 

average time interval, usually expressed in thousands or 

tens of thousands of hours (sometimes called power-on 

hours or POH), that will elapse before a hardware component 

fails and requires service. 

MTTR n. Acronym for mean time to repair. The average 

time interval, usually expressed in hours, that it takes to 

repair a failed component. 

MTU n. Acronym for Maximum Transmission Unit. The 

largest packet of data that can be transmitted on a network. 

MTU size varies, depending on the network—576 bytes 

on X.25 networks, for example, 1500 bytes on Ethernet, 

and 17,914 bytes on 16 Mbps Token Ring. Responsibility 

for determining the size of the MTU lies with the link 

layer of the network. When packets are transmitted across 

networks, the path MTU, or PMTU, represents the smallest 

packet size (the one that all networks can transmit 

without breaking up the packet) among the networks 

involved. 

MUD n. Acronym for multiuser dungeon. A virtual environment 

on the Internet in which multiple users simultaneously 

participate in a role-playing game—generally a 

medieval fantasy, hence the “dungeon”—and interact with 

each other in real time. Also called: multiuser simulation 

environment. 

MUD, object-oriented n. See MOO. 

multiband phone n. Wireless phone that operates on two 

or more broadcast frequencies. 

multiboot n. 1. Startup capability of some operating systems, 

such as Windows NT, OS/2, UNIX, and some Power 

Macs, that allows users to choose which of two or more 

installed operating systems—for example, Windows NT 

or UNIX—they want to use for the current session. See 

also boot. 2. A computer configuration that runs two or 

more operating systems. See also dual boot, startup. 

Multibus n. A computer expansion bus designed by Intel 

Corporation that is used extensively by designers of 

high-performance workstations. A high-bandwidth bus 

M

M 

multicast address dynamic client allocation protocol Multimedia PC 

(capable of extremely fast data transmission), Multibus 

also allows multiple bus masters. See also bus. 

multicast address dynamic client allocation 

protocol n. An extension to the DHCP protocol standard 

used to support dynamic assignment and configuration of 

IP multicast addresses on TCP/IP-based networks. Acronym: 

MADCAP. 

multicast backbone n. See MBONE. 

multicasting n. The process of sending a message simultaneously 

to more than one destination on a network. 

Compare anycasting. 

multichannel multipoint distribution service n. See 

MMDS. 

Multi-Color Graphics Array n. See MCGA. 

multi-element adj. Consisting of multiple data elements 

that all have the same format for storing the same kind of 

information. The data elements may be simple variables, 

as in an array of integer variables, or they may be more 

complicated data structures, as in an array of employee 

records each of which contains fields for an employee’s 

name, Social Security number, pay rate, and so on. 

multifile sorting n. The process of sorting a body of data 

that resides in more than one file. 

MultiFinder n. A version of the Macintosh Finder that 

provides support for multitasking. The primary use of 

MultiFinder is to allow multiple applications to be simultaneously 

resident in memory. A single mouse click 

switches between applications, and information from one 

application can be copied to another. If the active application 

allows true multitasking, background tasks can be 

processed. See also Finder. 

multifunction board n. A computer add-in board that 

provides more than one function. Multifunction boards for 

personal computers frequently offer additional memory, 

serial/parallel ports, and a clock/calendar. 

multifunction peripheral n. A multipurpose device that 

combines printing with faxing, scanning (color or black 

and white), and copying (color or black and white) in a 

single unit. Multifunction peripherals are especially popular 

with the SOHO (small office, home office) market, 

where cost-effectiveness and space limitations can be 

significant considerations. Acronym: MFP. Also 

called: multifunction printer. 

multifunction printer n. See multifunction peripheral. 

352 

multihoming n. 1. In Mac OS X, an automatic network 

selection feature that allows one computer to maintain 

multiple network addresses. Multihoming may be used 

with a computer that is used from multiple locations, 

such as home and office, or to create special connection 

settings, such as separate systems for communication 

inside and outside of an intranet. 2. The use of multiple 

addresses and/or multiple interfaces for a single node. A 

multihomed host has either multiple network interfaces 

connected to two or more networks, or a single network 

interface that has been assigned multiple IP addresses. 

Multihoming can be used to provide redundancy to 

achieve quality of service. 

multilayer adj. 1. In board design, of or pertaining to a 

printed circuit board consisting of two or more layers of 

board material. Each separate layer has its own metallic 

tracings to provide electrical connections between various 

electronic components and to provide connections to the 

other layers. The layers are laminated together to produce 

a single circuit board to which the components, such as 

integrated circuits, resistors, and capacitors, are attached. 

Multilayer design allows many more discrete paths 

between components than single-layer boards do. 2. In 

computer-aided design (CAD), of or pertaining to drawings, 

such as electronic circuits, that are built up using 

multiple layers, each with a different level of detail or a 

different object, so that distinct parts of the drawing can 

easily be manipulated, overlaid, or peeled off. 

multilayer switch n. A network switch that uses information 

from more than one ISO/OSI layer (Layer 2, Layer 

3, Layer 4, and/or Layer 7) to forward traffic. See also 

ISO/OSI reference model, switch (definition 4). 

Multilink Point-to-Point Protocol n. An Internet protocol 

that allows computers to establish multiple physical 

links to combine their bandwidths. This technology creates 

a virtual link with more capacity than a single physical 

link. Acronym: MPPP. See also PPP. 

multimedia n. The combination of sound, graphics, animation, 

and video. In the world of computers, multimedia 

is a subset of hypermedia, which combines the aforementioned 

elements with hypertext. See also hypermedia, 

hypertext. 

Multimedia Extensions n. See MMX. 

Multimedia PC n. Software and hardware standards set 

forth by the Multimedia PC Marketing Council, which

Multimedia Personal Computer multiplicand 

sets minimum standards for a PC’s sound, video, and CD- 

ROM playing capabilities. Acronym: MPC. 

Multimedia Personal Computer n. See Multimedia PC. 

multimode phone n. Wireless phone that operates on 

both analog and digital networks. A multimode phone 

may be dual-mode (analog and one digital network) or trimode 

(analog and two digital networks). 

multinode computer n. A computer that uses multiple 

processors to share in the computation of a complex task. 

See also central processing unit, parallel processing. 

multipart forms n. Computer printer paper arranged in 

sets with carbon paper between the sheets (or with a 

chemical coating that emulates carbon on the back of each 

sheet except the last) to produce copies of output from 

impact printers. Multipart forms are designated by the 

number of copies in a set, such as two-part, three-part, and 

so on. 

multipartite virus n. A type of virus that combines characteristics 

and techniques of both boot sector and file 

viruses. Multipartite viruses first infect either system sectors 

or files and then spread quickly to infect the entire 

system. Because of their multiple capabilities, multipartite 

viruses are difficult to remove from an infected system. 

Also called: bimodal virus, bipartite virus. See also boot. 

multipass sort n. A sorting operation that, usually 

because of the sorting algorithm being used, requires two 

or more passes through the data before completion. See 

also bubble sort, insertion sort, Shell sort, sort algorithm. 

multiple-document interface n. See MDI. 

multiple inheritance n. A feature of some object-oriented 

programming languages that allows a new class to 

be derived from several existing classes. Multiple inheritance 

both extends and combines existing types. Acronym: 

MI. See also class, inherit, type. 

multiple instruction, multiple data streams n. See 

MIMD. 

multiple master font n. An advanced font creation and 

management classification developed by Adobe. A multiple 

master font contains two or more sets of font outlines 

or master designs that determine the dynamic range of 

each design axis in a typeface. Multiple master fonts 

include one or more design axes—weight, width, style, 

and optical size—that allow the user to create thousands of 

variations on a single typeface. 

353 

multiple-pass printing n. A form of dot-matrix printing 

in which the print head makes more than one pass across 

the page for each printed line, printing each line a second 

time exactly on top of the first pass. Multiple-pass printing 

can be used with dot-matrix printers to darken the print 

and smooth out errors in alignment. On better printers, a 

second pass might occur after the paper is moved up 

slightly, so that the dots in the characters overlap to create 

a crisper, darker image. 

multiple recipients n. 1. The capability of sending e-mail 

to more than one user at a time by listing more than one 

e-mail address on a line. Delimiters such as commas or 

semicolons are used to separate the e-mail addresses. See 

also e-mail1 (definition 1), mailing list. 2. The subscribers 

on a mailing list. A message sent to the list is addressed to 

the “multiple recipients of” the list. 

multiple regression n. A statistical technique that seeks 

to describe the behavior of a so-called “dependent” variable 

in terms of the observed behavior of numerous other, 

“independent” variables thought to affect it. For each independent 

variable, a regression analysis can determine the 

correlation coefficient of the independent variable—that 

is, the degree to which variations in the independent variable 

cause changes in the dependent variable. See also 

dependent variable. 

multiple-user system n. See multiuser system. 

multiplexer n. A device for funneling several different 

streams of data over a common communications line. 

Multiplexers are used either to attach many communications 

lines to a smaller number of communications ports 

or to attach a large number of communications ports to a 

smaller number of communications lines. Acronym: 

MUX. 

multiplexer channel n. One of the inputs to a multiplexer. 

See also multiplexer. 

multiplexing n. A technique used in communications and 

input/output operations for transmitting a number of separate 

signals simultaneously over a single channel or line. 

To maintain the integrity of each signal on the channel, 

multiplexing can separate the signals by time, space, or 

frequency. The device used to combine the signals is a 

multiplexer. See also FDM, space-division multiplexing, 

time-division multiplexing. 

multiplicand n. In arithmetic, the number that is multiplied 

by another number (the multiplier). In mathematics, 

the multiplicand and the multiplier are interchangeable, 

depending on how the problem is stated, because the result 

M

M 

multiplier multiuser system 

is the same if the two are reversed—for example, 2 x 3 and 

3 x 2. In arithmetic performed by computers, however, the 

multiplicand is different from the multiplier because computer 

multiplication is usually performed as addition. 

Therefore, 2 x 3 means “add 2 three times,” whereas 3 x 2 

means “add 3 two times.” See also factor. Compare multiplier 


multiplier n. 1. In arithmetic, the number that indicates 

how many times another number (the multiplicand) is 

multiplied. See also factor. Compare multiplicand. 2. In 

computing, an electronic device independent of the central 

processing unit (CPU) that performs multiplication by 

adding the multiplicand according to the value of the digits 

in the multiplier. 

multipoint configuration n. A communications link in 

which multiple stations are connected sequentially to the 

same communications line. Typically, the communications 

line is controlled by a primary station, such as a computer, 

and the stations attached to the line are secondary. See the 

illustration. 

Primary 

station 

Secondary 

station 1 

F0Mgn09.eps 

Multipoint configuration. 

Secondary 

station 2 

Secondary 

station 3 

multiport repeater n. See active hub. 

multiprocessing n. A mode of operation in which two or 

more connected and roughly equal processing units each 

carry out one or more processes (programs or sets of 

instructions) in tandem. In multiprocessing, each processing 

unit works on a different set of instructions or on different 

parts of the same process. The objective is increased 

speed or computing power, the same as in parallel processing 

and in the use of special units called coprocessors. 

Compare coprocessor, parallel processing. 

multiprogramming n. A form of processing in which a 

computer holds more than one program in memory and 

works on them in round-robin fashion—that is, by sharing 

out the processor’s time so that each program receives some 

354 

attention some of the time. This way of working is in contrast 

to using the processor to run one program at a time. 

Multiprotocol Label Switching n. See MPLS. 

Multi-Protocol Over ATM n. See MPOA. 

Multipurpose Internet Mail Extensions n. See MIME. 

Multipurpose Internet Mail Extensions HTML n. See 

MHTML. 

multiscan monitor n. A computer monitor capable of 

adapting to different video frequencies to accommodate 

multiple screen resolutions and to support different video 

adapters and graphics display methods. 

Multistation Access Unit n. See MAU. 

multisystem network n. A communications network in 

which two or more host computers can be accessed by network 

users. 

multitasking n. A form of processing supported by most 

current operating systems in which a computer works on 

multiple tasks—roughly, separate “pieces” of work— 

seemingly at the same time by parceling out the processor’s 

time among the different tasks. Multitasking can be 

either cooperative or preemptive. In the former, the operating 

system relies on the task to voluntarily cede control to 

another task; in the latter, the operating system decides 

which task receives priority. See also background1 , context 

switching, cooperative multitasking, foreground1 , 

time slice. 

multithreaded application n. A program capable of running 

more than one program thread simultaneously. See 

also multithreading (definition 1), thread (definition 1). 

multithreading n. 1. The running of several processes in 

rapid sequence (multitasking) within a single program. 

See also thread (definition 1). 2. In data manipulation, a 

technique in which nodes in a tree data structure contain 

pointers to higher nodes to make traversal of the structure 

more efficient. See also thread (definition 2). 

multi-tier n. See three-tier. 

multiuser n. See multiuser system. 

multiuser dungeon n. See MUD. 

multiuser simulation environment n. See MUD. 

multiuser system n. Any computer system that can be 

used by more than one person. Although a microcomputer

multum in parvo mapping my two cents 

shared by several people can be considered a multiuser 

system, the term is generally reserved for machines that 

can be accessed simultaneously by several people through 

communications facilities or via network terminals. Compare 

single-user computer. 

multum in parvo mapping n. See MIP mapping. 

MUMPS n. Acronym for Mass(achusetts) Utility Multi 

Programming System. An advanced, high-level programming 

language and integrated database developed in 1966 

at Massachusetts General Hospital and used widely by 

health care businesses. A unique feature of MUMPS is its 

ability to store both data and program fragments in its 

database. 

munging n. See address munging. 

MUSE n. Short for multiuser simulation environment. See 

MUD. 

.museum n. One of seven new top-level domain names 


Names and Numbers (ICANN), .museum is meant for use 

by museum Web sites. 

Musical Instrument Digital Interface n. See MIDI. 

mutual exclusion n. A programming technique that 

ensures that only one program or routine at a time can 

355 

access some resource, such as a memory location, an I/O 

port, or a file, often through the use of semaphores, which 

are flags used in programs to coordinate the activities of 

more than one program or routine. See also semaphore. 

MUX n. See multiplexer. 

My Briefcase n. A Windows 9x utility, helpful for workers 

away from the office, that manages the updating of 

modified files once the remote user’s computer is connected 

back on the office network. 

Mylar n. A polyester film product created by DuPont, 

often used as the base for magnetically coated storage 

media (disks and tape) and for carbon ribbons used with 

impact printers. 

Mylar ribbon n. See carbon ribbon. 

MYOB n. Acronym for Mind your own business. An 

expression used in e-mail and newsgroups. 

my two cents n. An expression used informally in newsgroup 

articles and, less frequently, e-mail messages or 

mailing lists, to indicate that the message is the writer’s 

contribution to an ongoing discussion. Also called: $0.02. 

See also mailing list, newsgroup. 

M

N 

n prefix See nano-. 

NACN n. See North American Cellular Network. 

nagware n. Slang for computer shareware that, on starting 

or before closing, displays a prominent reminder to 

pay for the program. See also shareware. 

NAK n. Acronym for negative acknowledgement. A control 

code, ASCII character 21 (hexadecimal 15), transmitted 

to a sending station or computer by the receiving unit 

as a signal that transmitted information has arrived incorrectly. 

Compare ACK. 

NAK attack n. Acronym for negative acknowledgement 

attack. A hacker attack that uses the negative acknowledgement 

control code character to enter a seemingly 

secure system. A NAK attack uses weaknesses in the system 

handling NAK replies that may leave it temporarily 

unprotected. See also NAK. 

naked PC n. A personal computer sold without an operating 

system (OS) installed. The purchaser of a naked PC 

must then choose and install an OS before the computer 

can be used. Naked PCs are chiefly purchased by users 

with some degree of expertise with computer equipment 

who may want to install a version of Linux or an offshoot 

OS. Computer and software manufacturers have expressed 

concern over the possibility of software piracy with the 

sale of naked PCs. 

.name n. One of seven new top-level domain names 


Names and Numbers (ICANN), .name is meant for registration 

by individuals for personal Web sites. The seven 


of 2001. 

Name Binding Protocol n. See NBP. 

named anchor n. In HTML, a tag within a document that 

can act as a destination for a hyperlink. Named anchors 

are useful because they allow a link to a specific location 

within a document. Also called: named target. See also 

anchor (definition 2), HTML, hyperlink. 

named entity n. See character entity. 

N 

356 

named pipes n. In programming, one-way (simplex) or 

two-way (duplex) connections used to transfer data 

between processes. Named pipes are portions of memory 

set aside for temporary data storage. They are created by 

server processes and can be used simultaneously by more 

than one client process, each accessing a separate instance 

with its own buffers and handles. Named pipes can be 

used to transfer data either locally or on a network. 

named target n. See named anchor. 

name server n. See CSO name server, DNS server. 

namespace n. 1. A grouping of one or more names that 

represent individual objects within the group in a shared 

computing environment, such as a network. The names 

within a namespace are unique, are created according to 

the same rules, and can be resolved into a particular identifying 

item of information, such as an IP address or a 

network device. A namespace can be either flat—a single 

collection of unique names—or hierarchical, as is the 

Internet’s DNS (Domain Name System), which is based 

on a treelike structure that is refined through successive 

levels beginning with the root server and the Internet’s 

top-level domains (.com, .net, .org, and so on). In everyday 

terms, a namespace is comparable to a telephone 

book, in which each name is unique and resolves to the 

phone number and address of a particular individual, 

business, or other entity. 2. A means of identifying elements 

and attributes in an XML document by assigning 

them a two-part name with the first part being the 

namespace and the second part being the functional 

name. A namespace identifies a set of names to prevent 

confusion when multiple objects with identical functional 

names are taken from different sources and brought 

together in the same XML document. Namespaces typically 

reference a Uniform Resource Identifier (URI) 

because each URI will be unique. 

name-value pair n. 1. In the Perl programming language, 

a data set in which the data is associated with a name. See 

also Perl. 2. In CGI programming, one of the data items 

collected from an HTML form by the browser and passed

naming container National Computer Security Association 

through the server to a CGI script for processing. See also 

CGI, CGI script, HTML. 

naming container n. Any ASP.NET control that implements 

the INamingContainer interface. This is a marker 

interface that enables a control to create a new naming 

scope under itself so that ID attributes assigned to its child 

controls are unique within the entire ASP.NET page that 

contains the control. 

NAMPS n. Acronym for Narrow-band Analog Mobile 

Phone Service. A standard proposed by Motorola Corporation 

that combines the current AMPS cellular telephone 

standard with digital signaling information, resulting in 

higher performance and increased capabilities. See also 

AMPS. 

NAND n. Short for NOT AND. A logical operation that 

combines the values of two bits (0,1) or two Boolean values 

(false, true) that returns a value of 1 (or true) if one 

input value is 0 (or false), and returns a 0 (false) only if 

both inputs are true. 

NAND gate n. Short for NOT AND gate. A digital circuit 

whose output is true (1) if any input is false (0). A NAND 

gate is an AND circuit (output with the value of 1 when all 

input values are 1) followed by a NOT circuit (output that 

is the logical complement of the input). Thus, NAND gate 

output is high if any of its inputs are low. See also AND 

gate, gate (definition 1), NOT gate. 

nano- prefix Abbreviated n. Metric prefix meaning 10 –9 

(one billionth). 

nanosecond n. One billionth of a second. A nanosecond 

is a time measure used to represent computing speed, particularly 

the speed at which electrical signals travel 

through circuits within the computer. Acronym: ns. 

NAP n. See Network Access Point. 

Napster n. An Internet music search application that 

allows users to search for and swap MP3 files over the 

Web. In response to a user request for a song or an artist, 

Napster searches the hard drives of all other Napster users 

on line. When the requested item is found, the file is 

downloaded to the computer making the request. Napster 

also includes a chat room and a library of most popular 

items. The introduction of Napster in 1999 sparked heated 

debate over copyright and digital distribution issues. See 

also MP3. 

357 

narrowband n. A bandwidth set aside by the FCC for 

mobile or portable radio services, such as advanced twoway 

paging systems, including transmission rates between 

50 bps and 64 Kbps. Narrowband formerly referred to the 

bandwidth from 50 to 150 bps. See also bandwidth, FCC. 

Compare broadband. 

narrowband ISDN n. Name used to distinguish current 

ISDN lines from the developing broadband ISDN technology. 

See also broadband ISDN, ISDN. 

narrowcast vb. To transmit data or programming to a 

defined or limited area or audience. A cable television 

company narrowcasts its programs only to subscribers, 

whereas network television stations broadcast to everyone 

with reception equipment in their transmission range. On 

the Web, content delivered to users via push technology 

represents a form of narrowcasting. See also unicast. Compare 

broadcast (definition 2), multicasting. 

Narrow SCSI n. A SCSI or SCSI-2 interface that can 

transfer data only 8 bits at a time. See also SCSI, SCSI-2. 

Compare Fast/Wide SCSI, Wide SCSI. 

NAS n. Acronym for Network-Attached Storage. A 

platform-independent storage appliance connected to a 

network. NAS uses a storage unit with a built-in server 

that can communicate with clients over a network. NAS 

devices are popular for ease of maintenance, manageability, 

and scalability. Compare SAN. 

NAT n. Acronym for Network Address Translation. The 

process of converting between IP addresses used within an 

intranet or other private network and Internet IP addresses. 

This approach makes it possible to use a large number of 

addresses within the private network without depleting the 

limited number of available numeric Internet IP addresses. 

Variations of NAT displaying similar functions include IP 

aliasing, IP masquerading, and Port Address Translation. 

national attachment point n. See Network Access Point. 

National Center for Supercomputing 

Applications n. See NCSA (definition 1). 

National Committee for Information Technology 

Standards n. A committee formed by the Information 

Technology Industry Council to develop national standards 

for use in the information technology industry and 

to promote those standards for international use. Acronym: 

NCITS. 

National Computer Security Association n. See ICSA. 

N

N 

National Information Infrastructure navigation keys 

National Information Infrastructure n. A U.S. government 

program to extend and oversee the development of 

the Information Superhighway. The National Information 

Infrastructure is made up of a high-bandwidth, wide area 

network that can carry data, fax, video, and voice transmissions 

to users throughout the United States. The network 

is being developed mostly by private carriers. Many 

of the services, which are aimed at enabling the efficient 

creation and dissemination of information, are already 

available on the Internet itself, including increased accessibility 

to quality education through distance learning and 

increased access to government services. Acronym: NII. 

See also Information Superhighway, Internet2, Next Generation 

Internet. Compare Internet. 

National Institute of Standards and Technology n. A 

branch of the U.S. Commerce Department that works to 

develop and encourage standards for measurement, science, 

and technology in order to promote commerce and improve 

productivity in the marketplace. Prior to 1988, the National 

Institute of Standards and Technology was known as the 

National Bureau of Standards. Acronym: NIST. 

national language support n. 1. The practice of creating 

programs that can display text in any language necessary. 

2. A function in Windows that enables you to specify 

system and user locale information. Acronym: NLS. 

National Science Foundation n. A U.S. government 

agency intended to promote scientific research by funding 

both research projects and projects that facilitate scientific 

communication, such as NSFnet, the former backbone of 

the Internet. Acronym: NSF. See also backbone (definition 

1), NSFnet. 

National Television System Committee n. See NTSC. 

native adj. Of, pertaining to, or characteristic of something 

that is in its original form. For example, many applications 

are able to work with files in a number of formats; 

the format the application uses internally is its native file 

format. Files in other formats must be converted to the 

application’s native format before they can be processed 

by the application. 

native application n. A program that is designed specifically 

for a particular type of microprocessor, that is, a program 

that is binary compatible with a processor. A native 

application generally will run much faster than a nonnative 

application, which must be run with the help of an emulator 

program. See also binary compatibility, emulator. 

358 

native code n. Code that has been compiled to processorspecific 

machine code. 

native compiler n. A compiler that produces machine 

code for the computer on which it is running, as opposed 

to a cross-compiler, which produces code for another type 

of computer. Most compilers are native compilers. See 

also compiler (definition 2), cross-compiler. 

native file format n. The format an application uses 

internally to process data. The application must convert 

files in other formats to the native format before it can 

work with them. For example, a word processor might recognize 

text files in ASCII text format, but it will convert 

them to its own native format before it displays them. 

native language n. See host language. 

natural language n. A language spoken or written by 

humans, as opposed to a programming language or a 

machine language. Understanding natural language and 

approximating it in a computer environment is one goal of 

research in artificial intelligence. 

natural-language processing n. A field of computer 

science and linguistics that studies computer systems that 

can recognize and react to human language, either spoken 

or written. See also artificial intelligence. Compare speech 

recognition. 

natural language query n. A query to a database system 

that is composed in a subset of a natural language, such as 

English or Japanese. The query must conform to some 

restrictive syntax rules so that the system can parse it. See 

also parse, syntax. 

natural-language recognition n. See speech recognition. 

natural language support n. A voice recognition system 

that allows the user to use verbal commands in his 

or her own language to direct a computer’s actions. 

Acronym: NLS. 

natural number n. An integer, or whole number, that is 

equal to or greater than zero. See also integer. 

navigation bar n. On a Web page, a grouping of hyperlinks 

for getting around in that particular Web site. See 

also hyperlink. 

navigation keys n. The keys on a keyboard controlling 

cursor movement, including the four arrow keys and the 

Backspace, End, Home, Page Down, and Page Up keys. 

See also arrow key, Backspace key, End key, Home key, 

Page Down key, Page Up key.

Navigator net.- 

Navigator n. See Netscape Navigator. 

NBP n. Acronym for Name Binding Protocol. A protocol 

used on AppleTalk local area networks to translate 

between node names (known to users) and numeric Apple- 

Talk addresses. NBP operates at the transport level (level 4 

of the ISO/OSI reference model). See also AppleTalk, 

communications protocol, ISO/OSI reference model. 

NC n. See network computer. 

NCC n. See network-centric computing. 

N-channel MOS n. See NMOS. 

NCITS n. See National Committee for Information Technology 

Standards. 

NCP n. See Point-to-Point Protocol. 

NCR paper n. Short for no carbon required paper. A special 

paper used for multipart forms. NCR paper is impregnated 

with a chemical that darkens it when pressure is 

applied. See also multipart forms. 

NCSA n. 1. Acronym for National Center for Supercomputing 

Applications. A research center located at the University 

of Illinois at Urbana-Champaign. NCSA was 

founded in 1985 as a part of the National Science Foundation, 

specializing in scientific visualization tasks, but is 

best known as the home of NCSA Mosaic, the first graphical 

Web browser, and of NCSA Telnet. See also Mosaic, 

NCSA Telnet. 2. See ICSA. 

NCSA Mosaic n. See Mosaic. 

NCSA server n. The HTTP server developed by the 

National Center for Supercomputing Applications of the 

University of Illinois. This server and the CERN server 

were the first HTTP servers developed for the World Wide 

Web and are available free through downloading. See also 

HTTP server (definition 1), NCSA (definition 1). Compare 

CERN server. 

NCSA Telnet n. A freeware telnet client program developed 

and distributed by the National Center for Supercomputing 

Applications. See also client (definition 2), NCSA 


NDIS n. Acronym for Network Driver Interface Specification, 

a software interface, or set of rules, designed to 

enable different network protocols to communicate with a 

variety of network adapters. Providing a standard—a common 

“language”—for the drivers used by network adapters, 

NDIS enables a single network adapter to support 

multiple protocols and, conversely, also enables a single 

359 

protocol to work with network adapters from different 

vendors. See also device driver. 

NDMP n. Acronym for Network Data Management Protocol. 

An open protocol for network-based backups of file 

servers that allows platform-independent data storage. See 

also backup, communications protocol, file server. 

NDR n. See nondestructive readout. 

NDRO n. See nondestructive readout. 

NDS n. Acronym for Novell Directory Services. A feature 

introduced in Novell Netware 4.0 that provides access to 

directories that may be located on one or more servers. 

near-letter-quality adj. A print mode on high-end dotmatrix 

printers that produces clearer, darker characters 

than normal (draft-quality) printing. Near-letter-quality 

printing, although it is sharper than plain dot-matrix printing, 

is not as legible as output from a fully-formed-character 

printer, such as a daisy-wheel printer. Acronym: NLQ. See 

also print quality. Compare draft quality, letter quality. 

negation n. The conversion of a two-state (binary) signal 

or bit pattern to its opposite state—for example, the conversion 

of 1001 to 0110. 

negative acknowledgement n. See NAK. 

negative entry n. The act of assigning a negative sign to 

a number that has been entered into a calculator, thereby 

transforming the number to a negative number. 

nest vb. To embed one construct inside another. For 

example, a database may contain a nested table (a table 

within a table), a program may contain a nested procedure 

(a procedure declared within a procedure), and a data 

structure may include a nested record (a record containing 

a field that is itself a record). 

nested transaction n. In programming, an operation 

or sequence of operations taking place within a larger 

transaction. A nested transaction can be aborted without 

requiring abortion of the larger transaction. Also 

called: subtransaction. See also nest. 

.net n. In the Internet’s Domain Name System, the toplevel 

domain that identifies addresses of network providers. 

The designation .net appears at the end of the address. 

See also DNS (definition 1), domain (definition 3). Compare 

.com, .edu, .gov, .mil, .org. 

net.- prefix A prefix used to describe people and institutions 

on the Internet. For example, a very well respected 

person might be described as a net.god. 

N

N 

Net .NET Framework data provider 

Net n. 1. Short for Internet. 2. Short for Usenet. 

.NET n. The set of Microsoft technologies that provides 

tools for connecting information, people, systems, and 

devices. The technologies provide individuals and organizations 

with the ability to build, host, deploy, and use 

XML Web service connected solutions. 

net address n. 1. A World Wide Web address (URL). See 

also URL. 2. An e-mail address. 3. The DNS name or IP 

address of a machine. See also DNS (definition 1), IP 

address. 4. The address, burned into a network adapter, 

that is used to uniquely identify a node on a network. See 

also network interface card. 

NetBEUI n. Short for NetBIOS Extended User Interface. 

NetBEUI is a network protocol created by IBM and now 

used by Microsoft, HP, and Compaq. It is usually used in 

small, department-size local area networks (LANs) of 1 to 

200 clients. It can use Token Ring source routing as its 

only method of routing. It is the extended version of the 

NetBIOS standard. See also CCP, communications protocol, 

LAN, NetBIOS. 

NetBIOS n. An application programming interface (API) 

that can be used by application programs on a local area 

network consisting of IBM and compatible microcomputers 

running MS-DOS, OS/2, or some version of UNIX. 

Primarily of interest to programmers, NetBIOS provides 

application programs with a uniform set of commands for 

requesting the lower-level network services required to 

conduct sessions between nodes on a network and to 

transmit information back and forth. See also application 

programming interface. 

NetBIOS Extended User Interface n. See NetBEUI. 

net boot n. See PXE boot. 

NetBSD n. A free version of the BSD UNIX operating system 

developed as a result of a volunteer effort. NetBSD is 

highly interoperable, runs on many hardware platforms, and 

is nearly POSIX compliant. See also BSD UNIX, POSIX. 

Netcaster n. See netcasting (definition 2). 

netcasting n. 1. Synonym for webcasting. 2. A Netscape 

technology used in Netscape Netcaster that enabled a user 

to subscribe to channels that pushed Web content to the 

user’s desktop without actively retrieving the information. 

Netscape Netcaster, which was part of previous versions 

of Netscape Navigator, competed with Microsoft Active 

Desktop. Unlike Active Desktop, which uses Microsoft’s 

360 

Channel Definition Format (CDF), the Netcaster push client 

was based on existing open standards (HTML, Java, 

and JavaScript). See also push (definition 2). Compare 

Active Desktop. 

.NET Compact Framework n. A hardware-independent 

environment for running programs on resource-constrained 

computing devices. It inherits the full .NET Framework 

architecture of the common language runtime, supports a 

subset of the .NET Framework class library, and contains 

classes designed exclusively for the .NET Compact 

Framework. Supported devices include personal data 

assistants (PDAs) (such as the Pocket PC), mobile phones, 

set-top boxes, automotive computing devices, and customdesigned 

embedded devices built with the Microsoft Windows 

CE operating system. 

.NET data provider n. A component of ADO.NET that 

provides access to data from a relational database. 

netfilter n. The packet-filtering system for Linux introduced 

in the 2.4 kernel. Netfilter is the first stateful firewall 

implemented in Linux. See also firewall, iptables. 

Compare IP Filter. 

NetFind n. See AOL NetFind. 

.NET Framework n. A platform for building, deploying, 

and running XML Web services and applications. It provides 

a highly productive, standards-based, multilanguage 

environment for integrating existing investments with next 

generation applications and services, as well as the agility 

to solve the challenges of deployment and operation of 

Internet-scale applications. The .NET Framework consists 

of three main parts: the common language runtime, a hierarchical 

set of unified class libraries, and a componentized 

version of ASP called ASP.NET. See also ASP.NET, common 

language runtime, .NET Framework class library. 

.NET Framework class library n. A Common Language 

Specification (CLS)–compliant library of classes, interfaces, 

and value types that are included in the Microsoft 

.NET Framework SDK. This library provides access to 

system functionality and is designed to be the foundation 

on which .NET Framework applications, components, and 

controls are built. 

.NET Framework data provider n. A component of 

ADO.NET that provides access to data from a relational 

data source. A .NET Framework data provider contains 

classes to connect to a data source, execute commands at 

the data source, and return query results from the data

net.god netspionage 

source, including the ability to execute commands within 

transactions. A .NET Framework data provider also contains 

classes to populate a DataSet with results from a data 

source and propagate changes in a DataSet back to the 

data source. 

net.god n. A highly respected person within the Internet 

community. 

nethead n. 1. A person who uses the Internet as if 

addicted to it. 2. A Grateful Dead fan who participates in 

the rec.music.gdead newsgroup or some other forum dedicated 

to that band. 

netiquette n. Short for network etiquette. Principles of 

courtesy observed in sending electronic messages, such as 

e-mail and Usenet postings. The consequences of violating 

netiquette include being flamed and having one’s name 

placed in the bozo filter of one’s intended audience. Disapproved 

behavior includes gratuitous personal insults; posting 

of large amounts of irrelevant material; giving away the 

plot of a movie, television show, or novel without warning; 

posting offensive material without encrypting it; and excessive 

cross-posting of a message to multiple groups without 

regard to whether the group members are likely to find it 

interesting. See also bozo filter, flame2 . 

netizen n. A person who participates in online communication 

through the Internet and other networks, especially 

conference and chat services, such as Internet news or 

Fidonet. Compare lurker. 

NetMeeting n. A software application developed by 

Microsoft Corporation to allow video conferencing among 

parties using personal computers connected via the Internet. 

NetMeeting allows participants in different locations 

to view each other, engage in text chat conversations, send 

and receive videos, exchange information graphically via 

an electronic whiteboard, share Windows-based applications, 

and transfer files. 

.NET Messenger Service n. A popular instant-messaging 

service provided by Microsoft as part of the .NET 

strategy. With .NET Messenger Service, formerly called 

MSN Messenger Service, users can communicate using 

the Windows Messenger, included in Windows XP, or 

MSN Messenger applications. See also instant messaging. 

Compare AIM, ICQ, Yahoo! Messenger. 

.NET My Services n. A suite of XML Web services for 

managing and protecting personal information and interactions 

across applications, devices, and services. Formerly 

361 

code-named HailStorm, .NET My Services is based on the 

Microsoft .NET Passport user-authentication system. The 

suite of .NET My Services includes services such as .NET 

ApplicationSettings, .NET Calendar, .NET Contacts, .NET 

Devices, .NET Documents, .NET Inbox, .NET Locations, 

.NET Profile, and .NET Wallet. See also .NET, Passport. 

NetPC n. Short for Network PC. An industry-defined, 

Windows-based PC system that is small and meant to act 

as simply an access point. These PCs generally have very 

small hard drives, no disk drives, and are built to have a 

very low cost. Some older NetPCs can boot through 

remote access to a server and user server-based resources 

for most computing actions. 

net.personality n. A slang term for a person who has 

attained some degree of celebrity on the Internet. 

net.police n. Persons (usually self-appointed) who try to 

enforce their understanding of the “rules” that apply to 

conduct on the Internet. Their activities may be directed 

toward users who violate the rules of netiquette, spammers 

who send unsolicited advertising as e-mail or to 

newsgroups, or even people who post “politically incorrect” 

comments to newsgroups or mailing lists. See also 

netiquette, spam. 

Netscape Navigator n. The widely used family of Web 

browser programs, made by Netscape Corporation. Versions 

of Netscape Navigator are available for the Windows 

and Macintosh platforms, and for many varieties 

of UNIX. Netscape Navigator, which is based on 

NCSA’s Mosaic Web browser, was one of the first commercially 

available Web browsers. In 1999, Netscape 

Corporation was purchased by America Online. See also 

Mosaic, Web browser. 

Netscape Netcaster n. See netcasting (definition 2). 

Netscape Server Application Programming 

Interface n. See NSAPI. 

Netspeak n. The set of conventions for writing English in 

e-mail, IRCs, and newsgroups. Netspeak is characterized 

by acronyms (such as IMHO or ROFL) and clarifying 

devices such as emotags and emoticons. Use of Netspeak 

should be governed by netiquette. See also emotag, emoticon, 

IMHO, IRC, netiquette, ROFL. 

netspionage n. Corporate-sponsored hacking of a competitor’s 

digital information for the theft of trade secrets. 

N

N 

Net surfing Network Control Protocol 

Net surfing n. The practice of exploring the Internet 

without a specific goal in mind. The concept of Net surfing 

is similar to (and probably derived from) “channel 

surfing” in reference to watching television. 

Net TV n. See Internet television. 

NetWare n. A family of LAN (local area network) operating 

system products developed by Novell, Inc. Designed 

to run on PCs and Macintoshes, Novell NetWare allows 

users to share files and system resources such as hard 

disks and printers. See also network operating system. 

network n. A group of computers and associated devices 

that are connected by communications facilities. A network 

can involve permanent connections, such as cables, or temporary 

connections made through telephone or other communication 

links. A network can be as small as a LAN 

(local area network) consisting of a few computers, printers, 

and other devices, or it can consist of many small and large 

computers distributed over a vast geographic area (WAN, or 

wide area network). See also ALOHAnet, Ethernet (definition 

1), LAN, WAN. 

Network Access Point n. One of the interchange points 

for Internet traffic, where various Internet network carriers 

and major ISPs exchange data. When Internet traffic originates 

on one network and goes to another network, it 

almost always passes through at least one Network Access 

Point, or NAP. In the United States, major NAPs include 

MAE East, in Vienna, Virginia, and MAE West, in San 

Jose, California (both operated by MCI WorldCom); the 

Chicago NAP (operated by Ameritech); the Pacific Bell 

NAP (with multiple locations in California); the Digital 

Internet Exchange in Palo Alto, California (operated by 

Digital/Compaq); and the Sprint NAP in Pennsauken, 

New Jersey. Additional local and regional exchange points 

are located in many other locations around the world. 

Acronym: NAP. Also called: National Attachment Point. 

network adapter n. See network interface card. 

Network Address Translation n. See NAT. 

network administrator n. The person in charge of operations 

on a computer network. The duties of a network 

administrator can be broad and might include such tasks 

as installing new workstations and other devices, adding 

and removing individuals from the list of authorized users, 

archiving files, overseeing password protection and other 

security measures, monitoring usage of shared resources, 

and handling malfunctioning equipment. See also system 

administrator. 

362 

network architecture n. The underlying structure of a 

computer network, including hardware, functional layers, 

interfaces, and protocols, used to establish communication 

and ensure the reliable transfer of information. Network 

architectures are designed to provide both philosophical 

and physical standards for the complexities of establishing 

communications links and transferring information without 

conflict. Various network architectures exist, including 

the internationally accepted seven-layer ISO Open Systems 

Interconnection (OSI) model and IBM’s Systems 

Network Architecture (SNA). See also ISO/OSI reference 

model, SNA. 

Network-Attached Storage n. See NAS. 

network boot n. See PXE boot. 

network card n. See network interface card. 

network-centric computing n. A computing environment 

in which a network server or servers represent the 

hub of activity. Considered the “third wave” in large-system 

computing after mainframe and desktop developments, 

network-centric computing establishes servers as 

the main source of computing power, to give users direct 

access to network-based applications and information. In 

network-centric computing systems, applications are not 

preinstalled or uninstalled locally, that is, on the desktop; 

they are accessed on an as-needed, “on-the-fly” basis. 

Thus, individual desktop computers do not have to maintain 

large amounts of disk storage or load and manage 

application programs. See also server. 

network computer n. A computer designed for use on a 

network in which programs and storage are provided by 

servers. Network computers, unlike dumb terminals, have 

their own processing power, but their design does not 

include local storage and they depend on network servers 

for applications. Acronym: NC. 

network congestion n. See congestion. 

network connection n. See Ethernet. 

network control program n. In a communications network 

that includes a mainframe computer, a program that 

usually resides in a communications controller and takes 

over communications tasks such as routing, error control, 

line control, and polling (checking terminals for transmissions), 

leaving the main computer free for other functions. 

See also communications controller. 

Network Control Protocol n. See Point-to-Point Protocol.

network database network modem 

network database n. 1. A database that runs in a network. 

2. A database containing the address of other users 

in the network. 3. In information management, a type of 

database in which data records can be related to one 

another in more than one way. A network database is similar 

to a hierarchical database in the sense that it contains a 

progression from one record to another. It differs in being 

less rigidly structured: any single record can point to more 

than one other record and, conversely, can be pointed to by 

one or more records. In effect, a network database allows 

more than one path between any two records, whereas a 

hierarchical database allows only one, from parent 

(higher-level record) to child (lower-level record). Compare 

hierarchical database, relational database. 

Network Data Management Protocol n. See NDMP. 

network device driver n. Software that coordinates communication 

between the network adapter card and the 

computer’s hardware and other software, controlling the 

physical function of the network adapter card. 

network directory n. On a local area network, a directory 

on a disk that is located on a computer other than the 

one the user is operating. A network directory differs from 

a network drive in that the user has access to only that 

directory. Whether the rest of the disk is accessible to the 

user depends on whether he or she has been granted access 

rights by the network administrator. On the Macintosh, a 

network directory is referred to as a shared folder. Also 

called: networked directory, shared directory. See also 

network drive, shared folder. 

network drive n. On a local area network, a disk drive 

whose disk is available to other computers on the network. 

Access to a network drive might not be allowed to all 

users of the network; many operating systems contain 

security provisions that enable a network administrator to 

grant or deny access to part or all of a network drive. Also 

called: networked drive. See also network directory. 

Network Driver Interface Specification n. See NDIS. 

networked directory n. See network directory. 

networked drive n. See network drive. 

networked home n. See smart home. 

Network File System n. See NFS. 

network information center n. See NIC (definition 2). 

network interface card n. An expansion card or other 

device used to provide network access to a computer or 

other device, such as a printer. Network interface cards 

363 

mediate between the computer and the physical media, 

such as cabling, over which transmissions travel. Acronym: 

NIC. Also called: network adapter, network card. 

Network Kernel Extension n. See NKE. 

network latency n. The time it takes for information to 

be transferred between computers in a network. 

network layer n. The third of the seven layers in the ISO/ 

OSI reference model for standardizing computer-to-computer 

communications. The network layer is one level above 

the data-link layer and ensures that information arrives at its 

intended destination. It is the middle of the three layers 

(data-link, network, and transport) concerned with the actual 

movement of information from one device to another. See 

the illustration. See also ISO/OSI reference model. 

ISO/OSI Layer 

Application 

(highest level) 

Presentation 

Session 

Transport 

Network 

Data-link 

Physical 

F0ngn01.eps 

Network layer. 

ISO/OSI MODEL 

Focus 

Program-to-program transfer 

of information 

Text formatting and display, code 

conversion 

Establishing, maintaining, and 


Accurate delivery, service quality 

Transport routes, message 


Coding, addressing, and 


Hardware connections 

network meltdown n. See broadcast storm, meltdown. 

network model n. A database structure, or layout, similar 

to a hierarchical model, except that records can have multiple 

parent records as well as multiple child records. A 

database management system that supports a network 

model can be used to simulate a hierarchical model. See 

also CODASYL, network database (definition 3). Compare 

hierarchical model. 

network modem n. A modem that is shared by users of a 

network for calling an online service provider, an ISP, a 

service bureau, or other online source. See also ISP, 

modem online information service, service bureau (definition 

2). 

N

N 

network news news 

network news n. The newsgroups on the Internet, especially 

those in the Usenet hierarchy. 

Network News Transfer Protocol n. See NNTP. 

network operating system n. An operating system specifically 

designed to support networking. A server-based 

network operating system provides networking support for 

multiple simultaneous users as well as administrative, 

security, and management functions. On the desktop, a 

network-aware operating system provides users with the 

ability to access network resources. Unlike a single-user 

operating system, a network operating system must 

acknowledge and respond to requests from many workstations, 

managing such details as network access and communications, 

resource allocation and sharing, data 

protection, and error control. Acronym: NOS. Also 

called: network OS. 

network operation center n. The office in an enterprise 

that is responsible for maintaining network integrity and 

improving network efficiency while reducing system 

downtime. Acronym: NOC. 

network OS n. See network operating system. 

network protocol n. A set of rules and parameters that 

defines and enables communication through a network. 

Network Query Language n. A scripting language for 

controlling intelligent agents for Web applications. Acronym: 

NQL. 

network server n. See server. 

network services n. 1. In a corporate environment, the 

division that maintains the network and the computers. 

2. In a Windows environment, extensions to the operating 

system that allow it to perform network functions such as 

network printing and file sharing. 

network software n. Software including a component 

that facilitates connection to or participation in a network. 

Network Solutions, Inc. n. See NSI. 

network structure n. The record organization used in a 

particular network model. 

Network Terminator 1 n. An ISDN device that acts as 

an interface between an ISDN telephone line and one or 

more terminal adapters or terminal devices, such as an 

ISDN telephone. Acronym: NT-1. See also ISDN, ISDN 

terminal adapter. 

364 

Network Time Protocol n. An Internet protocol used to 

synchronize the clocks in computers connected to the Internet. 

Acronym: NTP. See also communications protocol. 

network topology n. See topology. 

network weaving n. See leapfrog attack. 

NetWorld+Interop n. International conference and exhibition 

for the networking and information technology 

industry. NetWorld+Interop draws attendees from a variety 

of industries, including telecommunications, Internet 

services, and e-commerce. NetWorld+Interop features 

product exhibits, educational conferences, tutorials, and 

workshops. 

NeuralCast Technology n. Technology developed by 

RealNetworks to improve the transmission of digital 

media over RealNetworks servers. NeuralCast Technology 

uses a variety of protocols, introduces new techniques to 

correct errors in streaming signals, and uses telephone and 

satellite transmissions to coordinate server networks to 

optimize digital media transmission. 

neural network n. A type of artificial-intelligence system 

modeled after the neurons (nerve cells) in a biological nervous 

system and intended to simulate the way a brain processes 

information, learns, and remembers. A neural 

network is designed as an interconnected system of processing 

elements, each with a limited number of inputs and an 

output. These processing elements are able to “learn” by 

receiving weighted inputs that, with adjustment, time, and 

repetition, can be made to produce appropriate outputs. 

Neural networks are used in areas such as pattern recognition, 

speech analysis, and speech synthesis. See also artificial 

intelligence (definition 1), pattern recognition. 

newbie n. 1. An inexperienced user on the Internet. 2. In 

a particularly derogatory sense, an inexperienced Usenet 

user who asks for information that is readily available in 

the FAQ. See also FAQ. 

newline character n. A control character that causes the 

cursor on a display or the printing mechanism on a printer 

to move to the beginning of the next line. It is functionally 

equivalent to a combination of the carriage return (CR) 

and linefeed (LF) characters. Acronym: NL. See also carriage 

return, linefeed. 

news n. The Internet protocol for retrieving files from an 

Internet newsgroup. You can create hyperlinks to newsgroups 

using news://.

news.announce.newusers NiCad battery 

news.announce.newusers n. A newsgroup that contains 

general information for new users about using Internet 

newsgroups. 

newsfeed or news feed n. Deliveries, exchanges, or distributions 

of newsgroup articles to and from news servers. 

Newsfeeds are accomplished through cooperating news 

servers, which communicate via NNTP through network 

connections. Also called: feed. See also newsgroup, news 

server, NNTP. 

newsgroup n. A forum on the Internet for threaded discussions 

on a specified range of subjects. A newsgroup 

consists of articles and follow-up posts. An article with all 

of its follow-up posts—which are (supposed to be) related 

to the specific subject named in the original article’s subject 

line—constitutes a thread. Each newsgroup has a 

name that consists of a series of words, separated by periods, 

indicating the newsgroup’s subject in terms of 

increasingly narrow categories, such as rec.crafts.textiles.needlework. 

Some newsgroups can be read and 

posted to only on one site; others, such as those in the 

seven Usenet hierarchies or those in ClariNet, circulate 

throughout the Internet. See also article, bit. newsgroups, 

ClariNet, follow-up, Great Renaming, local newsgroups, 

mail reflector, threaded discussion, traditional newsgroup 

hierarchy, Usenet. Compare mailing list. 

newsmaster n. The person in charge of maintaining the 

Internet news server at a particular host. Sending e-mail to 

“newsmaster@domain.name” is the standard way to reach 

a given newsmaster. 

news. newsgroups n. Usenet newsgroups that are part of 

the news. hierarchy and begin with “news.” These newsgroups 

cover topics that deal with Usenet itself, such as 

Usenet policy and the creation of new Usenet newsgroups. 

See also newsgroup, traditional newsgroup hierarchy, 

Usenet. Compare comp. newsgroups, misc. newsgroups, 

rec. newsgroups, sci. newsgroups, soc. newsgroups, talk. 

newsgroups. 

.newsrc n. The file extension that identifies a setup file 

for UNIX-based newsreaders. The setup file typically contains 

a current list of newsgroups that the user subscribes 

to and the articles in each newsgroup that the user has 

already read. See also newsreader, setup (definition 2). 

newsreader n. A Usenet client program that enables a 

user to subscribe to Usenet newsgroups, read articles, post 

follow-ups, reply by e-mail, and post articles. Many Web 

browsers also provide these functions. See also article, 

365 

e-mail (definition 1), follow-up, newsgroup, Usenet, Web 

browser. 

news server n. A computer or program that exchanges 

Internet newsgroups with newsreader clients and other 

servers. See also newsgroup, newsreader. 

Newton n. A personal digital assistant (PDA) developed 

by Apple Computer, Inc. See also PDA. 

Newton OS n. The operating system that controls the 

Newton MessagePad personal digital assistant (PDA). See 

also PDA. 

NeXT n. A computer designed and produced by NeXT 

Computer, Inc. (later NeXT Software, Inc.), a computer 

manufacturer and software developer founded in 1985 by 

Steven Jobs. NeXT was purchased by Apple Computer in 

1997. 

Next Generation Internet n. An initiative funded by the 

U.S. federal government designed to develop faster, more 

powerful networking technologies than are available on 

the current global Internet. The Next Generation Internet, 

or NGI, was begun in 1997 under the auspices of a number 

of government agencies, including DARPA (Defense 

Advanced Research Projects Agency), NASA (National 

Aeronautics & Space Administration), and the NSF 

(National Science Foundation). Its objective is to develop 

advanced networking technologies and to demonstrate 

them on university and government test networks running 

100 to 1000 times faster than the current Internet. The 

technologies developed are intended for eventual use by 

schools, businesses, and the general public. Acronym: 

NGI. Compare Internet, Internet2. 

NFS n. Acronym for Network File System. A distributed 

file system that allows users to access remote files and 

directories on a network as if they were local. NFS is compatible 

with Microsoft Windows and UNIX-based systems, 

including Linux and Mac OS X. 

NGI n. See Next Generation Internet. 

nibble or nybble n. Half a byte (4 bits). Compare quadbit. 

NIC n. 1. See network interface card. 2. Acronym for network 

information center. An organization that provides 

information about a network and other support to users of 

the network. The principal NIC for the Internet is Inter- 

NIC. Intranets and other private networks may have their 

own NICs. See also InterNIC. 

NiCad battery n. See nickel cadmium battery. 

N

N 

NIC handle node 

NIC handle n. See handle. 

nickel cadmium battery n. A rechargeable battery that 

uses an alkaline electrolyte. Nickel cadmium batteries typically 

have a longer operating life and storage life than 

similar lead-acid batteries. Also called: NiCad battery. 

Compare lead ion battery, lithium ion battery, nickel metal 

hydride battery. 

nickel metal hydride battery n. A rechargeable battery 

that offers longer life and superior performance compared 

with similar nickel cadmium or other alkaline batteries. 

Also called: NiMH battery. Compare lead ion battery, 

lithium ion battery, nickel cadmium battery. 

nickname n. A name used in the destination field of an 

e-mail editor in place of one or more complete network 

addresses. For example “Fred” might be a nickname for 

fred@history.washington.edu. If the nickname has been 

established within the program, a user need only type 

“Fred” instead of the entire address, or perhaps “history 

faculty” instead of all the individual faculty addresses. See 

also alias (definition 2). 

NIDS n. Acronym for network-based intrusion-detection 

System. A type of intrusion detection system (IDS) that 

analyzes the individual packets moving across a network. 

NIDS can detect packets that a firewall might not catch. 

See also IDS. 

NII n. See National Information Infrastructure. 

nil pointer n. See null pointer. 

Nimda worm n. A persistent worm that can slow or freeze 

mail servers, take control of Web pages, and infect systems 

through several different means. The Nimda worm 

spreads as an attached file through e-mail, through an 

Internet scan for vulnerable Web servers, through a Java- 

Script on an infected Web page, or through network sharing. 

The Nimda worm first appeared in 2001, with several 

variants following the original version. 

NiMH battery n. See nickel metal hydride battery. 

nine’s complement n. A number in the base-10 (decimal) 

system that is the complement of another number. It 

is derived by subtracting each digit of the number to be 

complemented from 1 less than the base. For example, the 

nine’s complement of 64 is 35—the number derived by 

subtracting 6 from 9 and 4 from 9. See also complement. 

NIS n. Acronym for Network Information Service. See 

Yellow Pages (definition 1). 

366 

NIST n. See National Institute of Standards and Technology. 

*NIX n. Slang for any UNIX-related operating system, or 

all UNIX-related operating systems. *NIX typically refers 

to UNIX and Linux, and may also include Mac OS X. 

nixpub n. A list of ISPs (Internet service providers) available 

in the newsgroups comp.bbs.misc and alt.bbs. See 

also ISP. 

NKE n. Acronym for Network Kernel Extension. A modification 

or extension of the Mac OS X networking infrastructure. 

NKEs may be loaded or unloaded dynamically, 

without recompiling the kernel or without the need to 

reboot the system. NKEs allow the creation and configuration 

of protocol stacks and modules that may monitor or 

modify network traffic or add other networking features to 

the kernel. 

NL n. See newline character. 

NLQ n. See near-letter-quality. 

NLS n. See natural language support. 

NMI n. See nonmaskable interrupt. 

NMOS or N-MOS n. Acronym for N-channel metal-oxide 

semiconductor. A semiconductor technology in which the 

conduction channel in MOSFETs is formed by the movement 

of electrons rather than holes (electron “vacancies” 

created as electrons move from atom to atom). Because 

electrons move faster than holes, NMOS is faster than 

PMOS, although it is more difficult and more expensive to 

fabricate. See also MOS, MOSFET, N-type semiconductor. 

Compare CMOS, PMOS. 

NNTP n. Acronym for Network News Transfer Protocol. 

A de facto protocol standard on the Internet used to distribute 

news articles and query news servers. 

NOC n. See network operation center. 

node n. 1. A junction of some type. 2. In networking, a 

device, such as a client computer, a server, or a shared 

printer, that is connected to the network and is capable of 

communicating with other network devices. 3. In tree 

structures, a location on the tree that can have links to 

one or more nodes below it. Some authors make a distinction 

between node and element, with an element 

being a given data type and a node comprising one or 

more elements as well as any supporting data structures. 

See also element (definition 1), graph, pointer (definition 

1), queue, stack, tree.

noise NO-OP 

noise n. 1. Any interference that affects the operation of a 

device. 2. Unwanted electrical signals, produced either 

naturally or by the circuitry, that distort or degrade the 

quality or performance of a communications channel. See 

also distortion. 

nonbreaking space n. A character that replaces the 

standard space character in order to keep two words 

together on one line rather than allowing a line to break 

between them. 

noncompetes n. An agreement between employer and 

employee that states that the employee will not accept 

work with a competing company for a specified length of 

time after leaving the employer’s company. Noncompete 

agreements are common in high-tech companies and are 

typically requested to help maintain company secrets and 

retain valuable employees. 

nonconductor n. See insulator. 

noncontiguous data structure n. In programming, a 

data structure whose elements are not stored contiguously 

in memory. Data structures such as graphs and trees, whose 

elements are connected by pointers, are noncontiguous data 

structures. Compare contiguous data structure. 

nondedicated server n. A computer on a network that 

can function as both a client and a server; typically, a 

desktop machine on a peer-to-peer network. Compare 

dedicated server. 

nondestructive readout n. A reading operation that 

does not destroy the data read, either because the storage 

technology is capable of retaining the data or because the 

reading operation is accompanied by a data refresh 

(update) function. Acronym: NDR, NDRO. Compare 

destructive read. 

nonexecutable statement n. 1. A program statement 

that cannot be executed because it lies outside the flow of 

execution through the program. For example, a statement 

immediately following a return() statement but before the 

end of the block in C is nonexecutable. 2. A type definition, 

variable declaration, preprocessor command, comment, 

or other statement in a program that is not translated 

into executable machine code. 

nonimpact printer n. Any printer that makes marks on 

the paper without striking it mechanically. The most common 

types are ink-jet, thermal, and laser printers. See also 

ink-jet printer, laser printer, thermal printer. Compare 

impact printer. 

367 

noninterlaced adj. Pertaining to a display method on raster-scan 

monitors in which the electron beam scans each 

line of the screen once during each refresh cycle. Compare 

interlaced. 

nonmaskable interrupt n. A hardware interrupt that 

bypasses and takes priority over interrupt requests generated 

by software and by the keyboard and other such 

devices. A nonmaskable interrupt cannot be overruled 

(masked) by another service request and is issued to the 

microprocessor only in disastrous circumstances, such as 

severe memory errors or impending power failures. Acronym: 

NMI. Compare maskable interrupt. 

nonprocedural language n. A programming language 

that does not follow the procedural paradigm of executing 

statements, subroutine calls, and control structures 

sequentially but instead describes a set of facts and relationships 

and then is queried for specific results. Compare 

procedural language. 

nonreturn to zero n. 1. In data transmission, a method of 

encoding data in which the signal representing binary digits 

alternates between positive and negative voltage when 

there is a change in digits from 1 to 0 or vice versa. In 

other words, the signal does not return to a zero, or neutral, 

level after transmission of each bit. Timing is used to 

distinguish one bit from the next. 2. In the recording of 

data on a magnetic surface, a method in which one magnetic 

state represents a 1 and, usually, the opposite state 

represents a 0. Acronym: NRZ. 

nontrivial adj. Being either difficult or particularly meaningful. 

For example, a complicated programmed procedure 

to handle a difficult problem would represent a 

nontrivial solution. 

Non-Uniform Memory Access n. See NUMA. 

nonuniform memory architecture n. A system architecture 

designed for Sequent’s Non-Uniform Access 

Memory, a type of distributed shared memory using a 

number of shared memory segments instead of a single 

centralized physical memory. Acronym: NUMA. 

nonvolatile memory n. A storage system that does not 

lose data when power is removed from it. Intended to refer 

to core memory, ROM, EPROM, flash memory, bubble 

memory, or battery-backed CMOS RAM, the term is occasionally 

used in reference to disk subsystems as well. See 

also bubble memory, CMOS RAM, core, EPROM, flash 

memory, ROM. 

NO-OP n. See no-operation instruction. 

N

N 

no-operation instruction NPN transistor 

no-operation instruction n. A machine instruction that 

has no results other than to cause the processor to use up 

clock cycles. Such instructions are useful in certain situations, 

such as padding out timing loops or forcing subsequent 

instructions to align on certain memory boundaries. 

Acronym: NO-OP, NOP. See also machine instruction. 

NOP n. See no-operation instruction. 

NOR gate n. Short for NOT OR gate. A digital circuit 

whose output is true (1) only if all inputs are false (0). A 

NOR gate is an OR circuit (output with the value of 1 if 

any input value is 1) followed by a NOT circuit (output 

that is the logical complement of the input). See also gate 

(definition 1), NOT gate, OR gate. 

normal distribution n. In statistics, a type of function 

that describes the probabilities of the possible values of a 

random variable. The function, whose graph is the familiar 

bell-shaped curve, can be used to determine the probability 

that the value of the variable will fall within a particular 

interval of values. 

normal form n. 1. In a relational database, an approach to 

structuring (organizing) information in order to avoid 

redundancy and inconsistency and to promote efficient 

maintenance, storage, and updating. Several “rules” or 

levels of normalization are accepted, each a refinement of 

the preceding one. Of these, three forms are commonly 

used: first normal (1NF), second normal (2NF), and third 

normal (3NF). First normal forms, the least structured, are 

groups of records (such as employee lists) in which each 

field (column) contains unique and nonrepeating information. 

Second and third normal forms break down first normal 

forms, separating them into different tables by 

defining successively finer interrelationships between 

fields. Second normal forms do not include fields that are 

subsets of fields other than the primary (key) field; for 

example, a second normal form keyed to employee name 

would not include both job grade and hourly rate if pay 

were dependent on job grade. Third normal forms do not 

include fields that provide information about fields other 

than the key field; for example, a third normal form keyed 

to employee name would not include project name, crew 

number, and supervisor unless the crew number and supervisor 

were assigned only to the project the employee was 

working on. Further normalization refinements include 

Boyce-Codd Normal Form (BCNF), fourth normal form 

(4NF), and projection-join (or fifth) normal form (PJ/NF 

or 5NF). These levels, however, are not as commonly used 

as the first, second, and third normal forms. 2. In program- 

368 

ming, the metalanguage sometimes called the Backus normal 

form (Backus-Naur form)—a language used for 

describing the syntax of other languages, specifically 

ALGOL 60, for which it was invented. See also Backus- 

Naur form. 

normal hyphen n. See hyphen. 

normalize vb. 1. In programming, to adjust the fixedpoint 

and exponent portions of a floating-point number to 

bring the fixed-point portions within a specific range. 2. In 

database management, to apply a body of techniques to a 

relational database in order to minimize the inclusion of 

duplicate information. Normalization greatly simplifies 

query and update management, including security and 

integrity considerations, although it does so at the expense 

of creating a larger number of tables. See also normal 

form (definition 1). 

North American Cellular Network n. Telecommunications 

network that enables wireless phone users in North 

America to send and receive calls when roaming outside 

their service area. Acronym: NACN. 

NOS n. See network operating system. 

NOT n. An operator that performs Boolean or logical 

negation. See also Boolean operator, logical operator. 

NOT AND n. See NAND. 

notation n. In programming, the set of symbols and formats 

used to describe the elements of programming, mathematics, 

or a scientific field. A language’s syntax is 

defined in part by notation. See also syntax. 

notebook computer n. See portable computer. 

NOT gate n. One of the three basic logic gates (with 

AND and OR) from which all digital systems can be built. 

The NOT circuit, also referred to as an inverter, has output 

that is the reverse of its input—that is, the output is true 

(1) if the input is false (0) and false (0) if the input is true 

(1). See also AND gate, gate (definition 1), OR gate. 

notification n. A signal from the operating system that an 

event has occurred. 

Novell Directory Services n. See NDS. 

Novell NetWare n. See NetWare. 

NPN transistor n. A type of transistor in which a base of 

P-type material is sandwiched between an emitter and a 

collector of N-type material. The base, emitter, and collector 

are the three terminals through which current flows. In

NQL NTSC 

an NPN transistor, electrons represent the majority of the 

charge carriers, and they flow from the emitter to the collector. 

See the illustration. See also N-type semiconductor, 

P-type semiconductor. Compare PNP transistor. 

F0ngn02.eps 

NPN transistor. 

Internal diagram 

Emitter Collector 

Base 

Schematic diagram 

Base 

Collector 

Emitter 

NQL n. See Network Query Language. 

NRZ n. See nonreturn to zero. 

ns n. See nanosecond. 

NSAPI n. Acronym for Netscape Server Application 

Programming Interface. A specification for interfaces 

between the Netscape HTTP server and other application 

programs. NSAPI can be used to provide access to application 

programs from a Web browser through a Web 

server. See also HTTP server (definition 1), Web browser. 

NSF n. See National Science Foundation. 

NSFnet n. Short for the National Science Foundation Network. 

A WAN (wide area network), developed by the 

National Science Foundation to replace ARPANET for 

civilian purposes. NSFnet served as a major backbone for 

the Internet until mid-1995. Backbone services in the 

United States for the Internet are now provided by commercial 

carriers. See also ARPANET, backbone (definition 1). 

NSFnet Network Information Center n. See InterNIC. 

NSI n. Acronym for Network Solutions, Inc. The organization 

responsible, since 1992, for registering top-level 

369 

Internet domain names and maintaining the authoritative 

(“A”) database of top-level domains replicated daily on 12 

other root servers on the Internet. In 1998, with the privatization 

of Internet administration, the functions performed 

by NSI (under cooperative agreement with the U.S. 

National Science Foundation) became the responsibility of 

ICANN, a new, nonprofit organization. NSI remains 

active, but its association with the U.S. government 

entered the “ramping down” phase in 1998/1999. See also 

IANA, ICANN. 

NT n. See Windows NT. 

NT-1 n. See Network Terminator 1. 

NT file system n. See NTFS. 

NTFS n. Acronym for NT file system. An advanced file 

system designed for use specifically with the Windows NT 

operating system. It supports long filenames, full security 

access control, file system recovery, extremely large storage 

media, and various features for the Windows NT 

POSIX subsystem. It also supports object-oriented applications 

by treating all files as objects with user-defined 

and system-defined attributes. See also FAT file system, 

HPFS, POSIX. 

NTLM authentication protocol n. A challenge/response 

authentication protocol. The NTLM authentication protocol 

was the default for network authentication in Windows 

NT version 4.0 and earlier and Windows Millennium Edition 

(Windows Me) and earlier. The protocol continues to 

be supported in Windows 2000 and Windows XP but no 

longer is the default. See also Kerberos. 

NTP n. Acronym for Network Time Protocol. A protocol 

used for synchronizing the system time on a computer to 

that of a server or other reference source such as a radio, 

satellite receiver, or modem. NTP provides time accuracy 

within a millisecond on local area networks and a few tens 

of milliseconds on wide area networks. NTP configurations 

may utilize redundant servers, diverse network paths, 

and cryptographic authentication to achieve high accuracy 

and reliability. 

NTSC n. Acronym for National Television System (later 

changed to Standards) Committee. The standards-setting 

body for television and video in the United States. It is 

the sponsor of the NTSC standard for encoding color, a 

coding system compatible with black-and-white signals 

and the system used for color broadcasting in the United 

States. 

N

N 

N-type semiconductor NUMA 

N-type semiconductor n. Semiconductor material in 

which electrical conduction is carried by electrons, in contrast 

to P-type semiconductors, in which conduction is carried 

by holes—that is, electron “vacancies.” N-type 

semiconductors are created by adding a dopant with an 

excess of electrons during the manufacturing process. See 

also semiconductor. Compare P-type semiconductor. 

NuBus n. A high-performance expansion bus used in 

Macintosh computers, offering high bandwidth and multiple 

bus controllers. Invented at the Massachusetts Institute 

of Technology (MIT), NuBus was eventually licensed to 

Texas Instruments and other companies. See also bus. 

nudge vb. To move an object one pixel at a time. 

nuke vb. 1. To erase a file, directory, or entire hard disk. 

2. To stop a process in an operating system, an application, 

or a program. Also called: kill. 

NUL n. 1. A character code with a null value; literally, a 

character meaning “nothing.” Although it is real in the 

sense of being recognizable, occupying space internally in 

the computer, and being sent or received as a character, a 

NUL character displays nothing, takes no space on the 

screen or on paper, and causes no specific action when 

sent to a printer. In ASCII, NUL is represented by the 

character code 0. See also ASCII. 2. A “device,” recognized 

by the operating system, that can be addressed like a 

physical output device (such as a printer) but that discards 

any information sent to it. 

null character n. See NUL. 

null cycle n. The shortest amount of time required for 

execution of a program; the time needed to cycle through 

the program without requiring it to process new data or 

loop through sets of instructions. 

null modem n. A way of connecting two computers via a 

cable that enables them to communicate without the use of 

modems. A null modem cable accomplishes this by crossing 

the sending and receiving wires so that the wire used 

for transmitting by one device is used for receiving by the 

other and vice versa. See the illustration. 

370 

Female 

DB25 

2 

3 

7 

Pin 

number 

Female 

DB25 

2 

3 

7 

Pin 

number 

Female 

DB25 

2 

3 

7 

Pin 

number 

Female 

DB9 

2 

3 

5 

Pin 

number 

Female 

DB9 

F0ngn03.eps 

Null modem. Null modem cable-wiring schematics for IBM 

PC-compatible computers. 

null modem cable n. A serial data cable used to connect 

two personal computers, without a modem or other DCE 

device in between, through the computers’ serial ports. 

Because both computers use the same pins to send data, a 

null modem cable connects the output pins in one computer’s 

serial port to the input pins in the other. A null 

modem cable is used to transfer data between two personal 

computers in close proximity. See also serial port. 

null pointer n. A pointer to nothing—usually a standardized 

memory address, such as 0. A null pointer usually 

marks the last of a linear sequence of pointers or indicates 

that a data search operation has come up empty. Also 

called: nil pointer. See also pointer (definition 1). 

null string n. A string containing no characters; a string 

whose length is zero. See also string. 

null-terminated string n. See ASCIIZ string. 

NUMA n. Acronym for Non-Uniform Memory Access. A 

multiprocessing architecture that manages memory 

according to its distance from the processor. Banks of 

memory at various distances require different amounts of 

access time, with local memory accessed faster than 

remote memory. See also SMP. 

2 

3 

5 

Pin 

number 

Female 

DB9 

2 

3 

5 

Pin 

number 

Female 

DB9 

2 

3 

5 

Pin 

number 

Female 

DB25 

2 

3 

7 

Pin 

number

number cruncher nybble 

number cruncher n. 1. A computer that is able to quickly 

perform large amounts of mathematical computations. 

2. A powerful workstation. 3. A program whose main task 

is to perform mathematical computations—for example, a 

statistical program. 4. A person who uses a computer to 

analyze numbers. 

number crunching vb. The calculation of large amounts 

of numeric data. Number crunching can be repetitive, 

mathematically complex, or both, and it generally involves 

far more internal processing than input or output functions. 

Numeric coprocessors greatly enhance the ability of 

computers to perform these tasks. 

numerical analysis n. The branch of mathematics 

devoted to finding ways to solve abstract mathematical 

problems and finding concrete or approximate solutions 

for them. 

numeric coprocessor n. See floating-point processor. 

numeric keypad n. A calculator-style block of keys, usually 

at the right side of a keyboard, that can be used to 

enter numbers. In addition to keys for the digits 0 through 

9 and keys for indicating addition, subtraction, multiplication, 

and division, a numeric keypad often includes an 

Enter key (usually not the same as the Enter or Return key 

on the main part of the keyboard). On Apple keyboards, 

the numeric keypad also includes a Clear key that usually 

functions like the Backspace key for deleting characters. 

In addition, many of the keys can serve dual purposes, 

such as cursor movement, scrolling, or editing tasks, 

depending on the status of the Num Lock key. See the 

illustration. See also Num Lock key. 

Num 

Lock 

7 

Home 

1 

End 

/ * - 

4 5 6 

0 

Ins 

2 3 

PgDn 

. 

Del 

F0ngn04.eps 

Numeric keypad. 

Numeric Keypad 

8 9 

PgUp 

+ 

Enter 

371 

numeric messaging n. Service that enables wireless 

phones and pagers to receive messages consisting only of 

numeric information, such as phone numbers. 

numeric paging n. See numeric messaging. 

Num Lock key n. Short for Numeric Lock key. A toggle 

key that, when turned on, activates the numeric keypad so 

that its keys can be used for calculator-style data entry. 

When the Num Lock key is toggled off, most of the 

numeric keypad keys are used for cursor movement and 

on-screen scrolling. See also numeric keypad. 

NVM n. Acronym for Non-Volatile Memory. Memory 

that persists in its state when the power is removed. Also 

called: Flash memory. 

NVRAM n. Acronym for Non-Volatile Random Access 

Memory. Non-volatile read/write memory or normally 

volatile memory that has been fitted with a battery backup 

to retain data. See also NVM. 

NWLink n. An implementation of the Internetwork Packet 

Exchange (IPX), Sequenced Packet Exchange (SPX), and 

NetBIOS protocols used in Novell networks. NWLink is a 

standard network protocol that supports routing and can 

support NetWare client-server applications, where Net- 

Ware-aware Sockets-based applications communicate 

with IPX/SPX Sockets-based applications. See also IPX/ 

SPX, NetBIOS, RIPX. 

nybble n. See nibble. 

N

O 

OAGI n. Acronym for Open Applications Group, Inc. A 

nonprofit consortium of software vendors and businesses 

created to develop and define XML-based interoperability 

specifications and standards among enterprise-scale applications. 

The OAGI was formed in 1995 by a small number 

of business enterprise software companies and organizations 

and has grown to more than sixty member companies. 

OAGIS n. Acronym for Open Applications Group Integration 

Specification. A set of XML-based specifications 

and standards designed to promote B2B e-commerce by 

providing interoperability between enterprise-scale applications 

and between companies. OAGIS includes business 

document specifications and definitions, business process 

scenarios, and templates for business forms such as 

invoices and requisitions. OAGIS is overseen by the Open 

Applications Group, Inc., a nonprofit consortium of software 

vendors and customers. See also OAGI. 

OASIS n. Acronym for Organization for the Advancement 

of Structured Information Standards. A consortium of 

technology companies formed to develop guidelines for 

use of XML (Extensible Markup Language) and related 

information standards. 

Oberon n. An extensible object-oriented language based 

on Modula-2, whose later versions support the .NET 

Framework. Also called: Active Oberon for .NET. 

object n. 1. Short for object code (machine-readable 

code). 2. In object-oriented programming, a variable comprising 

both routines and data that is treated as a discrete 

entity. See also abstract data type, module (definition 1), 

object-oriented programming. 3. In graphics, a distinct 

entity. For example, a bouncing ball might be an object in 

a graphics program. 4. A single, runtime instance of object 

type that the operating system defines. Objects visible in 

user mode include event, file, I/O completion port, key, 

object directory, port, process, section, semaphore, symbolic 

link, thread, timer, and token objects. Many usermode 

objects are implemented through the use of a corresponding 

kernel-mode object. Kernel-mode-only objects 

O 

372 

include adapter, APC, controller, device, device queue, 

DPC, driver, interrupt, mutex, and stream file objects. 

object code n. The code, generated by a compiler or an 

assembler, that was translated from the source code of a 

program. The term most commonly refers to machine 

code that can be directly executed by the system’s central 

processing unit (CPU), but it can also be assembly language 

source code or a variation of machine code. See 

also central processing unit. 

object computer n. The computer that is the target of a 

specific communications attempt. 

object database n. See object-oriented database. 

Object Database Management Group n. An organization 

that promotes standards for object databases and 

defines interfaces to object databases. Acronym: ODMG. 

See also OMG. 

object file n. A file containing object code, usually the 

output of a compiler or an assembler and the input for a 

linker. See also assembler, compiler (definition 2), linker, 

object code. 

Objective-C n. An object-oriented version of the C language 

developed in 1984 by Brad Cox. It is most widely 

known for being the standard development language for 

the NeXT operating system. See also object-oriented programming. 

object linking and embedding n. See OLE. 

Object Management Architecture n. See OMA. 

Object Management Group n. See OMG. 

object model n. 1. The structural foundation for an 

object-oriented language, such as C++. This foundation 

includes such principles as abstraction, concurrency, 

encapsulation, hierarchy, persistence, polymorphism, and 

typing. See also abstract data type, object (definition 2), 

object-oriented programming, polymorphism. 2. The 

structural foundation for an object-oriented design. See 

also object-oriented design. 3. The structural foundation 

for an object-oriented application.

object module OCR 

object module n. In programming, the object-code (compiled) 

version of a source-code file that is usually a collection 

of routines and is ready to be linked with other object 

modules. See also linker, module (definition 1), object code. 

object-oriented adj. Of, pertaining to, or being a system 

or language that supports the use of objects. See also 

object (definition 2). 

object-oriented analysis n. A procedure that identifies 

the component objects and system requirements of a system 

or process that involves computers and describes how 

they interact to perform specific tasks. The reuse of existing 

solutions is an objective of this sort of analysis. 

Object-oriented analysis generally precedes object-oriented 

design or object-oriented programming when a new 

object-oriented computer system or new software is developed. 

See also object (definition 2), object-oriented 

design, object-oriented programming. 

object-oriented database n. A flexible database that 

supports the use of abstract data types, objects, and classes 

and that can store a wide range of data, often including 

sound, video, and graphics, in addition to text and numbers. 

Some object-oriented databases allow data retrieval 

procedures and rules for processing data to be stored along 

with the data or in place of the data. This allows the data to 

be stored in areas other than in the physical database, 

which is often desirable when the data files are large, such 

as those for video files. Acronym: OODB. See also 

abstract data type, class, object (definition 2). Compare 

relational database. 

object-oriented design n. A modular approach to creating 

a software product or computer system, in which the 

modules (objects) can be easily and affordably adapted to 

meet new needs. Object-oriented design generally comes 

after object-oriented analysis of the product or system and 

before any actual programming. See also object (definition 

2), object-oriented analysis. 

object-oriented graphics n. Computer graphics that are 

based on the use of graphics primitives, such as lines, 

curves, circles, and squares. Object-oriented graphics, 

used in applications such as computer-aided design and 

drawing and illustration programs, describe an image 

mathematically as a set of instructions for creating the 

objects in the image. This approach contrasts with the use 

of bitmapped graphics, in which a graphic is represented 

as a group of black-and-white or colored dots arranged in 

a certain pattern. Object-oriented graphics enable the user 

to manipulate objects as units. Because objects are 

373 

described mathematically, object-oriented graphics can be 

layered, rotated, and magnified relatively easily. Also 

called: structured graphics. See also graphics primitive. 

Compare bitmapped graphics, paint program. 

object-oriented interface n. A user interface in which 

elements of the system are represented by visible screen 

entities, such as icons, that are used to manipulate the system 

elements. Object-oriented display interfaces do not 

necessarily imply any relation to object-oriented programming. 

See also object-oriented graphics. 

object-oriented operating system n. An operating 

system based on objects and designed in a way that facilitates 

software development by third parties, using an objectoriented 

design. See also object (definition 2), object-oriented 

design. 

object-oriented programming n. A programming paradigm 

in which a program is viewed as a collection of discrete 

objects that are self-contained collections of data 

structures and routines that interact with other objects. 

Acronym: OOP. See also C++, object (definition 2), 

Objective-C. 

Object Pascal n. An object-oriented derivative of Pascal. 

See also Pascal. 

object-relational server n. A database server that supports 

object-oriented management of complex data types 

in a relational database. See also database server, relational 

database. 

object request broker n. See ORB. 

object wrapper n. In object-oriented applications, a 

means of encapsulating a set of services provided by a 

non-object-oriented application so that the encapsulated 

services can be treated as an object. See also object (definition 

2). 

oblique adj. Describing a style of text created by slanting 

a roman font to simulate italics when a true italic font isn’t 

available on the computer or printer. See also font, italic, 

roman. 

OC3 n. Short for optical carrier 3. One of several optical 

signal circuits used in the SONET high-speed fiberoptic 

data transmission system. OC3 carries a signal of 155.52 

Mbps, the minimum transmission speed for which 

SONET and the European standard, SDH, are fully 

interoperable. See also SONET. 

OCR n. See optical character recognition. 

O

O 

octal office automation 

octal n. The base-8 number system consisting of the digits 

0 through 7, from the Latin octo, meaning “eight.” The octal 

system is used in programming as a compact means of representing 

binary numbers. See also base (definition 2). 

octet n. A unit of data that consists of exactly 8 bits, 

regardless of the number of bits a computer uses to represent 

a small amount of information such as a character. 

Compare byte. 

OCX n. Short for OLE custom control. A software module 

based on OLE and COM technologies that, when called by 

an application, produces a control that adds some desired 

feature to the application. OCX technology is portable 

across platforms, works on both 16-bit and 32-bit operating 

systems, and can be used with many applications. It is 

the successor to VBX (Visual Basic custom control) technology, 

which supported only Visual Basic applications, 

and is the basis for ActiveX controls. OCXs have, in fact, 

been superseded by ActiveX controls, which are much 

smaller and therefore work much better over the Internet. 

See also ActiveX control, COM (definition 2), control 

(definition 2), OLE, VBX, Visual Basic. 

ODBC n. Acronym for Open Database Connectivity. In 

the Microsoft WOSA (Windows Open System Architecture) 

structure, an interface providing a common language 

for Windows applications to gain access to a database on a 

network. See also WOSA. 

ODBC driver n. Short for Open Database Connectivity 

driver. A program file used to connect to a particular 

database. Each database program, such as Access or 

dBASE, or database management system, such as SQL 

Server, requires a different driver. 

ODBMG n. See Object Database Management Group. 

odd parity n. See parity. 

ODI n. Acronym for Open Data-link Interface. A specification 

developed by Novell to enable a network interface 

card (NIC) to support multiple protocols, such as TCP/IP 

and IPX/SPX. ODI also simplifies development of device 

drivers by eliminating concern about the particular protocol 

to be used in transferring information over the network. 

ODI is comparable in some ways to the Network 

Driver Interface Specification, or NDIS. See also NDIS, 

network adapter. 

ODMA n. Acronym for Open Document Management 

API. A specification for a standard application program 

interface that enables desktop applications, such as 

374 

Microsoft Word, to interact seamlessly with specialized 

document management systems (DMS) installed on network 

servers. The ODMA specification is the property of 

the Association for Information & Image Management 

(AIIM). See also API, document management system. 

OEM n. See original equipment manufacturer. 

OFC n. See Open Financial Connectivity. 

Office n. Microsoft’s family of individual and business 

application software suites for the Windows and Macintosh 

platforms. Office is built around three core products: Word 

for word processing, Excel for spreadsheets, and Outlook 

for e-mail and collaboration. Office XP, the most recent 

version for the Windows platform, is available in several 

versions: the Office XP Standard or Standard for Students 

and Teachers version, which includes Word, Excel, Outlook, 

and PowerPoint; the Office XP Professional version, 

which adds Access; Office XP Developer, which includes 

Word, Excel, Outlook, PowerPoint, Access, FrontPage, 

Microsoft’s new SharePoint Team Services collaboration 

and team Web solution, and Developer Tools; and finally, 

Office XP Professional Special Edition, which offers all the 

programs in Office XP Professional plus FrontPage, Share- 

Point Team Services, Publisher, and IntelliMouse Explorer. 

Office v. X for Mac is the most recent version for the Macintosh 

and includes Word, Entourage (for e-mail and collaboration), 

Excel, and PowerPoint. See the table. 

Table O.1 Application Specifications 

Product Function Platform 

Word Word processing Windows, 

Macintosh 

Excel Spreadsheets Windows, 

Macintosh 

Outlook E-mail, collaboration Windows 

Entourage E-mail, collaboration Macintosh 

Publisher Desktop publishing Windows 

Access Database management Windows 

PowerPoint Presentation graphics Windows, 

Macintosh 

FrontPage Web site creation Windows 

SharePoint 

Team Services Team Web solution Windows 

office automation n. The use of electronic and communications 

devices, such as computers, modems, and fax 

machines and any associated software, to perform office 

functions mechanically rather than manually.

offline OMG 

offline adj. 1. In reference to a computing device or a program, 

unable to communicate with or be controlled by a 

computer. Compare online (definition 1). 2. In reference 

to one or more computers, being disconnected from a network. 

Compare online (definition 2). 3. Colloquially, a 

reference to moving a discussion between interested parties 

to a later, more appropriate, time. For example, “We 

can talk about this offline. Let’s get back on topic now.” 

offline navigator n. Software designed to download email, 

Web pages, or newsgroup articles or postings from 

other online forums and save them locally to a disk, where 

they can be browsed without the user paying the cost of 

idle time while being connected to the Internet or an 

online information service. Also called: offline reader. 

offline reader n. See offline navigator. 

offline storage n. A storage resource, such as a disk, that 

is not currently available to the system. 

offload vb. To assume part of the processing demand from 

another device. For example, some LAN-attached gateways 

can offload TCP/IP processing from the host 

machine, thereby freeing up significant processing capacity 

in the CPU. See also central processing unit, gateway, 

host, TCP/IP. 

offset n. In relative addressing methods, a number that 

tells how far from a starting point a particular item is 

located. See also relative address. 

off-the-shelf adj. Ready-to-use; packaged. The term can 

refer to hardware or software. 

ohm n. The unit of measure for electrical resistance. A 

resistance of 1 ohm will pass 1 ampere of current when a 

voltage of 1 volt is applied. 

OLAP n. See OLAP database. 

OLAP database n. Short for online analytical processing 

database. A relational database system capable of handling 

queries more complex than those handled by standard 

relational databases, through multidimensional 

access to data (viewing the data by several different criteria), 

intensive calculation capability, and specialized 

indexing techniques. See also database, query (definition 

1), relational database. 

OLAP provider n. A set of software that provides access to 

a particular type of OLAP database. This software can 

include a data source driver and other client software that is 

necessary to connect to a database. See also OLAP database. 

375 

OLE n. Acronym for object linking and embedding. A 

technology for transferring and sharing information 

among applications. When an object, such as an image file 

created with a paint program, is linked to a compound 

document, such as a spreadsheet or a document created 

with a word processing program, the document contains 

only a reference to the object; any changes made to the 

contents of a linked object will be seen in the compound 

document. When an object is embedded in a compound 

document, the document contains a copy of the object; any 

changes made to the contents of the original object will 

not be seen in the compound document unless the embedded 

object is updated. 

OLED n. Acronym for Organic Light-Emitting Device. 

Technology developed for the production of thin, lightweight 

digital displays. An OLED features a series of thin 

organic films between two conductors. When current is 

applied, bright light is emitted. OLED displays are lightweight, 

durable, and power-efficient. 

OLE Database n. An application programming interface 

developed by Microsoft for accessing databases. OLE 

Database is an open specification that can interface with 

all types of data files on a computer network. Acronym: 

OLE DB. 

OLTP n. Acronym for online transaction processing. A 

system for processing transactions as soon as the computer 

receives them and updating master files immediately 

in a database management system. OLTP is useful in 

financial record keeping and inventory tracking. See also 

database management system, transaction processing. 


OM-1 n. See OpenMPEG Consortium. 

OMA n. Acronym for Object Management Architecture. 

A definition developed by the Object Management Group 

(OMG) for object-oriented distributed processing. OMA 

includes the Common Object Request Broker Architecture 

(CORBA). See also CORBA, OMG. 

OMG n. Acronym for Object Management Group. A nonprofit 

organization that provides a framework of standards 

for object-oriented interfaces. The open and nonproprietary 

architecture developed and managed by the OMG 

allows developers to work with a large toolkit of standard 

components in building applications with a solid common 

foundation. The OMG was formed in 1989 by a group of 

software developers and system vendors and now has 

more than six hundred member companies. 

O

O 

on-board computer online state 

on-board computer n. A computer that resides within 

another device. 

on-chip cache n. See L1 cache. 

on-demand publishing point n. A type of publishing 

point that streams content in such a way that the client can 

control (start, stop, pause, fast-forward, or rewind) the 

content. Typically, the on-demand content is a Windows 

Media file or a directory of files. Content streamed from 

an on-demand publishing point is always delivered as a 

unicast stream. Formerly called a station. 

one-off n. 1. A product that is produced one at a time, 

instead of being mass produced. 2. A CD-ROM created on 

a CD-R machine, which can create only one copy of a CD- 

ROM at a time. 

one-pass compiler n. A compiler that needs to read 

through a source file only once to produce the object code. 

The syntax of some languages makes it impossible to 

write a one-pass compiler for those languages. See also 

compiler (definition 2). 

one’s complement n. A number in the binary (base-2) 

system that is the complement of another number. See also 

complement. 

one-to-many relationship n. An association between 

two tables in which the primary key value of each record 

in the primary table corresponds to the value in the matching 

field or fields of many records in the related table. 

one-to-many replication n. A server configuration 

allowing replication of data from one or more large servers 

to a greater number of smaller servers. 

one-to-one relationship n. An association between two 

tables in which the primary key value of each record in the 

primary table corresponds to the value in the matching field 

or fields of one and only one record in the related table. 

one-way trust n. A type of trust relationship in which 

only one of the two domains trusts the other domain. For 

example, domain A trusts domain B and domain B does 

not trust domain A. All one-way trusts are nontransitive. 

See also transitive trust, two-way trust. 

onion routing n. An anonymous communication technique 

first developed by the U.S. Navy, in which a message 

is wrapped in layers of encryption and passed 

through several intermediate stations to obscure its point 

of origin. In onion routing, data packets are sent through a 

complex network of routers, each of which opens an anon- 

376 

ymous connection to the next, until it reaches its destination. 

When the packet is received by the first onion router, 

it is encrypted once for each additional router it will pass 

through. Each subsequent onion router unwraps one layer 

of encryption until the message reaches its destination as 

plain text. 

online adj. 1. In reference to a computing device or a program, 

activated and ready for operation; capable of communicating 

with or being controlled by a computer. 

Compare offline (definition 1). 2. In reference to one or 

more computers, connected to a network. Compare offline 

(definition 2). 3. In reference to a user, currently connected 

to the Internet, an online service, or a BBS or using 

a modem to connect to another modem. 4. In reference to 

a user, being able to connect to the Internet, an online service, 

or a BBS by virtue of having an account that gives 

one access. 

online analytical processing n. See OLAP database. 

online community n. 1. All users of the Internet and 

World Wide Web collectively. 2. A local community that 

places political forums on line for the discussion of local 

government or issues of public concern. 3. Members of a 

specific newsgroup, mailing list, MUD, BBS, or other 

online forum or group. See also BBS (definition 1), mailing 

list, MUD, newsgroup. 

online game n. A game that is meant to be played while 

connected to the Internet, intranet, or other network, with 

one or more other people simultaneously connected. 

Online games allow gamers to interact with other players 

without having their physical presence necessary. See also 

computer game. 

online help n. See help. 

online information service n. A business that provides 

access to databases, file archives, conferences, chat 

groups, and other forms of information through dial-up, or 

dedicated communications links, or through the Internet. 

Most online information services also offer access to the 

Internet connections along with their own proprietary services. 

The largest consumer online information services in 

the U.S. are America Online, CompuServe, and MSN. 

Online Privacy Alliance n. See OPA. 

online service n. See online information service. 

online state n. The state of a modem when it is communicating 

with another modem. Compare command state.

online transaction processing Open Profiling Standard 

online transaction processing n. See OLTP. 

on-screen keyboard n. An interactive keyboard that 

appears as a graphical image on the display screen of a 

computing device. A user spells words by tapping the letters 

on the screen with a stylus. On-screen keyboards 

appear primarily on personal digital assistants (PDAs) and 

other handheld computing devices that are too small to 

contain a traditional keyboard. 

on the fly adv. Doing a task or process as needed without 

suspending or disturbing normal operations. For example, 

it is often said that an HTML document can be edited on 

the fly because its content can be revised without the need 

to completely shut down or re-create the Web site on 

which it resides. See also HTML document, Web site. 

OO adj. See object-oriented. 

OOP n. See object-oriented programming. 

OPA n. Acronym for Online Privacy Alliance. An organization 

of over eighty Internet companies and trade associations 

created to be the voice of the industry on digital 

privacy issues. The OPA stresses the need for consumer 

trust and encourages online businesses to post privacy policies. 

The OPA created a set of guidelines for privacy policies 

that have become the industry standard. 

opacity n. The quality that defines how much light passes 

through an object’s pixels. If an object is 100 percent 

opaque, no light passes through it. 

opcode n. See operation code. 

open1 adj. Of, pertaining to, or providing accessibility. 

For example, an open file is one that can be used because a 

program has issued an open file command to the operating 

system. 

open2 vb. To make an object, such as a file, accessible. 

Open Applications Group, Inc. n. See OAGI. 

open architecture n. 1. Any computer or peripheral 

design that has published specifications. A published 

specification lets third parties develop add-on hardware 

for a computer or device. Compare closed architecture 

(definition 1). 2. A design that provides for expansion 

slots on the motherboard, thereby allowing the addition of 

boards to enhance or customize a system. Compare closed 

architecture (definition 2). 

OpenCyc n. An open source artificial intelligence platform. 

OpenCyc forms the foundation of knowledgedependent 

applications such as speech understanding, 

377 

database integration, and e-mail routing and prioritizing. 

OpenCyc development is administered through Open- 

Cyc.org. 

Open Data-link Interface n. See ODI. 

OpenDoc n. An object-oriented application programming 

interface (API) that enables multiple independent 

programs (component software) on several platforms to 

work together on a single document (compound document). 

Similar to OLE, OpenDoc allows images, sound, 

video, other documents, and other files to be embedded or 

linked to the document. OpenDoc is supported by an alliance 

that includes Apple, IBM, the Object Management 

Group, and the X Consortium. See also application programming 

interface, component software. Compare 

ActiveX, OLE. 

Open Document Management API n. See ODMA. 

open file n. A file that can be read from, written to, or 

both. A program must first open a file before the file’s 

contents can be used, and it must close the file when done. 

See also open2 . 

Open Financial Connectivity n. The Microsoft specification 

for an interface between electronic banking services 

and Microsoft Money personal finance software. 

Acronym: OFC. 

OpenGL n. An industry standard application programming 

interface (API) for 3D graphics rendering and 3D 

hardware acceleration. OpenGL is cross-platform and is 

available for all major operating systems. 

Open Group n. A consortium of computer hardware and 

software manufacturers and users from industry, government, 

and academia that is dedicated to the advancement 

of multi-vendor information systems. The Open Group 

was formed in 1996 as a consolidation of the Open Software 

Foundation and X/Open Company Limited. 

OpenMPEG Consortium n. An international organization 

of hardware and software developers for promoting 

the use of the MPEG standards. Acronym: OM-1. See also 

MPEG. 

Open Prepress Interface n. See OPI. 

Open Profiling Standard n. An Internet personalization 

and privacy specification submitted for consideration to 

the World Wide Web Consortium by Netscape Communications 

Corporation, Firefly Network, Inc., and VeriSign, 

Inc. Open Profiling Standard (OPS) enables users to customize 

online services while protecting their privacy. To 

O

O 

open shop operator associativity 

achieve personalization and privacy concomitantly, OPS is 

based on the concept of a Personal Profile, which is stored 

on the individual’s computer and contains the user’s 

unique identification, demographic and contact data, and 

possibly content preferences. This information remains 

under the user’s control and can be released wholly or in 

part to the requesting site. Acronym: OPS. See also 

cookie, digital certificate. 

open shop n. A computer facility that is open to users 

and not restricted to programmers or other personnel. An 

open shop is one in which people can work on or attempt 

to solve computer problems on their own rather than handing 

them over to a specialist. 

Open Shortest Path First n. See OSPF. 

Open Software Foundation n. See OSF. 

open source n. The practice of making the source code 

(program instructions) for a software product freely available, 

at no cost, to interested users and developers, even 

though they were not involved in creating the original 

product. The distributors of open source software expect 

and encourage users and outside programmers to examine 

the code in order to identify problems, and to modify the 

code with suggested improvements and enhancements. 

Widely used open source products include the Linux operating 

system and the Apache Web server. 

open standard n. A publicly available set of specifications 

describing the characteristics of a hardware device or 

software program. Open standards are published to 

encourage interoperability and thereby help popularize 

new technologies. See also standard (definition 2). 

open system n. 1. In communications, a computer network 

designed to incorporate all devices—regardless of 

the manufacturer or model—that can use the same communications 

facilities and protocols. 2. In reference to 

computer hardware or software, a system that can accept 

add-ons produced by third-party suppliers. See also open 

architecture (definition 1). 

Open Systems Interconnection reference model n. 

See ISO/OSI reference model. 

OpenType n. A collaborative initiative by Microsoft and 

Adobe to unify support for Microsoft TrueType and 

Adobe PostScript Type 1 fonts. The OpenType font format 

enables font creators and users to work with the font type 

that best suits their needs without having to worry about 

378 

whether the font is based on TrueType or PostScript technology. 

Also called: TrueType Open version 2. See also 

PostScript font, TrueType. 

Opera n. A Web browser developed by Opera Software 

S/A. Opera is notable for its strict W3C standards support. 

Opera is often chosen by Web developers to test Web 

sites for W3C compliance. See also W3C, Web browser. 

operand n. The object of a mathematical operation or a 

computer instruction. 

operating system n. The software that controls the allocation 

and usage of hardware resources such as memory, 

central processing unit (CPU) time, disk space, and 

peripheral devices. The operating system is the foundation 

software on which applications depend. Popular operating 

systems include Windows 98, Windows NT, Mac OS, and 

UNIX. Acronym: OS. Also called: executive. 

operation n. 1. A specific action carried out by a computer 

in the process of executing a program. 2. In mathematics, 

an action performed on a set of entities that 

produces a new entity. Examples of mathematical operations 

are addition and subtraction. 

operation code n. The portion of a machine language or 

assembly language instruction that specifies the type of 

instruction and the structure of the data on which it operates. 

Also called: opcode. See also assembly language, 

machine code. 

operations research n. The use of mathematical and scientific 

approaches to analyze and improve efficiency in 

business, management, government, and other areas. 

Developed around the beginning of World War II, operations 

research was initially used to improve military operations 

during the war. The practice later spread to business 

and industry as a means of breaking down systems and 

procedures and studying their parts and interactions to 

improve overall performance. Operations research 

involves use of the critical path method, statistics, probability, 

and information theory. 

operator n. 1. In mathematics and in programming and 

computer applications, a symbol or other character indicating 

an operation that acts on one or more elements. See 

also binary1 , unary. 2. A person who controls a machine 

or system such as a computer or telephone switchboard. 

operator associativity n. A characteristic of operators 

that determines the order of evaluation in an expression

operator overloading optical scanner 

when adjacent operators have equal precedence. The two 

possibilities are left to right and right to left. The associativity 

for most operators is left to right. See also expression, 

operator (definition 1), operator precedence. 

operator overloading n. The assignment of more than 

one function to a particular operator, with the implication 

that the operation performed will vary depending on the 

data type (operands) involved. Some languages, such as 

Ada and C++, specifically allow for operator overloading. 

See also Ada, C++, function overloading, operator 


operator precedence n. The priority of the various operators 

when more than one is used in an expression. In the 

absence of parentheses, operations with higher precedence 

are performed first. See also expression, operator (definition 

1), operator associativity. 

OPI n. Acronym for Open Prepress Interface. A format 

for preparing digital publication text and graphics for 

printing, introduced by Aldus (now Adobe), creating a 

low-resolution graphic for layout and a high-resolution 

graphic for print. Depending on the method used, the OPI 

process creates a single file that allows for color layer 

extraction though a desktop color separation program or 

creates multiple color-separated files when using DCS 

(Desktop Color Separation). Compare DCS. 

OPS n. See Open Profiling Standard. 

optical character recognition n. The process in which 

an electronic device examines printed characters on 

paper and determines their shapes by detecting patterns 

of dark and light. Once the scanner or reader has determined 

the shapes, character recognition methods—pattern 

matching with stored sets of characters—are used to 

translate the shapes into computer text. Acronym: OCR. 

See also character recognition. Compare magnetic-ink 

character recognition. 

optical communications n. The use of light and of 

light-transmitting technology, such as optical fibers and 

lasers, in sending and receiving data, images, or sound. 

optical disc n. See compact disc. 

optical drive n. A disk drive that reads and often can 

write data on optical (compact) discs. Examples of optical 

drives include CD-ROM drives and WORM disk drives. 

See also CD-ROM drive, compact disc, WORM. 

379 

optical fiber n. A thin strand of transparent material used 

to carry optical signals. Optical fibers are constructed 

from special kinds of glass and plastic, and they are 

designed so that a beam of light introduced at one end will 

remain within the fiber, reflecting off the inner surfaces as 

it travels down the length of the fiber. Optical fibers are 

inexpensive, compact, and lightweight and are often packaged 

many hundred to a single cable. See also fiber optics. 

optical mouse n. 1. A type of mouse that uses a CMOS 

digital camera and a digital signal processor to detect 

motion. The camera photographs the surface over which 

the mouse moves 1500 times per second, and the digital 

signal processor uses the photographs to convert the 

mouse movement into onscreen movements of the cursor. 

IntelliMouse Explorer and IntelliMouse with IntelliEye, 

two optical mouse models with no moving parts and 

requiring no special mouse pad, were introduced by 

Microsoft in 1999. See also mouse. 2. A type of mouse 

that uses a pair of light-emitting diodes (LEDs) and a special 

reflective grid pad to detect motion. The two lights are 

of different colors, and the special mouse pad has a grid of 

lines in the same colors, one color for vertical lines and 

another for horizontal lines. Light detectors paired with 

the LEDs sense when a colored light passes over a line of 

the same color, indicating the direction of movement. See 

also mouse. Compare mechanical mouse, optomechanical 

mouse. 

optical reader n. A device that reads text from printed 

paper by detecting the pattern of light and dark on a 

page and then applying optical character recognition 

methods to identify the characters. See also optical character 

recognition. 

optical recognition n. See optical character recognition. 

optical scanner n. An input device that uses light-sensing 

equipment to scan paper or another medium, translating 

the pattern of light and dark or color into a digital 

signal that can be manipulated by either optical character 

recognition software or graphics software. Scanners have 

different methods for holding the input medium, including 

flatbed, whereby the medium is held on a piece of glass; 

sheet-fed, whereby sheets of paper are pulled over a stationary 

scanning mechanism; handheld, whereby the user 

moves the device over the document to be scanned; and 

overhead, whereby the document is placed face up on a 

stationary bed below a small tower, which moves across 

O

O 

optical switching optomechanical mouse 

the page. Compare magnetic-ink character recognition, 

spatial digitizer. 

optical switching n. A technology in which transmissions 

are sent as light from origin to destination. With 

optical switching, transmissions are switched through 

banks of adjustable, circular millimeter mirrors at cross 

connections, meaning signals don’t need to be converted 

from light to electronic and back during transmission. 

When used with wave-division multiplexing (WDM), alloptical 

traffic may be 100 times faster than electrical 

transmission. See also photonics. 

optimization n. 1. In programming, the process of producing 

more efficient (smaller or faster) programs through 

selection and design of data structures, algorithms, and 

instruction sequences. 2. The process of a compiler or 

assembler in producing efficient executable code. See also 

optimizing compiler. 

optimize vb. 1. In Web design functions, to reduce the file 

size of a photo or graphic to allow faster loading. Files are 

typically optimized through a combination of means such 

as reducing overall image quality and fine-tuning color 

information. 2. To fine-tune an application for improved 

performance. See also optimization. 

optimizer n. A program or device that improves the performance 

of a computer, network, or other device or system. 

For example, a disk optimizer program reduces file 

access time. 

optimizing compiler n. A compiler that analyzes its output 

(assembly language or machine code) to produce more 

efficient (smaller or faster) instruction sequences. 

opt-in vb. To choose to receive certain services or features 

offered by an e-business. With the opt-in process, a user is 

not automatically enrolled in services or features. The user 

must choose to enroll in a service or feature. 

optional hyphen n. See hyphen. 

Option key n. A key on Apple Macintosh keyboards that, 

when pressed in combination with another key, produces 

special characters—graphics, such as boxes; international 

characters, such as currency symbols; and special punctuation 

marks, such as en dashes and em dashes. The Option 

key serves a purpose similar to that of the Control key or 

the Alt key on IBM and compatible keyboards in that it 

changes the meaning of the key with which it is used. 

Options n. See Preferences. 

optoelectronics n. The branch of electronics in which 

the properties and behavior of light are studied. Optoelec- 

380 

tronics deals with electronic devices that generate, sense, 

transmit, and modulate electromagnetic radiation in the 

infrared, visible, and ultraviolet portions of the electromagnetic 

spectrum. 

optomechanical mouse n. A type of mouse in which 

motion is translated into directional signals through a 

combination of optical and mechanical means. The optical 

portion includes pairs of light-emitting diodes (LEDs) and 

matching sensors; the mechanical portion consists of 

rotating wheels with cutout slits. When the mouse is 

moved, the wheels turn and the light from the LEDs either 

passes through the slits and strikes a light sensor or is 

blocked by the solid portions of the wheels. These changes 

in light contact are detected by the pairs of sensors and 

interpreted as indications of movement. Because the sensors 

are slightly out of phase with one another, the direction 

of movement is determined based on which sensor is 

the first to regain light contact. Because it uses optical 

equipment instead of mechanical parts, an optomechanical 

mouse eliminates the need for many of the wear-related 

repairs and maintenance necessary with purely mechanical 

mice, but it does not require the special operating surfaces 

associated with optical mice. See the illustration. See 

also mouse. Compare mechanical mouse, optical mouse. 

LED 

Phototransistor 

F0Ogn01.eps 

Optomechanical mouse.

opt-out OS/2 

opt-out vb. To choose not to receive certain services or 

features offered by an e-business. Some e-businesses automatically 

enroll users in a predetermined range of services, 

but allow users to opt-out of features in which they 

do not choose to participate. 

OR n. A logical operation for combining two bits (0 or 1) 

or two Boolean values (false or true). If one or both values 

are 1 (true), it returns the value 1 (true). See the table. 

Table O.2 The results of the OR logical operation. 

a b a OR b 

0 0 0 

0 1 1 

1 0 1 

1 1 1 

Orange Book n. 1. A U.S. Department of Defense standards 

document entitled “Trusted Computer System Evaluation 

Criteria, DOD standard 5200.28-STD, December, 

1985,” which defines a system of ratings from A1 (most 

secure) to D (least secure), indicating the ability of a computer 

system to protect sensitive information. Compare 

Red Book (definition 1). 2. A specifications book written 

by the Sony and Philips Corporations, covering the compact 

disc write-once formats (CD-R, PhotoCD). See also 

CD-R, ISO 9660, PhotoCD. Compare Green Book, Red 

Book (definition 2). 

ORB n. Acronym for object request broker. In client/ 

server applications, an interface to which the client makes 

a request for an object. The ORB directs the request to the 

server containing the object and then returns the resulting 

values to the client. See also client (definition 1), CORBA. 

order1 n. 1. In computing, the relative significance of a 

digit or byte. High-order refers to the most significant 

(usually leftmost) digit or byte; low-order refers to the 

least significant (usually rightmost) digit or byte. 2. The 

magnitude of a database in terms of the number of fields it 

contains. 3. The sequence in which arithmetic operations 

are performed. 

order2 vb. To arrange in a sequence, such as alphabetic or 

numeric. 

ordinal number n. A number whose form indicates position 

in an ordered sequence of items, such as first, third, or 

twentieth. Compare cardinal number. 

.org n. In the Internet’s Domain Name System, the toplevel 

domain that identifies addresses operated by organizations 

that do not fit any of the other standard domains. For 

381 

instance, the Public Broadcasting System (PBS) is neither a 

commercial, for-profit corporation (.com) nor an educational 

institution with enrolled students (.edu), so it has the 

Internet address pbs.org. The designation .org appears at the 

end of the address. See also DNS (definition 1), domain 

(definition 3). Compare .com, .edu, .gov, .mil, .net. 

Organic Light-Emitting Device n. See OLED. 

Organization for the Advancement of Structured 

Information Standards n. See OASIS. 

OR gate n. One of the three basic logic gates (with AND 

and NOT) from which all digital systems can be built. The 

output of an OR circuit is true (1) if any input is true. See 

also AND gate, gate (definition 1), NOT gate. 

orientation n. See landscape mode, portrait mode. 

original equipment manufacturer n. The maker of a 

piece of equipment. In making computers and related 

equipment, manufacturers of original equipment typically 

purchase components from other manufacturers of original 

equipment, integrate them into their own products, and 

then sell the products to the public. Acronym: OEM. Compare 

value-added reseller. 

original Macintosh keyboard n. The keyboard supplied 

as standard equipment with the 128-KB Apple Macintosh 

and the Mac 512K. The original Macintosh keyboard is 

small and has no numeric keypad or function keys. Also, 

because the overall design goal was that the Macintosh 

should feel familiar, the only elements of this 58-key keyboard 

that differ from a typewriter keyboard are the 

Option keys at both ends of the bottom row, the Command 

key to the left of the Spacebar, and the Enter key to the 

right of the Spacebar. 

orphan n. The first line of a paragraph printed alone at the 

bottom of a page or column of text, or the last line of a 

paragraph printed alone at the top of a page or column. 

Orphans are visually unattractive and thus undesirable in 

printed materials. Compare widow. 

orphan file n. A file that remains on a system after it has 

ceased to be of use. For example, a file may be created to 

support a particular application but may remain after the 

application has been removed. 

OS n. See operating system. 

OS/2 n. Short for Operating System/2. A protectedmode, 

virtual-memory, multitasking operating system for 

personal computers based on the Intel 80286, 80386, i486, 

and Pentium processors. OS/2 can run most MS-DOS 

O

O 

oscillation output channel 

applications and can read all MS-DOS disks. OS/2’s Presentation 

Manager provides a graphical user interface. The 

latest version, known as OS/2 Warp 4, is a 32-bit operating 

system that provides networking, Internet, and Java support, 

as well as speech recognition technology. OS/2 was 

initially developed as a joint project of Microsoft and IBM 

but later became an IBM product. See also protected 

mode, virtual memory. 

oscillation n. A periodic change or alternation. In electronics, 

oscillation refers to a periodic change in an electrical 

signal. 

oscillator n. An electronic circuit that produces a periodically 

varying output at a controlled frequency. Oscillators, 

an important type of electronic circuit, can be designed to 

provide a constant or an adjustable output. Some oscillator 

circuits use a quartz crystal to generate a stable frequency. 

Personal computers use an oscillator circuit to provide the 

clock frequency—typically 1 to 200 megahertz (MHz)— 

that drives the processor and other circuits. 

oscilloscope n. A test and measurement instrument that 

provides a visual display for an electrical signal. Most 

commonly, oscilloscopes are used to create a display of 

voltage over time. Also called: cathode-ray oscilloscope. 

OSF n. Acronym for Open Software Foundation. A nonprofit 

consortium of firms (including DEC, Hewlett-Packard, 

and IBM), formed in 1988, that promotes standards 

and specifications for programs operating under UNIX 

and licenses software (as source code) to its members. 

OSF’s products include the Distributed Computing Environment, 

the graphical user interface Motif, and the OSF/1 

operating system (a variant of UNIX). 

OSI n. See ISO/OSI reference model. 

OSI protocol stack n. The set of protocols based on— 

and corresponding to—the ISO/OSI reference model. 

OSI reference model n. See ISO/OSI reference model. 

OSPF n. Acronym for Open Shortest Path First. A routing 

protocol for IP networks, such as the Internet, that allows a 

router to calculate the shortest path to each node for sending 

messages. The router sends information on the nodes it 

is linked to, called link-state advertisements, to other routers 

on the network to accumulate link-state information to 

make its calculations. See also communications protocol, 

node (definition 2), path (definition 1), router. 

OS X n. See Mac OS X. 

382 

OTOH n. Acronym for on the other hand. A shorthand 

expression often used in e-mail, Internet news, and discussion 

groups. 

Outbox n. In many e-mail applications, the default mailbox 

where the program stores outgoing messages. See also 

e-mail1 (definition 1), mailbox. Compare Inbox. 

outdent n. See hanging indent. 

outer join n. In database management, an operator in 

relational algebra. An outer join performs an extended join 

operation in which the tuples (rows) in one relation (table) 

that have no counterpart in the second relation appear in 

the resulting relation concatenated with all null values. 

Compare inner join. 

outline font n. A font (type design) stored in a computer 

or printer as a set of outlines for drawing each of the 

alphabetic and other characters in a character set. Outline 

fonts are templates rather than actual patterns of dots and 

are scaled up or down to match a particular type size. Such 

fonts are most often used for printing, as is the case with 

most PostScript fonts on a PostScript-compatible laser 

printer and TrueType fonts. Compare bitmapped font, 

screen font, stroke font. 

Outlook n. Microsoft’s messaging and collaboration 

application software. A member of the Microsoft Office 

suite, Outlook includes e-mail, an integrated calendar, and 

contact-management and task-management features, and 

it also provides support for building customized tools, 

such as special-purpose forms, for collaborative functions. 

out-of-band signaling n. Transmission of some signals, 

such as control information, on frequencies outside the 

bandwidth available for voice or data transfer on a communications 

channel. Compare in-band signaling. 

output1 n. The results of processing, whether sent to the 

screen or printer, stored on disk as a file, or sent to another 

computer in a network. 

output2 vb. To send out data by a computer or sound by a 

speaker. 

output area n. See output buffer. 

output-bound n. See input/output-bound. 

output buffer n. A portion of memory set aside for temporary 

storage of information, leaving main memory for storage, 

display, printing, or transmission. See also buffer1 . 

output channel n. See channel (definition 1), input/output 

channel.

output simulation overstrike 

output simulation n. A feature of color management 

applications in which a computer display is calibrated to 

help predict the results of printing a graphics file on a specific 

device. Also called: soft proofing. 

output stream n. A flow of information that leaves a 

computer system and is associated with a particular task or 

destination. In programming, an output stream can be a 

series of characters sent from the computer’s memory to a 

display or to a disk file. Compare input stream. 

outsourcing n. The assignment of tasks to independent 

contractors, such as individual consultants or service 

bureaus. Tasks such as data entry and programming are 

often performed via outsourcing. 

OverDrive n. A type of microprocessor from Intel 

designed to replace a computer’s existing i486SX or 

i486DX microprocessor. The OverDrive is functionally 

identical to Intel’s i486DX2 microprocessor, but it is an 

end-user product, whereas the i486DX2 is sold only to 

computer manufacturers who build it into their own systems. 

Upgrading a system with an OverDrive processor 

differs from system to system, and some systems might 

not be able to support an OverDrive processor. See also 

i486DX, i486SL, i486SX, microprocessor. Compare 

i486DX2. 

overflow n. 1. Generally, the condition that occurs when 

data resulting from input or processing requires more bits 

than have been provided in hardware or software to store 

the data. Examples of overflow include a floating-point 

operation whose result is too large for the number of bits 

allowed for the exponent, a string that exceeds the bounds 

of the array allocated for it, and an integer operation 

whose result contains too many bits for the register into 

which it is to be stored. See also overflow error. Compare 

underflow. 2. The part of a data item that cannot be stored 

because the data exceeds the capacity of the available data 

structure. 

overflow error n. An error that arises when a number, 

often the result of an arithmetic operation, is too large to 

be contained in the data structure that a program provides 

for it. 

overhead n. Work or information that provides support— 

possibly critical support—for a computing process but is 

not an intrinsic part of the operation or data. Overhead 

often adds to processing time but is generally necessary. 

overlaid windows n. See cascading windows. 

383 

overlapped communication operation n. The performance 

of two distinct communication operations simultaneously; 

for example, a simultaneous read/write 

operation. Windows CE does not support overlapped 

communication operation, but it does support multiple 

read/writes pending on a device. 

overlay1 n. 1. A section of a program designed to reside 

on a designated storage device, such as a disk, and to be 

loaded into memory when needed, usually overwriting 

one or more overlays already in memory. Use of overlays 

allows large programs to fit into a limited amount of memory, 

but at the cost of speed. 2. A printed form positioned 

over a screen, tablet, or keyboard for identification of particular 

features. See also keyboard template. 

overlay2 vb. 1. In computer graphics, to superimpose one 

graphic image over another. 2. In video, to superimpose a 

graphic image generated on a computer over video signals, 

either live or recorded. 

overprint vb. The process of printing an element of one 

color over one of another color without removing, or 

knocking out, the material underneath. Compare knockout 


override vb. To prevent something from happening in a 

program or in an operating system or to initiate another 

response. For example, a user can often override and thus 

abort a lengthy sorting procedure in a database program 

by pressing the Escape key. 

overrun n. In information transfer, an error that occurs 

when a device receiving data cannot handle or make use of 

the information as rapidly as it arrives. See also input/output-bound. 

overscan n. The part of a video signal sent to a raster display 

that controls the area outside the rectangle containing 

visual information. The overscan area is sometimes colored 

to form a border around the screen. 

overshoot n. The phenomenon in which a system suffers 

from a time delay in responding to input and continues to 

change state even after it has reached the desired state. 

This situation requires that correcting input be made so 

that the system reaches the desired state. For example, the 

arm carrying the heads in a hard disk drive might move 

slightly past the desired track before it stops, requiring 

another signal to pull it back. 

overstrike vb. To type or print one character directly over 

another so that the two occupy the same space on the page 

or screen. 

O

O 

overtype mode Oz 

overtype mode n. See overwrite mode. 

overwrite mode n. A text-entry mode in which newly 

typed characters replace existing characters under or to the 

left of the cursor insertion point. Also called: overtype 

mode, typeover mode. Compare insert mode. 

384 

overwriting virus n. A type of virus that overwrites the 

host file it has infected, destroying the original data. Also 

called: overwrite virus. 

Oz n. A concurrent, object-oriented programming language.

p prefix See pico-. 

P prefix See peta-. 

P2P or P-to-P n. An Internet-based networking option in 

which two or more computers connect directly to each 

other to communicate and share files without use of a central 

server. Interest in P2P networking blossomed with the 

introduction of Napster and Gnutella. Short for Peer-to- 

Peer. See also peer-to-peer architecture, peer-to-peer 


P3P n. Acronym for Platform for Privacy Preferences. 

An open W3C protocol that allows Internet users to control 

the type of personal information that is collected by 

the Web sites they visit. P3P uses User Agents built into 

browsers and Web applications to allow P3P-enabled Web 

sites to communicate privacy practices to users before they 

log on to the Web site. P3P compares the Web site’s privacy 

policies with the user’s personal set of privacy preferences, 

and it reports any disagreements to the user. 

P5 n. Intel’s internal working name for the Pentium microprocessor. 

Although it was not intended to be used publicly, 

the name P5 leaked out to the computer-industry trade 

press and was commonly used to reference the microprocessor 

before it was released. See also 586, Pentium. 

pack vb. To store information in a more compact form. 

Packing eliminates unnecessary spaces and other such 

characters and may use other special methods of compressing 

data as well. It is used by some programs to minimize 

storage requirements. 

package n. 1. A computer application consisting of one 

or more programs created to perform a particular type of 

work—for example, an accounting package or a spreadsheet 

package. 2. In electronics, the housing in which an 

electronic component is packaged. See also DIP. 3. A 

group of classes or interfaces and a keyword in the Java 

programming language. Packages are declared in Java by 

using the “package” keyword. See also class, declare, 

interface (definition 1), keyword. 

P 

385 

packaged software n. A software program sold through 

a retail distributor, as opposed to custom software. See 

also canned software. 

packed decimal adj. A method of encoding decimal 

numbers in binary form that maximizes storage space by 

using each byte to represent two decimal digits. When 

signed decimal numbers are stored in packed decimal format, 

the sign appears in the rightmost four bits of the 

rightmost (least significant) byte. 

packet n. 1. A unit of information transmitted as a whole 

from one device to another on a network. 2. In packetswitching 

networks, a transmission unit of fixed maximum 

size that consists of binary digits representing both 

data and a header containing an identification number, 

source and destination addresses, and sometimes errorcontrol 

data. See also packet switching. 

packet assembler and disassembler n. See packet 

assembler/disassembler. 

packet assembler/disassembler n. An interface 

between non-packet-switching equipment and a packetswitching 

network. Acronym: PAD. 

packet filtering n. The process of controlling network 

access based on IP addresses. Firewalls will often incorporate 

filters that allow or deny users the ability to enter or 

leave a local area network. Packet filtering is also used to 

accept or reject packets such as e-mail, based on the origin 

of the packet, to ensure security on a private network. See 

also firewall, IP address, packet (definition 1). 

packet flooding n. A technique employed in a number of 

DoS (denial of service) attacks in which a flood of packets 

of data are sent to a target server, overwhelming the computer 

and rendering it unable to respond to legitimate network 

requests. Examples of specific types of packet 

flooding include smurf attacks and SYN flood attacks. See 

also DoS, packet, smurf attack, SYN flood. 

packet header n. The portion of a data packet that precedes 

the body (data). The header contains data, such as 

P

P 

Packet Internet Groper page banner 

source and destination addresses and control and timing 

information, that is needed for successful transmission. 

Packet Internet Groper n. See ping1 (definition 1). 

packet sniffer n. A hardware and/or software device that 

examines every packet sent across a network. To work, a 

packet sniffer must be installed in the same network block 

as the network it is intended to sniff. Designed as a problem-solving 

tool to isolate problems degrading network 

performance, packet sniffers have become security risks 

on some networks because crackers can use them to capture 

nonencrypted user IDs, passwords, credit card numbers, 

e-mail addresses, and other confidential information. 

See also cracker, packet. Compare monitoring software. 

packet switching n. A message-delivery technique in 

which small units of information (packets) are relayed 

through stations in a computer network along the best 

route available between the source and the destination. A 

packet-switching network handles information in small 

units, breaking long messages into multiple packets before 

routing. Although each packet may travel along a different 

path, and the packets composing a message may arrive at 

different times or out of sequence, the receiving computer 

reassembles the original message correctly. Packetswitching 

networks are considered to be fast and efficient. 

To manage the tasks of routing traffic and assembling/disassembling 

packets, such a network requires some intelligence 

from the computers and software that control 

delivery. The Internet is an example of a packet-switching 

network. Standards for packet switching on networks are 

documented in the International Telecommunication 

Union (ITU) recommendation X.25. Compare circuit 

switching. 

Packet Switching Exchange n. An intermediary 

switching station in a packet-switching network. 

packet trailer n. The portion of a data packet that follows 

the body (data). The trailer typically contains information 

related to error checking and correction. See also packet. 

packing density n. The number of storage units per 

length or area of a storage device. Bits per inch is one 

measure of packing density. 

PackIT n. A file format used on the Apple Macintosh to 

represent collections of Mac files, possibly Huffman compressed. 

See also Huffman coding, Macintosh. 

PAD n. See packet assembler/disassembler. 

386 

pad character n. In data input and storage, an extra character 

inserted as filler to use up surplus space in a predefined 

block of a specified length, such as a fixed-length field. 

padding n. In data storage, the addition of one or more 

bits, usually zeros, to a block of data to fill it, to force the 

actual data bits into a certain position, or to prevent the 

data from duplicating a bit pattern that has an established 

meaning, such as an embedded command. 

paddle n. An early type of input device often used with 

computer games especially for side-to-side or up-anddown 

movements of an on-screen object. A paddle is less 

sophisticated than a joystick because it permits the user, 

by turning a dial, to specify movement along only a single 

axis. The paddle got its name because its most popular use 

was to control the on-screen paddles in the simple early 

video games, such as Pong. See the illustration. 

F0Pgn01.eps 

Paddle. 

paddle switch n. Any switch that has a wide handle. The 

large on/off switch on many IBM personal computers is 

one type of paddle switch. 

page n. 1. In word processing, the text and display elements 

to be printed on one side of a sheet of paper, subject 

to formatting specifications such as depth, margin size, 

and number of columns. 2. A fixed-size block of memory. 

When used in the context of a paging memory system, a 

page is a block of memory whose physical address can be 

changed via mapping hardware. See also EMS, memory 

management unit, virtual memory. 3. In computer graphics, 

a portion of display memory that contains one complete 

full-screen image; the internal representation of a 

screenful of information. 4. See Web page. 

page banner n. A section of a Web page containing a 

graphic element and text, such as the page title. Page banners 

are usually displayed at the top of a Web page. Page 

banners can also be used to link to other Web sites for 

advertising purposes. Also called: banner.

page break page-jacking 

page break n. The point at which the flow of text in a 

document moves to the top of a new page. Most word processors 

automatically place page breaks when the material 

on the page reaches a specified maximum. By contrast, a 

“hard” or “manual” page break is a command or a code 

inserted by the user to force a page break at a specific 

place in the text. See also form feed. 

paged address n. In the 80386, i486, and Pentium paged 

memory architecture, an address in memory created by 

combining the processes of segment translation and page 

translation. In the paged-memory scheme, which requires 

that the microprocessor’s paging feature be enabled, logical 

addresses are transformed into physical addresses in 

two steps: segment translation and page translation. The 

first step, segment translation, converts a logical to a linear 

address—an address that refers indirectly to a physical 

address. After the linear address is obtained, the microprocessor’s 

paging hardware converts the linear address to a 

physical address by specifying a page table (an array of 

32-bit page specifiers), a page (a 4-KB unit of contiguous 

addresses within physical memory) within that table, and 

an offset within that page. This information collectively 

refers to a physical address. 

page-description language n. A programming language, 

such as PostScript, that is used to describe output 

to a printer or a display device, which then uses the 

instructions from the page-description language to construct 

text and graphics to create the required page image. 

Page-description languages are like other computer languages, 

with logical program flow allowing for sophisticated 

manipulation of the output. A page-description 

language, like a blueprint, sets out specifications (as for 

fonts and type sizes) but leaves the work of drawing characters 

and graphics to the output device itself. Because 

this approach delegates the detail work to the device that 

produces the output, a page-description language is 

machine-independent. These abilities come at a price, 

however. Page-description languages require printers with 

processing power and memory comparable to, and often 

exceeding, that of personal computers. Acronym: PDL. 

See also PostScript. 

paged memory management unit n. A hardware unit 

that performs tasks related to accessing and managing 

387 

memory used by different applications or by virtual-memory 

operating systems. Acronym: PMMU. 

Page Down key n. A standard key (often labeled 

“PgDn”) on most computer keyboards whose specific 

meaning is different in different programs. In many cases, 

it moves the cursor down to the top of the next page or a 

specific number of lines. 

page fault n. The interrupt that occurs when software 

attempts to read from or write to a virtual memory location 

that is marked “not present.” The mapping hardware 

of a virtual memory system maintains status information 

about every page in the virtual address space. A page 

either is mapped onto a physical address or is not present 

in physical memory. When a read or write to an unmapped 

virtual address is detected, the memory management hardware 

generates the page fault interrupt. The operating system 

must respond to the page fault by swapping in the data 

for the page and updating the status information in the 

memory management unit. See also page (definition 2), 

swap (definition 2), virtual memory. 

page frame n. A physical address to which a page of virtual 

memory may be mapped. In a system with 4096-byte 

pages, page frame 0 corresponds to physical addresses 0 

through 4095. See also paging, virtual memory. 

page-image buffer n. Memory in a page printer used to 

hold the bit map (image) of a page as the printer’s raster 

image processor builds the page and as the printer produces 

the page. See also page printer, raster image processor. 

page-image file n. A file containing the necessary code 

for a printer or other display device to create the page or 

screen image. See also PostScript. 

page-jacking n. A deceptive practice that detours Web 

visitors from legitimate sites generated as search engine 

results to copycat Web pages, from which they will be 

redirected to pornographic or other unwanted sites. Pagejacking 

is accomplished by copying the contents and 

metatags of a Web page, altering its title and content so 

that, on search results, it displays before the original, and 

then submitting the copied page to search engines. When 

clicking on the link to the copied site, the visitor will 

instead be redirected to an unwanted and unrelated site. 

See also metatag. Compare mousetrapping. 

P

P 

page layout palette 

page layout n. In desktop publishing, the process of 

arranging text and graphics on the pages of a document. 

Page-layout programs excel in text placement and management 

of special effects applied to text. Although pagelayout 

programs are generally slower than word-processing 

programs, they can perform such advanced tasks as flowing 

text into complex multicolumn page designs, printing documents 

in signatures, managing color separations, and supporting 

sophisticated kerning and hyphenation. 

page makeup n. The assembling of graphics and text on 

a page in preparation for printing. 

page mode RAM n. A specially designed dynamic RAM 

that supports access to sequential memory locations with a 

reduced cycle time. This is especially attractive in video 

RAM, in which each location is accessed in ascending 

order to create the screen image. Page mode RAM can 

also improve the execution speed of code because code 

tends to execute sequentially through memory. See also 

cycle time, dynamic RAM. 

page orientation n. See landscape mode, portrait mode. 

page printer n. Any printer, such as a laser printer, that 

prints an entire page at once. Because page printers must 

store the entire page in memory before printing, they 

require relatively large amounts of memory. Compare line 

printer. 

pager n. Pocket-sized wireless electronic device that uses 

radio signals to record incoming phone numbers or short 

text messages. Some pagers allow users to send messages 

as well. Also called: beeper. 

page reader n. See document reader. 

page setup n. A set of choices that affect how a file is 

printed on the page. Page setup might reflect the size of 

paper going into the printer, the page margins, the specific 

pages in the document to be printed, whether the image is 

to be reduced or enlarged when printed, and whether 

another file is to be printed immediately after the first file 

is printed. 

pages per minute n. See PPM. 

Page Up key n. A standard key (often labeled “PgUp”) 

on most computer keyboards whose specific meaning is 

different in different programs. In many cases, it moves 

the cursor up to the top of the previous page or a specific 

number of lines. 

388 

pagination n. 1. The process of dividing a document into 

pages for printing. 2. The process of adding page numbers, 

as in a running head. 

paging n. A technique for implementing virtual memory. 

The virtual address space is divided into a number of 

fixed-size blocks called pages, each of which can be 

mapped onto any of the physical addresses available on 

the system. Special memory management hardware 

(MMU or PMMU) performs the address translation from 

virtual addresses to physical addresses. See also memory 

management unit, paged memory management unit, virtual 

memory. 

paging file n. A hidden file on the hard disk that operating 

systems (such as Windows, Mac OS X, and UNIX) 

use to hold parts of programs and data files that do not fit 

in memory. The paging file and physical memory, or 

RAM, make up virtual memory. Data is moved from the 

paging file to memory as needed and moved from memory 

to the paging file to make room for new data in memory. 

Also called: swap file. See also virtual memory. 

paint1 n. A color and pattern used with graphics programs 

to fill areas of a drawing, applied with tools such as a 

paintbrush or a spraycan. 

paint2 vb. To fill a portion of a drawing with paint (color 

or a pattern). 

paintbrush n. An artist’s tool in a paint program or 

another graphics application for applying a streak of solid 

color to an image. The user can usually select the width of 

the streak. See also paint program. Compare spraycan. 

paint program n. An application program that creates 

graphics as bit maps. A paint program, because it treats a 

drawing as a group of dots, is particularly appropriate for 

freehand drawing. Such a program commonly provides 

tools for images requiring lines, curves, and geometric 

shapes but does not treat any shape as an entity that can be 

moved or modified as a discrete object without losing its 

identity. Compare drawing program. 

palette n. 1. In paint programs, a collection of drawing 

tools, such as patterns, colors, brush shapes, and different 

line widths, from which the user can choose. 2. A subset 

of the color look-up table that establishes the colors that 

can be displayed on the screen at a particular time. The 

number of colors in a palette is determined by the number 

of bits used to represent a pixel. See also color bits, color 

look-up table, pixel.

palmtop parallel adder 

palmtop n. A portable personal computer whose size 

enables it to be held in one hand while it is operated with 

the other hand. A major difference between palmtop computers 

and laptop computers is that palmtops are usually 

powered by off-the-shelf batteries such as AA cells. Palmtop 

computers typically do not have disk drives; rather, 

their programs are stored in ROM and are loaded into 

RAM when they are switched on. More recent palmtop 

computers are equipped with PCMCIA slots to provide 

wider flexibility and greater capability. See also handheld 

PC, PCMCIA slot, portable computer. Compare laptop. 

PAM n. See pulse amplitude modulation. 

panning n. In computer graphics, a display method in 

which a viewing window on the screen scans horizontally 

or vertically, like a camera, to bring offscreen extensions 

of the current image smoothly into view. 

PANTONE MATCHING SYSTEM n. In graphic arts and 

printing, a standard system of ink color specification 

consisting of a swatch book in which each of about 500 

colors is assigned a number. Acronym: PMS. See also 

color model. 

PAP n. 1. Acronym for Password Authentication Protocol. 

A method for verifying the identity of a user attempting 

to log on to a Point-to-Point Protocol (PPP) server. 

PAP is used if a more rigorous method, such as the Challenge 

Handshake Authentication Protocol (CHAP), is not 

available or if the user name and password that the user 

submitted to PAP must be sent to another program without 

encryption. 2. Acronym for Printer Access Protocol. The 

protocol in AppleTalk networks that governs communication 

between computers and printers. 

paper feed n. A mechanism that moves paper through a 

printer. In laser printers and other page printers, the paper 

feed is usually a series of rollers that firmly grip and align 

the paper. In dot-matrix printers, the paper feed is usually 

a pin feed or tractor feed, in which small pins drag or push 

paper that has detachable edges punched with sprocket 

holes. Friction feed is another type of paper feed, in which 

the paper is gripped between the platen and pressure rollers 

and pulled by rotation of the platen. 

paperless office n. The idealized office in which information 

is entirely stored, manipulated, and transferred 

electronically rather than on paper. 

389 

paper-white adj. Of, pertaining to, or being a type of 

monochrome computer monitor whose default operating 

colors are black text on a white background. Paper-white 

monitors are popular in desktop publishing and word 

processing environments because the monitor most 

closely resembles a white sheet of paper printed with 

black characters. 

paper-white monitor n. A display monitor in which text 

and graphics characters are displayed in black against a 

white background to resemble the appearance of a printed 

page. Some manufacturers use the name to refer to a 

background that is tinted in a manner corresponding to 

bonded paper. 

paradigm n. An archetypal example or pattern that provides 

a model for a process or system. 

paragraph n. 1. In word processing, any part of a document 

preceded by one paragraph mark and ending with 

another. To the program, a paragraph represents a unit of 

information that can be selected as a whole or given formatting 

distinct from the surrounding paragraphs. 2. On 

IBM and other computers built around the Intel 8088 or 

8086 microprocessor, a 16-byte section of memory beginning 

at a location (address) that can be divided evenly by 

16 (hexadecimal 10). 

parallel adj. 1. Of or relating to electronic circuits in which 

the corresponding terminals of two or more components are 

connected. 2. In geometry and graphics, of, relating to, or 

being lines that run side by side in the same direction in the 

same plane without intersecting. 3. In data communications, 

of, relating to, or being information that is sent in 

groups of bits over multiple wires, one wire for each bit in a 

group. See also parallel interface. Compare serial. 4. In data 

handling, of or relating to handling more than one event at a 

time, with each event having its own portion of the system’s 

resources. See also parallel processing. 

parallel access n. The ability to store or retrieve all of 

the bits composing a single unit of information, such as a 

byte or a word (usually two bytes), at the same time. Also 

called: simultaneous access. 

parallel adder n. A logic device that processes the addition 

of several (typically 4, 8, or 16) binary inputs simultaneously 

rather than sequentially, as is the case with half 

adders and full adders. Parallel adders speed processing 

P

P 

parallel algorithm parallel processing 

because they require fewer steps to produce the result. 

Compare full adder, half adder. 

parallel algorithm n. An algorithm in which more than 

one portion of the algorithm can be followed at one time. 

Parallel algorithms are usually used in multiprocessing 

environments. Compare sequential algorithm. 

parallel circuit n. A circuit in which the corresponding 

leads of two or more of the circuit components are connected. 

In a parallel circuit, there are two or more separate 

pathways between points. The individual components in a 

parallel circuit all receive the same voltage but share the 

current load. See the illustration. Compare series circuit. 

F0Pgn02.eps 

Parallel circuit. 

parallel computer n. A computer that uses several processors 

that work concurrently. Software written for parallel 

computers can increase the amount of work done in a 

specific amount of time by dividing a computing task 

among several simultaneously functioning processors. See 

also parallel processing. 

parallel computing n. The use of multiple computers or 

processors to solve a problem or perform a function. See 

also array processor, massively parallel processing, pipeline 

processing, SMP. 

parallel connection n. See parallel interface. 

parallel database n. A database system involving the 

concurrent use of two or more processors or operating system 

processes to service database management requests 

such as SQL queries and updates, transaction logging, I/O 

handling, and data buffering. A parallel database is capable 

of performing a large number of simultaneous tasks across 

multiple processors and storage devices, providing quick 

access to databases containing many gigabytes of data. 

Parallel Data Structure n. See PDS (definition 2). 

parallel execution n. See concurrent execution. 

parallel interface n. The specification of a data transmission 

scheme that sends multiple data and control bits 

simultaneously over wires connected in parallel. The most 

390 

common parallel interface is the Centronics interface. See 

also Centronics parallel interface. Compare serial interface. 

parallel port n. An input/output connector that sends and 

receives data 8 bits at a time, in parallel, between a computer 

and a peripheral device such as a printer, scanner, 

CD-ROM, or other storage device. The parallel port, often 

called a Centronics interface after the original design standard, 

uses a 25-pin connector called a DB-25 connector 

that includes three groups of lines: four for control signals, 

five for status signals, and eight for data. See also Centronics 

parallel interface, ECP, EPP, IEEE 1284, input/ 

output port. Compare serial port. 

F0Pgn03.eps 

Parallel port. 

Parallel port 

parallel printer n. A printer that is connected to the computer 

via a parallel interface. In general, a parallel connection 

can move data between devices faster than a serial 

connection can. The parallel interface is preferred in the 

IBM PC world because its cabling is more standardized 

than that of the serial interface and because the computer’s 

operating system assumes that the system printer is 

attached to the parallel port. See also parallel interface. 

Compare serial printer. 

parallel processing n. A method of processing that can 

run only on a computer that contains two or more processors 

running simultaneously. Parallel processing differs 

from multiprocessing in the way a task is distributed over 

the available processors. In multiprocessing, a process 

might be divided up into sequential blocks, with one processor 

managing access to a database, another analyzing 

the data, and a third handling graphical output to the 

screen. Programmers working with systems that perform 

parallel processing must find ways to divide a task so that 

it is more or less evenly distributed among the processors 

available. Compare coprocessor, multiprocessing.

parallel server park 

parallel server n. A computer system that implements 

some form of parallel processing to improve its performance 

as a server. See also SMP server. 

parallel transmission n. The simultaneous transmission 

of a group of bits over separate wires. With microcomputers, 

parallel transmission refers to the transmission of 1 

byte (8 bits). The standard connection for parallel transmission 

is known as the Centronics interface. See also 

Centronics parallel interface. Compare serial transmission. 

parameter n. In programming, a value that is given to a 

variable, either at the beginning of an operation or before 

an expression is evaluated by a program. Until the operation 

is completed, a parameter is effectively treated as a 

constant value by the program. A parameter can be text, a 

number, or an argument name assigned to a value that is 

passed from one routine to another. Parameters are used as 

a means of customizing program operation. See also argument, 

pass by address, pass by value, routine. 

parameter-driven adj. Of, pertaining to, or being a program 

or an operation whose character or outcome is determined 

by the values of the parameters that are assigned to it. 

parameter passing n. In programming, the substitution 

of an actual parameter value for a formal parameter when 

a procedure or function call is processed. 

parameter RAM n. A few bytes of battery-backed 

CMOS RAM on the motherboards of Apple Macintosh 

computers. Information about the configuration of the system 

is stored in parameter RAM. Acronym: PRAM. See 

also CMOS RAM. Compare CMOS (definition 2). 

PARC n. See Xerox PARC. 

parent/child adj. 1. Pertaining to or constituting a relationship 

between processes in a multitasking environment 

in which the parent process calls the child process and 

most often suspends its own operation until the child process 

aborts or is completed. 2. Pertaining to or constituting 

a relationship between nodes in a tree data structure in 

which the parent is one step closer to the root (that is, one 

level higher) than the child. 

parity n. The quality of sameness or equivalence, in the 

case of computers usually referring to an error-checking 

procedure in which the number of 1s must always be the 

same—either even or odd—for each group of bits trans- 

391 

mitted without error. If parity is checked on a per-character 

basis, the method is called vertical redundancy checking, 

or VRC; if checked on a block-by-block basis, the method 

is called longitudinal redundancy checking, or LRC. In 

typical modem-to-modem communications, parity is one 

of the parameters that must be agreed upon by sending and 

receiving parties before transmission can take place. See 

the table. See also parity bit, parity check, parity error. 

Table P.1 Types of Parity. 

Type Description 

Even parity The number of 1s in each successfully 

transmitted set of bits must be 

an even number. 

Odd parity The number of 1s in each successfully 

transmitted set of bits must be 

an odd number. 

No parity No parity bit is used. 

Space parity A parity bit is used and is always set 

to 0. 

Mark parity A parity bit is used and is always set 

to 1. 

parity bit n. An extra bit used in checking for errors in 

groups of data bits transferred within or between computer 

systems. With PCs, the term is frequently encountered in 

modem-to-modem communications, in which a parity bit is 

often used to check the accuracy with which each character 

is transmitted, and in RAM, where a parity bit is often used 

to check the accuracy with which each byte is stored. 

parity check n. The use of parity to check the accuracy 

of transmitted data. See also parity, parity bit. 

parity error n. An error in parity that indicates an error in 

transmitted data or in data stored in memory. If a parity 

error occurs in communications, all or part of a message 

must be retransmitted; if a parity error occurs in RAM, the 

computer usually halts. See also parity, parity bit. 

park vb. To position the read/write head over a portion of 

a disk that stores no data (and therefore can never be damaged) 

or beyond the surface of the disk, prior to shutting 

down the drive, especially in preparation for moving it. 

Parking can be performed manually, automatically, or by a 

disk utility program. 

P

P 

parrallaxing passive-matrix display 

parrallaxing n. A 3-D animation technique, often used by 

computer game developers, where backgrounds are displayed 

using different levels of speed to achieve realism. 

For example, distant levels move at a slower speed than 

closer levels, thereby giving the illusion of depth. See also 

animation. 

parse vb. To break input into smaller chunks so that a 

program can act upon the information. 

parser n. An application or device that breaks data into 

smaller chunks so that an application can act on the information. 

See also parse. 

partition n. 1. A logically distinct portion of memory or a 

storage device that functions as though it were a physically 

separate unit. 2. In database programming, a subset 

of a database table or file. 

Partition Boot Sector n. The first sector in the system 

(startup) partition of a computer’s bootable hard disk, or 

the first sector of a bootable floppy disk. On an x86-based 

computer, the Partition Boot Sector is read into memory at 

startup by the Master Boot Record. It is the Partition Boot 

Sector that contains the instructions required to begin the 

process of loading and starting the computer’s operating 

system. See also Master Boot Record, partition table. 

partition table n. A table of information in the first sector 

of a computer’s hard disk that tells where each partition 

(discrete portion of storage) on the disk begins and 

ends. The physical locations are given as the beginning 

and ending head, sector, and cylinder numbers. In addition 

to these “addresses,” the partition table identifies the type 

of file system used for each partition and identifies 

whether the partition is bootable—whether it can be used 

to start the computer. Although it is a small data structure, 

the partition table is a critical element on the hard disk. 

partnership n. The settings on a desktop computer and 

Windows CE device that allow information to be synchronized, 

as well as copied or moved between the computer 

and device. The mobile device can have partnerships with 

up to two desktop computers. See also synchronization 


Pascal n. A concise procedural language designed 

between 1967 and 1971 by Niklaus Wirth. Pascal, a compiled, 

structured language built upon ALGOL, simplifies 

syntax while adding data types and structures such as 

392 

subranges, enumerated data types, files, records, and sets. 

See also ALGOL, compiled language. Compare C. 

pASP n. See pocket Active Server Pages. 

pass1 n. In programming, the carrying out of one complete 

sequence of events. 

pass2 vb. To forward a piece of data from one part of a 

program to another. See also pass by address, pass by value. 

pass by address n. A means of passing an argument or 

parameter to a subroutine. The calling routine passes the 

address (memory location) of the parameter to the called 

routine, which can then use the address to retrieve or modify 

the value of the parameter. Also called: pass by reference. 

See also argument, call1 . Compare pass by value. 

pass by reference n. See pass by address. 

pass by value n. A means of passing an argument or a 

parameter to a subroutine. A copy of the value of the argument 

is created and passed to the called routine. When this 

method is used, the called routine can modify the copy of 

the argument, but it cannot modify the original argument. 

See also argument, call1 . Compare pass by address. 

passivation n. In Sun Microsystems’s J2EE network platform, 

the process of “turning off” an enterprise java bean 

(EJB) by caching it from memory to secondary storage. 

See also Enterprise JavaBeans, J2EE. Compare activation. 

passive hub n. A type of hub used on ARCnet networks 

that passes signals along but has no additional capability. 

See also ARCnet. Compare active hub, Intelligent hub. 

passive-matrix display n. An inexpensive, low-resolution 

liquid crystal display (LCD) made from a large array 

of liquid crystal cells that are controlled by transistors outside 

of the display screen. One transistor controls an entire 

row or column of pixels. Passive-matrix displays are commonly 

used in portable computers, such as laptops and 

notebooks, because of their thin width. While these displays 

have good contrast for monochrome screens, the resolution 

is weaker for color screens. These displays are also 

difficult to view from any angle other than straight on, 

unlike active-matrix displays. However, computers with 

passive-matrix displays are considerably cheaper than 

those with active-matrix screens. See the illustration. Also 

called: dual-scan display. See also liquid crystal display, 

supertwist display, transistor, twisted nematic display. 

Compare active-matrix display.

passive node patch2 patch 

LCD panel 

matrix 

Pixel 

element 

Indium Tin 

Oxide (ITO) 

electrodes in 

rows on one 

side of the 

LCD panel 

F0Pgn04.eps 

Passive-matrix display. 

ITO electrodes in columns on 

opposite side of the LCD panel 

passive node n. A network node that “listens” for transmissions 

but is not actively involved in passing them along 

the network; typical of a node on a bus network. See also 

bus network, node (definition 2). 

Passport n. A suite of personal identification services 

from Microsoft that consolidates user names, passwords, 

and other information. With the Passport single sign-in 

service, a user enters one name and password at any Passport 

site on the Internet; after signing in to one Passport 

site, a user can sign in to others without reentering the 

information. Passport also provides a server-based wallet 

service that stores credit card and billing information, a 

Kids Passport service, and a public-profile service. Passport 

is one of the foundation services of the Microsoft 

.NET initiative. See also .NET, .NET My Services, single 

sign-on, wallet. 

pass-through adj. 1. In general, a reference to something 

that acts as an intermediary between other entities. For 

example, a pass-through proxy server allows external 

access to an internal (protected) server by passing requests 

from the requesting client to the server without allowing 

direct access. 2. Pertaining to a device or connector that 

393 

moves a signal or set of signals from the input to the output 

without making any changes. For example, a peripheral 

device such as a SCSI adapter might have a passthrough 

parallel I/O port for connecting a printer through 

the same connector. 

password n. The string of characters entered by a user to 

verify his or her identity to the network. The system compares 

the code against a stored list of authorized passwords 

and users. If the code is legitimate, the system 

allows the user access at whatever security level has been 

approved for the owner of the password. Ideally a password 

is a combination of text, numbers, and punctuation 

or other characters that cannot be guessed at or easily 

cracked by intruders. 

password attack n. An attack on a computer or network 

in which a password is stolen and decrypted or is revealed 

by a password dictionary program. The compromised 

password opens the network to the hacker and may also be 

used to reveal additional network passwords. See also 

password sniffing. 

Password Authentication Protocol n. See PAP (definition 

1). 

password protection n. The use of passwords as a 

means of allowing only authorized users access to a computer 

system or its files. 

password shadowing n. A security system in which an 

encrypted password is stored in a separate “shadow” file, 

and its place is taken by a token representing the password. 

Password shadowing is used as protection from 

password attacks. See also password attack, password 

sniffing. 

password sniffing n. A technique employed by hackers 

to capture passwords by intercepting data packets and 

searching them for passwords. Also called: packet sniffing. 

paste vb. To insert text or a graphic that has been cut or 

copied from one document into a different location in the 

same or a different document. See also cut, cut and paste. 

patch1 n. A piece of object code that is inserted in an executable 

program as a temporary fix for a bug. 

patch2 vb. In programming, to repair a deficiency in the 

functionality of an existing routine or program, generally 

in response to an unforeseen need or set of operating 

P

P 

path PC Card 

circumstances. Patching is a common means of adding a 

feature or a function to a program until the next version 

of the software is released. Compare hack (definition 2), 

kludge (definition 2). 

path n. 1. In communications, a link between two nodes 

in a network. 2. A route through a structured collection of 

information, as in a database, a program, or files stored on 

disk. 3. In programming, the sequence of instructions a 

computer carries out in executing a routine. 4. In information 

processing, such as the theory underlying expert 

(deductive) systems, a logical course through the branches 

of a tree of inferences leading to a conclusion. 5. In file 

storage, the route followed by the operating system 

through the directories in finding, sorting, and retrieving 

files on a disk. 6. In graphics, an accumulation of line segments 

or curves to be filled or drawn. 

path menu n. In windowed environments, the menu or 

drop box used to enter the universal naming convention 

path to a shared network resource. 

pathname n. In a hierarchical filing system, a listing of 

the directories or folders that lead from the current directory 

to a file. Also called: directory path. 

pattern recognition n. 1. A broad technology describing 

the ability of a computer to identify patterns. The term 

usually refers to computer recognition of visual images or 

sound patterns that have been converted to arrays of numbers. 

2. The recognition of purely mathematical or textual 

patterns. 

Pause key n. 1. A key on a keyboard that temporarily 

stops the operation of a program or a command. The Pause 

key is used, for example, to halt scrolling so that a multiscreen 

listing or document can be read. 2. Any key that 

creates a pause in an operation. For example, many game 

programs have a Pause key, often simply the P key, that 

temporarily suspends the game. 

payload n. The effects caused by a virus or other malicious 

code. The payload of a virus may include moving, 

altering, overwriting, and deleting files, or other destructive 

activity. A virus or worm may contain more than one 

payload, each with a separate trigger. 

PB n. See petabyte. 

PB SRAM n. See pipeline burst static RAM. 

394 

PBX n. Acronym for Private Branch Exchange. An automatic 

telephone switching system that enables users 

within an organization to place calls to each other without 

going through the public telephone network. Users can 

also place calls to outside numbers. 

PC n. 1. A microcomputer that conforms to the standard 

developed by IBM for personal computers, which uses a 

microprocessor in the Intel 80x86 family (or compatible) 

and can execute the BIOS. See the illustration. See also 

8086, BIOS, clone, IBM PC. 2. A computer in IBM’s Personal 

Computer line. Also called: IBM PC. See also PCcompatible 

(definition 1), personal computer. 

F0Pgn05.eps 

PC. 

PCB n. See printed circuit board. 

PC board n. See printed circuit board. 

PC Card n. An add-in card that conforms to the PCMCIA 

specification. A PC Card is a removable device, approximately 

the same size as a credit card, that is designed to 

plug into a PCMCIA slot. Release 1 of the PCMCIA specification, 

introduced in June 1990, specified a Type I card 

that is 3.3 millimeters thick and is intended to be used primarily 

as a memory-related peripheral. Release 2 of the 

PCMCIA specification, introduced in September 1991, 

specifies both a 5-millimeter-thick Type II card and a 

10.5-millimeter-thick Type III card. Type II cards accommodate 

devices such as modem, fax, and network cards. 

Type III cards accommodate devices that require more 

space, such as wireless communications devices and rotating 

storage media (such as hard disks). See also PCMCIA, 

PCMCIA slot.

PC Card slot PC memory card 

PC Card slot n. See PCMCIA slot. 

PC-compatible adj. Conforming to IBM PC/XT and PC/ 

AT hardware and software specifications, which have been 

the de facto standard in the computing industry for personal 

computers that use the Intel 80x86 family or compatible 

chips. Most PC-compatible computers today are 

developed outside of IBM; they are still sometimes 

referred to as clones. Also called: IBM PC. See also 8086, 

clone, de facto standard, IBM AT, Wintel. 

PC-DOS n. Acronym for Personal Computer Disk Operating 

System. The version of MS-DOS sold by IBM. MS- 

DOS and PC-DOS are virtually identical, although filenames 

of utility programs sometimes differ in the two versions. 

See also MS-DOS. 

PC Expo n. Annual exposition centering on issues relating 

to the personal computer industry. PC Expo encompasses 

product exhibitions and educational events covering a wide 

range of topics affecting personal computing. 

P-channel MOS n. See PMOS. 

PCI n. See PCI local bus. 

PCI card n. Short for Peripheral Component Interconnect 

card. A card that fits into a PCI local bus to add functionality 

to a PC. Examples of the types of PCI cards available 

include TV tuner cards, video adapters, and network interface 

cards. See also card, PCI local bus. 

PCI expansion slot n. A connection socket for a peripheral 

designed for the Peripheral Component Interconnect 

(PCI) local bus on a computer motherboard. 

PCI Industrial Computer Manufacturers Group n. See 

PICMG. 

PCI local bus n. Short for Peripheral Component Interconnect 

local bus. A specification introduced by Intel Corporation 

that defines a local bus system that allows up to 10 

PCI-compliant expansion cards to be installed in the computer. 

A PCI local bus system requires the presence of a PCI 

controller card, which must be installed in one of the PCIcompliant 

slots. Optionally, an expansion bus controller for 

the system’s ISA, EISA, or Micro Channel Architecture 

slots can be installed as well, providing increased synchronization 

over all the system’s bus-installed resources. The 

PCI controller can exchange data with the system’s CPU 

395 

either 32 bits or 64 bits at a time, depending on the implementation, 

and it allows intelligent, PCI-compliant adapters 

to perform tasks concurrently with the CPU using a technique 

called bus mastering. The PCI specification allows for 

multiplexing, a technique that permits more than one electrical 

signal to be present on the bus at one time. See also local 

bus. Compare VL bus. 

PCIX n. 1. Acronym for Peripheral Component Interconnect 

Extended. A computer bus technology developed by 

IBM, Compaq, and Hewlett-Packard that allows data to be 

transferred at greater speeds. PCIX increases the speed of 

data from 66 MHz to 133 MHz, but it will not run faster 

than the connected peripherals or computer processor will 

allow. PCI and PCIX peripherals are compatible with one 

another. Also called: PCI-X. 2. Acronym for Permissionbased 

Customer Information Exchange. A framework for 

the organization and exchange of information between customer 

and vendor. PCIX allows different companies to map 

information into a customer-friendly, permission-based format 

without changing internal database structures. 

PCL n. See Printer Control Language. 

PCM n. See pulse code modulation. 

PCMCIA n. Acronym for Personal Computer Memory 

Card International Association. A group of manufacturers 

and vendors formed to promote a common standard for 

PC Card–based peripherals and the slot designed to hold 

them, primarily on laptop, palmtop, and other portable 

computers, as well as for intelligent electronic devices. 

PCMCIA is also the name of the standard for PC Cards, 

first introduced in 1990 as release 1. See also PC Card, 

PCMCIA slot. 

PCMCIA card n. See PC Card. 

PCMCIA connector n. The 68-pin female connector 

inside a PCMCIA slot designed to hold the 68-pin male 

connector on a PC Card. See also PC Card, PCMCIA slot. 

PCMCIA slot n. An opening in the housing of a computer, 

peripheral, or other intelligent electronic device 

designed to hold a PC Card. Also called: PC Card slot. See 

also PC Card, PCMCIA connector. 

PC memory card n. 1. An add-in circuit card that 

increases the amount of RAM in a system. See also memory 

card. 2. A Type I PC Card as specified by PCMCIA. In 

P

P 

PCMIA device Peachy virus 

this context, such a card consists of conventional static 

RAM chips powered by a small battery and is designed to 

provide additional RAM to the system. See also PC Card. 

Compare flash memory. 

PCMIA device n. See PC Card. 

p-code n. See pseudocode. 

PCS n. See Personal Communications Services. 

PCT n. 1. Acronym for program comprehension tool. A 

software engineering tool that facilitates the process of 

understanding the structure and/or functionality of computer 

programs. 2. Acronym for Private Communications 

Technology, a protocol standard drafted by Microsoft and 

submitted to the IETF for consideration. PCT, like the 

Netscape-designed SSL (Secure Sockets Layer), supports 

authentication and encryption for securing privacy in Internet 

communications. 3. Acronym for Personal Communications 

Technology. An enhanced version of Secure 

Sockets Layer (SSL). 

.pcx n. The file extension that identifies bitmapped 

images in the PC Paintbrush file format. 

PC/XT n. The second-generation of the original IBM Personal 

Computer. The IBM PC/XT was introduced in 1983 

and was the first of the PC computers to support hard 

disks. See also IBM PC. 

PC/XT keyboard n. The keyboard for the PC/XT. 

Strong, reliable, and equipped with 83 keys, the PC/XT 

keyboard offers a typist an audible click. See also IBM 

PC, PC/XT. 

PDA n. Acronym for Personal Digital Assistant. A lightweight 

palmtop computer designed to provide specific 

functions like personal organization (calendar, note taking, 

database, calculator, and so on) as well as communications. 

More advanced models also offer multimedia 

features. Many PDA devices rely on a pen or other pointing 

device for input instead of a keyboard or mouse, 

although some offer a keyboard too small for touch typing 

to use in conjunction with a pen or pointing device. For 

data storage, a PDA relies on flash memory instead of 

396 

power-hungry disk drives. See also firmware, flash memory, 

handheld PC, PC Card, pen computer. 

PDC n. See Primary Domain Controller. 

PD-CD drive n. Short for phase change rewritable disc– 

compact disc drive. A storage device that combines a CD- 

ROM drive and a phase change rewritable disc (PD) drive, 

which can store up to 650 megabytes of data on cartridges 

of rewritable optical discs. See also phase-change recording. 

PDD n. Acronym for Portable Digital Document. A 

graphics file created from a document by QuickDraw GX 

under Mac OS. PDDs are stored in a form that is independent 

of printer resolution; they print at the highest resolution 

available on the printer used; and they can contain the 

original fonts used in the document. Therefore, a PDD can 

be printed by a computer other than the one on which it 

was created. 

.pdf n. The file extension that identifies documents 

encoded in the Portable Document Format developed by 

Adobe Systems. To display or print a .pdf file, the user 

should obtain the freeware Adobe Acrobat Reader. See 

also Acrobat, Portable Document Format. 

PDL n. See page-description language. 

PDM n. See pulse duration modulation. 

PDO n. See Portable Distributed Objects. 

PDS n. 1. Acronym for Processor Direct Slot. An expansion 

slot in Macintosh computers that is connected 

directly to the CPU signals. There are several kinds of 

PDS slots with different numbers of pins and different sets 

of signals, depending on which CPU is used in a particular 

computer. 2. Acronym for Parallel Data Structure. A hidden 

file, located in the root directory of a disk that is 

shared under AppleShare, that contains access privilege 

information for folders. 

Peachy virus n. A virus, first detected in 2001, that was 

the first to attempt to spread itself through PDF files. The 

Peachy virus takes advantage of an Adobe Acrobat feature 

that enables users to embed files in PDF documents. The 

embedded Peachy virus file infects the computer of a user

peek Pentium upgradable 

who downloads the PDF file and then opens the file in 

Adobe Acrobat. 

peek vb. 1. To read a byte from an absolute memory location. 

Peek commands are often found in programming languages 

such as Basic that do not normally allow access to 

specific memory locations. 2. To look at the next character 

in a buffer associated with an input device without actually 

removing the character from the buffer. 

peer n. Any of the devices on a layered communications 

network that operate on the same protocol level. See also 

network architecture. 

peer-to-peer architecture n. A network of two or more 

computers that use the same program or type of program to 

communicate and share data. Each computer, or peer, is 

considered equal in terms of responsibilities and each acts 

as a server to the others in the network. Unlike a client/ 

server architecture, a dedicated file server is not required. 

However, network performance is generally not as good as 

under client/server, especially under heavy loads. Also 

called: peer-to-peer network. See also peer, peer-to-peer 

communications, server. Compare client/server architecture. 

peer-to-peer communications n. Interaction between 

devices that operate on the same communications level on 

a network based on a layered architecture. See also network 

architecture. 

peer-to-peer network n. See peer-to-peer architecture. 

PE file n. See portable executable file. 

pel n. Short for picture element. See pixel. 

PEM n. See Privacy Enhanced Mail. 

pen n. See light pen, stylus. 

pen-based computing n. The process of entering handwritten 

symbols into a computer via a stylus and pressuresensitive 

pad. See also pen computer. 

pen computer n. Any of a class of computers whose primary 

input device is a pen (stylus) instead of a keyboard. 

A pen computer is usually a smaller, handheld device and 

397 

has a flat semiconductor-based display such as an LCD 

display. It requires either a special operating system 

designed to work with the pen input device or a proprietary 

operating system designed to work with a specificpurpose 

device. The pen computer is the primary model 

for an emerging class of computers known as personal 

digital assistants (PDAs). See also clipboard computer, PC 

Card, PDA. 

Penguin n. Slang for the Linux operating system or a 

Linux user. The name comes from the penguin character 

used as the Linux mascot. See also Tux. 

pen plotter n. A traditional graphics plotter that uses 

pens to draw on paper. Pen plotters use one or more colored 

pens, either fiber-tipped pens or, for highest-quality 

output, drafting pens. See also plotter. Compare electrostatic 

plotter. 

Pentium n. A family of 32-bit microprocessors introduced 

by Intel in March 1993 as the successor to the i486. 

The Pentium family is composed of superscalar, CISCbased 

microprocessors containing between 3 million (earlier 

models) and 28 million transistors. They have a 32-bit 

address bus, a 64-bit data bus, a built-in floating-point unit 

and memory management unit, built-in caches, and a System 

Management Mode (SMM), which provides the 

microprocessor with the ability to slow or halt some system 

components when the system is idle or performing 

non-CPU-intensive tasks, thereby lessening power consumption. 

The Pentium also employs branch prediction, 

resulting in faster system performance. In addition, the 

Pentium has built-in features to ensure data integrity, and 

it supports functional redundancy checking (FRC). The 

Pentium II introduced MMX media enhancement support. 

See also branch prediction, CISC, functional redundancy 

checking, i486DX, L1 cache, L2 cache, microprocessor, 

MMX, P5, SIMD, superscalar. 

Pentium upgradable n. 1. An i486 motherboard capable 

of being adapted to run a Pentium-class processor. See 

also i486DX, microprocessor, motherboard, Pentium. 

P

P 

perfboard perpendicular recording 

2. A 486 PC that can be upgraded to Pentium class by adding 

a Pentium processor. See also i486DX. 

perfboard n. Short for perforated fiber board. See breadboard. 

performance monitor n. A process or program that 

appraises and records status information about various 

system devices and other processes. 

period n. The length of time required for an oscillation to 

complete one full cycle. For an oscillating electrical signal, 

the period is the time between waveform repetitions. 

If f is the frequency of oscillation in hertz, and t is the 

period in seconds, then t = 1/f. See the illustration. 

Amplitude 

1 

period 

F0Pgn06.eps 

Period. The period of an oscillating signal. 

Time 

peripheral n. In computing, a device, such as a disk drive, 

printer, modem, or joystick, that is connected to a computer 

and is controlled by the computer’s microprocessor. 

Also called: peripheral device. See also console. 

Peripheral Component Interconnect n. See PCI local 

bus. 

peripheral device n. See peripheral. 

peripheral power supply n. An auxiliary source of electricity 

used by a computer or a device as a backup in case 

of a power failure. Acronym: PPS. 

Perl n. Acronym for Practical Extraction and Report Language. 

An interpreted language, based on C and several 

UNIX utilities. Perl has powerful string-handling features 

for extracting information from text files. Perl can assemble 

a string and send it to the shell as a command; hence, it 

398 

is often used for system administration tasks. A program 

in Perl is known as a script. Perl was devised by Larry 

Wall at NASA’s Jet Propulsion Laboratory. 

permanent storage n. A recording medium that retains 

the data recorded on it for long periods of time without 

power. Ink on paper is by far the most widely used permanent 

storage, but data can be transferred from paper to a 

computer only with difficulty. Typically, some form of 

magnetic medium, such as floppy disk or tape, is preferable. 

Magnetic media are generally accepted as permanent, 

even though the magnetic fields that encode data in the 

media tend to fade eventually (in five years or more). See 

also nonvolatile memory. 

permanent swap file n. In Windows, a file composed of 

contiguous disk sectors used for virtual memory operations. 

See also swap file, virtual memory. 

permanent virtual circuit n. See PVC. 

permission n. In a networked or multiuser computer 

environment, the ability of a particular user to access a 

particular resource by means of his or her user account. 

Permissions are granted by the system administrator or 

other authorized person. Several levels of access can be 

given: read only, read and write (view and change), or 

read, write, and delete. Also called: Access permission. 

permission class n. A class that defines access to a 

resource or defines an identity by supporting authorization 

checks. 

permission object n. An instance of a permission class 

that represents access rights to resources or identity. A 

permission object can be used to specify a request, a 

demand, or a grant of permission. 

permissions log n. A file on a network or multiuser computer 

environment where permissions for users are stored. 

When a user attempts to access a resource on the system, 

the permissions log is checked to see whether the user has 

permission to use it. 

perpendicular recording n. A method of increasing storage 

capacity on magnetic media by aligning the magnetic 

dipoles, whose orientation determines bit values, in a 

direction that is perpendicular to the recording surface. 

Also called: vertical recording.

per-pixel lighting Personal Web Server 

per-pixel lighting n. A lighting scheme used in 3D computer 

game rendering and other digital animation applications 

that calculates proper lighting for every pixel 

displayed. Per-pixel lighting allows highly realistic 

lighting effects but requires significant video card capabilities 

to display properly. Also called: Phong shading. 

Per Seat Licensing n. A licensing mode that requires a 

separate Client Access License for each client computer, 

regardless of whether all the clients access the server at the 

same time. See also client. Compare Per Server Licensing. 

Per Server Licensing n. A licensing mode that requires a 

separate Client Access License for each concurrent connection 

to the server, regardless of whether there are other 

client computers on the network that do not happen to 

connect concurrently. Compare Per Seat Licensing. 

persistence n. A characteristic of some light-emitting 

materials, such as the phosphors used in CRTs, that causes 

an image to be retained for a short while after being irradiated, 

as by an electron beam in a CRT. The decay in persistence 

is sometimes called luminance decay. 

persistent client connection n. See persistent connection. 

persistent connection n. A connection to a client that 

remains open after a server sends a response. Included in 

HTTP 1.1 and similar to the Netscape HTTP 1.0 Keep- 

Alive extension, persistent connections are used to 

improve Internet efficiency and performance by eliminating 

the overhead associated with multiple connections. 

Also called: persistent client connection. See also pipelining 


persistent data n. Data that is stored in a database or on 

tape so that it is retained by the computer between sessions. 

persistent link n. See hot link (definition 1). 

persistent storage n. Memory that remains intact when 

the power to a device is turned off, such as ROM. See also 

memory. 

Personal Communications Services n. Term used by 

the United States Federal Communications Commission 

(FCC) to cover a range of wireless, all-digital communications 

technologies and services, including cordless phones, 

voice mail, paging, faxing, and personal digital assistants 

(PDAs). Personal Communications Services, or PCS, is 

399 

divided into narrowband and broadband categories. Narrowband, 

which operates in the 900 MHz band of frequencies, 

provides paging, data messaging, faxing, and one- and 

two-way electronic messaging capabilities. Broadband, 

which operates in the 1850 MHz to 1990 MHz range and is 

considered the next-generation PCS, enables two-way 

voice, data, and video communications. The cellular phone 

technologies known as GSM (Global System for Mobile 

Communications), CDMA (Code Division Multiple 

Access), and TDMA (Time Division Multiple Access) are 

included in the PCS category. Acronym: PCS. Compare 

Code Division Multiple Access, Global Systems for 

Mobile Communications, Time Division Multiple Access. 

personal computer n. A computer designed for use by 

one person at a time. Personal computers do not need to 

share the processing, disk, and printer resources of another 

computer. IBM PC–compatible computers and Apple 

Macintoshes are both examples of personal computers. 

Acronym: PC. 

Personal Computer n. See IBM PC. 

Personal Computer Memory Card International 

Association n. See PCMCIA. 

personal digital assistant n. See PDA. 

personal finance manager n. A software application 

designed to assist the user in performing simple financial 

accounting tasks, such as balancing checkbooks and paying 

bills. 

Personal Handyphone System n. A device developed in 

Japan to act as a cellular phone that can handle phone, 

FAX, and voice. Acronym: PHS. 

personal identification number n. See PIN. 

personal information manager n. See PIM. 

personalization technology n. An e-commerce marketing 

technique in which Web sites and services analyze the 

interests of individual customers. The e-business then uses 

this information to deliver services, product offerings, and 

advertising that match each customer’s personal interests. 

Personal Web Server n. Microsoft applications that 

allow a computer running the Windows family of operating 

systems to function as a Web server for publishing 

personal Web pages and intranet sites. Personal Web 

P

P 

perspective view phase modulation 

Server is available as part of Microsoft Windows NT 4.0 

Option Pack (NTOP), Windows 98, and Windows 95 

OEM Service Release 2. FrontPage Personal Web Server 

is available as part of FrontPage 1.1, FrontPage 97, 

FrontPage 98, and FrontPage 2000. 

perspective view n. In computer graphics, a display 

method that shows objects in three dimensions (height, 

width, and depth), with the depth aspect rendered according 

to the desired perspective. An advantage of perspective 

view is that it presents a more accurate representation of 

what the human eye perceives. Compare isometric view. 

peta- prefix Denotes 1 quadrillion (1015 ). In computing, 

which is based on the binary (base 2) numbering system, 

peta- has a literal value of 1,125,899,906,842,624, 

which is the power of 2 (250 ) closest to 1 quadrillion. 

Abbreviation: P. 

petabyte n. Either 1 quadrillion bytes or 

1,125,899,906,842,624 bytes. Abbreviation: PB. 

PGA n. See pin grid array, Professional Graphics Adapter. 

PgDn key n. See Page Down key. 

PGP n. Acronym for Pretty Good Privacy. A program for 

public key encryption, using the RSA algorithm, developed 

by Philip Zimmermann. PGP software is available in unsupported 

free versions and supported commercial versions. 

See also privacy, public key encryption, RSA encryption. 

PgUp key n. See Page Up key. 

phage virus n. A destructive virus that affects the Palm 

operating system (OS). Phage copies itself, overwriting 

application files and destroying them. Once the first host 

file is infected, Phage will spread to all available files. 

Phage may be spread from one Palm device to another by 

beaming or connection with a docking station. Phage was 

one of the first viruses created specifically to affect handheld 

wireless devices and the first to impact the Palm OS. 

phase n. A relative measurement that describes the temporal 

relationship between two signals that have the same 

frequency. Phase is measured in degrees, with one full 

oscillation cycle having 360 degrees. The phase of one 

signal can lead or follow the other by 0 through 180 

degrees. See the illustration. 

400 

Amplitude 

Phase 

difference 

a 

b 

Signal 

1 

Signal 

2 

Time 

F0Pgn07.eps 

Phase. The ratio of a to b is the phase difference, expressed in 

degrees. 

phase-change recording n. In optical media, a recording 

technique that uses a laser beam focused on a microscopic 

portion of metallic crystal to alter the reflectiveness 

of its structure in such a way that the change can be read 

as a 0 bit or 1 bit, depending on whether the resulting 

structure reflects or absorbs the laser light. See also PD- 

CD drive. 

phase encoding n. 1. The process of placing digital 

information on an analog carrier wave while periodically 

changing the phase of the carrier to increase the bit density 

of the transmission. See also Manchester coding, phase. 

2. A recording technique used with magnetic storage 

devices in which each data-holding unit is divided into 

two parts, each of which is magnetized so that it is opposite 

in polarity to the other. 

phase-locked adj. Of, pertaining to, or characteristic of 

the relationship between two signals whose phases relative 

to each other are kept constant by a controlling mechanism, 

such as an electronic device. 

phase modulation n. A method of imposing information 

onto a waveform signal by shifting the phase of the wave 

to represent information, such as the binary digits 0 and 1. 

See the illustration. See also phase-shift keying.

phase-shift keying phosphor 

0° 

90° 

Phase 180° phase shift Baseline 

180° 360° 

270° 

F0Pgn08.eps 

Phase modulation. A phase shift of 180 degrees. 

phase-shift keying n. A communications method used 

by modems to encode data that relies on phase shifts in a 

carrier wave to represent digital information. In its simplest 

form, phase-shift keying allows the phase of the carrier 

wave to be in either of two states: shifted 0 degrees or 

shifted 180 degrees, effectively reversing the phase of the 

wave. This straightforward phase-shift keying, however, is 

useful only when each phase can be measured against an 

unchanging reference value, so a more sophisticated technique 

called differential phase-shift keying, or DPSK, is 

used in many modems. In differential phase-shift keying, 

the phase of the carrier wave is shifted to represent more 

than two possible states, and each state is interpreted as a 

relative change from the state preceding it. No reference 

values or timing considerations are required and because 

more than two states are possible, more than one binary 

digit can represent each state. Acronym: PSK. See also 

phase modulation. 

Phoenix BIOS n. An IBM-compatible ROM BIOS manufactured 

by Phoenix Technologies, Ltd. A popular ROM 

BIOS in many so-called PC clone computers, the Phoenix 

BIOS was an early leader among the IBM-compatible 

computers shortly after they began to appear in the marketplace. 

See also BIOS, ROM BIOS. Compare AMI BIOS. 

phone connector n. An attachment, usually an RJ-11 

connector, used to join a telephone line to a device such as 

a modem. See the illustration. 

401 

Time 

F0Pgn09.eps 

Phone connector. 

phoneline networking n. The use of telephone wiring 

for connecting computers and other devices in a small network, 

such as a home network. See also HomePNA. 

phoneme n. In linguistics, the smallest unit of speech that 

distinguishes one word sound from another. Phonemes are 

the elements on which computer speech is based. 

phono connector n. An attachment used to connect a 

device, such as a microphone or a pair of headphones, to a 

piece of audio equipment or to a computer peripheral or 

adapter with audio capability. See the illustration. 

F0Pgn10.eps 

Phono connector. 

phosphor n. Any substance capable of emitting light 

when struck by radiation. The inside surface of a CRT 

screen is coated with a phosphor that, when excited by an 

electron beam, displays an image on the screen. See also 

persistence. 

P

P 

PhotoCD PHP 

PhotoCD n. A digitizing system from Kodak that allows 

35mm film pictures, negatives, slides, and scanned images 

to be stored on a compact disc. Images are stored in a file 

format called Kodak PhotoCD IMAGE PAC File Format, 

or PCD. Many photography or film development businesses 

offer this service. Images stored on a PhotoCD can 

usually be viewed by any computer with CD-ROM capabilities 

and the software required to read PCD. Such 

images can also be viewed using one of a variety of players 

designed to display images stored on CDs. 

photo cell n. See photoelectric device. 

photocomposition n. In traditional typesetting, the use 

of photographic and electronic equipment in laying out 

and producing a printed page. In desktop publishing, phototypesetters 

are used to accomplish the same ends. See 

also phototypesetter. Compare imagesetter. 

photoconductor n. A material that exhibits increased 

conductivity when it is exposed to a source of light. Photoconductors 

are used in photodetectors, which are used in 

fiber optics to register light and convert it into electrical 

pulses. See also fiber optics. 

photo editor n. A graphics application used to manipulate 

an image, such as a scanned photograph, digitally. 

photoelectric device n. A device that uses light to create 

or modulate an electric signal. A photoelectric device uses 

semiconductor material and falls in one of two categories. 

In one type (photocell), light falling on the semiconductor 

generates an electrical current. In another type of device 

(photosensor), light changes the resistance of the semiconductor 

material, modulating an applied voltage. 

photolithography n. A technique used in the fabrication 

of integrated circuits. The circuit pattern is drawn, photographed, 

and reduced to a negative having the desired final 

size. This negative is called the photomask. Light is passed 

through the photomask onto a wafer made of semiconductor 

material that has been coated with a photoresistive 

material. Where light strikes the photoresistive material, 

its composition is changed. In the next step, the photoresistive 

material not affected by light is washed off. Finally, 

the semiconductor material is exposed to an etching solution 

that eats away the surface not protected by the photoresistive 

material, creating the desired circuit pattern on 

the surface of the wafer. See also photomask, photoresist. 

402 

photomask n. A photographic negative image of a circuit 

pattern used in fabrication of integrated circuits. See also 

photolithography. 

photonics n. Optoelectronic systems that transmit visible 

light or infrared energy. Photonic systems are used with 

fiber optic networks and optical circuits. Photonic networks 

offer dramatic increases in speed and bandwidth, 

allowing significantly greater amounts of information to 

be encoded and transmitted than with traditional cabling 

solutions. 

photorealism n. The process of creating images that are 

as close to photographic or “real-life” quality as possible. 

In computer graphics, photorealism requires powerful 

computers and highly sophisticated software and is 

heavily mathematical. See also ray tracing. 

photoresist n. A compound that is used in photolithographic 

fabrication of integrated circuits and printed circuit 

boards. When exposed to ultraviolet light through a 

photomask, the photoresistive material exposed to the 

light polymerizes (hardens); the areas not exposed can be 

washed away, leaving the pattern of traces on the substrate. 

Subsequent etching removes areas not protected by 

the polymerized photoresist. 

photosensor n. See photoelectric device. 

Photoshop n. Adobe software product for digital image 

editing and enhancement, photo retouching, and color 

management of graphic images. Photoshop includes such 

features as multiple undo, text editing with formatting 

control, and enhanced color management and controls. 

The program supports numerous Web and graphics file 

formats and runs on both the Windows and Power Macintosh 

platforms. 

phototypesetter n. A printer similar to a laser printer but 

capable of resolutions over 2,000 dots per inch. Phototypesetters 

apply light directly to a photographic film or 

photosensitive paper. See also photocomposition. Compare 

imagesetter. 

photovoltaic cell n. See solar cell. 

PHP n. Acronym for PHP: Hypertext Preprocessor. An 

open source scripting language used with HTML documents 

to execute server-side interactive functions. PHP 

runs on all major operating systems and is primarily used 

with Linux and UNIX Web servers or on Windows servers 

with add-on software. PHP may be embedded in a Web

phreak1 phreak 

pica 

page and used to access and present database information. 

An HTML document that contains a PHP script usually 

has a .php filename extension. Originally PHP stood for 

“Personal Home Page,” with later versions standing for 

“PHP Hypertext Preprocessor” or simply PHP. The syntax 

of PHP is fairly simple and very similar to that of Perl, 

with some aspects of Bourne shell, JavaScript, and C. It 

can also be regarded as a technology (server-side environment 

for ported script engines, like ASP). 

phreak1 n. A person who breaks into, or cracks, telephone 

networks or other secured systems. In the 1970s, 

the telephone system used audible tones as switching signals, 

and phone phreaks used homebrew hardware to 

match the tones and steal long-distance service. See also 

homebrew. Compare cracker, hacker (definition 2). 

phreak2 vb. To break into, or crack, phone networks or 

computer systems. See also homebrew. Compare hack. 

PHS n. See Personal Handyphone System. 

physical adj. In computing, of, pertaining to, or characteristic 

of a real, as opposed to a conceptual, piece of 

equipment or frame of reference. Compare logical (definition 

2). 

physical address n. An address that corresponds to a 

hardware memory location. In simple processors such as 

the 8088 and the 68000, every address is a physical 

address. In processors supporting virtual memory, programs 

reference virtual addresses, which are then mapped 

by memory management hardware onto physical 

addresses. Also called: hardware address. See also memory 

management unit, paging, virtual memory. 

physical-image file n. A hard disk copy of the material to 

be recorded onto a CD-ROM. Creating a complete copy 

precludes problems in writing the CD-ROM because of 

delays in assembling the material from a scattered group 

of files. See also CD-ROM. Compare virtual-image file. 

physical layer n. The first, or lowest, of the seven layers 

in the ISO/OSI reference model for standardizing computer-to-computer 

communications. The physical layer is 

totally hardware-oriented and deals with all aspects of 

establishing and maintaining a physical link between communicating 

computers. Among specifications covered on 

the physical layer are cabling, electrical signals, and 

mechanical connections. See the illustration. See also 


403 

ISO/OSI Layer 

Application 


Presentation 

Session 

Transport 

Network 

Data-link 

Physical 

ISO/OSI MODEL 

Focus 




conversion 









F0Pgn11.eps 

Physical layer. Lowest layer in the ISO/OSI reference model. 

physical memory n. Memory actually present in the system, 

as opposed to virtual memory. A computer might 

have 64 megabytes of physical RAM but support a virtual 

memory capacity of 1 gigabyte or more. Compare virtual 

memory. 

physical network n. One of two ways of describing the 

topology, or layout, of a computer network; the other is 

logical network. A physical network refers to the actual 

configuration of the hardware forming a network—that is, 

to the computers, connecting hardware, and especially the 

cabling patterns that give the network its shape. Basic 

physical layouts include the bus, ring, and star topologies. 

See also bus network, logical network, ring network, star 

network. 

physical storage n. See real storage. 

pi n. A mathematical constant equal to approximately 

3.1415926535897932, describing the ratio of the circumference 

of a circle to its diameter. 

PIC n. See programmable interrupt controller. 

pica n. 1. With reference to typewriters, a fixed-width 

type font that fits 10 characters to the linear inch. See also 

pitch. 2. As used by typographers, a unit of measure equal 

to 12 points or approximately 1/6 inch. See also point1 (definition 1). 

P

P 

PICMG pin-compatible 

PICMG n. Acronym for the PCI Industrial Computer 

Manufacturers Group. A consortium of more than 350 

computer product vendors, this non-profit organization 

develops specifications for PCI-based devices, such as the 

CompactPCI specification. See also CompactPCI. 

pico- prefix Denotes one trillionth (10 –12 ), or, in the British 

numbering system, one million millionth. 

Abbreviation: p. 

picoJava n. A microprocessor developed by Sun Microsystems, 

Inc., that executes Java code. See also Java. 

picosecond n. One trillionth of a second. 

Abbreviation: psec. 

PICS n. See Platform for Internet Content Selection. 

.pict n. The file extension that identifies graphic images 

in the Macintosh PICT format. See also PICT. 

PICT n. A file-format standard for encoding graphical 

images, both object-oriented and bitmapped. The PICT 

file format was first used in Macintosh applications, but 

many PC applications can read the format too. See also 

bitmapped graphics, object-oriented graphics. 

picture element n. See pixel. 

pie chart n. A type of graph that presents values as percentages 

(slices) of a whole (a pie). 

piezoelectric adj. Of, pertaining to, or characteristic of 

crystals that can convert between mechanical and electrical 

energy. An electric potential applied to a piezoelectric 

crystal causes a small change in the shape of the crystal. 

Likewise, physical pressure applied to the crystal creates 

an electrical potential difference between the surfaces of 

the crystal. 

piggyback board n. A printed circuit board that plugs 

into another circuit board to enhance its capabilities. A piggyback 

board is sometimes used to replace a single chip, in 

which case the chip is removed and the piggyback board is 

inserted into the empty socket. See also daughterboard. 

Pilot n. A series of popular handheld personal digital 

assistants (PDAs) designed by Palm and based on the 

Palm OS operating system. Palm introduced its first Pilot 

model in 1996, followed in 1997 by the PalmPilot, and 

thereafter by a series of other Palm handheld models. 

404 

PILOT n. Acronym for Programmed Inquiry, Learning or 

Teaching. A programming language developed in 1976 by 

John A. Starkweather and designed primarily for creating 

applications for computer-aided instruction. 

PIM n. Acronym for personal information manager. An 

application that usually includes an address book and 

organizes unrelated information, such as notes, appointments, 

and names, in a useful way. 

pin n. A slender prong. Pins are commonly encountered 

as the contacts protruding from a male connector. Connectors 

are often identified by the number of pins they have. 

Other types of pins are the spidery, leglike metal appendages 

that connect computer chips to sockets on a circuit 

board or directly to the circuit board. See the illustration. 

Pins 

F0Pgn12.eps 

Pin. A 16-pin DIP (top) and a 6-pin DIN (bottom). 

PIN n. Acronym for personal identification number. A 

unique code number used to gain access to personal information 

or assets via an electronic device. PINs are used by 

a variety of electronic services such as automated bank 

tellers, Internet sites, and wireless phone services. 

pinch roller n. A small cylindrical pulley that presses 

magnetic tape against the drive’s capstan to move the tape 

over the tape machine’s heads. See also capstan. 

pinch-roller plotter n. A type of plotter, intermediate 

between drum and flatbed types, that uses hard rubber or 

metal wheels to hold the paper against the main roller. See 

also plotter. Compare drum plotter, flatbed plotter. 

pin-compatible adj. Having pins that are equivalent to the 

pins on another chip or device. A chip, for example, might 

have different internal circuitry from that used in another 

chip, but if the two chips use the same pins for input and 

output of identical signals, they are pin-compatible. Compare 

plug-compatible.

pine pipeline burst static RAM 

pine n. Acronym for pine is not elm, or for Program for 

Internet News and E-mail. One of the most commonly 

encountered programs for reading and composing e-mail 

on character-based UNIX systems. The pine program was 

developed as an improved version of elm at the University 

of Washington. Compare elm. 

pin feed n. A method of feeding paper through a printer 

in which small pins, mounted on rollers on the ends of the 

platen, engage holes near the edges of continuous-form 

paper. See also continuous-form paper, paper feed. Compare 

tractor feed. 

ping1 n. 1. Acronym for Packet Internet Groper. A protocol 

for testing whether a particular computer is connected 

to the Internet by sending a packet to its IP address and 

waiting for a response. The name actually comes from 

submarine active sonar, where a sound signal—called a 

“ping”—is broadcast, and surrounding objects are 

revealed by their reflections of the sound. 2. A UNIX utility 

that implements the ping protocol. 

ping2 vb. 1. To test whether a computer is connected to 

the Internet using the ping utility. 2. To test which users on 

a mailing list are current by sending e-mail to the list asking 

for a response. 

Ping of Death n. A form of Internet vandalism that 

entails sending a packet that is substantially larger than the 

usual 64 bytes over the Internet via the ping protocol to a 

remote computer. The size of the packet causes the computer 

to crash or reboot. See also packet (definition 2), 

ping1 (definition 1). 

ping packet n. An “are you there” message transmitted 

by a Packet Internet Groper program. A ping packet is sent 

from one node to the IP (Internet Protocol) address of a 

network computer to determine whether that node is able 

to send and receive transmissions. Many shareware and 

freeware ping utilities for PCs are available for download 

from the Internet. See also ping1 (definition 1), packet1 (definition 1). 

ping pong n. 1. In communications, a technique that 

changes the direction of transmission so that the sender 

becomes the receiver and vice versa. 2. In information 

processing and transfer, the technique of using two temporary 

storage areas (buffers) rather than one to hold both 

input and output. 

405 

ping-pong buffer n. A double buffer in which each part is 

alternately filled and flushed, resulting in a more or less 

continuous stream of input and output data. See also ping 

pong (definition 2). 

pin grid array n. A method of mounting chips on boards, 

preferred for chips with a very large number of pins. Pin 

grid array packages have pins protruding from the bottom 

surface of the chip, as opposed to dual in-line packages 

and leaderless chip carrier packages, which have pins protruding 

from the edges. Acronym: PGA. Compare DIP, 

leadless chip carrier. 

pink contract n. A non-standard addendum to a contract 

with an Internet service provider (ISP), specifically offering 

the client the opportunity to send unsolicited commercial email 

and put up spam-related Web sites. See also spam. 

pinout n. A description or diagram of the pins of a chip or 

connector. See also pin. 

PIO n. Acronym for Programmed Input/Output (or, less 

frequently, Processor Input/Output). One of two transfer 

methods used in moving data between a disk drive and 

memory. With PIO, the disk controller moves a block of 

data into the CPU’s registers, and the CPU then moves the 

data to its intended destination. PIO is characteristic of 

IDE drives. The alternative data-transfer method, direct 

memory access (DMA), bypasses the CPU and moves 

data directly between disk and memory. See also Bus, bus 

mastering, controller. Compare direct memory access. 

pipe n. 1. A portion of memory that can be used by one 

process to pass information along to another. Essentially, a 

pipe works like its namesake: it connects two processes so 

that the output of one can be used as the input to the other. 

See also input stream, output stream. 2. The vertical line 

character (|) that appears on a PC keyboard as the shift 

character on the backslash (\) key. 3. In MS-DOS and 

UNIX, a command function that transfers the output of 

one command to the input of a second command. 

pipeline burst static RAM n. A type of static RAM that 

uses burst and pipelining technologies to increase the 

speed at which information can be provided to a computer’s 

CPU. By pipelining requests so that one is being 

acted upon at the same time the next is getting underway, 

pipeline burst static RAM, or PB SRAM, can provide 

information to the CPU at high speed. PB SRAM is used 

in L2 caches (rapid-response memory dedicated to storing 

P

P 

pipeline processing pixel image 

frequently requested data) on computers running at bus 

speeds of 75 MHz or higher. Acronym: PB SRAM. See 

also burst (definition 2), L2 cache, pipelining, static RAM. 

Compare asynchronous static RAM, dynamic RAM, synchronous 

burst static RAM. 

pipeline processing n. A method of processing on a 

computer that allows fast parallel processing of data. This 

is accomplished by overlapping operations using a pipe, or 

a portion of memory that passes information from one 

process to another. See also parallel processing, pipe (definition 

1), pipelining (definition 3). 

pipelining n. 1. A method of fetching and decoding 

instructions (preprocessing) in which, at any given time, 

several program instructions are in various stages of being 

fetched or decoded. Ideally, pipelining speeds execution 

time by ensuring that the microprocessor does not have to 

wait for instructions; when it completes execution of one 

instruction, the next is ready and waiting. See also superpipelining. 

2. In parallel processing, a method in which 

instructions are passed from one processing unit to 

another, as on an assembly line, and each unit is specialized 

for performing a particular type of operation. 3. The 

use of pipes in passing the output of one task as input to 

another until a desired sequence of tasks has been carried 

out. See also pipe (definition 1), pour. 

piracy n. 1. The theft of a computer design or program. 

2. Unauthorized distribution and use of a computer 

program. 

.pit n. A file extension for an archive file compressed with 

PackIT. See also PackIT. 

pitch n. A measure, generally used with monospace fonts, 

that describes the number of characters that fit in a horizontal 

inch. See also characters per inch, screen pitch. 

Compare point1 (definition 1). 

PivotChart adj. A graphical tool in Microsoft Excel or 

Access that can be used to display data from a list or database 

in chart form. Based on user-selected information 

incorporated in an Excel PivotTable report or list, a Pivot- 

Chart report provides the ability to chart the data interactively—for 

example, to “pivot” the chart’s point of view 

from product sales by category to product sales by region 

or by salesperson. See also PivotTable. 

406 

PivotTable adj. An interactive table in Microsoft Excel or 

Access that can show the same data from a list or a database 

in more than one arrangement. A user can manipulate 

the rows and columns in a PivotTable to view or summarize 

the information in different ways for purposes of analysis. 

In Excel, a PivotTable report is the basis for creating a PivotChart 

report that displays the same data in chart form. 

See also PivotChart. 

pivot year n. In Year 2000 windowing, a date in a 100year 

period that serves as the point from which correct 

dates can be calculated in systems or software that can 

store only 2-digit years. For example, a pivot year of 1970 

means that the numbers 70 through 99 are interpreted as 

the years 1970 to 1999, and the numbers 00 through 69 as 

the years 2000 through 2069. See also windowing. 

pixel n. Short for picture (pix) element. One spot in a rectilinear 

grid of thousands of such spots that are individually 

“painted” to form an image produced on the screen by 

a computer or on paper by a printer. A pixel is the smallest 

element that display or print hardware and software can 

manipulate in creating letters, numbers, or graphics. See 

the illustration. Also called: pel. 

Pixel 

F0Pgn13.eps 

Pixel. The letter A is actually made up of a pattern of pixels in 

a grid, as is the cat’s eye. 

pixel image n. The representation of a color graphic in a 

computer’s memory. A pixel image is similar to a bit 

image, which also describes a screen graphic, but a pixel 

image has an added dimension, sometimes called depth, 

that describes the number of bits in memory assigned to 

each on-screen pixel.

pixel map platform 

pixel map n. A data structure that describes the pixel 

image of a graphic, including such features as color, 

image, resolution, dimensions, storage format, and number 

of bits used to describe each pixel. See also pixel, pixel 

image. 

PJL n. See Printer Job Language. 

PJ/NF n. Acronym for projection-join normal form. See 

normal form (definition 1). 

PKUNZIP n. A shareware utility program that uncompresses 

files compressed by the PKZIP shareware utility 

program. PKUNZIP is generally made available with 

PKZIP; distribution of PKUNZIP for commercial purposes 

is not permitted without obtaining permission from 

its publisher, PKware, Inc. See also PKZIP. 

PKZIP n. A widely used shareware utility program for 

compressing files. Developed by PKware, Inc., in 1989 

and available from a wide variety of sources, PKZIP can 

combine one or more files into a compressed output file 

having the extension .zip. A companion utility program, 

PKUNZIP, is required to uncompress the compressed 

files. See also PKUNZIP, shareware, utility program. 

PLA n. Acronym for programmable logic array. See fieldprogrammable 

logic array. 

placeholder n. 1. A character that masks or hides another 

character for security reasons. For example, when a user 

types a password, an asterisk is displayed on the screen to 

take the place of each character typed. 2. Text or some 

other element used in an application as an indicator that 

the user should enter in his or her own text. 

Plain Old Telephone Service n. See POTS. 

plaintext n. 1. Nonencrypted or decrypted text. See also 

decryption, encryption. 2. A file that is stored as plain 

ASCII data. Compare ciphertext. 

plain vanilla adj. Ordinary; the standard version of hardware 

or software without any enhancements. For example, 

a plain vanilla modem might have data transfer capability 

but no fax or voice features. 

.plan n. A file in a UNIX user’s home directory that is displayed 

when other users finger that account. Users can 

enter information into .plan files at their discretion to provide 

information in addition to that normally displayed by 

the finger command. See also finger. 

407 

planar adj. 1. In computer graphics, lying within a plane. 

2. In the fabrication of semiconductor materials, maintaining 

the original flat surface of the silicon wafer throughout 

processing, while the chemicals that make up the elements 

that control the flow of current are diffused into (and 

beneath) the surface. 

planar transistor n. A special form of transistor that is 

fabricated with all three elements (collector, emitter, and 

base) on a single layer of semiconductor material. The 

structure of a planar transistor permits it to dissipate relatively 

large amounts of heat, making this design suitable 

for power transistors. See the illustration. 

Insulating layer 

Emitter 

Base 

Collector 

F0Pgn14.eps 

Planar transistor. 

plasma display n. See gas-discharge display. 

plastic leadless chip carrier n. See PLCC. 

plastic transistor n. A transistor produced entirely from 

plastic rather than the traditional silicon. A plastic transistor 

is flexible enough to be embedded in curved surfaces 

or folded. Production of plastic transistors begins with a 

thin piece of clear plastic, onto which layers of plastic are 

printed or sprayed through a mesh. The result is a lightweight, 

flexible and transparent transistor that can be manufactured 

in high volumes for a fraction of the cost of 

silicon transistors. The flexibility and low-cost of plastic 

transistors make them useful in applications from transparent 

foldable displays to one-use product containers. See 

also electronic paper. 

platen n. The cylinder in most impact printers and typewriters, 

around which the paper wraps and against which 

the print mechanism strikes the paper. The paper bail, a 

spring-loaded bar with small rollers, holds the paper 

smoothly against the platen just above the print mechanism. 

platform n. 1. The foundation technology of a computer 

system. Because computers are layered devices composed 

P

P 

Platform for Internet Content Selection plotter 

of a chip-level hardware layer, a firmware and operatingsystem 

layer, and an applications program layer, the bottommost 

layer of a machine is often called a platform. 

2. In everyday usage, the type of computer or operating 

system being used. 

Platform for Internet Content Selection n. A specification 

for rating and labeling Internet content. Originally 

developed by the World Wide Web Consortium to enable 

parents, teachers, administrators, and other caretakers to 

control the material to which children have online access, 

its use has expanded to include the protection of privacy 

and intellectual property. PICS is not itself a system for rating 

Internet content. Rather, it specifies the format conventions 

to be used by rating systems in devising labels that 

can be read by PICS-compatible software. Acronym: PICS. 

Platform for Privacy Preference Project n. See P3P. 

Platform for Privacy Preferences n. See P3P. 

platform invoke n. The functionality provided by the run 

time to enable managed code to call unmanaged native 

DLL entry points. 

platter n. One of the individual metal data storage disks 

within a hard disk drive. Most hard disks have from two to 

eight platters. See the illustration. See also hard disk. 

F0Pgn15.eps 

Platter. 

Platters 

player n. In relation to digital audio, a program that plays 

music and other audio files that have been ripped (transferred 

from a compact disc to a hard disk) and then 

encoded in a playable format, such as MP3. See also 

encoder, MP3, ripper. 

PlayStation n. Sony Corporation’s console computer 

entertainment gaming system. PlayStation 2, the latest 

version, is a 128-bit system that features a 300-Mhz pro- 

408 

cessor, 32 MB of Direct RDRAM main memory, and a 

floating-point performance of 6.2 GFLOPS. PlayStation 2 

also offers the capability to play CDs and DVDs. See also 

computer game, console game. Compare Dreamcast, 

GameCube, Xbox. 

PL/C n. A version of the PL/I programming language 

developed at Cornell University and used on mainframe 

computers. See also PL/I. 

PLCC n. Acronym for plastic leadless chip carrier. An 

inexpensive variation of the leadless chip carrier (LCC) 

method of mounting chips on boards. Although the two 

carriers are similar in appearance, PLCCs are physically 

incompatible with leadless chip carriers, which are made 

from a ceramic material. See also leadless chip carrier. 

PLD n. See programmable logic device. 

PL/I n. Acronym for Programming Language I (One). A 

programming language developed by IBM (1964–1969), 

designed to bring together the key features of FORTRAN, 

COBOL, and ALGOL while introducing such new concepts 

as condition-based error handling and multitasking. 

The result of this effort was a compiled, structured language 

that was so complex that it never gained widespread 

acceptance. Nevertheless, PL/I is still used in some academic 

and research environments. See also ALGOL, 

COBOL, compiled language, FORTRAN. 

PL/M n. Acronym for Programming Language for 

Microcomputers. A programming language derived from 

PL/I and developed in the early 1970s by Intel Corporation 

for microprocessors. PL/M was used primarily for the 

creation of operating systems. See also PL/I. 

plot vb. To create a graphic or a diagram by connecting 

points representing variables (values) that are defined by 

their positions in relation to a horizontal (x) axis and a vertical 

(y) axis (and sometimes a depth, or z, axis). 

plotter n. Any device used to draw charts, diagrams, and 

other line-based graphics. Plotters use either pens or electrostatic 

charges and toner. Pen plotters draw on paper or 

transparencies with one or more colored pens. Electrostatic 

plotters “draw” a pattern of electrostatically charged 

dots on the paper and then apply toner and fuse it in place. 

Plotters use three basic types of paper handling: flatbed,

PL/SQL PNP transistor 

drum, and pinch roller. Flatbed plotters hold the paper still 

and move the pen along both x and y axes. Drum plotters 

roll the paper over a cylinder. The pen moves along one 

axis while the drum, with the paper attached, moves along 

the other. Pinch-roller plotters are a hybrid of the two, in 

which the pen moves only along one axis while the paper 

is moved back and forth by small rollers. 

PL/SQL n. Short for Procedural Language Extension to 

SQL. Oracle’s data manipulation language that allows 

sequenced or grouped execution of SQL statements and is 

commonly used to manipulate data in an Oracle database. 

The syntax is similar to the Ada programming language. 

plug n. A connector, especially a male connector, one that 

fits into a socket. See also male connector. 

plug and play n. 1. Generally, a reference to the ability of 

a computer system to automatically configure a device 

added to it. Plug and play capability exists in Macintoshes 

based on the NuBus and, since Windows 95, on PC-compatible 

computers. 2. When capitalized and, especially, 

when abbreviated PnP, a set of specifications developed by 

Intel and Microsoft that allows a PC to configure itself automatically 

to work with peripherals such as monitors, 

modems, and printers. A user can plug in a peripheral and 

“play” it without manually configuring the system. A Plug 

and Play PC requires both a BIOS that supports Plug and 

Play and a Plug and Play expansion card. Abbreviation: PnP. 

See also BIOS, expansion board, peripheral. 

plugboard n. A board that permits users to control the 

operation of a device by plugging cables into sockets. 

plug-compatible adj. Equipped with connectors that are 

equivalent both in structure and in usage. For example, 

most modems having DB-25 connectors on their rear panels 

are plug-compatible—that is, one can be replaced by 

another without the cable having to be rewired. Compare 

pin-compatible. 

plug-in n. 1. A small software program that plugs into a 

larger application to provide added functionality. 2. A 

software component that plugs into the Netscape Navigator. 

Plug-ins permit the Web browser to access and execute 

files embedded in HTML documents that are in formats 

the browser normally would not recognize, such as many 

animation, video, and audio files. Most plug-ins are devel- 

409 

oped by software companies who have proprietary software 

in which the embedded files are created. Compare 

helper application. 

p-machine n. See pseudomachine. 

PMML n. Acronym for Predictive Model Markup Language. 

An XML-based language that enables sharing of 

defined predictive models between compliant vendor 

applications. 

PMMU n. See paged memory management unit. 

PMOS n. Acronym for P-channel metal-oxide semiconductor. 

A MOSFET semiconductor technology in which 

the conduction channel is formed by the movement of 

holes (electron “vacancies” created as electrons move 

from atom to atom) rather than electrons. Because holes 

move more slowly than electrons do, PMOS is slower than 

NMOS, but it is also easier and less expensive to fabricate. 

See also MOS, MOSFET, P-type semiconductor. Compare 

CMOS, NMOS. 

PMS n. See PANTONE MATCHING SYSTEM. 

PNG n. Acronym for Portable Network Graphics. A file 

format for bitmapped graphic images, designed to be a 

replacement for the GIF format, without the legal restrictions 

associated with GIF. See also GIF. 

PNNI n. Short for Private Network-to-Network Interface. 

A routing protocol used in ATM networks that provides 

switches with the ability to communicate changes in the 

network. Through PNNI, switches can be informed of 

changes to the network as they occur and can then use the 

information to make appropriate routing decisions. See 

also ATM. 

PnP n. See plug and play (definition 2). 

PNP n. See PNP transistor. 

PNP transistor n. A type of bipolar transistor in which a 

base of N-type material is sandwiched between an emitter 

and a collector of P-type material. The base, emitter, and 

collector are the three terminals of the transistor through 

which current flows. In a PNP transistor, holes (electron 

“vacancies”) are the majority of the charge carriers, and 

they flow from the emitter to the collector. See the illustration. 

See also N-type semiconductor, P-type semiconductor. 

Compare NPN transistor. 

P

P 

pocket Active Server Pages point of presence 

F0Pgn16.eps 


Internal diagram 

Emitter Collector 

Base 

Schematic diagram 

Base 

Emitter 

Collector 

pocket Active Server Pages n. A scaled-down version 

of the Active Server Pages optimized for server-side 

Mobile Channels scripting. Acronym: pASP. 

pocket Excel n. A scaled-down version of Microsoft 

Excel for the Pocket PC. See also Microsoft Excel. 

Pocket PC n. A personal handheld computing device 

based on specifications designed by Microsoft and running 

the Microsoft Windows for Pocket PC operating system. 

Pocket PCs maintain the look of a Windows 

operating system display screen and offer compact versions 

of many of the applications that run on Windowspowered 

personal computers. A number of manufacturers 

produce Pocket PCs, including Hewlett-Packard, Compaq, 

and Casio. 

pocket Word n. A scaled-down version of Microsoft 

Word for the Pocket PC. See also Microsoft Word. 

point1 n. 1. A unit of measure used in printing, equal to 

approximately 1 /72 of an inch. Character height and the 

amount of space (leading) between lines of text are usually 

specified in points. 2. A single pixel on the screen, 

identified by its row and column numbers. 3. A location in 

410 

a geometric form, represented by two or more numbers 

that constitute its coordinates. 

point2 vb. To move an arrow or other such indicator to a 

particular item or position on the screen by using direction 

keys or by maneuvering a pointing device such as a mouse. 

point-and-click adj. Enabling a user to select data and 

activate programs by using a mouse or other pointing device 

to move a cursor to a desired location (“point”) and pressing 

a button on the mouse or other pointing device (“click”). 

PointCast n. An Internet service that delivers and displays 

a personalized set of news articles to individual 

users. Unlike the World Wide Web and other Internet 

applications, PointCast is a push technology, where the 

server automatically uploads data without a specific command 

from the client. See also server (definition 2). 

point chart n. See scatter diagram. 

point diagram n. See scatter diagram. 

pointer n. In programming and information processing, a 

variable that contains the memory location (address) of 

some data rather than the data itself. See also address1 (definition 1), handle (definition 1), mouse pointer, 

reference1 . 

pointing device n. An input device used to control an onscreen 

cursor for such actions as “pressing” on-screen buttons 

in dialog boxes, choosing menu items, and selecting 

ranges of cells in spreadsheets or groups of words in a 

document. A pointing device is often used to create drawings 

or graphical shapes. The most common pointing 

device is the mouse, which was popularized by its use 

with the Apple Macintosh. Other pointing devices include 

graphics tablets, styluses, light pens, joysticks, pucks, and 

trackballs. See also graphics tablet, joystick, light pen, 

mouse, puck, stylus, trackball. 

point listing n. A database of popular Web sites categorized 

by topics of interest and often rated by design 

and content. 

point of presence n. 1. A point in a wide area network to 

which a user can connect with a local telephone call. 2. A 

point at which a long distance telephone carrier connects 

to a local telephone exchange or to an individual user. 

Acronym: POP.

point of sale Pong 

point of sale n. See POS. 

point-to-point configuration n. A communications link 

in which dedicated links exist between individual origins 

and destinations, as opposed to a point-to-multipoint configuration, 

in which the same signal goes to many destinations 

(such as a cable TV system), or a switched configuration, in 

which the signal moves from the origin to a switch that 

routes the signal to one of several possible destinations. Also 

called: point-to-point connection. 

point-to-point connection n. See point-to-point configuration. 

point-to-point message system n. In Sun Microsystems’s 

J2EE network platform, a messaging system that 

uses message queues to store asynchronous, formatted 

data for coordinating enterprise applications. Each message 

is addressed to a specific queue, and client applications 

retrieve messages from the queues. See also 

asynchronous, J2EE. 

Point-to-Point Protocol n. See PPP. 

point-to-point tunneling n. A means of setting up secure 

communications over an open, public network such as the 

Internet. See also PPTP. 

Point-to-Point Tunneling Protocol n. See PPTP. 

Poisson distribution n. A mathematical curve often used 

in statistics and simulation to represent the likelihood of 

some event occurring, such as the arrival of a customer in 

a queue, when the average likelihood is known. This distribution, 

named after the French mathematician S. D. 

Poisson, is simpler to calculate than the normal and binomial 

distributions. See also binomial distribution, normal 

distribution. 

poke vb. To store a byte into an absolute memory location. 

PEEK (read a byte from memory) and POKE commands 

are often found in programming languages, such as 

Basic, that do not normally allow access to specific memory 

locations. 

polar coordinates n. Coordinates of the form (r, q) used 

to locate a point in two dimensions (on a plane). The polar 

coordinate r is the length of the line that starts at the origin 

and ends at the point, and q (Greek theta) is the angle 

between that line and the positive x-axis. Compare Cartesian 

coordinates. 

411 

polarity n. The sign of the potential (voltage) difference 

between two points in a circuit. When a potential difference 

exists between two points, one point has a positive 

polarity and the other a negative polarity. Electrons flow 

from negative to positive; by convention, however, current 

is considered to flow from positive to negative. 

polarized component n. A circuit component that must 

be installed with its leads in a particular orientation with 

respect to the polarity of the circuit. Diodes, rectifiers, and 

some capacitors are examples of polarized components. 

polarizing filter n. A transparent piece of glass or plastic 

that polarizes the light passing through it; that is, it allows 

only waves vibrating in a certain direction to pass through. 

Polarizing filters are often used to reduce glare on monitor 

screens. See also glare filter. 

Polish notation n. See prefix notation. 

polling n. See autopolling. 

polling cycle n. The time and sequence required for a 

program to poll each of its devices or network nodes. See 

also autopolling. 

polygon n. Any two-dimensional closed shape composed 

of three or more line segments, such as a hexagon, an octagon, 

or a triangle. Computer users encounter polygons in 

graphics programs. 

polyline n. An open shape consisting of multiple connected 

segments. Polylines are used in CAD and other 

graphics programs. See also CAD. 

polymorphism n. In an object-oriented programming language, 

the ability to redefine a routine in a derived class (a 

class that inherited its data structures and routines from 

another class). Polymorphism allows the programmer to 

define a base class that includes routines that perform 

standard operations on groups of related objects, without 

regard to the exact type of each object. The programmer 

then redefines the routines in the derived class for each 

type, taking into account the characteristics of the object. 

See also class, derived class, object (definition 2), objectoriented 

programming. 

Pong n. The first commercial video game, a table tennis 

simulation, created by Nolan Bushnell of Atari in 1972. 

P

P 

pop portable computer 

pop vb. To fetch the top (most recently added) element of 

a stack, removing that element from the stack in the process. 

Compare push2 (definition 1). 

POP n. See point of presence, Post Office Protocol. 

POP3 n. Acronym for Post Office Protocol 3. This is the 

current version of the Post Office Protocol standard in 

common use on TCP/IP networks. See also Post Office 

Protocol, TCP/IP. 

populate vb. 1. To put chips in the sockets of a circuit 

board. 2. To import prepared data into a database from a 

file using a software procedure rather than by having a 

human operator enter individual records. 

pop-under ad n. An advertisement on the Internet that 

appears in a new window in the background, behind the 

Web site content. Users may be unaware of the presence of 

pop-under ads until they close foreground windows at the 

end of a Web session. Pop-under ads may appear in 

response to a mouse click, a rollover, or after a user has 

spent a predetermined amount of time at a Web site. See 

also pop-up ad. 

pop-up ad n. An advertisement on the Internet that 

appears in a new window in the foreground, often whenever 

a new page is opened within a site. Pop-up ads may 

appear in response to a mouse click, a rollover, or after a 

user has spent a predetermined amount of time at a Web 

site. See also pop-under ad. 

pop-up Help n. An online help system whose messages 

appear as pop-up windows when the user clicks on a topic 

or area of the screen about which help is desired. Typically, 

a special form of click, such as clicking the right 

mouse button or Option-clicking, will activate pop-up 

Help, if it is available. See also Balloon Help. 

pop-up menu or popup menu n. In a graphical user 

interface, a menu that appears on-screen when a user 

selects a certain item. Pop-up menus can appear anywhere 

on the screen and generally disappear when the user 

selects an item in the menu. Also called: popup. Compare 

drop-down menu, pull-down menu. 

pop-up messages n. The messages that appear when 

pop-up Help is used. 

412 

pop-up window n. A window that appears when an 

option is selected. Typically, the window remains visible 

until the mouse button is released. 

port1 n. 1. An interface through which data is transferred 

between a computer and other devices (such as a printer, 

mouse, keyboard, or monitor), a network, or a direct connection 

to another computer. The port appears to the CPU 

as one or more memory addresses that it can use to send or 

receive data. Specialized hardware, such as in an add-on 

circuit board, places data from the device in the memory 

addresses and sends data from the memory addresses to 

the device. Ports may also be dedicated solely to input or 

to output. Ports typically accept a particular type of plug 

used for a specific purpose. For example, a serial data port, 

a keyboard, and a high-speed network port all use different 

connectors, so it’s not possible to plug a cable into the 

wrong port. Also called: input/output port. 2. port number. 

port2 vb. 1. To change a program in order to be able to run 

it on a different computer. 2. To move documents, graphics, 

and other files from one computer to another. 

port 25 blocking n. An anti-spam technique adopted by 

many ISPs to prevent bulk mailings of unsolicited commercial 

e-mail. Spammers may try to use SMTP servers to 

relay a single commercial e-mail to multiple recipients. 

Port 25 blocking filters prevent this spam distribution 

method. Although it is a popular remedy for some spam 

problems, port 25 blocking may cause problems for legitimate 

users of non-compatible e-mail programs. 

portable adj. 1. Capable of running on more than one 

computer system or under more than one operating system. 

Highly portable software can be moved to other systems 

with little effort, moderately portable software can be 

moved only with substantial effort, and nonportable software 

can be moved only with effort similar to or greater 

than the effort of writing the original program. 2. Light 

enough, rugged enough, and free enough of encumbering 

external connections to be carried by a user. 

portable computer n. Any computer designed to be 

moved easily. Portable computers can be characterized by 

size and weight. See the table.

Portable Digital Document port number 

Table P.2 Portable Computers. 

Type 

Approximate 

weight Power source Comments 

Transportable 15–30 lb. House current Sometimes called luggable; usually has floppy and harddrives; 

standard CRT screen. 

Laptop 8–15 lb. House current or Can be held on the lap; usually has a floppy drive;uses flat 

batteries 

LCD or plasma screen. 

Ultralight 2–8 lb. Batteries or trans- Easy to carry in a briefcase; sometimes uses RAM drive or 

former pack EPROM instead of floppy or hard drive; thinner models 

are known as notebook computers. 

Handheld Less than 2 lb. Batteries or trans- Also called palmtop or palm-sized; can be held in one 

former pack hand. 

Portable Digital Document n. See PDD. 

Portable Distributed Objects n. Software from NeXT, 

running under UNIX, that supports an object model in 

which objects to be stored at various locations on a network 

can be accessed as though they were at a single location. 

Acronym: PDO. 

Portable Document Format n. The Adobe specification 

for electronic documents that use the Adobe Acrobat family 

of servers and readers. Acronym: PDF. See also Acrobat, 

.pdf. 

portable executable file n. The file format used for 

executable programs as well as for files that are linked 

together to form executable programs. 

portable keyboard n. A portable keyboard for use with 

personal digital assistants (PDAs), wireless phones with 

advanced digital features, and other handheld mobile 

devices. Light, compact, and easy to carry, most portable 

keyboards fold for convenient storage and connect to the 

handheld device via a built-in cradle. 

portable language n. A language that runs in the same 

way on different systems and therefore can be used for 

developing software for all of them. C, FORTRAN, and 

Ada are portable languages because their implementations 

on different systems are highly uniform; assembly language 

is extremely nonportable. 

Portable Network Graphics n. See PNG. 

413 

portal n. A Web site that serves as a gateway to the Internet. 

A portal is a collection of links, content, and services 

designed to guide users to information they are likely to 

find interesting—news, weather, entertainment, commerce 

sites, chat rooms, and so on. Yahoo!, Excite, MSN.com, 

and Netscape NetCenter are examples of portals. See also 

home page (definition 1), Web site. 

port enumerator n. In Windows, part of the Plug and Play 

system that detects I/O ports and reports them to the configuration 

manager. See also plug and play (definition 2). 

port expander n. A hardware mechanism used for connecting 

several devices to a single port. Although several 

devices might be connected, only one can use the port at 

any given moment. 

portmapper n. A service used by Remote Procedure Call 

(RPC) to assign port numbers. RPC doesn’t follow the 

Well-Known Ports port designations, and only Portmapper 

is assigned a permanent port number. Because hackers 

may gain access to portmapper communication, various 

portmapper security tools are often used to prevent theft of 

information. See also remote procedure call. 

port number n. A number that enables IP packets to be 

sent to a particular process on a computer connected to the 

Internet. Some port numbers, called “well-known” port 

numbers, are permanently assigned; for example, e-mail 

data under SMTP goes to port number 25. A process such 

as a telnet session receives an “ephemeral” port number 

P

P 

portrait mode PostScript 

when it starts; data for that session goes to that port number, 

and the port number goes out of use when the session 

ends. A total of 65,535 port numbers are available for use 

with TCP, and the same number are available for UDP. See 

also IP, Simple Mail Transfer Protocol, socket (definition 

1), TCP, UDP. Compare IP address. 

portrait mode n. A vertical print orientation in which a 

document is printed across the narrower dimension of a 

rectangular sheet of paper. This is the print mode typical 

of most letters, reports, and other such documents. Compare 

landscape mode. 

portrait monitor n. A monitor with a screen shape higher 

than it is wide. The proportions (but not necessarily the 

size) of the screen are usually the same as for a sheet of 81 /2by-11-inch 

paper. Compare landscape monitor. 

port replicator n. A device that enables easy connection 

of portable computers to less portable devices, such as 

printers, monitors, and full-sized keyboards. Instead of having 

to connect each such device individually to a portable 

computer, a user can plug it permanently into a port replicator 

and use it simply by plugging the computer into a single 

socket, also on the port replicator. Port replicators are comparable 

to docking stations, but without the same capability 

for expansion and storage. Also called: convenience 

adapter. See also docking station, port. 

POS n. Acronym for point of sale. The place in a store at 

which goods are paid for. Computerized transaction systems, 

such as those in use at automated supermarkets, use 

scanners for reading tags and bar codes, electronic cash 

registers, and other special devices to record purchases at 

this point. 

POSIT n. Acronym for Profiles for Open Systems Internetworking 

Technology. A set of nonmandatory standards 

for U.S. government network equipment. POSIT, which 

recognizes the prevalence of TCP/IP, is the successor to 

GOSIP. See also GOSIP, TCP/IP. 

positional notation n. In mathematics, a form of notation 

whose meaning relies in part on the relative location 

of the elements involved. For example, common numeric 

notation is positional notation. In the decimal number 34, 

the position of the numeral 3 signifies three 10s and the 

position of the numeral 4 signifies four 1s. 

414 

POSIX n. Acronym for Portable Operating System Interface 

for UNIX. An Institute of Electrical and Electronics 

Engineers (IEEE) standard that defines a set of operatingsystem 

services. Programs that adhere to the POSIX standard 

can be easily ported from one system to another. 

POSIX was based on UNIX system services, but it was 

created in a way that allows it to be implemented by other 

operating systems. See also service (definition 2). 

post1 n. See article. 

post2 vb. 1. To submit an article in a newsgroup or other 

online conference or forum. The term is derived from the 

“posting” of a notice on a physical bulletin board. See also 

newsgroup. 2. To place a file on a server on a network or 

on a Web site. 

POST n. See power-on self test. 

posterization n. See contouring. 

postfix notation n. A form of algebraic notation in 

which the operators appear after the operands. Also 

called: reverse Polish notation. Compare infix notation, 

prefix notation. 

postmaster n. The logon name (and therefore the e-mail 

address) of an account that is responsible for maintaining 

e-mail services on a mail server. When an account holder 

is having trouble with e-mail, a message to postmaster or 

“postmaster@machine.org.domain.name” will usually 

reach a human who can solve the problem. 

post office n. The server and associated storage and mail 

handling services that provide the centralized location for 

collection and distribution of e-mail over a network. 

Post Office Protocol n. A protocol for servers on the 

Internet that receive, store, and transmit e-mail and for clients 

on computers that connect to the servers to download 

and upload e-mail. Acronym: POP. 

postprocessor n. A device or a software routine, such as 

a linker, that operates on data manipulated first by another 

processor. See also back-end processor (definition 2). 

Compare preprocessor. 

PostScript n. A page-description language from Adobe 

Systems that offers flexible font capability and high-quality 

graphics. The most well-known page-description lan-

PostScript font power-on self test 

guage, PostScript uses English-like commands to control 

page layout and to load and scale outline fonts. Adobe 

Systems is also responsible for Display PostScript, a 

graphics language for computer displays that gives users 

of both PostScript and Display PostScript absolute WYSI- 

WYG (what-you-see-is-what-you-get), which is difficult 

when different methods are used for displaying and printing. 

See also outline font, page-description language. 

PostScript font n. A font defined in terms of the Post- 

Script page-description language rules and intended to be 

printed on a PostScript-compatible printer. PostScript 

fonts are distinguished from bitmapped fonts by their 

smoothness, detail, and faithfulness to standards of quality 

established in the typographic industry. See also Post- 

Script. Compare screen font. 

pot n. See potentiometer. 

potential n. See electromotive force. 

potentiometer n. A circuit element that can be adjusted 

to provide varying amounts of resistance. The twist-knob 

and slider-type volume controls on many radios and television 

sets are potentiometers. Also called: pot. 

POTS n. Acronym for Plain Old Telephone Service. 

Basic dialup telephone connections to the public switched 

network without any added features or functions. A POTS 

line is nothing but a phone line connected to a simple, single-line 

telephone instrument. 

pour vb. To send a file or the output from a program to 

another file or to a device using a pipe. See also pipe (definition 

1). 

power n. 1. In mathematics, the number of times a value 

is multiplied by itself—for example, 10 to the third power 

means 10 times 10 times 10. 2. In computing, the electricity 

used to run a computer. 3. The speed at which a computer 

performs and the availability of various features. See 

also computer power. 

PowerBook n. Any of several computers in the family of 

portable Macintosh computers made by Apple. 

power conditioning n. A feature of uninterruptible 

power supply (UPS) that removes spikes, surges, sags, and 

415 

noise from the power supply. Also called: line conditioning. 

See also UPS. 

power down vb. To shut down (a computer); to turn off 

the power. 

power failure n. Loss of electricity, which causes a loss 

of unsaved data in a computer’s random access memory 

(RAM) if no backup power supply is connected to the 

machine. Compare surge. 

Power Mac n. See Power Macintosh. 

Power Macintosh n. A Macintosh computer based on 

the PowerPC processor. The first Power Macintoshes, 

6100/60, 7100/66, and 8100/80, were unveiled in 1994. 

Several upgraded versions followed, and in early 1999 the 

G3, a PowerPC 750, was released. This was followed later 

in the year with the unveiling of the Power Macintosh G4. 

The Power Mac G4 uses the PowerPC 7400 processor and 

features significant boosts in processing speed. The Power 

Mac G4 uses Apple’s Velocity Engine to process information 

in 128-bit chunks, allowing sustained performance in 

excess of one gigaflop. Also called: Power Mac. See also 

PowerPC. 

power management n. The regulation of power consumption 

on a computer, especially a portable batteryoperated 

device such as a laptop. Power management 

reduces power to certain components, such as the screen 

and CPU, to use power efficiently and extend battery life. 

See also ACPI, Advanced Power Management. 

Power-on key n. A special key on the Apple ADB and 

Extended keyboards used for turning on a Macintosh II. 

The Power-on key is marked with a left-pointing triangle 

and is used in lieu of the on/off switch. There is no Poweroff 

key; the system is shut down by choosing the Shut 

Down command from the Special menu. 

power-on self test n. A set of routines stored in a computer’s 

read-only memory (ROM) that tests various system 

components such as RAM, the disk drives, and the 

keyboard to see whether they are properly connected and 

operating. If problems are found, these routines alert the 

user by sounding a series of beeps or displaying a message, 

often accompanied by a diagnostic numeric value, to 

P

P 

PowerPC PPPoE 

the standard output or standard error device (usually the 

screen). If the power-on self test is successful, it passes 

control to the system’s bootstrap loader. Acronym: POST. 

See also bootstrap loader. 

PowerPC n. A microprocessor architecture developed in 

1992 by Motorola and IBM, with some participation by 

Apple. A PowerPC microprocessor is RISC-based and 

superscalar, with a 64-bit data bus and 32-bit address bus. It 

also has separate data and instruction caches, although the 

size of each varies by implementation. All PowerPC microprocessors 

have multiple integer and floating-point units. 

The voltage and operating speed varies with the implementation. 

Starting with the PowerPC 740, the microprocessors 

were manufactured with copper, instead of aluminum, for 

better performance and reliability. See also L1 cache, L2 

cache, microprocessor, RISC, superscalar. 

PowerPC Platform n. A platform developed by IBM, 

Apple, and Motorola based on the 601 and later chips. 

This platform supports the use of multiple operating systems 

such as Mac OS, Windows NT, and AIX as well as 

software designed for those individual operating systems. 

Acronym: PPCP. 

PowerPC Reference Platform n. An open system standard 

developed by IBM. IBM’s goal in designing the PowerPC 

Reference Platform was to ensure compatibility 

among PowerPC systems built by different companies. 

Apple’s PowerPC Macintoshes are not yet compliant with 

the PowerPC Reference Platform, but future versions are 

expected to be. Acronym: PReP. See also Common Hardware 

Reference Platform, open system, PowerPC. 

PowerPoint n. Microsoft’s presentation software. Power- 

Point includes text-editing and graphics tools that can create 

slides for public presentations. The presentations can 

be printed, projected, displayed on a monitor, or, in the 

version included with Office 2000, saved and published as 

Web pages. 

power supply n. An electrical device that transforms 

standard wall outlet electricity (115–120 VAC in the 

United States) into the lower voltages (typically 5 to 12 

volts DC) required by computer systems. Personal computer 

power supplies are rated by wattage; they usually 

416 

range from about 90 watts at the low end to 250 watts at 

the high end. 

power surge n. See surge. 

power up vb. To start up a computer; to begin a cold boot 

procedure; to turn on the power. 

power user n. A person adept with computers, particularly 

on an applications-oriented level rather than on a programming 

level. A power user is someone who knows a 

considerable amount about computers and is comfortable 

enough with applications to be able to work with their 

most sophisticated features. 

PPCP n. See PowerPC Platform. 

PPM or ppm n. 1. Acronym for pages per minute. A rating 

of a printer’s output capacity—that is, the number of 

printed pages the printer can produce in one minute. A 

printer’s PPM rating is usually provided by the manufacturer 

and is based on a “normal” page. Pages with excessive 

graphics or fonts may reduce a printer’s PPM rate 

dramatically. 2. See pulse position modulation. 

PPP n. Acronym for Point-to-Point Protocol. A widely 

used data link protocol for transmitting TCP/IP packets 

over dial-up telephone connections, such as between a 

computer and the Internet. PPP, which supports dynamic 

allocation of IP addresses, provides greater protection for 

data integrity and security and is easier to use than SLIP, at 

a cost of greater overhead. PPP itself is based on a Link 

Control Protocol (LCP) responsible for setting up a computer-to-computer 

link over telephone lines and a Network 

Control Protocol (NCP) responsible for negotiating network-layer 

details related to the transmission. It was 

developed by the Internet Engineering Task Force in 1991. 

Compare SLIP. 

PPPoE n. Acronym for Point-to-Point Protocol over 

Ethernet. A specification for connecting users on an 

Ethernet network to the Internet through a broadband connection, 

such as a single DSL line, wireless device, or 

cable modem. Using PPPoE and a broadband modem, 

LAN users can gain individual authenticated access to 

high-speed data networks. By combining Ethernet and 

Point-to-Point Protocol (PPP), PPPoE provides Internet 

Service Providers (ISPs) with the ability to manipulate a 

limited number of IP addresses by assigning an address

PPS Premiere 

only when the user is connected to the Internet. PPPoE is 

an efficient way to create a separate connection for each 

user to a remote server. When the Internet connection is 

broken, the IP address becomes available to be assigned to 

another user. 

PPS n. See peripheral power supply. 

PPTP n. Acronym for Point-to-Point Tunneling Protocol. 

An extension of the Point-to-Point Protocol used for communications 

on the Internet. PPTP was developed by 

Microsoft to support virtual private networks (VPNs), 

which allow individuals and organizations to use the Internet 

as a secure means of communication. PPTP supports 

encapsulation of encrypted packets in secure wrappers 

that can be transmitted over a TCP/IP connection. See also 

virtual network. 

PRAM n. Short for parameter RAM. A portion of RAM 

in Macintosh computers that contains configuration information 

such as the date and time, desktop pattern, and 

other control panel settings. See also RAM. 

P-rating n. Short for performance rating. A microprocessor 

rating system by IBM, Cyrix, and others, based on 

throughput in realistic applications. Formerly, microprocessor 

clock speed was widely used as a method of rating, 

but it does not account for differing chip architectures or 

different types of work people do with computers. See 

also central processing unit, clock (definition 1), microprocessor. 

precedence n. In applications, the order in which values 

in a mathematical expression are calculated. In general, 

application programs perform multiplication and division 

first, followed by addition and subtraction. Sets of parentheses 

can be placed around expressions to control the 

order in which they are calculated. See also operator associativity, 

operator precedence. 

precision n. 1. The extent of detail used in expressing a 

number. For example, 3.14159265 gives more precision— 

more detail—about the value of pi than does 3.14. Precision 

is related to, but different from, accuracy. Precision 

indicates degree of detail; accuracy indicates correctness. 

The number 2.83845 is also more precise than 3.14, but it 

is less accurate for pi. Compare accuracy. 2. In program- 

417 

ming, numeric values are often referred to as single-precision 

or double-precision values. The difference between 

the two is in the amount of storage space allotted to the 

value. See also double-precision, single-precision. 

precompiler n. A program that reads in a source file and 

makes certain changes to prepare the source file for compilation. 

Also called: preprocessor. See also compiler 


preemptive multitasking n. A form of multitasking in 

which the operating system periodically interrupts the execution 

of a program and passes control of the system to 

another waiting program. Preemptive multitasking prevents 

any one program from monopolizing the system. 

Also called: time-slice multitasking. See also multitasking. 

Compare cooperative multitasking. 

Preferences n. A menu choice in many graphical user 

interface applications that allows the user to specify how 

the application will act each time it is used. For example, 

in a word processing application the user may be allowed 

to specify whether the ruler will appear, whether the document 

will appear in the same way as it will print (including 

margins), and other choices. Also called: Options, Prefs. 

prefetch vb. Preloading buffering data for a streaming 

video clip before the clip begins playing. When prefetched 

data is stored on a computer, the video clip can be played 

without waiting for the initial buffering that usually occurs 

with streaming media. See also preroll. 

prefix notation n. A form of algebraic notation, developed 

in 1929 by Jan Lukasiewicz, a Polish logician, in 

which the operators appear before the operands. For 

example, the expression (a + b) x (c – d) would be written 

in prefix notation as x + a b – c d. Also called: Polish notation. 

See also infix notation, postfix notation. 

Prefs n. See Preferences. 

Premiere n. Digital video editing software developed by 

Adobe Systems. The Premiere user interface uses command 

menus, windows, and floating pallets to make modifications 

to video clips. A timeline feature presents a 

graphic presentation of the length of the individual scenes 

and the order in which they appear. The editor can modify 

P

P 

PReP pretty print 

the edits and preview the results before exporting the file 

into one of several video formats. 

PReP n. See PowerPC Reference Platform. 

preprocessor n. A device or routine that performs preliminary 

operations on input before passing it on for further 

processing. See also front-end processor (definition 

1). Compare postprocessor. 

preroll vb. Data buffering that occurs before a streaming 

media clip plays. Preroll time varies depending on available 

bandwidth and the size of the file being buffered. 

presence technology n. An application, such as instant 

messaging, which finds specific users when they are connected 

to the network and which may alert interested users 

to each other’s presence. Third-generation wireless networks 

will integrate presence technology with digital cell 

phones, PDAs, pagers, and other communications and 

entertainment devices. 

presentation broadcast n. A PowerPoint feature that 

allows you to run a presentation over the Web. The presentation 

is saved in HTML format and can contain audio and 

video. It can also be recorded and saved to be viewed later. 

presentation graphics n. The representation of business 

information, such as sales figures and stock prices, in 

chart form rather than as lists of numbers. Presentation 

graphics are used to give viewers an immediate grasp of 

business statistics and their significance. Common examples 

are area charts, bar charts, line charts, and pie charts. 

Also called: business graphics. 

presentation layer n. The sixth of the seven layers in the 

ISO/OSI reference model for standardizing computer-tocomputer 

communications. The presentation layer is 

responsible for formatting information so that it can be 

displayed or printed. This task generally includes interpreting 

codes (such as tabs) related to presentation, but it 

can also include converting encryption and other codes 

and translating different character sets. See the illustration. 

See also ISO/OSI reference model. 

418 

ISO/OSI Layer 

Application 


Presentation 

Session 

Transport 

Network 

Data-link 

Physical 

F0Pgn17.eps 

Presentation layer. 

ISO/OSI MODEL 

Focus 




conversion 









Presentation Manager n. The graphical user interface 

provided with OS/2 versions 1.1 and later. The Presentation 

Manager derives from the MS-DOS–based Windows 

environment and provides similar capabilities. The user 

sees a graphical, window-oriented interface, and the programmer 

uses a standard set of routines for handling 

screen, keyboard, mouse, and printer input and output, no 

matter what hardware is attached to the system. See also 

OS/2, Windows. 

pressure-sensitive adj. Of or pertaining to a device in 

which pressing on a thin surface produces an electrical 

connection and causes an event to be registered by the 

computer. Pressure-sensitive devices include touch-sensitive 

drawing pens, membrane keyboards, and some touch 

screens. See also touch screen. 

Pretty Good Privacy n. See PGP. 

pretty print n. A feature of some editors used in programming 

that formats code so that it is easier to read and 

understand when printed. For example, a pretty-print feature 

might insert blank lines to set off modules or indent 

nested routines to make them easier to spot. See also code1 (definition 1), editor, module (definition 1), routine.

preventive maintenance printed circuit board 

preventive maintenance n. Routine servicing of hardware 

intended to keep equipment in good operating condition 

and to find and correct problems before they develop 

into severe malfunctions. 

preview n. In word processors and other applications, the 

feature that formats a document for printing but displays it 

on the video monitor rather than sending it directly to the 

printer. 

PRI n. Acronym for Primary Rate Interface. One of two 

ISDN transmission rate services (the other is the basic rate 

interface, BRI). PRI has two variations. The first, which 

operates at 1.536 Mbps, transmits data over 23 B channels 

and sends signaling information at 64 Kbps over one D 

channel in the United States, Canada, and Japan. The second, 

which operates at 1.984 Mbps, transmits data over 30 B 

channels and sends signaling information at 64 Kbps over 

one D channel in Europe and Australia. See also BRI, ISDN. 

primary channel n. The data-transmission channel in a 

communications device, such as a modem. Compare secondary 

channel. 

Primary Domain Controller n. 1. In Windows NT, a 

database providing a centralized administration site for 

resources and user accounts. The database allows users to 

log onto the domain, rather than onto a specific host 

machine. A separate account database keeps track of the 

machines in the domain and allocates the domain’s 

resources to users. 2. In any local area network, the server 

that maintains the master copy of the domain’s user 

accounts database and that validates logon requests. Acronym: 

PDC. 

primary key n. In databases, the key field that serves as 

the unique identifier of a specific tuple (row) in a relation 

(database table). Also called: major key. See also alternate 

key (definition 1), candidate key. Compare secondary key. 

Primary Rate Interface n. See PRI. 

primary storage n. Random access memory (RAM); the 

main general-purpose storage region to which the microprocessor 

has direct access. A computer’s other storage 

options, such as disks and tape, are called secondary storage 

or (sometimes) backing storage. 

primitive n. 1. In computer graphics, a shape, such as a 

line, circle, curve, or polygon, that can be drawn, stored, 

and manipulated as a discrete entity by a graphics program. 

A primitive is one of the elements from which a large 

graphic design is created. 2. In programming, a fundamen- 

419 

tal element in a language that can be used to create larger 

procedures that do the work a programmer wants to do. 

print vb. In computing, to send information to a printer. 

The word is also sometimes used in the sense of “show 

me” or “copy this.” For example, the PRINT statement in 

Basic causes output to be displayed (printed) on the 

screen. Similarly, an application program that can be told 

to print a file to disk interprets the command as an instruction 

to route output to a disk file instead of to a printer. 

print buffer n. A section of memory to which print output 

can be sent for temporary storage until the printer is ready 

to handle it. A print buffer can exist in a computer’s random 

access memory (RAM), in the printer, in a separate 

unit between the computer and the printer, or on disk. 

Regardless of its location, the function of a print buffer is 

to free the computer for other tasks by taking print output 

at high speed from the computer and passing it along at 

the much slower rate required by the printer. Print buffers 

vary in sophistication: some simply hold the next few 

characters to be printed, and others can queue, reprint, or 

delete documents sent for printing. 

printed circuit board n. A flat board made of nonconducting 

material, such as plastic or fiberglass, on which 

chips and other electronic components are mounted, usually 

in predrilled holes designed to hold them. The component 

holes are connected electrically by predefined 

conductive metal pathways that are printed on the surface 

of the board. The metal leads protruding from the electronic 

components are soldered to the conductive metal 

pathways to form a connection. A printed circuit board 

should be held by the edges and protected from dirt and 

static electricity to avoid damage. See the illustration. 

Acronym: PCB. 

F0Pgn18.eps 

Printed circuit board. 

P

P 

printer printer file 

printer n. A computer peripheral that puts text or a computer-generated 

image on paper or on another medium, 

such as a transparency film. Printers can be categorized in 

any of several ways: impact versus nonimpact; print technology; 

character formation; method of transmission; 

method of printing; print capability; and print quality. 

● Impact versus nonimpact The most common distinction 

is impact versus nonimpact. Impact printers 

physically strike the paper and are exemplified by pin 

dot-matrix printers and daisy-wheel printers; nonimpact 

printers include every other type of print mechanism, 

including laser, ink-jet, and thermal printers. 

● Print technology Chief among types of print technology 

are pin dot-matrix, ink-jet, laser, thermal, and 

(although somewhat outdated) daisy-wheel or thimble 

printers. Pin dot-matrix printers can be further classified 

by the number of pins in the print head: 9, 18, 24, 

and so on. 

● Character formation Fully formed characters 

made of continuous lines (such as those produced by 

a daisy-wheel printer) versus dot-matrix characters 

composed of patterns of dots (such as those produced 

by standard dot-matrix, ink-jet, and thermal printers). 

Laser printers, while technically dot-matrix, are generally 

considered to produce fully formed characters 

because their output is very clear and the dots are 

extremely small and closely spaced. 

● Method of transmission Parallel (byte-by-byte 

transmission) versus serial (bit-by-bit transmission). 

These categories refer to the means by which output is 

sent to the printer rather than to any mechanical distinctions. 

Many printers are available in either parallel or 

serial versions, and still other printers offer both choices, 

yielding greater flexibility in installation options. 

● Method of printing Character by character, line by 

line, or page by page. Character printers include standard 

dot-matrix, ink-jet, thermal, and daisy-wheel printers. 

Line printers include the band, chain, and drum 

printers that are commonly associated with large computer 

installations or networks. Page printers include 

the electrophotographic printers, such as laser printers. 

● Print capability Text-only versus text-and-graphics. 

Text-only printers, including most daisy-wheel and 

thimble printers and some dot-matrix and laser printers, 

can reproduce only characters for which they have 

matching patterns, such as embossed type or internal 

420 

character maps. Text-and-graphics printers—dot-matrix, 

ink-jet, laser, and others—can reproduce all manner of 

images by “drawing” each as a pattern of dots. 

● Print quality Draft versus near-letter quality versus 

letter quality. 

Printer Access Protocol n. See PAP (definition 2). 

Printer Control Language n. A printer control language 

from Hewlett-Packard, used in its LaserJet, DeskJet, and 

RuggedWriter printer lines. Because of the LaserJet’s 

dominance in the laser printer market, Printer Control 

Language has become a de facto standard. Acronym: PCL. 

Also called: Hewlett-Packard Printer Control Language. 

printer controller n. The processing hardware in a 

printer, especially in a page printer. It includes the raster 

image processor, the memory, and any general-purpose 

microprocessors. A printer controller can also reside in a 

personal computer, attached via a high-speed cable to a 

printer that simply carries out its instructions. Compare 

printer engine. 

printer driver n. A software program designed to enable 

other programs to work with a particular printer without 

concerning themselves with the specifics of the printer’s 

hardware and internal language. Application programs can 

communicate properly with a variety of printers by using 

printer drivers, which handle all of the subtleties of each 

printer so that the application program doesn’t have to. 

Today graphical user interfaces offer their own printer 

drivers, eliminating the need for an application that runs 

under the interface to have its own printer driver. 

printer engine n. The part of a page printer, such as a 

laser printer, that actually performs the printing. Most 

printer engines are self-contained, replaceable cartridges. 

The engine is distinct from the printer controller, which 

includes all the processing hardware in the printer. The 

most widely used printer engines are manufactured by 

Canon. Compare printer controller. 

printer file n. Output that would normally be destined for 

the printer but has been diverted to a computer file instead. 

A printer file is created for any of several reasons. For 

example, it allows output to be transferred to another program 

or to another computer. It also allows additional copies 

to be made at any time by simply copying the print 

image to the printer. Occasionally, the term printer file is 

used, incorrectly, to refer to the printer driver.

printer font print spooler 

printer font n. A font residing in or intended for a printer. 

A printer font can be internal, downloaded, or on a font 

cartridge. Compare screen font. 

Printer Job Language n. The printer command language 

developed by Hewlett-Packard that provides printer control 

at the print-job level. Using PJL commands, you can 

change default printer settings such as the number of copies 

to print. PJL commands also permit switching printer 

languages between print jobs without action by the user. If 

bi-directional communication is supported, a PJL-compatible 

printer can send information such as printer model 

and job status to the print server. Also called: Hewlett- 

Packard Printer Job Language. Acronym: PJL. See also 

page-description language, PostScript, Printer Control 

Language. 

printer port n. A port through which a printer can be connected 

to a personal computer. On PC-compatible 

machines, printer ports are usually parallel ports and are 

identified in the operating system by the logical device 

name LPT. On many newer PCs, the parallel port on the 

case of the CPU has a printer icon beside it to identify it as 

a printer port. Serial ports can also be used for some printers 

(logical device name COM), although configuration is 

generally required. On Macintoshes, printer ports are usually 

serial ports and are also used to connect Macs to an 

AppleTalk network. See also AppleTalk, central processing 

unit, logical device, parallel port, serial port. 

printer server n. See print server. 

print head or printhead n. A component of an impact 

printer that contains the pins or other components that 

force ink from a ribbon onto paper. 

printing pool n. Two or more identical printers that are 

connected to one print server and act as a single printer. In 

this case, when you print a document, the print job will be 

sent to the first available printer in the pool. See also print 

job, printer. 

print job n. A single batch of characters printed as a unit. 

A print job usually consists of a single document, which 

can be one page or hundreds of pages long. To avoid having 

to print individual documents separately, some software 

can group multiple documents into a single print job. 

See also print spooler. 

print mode n. A general term for the format of print output 

by a printer. Print modes range from portrait or landscape 

orientation of the paper to letter quality and size of 

421 

the print. Dot-matrix printers support two print modes: 

draft and letter quality (LQ) or near-letter-quality (NLQ). 

Some printers can interpret both plain text (ASCII) and a 

page definition language such as PostScript. See also Post- 

Script, printer. 

printout n. See hard copy. 

print quality n. The quality and clarity of characters produced 

by a printer. Print quality varies with the type of 

printer; in general, dot-matrix printers produce lowerquality 

output than laser printers. The printer mode can 

also affect quality. See also resolution (definition 1). 

print queue n. A buffer for documents and images waiting 

to be printed. When an application places a document 

in a print queue, it is held in a special part of the computer’s 

memory, where it waits until the printer is ready to 

receive it. 

Print Screen key n. A key on IBM PC and compatible 

keyboards that normally causes the computer to send a 

character-based “picture” of the screen contents to the 

printer. The print screen feature works only when the display 

is in text mode or CGA graphics mode (the lowestresolution 

color and graphics mode available on IBM 

compatibles). It will not work properly in other graphics 

modes. Some programs use the Print Screen key to capture 

a screen image and record it as a file on disk. These programs 

can typically work in any graphics mode and record 

the file as a graphics image. When the user is working 

directly with the MS-DOS operating system, and with 

some programs, the combination Control-Print Screen 

toggles the printer on or off. With printing turned on, the 

system sends every character to the printer as well as to 

the screen. The Print Screen key on the Apple Extended 

Keyboard is included for compatibility with operating systems 

such as MS-DOS. Also called: PrtSc key. 

print server n. A workstation that is dedicated to managing 

printers on a network. The print server can be any station 

on the network. Also called: printer server. 

Print Server for Macintosh n. An AppleTalk network 

integration service that enables computers running the 

Macintosh and Windows operating systems to share printers. 

Also called: MacPrint. 

print spooler n. Computer software that intercepts a print 

job on its way to the printer and sends it to disk or memory 

instead, where the print job is held until the printer is 

P

P 

print to file privileged instruction 

ready for it. The term spooler is an acronym created from 

“simultaneous peripheral operations on line.” 

print to file n. A command in many applications that 

instructs the program to format a document for printing 

and store the formatted document as a file rather than 

sending it to a printer. 

print wheel n. See daisy wheel. 

priority n. Precedence in receiving the attention of the 

microprocessor and the use of system resources. Within a 

computer, unseen and unnoticed levels of priority are the 

means by which many different types of potential clashes 

and disruptions are avoided. Similarly, tasks running on a 

computer can be assigned priorities that determine when 

and for how long they receive time from the microprocessor. 

On networks, stations can be assigned priorities that 

determine when and how often they can control the communications 

line, and messages can be assigned priorities 

that indicate how soon they must be transmitted. See also 

interrupt. 

Priority Frame n. A telecommunications protocol developed 

by Infonet and Northern Telecom, Inc., designed to 

carry data, facsimile, and voice information. 

privacy n. The concept that a user’s data, such as stored 

files and e-mail, is not to be examined by anyone else 

without that user’s permission. A right to privacy is not 

generally recognized on the Internet. Federal law protects 

only e-mail in transit or in temporary storage, and only 

against access by Federal agencies. Employers often claim 

a right to inspect any data on their systems. To obtain privacy, 

the user must take active measures such as encryption. 

See also encryption, PGP, Privacy Enhanced Mail. 

Compare security. 

Privacy Enhanced Mail n. An Internet standard for 

e-mail systems that use encryption techniques to ensure 

the privacy and security of messages. Acronym: PEM. See 

also encryption, standard. Compare PGP. 

privacy policy n. Public statement delineating how a Web 

site uses the information it gathers from visitors to the site. 

Some Web sites sell this information to third parties or use 

the information for marketing purposes. Other sites have 

strict policies limiting how that information may be used. 

private adj. A keyword used in some programming languages 

to signify that methods or variables can be 

422 

accessed only by elements residing in the same class or 

module. See also class, keyword (definition 2), local variable, 

reserved word, scope. Compare public. 

private assembly n. An assembly that is used by only 

one application. A private assembly is deployed into the 

directory structure of the application that uses it. Also 

called: private side-by-side assembly. See also shared 

assembly. 

Private Branch Exchange n. See PBX. 

private channel n. In Internet relay chat (IRC), a channel 

reserved for the use of a certain group of people. Private 

channel names are hidden from view by the public at 

large. Also called: secret channel. See also IRC. 

Private Communications Technology n. See PCT (definition 

2). 

private folders n. In a shared network environment, 

those folders on a user’s computer that are not accessible 

by other users on the network. Compare public folders. 

private key n. One of two keys in public key encryption. 

The user keeps the private key secret and uses it to encrypt 

digital signatures and to decrypt received messages. See 

also public key encryption. Compare public key. 

private line n. See dedicated line (definition 1). 

Private Network-to-Network Interface n. See PNNI. 

privatization n. Generally, the process of turning something 

over from government to commercial industry control. 

In the context of computer science and the Internet, 

the term refers to the government’s turning over of various 

Internet backbones to private industry—for example, control 

of NSFnet was passed from the government to private 

business in 1992—and to the government’s more recent 

(1998) privatization of responsibility for domain names 

and addresses, which was shifted from IANA and NSI/ 

InterNIC to a new organization known as ICANN. See 

also IANA, ICANN, InterNIC. 

privileged instruction n. An instruction (usually a 

machine instruction) that can be executed only by the 

operating system. Privileged instructions exist because the 

operating system needs to perform certain operations that 

applications should not be allowed to perform; therefore, 

only the operating-system routines have the necessary 

privilege to execute these particular instructions.

privileged mode Prodigy 

privileged mode n. A mode of execution, supported by 

the protected mode of the Intel 80286 and higher microprocessors, 

in which software can carry out restricted 

operations that manipulate critical components of the system, 

such as memory and input/output ports (channels). 

Application programs cannot be executed in privileged 

mode; the heart (kernel) of the OS/2 operating system can 

be, as can the programs (device drivers) that control 

devices attached to the system. 

privileges n. See access privileges. 

PRN n. The logical device name for printer. A name 

reserved by the MS-DOS operating system for the standard 

print device. PRN usually refers to a system’s first 

parallel port, also known as LPT1. 

.pro n. One of seven new top-level domain names approved 

in 2000 by the Internet Corporation for Assigned Names 

and Numbers (ICANN), .pro is meant for use in Web sites 

relating to professions such as physicians, accountants, and 

lawyers. Six of the new domains became available for use 

in the spring of 2001; negotiations are still underway for the 

final registry agreement for the .pro domain. 

probability n. The likelihood that an event will happen, 

which can often be estimated mathematically. In mathematics, 

statistics and probability theory are related fields. 

In computing, probability is used to determine the likelihood 

of failure or error in a system or device. 

problem solving n. 1. The process of devising and implementing 

a strategy for finding a solution or for transforming 

a less desirable condition into a more desirable one. 

2. An aspect of artificial intelligence wherein the task of 

problem solving is performed solely by a program. See 

also artificial intelligence. 

procedural language n. A programming language in 

which the basic programming element is the procedure (a 

named sequence of statements, such as a routine, subroutine, 

or function). The most widely used high-level languages 

(C, Pascal, Basic, FORTRAN, COBOL, Ada) are 

all procedural languages. See also procedure. Compare 

nonprocedural language. 

procedural rendering n. The rendering of a two-dimensional 

image from three-dimensional coordinates with texturing 

according to user-specified conditions, such as 

direction and degree of lighting. 

423 

procedure n. In a program, a named sequence of statements, 

often with associated constants, data types, and 

variables, that usually performs a single task. A procedure 

can usually be called (executed) by other procedures, as 

well as by the main body of the program. Some languages 

distinguish between a procedure and a function, with the 

latter (the function) returning a value. See also function, 

parameter, procedural language, routine, subroutine. 

procedure call n. In programming, an instruction that 

causes a procedure to be executed. A procedure call can be 

located in another procedure or in the main body of the 

program. See also procedure. 

process1 n. A program or part of a program; a coherent 

sequence of steps undertaken by a program. 

process2 vb. To manipulate data with a program. 

process-bound adj. Limited in performance by processing 

requirements. See also computation-bound. 

process color n. A method of handling color in a document 

in which each block of color is separated into its subtractive 

primary color components for printing: cyan, 

magenta, and yellow (as well as black). All other colors 

are created by blending layers of various sizes of halftone 

spots printed in cyan, magenta, and yellow to create the 

image. See also color model, color separation (definition 

1). Compare spot color. 

processing n. The manipulation of data within a computer 

system. Processing is the vital step between receiving 

data (input) and producing results (output)—the task 

for which computers are designed. 

processor n. See central processing unit, microprocessor. 

Processor Direct Slot n. See PDS (definition 1). 

Processor Input/Output n. See PIO. 

Procmail n. An open-source e-mail-processing utility for 

Linux and other UNIX-based computers and networks. 

Procmail can be used to create mail servers and mailing 

lists, filter mail, sort incoming mail, preprocess mail, and 

perform other mail-related functions. 

Prodigy n. An Internet service provider (ISP) that offers 

Internet access and a wide range of related services. Prodigy 

was founded by IBM and Sears as a proprietary online 

service, was acquired by International Wireless in 1996, 

and in 1999 entered into a partnership with SBC Commu- 

P

P 

Prodigy Information Service program file 

nications. The addition of SBC’s Internet customer base 

made Prodigy the third largest ISP in the United States. 

Prodigy Information Service n. An online information 

service founded by IBM and Sears. Like its competitors 

America Online and CompuServe, Prodigy offers access 

to databases and file libraries, online chat, special interest 

groups, e-mail, and Internet connectivity. Also called: 

Prodigy. 

product n. 1. An operator in the relational algebra used in 

database management that, when applied to two existing 

relations (tables), results in the creation of a new table 

containing all possible ordered concatenations (combinations) 

of tuples (rows) from the first relation with tuples 

from the second. The number of rows in the resulting relation 

is the product of the number of rows in the two source 

relations. Also called: Cartesian product. Compare inner 

join. 2. In mathematics, the result of multiplying two or 

more numbers. 3. In the most general sense, an entity conceived 

and developed for the purpose of competing in a 

commercial market. Although computers are products, the 

term is more commonly applied to software, peripherals, 

and accessories in the computing arena. 

production system n. In expert systems, an approach to 

problem solving based on an “IF this, THEN that” 

approach that uses a set of rules, a database of information, 

and a “rule interpreter” to match premises with facts 

and form a conclusion. Production systems are also known 

as rule-based systems or inference systems. See also 

expert system. 

Professional Graphics Adapter n. A video adapter 

introduced by IBM, primarily for CAD applications. The 

Professional Graphics Adapter is capable of displaying 

256 colors, with a horizontal resolution of 640 pixels and a 

vertical resolution of 480 pixels. Acronym: PGA. 

Professional Graphics Display n. An analog display 

introduced by IBM, intended for use with their Professional 

Graphics Adapter. See also Professional Graphics 

Adapter. 

profile1 n. See user profile. 

profile2 vb. To analyze a program to determine how 

much time is spent in different parts of the program during 

execution. 

profiler n. A diagnostic tool for analyzing the run-time 

behavior of programs. 

424 

Profiles for Open Systems Internetworking 

Technology n. See POSIT. 

program1 n. A sequence of instructions that can be executed 

by a computer. The term can refer to the original 

source code or to the executable (machine language) version. 

Also called: software. See also program creation, 

routine, statement. 

program2 vb. To create a computer program, a set of 

instructions that a computer or other device executes to 

perform a series of actions or a particular type of work. 

program button n. On a handheld device, a navigation 

control that is pressed to launch an application. Also 

called: application button. 

program card n. See PC Card, ROM card. 

program cartridge n. See ROM cartridge. 

program comprehension tool n. A software engineering 

tool that facilitates the process of understanding the 

structure and/or functionality of computer applications. 

Acronym: PCT. Also called: software exploration tool. 

program counter n. A register (small, high-speed memory 

circuit within a microprocessor) that contains the 

address (location) of the instruction to be executed next in 

the program sequence. 

program creation n. The process of producing an executable 

file. Traditionally, program creation comprises 

three steps: (1) compiling the high-level source code into 

assembly language source code; (2) assembling the 

assembly language source code into machine-code object 

files; and (3) linking the machine-code object files with 

various data files, run-time files, and library files into an 

executable file. Some compilers go directly from highlevel 

source to machine-code object, and some integrated 

development environments compress all three steps into a 

single command. See also assembler, compiler (definition 

2), linker, program. 

program encapsulation n. A method of dealing with 

programs with Year 2000 problems that entailed modifying 

the data with which a program worked. The input data 

is modified to reflect a parallel date in the past that the 

program can handle. When output is generated, that data is 

changed again, to reflect the correct date. The program 

itself remains unchanged. 

program file n. A disk file that contains the executable 

portions of a computer program. Depending on its size and

program generator programming 

complexity, an application or other program, such as an 

operating system, can be stored in several different files, 

each containing the instructions necessary for some part of 

the program’s overall functioning. Compare document file. 

program generator n. A program that creates other programs 

(usually in source code) based on a set of specifications 

and relationships given by the user. Program 

generators are often used to simplify the task of creating 

an application. See also 4GL, application generator. 

program listing n. A copy, usually on paper, of the 

source code of a program. Some compilers can generate 

program listings with line numbers, cross-references, and 

so on. 

program logic n. The logic behind the design and construction 

of a program—that is, the reasons it works the 

way it does. See also logic error. 

programmable adj. Capable of accepting instructions for 

performing a task or an operation. Being programmable is 

a characteristic of computers. 

programmable function key n. Any of several, sometimes 

unlabeled, keys on some third-party keyboards that 

allow the user to “play back” previously stored key combinations 

or sequences of keystrokes called macros. The 

same effect can be achieved with a standard keyboard and 

a keyboard enhancer, the latter of which intercepts the 

keyboard codes and substitutes modified values; but programmable 

function keys accomplish this without requiring 

RAM-resident software. Compare keyboard enhancer. 

programmable interrupt controller n. An Intel chip 

that handles interrupt requests (IRQs). IBM AT machines 

use two programmable interrupt controllers to accommodate 

a maximum of 15 IRQs. The programmable interrupt 

controller has been replaced by the advanced programmable 

interrupt controller (APIC), which supports multiprocessing. 

Acronym: PIC. See also IBM AT, IRQ. 

programmable logic array n. See field-programmable 

logic array. 

programmable logic device n. A logic chip that is programmed 

by the customer rather than by the manufacturer. 

Like a gate array, a programmable logic device consists of 

a collection of logic gates; unlike a gate array, a programmable 

logic device need not have its programming completed 

as part of the manufacturing process. Acronym: 

PLD. See also logic chip. Compare gate array. 

425 

programmable read-only memory n. See PROM. 

program maintenance n. The process of supporting, 

debugging, and upgrading a program in response to feedback 

from individual or corporate users or the marketplace 

in general. 

programmatic interface n. 1. A user interface dependent 

on user commands or on a special programming language, 

as contrasted with a graphical user interface. UNIX 

and MS-DOS have programmatic interfaces; the Apple 

Macintosh and Microsoft Windows have graphical user 

interfaces. See also command-line interface, graphical 

user interface, iconic interface. 2. The set of functions any 

operating system makes available to a programmer developing 

an application. See also application programming 

interface. 

Programmed Input/Output n. See PIO. 

Programmed Inquiry, Learning or Teaching n. See 

PILOT. 

programmer n. 1. An individual who writes and debugs 

computer programs. Depending on the size of the project 

and the work environment, a programmer might work 

alone or as part of a team, be involved in part or all of the 

process from design through completion, or write all or a 

portion of the program. See also program. 2. In hardware, 

a device used to program read-only memory chips. See 

also PROM, ROM (definition 2). 

programmer’s switch n. A pair of buttons on Macintosh 

computers that enable the user to reboot the system or to 

enter a command-line interface at a low level of the operating 

system. Originally, only programmers testing software 

were expected to need those functions, so early 

models of the Macintosh hid the buttons inside the cabinet 

and supplied a plastic clip that could be attached so that 

the programmer could push them. In many later models 

the buttons are built into the cabinet; the button to reboot 

the system is marked with a triangle pointing leftward, and 

the other button is marked with a circle. 

programming n. The art and science of creating computer 

programs. Programming begins with knowledge of 

one or more programming languages, such as Basic, C, 

Pascal, or assembly language. Knowledge of a language 

alone does not make a good program. Much more can be 

involved, such as expertise in the theory of algorithms, 

user interface design, and characteristics of hardware 

devices. Computers are rigorously logical machines, and 

P

P 

programming language PROM 

programming requires a similarly logical approach to 

designing, writing (coding), testing, and debugging a program. 

Low-level languages, such as assembly language, 

also require familiarity with the capabilities of a microprocessor 

and the basic instructions built into it. In the modular 

approach advocated by many programmers, a project is 

broken into smaller, more manageable modules—standalone 

functional units that can be designed, written, tested, 

and debugged separately before being incorporated into 

the larger program. See also algorithm, kludge (definition 

2), modular design, object-oriented programming, spaghetti 

code, structured programming. 

programming language n. Any artificial language that 

can be used to define a sequence of instructions that can 

ultimately be processed and executed by the computer. 

Defining what is or is not a programming language can be 

tricky, but general usage implies that the translation process—from 

the source code expressed using the programming 

language to the machine code that the computer 

needs to work with—be automated by means of another 

program, such as a compiler. Thus, English and other natural 

languages are ruled out, although some subsets of 

English are used and understood by some fourth-generation 

languages. See also 4GL, compiler (definition 2), natural 

language, program. 

Programming Language I n. See PL/I. 

program specification n. In software development, a 

statement of the goals and requirements of a project, as 

well as the relation of the project to other projects. 

program state n. The condition of a program (stack contents, 

memory contents, instruction being executed) at a 

given moment. 

program statement n. The statement defining the name, 

briefly describing the operation, and possibly giving other 

information about a program. Some languages, such as 

Pascal, have an explicit program statement; others do not, 

or they use other forms (such as the main( ) function in C). 

progressive JPEG n. An enhancement to the JPEG 

graphics file format that gradually displays a photo-realistic 

picture in a Web browser, showing increasingly 

detailed versions of the picture until the entire file has finished 

downloading. 

progressive scanning n. 1. A display technique used on 

computer monitors in which the image is created, line by 

line, in a single top-to-bottom sweep of the electron gun. 

426 

The resulting image is of higher quality than is possible 

with the interlace scanning used for television sets. Progressive 

scanning might be used on next-generation digital 

television equipment. It does, however, require twice the 

signal bandwidth of interlace scanning. Compare interlace 

scanning. 2. A line-by-line (rather than every-other-line) 

technique used with some video cameras to capture images 

of moving objects. Such cameras are used primarily for 

tasks such as monitoring assembly lines and traffic flow. 

project n. An operator in the relational algebra used in 

database management. Given relation (table) A, the 

project operator builds a new relation containing only a 

specified set of attributes (columns) of A. 

Project 802 n. The IEEE project to define networking 

standards that resulted in the 802.x specifications. See also 

IEEE, IEEE 802.x. 

Project Gutenberg n. A project that makes the texts of 

books that are in the public domain available over the Internet. 

The files for the books are in plain ASCII, to make 

them accessible to as many people as possible. Project 

Gutenberg, based at the University of Illinois at Urbana- 

Champaign, can be reached at mrcnext.cso.uiuc.edu via 

FTP or through the Web page http://www.promo.net/pg/. 

See also ASCII. 

projection-join normal form n. See normal form (definition 

1). 

project life cycle n. A sequence of preplanned stages for 

taking a project from beginning to end. 

project management n. The process of planning, monitoring, 

and controlling the course and development of a 

particular undertaking. 

Prolog n. Short for Programming in Logic. A language 

designed for logic programming. Prolog evolved during 

the 1970s in Europe (primarily France and Scotland), and 

the first Prolog compiler was developed in 1972 by Philippe 

Roussel, at the University of Marseilles. The language 

has subsequently attained wide use in the field of 

artificial intelligence. Prolog is a compiled language that 

works with the logical relationship between pieces of data 

rather than mathematical relationships. See also artificial 

intelligence. 

PROM n. Acronym for programmable read-only memory. 

A type of read-only memory (ROM) that allows data 

to be written into the device with hardware called a PROM 

programmer. After a PROM has been programmed, it is

PROM blaster protocol analyzer 

dedicated to that data, and it cannot be reprogrammed. See 

also EEPROM, EPROM, ROM (definition 2). 

PROM blaster n. See PROM programmer. 

PROM blower n. See PROM programmer. 

promiscuous-mode transfer n. In network communications, 

a transfer of data in which a node accepts all packets 

regardless of their destination address. 

PROM programmer n. A hardware device that records 

instructions or data on a PROM (programmable read-only 

memory) chip or an EPROM (erasable programmable 

read-only memory) chip. Also called: PROM blaster, 

PROM blower. See also EPROM, PROM. 

prompt n. 1. In command-driven systems, one or more 

symbols that indicate where users are to enter commands. 

For instance, in MS-DOS, the prompt is generally a drive 

letter followed by a greater than symbol (C>). In UNIX, it 

is usually %. See also command-driven system, DOS 

prompt. 2. Displayed text indicating that a computer program 

is waiting for input from the user. 

propagated error n. An error used as input to another 

operation, thus producing another error. 

propagation n. Travel of a signal, such as an Internet 

packet, from its source to one or more destinations. Propagation 

of messages over different paths with different 

lengths can cause messages to appear at a user’s computer 

with varying delivery times. See also propagation delay. 

propagation delay n. The time needed by a communications 

signal to travel between two points; in satellite links, 

a noticeable delay of between one-quarter second and onehalf 

second, caused by the signal traveling through space. 

propeller head n. Slang for a person who is obsessed with 

computers or other technology; a geek. The name refers to 

a child’s beanie cap topped by a spinning propeller. 

property n. In Windows 9x, a characteristic or parameter 

of an object or device. Properties of a file, for example, 

include type, size, and creation date and can be identified by 

accessing the file’s property sheet. See also property sheet. 

property sheet n. A type of dialog box in Windows 9x, 

accessed by choosing Properties in the File menu or by 

right-clicking on an object and selecting Properties, that 

lists the attributes or settings of an object such as a file, 

application, or hardware device. A property sheet presents 

the user with a tabbed, index-card-like selection of prop- 

427 

erty pages, each of which features standard dialog-style 

controls for customizing parameters. 

proportional font n. A set of characters in a particular 

style and size in which a variable amount of horizontal 

space is allotted to each letter or number. In a proportional 

font, the letter i, for example, is allowed less space than 

the letter m. Compare monospace font. 

proportional spacing n. A form of character spacing in 

which the horizontal space each character occupies is proportional 

to the width of the character. The letter w, for 

example, takes up more space than the letter i. Compare 

monospacing. 

proprietary adj. Of, pertaining to, or characteristic of 

something that is privately owned. Generally, the term 

refers to technology that has been developed by a particular 

corporation or entity, with specifications that are considered 

by the owner to be trade secrets. Proprietary 

technology may be legally used only by a person or entity 

purchasing an explicit license. Also, other companies are 

unable to duplicate the technology, both legally and 

because its specifications have not been divulged by the 

owner. Compare public domain. 

proprietary software n. A program owned or copyrighted 

by an individual or a business and available for use 

only through purchase or by permission of the owner. 

Compare open source, public-domain software. 

protected n. A keyword in a programming language 

(such as Java or C++) used in a method or variable declaration. 

It signifies that the method or variable can be 

accessed only by elements residing in its class, subclasses, 

or classes in the same package. See also class, declaration, 

method, package, variable. 

protected mode n. An operating mode of the Intel 80286 

and higher microprocessors that supports larger address 

spaces and more advanced features than real mode. When 

started in protected mode, these CPUs provide hardware 

support for multitasking, data security, and virtual memory. 

The Windows (version 3.0 and later) and OS/2 operating 

systems run in protected mode, as do most versions of 

UNIX for these microprocessors. Compare real mode. 

protocol n. See communications protocol. 

protocol analyzer n. A management tool designed to 

identify and diagnose computer network problems. A protocol 

analyzer looks at LAN (local area network) or WAN 

(wide area network) traffic and finds protocol errors, connection 

delays, and other network faults. The protocol 

P

P 

protocol layer pseudo-streaming 

analyzer can filter and decode traffic, suggest solutions to 

problems, provide graphical reports, and show traffic by 

protocol and percent utilization. See also communications 

protocol. 

protocol layer n. See layer. 

protocol stack n. The set of protocols that work together 

on different levels to enable communication on a network. 

For example, TCP/IP, the protocol stack on the Internet, 

incorporates more than 100 standards including FTP, IP, 

SMTP, TCP, and Telnet. See also ISO/OSI reference 

model. Compare protocol suite. 

protocol suite n. A set of protocols designed, usually by 

one vendor, as complementary parts of a protocol stack. 

Compare protocol stack. 

prototyping n. The creation of a working model of a new 

computer system or program for testing and refinement. 

Prototyping is used in the development of both new hardware 

and software systems and new systems of information 

management. Tools used in the former include both 

hardware and support software; tools used in the latter can 

include databases, screen mockups, and simulations that, 

in some cases, can be developed into a final product. 

proxy n. A computer (or the software that runs on it) that 

acts as a barrier between a network and the Internet by 

presenting only a single network address to external sites. 

By acting as a go-between representing all internal computers, 

the proxy protects network identities while still 

providing access to the Internet. See also proxy server. 

proxy server n. A firewall component that manages Internet 

traffic to and from a local area network (LAN) and can 

provide other features, such as document caching and 

access control. A proxy server can improve performance 

by supplying frequently requested data, such as a popular 

Web page, and can filter and discard requests that the 

owner does not consider appropriate, such as requests for 

unauthorized access to proprietary files. See also firewall. 

PrtSc key n. See Print Screen key. 

.ps n. The file extension that identifies PostScript printer 

files. See also PostScript. 

PS/2 bus n. See Micro Channel Architecture. 

PSD n. A graphics file format used to create, modify, and 

display still images in Photoshop, a software application 

designed by Adobe Systems. PSD files have a file extension 

of .psd. 

428 

PSE n. See Packet Switching Exchange. 

psec n. See picosecond. 

pseudocode n. 1. A machine language for a nonexistent 

processor (a pseudomachine). Such code is executed by a 

software interpreter. The major advantage of p-code is that 

it is portable to all computers for which a p-code interpreter 

exists. The p-code approach has been tried several times in 

the microcomputer industry, with mixed success. The best 

known attempt was the UCSD p-System. Abbreviation: pcode. 

See also pseudomachine, UCSD p-System. 2. Any 

informal, transparent notation in which a program or algorithm 

description is written. Many programmers write 

their programs first in a pseudocode that looks much like a 

mixture of English and their favorite programming language, 

such as C or Pascal, and then translate it line by 

line into the actual language being used. 

pseudo compiler n. A compiler that generates a pseudolanguage. 

See also pseudolanguage. 

pseudocomputer n. See pseudomachine. 

pseudolanguage n. A nonexistent programming language—that 

is, one for which no implementation exists. 

The term can refer either to the machine language for a 

nonexistent processor or to a high-level language for 

which no compiler exists. See also pseudocode. 

pseudomachine n. A processor that doesn’t actually exist 

in hardware but that is emulated in software. A program 

written for the pseudomachine can run on several platforms 

without having to be recompiled. Abbreviation: pmachine. 

See also pseudocode, UCSD p-System. 

pseudo-op n. See pseudo-operation. 

pseudo-operation n. In programming, a program instruction 

that conveys information to an assembler or compiler 

but is not translated into a machine language instruction— 

for example, an instruction that establishes the value of a 

constant or the manner in which Boolean (logical) expressions 

are to be evaluated. Abbreviation: pseudo-op. 

pseudo-streaming n. A method used for real-time display 

of audio and video over the Web. Unlike sound or 

video files that are downloaded to a computer in their 

entirety before they can be played back, pseudo-streaming 

enables playback after only a portion of the file—enough 

to fill a buffer on the receiving computer—has been downloaded. 

Pseudo-streaming, unlike “true,” or Web, streaming, 

does not depend on server software to dynamically 

monitor the transmission. It can, however, play back only

PSK puck 

from the beginning of the file, rather than from any point, 

as can be the case with true streaming. See also stream. 

PSK n. See phase-shift keying. 

PSN n. Acronym for packet-switching network. See 

packet switching. 

PSTN n. See Public Switched Telephone Network. 

p-system n. An operating system based on a pseudomachine 

implemented in software. A program written for the 

p-system is more portable than one written for a machinedependent 

operating system. See also UCSD p-System. 

P-type semiconductor n. Semiconductor material in 

which electrical conduction is carried by holes (“vacancies” 

left by electrons). Whether a semiconductor is N-type 

or P-type depends on the kind of dopant added during manufacture. 

A dopant with a shortage of electrons results in a 

P-type semiconductor. Compare N-type semiconductor. 

pub n. See /pub. 

/pub n. Short for public. A directory in an anonymous 

FTP archive that is accessible by the public and that generally 

contains files available for free download. See also 

anonymous FTP. 

public adj. A keyword in some programming languages 

to signify that methods or variables can be accessed by 

elements residing in other classes or modules. See also 

class., keyword (definition 2), global variable, reserved 

word, scope. Compare private. 

public directory n. A directory on an FTP server that is 

accessible by anonymous users for the purpose of retrieving 

or storing files. Often the directory is called /pub. See 

also anonymous FTP, FTP (definition 1), FTP server /pub. 

public domain n. The set of all creative works, such as 

books, music, or software, that are not covered by copyright 

or other property protection. Works in the public 

domain can be freely copied, modified, and otherwise 

used in any manner for any purpose. Much of the information, 

texts, and software on the Internet is in the public 

domain, but putting a copyrighted work on the Internet 

does not put it in the public domain. Compare proprietary. 

public-domain software n. A program donated for public 

use by its owner or developer and freely available for 

copying and distribution. Compare free software, freeware, 

proprietary software, shareware. 

public files n. Files with no access restrictions. 

429 

public folders n. The folders that are made accessible on 

a particular machine or by a particular user in a shared networking 

environment. Compare private folders. 

public key n. One of two keys in public key encryption. 

The user releases this key to the public, who can use it for 

encrypting messages to be sent to the user and for decrypting 

the user’s digital signature. See also public key 

encryption. Compare private key. 

public key cryptography n. See public key encryption. 

public key encryption n. An asymmetric scheme that 

uses a pair of keys for encryption: the public key encrypts 

data, and a corresponding secret key decrypts it. For digital 

signatures, the process is reversed: the sender uses the 

secret key to create a unique electronic number that can be 

read by anyone possessing the corresponding public key, 

which verifies that the message is truly from the sender. 

See also private key, public key. 

public rights n. In the context of the Internet, the extent 

to which members of the public are permitted to use (and 

to place) information on the Internet under intellectual 

property law. See also fair use, public domain, publicdomain 

software. 

Public Switched Telephone Network n. The public 

telephone system. 

Publisher n. A software application developed by 

Microsoft Corporation to help businesses create highquality 

marketing and business material. A part of the 

Office product family, Publisher provides business users 

with design options for a variety of publications, such as 

newsletters, flyers, brochures, and Web pages. 

publishing point n. A publishing point is a virtual directory 

used for storing content or delivering a live stream. 

End users reach a publishing point through its URL. There 

are two types of unicast publishing points: on-demand for 

stored content and broadcast for live streams. See also ondemand 

publishing point, broadcast publishing point. 

Compare unicast. 

puck n. A pointing device used with a graphics tablet. A 

puck, which is often used in engineering applications, is a 

mouselike device with buttons for selecting items or 

choosing commands and a clear plastic section extending 

from one end with cross hairs printed on it. The intersection 

of the cross hairs on the puck points to a location on 

the graphics tablet, which in turn is mapped to a specific 

P

P 

puff and sip device pulse position modulation 

location on the screen. Because the puck’s cross hairs are 

on a transparent surface, a user can easily trace a drawing 

by placing it between the graphics tablet and the puck and 

moving the cross hairs over the lines of the drawing. See 

also graphics tablet, stylus. 

F0Pgn19.eps 

Puck. 

puff and sip device n. An assistive computer technology 

for people with mobility impairments. A puff and sip 

device is a head-mounted alternative to using a mouse or 

keyboard. For mouse functionality, the device allows a 

user to move the mouse pointer without using his or her 

hands by puffing air into a tube. 

pull vb. The process of retrieving data from a network 

server. Compare push (definition 2). See pop. 

pull-down menu n. A menu that is pulled down from the 

menu bar and that remains available as long as the user 

holds it open. Compare drop-down menu. 

pulse n. A transient signal, usually brief and with a discrete 

onset and offset. 

pulse amplitude modulation n. A method of encoding 

information in a signal by varying the amplitude of pulses. 

The unmodulated signal consists of a continuous train of 

pulses of constant frequency, duration, and amplitude. 

During modulation the pulse amplitudes are changed to 

reflect the information being encoded. See the illustration. 

Acronym: PAM. Compare pulse code modulation, pulse 

duration modulation, pulse position modulation. 

F0Pgn20.eps 

Pulse amplitude modulation. 

430 

pulse code modulation n. A method of encoding information 

in a signal by varying the amplitude of pulses. 

Unlike pulse amplitude modulation (PAM), in which pulse 

amplitude can vary continuously, pulse code modulation 

limits pulse amplitudes to several predefined values. 

Because the signal is discrete, or digital, rather than analog, 

pulse code modulation is more immune to noise than PAM. 

Acronym: PCM. Compare pulse amplitude modulation, 

pulse duration modulation, pulse position modulation. 

pulse dialing n. See rotary dialing. 

pulse duration modulation n. A method of encoding 

information in a signal by varying the duration of pulses. 



During modulation, the pulse durations are changed to 


Acronym: PDM. Also called: pulse length modulation, 

pulse width modulation. 

F0Pgn21.eps 

Pulse duration modulation. 

pulse length modulation n. See pulse duration modulation. 

pulse position modulation n. A method of encoding 

information in a signal by varying the position of pulses. 



During modulation, the pulse positions are changed to 


Acronym: PPM. Compare pulse amplitude modulation, 

pulse code modulation, pulse duration modulation. 

F0Pgn22.eps 

Pulse position modulation.

pulse width modulation Python 

pulse width modulation n. See pulse duration modulation. 

punched card n. An outdated computer-input medium 

made of stiff paper that stores data bits in columns containing 

patterns of punched holes. The method for creating the 

patterns used for different byte values is called Hollerith 

coding. See also Hollerith tabulating/recording machine. 

punched-card reader n. See card reader. 

pure procedure n. Any procedure that modifies only data 

that is dynamically allocated (usually on the stack). A pure 

procedure cannot modify either global data or its own 

code. This restriction allows a pure procedure to be called 

simultaneously by separate tasks. See also reentrant code. 

purge vb. To eliminate old or unneeded information systematically; 

to clean up, as files. 

push1 n. A technology developed in relation to the World 

Wide Web, designed to provide end users with personalized 

Web access by having a site actively “push” requested information 

to the user’s desktop, either automatically or at specified 

intervals. Push was developed as a means of relieving 

users from having to actively retrieve (“pull”) information 

from the Web. It is not, as yet, especially popular. 

push2 vb. 1. To add a new element to a stack, a data structure 

generally used to temporarily hold pieces of data 

being transferred or the partial result of an arithmetic 

operation. See also stack. Compare pop. 2. In networks 

and the Internet, to send data or a program from a server to 

a client at the instigation of the server. See also push2 . 

Compare pull. 

431 

put vb. In programming, to write data, typically to a file; 

in particular, to write a very small unit of data, such as a 

character. 

PVC n. Acronym for permanent virtual circuit. A permanent 

logical connection between two nodes on a packetswitching 

network. The PVC appears as a dedicated line 

to the nodes, but the data can be transmitted on a common 

carrier. See also common carrier, node (definition 2 ), 

packet switching, virtual private network. Compare SVC. 

pwd n. Acronym for print working directory. The UNIX 

command for displaying the current directory. 

PWM n. Acronym for pulse width modulation. See pulse 

duration modulation. 

PXE boot n. Acronym for Preboot Execution Environment 

boot. A BIOS-supported technology used to boot a 

PC remotely. To power on a PC and boot it from the network, 

PXE must be enabled in the BIOS, and the NIC in 

the PC must be PXE compliant. PXE boot is specified in 

the Intel Wired for Management (WfM) standard. Also 

called: network boot. 

pyramid diagram n. A diagram that is used to show foundation-based 

relationships. 

Python n. A portable, interpreted, object-oriented programming 

language developed and freely distributed by its 

developer. Python runs on many platforms, including 

UNIX, Windows, OS/2, and Macintosh, and is used for 

writing TCP/IP applications. 

P

Q 

QAM n. See quadrature amplitude modulation, queued 

access method. 

QBasic n. An interpreted language. QBasic is a dialect of 

Basic created by Microsoft for the MS-DOS platform. 

This language is no longer supported. 

QBE n. See query by example. 

QIC n. 1. Acronym for quarter-inch cartridge. A storage 

technology used with tape backup drives and cartridges. A 

means of backing up data on computer systems, QIC represents 

a set of standards devised to enable tapes to be 

used with drives from different manufacturers. The QIC 

standards specify the length of tape, the number of recording 

tracks, and the magnetic strength of the tape coating, 

all of which determine the amount of information that can 

be written to the tape. Older QIC-80 drives can hold up to 

340 MB of compressed data. Newer versions can hold 

more than 1 GB of information. 2. A consortium of quarter-inch 

tape manufacturers. Quarter-Inch Cartridge 

Drive Standards Inc. (QIC) establishes standards for the 

production of quarter-inch tapes. For example, QIC-40 

and QIC-80, designed to use a PC’s floppy disk drive 

controller, are called the “floppy tape standards.” 

QOS or QoS n. See quality of service. 

quadbit n. A set of 4 bits representing one of 16 possible 

combinations. In communications, quadbits are a means 

of increasing transmission rates by encoding 4 bits at a 

time, instead of 1 or 2. The 16 quadbits are 0000, 0001, 

0010, 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1010, 

1011, 1100, 1101, 1110, and 1111. Compare nibble. 

quadrature amplitude modulation n. In communications, 

an encoding method that combines amplitude modulation 

and phase modulation to create a constellation of 

signal points, each representing one unique combination 

of bits that can be identified with one possible state that 

the carrier wave can be in. Acronym: QAM. See also 

amplitude modulation, constellation, phase-shift keying, 

trellis-coded modulation. 

quadrature encoding n. The most common method used 

to determine in which direction a mouse is moving. In 

Q 

432 

mechanical mice, movement of the mouse ball is translated 

into horizontal or vertical movement by a pair of 

turning disks, one disk for horizontal movement and one 

disk for vertical movement, each of which makes and 

breaks contact with two sensors located on it. The two sensors 

are placed out of phase with each other, and the mouse 

notes which sensor receives contact first. The phrase 

quadrature encoding comes from the fact that each sensor 

sends a square-wave signal 90 degrees out of phase with the 

other. If the first signal occurs before the second, the mouse 

is assumed to have been moved in one direction; if the second 

signal occurs before the first, the mouse is assumed to 

have been moved in the opposite direction. See also 

mechanical mouse, mouse, optomechanical mouse. 

quality assurance n. A system of procedures carried out 

to ensure that a product or a system adheres or conforms 

to established standards. Also called: quality control. 

quality of service n. 1. Generally, the handling capacity 

of a system or service; the time interval between request 

and delivery of a product or service to the client or customer. 

2. In computer technology, the guaranteed throughput 

(data transfer rate) level. 

quantity n. A number—positive or negative, whole or 

fractional—that is used to indicate a value. 

quantize vb. To divide an element into separate, distinct 

units (quanta) and to assign a value to each resulting unit, 

especially in the domain of time. Compare digitize. 

quantum n. 1. In communications, the unit resulting from 

division of a signal by quantization. 2. A portion of time 

allotted on a time-sharing system. Compare time slice. 

3. An amount of something; for example, in physics, a 

unit of radiant energy. 

quantum bit n. See qubit. 

quantum computing n. A theoretical design for computers 

based on quantum mechanics. Unlike classic (current) 

digital computers, which calculate sets of values sequentially 

because a single bit can represent only 1 or 0 at any 

given time, a quantum computer is based on the ability of 

each bit to represent more than one value at the same time.

quarter-inch cartridge quicksort 

Because each quantum bit—called a qubit—represents 

multiple values, a quantum computer can be in multiple 

states simultaneously and can thus work on numerous 

problems at the same time to offer far more computing 

power than is currently available. Quantum computing is 

under investigation by the United States Defense 

Advanced Research Projects Agency (DARPA) and other 

groups. Although atoms of hydrogen and carbon have 

been used to create the rudiments of a quantum computer, 

the technology is still in its infancy. 

quarter-inch cartridge n. See QIC (definition 1). 

Quartz n. The 2-D drawing engine that forms the imaging 

foundation of the Mac OS X Aqua interface. The Quartz 

graphics application programming interface (API) is based 

on Adobe’s Portable Document Format (PDF) standard. 

quartz crystal n. A precisely shaped and precisely sized 

piece of the mineral quartz, used for its piezoelectric properties. 

When a voltage is applied to a quartz crystal, it 

vibrates at a frequency determined by its size and shape. 

Quartz crystals are commonly used to control the frequency 

of oscillator circuits such as the clocks in microcomputers. 

See also piezoelectric. 

quasi-language n. A derogatory term for any programming 

language that, because of deficiencies, is not suitable 

for any serious work. 

qubit n. Short for quantum bit. The bits (currently, 

atomic particles) that make up the theoretical machines 

known as quantum computers. Qubits are unlike bits in 

current computers in that they exist in more than one state 

at the same time. They can, therefore, represent both 0 and 

1 simultaneously. Qubits, like quantum computers, are 

based on the science of quantum mechanics. 

query1 n. A specific set of instructions for extracting particular 

data. 

query2 vb. To extract data from a database and present it 

for use. 

query by example n. A simple-to-use query language 

implemented on several relational database management 

systems. Using query by example, the user specifies fields 

to be displayed, intertable linkages, and retrieval criteria 

directly onto forms displayed on the screen. These forms 

are a direct pictorial representation of the table and row 

structures that make up the database. Thus, the construction 

of a query becomes a simple “checkoff” procedure 

from the viewpoint of the user. Acronym: QBE. 

433 

query language n. A subset of the data manipulation language; 

specifically, that portion relating to the retrieval 

and display of data from a database. It is sometimes used 

loosely to refer to the entire data manipulation language. 

See also data manipulation language. 

question mark n. See ?. 

queue1 n. A multi-element data structure from which (by 

strict definition) elements can be removed only in the 

same order in which they were inserted; that is, it follows 

a first in, first out (FIFO) constraint. There are also several 

types of queues in which removal is based on factors other 

than order of insertion—for example, some priority value 

assigned to each element. See also deque, element (definition 

1). Compare stack. 

queue2 vb. To place (an item) in a queue. 

queued access method n. A programming technique 

that minimizes input/output delays by synchronizing the 

transfer of information between the program and the computer’s 

input and output devices. Acronym: QAM. 

queuing n. In networking, the process of buffering data in 

preparation for transmission. See also fair queuing; first 

in, first out; last in, first out; weighted fair queuing. 

QuickDraw n. On the Apple Macintosh, the built-in group 

of routines within the operating system that controls the 

display of graphics and text. Application programs call 

QuickDraw for on-screen displays. See also Toolbox. 

QuickDraw 3-D n. A version of the Macintosh Quick- 

Draw library that includes routines for doing 3-D graphics 

calculations. See also QuickDraw. 

Quicken n. Financial-management software from Intuit, 

Inc. The personal-finance version, introduced by Intuit in 

1984, includes tools for balancing and tracking bank 

accounts and investments, budgeting, paying bills, planning 

and preparing tax returns, financial planning, and 

estate planning. A small-business version, Quicken Home 

& Business, adds tools for business-related matters, such 

as invoicing and accounts receivable and payable. 

quicksort n. An efficient sort algorithm, described by 

C.A.R. Hoare in 1962, in which the essential strategy is to 

“divide and conquer.” A quicksort begins by scanning the 

list to be sorted for a median value. This value, called the 

pivot, is then moved to its final position in the list. Next, 

all items in the list whose values are less than the pivot 

value are moved to one side of the list, and the items with 

values greater than the pivot value are moved to the other 

Q

Q 

QuickTime QWERTY keyboard 

side. Each resulting side is sorted the same way, until a 

fully sorted list results. See also sort algorithm. Compare 

bubble sort, insertion sort, merge sort. 

QuickTime n. Software components developed by Apple 


content. QuickTime, which supports video, animation, 

graphics, 3-D, VR (virtual reality), MIDI, music, sound, 

and text, has been part of the Mac OS since version 7 of 

the operating system and is used in many Macintosh applications. 

Windows applications can also run QuickTime 

files but require the installation of special player software. 

QuickTime is often used on the Web to provide Web pages 

with video and animation. Most Web browsers support 

plug-ins for running these types of files. QuickTime is also 

part of the new MPEG-4 specification. See also MPEG-4. 

Quick View n. A feature, optionally installed as part of 

Windows 9x, that provides a set of file viewers for previewing 

the contents of files without having to start the 

application(s) that created them. The feature is accessed 

through the Quick View command, available either from 

the File menu or by right-clicking a filename. If the feature 

has been installed but the file type is not supported by 

a viewer, the Quick View command does not appear. 

434 

quiet answer n. A telephone-answering protocol in 

which incoming calls are answered with silence instead of 

a tone signal. Some telephone-switching systems use quiet 

answering. These switching systems expect the caller to 

provide another phone number, code, or extension after 

the quiet answer. 

quit1 n. 1. An FTP command that instructs the server to 

drop the current connection with the client from which it 

received the command. 2. A command in many applications 

for exiting the program. 

quit2 vb. 1. To stop in an orderly manner. 2. To execute 

the normal shutdown of a program and return control to 

the operating system. Compare abort, bomb2 , crash2 (definition 

1), hang. 

QWERTY keyboard n. A keyboard layout named for the 

six leftmost characters in the top row of alphabetic characters 

on most keyboards—the standard layout of most typewriters 

and computer keyboards. Compare Dvorak 

keyboard.

R&D n. Acronym for research and development. 

race condition n. 1. A condition in which a feedback circuit 

interacts with internal circuit processes in a way that 

produces chaotic output behavior. 2. A condition in which 

data propagates rapidly through a logic circuit far ahead of 

the clock signal intended to control its passage. 

rack-mounted adj. Built for installation in a metal frame 

or cabinet of standard width (typically 19 inches or 23 

inches) and mounting arrangements. 

RAD n. Acronym for rapid application development. A 

method of building computer systems in which the system 

is programmed and implemented in segments, rather than 

3.14159 radians 

F0Rgn01.EPS 

Radian. 

1 radian 

1 radian 

57.296° 

57.296° 

57.296° 

57.296° 

1 radian 

1 radian 

57.296° 

57.296° 

Radians = (3.14159 x (angle of degree)) ÷ 180 

1 degree = 0.017453 radian 

R 

1 radian 

1 radian 

435 

waiting until the entire project is completed for implementation. 

Developed by programmer James Martin, RAD 

uses such tools as CASE and visual programming. See 

also CASE, visual programming. 

radian n. The angle between two radii of a circle such that 

the length of the arc between them is equal to the radius. 

The circumference of a circle is equal to 2p times the 

radius, so one radian contains 360/(2p) = 180/p = approximately 

57.2958 degrees. Conversely, multiplying the number 

of degrees by p/180 gives the number of radians; 360 

degrees equals 2p radians. See the illustration. 

Begin and end at 3 o’clock— 

work counterclockwise 

6.28318 radians 

R

R 

radio RADSL 

radio n. 1. Electromagnetic waves longer than about 0.3 

mm (frequencies lower than about 1 THz). Radio is used 

to transmit a wide variety of signals, using various frequency 

ranges and types of modulation, such as AM and 

FM broadcasts, microwave relays, and television broadcasts. 

See also hertz, radio frequency. 2. Audio signals 

transmitted over the Internet of quality comparable to 

those broadcast by commercial radio stations. See also 

Internet Talk Radio, MBONE, RealAudio. 

radio button n. In graphical user interfaces, a means of 

selecting one of several options, usually within a dialog 

box. A radio button appears as a small circle that, when 

selected, has a smaller, filled circle inside it. Radio buttons 

act like the station selector buttons on a car radio. Selecting 

one button in a set deselects the previously selected 

button, so one and only one of the options in the set can be 

selected at any given time. In contrast, check boxes are 

used when more than one option in the set can be selected 

at the same time. Compare check box. 

radio clock n. A device that receives a broadcast containing 

a standard time signal. Radio clocks are used in network 

communications to synchronize the host’s hardware 

clock to the Universal Time Coordinate format in accordance 

with the Network Time Protocol (NTP). See also 

NTP, Universal Time Coordinate. 

radio frequency n. The portion of the electromagnetic 

spectrum with frequencies between 3 kilohertz and 300 

gigahertz. This corresponds to wavelengths between 30 

kilometers and 0.3 millimeter. Acronym: RF. See also 

radio (definition 1). 

radio frequency interference n. See RFI. 

radiosity n. A method used in computer graphics to render 

photographic-quality, realistic images. Radiosity is 

based on dividing an image into smaller polygons, or 

patches, for purposes of calculating the global illumination 

emitted by sources of light and reflected from surfaces. 

Unlike ray tracing, which follows rays of light 

between a light source and the objects it illuminates, radiosity 

takes into account both the light emitted from a light 

source and the light reflected by all objects in the image 

environment. Radiosity thus accounts not only for a 

source of illumination (such as a lightbulb) but also for 

the effects of that illumination as it is absorbed by, and 

reflected from, every object in the “picture.” See also form 

factor. Compare ray tracing. 

436 

RADIUS n. Acronym for Remote Authentication Dial-In 

User Service protocol. A proposed Internet protocol in 

which an authentication server provides authorization and 

authentication information to a network server to which a 

user is attempting to link. See also authentication, communications 

protocol, server (definition 2). 

radix n. The base of a number system—for example, 2 in 

the binary system, 10 in the decimal system, 8 in the octal 

system, and 16 in the hexadecimal system. See also base 


radix-minus-1 complement n. In a system for representing 

numbers using a fixed number of possible digits 

(radix) and a fixed number of positions for them, the number 

obtained from another number by subtracting each of 

the digits of the other number from the largest possible 

digit (equal to the radix minus 1). For example, in a system 

of five-digit decimal numbers, the radix-minus-1 

complement of 1,234 is 98,765. Adding any number to its 

radix-minus-1 complement produces the largest possible 

number in the system (in the example, 99,999). Adding 

another 1 to this number produces, in our example, 

100,000—but since only the lower five digits are used, the 

result is zero. Thus, the negative of any number in the system 

is its radix-minus-1 complement plus 1, because –a + 

a = 0. In the binary system, the radix-minus-1 complement 

is the one’s complement, which is easily formed electronically 

by inverting all bits. 

radix point n. The period or other character that separates 

the integer portion of a number from the fractional portion. 

In the decimal system, the radix point is the decimal 

point, as in the number 1.33. 

radix sort n. See digital sort. 

radix sorting algorithm n. A sorting algorithm that sorts 

by grouping elements according to successive parts of 

their keys. A simple example is sorting a list of numbers in 

the range 0–999. First the list is sorted by the hundreds 

digit into a set of (up to) 10 lists; then each list, one at a 

time, is sorted into a set of (up to) 10 lists based on the 

tens digit; and finally each of those lists is sorted by the 

ones digit. This algorithm is usually most efficient when 

the sorting is done using binary values, which simplifies 

comparisons (is a given bit on or off?) and reduces the 

number of lists (each pass produces at most two lists). 

RADSL n. Acronym for rate-adaptive asymmetric digital 

subscriber line. A flexible, high-speed version of ADSL

ag RAM compression 

(asymmetric digital subscriber line) that is capable of 

adjusting transmission speed (bandwidth) based on signal 

quality and length of the transmission line. As the signal 

quality improves or deteriorates while a transmission line 

is being used, the transmission speed is adjusted accordingly. 

See also ADSL, xDSL. 

rag n. Irregularity along the left or right edge of a set of 

lines of text on a printed page. Rag complements justification, 

in which one or both edges of the text form a straight 

vertical line. See the illustration. See also justify, ragged 

left, ragged right. 

Ragged right Justified Ragged left 

F0Rgn02.EPS 

Rag. 

ragged left adj. Of, relating to, or being lines of text 

whose left ends are not vertically aligned but form an 

irregular edge. Text may be right-justified and have a 

ragged left margin. Ragged-left text is used infrequently— 

typically, for visual effect in advertisements. See also rag, 

right-justify. 

ragged right adj. Of, relating to, or being lines of text 

whose right ends are not vertically aligned but form an 

irregular edge. Letters and other word-processed documents 

are commonly left-justified, with ragged-right margins. 

See also left-justify, rag. 

RAID n. Acronym for redundant array of independent (or 

inexpensive) disks. A data storage method in which data is 

distributed across a group of computer disk drives that 

function as a single storage unit. All the information 

stored on each of the disks is duplicated on other disks in 

the array. This redundancy ensures that no information 

will be lost if one of the disks fails. RAID is generally 

used on network servers where data accessibility is critical 

and fault tolerance is required. There are various defined 

levels of RAID, each offering differing trade-offs among 

access speed, reliability, and cost. See also disk controller, 

error-correction coding, Hamming code, hard disk, parity 

bit, server (definition 1). 

RAID array n. See RAID. 

437 

RAM n. Acronym for random access memory. Semiconductor-based 

memory that can be read and written by the 

central processing unit (CPU) or other hardware devices. 

The storage locations can be accessed in any order. Note 

that the various types of ROM memory are capable of random 

access but cannot be written to. The term RAM, however, 

is generally understood to refer to volatile memory 

that can be written to as well as read. Compare core, 

EPROM, flash memory, PROM, ROM (definition 2). 

RAMAC n. 1. Acronym for Random Access Method of 

Accounting Control. Developed by an IBM team led by 

Reynold B. Johnson, RAMAC was the first computer disk 

drive. It was introduced in 1956. The original RAMAC 

consisted of a stack of 50 24-inch platters, with a storage 

capacity of 5 megabytes and an average access time of 1 

second. 2. A high-speed, high-capacity disk storage system 

introduced by IBM in 1994. Based on the original 

RAMAC storage device, it was designed to fulfill enterprise 

requirements for efficient and fault-tolerant storage. 

Rambus DRAM n. See RDRAM. 

Rambus dynamic random access memory n. See 

RDRAM. 

RAM cache n. Short for random access memory cache. 

Cache memory that is used by the system to store and 

retrieve data from the RAM. Frequently accessed segments 

of data may be stored in the cache for quicker 

access compared with secondary storage devices such as 

disks. See also cache, RAM. 

RAM card n. Short for random access memory card. An 

add-in circuit board containing RAM memory and the 

interface logic necessary to decode memory addresses. 

RAM cartridge n. See memory cartridge. 

RAM chip n. Short for random access memory chip. A 

semiconductor storage device. RAM chips can be either 

dynamic or static memory. See also dynamic RAM, RAM, 

static RAM. 

RAM compression n. Short for random access memory 

compression. This technology was an attempt by a number 

of software vendors to solve the problem of running out of 

global memory under Windows 3.x. Compression of the 

usual contents of RAM may lessen the system’s need to 

read or write to virtual (hard disk–based) memory and thus 

speed up the system, as virtual memory is much slower than 

physical RAM. Because of the falling prices of RAM and 

the introduction of operating systems that handle RAM 

R

R 

RAMDAC raster display 

more efficiently, such as Windows 9x, Windows NT, and 

OS/2, RAM compression is generally used only on older 

PCs. See also compression, RAM, Windows. 

RAMDAC n. Acronym for random access memory digital-to-analog 

converter. A chip built into some VGA and 

SVGA video adapters that translates the digital representation 

of a pixel into the analog information needed by the 

monitor to display it. The presence of a RAMDAC chip 

generally enhances overall video performance. See also 

SVGA, VGA. 

RAM disk n. Short for random access memory disk. A 

simulated disk drive whose data is actually stored in RAM 

memory. A special program allows the operating system 

to read from and write to the simulated device as if it were 

a disk drive. RAM disks are extremely fast, but they 

require that system memory be given up for their use. 

Also, RAM disks usually use volatile memory, so the data 

stored on them disappears when power is turned off. Many 

portables offer RAM disks that use battery-backed CMOS 

RAM to avoid this problem. See also CMOS RAM. Compare 

disk cache. 

RAM refresh n. See refresh (definition 2). 

RAM resident adj. See memory-resident. 

RAM-resident program n. See terminate-and-stayresident 

program. 

random adj. Specifically, a reference to an arbitrary or 

unpredictable situation or event. The term is also given an 

extended, pejorative or semi-pejorative meaning, however, 

in which it is used in the sense of nonspecific, incoherent, 

poorly organized, loser, and so on. 

random access n. The ability of a computer to find and 

go directly to a particular storage location without having 

to search sequentially from the beginning location. The 

human equivalent of random access would be the ability to 

find a desired address in an address book without having 

to proceed sequentially through all the addresses. A computer’s 

semiconductor memory (both RAM and ROM) 

provides random access. Certain types of files stored on 

disk under some operating systems also allow random 

access. Such files are best used for data in which each 

record has no intrinsic relationship to what comes physically 

before or after it, as in a client list or an inventory. 

Also called: direct access. See also RAM, ROM (definition 

2). Compare indexed sequential access method, 

sequential access. 

438 

random access memory n. See RAM. 

random noise n. A signal in which there is no relationship 

between amplitude and time and in which many frequencies 

occur randomly, without pattern or predictability. 

random number generation n. Production of an unpredictable 

sequence of numbers in which no number is any 

more likely to occur at a given time or place in the 

sequence than any other. Truly random number generation 

is generally viewed as impossible. The process used in 

computers would be more properly called “pseudorandom 

number generation.” 

range n. 1. A block of cells selected for similar treatment 

in a spreadsheet. A range of cells can extend across a row, 

down a column, or over a combination of the two, but all 

cells in the range must be contiguous, sharing at least one 

common border. Ranges allow the user to affect many 

cells with a single command—for example, to format 

them similarly, enter the same data into all of them, give 

them a name in common and treat them as a unit, or select 

and incorporate them into a formula. 2. In more general 

usage, the spread between specified low and high values. 

Range checking is an important method of validating data 

entered into an application. 

range check n. In programming, a limit check of both 

the upper and lower limits of a value, thus determining 

whether the value lies within an acceptable range. See also 

limit check. 

RAPI n. See Remote Application Programming Interface. 

RARP n. Acronym for Reverse Address Resolution Protocol. 

A TCP/IP protocol for determining the IP address 

(or logical address) of a node on a local area network connected 

to the Internet, when only the hardware address (or 

physical address) is known. While RARP refers only to 

finding the IP address and ARP technically refers to the 

opposite procedure, ARP is commonly used for both 

senses. See also ARP. 

RAS n. 1. See remote access server, Remote Access Service. 

2. Acronym for reliability, availability, serviceability. 

See high availability. 

raster n. A rectangular pattern of lines; on a video display, 

the horizontal scan lines from which the term raster 

scan is derived. 

raster display n. A video monitor (typically a CRT) that 

displays an image on the screen as a series of horizontal

aster fonts RDRAM 

scan lines from top to bottom. Each scan line consists of 

pixels that can be illuminated and colored individually. 

Television screens and most computer monitors are raster 

displays. See also CRT, pixel. Compare vector display. 

raster fonts n. Fonts that are stored as bitmaps. Raster 

fonts are designed with a specific size and resolution for a 

specific printer and cannot be scaled or rotated. If a printer 

does not support raster fonts, it will not print them. The 

five raster fonts are Courier, MS Sans Serif, MS Serif, 

Small, and Symbol. Also called: bitmapped fonts. See also 

font, printer. 

raster graphics n. A method of generating graphics that 

treats an image as a collection of small, independently 

controlled dots (pixels) arranged in rows and columns. 

Compare vector graphics. 

raster image n. A display image formed by patterns of 

light and dark or differently colored pixels in a rectangular 

array. See also raster graphics. 

raster image processor n. A device, consisting of hardware 

and software, that converts vector graphics or text 

into a raster (bitmapped) image. Raster image processors 

are used in page printers, phototypesetters, and electrostatic 

plotters. They compute the brightness and color 

value of each pixel on the page so that the resulting pattern 

of pixels re-creates the vector graphics and text originally 

described. Acronym: RIP. 

rasterization n. The conversion of vector graphics 

(images described in terms of mathematical elements, 

such as points and lines) to equivalent images composed 

of pixel patterns that can be stored and manipulated as sets 

of bits. See also pixel. 

raster-scan display n. See raster display. 

rate-adaptive asymmetric digital subscriber line n. 

See RADSL. 

raw data n. 1. Unprocessed, typically unformatted, data, 

such as a stream of bits that has not been filtered for commands 

or special characters. See also raw mode. Compare 

cooked mode. 2. Information that has been collected but 

not evaluated. 

raw infrared n. A method of receiving data through an 

infrared (IR) transceiver. Raw infrared treats the IR transceiver 

like a serial cable and does not process data in any 

way. The application is responsible for handling collision 

detection and other potential problems. 

439 

raw mode n. A way in which the UNIX and MS-DOS 

operating systems “see” a character-based device. If the 

identifier for the device indicates raw mode, the operating 

system does not filter input characters or give special 

treatment to carriage returns, end-of-file markers, and 

linefeed and tab characters. Compare cooked mode. 

ray tracing n. A sophisticated and complex method of producing 

high-quality computer graphics. Ray tracing calculates 

the color and intensity of each pixel in an image by 

tracing single rays of light backward and determining how 

they were affected on their way from a defined source of 

light illuminating the objects in the image. Ray tracing is 

demanding in terms of processing capability because the 

computer must account for reflection, refraction, and absorption 

of individual rays, as well as for the brightness, transparency 

level, and reflectivity of each object and the positions 

of the viewer and the light source. Compare radiosity. 

RCA connector n. A connector used for attaching audio 

and video devices, such as stereo equipment or a composite 

video monitor, to a computer’s video adapter. See the 

illustration. See also composite video display. Compare 

phono connector. 

F0Rgn03.EPS 

RCA connector. A female version (left) and a male version 

(right). 

RDBMS n. Acronym for relational data base management 

system. See relational database. 

RDF n. See Resource Description Framework. 

RDO n. See Remote Data Objects. 

RDRAM n. Acronym for Rambus dynamic random 

access memory. A type of DRAM designed by Rambus, 

Inc. In its fastest form, known as Direct RDRAM, this 

technology provides a 16-bit data path and a peak bandwidth 

of 1.6 GB per second (approximately eight to ten 

times faster than synchronous DRAM, or SDRAM). 

RDRAM has been used in graphics and video chips; 

Direct RDRAM is expected to replace DRAM and 

SDRAM in personal computers. Also called: Rambus 

DRAM. See also dynamic RAM, SDRAM. 

R

R 

read1 read 

real mode 

read1 n. The action of transferring data from an input 

source into a computer’s memory or from memory into the 

CPU (central processing unit). Compare write1 . 

read2 vb. To transfer data from an external source, such as 

from a disk or the keyboard, into memory or from memory 

into the central processing unit (CPU). Compare write2 . 

read-after-write n. A feature of certain data storage 

devices, such as tape drives, in which the device reads data 

immediately after it is written as a means of verifying data 

integrity. 

reader n. See card reader. 

Reader n. See Microsoft Reader. 

read error n. An error encountered while a computer is in 

the process of obtaining information from storage or from 

another source of input. Compare write error. 

README n. A file containing information that the user 

either needs or will find informative and that might not 

have been included in the documentation. README files 

are placed on disk in plain-text form (without extraneous 

or program-specific characters) so that they can be read 

easily by a variety of word processing programs. 

read notification n. An e-mail feature providing feedback 

to the sender that a message has been read by the 

recipient. 

read-only adj. Capable of being retrieved (read) but not 

changed (written). A read-only file or document can be 

displayed or printed but not altered in any way. Read-only 

memory (ROM) holds programs that cannot be changed; a 

read-only storage medium, such as CD-ROM, can be 

played back but cannot be used for recording information. 

Compare read/write. 

read-only attribute n. A file attribute, stored with a file’s 

directory entry, indicating whether or not a file may be 

changed or erased. When the read-only attribute is off, the 

file can be modified or deleted; when it is on, the file can 

only be displayed. 

read-only memory n. See ROM. 

read-only terminal n. See RO terminal. 

read/write adj. Able to be both read from and written to. 

Abbreviation: R/W. Compare read-only. 

440 

read/write channel n. See input/output channel. 

read/write head n. See head. 

read/write memory n. Memory that can be both read 

from and written to (modified). Semiconductor RAM and 

core memory are typical read/write memory systems. 

Compare ROM (definition 2). 

real address n. An absolute (machine) address specifying 

a physical location in memory. See also physical 

address. Compare relative address, virtual address. 

RealAudio n. Streaming audio technology developed by 

RealNetworks, Inc., for distributing radio and FM-quality 

sound files over the Internet in real time. RealAudio is 

based on two components: client software for decompressing 

the sound on the fly and server software for delivering 

it. The client software is free, distributed either as a downloadable 

program or as part of browser software. See also 

RealPlayer, RealVideo, stream, streaming. 

reallocate n. A function in C that allows the programmer 

to request a larger portion of heap memory than was previously 

assigned to a particular pointer. See also dynamic 

memory allocation, heap (definition 1). 

reallysafe palette n. A color look-up table (CLUT) consisting 

of 22 colors from the 216-color websafe palette 

that are completely consistent when viewed with all Web 

browsers on all major computer platforms. The reallysafe 

palette arose from an experiment that indicated that most 

of the colors of the websafe palette shift to some degree in 

different viewing environments. See also browser CLUT, 

websafe palette. 

real mode n. An operating mode in the Intel 80x86 family 

of microprocessors. In real mode, the processor can 

execute only one program at a time. It can access no more 

than about 1 MB of memory, but it can freely access system 

memory and input/output devices. Real mode is the 

only mode possible in the 8086 processor and is the only 

operating mode supported by MS-DOS. In contrast, the 

protected mode offered in the 80286 and higher microprocessors 

provides the memory management and memory 

protection needed for multitasking environments such as 

Windows. See also 8086, privileged mode. Compare protected 

mode, virtual real mode.

eal-mode mapper real-time conferencing 

real-mode mapper n. An enhancement for Windows 3.x 

systems that allows 32-bit file system access. The realmode 

mapper provides a 32-bit disk access interface to the 

DOS device driver chain. Acronym: RMM. 

real number n. 1. A number that can be represented in a 

number system with a given base, such as the decimal system, 

by a finite or infinite sequence of digits and a radix 

point. For example, 1.1 is a real number, as is 0.33333.... 

See also irrational number. Compare complex number, 

imaginary number. 2. A data type, in a programming language 

such as Pascal, that is used for storing, to some limit 

of precision, values that include both integer and fractional 

parts. See also double-precision, single-precision. 

Compare floating-point number, integer. 

RealPlayer n. An Internet media player and browser 

plug-in developed by RealNetworks, Inc., that supports 

playback of RealAudio and RealVideo, as well as certain 

other formats, after installation of appropriate plug-ins. 

The current version allows RealPlayer users to surf for 

media content directly from the player or through a Web 

browser. See also RealAudio, RealVideo. 

Real Soon Now adv. Soon, but not really expected to be 

as soon as claimed. One might say, for example, that a 

commercial program will have some desired feature Real 

Soon Now if several versions ago the vendor knew of the 

need for the feature and has done nothing. Acronym: RSN. 

real storage n. The amount of RAM memory in a 

system, as distinguished from virtual memory. Also 

called: physical memory, physical storage. See also virtual 

memory. 

RealSystem G2 n. An open, standards-based platform 

for delivery of streaming audio and video over the Internet 

and other TCP/IP networks developed by RealNetworks, 

Inc. RealSystem G2 was introduced by RealNetworks in 

its audio and video players, servers, and development 

tools in 1998. Among other features, RealSystem G2 

scales to different bandwidths, includes streaming that 

adjusts delivery to available bandwidth, and supports 

SMIL (Synchronized Multimedia Integration Language) 

for multimedia presentations. See also RealPlayer, 

RealVideo, SMIL, streaming. 

441 

RealSystem Producer n. A software application developed 

by RealNetworks that converts most types of video 

and sound files into RealMedia formats for use as streaming 

media over the Internet or within a corporate intranet. 

RealSystem Server n. Software developed by RealNetworks 

to enable a server to broadcast streaming media. 

Several versions of RealSystem Server are available, 

designed to meet needs ranging from small intranet servers 

to large proxy servers. 

real-time adj. Of, or relating to, a time frame imposed by 

external constraints. Real-time operations are those in 

which the machine’s activities match the human perception 

of time or those in which computer operations proceed 

at the same rate as a physical or external process. 

Real-time operations are characteristic of aircraft guidance 

systems, transaction-processing systems, scientific 

applications, and other areas in which a computer must 

respond to situations as they occur (for example, animating 

a graphic in a flight simulator or making corrections 

based on measurements). 

real-time animation n. Computer animation in which 

images are computed and updated on the screen at the 

same rate at which the objects simulated might move in 

the real world. Real-time animation allows dynamic 

involvement by the user because the computer can accept 

and incorporate keystrokes or controller movements as it 

is drawing the next image in the animation sequence. 

Arcade-style animation (such as in a flight simulator program) 

makes use of real-time animation in translating 

game plays into on-screen actions. In contrast, in animation 

done in virtual time, image frames are first calculated 

and stored and later replayed at a higher rate to achieve 

smoother movement. See also animation, bit block. 

real-time clock n. In PCs, a circuit or other hardware element 

that provides the system with real-world time. Upon 

startup of the system, the real-time clock puts the date and 

time in memory, where it can then be systematically incremented 

by the BIOS. A real-time clock generally has a 

battery that is separate from the rest of the system, so it’s 

not dependent upon the system’s power source. This is not 

the same thing as a system clock, which synchronizes the 

processor. Acronym: RTC. See also clock (definition 2). 

real-time conferencing n. See teleconferencing. 

R

R 

Real-Time Control Protocol record1 record 

Real-Time Control Protocol n. A scalable transport control 

protocol that works with the Real-Time Protocol 

(RTP) to monitor real-time transmissions to multiple participants 

over a network—for example, during videoconferencing. 

The Real-Time Control Protocol, or RTCP, 

transmits packets of control information at regular intervals 

and is used to determine how well information is 

being delivered to recipients. Acronym: RTCP. See also 

Real-Time Protocol, Real-Time Streaming Protocol, 

Resource Reservation Setup Protocol. 

real-time operating system n. An operating system 

designed for the needs of a process-controlled environment. 

A real-time operating system recognizes that 

responses must be made and tasks handled instantly, with 

no lag time. Real-time operating systems are typically 

used as embedded systems in devices and applications 

requiring time-critical reaction, such as telecommunications, 

air traffic control, and robotic functions. Acronym: 

RTOS. See also real-time system. 

Real-Time Protocol n. An Internet-standard network 

transport protocol used in delivering real-time data, including 

audio and video. The Real-Time Protocol, or RTP, 

works with both unicast (single sender, single recipient) and 

multicast (single sender, multiple recipients) services. RTP 

is often used in conjunction with the Real-Time Control 

Protocol (RTCP), which monitors delivery. Acronym: RTP. 

See also Real-Time Control Protocol, Real-Time Streaming 

Protocol, stream. 

real-time streaming n. The process of delivering a 

streaming media file via a specialized streaming media 

server using real-time streaming protocol (RTSP). With 

real-time streaming, the file itself actually plays on the 

streaming media server, even though it is viewed on the 

computer that opened the file. Real-time streaming transmits 

at a higher bandwidth than HTTP streaming. It is 

often used to broadcast live events, such as concerts or 

keynote conference addresses. See also HTTP streaming. 

Real-Time Streaming Protocol n. A control protocol 

for the delivery of streamed multimedia data over Internet 

Protocol (IP) networks. The Real-Time Streaming Protocol, 

or RTSP, was developed by Columbia University, Progressive 

Networks, and Netscape and has been submitted 

as a proposed standard to the IETF (Internet Engineering 

Task Force). RTSP is designed to deliver real-time, live, or 

stored audio and video efficiently over a network. It can be 

used either for groups of recipients or for on-demand 

442 

delivery to a single recipient. Acronym: RTSP. See also 

Advanced Streaming Format, Real-Time Protocol, 

Resource Reservation Setup Protocol, stream. 

real-time system n. A computer and/or a software system 

that reacts to events before the events become obsolete. 

For example, airline collision avoidance systems 

must process radar input, detect a possible collision, and 

warn air traffic controllers or pilots while they still have 

time to react. 

RealVideo n. The streaming technology developed by 

RealNetworks, Inc., for distributing video over intranets 

and the Internet. RealVideo transmits video from a server 

in encoded (compressed) form. The video and accompanying 

sound are viewed on the client end with the help of a 

software player. RealVideo works with both IP and IP 

multicasting and, as with RealAudio, does not require 

transmission of complete files before playback can begin. 

See also RealAudio, RealPlayer, streaming. 

reboot vb. To restart a computer by reloading the operating 

system. See also boot2 , cold boot, warm boot. 

receipt notification n. An e-mail feature providing feedback 

to the sender that a message has been received by the 

recipient. 

receive vb. To accept data from an external communications 

system, such as a local area network (LAN) or a telephone 

line, and store the data as a file. 

Receive Data n. See RXD. 

rec. newsgroups n. Usenet newsgroups that are part of the 

rec. hierarchy and whose names have the prefix rec. These 

newsgroups cover topics devoted to discussions of recreational 

activities, hobbies, and the arts. See also newsgroup, traditional 

newsgroup hierarchy, Usenet. Compare comp. newsgroups, 

misc. newsgroups, news. newsgroups, sci. newsgroups, soc. 

newsgroups, talk. newsgroups. 

recompile vb. To compile a program again, usually 

because of changes that needed to be made in the source 

code in response to error messages generated by the compiler. 

See also compile. 

record1 n. A data structure that is a collection of fields 

(elements), each with its own name and type. Unlike an 

array, whose elements all represent the same type of information 

and are accessed using an index, the elements of a 

record represent different types of information and are 

accessed by name. A record can be accessed as a collective

ecord2 record 

red-green-blue 

unit of elements, or the elements can be accessed individually. 

See also array, data structure, type1 (definition 1). 

record2 vb. To retain information, usually in a file. 

record format n. See record structure. 

record head n. The device in a tape machine that places 

data on the tape. In some tape machines, the record head is 

combined with the read head. 

record layout n. The organization of data fields within a 

record. See also record1 . 

record length n. The amount of storage space required to 

contain a record, typically given in bytes. See also record1 . 

record locking n. A strategy employed in distributed processing 

and other multiuser situations to prevent more 

than one user at a time from writing data to a record. See 

also record1 . 

record number n. A unique number assigned to a record 

in a database in order to identify it. A record number can 

identify an existing record by its position (for example, the 

tenth record from the beginning of a database), or it can be 

assigned to the record to serve as a key (for example, the 

number 00742 assigned to the tenth record from the beginning 

of the database). See also record1 . 

record structure n. An ordered list of the fields that 

compose a record, together with a definition of the domain 

(acceptable values) of each field. See also record1 . 

recover vb. 1. To return to a stable condition after some 

error has occurred. A program recovers from an error by 

stabilizing itself and resuming execution of instructions 

without user intervention. 2. To put back into a stable condition. 

A computer user may be able to recover lost or 

damaged data by using a program to search for and salvage 

whatever information remains in storage. A database 

may be recovered by restoring its integrity after some 

problem has damaged it, such as abnormal termination of 

the database management program. 

recoverable error n. An error that can be successfully 

managed by software. For example, when the user enters a 

number when a letter is required, the program can simply 

display an error message and prompt the user again. 

recovery n. The restoration of lost data or the reconciliation 

of conflicting or erroneous data after a system failure. 

Recovery is often achieved using a disk or tape backup 

and system logs. See also backup. 

443 

Recreational Software Advisory Council n. An independent, 

nonprofit organization established in the fall of 

1994 by a group of six trade organizations, led by the Software 

Publishers Association. The Council’s goal was to 

create a new, objective content-labeling rating system for 

recreational software and other media such as the Internet. 

Acronym: RSAC. 

rectangle ad n. An Internet ad format that is larger than a 

traditional banner ad and is generally inserted directly into 

page content for greater visibility. 

rectifier n. A circuit component that passes current flowing 

in one direction but stops current flowing in the other 

direction. Rectifiers are used to convert alternating current 

to direct current. 

recto n. The right-hand page of two facing pages. A recto 

is characteristically an odd-numbered page. Compare verso. 

recursion n. The ability of a routine to call itself. Recursion 

enables certain algorithms to be implemented with 

small, simple routines, but it does not guarantee speed or 

efficiency. Erroneous use of recursion can cause a program 

to run out of stack space during execution, causing 

the program, and sometimes the entire system, to crash. 

See also call1 (definition 2), routine. 

Recycle Bin n. A folder in Windows 9x, Windows CE, 

Windows NT, Windows 2000, and Windows XP represented 

by an icon on the screen resembling a basket decorated 

with the recycling logo. To remove a file, the user 

drags its icon to the Recycle Bin. However, a file in the 

Recycle Bin is not actually deleted from the disk until the 

user opens the Recycle Bin, selects the file, and presses 

the Delete key; until then, the user can retrieve it. Compare 

Trash. 

Red Book n. 1. The standards documents of the U.S. 

National Security Agency entitled “Trusted Network 

Interpretation of the Trusted Computer System Evaluation 

Criteria (NCSC-TG-005)” and “Trusted Network 

Interpretation (NCS-TG-011).” These documents define a 

system of ratings from A1 (most secure) to D (nonsecure), 

indicating the ability of a computer network to protect 

sensitive information. Compare Orange Book 

(definition 1). 2. A specifications book written by the 

Sony Corporation and Philips Corporation and endorsed 

by ISO, covering audio compact discs. Compare Green 

Book, Orange Book (definition 2). 3. Telecommunications 

standards published by the CCITT. 

red-green-blue n. See RGB. 

R

R 

redirection reformat 

redirection n. The process of writing to or reading from a 

file or device different from the one that would normally 

be the target or the source. For example, the MS-DOS or 

OS/2 command dir >prn redirects a directory listing from 

the screen to the printer. Compare pipe. 

redirector n. Software on a client computer that intercepts 

requests for information and, when appropriate, 

directs them to the network. Redirectors can either be built 

into the client operating system or be part of an added networking 

package. 

redlining n. A feature of a word processing application 

that marks changes, additions, or deletions made to a document 

by a coauthor or editor. The purpose of redlining is 

to produce a record of the changes made to a document 

during the course of its development. 

redraw n. See refresh (definition 1). 

reduce vb. In a graphical user interface, to decrease the 

size of a window. A user can reduce a window either by 

clicking the appropriate button in the title bar or by clicking 

the mouse on the border of the window and dragging 

the border toward the middle of the window. See also 

maximize, minimize. 

Reduced Instruction Set Computing n. See RISC. 

redundancy n. Using one or more servers on a Web site 

to perform identical tasks. If one of the servers crashes, 

another server assumes its tasks. Redundancy ensures that 

the Web site will continue to function if one of the servers 

stops working. 

redundancy check n. See CRC, LRC. 

redundant code n. Code that duplicates a function performed 

elsewhere—for example, code to sort a list that 

has already been sorted. 

reengineer vb. To rethink and redefine processes and procedures. 

In the context of computer systems, to reengineer 

means to change the way work is done in order to maximize 

the benefits of new technology. 

reengineering vb. 1. With regard to software, changing 

existing software to strengthen desirable characteristics and 

remove weaknesses. 2. With regard to corporate management, 

using information technology principles to address 

the challenges posed by a global economy and to consolidate 

management of a rapidly expanding work force. 

reentrant code n. Code written so that it can be shared 

by several programs at the same time. When a program is 

executing reentrant code, another program can interrupt 

444 

the execution and can then start or continue execution of 

that same code. Many operating-system routines are written 

to be reentrant so that only one copy needs to reside in 

memory to serve all executing applications. See also relocatable 

code. 

refactoring n. An optimization process in object-oriented 

programming intended to improve the design or structure 

of a program without changing its functionality. The goal 

of refactoring is to make the program clearer and easier to 

work with—in part by removing duplication, abstracting 

common behaviors, and refining class hierarchies—and to 

improve the extensibility and reusability of existing code. 

reference1 n. A data type in the C++ programming language. 

A reference must be initialized with a variable 

name. The reference then becomes an alias for that variable 

but actually stores the address of the variable. 

reference2 vb. To access a variable, such as an element in 

an array or a field in a record. 

reference parameter n. A parameter in which the 

address of a variable, rather than the explicit value, is 

passed to the called routine. See also parameter. 

reference type n. A data type that is represented by a reference 

(similar to a pointer) to the type’s actual value. If a 

reference type is assigned to a variable, that variable references 

(or “points to”) the original value. No copy is made. 

Reference types comprise classes, interfaces, delegates, 

and boxed value types. See also data type, value type. 

reflecting software n. See reflector. 

reflective liquid-crystal display n. A liquid crystal display 

that is not equipped with edge light or backlight to 

enhance readability but rather depends on reflecting ambient 

light, making it difficult to read in brightly lit environments 

such as the outdoors. Also called: reflective LCD. 

reflective routing n. In wide area networks, the process 

of using a reflector to distribute data, thereby reducing the 

load of the network server. See also reflector. 

reflector n. A program that sends messages to a number 

of users upon receipt of a signal from a single user. A 

common type of reflector is an e-mail reflector, which forwards 

any e-mail sent to it to the multiple recipients currently 

on its list. See also multiple recipients. Compare 

mail reflector. 

reformat vb. 1. In applications, to change the look of a 

document by altering stylistic details, such as font, layout, 

indention, and alignment. 2. In data storage, to prepare for

efresh registry 

reuse a disk that already contains programs or data, effectively 

destroying the existing contents. 

refresh vb. 1. To retrace a video screen at frequent intervals, 

even if the image does not change, so as to keep the 

phosphors irradiated. 2. To recharge dynamic random 

access memory chips (DRAMs) so that they continue to 

retain the information stored in them. Circuitry on the 

memory board automatically performs this function. See 

also refresh cycle. 

refreshable adj. In programming, referring to a program 

module capable of being replaced in memory without 

affecting processing of the program or the information 

being used by the program. 

refresh cycle n. The process in which controller circuitry 

provides repeated electric pulses to dynamic random access 

memory chips in order to renew the stored electric charges 

in those locations that contain binary 1. Each pulse is one 

refresh cycle. Without constant refreshing, dynamic semiconductor 

RAM loses any information stored in it—as it 

does when the computer is turned off or when the power 

fails. See also dynamic RAM, static RAM. 

refresh rate n. In reference to video hardware, the frequency 

with which the entire screen is redrawn to maintain 

a constant, flicker-free image. On TV screens and 

raster-scan monitors, the electron beam that lights the 

phosphor coating on the inner surface of the screen typically 

refreshes the entire image area at a rate of about 60 

hertz, or 60 times per second. Interlaced monitors, which 

redraw alternate lines during each sweep of the electron 

beam, actually refresh any particular line only 30 times 

per second. Because odd and even lines are refreshed on 

successive sweeps, however, the effective refresh rate is 60 

times per second. See also refresh (definition 1). 

REGEDIT n. See Registry Editor. 

regenerate vb. See rewrite. 

regeneration buffer n. See video buffer. 

regenerator n. See repeater. 

region n. 1. An area dedicated to or reserved for a particular 

purpose. 2. In video programming, a contiguous group 

of pixels that are treated as a unit. On the Apple Macintosh, 

for example, a region is an area in a grafPort that can 

be defined and manipulated as an entity. The visible working 

area within a window is an example of a region. See 

also grafPort. 

445 

region code n. Codes on DVD movie titles and DVD- 

ROM drives that prevent playback of certain DVDs in certain 

geographical regions. Region codes are part of the 

DVD specification. See also CSS, DeCSS. 

region fill n. In computer graphics, the technique of filling 

a defined region on the screen with a selected color, 

pattern, or other attribute. See also region (definition 2). 

register n. A set of bits of high-speed memory within a 

microprocessor or other electronic device, used to hold 

data for a particular purpose. Each register in a central 

processing unit is referred to in assembly language programs 

by a name such as AX (the register that contains the 

results of arithmetic operations in an Intel 80x86 processor) 

or SP (the register that contains the memory address 

of the top of the stack in various processors). 

registered file type n. File types that are tracked by the 

system registry and are recognized by the programs you 

have installed on your computer. See also file type. 

registration n. The process of precisely aligning elements 

or superimposing layers in a document or a graphic 

so that everything will print in the correct relative position. 

See also registration marks. 

registration marks n. Marks placed on a page so that in 

printing, the elements or layers in a document can be 

arranged correctly with respect to each other. Each element 

to be assembled contains its own registration marks; 

when the marks are precisely superimposed, the elements 

are in the correct position. See the illustration. 

F0Rgn04.EPS 

Registration marks. 

registry n. A central hierarchical database in Windows 

9x, Windows CE, Windows NT, and Windows 2000 used 

to store information necessary to configure the system for 

one or more users, applications, and hardware devices. 

The Registry contains information that Windows continually 

references during operation, such as profiles for each 

user, the applications installed on the computer and the 

types of documents each can create, property sheet settings 

for folders and application icons, what hardware 

exists on the system, and which ports are being used. The 

Registry replaces most of the text-based .ini files used in 

Windows 3. x and MS-DOS configuration files, such as 

AUTOEXEC.BAT and CONFIG.SYS. Although the Registry 

is common to the several Windows platforms, there 

R

R 

Registry Editor relative address 

are some differences among them. Also called: system 

registry. See also hierarchical database, .ini, input/output 

port, property sheet, Registry Editor. 

Registry Editor n. An application under Windows that 

allows the user to edit the entries in the registry. Acronym: 

REGEDIT. See also registry. 

regression analysis n. In statistics, an analysis of the 

degree to which variations in an independent variable affect 

a dependent variable (a variable whose value depends on 

the value of another variable). See also multiple regression. 

regression testing n. Complete retesting of a modified 

program, rather than a test of only the modified routines, 

to ensure that no errors have been introduced with the 

modifications. 

relation n. A structure composed of attributes (individual 

characteristics, such as name or address, corresponding to 

the columns in a table) and tuples (sets of attribute values 

describing particular entities, such as customers, corresponding 

to the rows in a table). Within a relation, tuples 

cannot be repeated; each must be unique. Further, tuples are 

unordered within a relation; interchanging two tuples does 

not change the relation. Finally, if relational theory is to be 

applicable, the domain of each attribute must be atomic— 

that is, a simple value, rather than a structure such as an 

array or a record. A relation in which the domains of all 

attributes are atomic is said to be normalized or in first normal 

form. See also normal form (definition 1). 

relational algebra n. A collection of rules and operators 

that permits relations (tables) to be manipulated. Relational 

algebra is usually described as having the following 

operators: SELECT, PROJECT, PRODUCT, UNION, 

INTERSECT, DIFFERENCE, JOIN (or INNER JOIN), 

and DIVIDE. In a relational database, relational algebra is 

used to develop procedures to build new relations based on 

the existing relations. 

relational calculus n. In database management, a nonprocedural 

method for manipulating relations (tables). 

There are two families of relational calculus: domain calculus 

and tuple calculus. The two families of relational 

calculus are mathematically equivalent to each other and 

to relational algebra. Using either family, one can formulate 

a description of a desired relation, based on the existing 

relations in the database. 

446 

relational database n. A database or database management 

system that stores information in tables—rows and 

columns of data—and conducts searches by using data in 

specified columns of one table to find additional data in 

another table. In a relational database, the rows of a table 

represent records (collections of information about separate 

items) and the columns represent fields (particular 

attributes of a record). In conducting searches, a relational 

database matches information from a field in one table 

with information in a corresponding field of another table 

to produce a third table that combines requested data from 

both tables. For example, if one table contains the fields 

EMPLOYEE-ID, LAST-NAME, FIRST-NAME, and 

HIRE-DATE, and another contains the fields DEPT, 

EMPLOYEE-ID, and SALARY, a relational database can 

match the EMPLOYEE-ID fields in the two tables to find 

such information as the names of all employees earning a 

certain salary or the departments of all employees hired 

after a certain date. In other words, a relational database 

uses matching values in two tables to relate information in 

one to information in the other. Microcomputer database 

products typically are relational databases. Compare flatfile 

database, inverted-list database. 

relational database management system n. See relational 

database. 

relational expression n. An expression that uses a relational 

operator such as “less than” or “greater than” to 

compare two or more expressions. A relational expression 

resolves to a Boolean (true/false) value. See also Boolean, 

relational operator. 

relational model n. A data model in which the data is 

organized in relations (tables). This is the model implemented 

in most modern database management systems. 

relational operator n. An operator that allows the programmer 

to compare two (or more) values or expressions. 

Typical relational operators are greater than (>), equal to 

(=), less than (=), and less than or equal to (

elative coordinates reliability 

address is typically computed by adding an offset to the 

base. In everyday terms, this is similar to creating the 

address 2001 Main Street, in which the base is the 2000 

block of Main Street and the offset is 1, which specifies 

the first house from the beginning of the block. Also 

called: indirect address. 

relative coordinates n. Coordinates that are defined in 

terms of their distance from a given starting point, rather 

than from the origin (intersection of two axes). For example, 

from a starting point on the screen, a square defined 

by relative coordinates can be drawn as a series of lines, 

each representing a displacement in distance and direction 

from the end of the preceding point. The entire square can 

be redrawn at another location simply by changing the 

coordinates of the starting point rather than by recalculating 

the coordinates of each corner with reference to the 

origin. See the illustration. Compare absolute coordinates. 

x-axis 

Origin 

F0Rxx05.eps 

Relative coordinates. 

y-axis 

Point at relative 

coordinate (2,3) 

from the point 

below 

Reference point 

relative movement n. 1. Motion whose distance and 

direction are relative to a starting point. For example, 

when a mouse pointer is moved on the screen, the coordinates 

of its new position are relative to the previous location 

of the pointer. See also relative coordinates, relative 

pointing device. 2. In computer graphics and cinematography, 

the movement of one object in relation to another, 

such as the movement of horse A from the perspective of 

horse B on a racetrack. 

relative path n. A path that is implied by the current 

working directory. When a user enters a command that 

refers to a file, if the full pathname is not entered the current 

working directory becomes the relative path of the file 

referred to. Compare full path. 

relative pointing device n. A cursor-control device, such 

as a mouse or a trackball, in which the movement of an onscreen 

cursor is linked to the movement of the device but 

not to the position of the device. For example, if a user picks 

447 

up a mouse and puts it down in a different location on a 

desk, the position of the on-screen cursor does not change 

because no movement (rolling) is detected. When the user 

rolls the mouse again, the cursor moves to reflect the mouse 

movement against the surface of the desk. Relative pointing 

devices differ from absolute pointing devices, such as 

graphics tablets, in which the device’s location within a 

defined area is always associated with a predefined onscreen 

position. See also relative coordinates, relative movement 

(definition 1). Compare absolute pointing device. 

relative URL n. Short for relative uniform resource locator. 

A form of URL in which the domain and some or all 

directory names are omitted, leaving only the document 

name and extension (and perhaps a partial list of directory 

names). The indicated file is found in a location relative to 

the pathname of the current document. Acronym: RELURL. 

See also file extension, URL. 

RELAX NG n. An XML schema language based on Tree 

Regular Expressions for XML (TREX) and Regular Language 

Description for XML (RELAX). RELAX NG supports 

XML namespaces, uses XML syntax, maintains the 

information set of the XML document, and provides unrestricted 

support for mixed or unordered content. 

relay n. A switch activated by an electrical signal. A relay 

allows another signal to be controlled without the need for 

human action to route the other signal to the control point, 

and it also allows a relatively low-power signal to control 

a high-power signal. 

release1 n. 1. A particular version of a piece of software, 

most commonly associated with the most recent version 

(as in “the latest release”). Some companies use the term 

release as an integral part of the product name (as in Lotus 

1-2-3 Release 2.2 ). 2. A version of a product that is available 

in general distribution. Compare alpha2 , beta2 . 

release2 vb. 1. To relinquish control of a block of memory, 

a device, or another system resource to the operating 

system. 2. To formally make a product available to the 

marketplace. 

reliability n. The likelihood of a computer system or device 

continuing to function over a given period of time and under 

specified conditions. Reliability is measured by different 

performance indexes. For example, the reliability of a hard 

disk is often given as mean time between failures (MTBF): 

the average length of time the disk can be expected to function 

without failing. See also MTBF, MTTR. 

R

R 

reliability, availability, serviceability remote login 

reliability, availability, serviceability n. Acronym: RAS. 

See high availability. 

reload vb. 1. To load a program into memory from a storage 

device again in order to run it, because the system has 

crashed or the program’s operation was otherwise interrupted. 

2. To retrieve a new copy of the Web page currently 

visible in a Web browser. 

relocatable address n. In programming, an address that 

is to be adjusted to reflect the actual place in memory into 

which a program is loaded for execution. In “Get the byte 

located 12 bytes from this instruction,” the address is relocatable; 

in “Get the byte located at address 255,” the 

address is not relocatable. This convention is comparable 

to describing the “address” of a parked car as “level 2, row 

G” on one day and “level 5, row B” on another. 

relocatable code n. A program written in such a way 

that it can be loaded into any part of available memory 

rather than having to be placed in one specific location. In 

relocatable code, address references that depend on the 

program’s physical location in memory are calculated at 

run time so that program instructions can be carried out 

correctly. See also reentrant code. 

relocate n. To move programs and blocks of memory 

about within available space so as to use memory 

resources flexibly and efficiently. A relocatable program 

can be loaded by the operating system into any part of 

available memory rather than into only one specific area. 

A relocatable block of memory is a portion of memory 

that can be moved around by the operating system as 

required; for example, the system might collect several 

available, relocatable blocks of memory to form one larger 

block of the size requested for use by a program. 

RELURL n. See relative URL. 

remailer n. A service that will forward e-mail while concealing 

the e-mail address of the originator of the message. 

Remailers may be used by individuals who wish to 

retain their privacy or avoid unsolicited commercial e-mail 

(UCE). Remailers may also be used to hide the identities 

of individuals and businesses sending spam or malicious 

or fraudulent e-mail. 

remark n. See comment, REM statement. 

remote adj. Not in the immediate vicinity, as a computer 

or other device located in another place (room, building, 

448 

or city) and accessible through some type of cable or communications 

link. 

remote access n. The use of a remote computer. 

remote access server n. A host on a LAN (local area 

network) that is equipped with modems to enable users to 

connect to the network over telephone lines. Acronym: RAS. 

Remote Access Service n. Windows software that 

allows a user to gain remote access to the network server 

via a modem. Acronym: RAS. See also remote access. 

remote administration n. The performance of system 

administration–related tasks via access from another 

machine in a network. 

Remote Application Programming Interface n. A 

Remote Procedure Call (RPC) mechanism that enables an 

application running on a desktop computer to make function 

calls on a Windows CE–based device. The desktop 

computer is known as the Remote Application Programming 

Interface (RAPI) client, and the Windows CE device 

is known as the RAPI server. RAPI runs over Winsock and 

TCP/IP. Acronym: RAPI. See also remote procedure call. 

Remote Authentication Dial-In User Service n. See 

RADIUS. 

remote communications n. Interaction with a remote 

computer through a telephone connection or another communications 

line. 

remote computer system n. See remote system. 

Remote Data Objects n. An object-oriented data access 

tool featured in Visual Basic 4 and later. Remote Data 

Objects have no native file format of their own; they can 

be used only with databases complying with the most 

recent ODBC standards. This feature is popular for its 

speed and minimal coding requirements. Acronym: RDO. 

See also ODBC, Visual Basic. 

Remote Installation Services n. Software services that 

allow an administrator to set up new client computers 

remotely, without having to visit each client. The target 

clients must support remote booting. Acronym: RIS. 

remote login n. The action of logging in to a computer at 

a distant location by means of a data communications connection 

with the computer that one is presently using. 

After remote login, the user’s own computer behaves like 

a terminal connected to the remote system. On the Inter-

emote monitoring replace 

net, remote login is done primarily by rlogin and telnet. 

See also rlogin1 (definition 1), telnet1 . 

remote monitoring n. See RMON. 

remote network monitoring n. See RMON. 

Remote PC n. See remote system. 

remote procedure call n. In programming, a call by one 

program to a second program on a remote system. The 

second program generally performs a task and returns the 

results of that task to the first program. Acronym: RPC. 

remote system n. The computer or network that a 

remote user is accessing via a modem. See also remote 

access. Compare remote terminal. 

remote terminal n. A terminal that is located at a site 

removed from the computer to which it is attached. 

Remote terminals rely on modems and telephone lines to 

communicate with the host computer. See also remote 

access. Compare remote system. 

removable disk n. A disk that can be removed from a 

disk drive. Floppy disks are removable; hard disks usually 

are not. Also called: exchangeable disk. 

REM statement n. Short for remark statement. A statement 

in the Basic programming language and the MS- 

DOS and OS/2 batch file languages that is used to add 

comments to a program or batch file. Any statement 

beginning with the word REM is ignored by the interpreter 

or compiler or the command processor. See also comment. 

rename n. A command in most file transfer protocol 

(FTP) clients and in many other systems that allows the 

user to assign a new name to a file or files. 

render vb. To produce a graphic image from a data file on 

an output device such as a video display or printer. 

rendering n. The creation of an image containing geometric 

models, using color and shading to give the image a 

realistic look. Usually part of a geometric modeling package 

such as a CAD program, rendering uses mathematics 

to describe the location of a light source in relation to the 

object and to calculate the way in which the light would 

create highlights, shading, and variations in color. The 

degree of realism can range from opaque, shaded polygons 

to images approximating photographs in their complexity. 

See also ray tracing. 

RenderMan Shading Language n. A C-like graphics 

and rendering language developed by Pixar. 

449 

repaginate vb. To recalculate the page breaks in a document. 

Repeat n. A command in Microsoft Word that causes all 

information contained in either the last command dialog 

box or the last uninterrupted editing session to be 

repeated. 

repeat counter n. A loop counter; typically, a register 

that holds a number representing how many times a repetitive 

process has been or is to be executed. 

Repeat delay n. A delay for the amount of time that 

elapses before a character begins repeating when you hold 

down a key. 

repeater n. A device used on communications circuits 

that decreases distortion by amplifying or regenerating a 

signal so that it can be transmitted onward in its original 

strength and form. On a network, a repeater connects two 

networks or two network segments at the physical layer of 

the ISO/OSI reference model and regenerates the signal. 

repeating Ethernet n. See repeater. 

repeat key n. On some keyboards, a key that must be 

held down at the same time as a character key to cause the 

character key’s key code to be sent repeatedly. On most 

computer keyboards, however, a repeat key is not needed 

because a key automatically repeats if held down for 

longer than a brief delay. Compare typematic. 

RepeatKeys n. A feature of Windows 9x and Windows NT 

that allows a user to adjust or disable the typematic keyboard 

feature so as to accommodate users with restricted mobility, 

who may activate typematic by accident because they have 

trouble lifting their fingers from the keys. See also typematic. 

Compare BounceKeys, FilterKeys, MouseKeys, 

ShowSounds, SoundSentry, StickyKeys, ToggleKeys. 

repetitive strain injury n. An occupational disorder of the 

tendons, ligaments, and nerves caused by the cumulative 

effects of prolonged repetitious movements. Repetitive strain 

injuries are appearing with increasing frequency among 

office workers who spend long hours typing at computerized 

workstations that are not equipped with safeguards such as 

wrist supports. Acronym: RSI. See also carpal tunnel syndrome, 

ergonomic keyboard, wrist support. 

replace vb. To put new data in the place of other data, 

usually after conducting a search for the data to be 

replaced. Text-based applications such as word processors 

typically include search-and-replace commands. In such 

R

R 

replay attack resistance 

operations, both old and new data must be specified, and 

search-and-replace procedures may or may not be sensitive 

to uppercase and lowercase, depending on the application 

program. See also search1 , search and replace. 

replay attack n. An attack in which a valid message is 

intercepted and then repeatedly retransmitted, either for 

fraudulent purposes or as part of a larger attack scheme. 

replication n. In a distributed database management system, 

the process of copying the database (or parts of it) to 

the other parts of the network. Replication allows distributed 

database systems to remain synchronized. See also distributed 

database, distributed database management system. 

report n. The presentation of information about a given 

topic, typically in printed form. Reports prepared with 

computers and appropriate software can include text, 

graphics, and charts. Database programs can include 

special software for creating report forms and generating 

reports. Desktop publishing software and laser printers 

or typesetting equipment can be used to produce 

publication-quality output. 

report generator n. An application, commonly part of a 

database management program, that uses a report “form” 

created by the user to lay out and print the contents of a 

database. A report generator is used to select specific 

record fields or ranges of records, to make the output 

attractive by including such features as headings, running 

heads, page numbers, and fonts. 

Report Program Generator n. See RPG (definition 2). 

report writer n. See report generator. 

repository n. 1. A collection of information about a computing 

system. 2. A superset of a data dictionary. See also 

data dictionary. 

reprogrammable PROM n. See EPROM. 

reprogrammable read-only memory n. See EPROM. 

requested permissions n. Optionally specified permissions 

in an assembly that represent the minimum required, 

optionally desired, and always refused permissions for all 

code in the assembly. If there is no request, the code is 

granted the maximum that policy allows. 

Request for Comments n. See RFC. 

Request for Discussion n. A formal proposal for a discussion 

concerning the addition of a newsgroup to the 

450 

Usenet hierarchy, the first step in a process that ends with 

a call for votes. Acronym: RFD. See also traditional newsgroup 

hierarchy, Usenet. 

Request to Send n. See RTS. 

required hyphen n. See hyphen. 

Research Libraries Information Network n. The combined 

online catalog of the Research Libraries Group, 

which includes many of the major research libraries in the 

United States. Acronym: RLIN. 

reserve n. A command that allocates contiguous disk 

space for the device instance’s workspace. Digital video 

devices recognize this command. 

reserve accumulator n. An auxiliary storage register 

generally used to store the intermediate results of an 

extended calculation. 

reserved character n. A keyboard character that has a 

special meaning to a program and, as a result, normally 

cannot be used in assigning names to files, documents, 

and other user-generated tools, such as macros. Characters 

commonly reserved for special uses include the asterisk 

(*), forward slash (/), backslash (\), question mark (?), and 

vertical bar (|). 

reserved date n. A date with a special meaning, rather 

than the date on the calendar. For example, some programs 

use 9999 to indicate an account or a database listing that 

does not expire. See also magic dates. 

reserved memory n. See UMA. 

reserved word n. A word that has special meaning to a 

program or in a programming language. Reserved words 

usually include those used for control statements (IF, 

FOR, END), data declarations, and the like. A reserved 

word can be used only in certain predefined circumstances; 

it cannot be used in naming documents, files, 

labels, variables, or user-generated tools such as macros. 

reset button n. A device that restarts a computer without 

turning off its power. Compare big red switch. 

resident font n. See internal font. 

resident program n. See TSR. 

resistance n. The ability to impede (resist) the flow of 

electric current. With the exception of superconductors, all 

substances have a greater or lesser degree of resistance. Substances 

with very low resistance, such as metals, conduct

esistor Resource Reservation Setup Protocol 

electricity well and are called conductors. Substances with 

very high resistance, such as glass and rubber, conduct electricity 

poorly and are called nonconductors or insulators. 

resistor n. A circuit component designed to provide a 

specific amount of resistance to current flow. 

resize vb. To make an object or space larger or smaller. 

Also called: scale. 

resolution n. 1. The fineness of detail attained by a 

printer or a monitor in producing an image. For printers 

that form characters from small, closely spaced dots, resolution 

is measured in dots per inch, or dpi, and ranges 

from about 125 dpi for low-quality dot-matrix printers to 

about 600 dpi for some laser and ink-jet printers (typesetting 

equipment can print at resolutions of over 1000 dpi). 

For a video display, the number of pixels is determined by 

the graphics mode and video adapter, but the size of the 

display depends on the size and adjustment of the monitor; 

hence the resolution of a video display is taken as the total 

number of pixels displayed horizontally and vertically. See 

also high resolution, low resolution. 2. The process of 

translation between a domain name address and an IP 

address. See also DNS, IP address. 

resolve vb. 1. To match one piece of information to 

another in a database or lookup table. 2. To find a setting 

in which no hardware conflicts occur. 3. To convert a logical 

address to a physical address or vice versa. 4. To convert 

an Internet domain name to its corresponding IP 

address. See also DNS, IP address. 

resource n. 1. Any part of a computer system or a network, 

such as a disk drive, printer, or memory, that can be allotted 

to a program or a process while it is running. 2. An item of 

data or code that can be used by more than one program or 

in more than one place in a program, such as a dialog box, a 

sound effect, or a font in a windowing environment. Many 

features in a program can be altered by adding or replacing 

resources without the necessity of recompiling the program 

from source code. Resources can also be copied and pasted 

from one program into another, typically by a specialized 

utility program called a resource editor. 3. Any nonexecutable 

data that is logically deployed with an application. A 

resource might be displayed in an application as error 

messages or as part of the user interface. Resources can 

contain data in a number of forms, including strings, 

images, and persisted objects. 

451 

resource allocation n. The process of distributing a 

computer system’s facilities to different components of a 

job in order to perform the job. 

resource data n. The data structures, templates, definition 

procedures, management routines, icon maps, and so 

forth associated with a particular resource, such as a 

menu, window, or dialog box. See also resource (definition 

2), resource fork. 

Resource Description Framework n. A specification 

developed by the World Wide Web Consortium (W3C) to 

define a flexible infrastructure for organizing and managing 

metadata (data about data) across the Web and the 

Internet. The Resource Description Framework is intended 

to provide a framework based on XML (eXtensible 

Markup Language) that can standardize the way applications 

exchange metadata (or metacontent). Possible uses 

include search engines, content rating systems, and other 

areas in which exchange of information about data is valuable. 

Acronym: RDF. See also XML. 

resource file n. A file that consists of resource data and 

the resource map that indexes it. See also resource (definition 

2), resource fork. 

resource fork n. One of the two forks of an Apple Macintosh 

file (the other being the data fork ). The resource 

fork of a program file contains reusable items of information 

that the program can use during the course of execution, 

such as fonts, icons, windows, dialog boxes, menus, 

and the program code itself. A user-created document typically 

stores its data in the data fork, but it can also use its 

resource fork for storing items that might be used more 

than once in the document. For example, in a HyperCard 

stack, the data that constitutes each card, or record, in the 

stack is stored in the data fork; digitized sounds and icons 

that might be used more than once are stored in the 

resource fork. The use of such resources makes program 

development easier because resources can be developed 

and altered independently of the program code. See also 

HyperCard, resource (definition 2). Compare data fork. 

resource ID n. A number that identifies a particular 

resource within a given resource type on the Apple Macintosh—for 

example, a particular menu among many 

resources of type MENU that a program might use. See 

also resource (definition 2). 

Resource Reservation Setup Protocol n. A communications 

protocol designed to allow for “bandwidth on 

demand.” A remote receiver requests that a certain amount 

R

R 

resource sharing reverse engineering 

of bandwidth be reserved by the server for a data stream; 

the server sends back a message (similar to the RSVP sent 

in reply to an invitation) indicating whether or not the 

request has been granted. Acronym: RSVP (Resource Reservation 

Setup Protocol). 

resource sharing n. The act of making files, printers, 

and other network resources available for use by others. 

resource type n. One of numerous classes of structural 

and procedural resources in the Macintosh operating system, 

such as code, fonts, windows, dialog boxes, templates, 

icons, patterns, strings, drivers, cursors, color 

tables, and menus. Resource types have characteristic 

identifying labels, such as CODE for blocks of program 

instructions, FONT for fonts, and CURS for mouse cursors. 

See also resource (definition 2), resource fork. 

response time n. 1. The time, often an average, that 

elapses between the issuance of a request and the provision 

of the data requested (or notification of inability to 

provide it). 2. The time required for a memory circuit or 

storage device to furnish data requested by the central processing 

unit (CPU). 

restart vb. See reboot. 

restore1 n. The act of restoring a file or files. See also 

backup, recovery. 

restore2 vb. To copy files from a backup storage device to 

their normal location, especially if the files are being copied 

to replace files that were accidentally lost or deleted. 

restricted function n. A function or an operation that 

can be executed only under certain circumstances, especially 

when the central processing unit (CPU) is in privileged 

mode. See also privileged mode. 

Restructured Extended Executor n. See REXX. 

retrace n. The path followed by the electron beam in a 

raster-scan computer monitor as it returns either from the 

right to the left edge of the screen or from the bottom to 

the top of the screen. The retrace positions the electron 

beam for its next sweep across or down the screen; during 

this interval, the beam is briefly turned off to avoid drawing 

an unwanted line on the screen. Retracing occurs 

many times each second and uses tightly synchronized 

signals to ensure that the electron beam is turned off and 

on during the retrace. See also blanking, horizontal 

retrace, raster display, vertical retrace. 

452 

retrieve vb. To obtain a specific requested item or set of 

data by locating it and returning it to a program or to the 

user. Computers can retrieve information from any source 

of storage—disks, tapes, or memory. 

retro virus n. A type of virus that avoids detection by 

attacking or disabling antivirus programs. Also called: 

anti-anti-virus. 

return vb. 1. To transfer control of the system from a 

called routine or program back to the calling routine or 

program. Some languages support an explicit return or 

exit statement; others allow return only at the end (last 

statement) of the called routine or program. See also call2 (definition 2). 2. To report the outcome of a called routine 

to the calling routine or program. 

return code n. In programming, a code that is used to 

report the outcome of a procedure or to influence subsequent 

events when a routine or process terminates 

(returns) and passes control of the system to another routine. 

Return codes can, for example, indicate whether an 

operation was successful or not and can thus be used to 

determine what is to be done next. 

return from the dead vb. To regain access to the Internet 

after having been disconnected. 

Return key n. A key on a keyboard that is used to terminate 

input of a field or record or to execute the default 

action of a dialog box. On IBM PCs and compatibles, this 

key is called ENTER. The corresponding key on a typewriter 

causes the carriage holding the paper to return to 

the starting position to begin a new line; hence the name. 

See also Enter key. 

return to zero n. A method of recording on magnetic 

media in which the reference condition, or “neutral state,” 

is the absence of magnetization. Abbreviation: RZ. Compare 

nonreturn to zero. 

reusability n. The ability of code or a design to be usable 

again in another application or system. 

Reverse Address Resolution Protocol n. See RARP. 

Reverse ARP n. See RARP. 

reverse byte ordering n. See little endian. 

reverse engineering n. A method of analyzing a product 

in which the finished item is studied to determine its 

makeup or component parts—for example, studying a

everse path forwarding RGB monitor 

completed ROM chip to determine its programming or 

studying a new computer system to learn about its design. 

For computer software, reverse engineering typically 

involves decompilation of a substantial portion of the 

object code and studying the resulting decompiled code. 

reverse path forwarding n. A technique that makes routing 

decisions through a TCP/IP network by using the 

source address of a datagram rather than the destination 

address. Reverse path forwarding is used in broadcast and 

multicast applications because it reduces redundant transmissions 

to multiple recipients. Acronym: RPF. See also 

datagram, TCP/IP. 

reverse Polish notation n. See postfix notation. 

reverse video n. The reversal of light and dark in the display 

of selected characters on a video screen. For example, 

if text is normally displayed as white characters on a black 

background, reverse video presents text as black letters on 

a white background. Programmers commonly use reverse 

video as a means of highlighting text or special items 

(such as menu choices or the cursor) on the screen. 

revert vb. To return to the last saved version of a document. 

Choosing this command tells the application to 

abandon all changes made in a document since the last 

time it was saved. 

Revisable-Form-Text DCA n. A standard within Document 

Content Architecture (DCA) for storing documents 

in such a way that the formatting can be changed by the 

receiver. A related standard is Final-Form-Text DCA. 

Acronym: RFTDCA. See also DCA. Compare Final- 

Form-Text DCA. 

revision mark n. A mark that shows where a deletion, 

insertion, or other editing change has been made in a 

document. 

rewind vb. To wind a magnetic tape spool or cassette to 

its beginning. 

rewritable digital video disc n. Technology for recording 

data on disks that have the same storage capacity as 

digital video discs (DVDs) but can be rewritten like the 

compact disc–rewritable (CD-RW) devices. See also digital 

video disc, PD-CD drive. 

rewrite vb. To write again, especially in situations where 

information is not permanently recorded, such as RAM or 

a video display. Also called: refresh, regenerate. See also 

dynamic RAM. 

453 

REXX n. Acronym for Restructured Extended Executor. A 

structured programming language used on IBM mainframes 

and with OS/2 Version 2.0. REXX programs invoke application 

programs and operating system commands. 

RF n. See radio frequency. 

RFC n. Acronym for Request for Comments. A document 

in which a standard, a protocol, or other information pertaining 

to the operation of the Internet is published. The 

RFC is actually issued, under the control of the IAB, after 

discussion and serves as the standard. RFCs can be 

obtained from sources such as InterNIC. 

RFD n. See Request for Discussion. 

RFI n. Acronym for radio frequency interference. Noise 

introduced into an electronic circuit, such as a radio or 

television, by electromagnetic radiation produced by 

another circuit, such as a computer. 

RF shielding n. A structure, generally sheet metal or 

metallic foil, designed to prevent the passage of radio frequency 

(RF) electromagnetic radiation. RF shielding is 

intended to keep RF radiation either inside a device or out 

of a device. Without proper RF shielding, devices that use 

or emit RF radiation can interfere with each other; for 

example, running an electric mixer might cause interference 

on a television. Computers generate RF radiation 

and, to meet Federal Communications Commission (FCC) 

standards, must be properly shielded to prevent this RF 

radiation from leaking out. The metal case of a PC provides 

most of the needed RF shielding. Devices meeting 

FCC type A standards are suitable for business use. 

Devices meeting the more stringent FCC type B standards 

are suitable for home use. See also radio frequency, RFI. 

RFTDCA n. See Revisable-Form-Text DCA. 

RGB n. Acronym for red-green-blue. A model for 

describing colors that are produced by emitting light, as on 

a video monitor, rather than by absorbing it, as with ink on 

paper. The three kinds of cone cells in the eye respond to 

red, green, and blue light, respectively, so percentages of 

these additive primary colors can be mixed to get the 

appearance of any desired color. Adding no color produces 

black; adding 100 percent of all three colors results 

in white. See also CMYK, RGB monitor. Compare CMY. 

RGB display n. See RGB monitor. 

RGB monitor n. A color monitor that receives its signals 

for red, green, and blue levels over separate lines. An RGB 

monitor generally produces sharper and cleaner images 

R

R 

ribbon cable ring topology 

than those produced by a composite monitor, which 

receives levels for all three colors over a single line. See 

also RGB. Compare composite video display. 

ribbon cable n. A flat cable containing up to 100 parallel 

wires for data and control lines. For example, ribbon 

cables are used inside a computer’s case to connect the 

disk drives to their controllers. 

ribbon cartridge n. A disposable module containing an 

inked fabric ribbon or a carbon-coated plastic film ribbon. 

Many impact printers use ribbon cartridges to make ribbon 

changing easier and cleaner. 

Rich Text Format n. An adaptation of DCA (Document 

Content Architecture) that is used for transferring formatted 

text documents between applications, even those applications 

running on different platforms, such as between 

IBM and compatibles and Macintoshes. Acronym: RTF. 

See also DCA. 

RIFF n. Acronym for Resource Interchange File Format. 

Developed jointly by IBM and Microsoft, RIFF is a broadbased 

specification designed to be used in defining standard 

formats for different types of multimedia files. A 

tagged-file specification, RIFF relies on headers that “tag” 

individual data elements in a file, identifying them by type 

and length. Because tags identify data elements, the RIFF 

specification can be extended to cover new types of elements 

while continuing to support older applications, 

which can simply ignore new, unrecognized elements they 

encounter in a file. See also AVI, MCI. 

right click vb. To make a selection using the button on 

the right side of a mouse or other pointing device. Doing 

so in Windows 9x and Windows NT 4.0 and later typically 

brings up a pop-up menu with options applicable to the 

object over which the cursor is positioned. See also 

mouse, pointing device. 

right click disabler n. A program or script that prevents 

a user from employing any functions controlled by clicking 

the right mouse button. A right click disabler script 

may be run when a user visits a Web site to control the 

user’s actions and options. 

right justification n. In typesetting, word processing, 

and desktop publishing, the process of aligning text evenly 

along the right margins of a column or page. The left edge 

of the text is ragged. See also justify (definition 1), rag. 

Compare full justification, left justification. 

454 

right-justify vb. To align lines of text and other display 

elements so that the right edges form a smooth line. See 

also align (definition 1), rag. Compare left-justify. 

rigid disk n. See hard disk. 

RIMM n. A plug-in module jointly developed by Rambus 

and Intel for the high-bandwidth computer memory 

known as Direct RDRAM. A RIMM is comparable to a 

DIMM in size and shape, but the two are not pin-compatible. 

See also DIMM, RDRAM. 

ring network n. A LAN (local area network) in which 

devices (nodes) are connected in a closed loop, or ring. 

Messages in a ring network pass around the ring from 

node to node in one direction. When a node receives a 

message, it examines the destination address attached to 

the message. If the address is the same as the node’s, the 

node accepts the message; otherwise, it regenerates the 

signal and passes the message along to the next node in 

the ring. Such regeneration allows a ring network to cover 

larger distances than star and bus networks. The ring can 

also be designed to bypass any malfunctioning or failed 

node. Because of the closed loop, however, adding new 

nodes can be difficult. See the illustration. Also called: ring 

topology. See also token passing, token ring network. 

Compare bus network, star network. 

F0Rgn06.EPS 

Ring network. 

ring topology n. See ring network.

ip RLL encoding 

rip vb. To convert audio data from a compact disc into a 

WAV file or other digital format, typically in preparation 

for further encoding as an MP3 file. See also MP3. 

RIP n. 1. Acronym for Routing Information Protocol. An 

Internet protocol, defined in RFC 1058, that defines the 

exchange of routing table information. Through RIP, each 

router on a network sends its routing table to its nearest 

neighbor every 30 seconds. Under RIP, routing is determined 

by the number of hops between source and destination. 

RIP is an interior gateway protocol (a protocol used by 

gateways for exchanging routing information). Because it is 

not the most efficient of routing protocols, it is being 

replaced by the more efficient Open Shortest Path First 

(OSPF) protocol. See also Bellman-Ford distance-vector 

routing algorithm, communications protocol, interior gateway 

protocol, OSPF. 2. See raster image processor. 

RIPE n. Acronym for Reseaux IP Européens. A voluntary 

organization of ISPs (Internet service providers) dedicated 

to the goal of a smoothly functioning, pan-European Internet 

network. Most of the work performed by RIPE is handled 

by discrete working groups that deal with issues such 

as management of the RIPE database and technical networking 

questions. RIPE also provides services that 

include registering domain names within top-level Internet 

domains and assigning IP (Internet Protocol) addresses. 

Member organizations of RIPE are supported by the RIPE 

NCC (Network Coordination Centre), based in Amsterdam, 

The Netherlands. See also American Registry for 

Internet Numbers. 

ripper n. Digital audio technology that converts audio 

data from a compact disc into a WAV file or other digital 

format. An encoder then converts this file into a file (typically 

an MP3 file) that can be played back by software 

known as a player. See also encoder, MP3. 

RIPX n. A protocol used by routers to exchange information 

between routers on an IPX network and by hosts to 

determine the best routers to use when forwarding IPX traffic 

to a remote IPX network. Also called: RIP for IPX. See 

also communications protocol, IPX, NWLink, router. 

RIS n. See Remote Installation Services. 

RISC n. Acronym for Reduced Instruction Set Computing. 

A microprocessor design that focuses on rapid and 

efficient processing of a relatively small set of simple 

instructions that comprises most of the instructions a 

computer decodes and executes. RISC architecture opti- 

455 

mizes each of these instructions so that it can be carried 

out very rapidly—usually within a single clock cycle. 

RISC chips thus execute simple instructions more 

quickly than general-purpose CISC (Complex Instruction 

Set Computing) microprocessors, which are 

designed to handle a much wider array of instructions. 

They are, however, slower than CISC chips at executing 

complex instructions, which must be broken down into 

many machine instructions that RISC microprocessors 

can perform. Families of RISC chips include Sun Microsystems’ 

SPARC, Motorola’s 88000, Intel’s i860, and the 

PowerPC developed by Apple, IBM, and Motorola. See 

also architecture, SPARC. Compare CISC. 

RISC86 n. A “hybrid” microprocessor technology in 

which CISC (Complex Instruction Set Computing) 

instructions are translated into RISC (Reduced Instruction 

Set Computing) instructions for processing. RISC86 is 

designed to support the 80x86 CISC architecture while 

providing the speed gains characteristic of RISC technology. 

RISC86 was developed by NexGen and is implemented 

in AMD’s K6 microprocessor. 

Rivest-Shamir-Adleman encryption n. See RSA 

encryption. 

RJ-11 connector n. See phone connector. 

RJ-11 jack n. See phone connector. 

RJ-45 connector n. Short for Registered Jack-45 connector. 

An eight-wire connector used to attach devices to 

cables. The eight wires are encased in a plastic sheath and 

color-coded to match corresponding slots in jacks. RJ-45 

jacks are used to connect computers to LANs (local area 

networks) and to link ISDN (Integrated Services Digital 

Network) devices to NT-1 (Network Terminator 1) 

devices. Also called: RJ-45 jack. See also ISDN. 

RJ-45 jack n. See RJ-45 connector. 

RLE n. Short for Run Length Encoding. A data compression 

format in which only the first of a series of consecutive 

identical pixels is saved, along with the total number 

of pixels in the run. When the file is decompressed, each 

representative pixel is copied the correct number of times 

to replace those not saved. RLE compression works best 

with simple black and white or flat color graphics. 

RLIN n. See Research Libraries Information Network. 

RLL encoding n. See run-length limited encoding. 

R

R 

rlogin1 rlogin 

ROM 

rlogin1 n. 1. A protocol used to log in to a networked computer 

in which the local system automatically supplies the 

user’s login name. See also communications protocol, 

logon. Compare telnet1. 2. A UNIX command in BSD 

UNIX that enables a user to log in to a remote computer on 

a network using the rlogin protocol. See also BSD UNIX. 

rlogin2 vb. To connect to a networked computer using the 

rlogin protocol. 

RLSD n. Acronym for Received Line Signal Detect. 

See DCD. 

RMI-IIOP n. Acronym for Remote Method Invocation 

over Internet Inter-ORB Protocol. A subsystem of the 

Java 2 Platform, Enterprise Edition (J2EE). It provides the 

ability to write CORBA applications for the Java platform 

without learning the CORBA Interface Definition Language 

(IDL). RMI-IIOP includes the full functionality of a 

CORBA Object Request Broker and allows the programming 

of CORBA servers and applications via the RMI 

application programming interface (API). RMI-IIOP is 

useful for developers using Enterprise Java Beans (EJBs), 

since the remote object model for an EJB is RMI-based. 

Also called: RMI over IIOP. See also CORBA, Enterprise 

JavaBeans, J2EE. 

RMM n. See real-mode mapper. 

RMON n. Acronym for remote monitoring or remote network 

monitoring. A protocol that enables network information 

to be monitored and analyzed at a central site. The 

nine management information bases (MIBs) defined by 

RMON provide statistics about network traffic. See also 

MIB. Compare SNMP. 

roaming user profile n. A server-based user profile that is 

downloaded to the local computer when a user logs on; it is 

updated both locally and on the server when the user logs 

off. A roaming user profile is available from the server 

when logging on to a workstation or server computer. When 

logging on, the user can use the local user profile if it is 

more current than the copy on the server. See also local user 

profile, mandatory user profile, user profile. 

robopost vb. To post articles to newsgroups automatically, 

usually by means of a bot. See also bot (definition 

3), newsgroup, post. 

robot n. 1. A machine that can sense and react to input 

and cause changes in its surroundings with some degree of 

intelligence, ideally without human supervision. Although 

robots are often designed to mimic human movements in 

456 

carrying out their work, they are seldom humanlike in 

appearance. Robots are commonly used in manufacturing 

products such as automobiles and computers. See also 

robotics. 2. See bot, spider. 

robotics n. The branch of engineering devoted to the creation 

and training of robots. Roboticists work within a 

wide range of fields, such as mechanical and electronic 

engineering, cybernetics, bionics, and artificial intelligence, 

all toward the end of endowing their creations with 

as much sensory awareness, physical dexterity, independence, 

and flexibility as possible. See also artificial intelligence, 

bionics, cybernetics. 

robust adj. Able to function or to continue functioning 

well in unexpected situations. 

ROFL n. Acronym for rolling on the floor, laughing. An 

expression, used mostly in newsgroups and online conferences, 

to indicate one’s appreciation of a joke or other 

humorous circumstance. Also called: ROTFL. 

role-playing game n. A game that is played on line, such 

as MUD, in which participants take on the identities of 

characters who interact with each other. These games 

often have a fantasy or science fiction setting and a set of 

rules that all players need to follow. Role-playing games 

may be similar to adventure games in terms of story line, 

but also feature management and decision making for the 

character assumed during the course of the game. Acronym: 

RPG. See also MUD. Compare adventure game. 

rollback n. 1. A return to a previous stable condition, as 

when the contents of a hard disk are restored from a 

backup after a destructive hard disk error. 2. The point in 

an online transaction when all updates to any databases 

involved in the transaction are reversed. 

rollover n. See Year 2000 rollover. 

ROM n. 1. Acronym for read-only memory. A semiconductor 

circuit into which code or data is permanently 

installed by the manufacturing process. The use of this technology 

is economically viable only if the chips are produced 

in large quantities; experimental designs or small 

volumes are best handled using PROM or EPROM. 

2. Acronym for read-only memory. Any semiconductor circuit 

serving as a memory that contains instructions or data 

that can be read but not modified (whether placed there by 

manufacturing or by a programming process, as in PROM 

and EPROM). See also EEPROM, EPROM, PROM.

oman root server 

roman adj. Having upright rather than slanted characters 

in a typeface. See also font family. Compare italic. 

ROM Basic n. Short for read-only memory Beginner’s 

All-purpose Symbolic Instruction Code. A Basic interpreter 

stored in ROM (read-only memory) so that the user 

can start programming after simply turning on the 

machine, without having to load Basic from a disk or tape. 

ROM Basic was a feature of many early home computers. 

ROM BIOS n. Acronym for read-only memory basic 

input/output system. See BIOS. 

ROM card n. Short for read-only memory card. A plugin 

module that contains one or more printer fonts, programs, 

or games or other information stored in ROM 

(read-only memory). A typical ROM card is about the size 

of a credit card and several times thicker. It stores information 

directly in integrated circuit boards. Also 

called: font card, game card. See also ROM (definition 1), 

ROM cartridge. 

ROM cartridge n. Short for read-only memory cartridge. 

A plug-in module that contains one or more printer 

fonts, programs, games, or other information stored in 

ROM (read-only memory) chips on a board enclosed in a 

plastic case with a connector exposed at one end so that it 

can easily plug into a printer, computer, game system, or 

other device. For example, a cartridge that plugs into a 

game system is a ROM cartridge. Also called: game cartridge. 

See also ROM (definition 1), ROM card. 

ROM emulator n. Short for read-only memory emulator. 

A special circuit containing RAM memory that is 

connected to a target computer in place of the target computer’s 

ROM chips. A separate computer writes the contents 

into the RAM, and then the target computer reads the 

RAM as if it were ROM. ROM emulators are used to 

debug ROM-resident software without the high cost and 

delay of manufacturing chips. Even though the use of a 

ROM emulator is more expensive than programming an 

EPROM, it is often preferred today because its contents 

can be changed much more quickly than those of an 

EPROM. Also called: ROM simulator. See also 

EEPROM, EPROM, ROM (definition 1). 

ROM simulator n. See ROM emulator. 

root n. The main or uppermost level in a hierarchically 

organized set of information. The root is the point from 

which subsets branch in a logical sequence that moves from 

a broad focus to narrower perspectives. See also leaf, tree. 

457 

root account n. On UNIX systems, the account having 

control over the operation of a computer. The system 

administrator uses this account for system maintenance. 

Also called: superuser. See also system administrator. 

root directory n. The point of entry into the directory 

tree in a disk-based hierarchical directory structure. 

Branching from this root are various directories and subdirectories, 

each of which can contain one or more files and 

subdirectories of its own. For example, in the MS-DOS 

operating system the root directory is identified by a name 

consisting of a single backslash character (\). Beneath the 

root are other directories, which may contain further directories, 

and so on. See the illustration. 

C:\ 

MYDATA 

LETTERS REPORTS 

Root directory 

F0Rgn07.EPS 

Root directory. 

root folder n. The folder on a drive from which all other 

folders branch. The root folder’s name consists of a single 

backslash character (\). For example, on drive C, this 

folder would be represented in the file system as C:\. 

rootless n. A mode in which an application belonging to a 

different user interface can run on top of a computer’s 

underlying operating system without affecting that desktop 

or applications it may be running. For example, programs 

belonging to a rootless version of the X Window System 

can be run on a Mac OS X computer without disturbing the 

Aqua desktop. See also Mac OS X, X Window System. 

root name n. In MS-DOS and Windows, the first part of a 

filename. In MS-DOS and earlier versions of Windows, 

the maximum length of the root name was eight characters; 

in Windows NT and later versions of Windows, the 

root name may be as long as 255 characters. See also 8.3, 

extension (definition 1), filename, long filenames. 

root name server n. See root server. 

root server n. A computer with the ability to locate 

DNS servers containing information about top-level 

Internet domains, such as com, org, uk, it, jp, and other 

country domains, in the Internet’s Domain Name System 

(DNS) hierarchy. Beginning with the root server and 

R

R 

root web routing table 

continuing through referrals to name servers at lower 

levels of the hierarchy, the DNS is able to match a 

“friendly” Internet address, such as microsoft.com, with 

its numerical counterpart, the IP address. Root servers 

thus contain the data needed for referrals to name servers 

at the highest level of the hierarchy. There are 13 root 

servers in the world, located in the United States, the 

United Kingdom, Sweden, and Japan. Also called: root 

name server. See also DNS (definition 1), DNS server, 

top-level domain. 

root web n. The default, top-level web provided by a Web 

server. To access the root web, you supply the URL of the 

server without specifying a page name or subweb. 

ROT13 encryption n. A simple encryption method in 

which each letter is replaced with the letter of the alphabet 

13 letters after the original letter, so that A is replaced by 

N, and so forth; N, in turn, is replaced by A, and Z is 

replaced by M. ROT13 encryption is not used to protect 

messages against unauthorized readers; rather, it is used in 

newsgroups to encode messages that a user may not want 

to read, such as sexual jokes or spoilers. Some newsreaders 

can automatically perform ROT13 encryption and 

decryption at the touch of a key. 

rotary dialing n. The signaling system used in telephones 

with rotary dials, in which each digit is associated with a 

set number of pulses. During dialing, these pulses, which 

are audible as series of clicks, momentarily turn the current 

in the telephone wires on and off. Also called: pulse 

dialing. Compare touch tone dialing. 

rotate vb. 1. To turn a model or other graphical image so 

that it is viewed at a different angle. 2. To move bits in a 

register to the left or to the right. The bit that moves out of 

the end position rotates to the newly vacated position at 

the opposite end of the register. Compare shift. 

rotational delay n. The time required for a desired disk 

sector to rotate to the read/write head. Also called: rotational 

latency. 

rotational latency n. See rotational delay. 

RO terminal n. Short for read-only terminal. A terminal 

that can receive data but cannot send data. Nearly all printers 

can be classified as RO terminals. 

ROTFL n. See ROFL. 

round vb. To shorten the fractional part of a number, 

increasing the last remaining (rightmost) digit or not, 

according to whether the deleted portion was over or 

458 

under five. For example, 0.3333 rounded to two decimal 

places is 0.33, and 0.6666 is 0.67. Computer programs 

often round numbers, sometimes causing confusion when 

the resulting values do not add up “correctly.” Percentages 

in a spreadsheet can thus total 99 percent or 101 percent 

because of rounding. 

round robin n. A sequential, cyclical allocation of 

resources to more than one process or device. 

roundtripping n. The process of converting files from one 

format to another for viewing or editing and then converting 

the files back to the original format again. In some 

cases, roundtripping can involve repeated conversions of 

the file from one format to another and back. Frequent 

roundtripping may be a concern because each conversion 

has the potential to introduce unwanted changes to the file. 

routable protocol n. A communications protocol that is 

used to route data from one network to another by means 

of a network address and a device address. TCP/IP is an 

example of a routable protocol. 

router n. An intermediary device on a communications 

network that expedites message delivery. On a single network 

linking many computers through a mesh of possible 

connections, a router receives transmitted messages and 

forwards them to their correct destinations over the most 

efficient available route. On an interconnected set of 

LANs (local area networks)—including those based on 

differing architectures and protocols—using the same 

communications protocols, a router serves the somewhat 

different function of acting as a link between LANs, 

enabling messages to be sent from one to another. See also 

bridge, gateway. 

routine n. Any section of code that can be invoked (executed) 

within a program. A routine usually has a name 

(identifier) associated with it and is executed by referencing 

that name. Related terms (which may or may not be 

exact synonyms, depending on the context) are function, 

procedure, and subroutine. See also function (definition 

3), procedure, subroutine. 

routing n. The process of forwarding packets between 

networks from source to destination. See also dynamic 

routing, static routing. 

Routing Information Protocol n. See RIP (definition 1). 

routing table n. In data communications, a table of information 

that provides network hardware (bridges and routers) 

with the directions needed to forward packets of data 

to locations on other networks. The information contained

ow Ruby 

in a routing table differs according to whether it is used by 

a bridge or a router. A bridge relies on both the source 

(originating) and destination addresses to determine where 

and how to forward a packet. A router relies on the destination 

address and on information in the table that gives 

the possible routes—in hops or in number of jumps— 

between itself, intervening routers, and the destination. 

Routing tables are updated frequently as new or more current 

information becomes available. See also bridge, hop, 

internetwork, router. 

row n. A series of items arranged horizontally within 

some type of framework—for example, a continuous 

series of cells running from left to right in a spreadsheet; a 

horizontal line of pixels on a video screen; or a set of data 

values aligned horizontally in a table. Compare column. 

royalty-free n. The absence of a requirement to pay the 

original owner of music, images, software, or other content 

for the right to use, edit, or distribute their content. 

RPC n. See remote procedure call. 

RPF n. See reverse path forwarding. 

RPG n. 1. See role-playing game. 2. Acronym for Report 

Program Generator. An IBM programming platform introduced 

in 1964. The earliest version of RPG was not a language 

but a program generator intended to aid in 

producing business reports. Versions of RPG have been 

developed for various platforms, including IBM’s AS/400 

server, UNIX, MS-DOS, and Windows. 

RPN n. Acronym for reverse Polish notation. See postfix 

notation. 

RPROM n. Short for reprogrammable PROM. See 

EPROM. 

RS-232-C standard n. An accepted industry standard for 

serial communications connections. Adopted by the Electrical 

Industries Association, this Recommended Standard 

(RS) defines the specific lines and signal characteristics 

used by serial communications controllers to standardize 

the transmission of serial data between devices. The letter C 

denotes that the current version of the standard is the third 

in a series. See also CTS, DSR, DTR, RTS, RXD, TXD. 

RS-422/423/449 n. Standards for serial communications 

with transmission distances over 50 feet. RS-449 

incorporates RS-422 and RS-423. Macintosh serial ports 

are RS-422 ports. See also RS-232-C standard. 

RSA n. A widely used public/private key algorithm. It is 

the default cryptographic service provider (CSP) for 

459 

Microsoft Windows. It was patented by RSA Data Security, 

Inc., in 1977. See also cryptographic service provider. 

RSAC n. See Recreational Software Advisory Council. 

RSA encryption n. Short for Rivest-Shamir-Adleman 

encryption. The public key encryption algorithm, 

introduced by Ronald Rivest, Adi Shamir, and Leonard 

Adleman in 1978, on which the PGP (Pretty Good Privacy) 

encryption program is based. See also PGP, public 

key encryption. 

RSI n. See repetitive strain injury. 

RSN adv. See Real Soon Now. 

R-squared value n. An indicator from 0 to 1 that reveals 

how closely the estimated values for the trendline correspond 

to your actual data. A trendline is most reliable 

when its R-squared value is at or near 1. Also called: the 

coefficient of determination. 

RSVP n. See Resource Reservation Setup Protocol. 

RTC n. See clock (definition 2). 

RTCP n. See Real-Time Control Protocol. 

RTF n. See Rich Text Format. 

RTFM n. Acronym for read the flaming (or friendly) 

manual. A common answer to a question in an Internet 

newsgroup or product support conference that is adequately 

explained in the instruction manual. (The F in this 

acronym is not necessarily assumed to represent polite 

language.) Also called: RTM. 

RTM n. Acronym for read the manual. See RTFM. 

RTOS n. See real-time operating system. 

RTP n. See Real-Time Protocol. 

RTS n. Acronym for Request to Send. A signal sent, as 

from a computer to its modem, to request permission to 

transmit; the signal is often used in serial communications. 

RTS is a hardware signal sent over pin 4 in RS-232-C connections. 

See also RS-232-C standard. Compare CTS. 

RTSP n. See Real-Time Streaming Protocol. 

rubber banding n. In computer graphics, changing the 

shape of an object made up of connected lines by “grabbing” 

a point on an anchored line and “pulling” it to the 

new location. 

Ruby n. An interpreted open source scripting language for 

object-oriented programming. Its simple syntax is partially 

based on the syntax of Eiffel and Ada. Considered to 

R

R 

rudder control run-time library 

be similar to Perl, it has many features to process text files 

and perform system management tasks. 

rudder control n. A device, consisting of a pair of pedals, 

that enables a user to input rudder movements in a flight 

simulation program. The rudder control is used along with 

a joystick (which controls the simulated ailerons and elevators) 

and possibly a throttle control. 

rule n. 1. A line printed above, below, or to the side of 

some element, either to set that item off from the remainder 

of the page or to improve the look of the page. Footnotes, 

for example, often appear below a short rule that 

sets them off from the main text on the page. The thickness 

of a rule is typically measured in points. (A point is 

approximately 1 /72 inch.) See also point1 (definition 1). 2. 

In expert systems, a statement that can be used to verify 

premises and to enable a conclusion to be drawn. See also 

expert system. 

rule-based system n. See expert system, production 

system. 

ruler n. In some application programs, such as word processors, 

an on-screen scale marked off in inches or other 

units of measure and used to show line widths, tab settings, 

paragraph indents, and so on. In programs in which 

the ruler is “live,” the on-screen ruler can be used with the 

mouse or with the keyboard to set, adjust, or remove tab 

stops and other settings. 

run vb. To execute a program. 

run around vb. In page composition, to position text so 

that it flows around an illustration or other display. 

run-length encoding n. A simple compression method 

that replaces a contiguous series (run) of identical values 

in a data stream with a pair of values that represent the 

length of the series and the value itself. For example, a 

data stream that contains 57 consecutive entries with the 

value 10 could replace them all with the much shorter pair 

of values 57, 10. Acronym: RLE. 

Run Length Encoding n. See RLE. 

run-length limited encoding n. A fast and highly efficient 

method of storing data on a disk (usually a hard disk) 

in which patterns in the bits representing information are 

translated into codes rather than being stored literally bit 

by bit and character by character. In RLL encoding, 

changes in magnetic flux are based on the number of zeros 

460 

that occur in sequence. This scheme allows data to be 

stored with fewer changes in magnetic flux than would 

otherwise be needed for the number of data bits involved 

and results in considerably higher storage capacity than is 

possible with older technologies, such as frequency modulation 

(FM) and modified frequency modulation (MFM) 

encoding. Abbreviation: RLL encoding. Compare frequency 

modulation encoding, modified frequency modulation 

encoding. 

running foot n. One or more lines of text in the bottom 

margin area of a page, composed of one or more elements 

such as the page number, the name of the chapter, and the 

date. Also called: footer. 

running head n. One or more lines of text in the top margin 

area of a page, composed of one or more elements 

such as the page number, the name of the chapter, and the 

date. Also called: header. 

RUNOFF n. A very early text editor/text formatting program, 

developed by J. E. Saltzer at M.I.T. for the CTSS 

(Compatible Time-Sharing System) operating system in the 

mid-1960s, in order to format his Ph.D. thesis. RUNOFF 

was the ancestor of many other text processors, including 

TeX, and the UNIX programs roff, nroff, and troff. 

run-time adj. Occurring after a program has begun to be 

executed, such as evaluation of variable expressions and 

dynamic allocation of memory. 

run time n. 1. The time period during which a program is 

running. See also compile time, dynamic allocation, 

dynamic binding, link time. 2. The amount of time 

needed to execute a given program. 

runtime n. See common language runtime. 

run-time binding n. Assignment of a meaning to an identifier 

(such as a variable) in a program at the time the program 

is executed rather than at the time the program is compiled. 

Compare compile-time binding, link-time binding. 

run-time error n. A software error that occurs while a 

program is being executed, as detected by a compiler or 

other supervisory program. 

run-time library n. A file containing one or more prewritten 

routines to perform specific, commonly used functions. 

A run-time library, used primarily in high-level 

languages such as C, saves the programmer from having to 

rewrite those routines.

un-time version RZ 

run-time version n. 1. Program code that is ready to be 

executed. Generally, this code has been compiled and 

can operate without error under most user command 

sequences and over most ranges of data sets. 2. A special 

release that provides the computer user with some, but 

not all, of the capabilities available in the full-fledged 

software package. 

461 

R/W adj. See read/write. 

RXD n. Short for Receive (rx) Data. A line used to carry 

received serial data from one device to another, such as 

from a modem to a computer. Pin 3 is the RXD line in 

RS-232-C connections. See also RS-232-C standard. 

Compare TXD. 

RZ n. See return to zero. 

R

S 

S-100 bus n. A 100-pin bus specification used in the 

design of computers built around the Intel 8080 and Zilog 

Z-80 microprocessors. System designs using the Motorola 

6800, 68000, and Intel iAPx86 family of microprocessors 

have also been built around the S-100 bus. S-100 computers 

were extremely popular with early computer enthusiasts. 

They had an open architecture, which permitted the 

configuration of systems with a wide range of add-on 

expansion boards. 

SA n. Identifier for Intel’s line of RISC-based microprocessors 

for portable and embedded devices. See also 

StrongARM. 

SAA n. Acronym for Systems Application Architecture. 

An IBM-developed standard for the appearance and operation 

of application software that will give programs written 

for all IBM computers—mainframe computers, 

minicomputers, and personal computers—a similar look 

and feel. SAA defines how an application interfaces with 

both the user and the supporting operating system. True 

SAA-compliant applications are compatible at the source 

level (before being compiled) with any SAA-compliant 

operating system—provided the system is capable of furnishing 

all the services required by the application. 

Sad Mac n. An error indication that occurs on Apple 

Macintosh computers when the system fails the initial 

diagnostic test. A Sad Mac is a picture of a Macintosh 

with a frowning face and X’s for eyes, with an error code 

beneath the picture. 

safe mode n. In some versions of Windows, such as Windows 

95, a boot mode that bypasses startup files and loads 

only the most basic drivers. Safe mode allows the user to 

correct some problem with the system—for example, if 

the system fails to boot or the registry has become corrupted. 

See also boot1 . 

salt n. Random data used to supplement encryption 

schemes. A salt value allows two identical packets of data 

to be encrypted into two different packets of ciphertext 

using the same key by changing the salt value with each 

packet. Also called: salt string, salt value. 

S 

462 

Samba n. A popular freeware program that provides file 

and print services, authentication and authorization, name 

resolution, and service announcement (browsing). As a 

file server, Samba enables the sharing of files, printers, 

and other resources on a UNIX Samba server with Windows 

clients over a network. Based on the Server Message 

Block (SMB) protocol, Samba originally was developed 

as a Network File System (NFS) for UNIX by Andrew 

Tridgell. See also NFS, SMB. 

sampling vb. 1. In statistics, gathering data from a representative 

subset of a larger group (called a population)— 

for example, determining a country’s presumed voting 

pattern by polling a demographic cross section of voters. 

Other uses of this type of sampling might include checking 

the accuracy and efficiency of computerized transactions 

by reviewing every hundredth transaction or 

predicting traffic volumes by measuring traffic flow in a 

few strategic streets. There are many statistical procedures 

for estimating how accurately a given sample reflects the 

behavior of a group as a whole. 2. The conversion of analog 

signals to a digital format; samples are taken at periodic 

intervals to measure and record some parameter, such 

as a signal from a temperature sensor or a microphone. 

Analog-to-digital converters are used in computers to 

sample analog signals as voltages and convert them to the 

binary form a computer can process. The two primary 

characteristics of this type of sampling are the sampling 

rate (usually expressed in samples per second) and the 

sampling precision (expressed in bits; 8-bit samples, for 

instance, can measure an input voltage accurate to 1/256 

of the measured range). 

sampling rate n. The frequency with which samples of a 

physical variable, such as sound, are taken. The higher the 

sampling rate (that is, the more samples taken per unit of 

time), the more closely the digitized result resembles the 

original. See also sampling (definition 2). 

sampling synthesizer n. A device designed to reproduce 

sounds, at differing frequencies, based on a digitized 

sound stored in read-only memory. For example, a

samurai scalability 

recorded piano note, digitized and stored in memory, is 

used by the synthesizer to create other piano-like notes. 

samurai n. A hacker employed by a company or organization 

to manage network security or conduct legal cracking 

operations. A samurai uses the skills of a hacker to 

meet the legitimate needs of an employer. 

SAN n. See storage area network. 

sandbox n. 1. Java Virtual Machine security area for 

downloaded (remote or untrusted) applets, an area in 

which such applets are confined and prevented from 

accessing system resources. Confinement to the sandbox 

prevents downloaded applets from carrying out potentially 

dangerous operations, maliciously or otherwise. They 

have to “play” inside the sandbox, and any attempt to 

“escape” is thwarted by the Java Security Manager. 

2. Slang for the research and development department at 

many software and computer companies. See also applet, 

Java Virtual Machine. 

sans serif adj. Literally, “without stroke”; describes any 

typeface in which the characters have no serifs (the short 

lines or ornaments at the upper and lower ends of the 

strokes). A sans serif typeface usually possesses a more 

straightforward, geometric appearance than a typeface 

with serifs and typically lacks the contrast between thick 

and thin strokes found in serif faces. Sans serif typefaces 

are used more frequently in display type, such as headlines, 

than in blocks of text. Compare serif1 . 

SAOL n. Acronym for Structured Audio Orchestra Language. 

Part of the MPEG-4 standard, SAOL describes a set 

of tools for producing computer music, audio for computer 

games, streaming Internet sound or music, and other multimedia 

applications. SAOL is a flexible computer language 

for describing music synthesis and integrating synthetic 

sound with recorded sound in an MPEG-4 bit stream. See 

also bit stream, MPEG-4, streaming (definition 1). 

SAP n. See Service Advertising Protocol. 

SAPI n. Acronym for Speech Application Programming 

Interface. A feature in Windows 9x and Windows NT that 

allows applications to include speech recognition or convert 

text to speech. Also called: Speech API. See also 

voice recognition. 

SAS n. See single attachment station. 

463 

SASL n. Acronym for Simple Authentication and Security 

Layer. An authentication support mechanism for use with 

connection-based protocols. SASL allows a client to 

request identification from a server and negotiate use of an 

added security layer for authentication during subsequent 

client/server interaction. 

satellite n. See communications satellite. 

satellite computer n. A computer that is connected to 

another computer, with which it interacts over a communications 

link. As its name indicates, a satellite computer is 

of lesser “stature” than the main, or host, computer; the 

host controls either the satellite itself or the tasks the satellite 

performs. See also remote communications. 

satellite dish n. A parabolic (dish-shaped) reflector and 

antenna that is used for transmitting and receiving signals 

between the ground and earth satellites. Satellite dishes 

are commonly used for receiving television transmissions. 

saturated mode n. The state in which a switching device 

or amplifier is passing the maximum possible current. A 

device is in saturated mode when increasing the control 

signal does not result in output of additional current. 

saturation n. 1. In a switching device or amplifier, the 

fully conducting state. At saturation, the device is passing 

the maximum possible current. The term is most commonly 

used with reference to circuits containing bipolar or 

field-effect transistors. 2. In color graphics and printing, 

the amount of color in a specified hue, often specified as a 

percentage. See also HSB. 

save vb. To write data (typically a file) to a storage 

medium, such as a disk or tape. 

SAX n. Acronym for Simple API for XML. An eventdriven 

application program interface (API) used to interpret 

an XML file. SAX works with an XML parser, providing 

an interface between the parser and an XML 

application. SAX is used as an alternative to the more 

complex object-based Document Object Model (DOM) 

interface. See also DOM. 

scalability n. A measure of how well a computer, service, 

or application can grow to meet increasing performance 

demands. For server clusters, it is the ability to incrementally 

add one or more systems to an existing cluster when 

the overall load of the cluster exceeds its capabilities. See 

also server cluster. 

S

S 

scalable scanner 

scalable adj. Of or relating to the characteristic of a piece 

of hardware or software or a network that makes it possible 

for it to expand—or shrink—to meet future needs and 

circumstances. For example, a scalable network allows the 

network administrator to add many additional nodes without 

the need to redesign the basic system. 

scalable font n. Any font that can be scaled to produce 

characters in varying sizes. Examples of scalable fonts are 

screen fonts in a graphical user interface, stroke fonts (such 

as Courier) and outline fonts common to most PostScript 

printers, TrueType fonts, and the method for screen font 

definition used in Macintosh System 7. In contrast, most 

text-based interfaces and printing devices (such as daisywheel 

printers) offer text in only one size. See also outline 

font, PostScript font, screen font, stroke font, TrueType. 

scalable parallel processing n. Multiprocessing architectures 

in which additional processors and additional 

users can easily be added without excessive increases in 

complexity and loss of performance. Acronym: SPP. 

Scalable Processor Architecture n. See SPARC. 

Scalable Vector Graphics n. See SVG. 

scalar n. A factor, coefficient, or variable consisting of a 

single value (as opposed to a record, an array, or some 

other complex data structure). Compare vector. 

scalar data type n. A data type defined as having a predictable 

and enumerable sequence of values that can be 

compared for greater-than/less-than relationships. Scalar 

data types include integers, characters, user-defined enumerated 

data types, and (in most implementations) Boolean 

values. Some debate exists as to whether or not 

floating-point numbers can be considered a scalar data 

type; although they can be ordered, enumeration is often 

questionable because of rounding and conversion errors. 

See also Boolean expression, enumerated data type, floating-point 

number. 

scalar processor n. A processor designed for high-speed 

computation of scalar values. A scalar value can be represented 

by a single number. 

scalar variable n. See scalar. 

scale1 n. A horizontal or vertical line on a graph that 

shows minimum, maximum, and interval values for the 

data plotted. 

scale2 vb. 1. To enlarge or reduce a graphic display, such 

as a drawing or a proportional character font, by adjusting 

464 

its size proportionally. 2. To alter the way in which values 

are represented so as to bring them into a different range— 

for example, to change linear feet to quarter inches on a 

blueprint drawing of a house. 3. In programming, to determine 

the number of digits occupied by fixed-point or 

floating-point numbers. See also fixed-point notation, 

floating-point number. 

scaling n. In computer graphics, the process of enlarging 

or reducing a graphical image—scaling a font to a desired 

size or scaling a model created with a CAD program, for 

example. See also CAD. 

scan vb. 1. In television and computer display technologies, 

to move an electron beam across the inner surface of 

the screen, one line at a time, to light the phosphors that 

create a displayed image. 2. In facsimile and other optical 

technologies, to move a light-sensitive device across an 

image-bearing surface such as a page of text, converting 

the light and dark areas on the surface to binary digits that 

can be interpreted by a computer. 

scan code n. A code number transmitted to an IBM or 

compatible computer whenever a key is pressed or 

released. Each key on the keyboard has a unique scan 

code. This code is not the same as the ASCII code for the 

letter, number, or symbol shown on the key; it is a special 

identifier for the key itself and is always the same for a 

particular key. When a key is pressed, the scan code is 

transmitted to the computer, where a portion of the ROM 

BIOS (read-only memory basic input/output system) dedicated 

to the keyboard translates the scan code into its 

ASCII equivalent. Because a single key can generate more 

than one character (lowercase a and uppercase A, for 

example), the ROM BIOS also keeps track of the status of 

keys that change the keyboard state, such as the Shift key, 

and takes them into account when translating a scan code. 

Compare key code. 

scan head n. An optical device found in scanners and fax 

machines that moves across the subject being scanned, 

converts light and dark areas to electrical signals, and 

sends those signals to the scanning system for processing. 

scan line n. 1. One of many horizontal lines of a graphics 

display screen, such as a television or raster-scan monitor. 

2. A single row of pixels read by a scanning device. 

scanner n. An optical input device that uses light-sensing 

equipment to capture an image on paper or some other 

subject. The image is translated into a digital signal that 

can then be manipulated by optical character recognition

scan rate scope 

(OCR) software or graphics software. Scanners come in a 

number of types, including flatbed (scan head passes over 

a stationary subject), feed (subject is pulled across a stationary 

scan head), drum (subject is rotated around a stationary 

scan head), and handheld (user passes device over 

a stationary subject). 

scan rate n. See refresh rate. 

scatter diagram n. A graph consisting of points whose 

coordinates represent values of data, often used to illustrate 

a correlation between one or more variables and a test 

group. See the illustration. Also called: point chart, point 

diagram. 

F0Sgn01.eps 

Scatter diagram. 

schedule vb. To program a computer to perform a specified 

action at a specified time and date. 

scheduler n. An operating-system process that starts and 

ends tasks (programs), manages concurrently running processes, 

and allocates system resources. Also called: 

dispatcher. 

scheduling algorithm n. An algorithm that governs the 

proper timing of a sequence of events in an operating system 

or application. For example, an effective motion 

graphics scheduling algorithm would be able to retrieve 

the graphic objects, process them, and display them without 

causing stutter or disruptions. See also algorithm. 

schema n. A description of a database to a database 

management system (DBMS) in the language provided 

by the DBMS. A schema defines aspects of the database, 

such as attributes (fields) and domains and parameters of 

the attributes. 

schematic n. A diagram that shows a circuit’s components 

and the connections between them using lines and a 

465 

set of standard symbols to represent various electronic 

components. See the illustration. 

F0Sgn02.eps 

Schematic. 

Schottky diode n. A type of diode (device that passes 

current in one direction) in which a semiconductor layer 

and a metal layer are brought into contact. It is characterized 

by very fast switching speeds. Also called: hot carrier 

diode, Schottky barrier diode. 

scientific notation n. A floating-point method of representing 

a number, especially a very large or very small 

one, in which numbers are expressed as products consisting 

of a number between 1 and 10 multiplied by a power 

of 10. Scientific notation commonly uses the letter E in 

place of “times 10,” as in 5.0E3, meaning 5.0 times 10 to 

the third power, or 103 . See also floating-point notation. 

sci. newsgroups n. Usenet newsgroups that are part of 

the sci. hierarchy and begin with “sci.” These newsgroups 

are devoted to discussions of scientific research and applications, 

except for computer science, which is discussed 

in the comp. newsgroups. See also newsgroup, traditional 

newsgroup hierarchy, Usenet. Compare comp. newsgroups, 

misc. newsgroups, news. newsgroups, rec. newsgroups, 

soc. newsgroups, talk. newsgroups. 

scissoring n. See clip. 

scope n. 1. In programming, the extent to which an identifier, 

such as a constant, data type, variable, or routine, 

can be referenced within a program. Scope can be global 

+ 

+ 

S

S 

score screen grabber 

or local. Scope can also be affected by redefining identifiers, 

such as by giving the same name to both a global variable 

and a local variable. See also block1 (definition 3), 

global, local. 2. In electronics, slang for oscilloscope. See 

also oscilloscope. 

score n. When referring to a spelling checker, a score is 

a number that indicates how much a replacement word 

differs from the original misspelled word. A low score 

indicates that the misspelled word was changed slightly, 

while a high score indicates that the word was changed a 

great deal. 

SCP n. Acronym for Simple Control Protocol. A lightweight 

peer-to-peer networking protocol for devices that 

have limited processing and memory resources and operate 

over limited-bandwidth networks such as powerline 

carrier (PLC) systems. Products using SCP can interoperate 

with products using the Universal Plug and Play 

(UPnP), CEBus, and Home Plug & Play (HPnP) standards. 

Developed by a team of companies including 

Microsoft and General Electric, SCP enables the interaction 

between UPnP devices, devices based on Internet Protocol 

(IP), and non-IP-capable devices such as 

coffeemakers and alarm clocks. SCP, which was designed 

as a stand-alone protocol, can be used in residential, commercial, 

industrial, and utility applications. See also UPnP 

networking. 

SCR n. See silicon-controlled rectifier. 

scrambler n. A device or program that reorders a signal 

sequence in order to render it indecipherable. See also 

encryption. 

scrap n. An application or system file maintained for 

storing data that has been marked for movement, copying, 

or deletion. See also clipboard (definition 1). 

scrapbook n. 1. A file in which a series of text and graphical 

images can be saved for subsequent use. 2. A Macintosh 

system file that can hold a number of text and 

graphical images for later use. Compare clipboard (definition 

1). 

scratch1 n. A memory region or file used by a program 

or operating system to hold work in progress temporarily. 

Created and maintained usually without the end user’s 

knowledge, the scratch is needed only until the current 

session is terminated, at which time the data is saved or 

discarded. Also called: scratch file. See also temporary 

file. Compare scrap. 

466 

scratch2 vb. To erase or discard data. 

scratch file n. See scratch1 . 

scratchpad n. 1. A temporary storage area used by a program 

or operating system for calculations, data, and other 

work in progress. See also scratch1 , temporary file. 2. A 

high-speed memory circuit used to hold small items of 

data for rapid retrieval. See also cache. 

scratchpad memory n. See cache. 

scratchpad RAM n. Memory used by a central processing 

unit (CPU) for temporary data storage. Also called: 

scratchpad, scratchpad memory. See also central processing 

unit, register. 

scream vb. To operate at very high speed. For example, a 

modem that can transfer data several times faster than the 

one it replaced or a computer with a very high clock speed 

could be said to “scream.” 

screamer n. Slang for a piece of computer equipment 

that operates at a very high speed. Generally, “screamers” 

are the newest versions of a particular piece of equipment, 

such as a PC with the latest, fastest microprocessor, or are 

comprised of multiple components that increase the operating 

speed over standard models, such as a PC that has a 

huge amount of RAM (Random Access Memory), a highperformance 

video board, a superfast CD-ROM drive, and 

the latest microprocessor. However, as technology evolves 

and new, faster devices are introduced, yesterday’s 

screamer rapidly becomes today’s snail. 

screen angle n. The angle at which the dots in a halftone 

screen are printed. A correct angle will minimize blur and 

other undesirable effects, such as moiré patterns. See also 

color separation (definition 1), halftone, moiré. 

screen buffer n. See video buffer. 

screen dump n. A duplicate of a screen image; essentially, 

a snapshot of the screen that is either sent to a 

printer or saved as a file. 

screen flicker n. See flicker. 

screen font n. A typeface designed for display on a computer 

monitor screen. Screen fonts often have accompanying 

PostScript fonts for printing to PostScript-compatible 

printers. See also derived font, intrinsic font. Compare 

PostScript font, printer font. 

screen frequency n. See halftone. 

screen grabber n. See grabber (definition 3).

screen name scroll box 

screen name n. A name under which an America Online 

user is known. The screen name may be the same as the 

user’s real name. See also America Online. 

screen phone n. A type of Internet appliance combining 

a telephone with an LCD display screen, a digital fax 

modem, and a computer keyboard, with ports for a mouse, 

printer, and other peripheral devices. Screen phones can 

be used as regular telephones for voice communications 

and can also be used as terminals to gain access to the 

Internet and other online services. 

screen pitch n. A measurement of a computer monitor’s 

screen density, representing the distance between phosphors 

on the display. The lower the number, the more detail can be 

displayed clearly. For example, a .28-dot-pitch screen has 

better resolution than one with .32. See the illustration. See 

also phosphor. 

.28-mm screen pitch 

F0Sgn03.eps 

Screen pitch. 

screen saver n. A utility that causes a monitor to blank 

out or display a certain image after a specified amount of 

time passes without the keyboard being touched or the 

mouse being moved. Touching a key or moving the mouse 

deactivates the screen saver. Screen savers were originally 

used to prevent images from becoming permanently 

etched on a monitor’s screen. Although modern monitors 

are not susceptible to this problem, screen savers remain 

popular for their decorative and entertainment value. See 

the illustration. 

F0Sgn04.eps 

Screen saver. 

screen shot n. An image that shows all or part of a computer 

display. 

467 

ScreenTips n. Notes that appear on the screen to provide 

information about a toolbar button, tracked change, or 

comment or to display a footnote or an endnote. Screen- 

Tips also display the text that will appear if you choose to 

insert a date or AutoText entry. 

script n. A program consisting of a set of instructions to 

an application or a utility program. The instructions usually 

use the rules and syntax of the application or utility. 

On the World Wide Web, scripts are commonly used to 

customize or add interactivity to Web pages. See also 

macro. 

scripting language n. A simple programming language 

designed to perform special or limited tasks, sometimes 

associated with a particular application or function. An 

example of a scripting language is Perl. See also Perl, script. 

script kiddie n. A would-be hacker who does not have 

the technical skills or knowledge needed for traditional 

hacking methods; one who relies on easy-to-use kiddie 

scripts. See also hacker, kiddie script. 

scriptlet n. A reusable Web page based on the features of 

Dynamic HTML (DHTML) that can be created with 

HTML text and a scripting language and then inserted as a 

control in another Web page or in an application. Developed 

by Microsoft and introduced in Internet Explorer version 4, 

scriptlets are implemented as .htm files that give developers 

a relatively easy, object-based means of creating components 

that reflect the Web metaphor and that can be used to 

add interactivity and functionality—for example, animation, 

color changes, pop-up menus, or drag-and-drop capability—to 

Web pages without requiring repeated trips to the 

server. Also called: Microsoft Scripting Component. See 

also dynamic HTML. Compare applet. 

scroll vb. To move a document or other data in a window 

in order to view a particular portion of the document. 

Scrolling may be controlled by the mouse, arrow keys, or 

other keys on the keyboard. See also scroll bar. 

scroll arrow n. See scroll bar. 

scroll bar n. In some graphical user interfaces, a vertical or 

horizontal bar at the side or bottom of a display area that 

can be used with a mouse for moving around in that area. 

Scroll bars often have four active areas: two scroll arrows 

for moving line by line, a sliding scroll box for moving to 

an arbitrary location in the display area, and gray areas for 

moving in increments of one window at a time. 

scroll box n. See elevator. 

S

S 

Scroll Lock key SDM 

Scroll Lock key n. On the IBM PC/XT and AT and compatible 

keyboards, a key on the top row of the numeric 

keypad that controls the effect of the cursor control keys 

and sometimes prevents the screen from scrolling. On the 

enhanced and Macintosh keyboards, this key is to the right 

of the function keys on the top row. Many modern applications 

ignore the Scroll Lock setting. 

scroll wheel n. A thumbwheel on a mouse that, when 

turned, enables the user to scroll or zoom without clicking 

the scroll bar or using the keyboard. Depending on the 

mouse, a scroll wheel can also double as a third mouse 

button. See also scroll bar. 

SCSI n. Acronym for Small Computer System Interface, 

a standard high-speed parallel interface defined by the 

X3T9.2 committee of the American National Standards 

Institute (ANSI). A SCSI (pronounced “scuzzy”) interface 

is used to connect microcomputers to SCSI peripheral 

devices, such as many hard disks and printers, and to other 

computers and local area networks. Also called: SCSI-1, 

SCSI I. Compare ESDI, IDE. 

SCSI-1 n. See SCSI. 

SCSI-2 n. An enhanced ANSI standard for SCSI (Small 

Computer System Interface) buses. Compared with the 

original SCSI standard (now called SCSI-1), which can 

transfer data 8 bits at a time at up to 5 MB per second, 

SCSI-2 offers increased data width, increased speed, or 

both. A SCSI-2 disk drive or host adapter can work with 

SCSI-1 equipment at the older equipment’s maximum 

speed. Also called: SCSI II. See also Fast SCSI, Fast/Wide 

SCSI, SCSI, Wide SCSI. Compare UltraSCSI. 

SCSI bus n. A parallel bus that carries data and control 

signals from SCSI devices to a SCSI controller. See also 

bus, controller, SCSI device. 

SCSI chain n. A set of devices on a SCSI bus. Each 

device (except the host adapter and the last device) is connected 

to two other devices by two cables, forming a daisy 

chain. See also daisy chain, SCSI. 

SCSI connector n. A cable connector used to connect a 

SCSI device to a SCSI bus. See the illustration. See also 

bus, connector (definition 1), SCSI device. 

468 

F0Sgn05.eps 

SCSI connector. 

SCSI device n. A peripheral device that uses the SCSI 

standard to exchange data and control signals with a computer’s 

CPU. See also peripheral, SCSI. 

SCSI I n. See SCSI. 

SCSI II n. See SCSI-2. 

SCSI ID n. The unique identity of a SCSI device. Each 

device connected to a SCSI bus must have a different 

SCSI ID. A maximum of eight SCSI IDs can be used on 

the same SCSI bus. See also bus, SCSI device. 

SCSI network n. A set of devices on a SCSI bus, which 

acts like a local area network. See also SCSI. 

SCSI port n. 1. A SCSI host adapter within a computer, 

which provides a logical connection between the computer 

and all of the devices on the SCSI bus. See also 

SCSI. 2. A connector on a device for a SCSI bus cable. 

See also SCSI. 

SDH n. See Synchronous Digital Hierarchy. 

SDK n. Acronym for software development kit. See developer’s 

toolkit. 

SDLC n. Acronym for Synchronous Data Link Control, 

the data transmission protocol most widely used by networks 

conforming to IBM’s Systems Network Architecture 

(SNA). SDLC is similar to the HDLC (High-level 

Data Link Control) protocol developed by the International 

Organization for Standardization (ISO). See also HDLC. 

SDM n. See space-division multiplexing.

SDMI second normal form 

SDMI n. See Secure Digital Music Initiative. 

SDRAM n. Acronym for synchronous DRAM. A form of 

dynamic random access memory (DRAM) that can run at 

higher clock speeds than conventional DRAM by employing 

a bursting technique in which the DRAM predicts the 

address of the next memory location to be accessed. See 

also dynamic RAM. 

SDSL n. Acronym for symmetric (or single-line) digital 

subscriber line, a digital telecommunications technology 

that is a variation of HDSL. SDSL uses one pair of copper 

wires rather than two pairs of wires and transmits at 1.544 

Mbps. Compare ADSL. 

.sea n. A file extension for a self-extracting Macintosh 

archive compressed with StuffIt. See also self-extracting 

file. 

seamless integration n. The favorable result that occurs 

when a new hardware component or program blends 

smoothly into the overall operation of the system. It is 

usually the result of thoughtful design and programming. 

search1 n. The process of seeking a particular file or specific 

data. A search is carried out by a program through 

comparison or calculation to determine whether a match 

to some pattern exists or whether some other criteria have 

been met. See also binary search, hash search, linear 

search, search and replace, wildcard character. 

search2 vb. 1. To look for the location of a file. 2. To seek 

specific data within a file or data structure. See also replace. 

search algorithm n. An algorithm designed to locate a 

certain element, called the target, in a data structure. See 

also algorithm, binary search, hash search, linear search. 

search and replace n. A common process in applications 

such as word processors in which the user specifies 

two strings of characters. The process finds instances of 

the first string and replaces them with the second string. 

search criteria n. The terms or conditions that a search 

engine uses to find items in a database. See also search 

engine. 

search engine n. 1. A program that searches for keywords 

in documents or in a database. 2. On the Internet, a 

program that searches for keywords in files and documents 

found on the World Wide Web, newsgroups, 

Gopher menus, and FTP archives. Some search engines 

are used for a single Internet site, such as a dedicated 

search engine for a Web site. Others search across many 

sites, using such agents as spiders to gather lists of avail- 

469 

able files and documents and store these lists in databases 

that users can search by keyword. Examples of the latter type 

of search engine are Lycos and Excite. Most search engines 

reside on a server. See also agent (definition 2), FTP, Gopher 

or gopher, newsgroup, spider, World Wide Web. 

search key n. 1. The particular field (or column) of the 

records to be searched in a database. See also primary key, 

secondary key. 2. The value that is to be searched for in a 

document or any collection of data. 

search path n. The route followed by an operating system 

to find the location of a stored file. The search path 

begins with a drive or volume (disk) designator or a network 

share, continues through a chain of directories and 

subdirectories, if any, and ends with the file name. 

C:\books\diction\start.exe is an example of a search path. 

Also called: access path. 

search string n. The string of characters to be matched in 

a search—typically (but not necessarily) a text string. 

seat1 n. One workstation or computer, in the context of 

software licensing on a per-seat basis. See also license 

agreement, workstation (definition 1). 

seat2 vb. To insert a piece of hardware fully and position 

it correctly in a computer or affiliated equipment, as in 

seating a single inline memory module (SIMM) in its 

socket. 

secondary channel n. A transmission channel in a communications 

system that carries testing and diagnostic 

information rather than actual data. Compare primary 

channel. 

secondary key n. A field that is to be sorted or searched 

within a subset of the records having identical primary key 

values. See also alternate key (definition 1), candidate key. 

Compare primary key. 

secondary service provider n. An Internet service provider 

that provides a Web presence but not direct connectivity. 

See also ISP. 

secondary storage n. Any data storage medium other 

than a computer’s random access memory (RAM)— 

typically tape or disk. Compare primary storage. 

Second Generation n. See 2G. 

second-level domain n. The level immediately beneath 

the top-level domain in the Internet’s DNS hierarchy. See 

also domain (definition 3). 

second normal form n. See normal form (definition 1). 

S

S 

secret channel security log 

secret channel n. See private channel. 

section n. A length of fiberoptic cable in a SONET network. 

See also line, path. 

sector n. A portion of the data storage area on a disk. A 

disk is divided into sides (top and bottom), tracks (rings on 

each surface), and sectors (sections of each ring). Sectors 

are the smallest physical storage units on a disk and are of 

fixed size; typically, they are capable of holding 512 bytes 

of information apiece. See the illustration. 

F0Sgn06.eps 

Sector. 

Sector 

sector interleave n. See interleave. 

sector map n. 1. A map that indicates the unusable sectors 

on a disk. 2. A table used to translate the sector numbers 

that are requested by the operating system into 

physical sector numbers. The sector map represents a different 

method of performing sector interleaving. When a 

sector map is used, the sectors are formatted on the disk in 

sequential order. The mapping enables the system to read 

sectors in a nonsequential order. For example, using a 3to-1 

sector interleaving map, a system request for sectors 1 

through 4 will result in the disk driver reading physical 

sectors 1, 4, 7, and 10. See also interleave. 

secure channel n. A communications link that has been 

protected against unauthorized access, operation, or use by 

means of isolation from the public network, encryption, or 

other forms of control. See also encryption. 

Secure Digital Music Initiative n. A coalition of companies 

from the recording, electronics, and information 

technology industries founded in February 1999 for the 

purpose of developing an open standard for the secure distribution 

of music in digital form. The Secure Digital 

Music Initiative specification is designed to provide consumers 

with flexibility and convenient access to electroni- 

470 

cally distributed music (that is, over the Internet) while 

also protecting the rights of artists. Acronym: SDMI. See 

also MP3, Windows Media Technologies. 

Secure Electronics Transactions protocol n. Protocol 

for conducting secure transactions over the Internet, the 

result of a joint effort by GTE, IBM, MasterCard, 

Microsoft, Netscape, SAIC, Terisa Systems, VeriSign, and 

Visa. Acronym: SET. 

Secure Hash Algorithm n. See SHA. 

Secure HTTP n. See S-HTTP, HTTPS. 

Secure Hypertext Transfer Protocol n. See S-HTTP. 

Secure/Multipurpose Internet Mail Extensions n. 

See S/MIME. 

Secure Password Authentication n. A feature that 

allows a server to confirm the identity of the person logging 

on. Acronym: SPA. 

secure site n. A Web site having the capability of providing 

secure transactions, ensuring that credit card numbers 

and other personal information will not be accessible 

to unauthorized parties. 

Secure Sockets Layer n. See SSL. 

Secure Transaction Technology n. The use of the SSL 

(Secure Sockets Layer), S-HTTP (Secure HTTP), or both 

in online transactions, such as form transmission or credit 

card purchases. Acronym: STT. See also S-HTTP, SSL. 

secure wide area network n. A set of computers that 

communicate over a public network, such as the Internet, 

but use security measures, such as encryption, authentication, 

and authorization, to prevent their communications 

from being intercepted and understood by unauthorized 

users. Acronym: S/WAN. See also authentication, authorization, 

encryption, virtual private network (definition 1). 

security n. The technologies used to make a service resistant 

to unauthorized access to the data that it holds or for 

which it is responsible. A major focus of computer security, 

especially on systems that are accessed by many people 

or through communications lines, is the prevention of 

system access by unauthorized individuals. 

security kernel n. An operating-system kernel that is 

protected from unauthorized use. See also kernel. 

security log n. A log, generated by a firewall or other 

security device, that lists events that could affect security, 

such as access attempts or commands, and the names of 

the users involved. See also firewall, log (definition 1).

seed self-extracting file 

seed n. A starting value used in generating a sequence of 

random or pseudorandom numbers. See also random number 

generation. 

seek n. The process of moving the read/write head in a 

disk drive to the proper site, typically for a read or write 

operation. 

seek time n. The time required to move a disk drive’s 

read/write head to a specific location on a disk. See also 

access time (definition 2). 

segment n. A section of a program that, when compiled, 

occupies a contiguous address space and that is usually 

position independent; that is, it can be loaded anywhere in 

memory. With Intel-based microcomputers, a native-mode 

segment is a logical reference to a 64-KB contiguous portion 

of RAM in which the individual bytes are accessed by 

means of an offset value. Collectively, the segment:offset 

values reference a single physical location in RAM. See 

also overlay1 (definition 1), real mode, segmentation. 

segmentation n. The act of breaking up a program into 

several sections, or segments. See also segment. 

segmented addressing architecture n. A memoryaccess 

technique typified by Intel 80x86 processors. 

Memory is divided into 64-KB segments in this architecture 

for addressing locations under the 16-bit address 

scheme; 32-bit schemes can address memory in segments 

as large as 4 GB. Also called: segmented instruction 

addressing, segmented memory architecture. Compare linear 

addressing architecture. 

segmented address space n. An address space that is 

logically divided into chunks called segments. To address 

a given location, a program must specify both a segment 

and an offset within that segment. (The offset is a value 

that references a specific point within the segment, based 

on the beginning of the segment.) Because segments may 

overlap, addresses are not unique; there are many logical 

ways to access a given physical location. The Intel 80x86 

real-mode architecture is segmented; most other microprocessor 

architectures are flat. See also segment. Compare 

flat address space. 

segmented instruction addressing n. See segmented 


segmented memory architecture n. See segmented 


471 

select vb. 1. In general computer use, to specify a block 

of data or text on screen by highlighting it or otherwise 

marking it with the intent of performing some operation 

on it. 2. In database management, to choose records 

according to a specified set of criteria. See also sort. 3. In 

information processing, to choose from a number of 

options or alternatives, such as subroutines or input/output 

channels. 

selected cell n. See active cell. 

selection n. 1. In applications, the highlighted portion of 

an on-screen document. 2. In communications, the initial 

contact made between a computer and a remote station 

receiving a message. 3. In programming, a conditional 

branch. See also conditional branch. 

selective calling n. The capability of a station on a communications 

line to designate the station that is to receive a 

transmission. 

selector channel n. An input/output data transfer line 

used by one high-speed device at a time. 

selector pen n. See light pen. 

select query n. A query that asks a question about the 

data stored in your tables and returns a result set in the 

form of a datasheet, all without changing the data. 

self-adapting adj. The ability of systems, devices, or processes 

to adjust their operational behavior to environmental 

conditions. 

self-checking digit n. A digit, appended to a number 

during its encoding, whose function is to confirm the 

accuracy of the encoding. See also checksum, parity bit. 

self-clocking n. A process in which timing signals are 

inserted into a data stream rather than being provided by 

an external source, such as in phase encoding. 

self-documenting code n. Program source code that, 

through its use of a high-level language and descriptive 

identifiers, can be understood by other programmers without 

the need for additional comments. 

self-extracting archive n. See self-extracting file. 

self-extracting file n. An executable program file that 

contains one or more compressed text or data files. When 

a user runs the program, it uncompresses the compressed 

files and stores them on the user’s hard drive. See the 

illustration. 

S

S 

self-modifying code sensor glove 

logvu.exe 

(self-extracting file) 

F0Sgn07.eps 

Self-extracting file. 

logview.exe 

readme.txt 

license.txt 

self-modifying code n. Program code, usually object 

code generated by a compiler or an assembler, that modifies 

itself during instruction by writing new operation 

codes, addresses, or data values over existing instructions. 

See also pure procedure. 

self-monitoring analysis and reporting technology 

system n. See SMART system. 

self-organizing map n. See SOM (definition 2). 

self-test n. A set of one or more diagnostic tests that a 

computer or peripheral device (such as a printer) performs 

on itself. See also power-on self test. 

self-validating code n. Program code that can test itself 

to verify that it behaves correctly, usually by feeding itself 

a set of standard input values and testing the results 

against a set of expected output values. 

semantic error n. An error in meaning; a statement in a 

program that is syntactically correct (legal) but functionally 

incorrect. See also logic, semantics (definition 1), 

syntax. 

semantics n. 1. In programming, the relationship 

between words or symbols and their intended meanings. 

Programming languages are subject to certain semantic 

rules; thus, a program statement can be syntactically correct 

but semantically incorrect; that is, a statement can be 

written in an acceptable form and still convey the wrong 

meaning. See the illustration. See also syntax. 2. In artificial-intelligence 

research, the capacity of a network to represent 

relationships among objects, ideas, or situations in a 

humanlike way. Compare syntax. 

472 

CANARY is a BIRD 

has 

FEATHERS 

F0Sgn08.eps 

Semantics. 

semaphore n. In programming, a signal—a flag variable—used 

to govern access to shared system resources. A 

semaphore indicates to other potential users that a file or 

other resource is in use and prevents access by more than 

one user. See also flag (definition 1). 

Semicon n. Short for Semiconductors Equipment and 

Material International Conference. A series of international 

conferences sponsored by the Semiconductors 

Equipment and Material International (SEMI), a trade 

group for the international semiconductor industry. The 

conference provides members with up-to-date information 

on issues affecting the semiconductor industry and provides 

SEMI members with a forum for showcasing products 

and services. 

semiconductor n. A substance, commonly silicon or germanium, 

whose ability to conduct electricity falls between 

that of a conductor and that of a nonconductor (insulator). 

The term is used loosely to refer to electronic components 

made from semiconductor materials. 

send vb. To transmit a message or file through a communications 

channel. 

sendmail n. A popular open-source UNIX-based implementation 

of the Simple Mail Transfer Protocol (SMTP) 

for delivering e-mail. Written in 1981 by Eric Allman at 

the University of California at Berkeley, sendmail was the 

first Internet message transfer agent (MTA). 

send statement n. In SLIP and PPP scripting languages, 

a statement that tells the program that dials an Internet service 

provider’s number (a dialer program) to send certain 

characters. See also ISP, PPP, scripting language, SLIP. 

sensor n. A device that detects or measures something by 

converting nonelectrical energy to electrical energy. A 

photocell, for example, detects or measures light by converting 

it to electrical energy. See also transducer. 

sensor glove n. A hand-worn computer input device for 

virtual-reality environments. The glove translates finger 

movements by the user to commands for manipulating 

objects in the environment. Also called: data glove. See 

also virtual reality.

SEPP serial port 

SEPP n. Acronym for Software Engineering for Parallel 

Processing. A project of nine European universities and 

research institutions to develop tools for the development 

of parallel application programs for distributed memory 

multiprocessors. 

sequence n. An ordered arrangement, as in a set of numbers, 

such as the Fibonacci sequence. See also Fibonacci 

numbers. 

sequence check n. A process that verifies that data or 

records conform to a particular order. Compare completeness 

check, consistency check, duplication check. 

Sequenced Packet Exchange n. See SPX (definition 1). 

sequential access n. A method of storing or retrieving 

information that requires the program to start reading at 

the beginning and continue until it finds the desired data. 

Sequential access is best used for files in which each piece 

of information is related to the information that comes 

before it, such as mailing list files and word processing 

documents. Also called: serial access. See also indexed 

sequential access method. Compare random access. 

sequential algorithm n. An algorithm in which each 

step must occur in a particular order. See also algorithm. 

Compare parallel algorithm. 

sequential execution n. The act of executing routines 

or programs in a linear sequence. Compare concurrent 

execution. 

sequential logic element n. A logic circuit element that 

has at least one input and one output and in which the output 

signal depends on the present and past states of the 

input signal or signals. 

sequential processing n. 1. The processing of items of 

information in the order in which they are stored or input. 

2. The execution of one instruction, routine, or task followed 

by the execution of the next in line. Compare multiprocessing, 

parallel processing, pipelining (definition 1). 

sequential search n. See linear search. 

serial adj. One by one. For example, in serial transmission, 

information is transferred one bit at a time; a serial 

computer has only one arithmetic logic unit, which must 

execute the whole program one step at a time. Compare 

parallel (definition 3). 

serial access n. See sequential access. 

serial adder n. A circuit that adds two numbers one bit 

position (one digit place) at a time. 

473 

serial communication n. The exchange of information 

between computers or between computers and peripheral 

devices one bit at a time over a single channel. Serial communications 

can be synchronous or asynchronous. Both 

sender and receiver must use the same baud rate, parity, 

and control information. See also baud rate, parity, start 

bit, stop bit. 

Serial Infrared n. A system developed by Hewlett-Packard 

for transmitting data between two devices up to 1 

meter apart using an infrared light beam. Infrared ports on 

the receiving and the sending devices must be aligned. 

Generally, Serial Infrared is used with laptops and many 

notebook computers, as well as with peripherals such as 

printers. Acronym: SIR. See also infrared port. 

serial interface n. A data transmission scheme in which 

data and control bits are sent sequentially over a single 

channel. In reference to a serial input/output connection, 

the term usually implies the use of an RS-232 or RS-422 

interface. See also RS-232-C standard, RS-422/423/449. 

Compare parallel interface. 

serialize vb. To change from parallel transmission (byte 

by byte) to serial transmission (bit by bit). Compare 

deserialize. 

SerialKey device n. Enables you to attach an alternative 

input device (also called an augmentative communication 

device) to your computer’s serial port. This feature is 

designed for people who are unable to use the computer’s 

standard keyboard and mouse. 

SerialKeys n. A feature of Windows 9x, Windows NT, 

Windows 2000, and Windows XP that, in conjunction 

with a communications aid interface device, allows keystrokes 

and mouse controls to be accepted through a computer’s 

serial port. 

Serial Line Internet Protocol n. See SLIP. 

serial mouse n. A pointing device that attaches to the 

computer through a standard serial port. See also mouse. 

Compare bus mouse. 

serial port n. An input/output location (channel) that 

sends and receives data to and from a computer’s central 

processing unit or a communications device one bit at a 

time. Serial ports are used for serial data communication 

and as interfaces with some peripheral devices, such as 

mice and printers. 

S

S 

serial port adapter Server Message Block 

serial port adapter n. An interface card or device that 

either provides a serial port or converts a serial port to 

another use. See also adapter, serial port. 

serial printer n. A printer connected to the computer via 

a serial interface (commonly RS-232-C or compatible). 

Connectors for this type of printer vary widely, which is 

one reason they are less popular than parallel printers 

among those who use IBM and IBM-compatible PCs. 

Serial printers are standard for Apple computers. See also 

DB connector, serial, serial transmission. Compare parallel 

printer. 

serial processing n. See sequential processing (definition 

2). 

Serial Storage Architecture n. See SSA. 

serial transmission n. The transfer of discrete signals 

one after another. In communications and data transfer, 

serial transmission involves sending information over a 

single line one bit at a time, as in modem-to-modem connections. 

Compare parallel transmission. 

series circuit n. A circuit in which two or more components 

are linked in series. All the current passes through 

each component in a series circuit, but the voltage is 

divided among the components. See the illustration. Compare 

parallel circuit. 

F0Sgn09.eps 

Series circuit. 

serif 1 adj. Marked by the use of serifs. For example, 

Goudy is a serif typeface, whereas Helvetica is a sans serif 

typeface. See the illustration. See also serif 2 . Compare 

sans serif. 

Serifs 

F0Sgn10.eps 

Serif. A serif typeface (top) and a sans serif typeface (bottom). 

serif 2 n. Any of the short lines or ornaments at the ends of 

the strokes that form a typeface character. 

474 

server n. 1. On a local area network (LAN), a computer 

running administrative software that controls access to the 

network and its resources, such as printers and disk drives, 

and provides resources to computers functioning as workstations 

on the network. 2. On the Internet or other network, 

a computer or program that responds to commands 

from a client. For example, a file server may contain an 

archive of data or program files; when a client submits a 

request for a file, the server transfers a copy of the file to 

the client. See also application server (definitions 1 and 2), 

client/server architecture. Compare client (definition 3). 

server appliance n. A device designed to deliver one or 

more specific network services in a single turnkey package 

that includes both hardware and software. All necessary 

programs are preinstalled on a server appliance, 

which has minimal, simplified options and controls. 

Server appliances can be used to complement or replace 

traditional servers on a network and can provide such services 

as file and printer sharing and Internet connectivity. 

Also called: appliance. See also information appliance. 

server-based application n. A program that is shared 

over a network. The program is stored on the network 

server and can be used at more than one client machine at 

a time. 

server cluster n. A group of independent computer systems, 

known as nodes, working together as a single system 

to ensure that mission-critical applications and resources 

remain available to clients. A server cluster is the type of 

cluster that Cluster service implements. See also cluster. 

server control n. See ASP.NET server control. 

server error n. A failure to complete a request for information 

through HTTP that results from an error at the 

server rather than an error by the client or the user. Server 

errors are indicated by HTTP status codes beginning with 

5. See also HTTP, HTTP status codes. 

server farm n. A centralized grouping of network servers 

maintained by an enterprise or, often, an Internet service 

provider (ISP). A server farm provides a network with 

load balancing, scalability, and fault tolerance. Individual 

servers may be connected in such a way that they appear 

to represent a single resource. 

serverlet n. See servlet. 

Server Message Block n. See SMB.

server push-pull session bean 

server push-pull n. A combination of Web client/server 

techniques individually called “server push” and “client 

pull.” In server push, the server loads data to the client, but 

the data connection stays open. This allows the server to 

continue sending data to the browser as necessary. In client 

pull, the server loads data to the client, but the data 

connection does not stay open. The server sends an HTML 

directive to the browser telling it to reopen the connection 

after a certain interval to get more data or possibly to open 

a new URL. See the illustration. See also HTML, server 

(definition 2), URL. 

Server push Client pull 

doc1 

doc2 

Server Client 

F0Sgn11.eps 

Server push-pull. 

Send doc1 

doc1 

Send doc2 

doc2 

Server 

Client 

server-side include n. A mechanism for including 

dynamic text in World Wide Web documents. Server-side 

includes are special command codes that are recognized 

and interpreted by the server; their output is placed in the 

document body before the document is sent to the 

browser. Server-side includes can be used, for example, to 

include the date/time stamp in the text of the file. Acronym: 

SSI. See also server (definition 2). 

service n. 1. A customer-based or user-oriented function, 

such as technical support or network provision. 2. In reference 

to programming and software, a program or routine 

that provides support to other programs, particularly at a 

low (close to the hardware) level. 3. In networking, specialized, 

software-based functionality provided by network 

servers—for example, directory services that 

provide the network equivalent of “phone books” needed 

for locating users and resources. See also utility. 

Service Advertising Protocol n. A method used by a 

service-providing node in a network (such as a file server 

or application server) to notify other nodes on the network 

that it is available for access. When a server boots, 

it uses the protocol to advertise its service; when the 

same server goes off line, it uses the protocol to 

announce that it is no longer available. Acronym: SAP. 

See also server (definition 1). 

475 

service bureau n. 1. A company that provides various 

services related to publishing, such as prepress production, 

desktop publishing, typesetting, imagesetting, and 

optical scanning of graphics. 2. An organization that provides 

data processing services and access to software 

packages for a fee. 

service provider n. See ISP. 

servlet or servelet n. A small Java program that runs on 

a server. The term is a companion to applet, a Java program 

that usually runs on the client. Servlets perform 

lightweight Web services, such as redirecting a Web user 

from an outdated address to the correct page—tasks traditionally 

handled by CGI (Common Gateway Interface) 

applications. Because servlets are automatically threaded 

and highly responsive, they execute quickly, thereby 

reducing system overhead. Also called: serverlet. See also 

applet, CGI. 

servlet container n. In Sun Microsystems’s J2EE network 

platform, a container that decodes requests, formats 

responses, and provides the network services over which 

requests and responses are sent. All servlet containers 

must support HTTP as a protocol for requests and 

responses, but they may also support additional requestresponse 

protocols such as HTTPS. See also container, 

HTTP, HTTPS, J2EE. 

servo n. The part of a servomechanism, controlled by the 

servomechanism’s feedback circuit, that produces the final 

mechanical output. Also called: servomotor. See also servomechanism. 

servomechanism n. A control system in which the final 

output is mechanical movement. A servomechanism uses 

feedback to control the position, velocity, or acceleration 

of a mechanical component. Also called: servo system. 

servomotor n. See servo. 

servo system n. See servomechanism. 

session n. 1. The time during which a program is running. 

In most interactive programs, a session is the time 

during which the program accepts input and processes 

information. 2. In communications, the time during which 

two computers maintain a connection. 3. A specific protocol 

layer in the ISO/OSI reference model that manages 

communication between remote users or processes. See 

also ISO/OSI reference model, session layer. 

session bean n. In the Java programming language and 

J2EE network platform, an enterprise bean that is created 

S

S 

session layer SGML 

by a client and usually exists only for the duration of a single 

client/server session. It performs operations, such as 

calculations or accessing a database, for the client. While 

a session bean may be transactional, it is not recoverable 

should a system crash occur. Session bean objects can 

either be stateless or can maintain conversational state 

across methods and transactions. If a session bean maintains 

state, the Enterprise JavaBean (EJB) container manages 

this state if the object must be removed from 

memory. However, the session bean object itself must 

manage its own persistent data. See also EJB, stateless. 

session layer n. The fifth of seven layers in the ISO/OSI 

reference model. The session layer handles the details that 

must be agreed on by the two communicating devices. See 

the illustration. See also ISO/OSI reference model. 

ISO/OSI Layer 

Application 


Presentation 

Session 

Transport 

Network 

Data-link 

Physical 

F0Sgn12.eps 

Session layer. 

ISO/OSI MODEL 

Focus 




conversion 









set1 n. In printing and display, a group of related characters, 

such as a character set. See also character set. 

set2 vb. 1. To change the value of a bit to 1. 2. To establish 

a particular condition, such as setting tab stops, setting 

a counter to 0, or setting a breakpoint. See also breakpoint. 

SET protocol n. See Secure Electronics Transactions 

protocol. 

settling time n. The time required for a disk drive’s read/ 

write head to stabilize over a new location on the disk after 

being moved. 

set-top box n. A device that converts a cable TV signal to 

an input signal to the TV set. Set-top boxes can be used to 

476 

access the World Wide Web and are a type of information 

appliance. See also information appliance. 

setup n. 1. A computer along with all its devices. 2. The 

procedures involved in preparing a software program or 

application to operate within a computer. 

setup program n. 1. A built-in BIOS program for reconfiguring 

system parameters to accommodate a new disk 

drive. See also BIOS. 2. See installation program. 

setup string n. See control code. 

setup wizard n. In Windows, a utility that asks users a 

structured series of questions and gives them options to 

aid the process of installing a new program. 

seven-segment display n. A light-emitting diode (LED) 

display or liquid crystal display (LCD) that can show any 

of the 10 decimal digits. The seven segments are the seven 

bars that form a numeral 8 as in a calculator display. 

sex changer n. See gender changer. 

sfx n. A computer language used to generate digital audio 

effects and synthesizer instrument audio. It is a superset of 

the MPEG-4 standard SAOL audio compiler language. 

Sfx provides professional-quality audio synthesis, realtime 

MIDI and audio generation, and fully customizable 

instruments and effects. Because the sfx compiler is a C++ 

front-end compiler, code is converted to C++ and then 

compiled into executable orchestras that are used to generate 

real-time audio. As a result, the current release of sfx 

requires that Microsoft Visual C++ be installed on the system 

on which sfx is running. See also C++, compiler, 

MIDI, MPEG-4, SAOL, Visual C++. 

.sgm n. The MS-DOS/Windows 3.x file extension that 

identifies files encoded in Standard Generalized Markup 

Language (SGML). Because MS-DOS and Windows 3.x 

cannot recognize file extensions longer than three letters, 

the .sgml extension is truncated to three letters in those 

environments. See also SGML. 

.sgml n. The file extension that identifies files encoded in 

Standard Generalized Markup Language. See also SGML. 

SGML n. Acronym for Standard Generalized Markup 

Language. An information management standard adopted 

by the International Organization for Standardization 

(ISO) in 1986 as a means of providing platform- and 

application-independent documents that retain formatting, 

indexing, and linked information. SGML provides a grammarlike 

mechanism for users to define the structure of

SGRAM sheet 

their documents and the tags they will use to denote the 

structure in individual documents. See also ISO. 

SGRAM n. See synchronous graphics RAM. 

sh n. See Bourne shell. 

SHA n. Acronym for Secure Hash Algorithm. A technique 

that computes a 160-bit condensed representation of 

a message or data file, called a message digest. The SHA 

is used by the sender and the receiver of a message in 

computing and verifying a digital signature, for security 

purposes. See also algorithm, digital signature. 

shade1 n. A particular color variation produced by mixing 

black with a pure color. See also brightness, IRGB. 

shade2 vb. To give added dimension to an image by 

including changes in appearance caused by light and 

shadow. See also color model. 

shadow mask n. A type of mask used in cathode ray tube 

(CRT) monitors in which an opaque sheet perforated by 

tiny pinholes ensures that the electron beam for a particular 

color strikes only the phosphor it is supposed to illuminate. 

Like the aperture grill, which relies on vertical 

stripes, and the slot mask, which is based on elliptical 

openings, a shadow mask helps create a clear, sharp image 

by narrowly focusing the electron beam. See also CRT, 

mask (definition 2). Compare aperture grill, slot mask. 

shadow memory n. A technique employed by the BIOS 

in some 80x86-based computers to copy the system’s ROM 

BIOS routines into an unused section of RAM during the 

computer’s startup process. This helps boost system performance 

by diverting system requests for the BIOS routines to 

their “shadow” copies. Also called: shadow RAM, shadow 

ROM. 

shadow print n. A style applied to text in which a duplicate 

of each character is shifted, typically down and to the 

right, to create a shadow effect. See the illustration. 

F0Sgn13.eps 

Shadow print. 

shadow RAM n. See shadow memory. 

477 

shadow ROM n. See shadow memory. 

share vb. To make files, directories, or folders accessible 

to other users over a network. 

shared assembly n. An assembly that can be referenced 

by more than one application. An assembly must be 

explicitly built to be shared by giving it a cryptographically 

strong name. See also private assembly, strong name. 

shared directory n. See network directory. 

shared folder n. On a Macintosh computer connected to 

a network and running System 6.0 or higher, a folder that a 

user has made available to others on the network. A shared 

folder is analogous to a network directory on a PC. See 

also network directory. 

shared logic n. The use, by multiple circuits or software 

routines, of common circuits or routines to implement an 

operation. 

shared medium n. The communications medium shared 

by network nodes; essentially, the network bandwidth. 

shared memory n. 1. Memory accessed by more than 

one program in a multitasking environment. 2. A portion 

of memory used by parallel-processor computer systems 

to exchange information. See also parallel processing. 

shared name n. See strong name. 

shared network directory n. See network directory. 

shared printer n. A printer that receives input from more 

than one computer. 

shared resource n. 1. Any device, data, or program used 

by more than one device or program. 2. On a network, any 

resource made available to network users, such as directories, 

files, and printers. 

SharePoint team Web site n. A customizable Web site 

with features that help a team work together. The default 

site has pages for document libraries, announcements, and 

team events. Only members, specified by the site creator, 

can use the site. 

shareware n. Copyrighted software that is distributed on 

a try-before-you-buy basis. Users who want to continue 

using the program after the trial period are encouraged to 

send a payment to the program’s author. Compare free 

software, freeware, public-domain software. 

sharpness n. See resolution (definition 1). 

sheet n. A feature for handling dialog boxes included in 

the Mac OS X Aqua interface. When the user chooses to 

S

S 

sheet-fed scanner shopping cart 

save or print a document, a translucent sheet emerges from 

the window title bar and remains attached to that window 

even if it is moved to the background. The sheet allows the 

user to continue working in the window, or in other windows, 

without closing the sheet. 

sheet-fed scanner n. A scanner with a single-sheet feed 

mechanism, in which sheets of paper are pulled in by the 

scanner and scanned as they pass over a stationary scanning 

mechanism. Sheet-fed scanners allow for automatic scanning 

of multiple-sheet documents. See also scanner. Compare 

drum scanner, flatbed scanner, handheld scanner. 

sheet feeder n. A device that accepts a stack of paper 

and feeds it to a printer one page at a time. 

shelfware n. Software that has been unsold or unused 

for a long time, and so has remained on a retailer’s or 

user’s shelf. 

shell1 n. A piece of software, usually a separate program, 

that provides direct communication between the user and 

the operating system. Examples of shells are Macintosh 

Finder and the MS-DOS command interface program 

COMMAND.COM. See also Bourne shell, C shell, 

Finder, Korn shell. Compare kernel. 

shell2 vb. See shell out. 

shell account n. A computer service that permits a user 

to enter operating-system commands on the service provider’s 

system through a command-line interface (usually 

one of the UNIX shells) rather than having to access the 

Internet through a graphical user interface. Shell accounts 

can provide Internet access through character-based tools 

such as Lynx for browsing the World Wide Web. See also 

shell1 . 

shell archive n. In UNIX and GNU, a collection of compressed 

files that has been prepared for transmission by an 

e-mail service using the shar command. 

shell out vb. To obtain temporary access to the operatingsystem 

shell without having to shut down the current application 

and return to that application after performing the 

desired shell function. Many UNIX programs allow the user 

to shell out; the user can do the same in windowing environments 

by switching to the main system window. 

shell script n. A script executed by the command interpreter 

(shell) of an operating system. The term generally 

refers to scripts executed by the Bourne, C, and Korn 

shells on UNIX platforms. Also called: batch file. See also 

batch file, script, shell1 . 

478 

Shell sort n. A programming algorithm used for ordering 

data in which data are sorted in subsets so that the process 

works its way from unsorted to progressively more sorted. 

Named after its inventor, Donald Shell, it is faster than the 

bubble sort and the insertion sort. See also algorithm. 

Compare bubble sort, insertion sort. 

Sherlock n. An advanced search mechanism included 

with the Macintosh OS. Sherlock provides the ability to 

search multiple Internet search engines simultaneously 

and incorporates the Macintosh Find File interface for 

searches of local volumes. Additional plug-ins can expand 

the number of search engines available for access and 

increase search options. 

shielded twisted-pair wiring n. See twisted-pair wiring. 

shift vb. In programming, to move the bit values one position 

to the left or right in a register or memory location. 

See also end-around shift. Compare rotate (definition 2). 

Shift+click or Shift click vb. To click the mouse button 

while holding down the Shift key. Shift+clicking performs 

different operations in different applications, but its most 

common use in Windows is to allow users to select multiple 

items in a list, for example, to select a number of files 

for deletion or copying. 

Shift key n. A keyboard key that, when pressed in combination 

with another key, gives that key an alternative 

meaning; for example, producing an uppercase character 

when a letter key is pressed. The Shift key is also used in 

various key combinations to create nonstandard characters 

or to perform special operations. The term is adapted from 

usage in relation to manual typewriters, in which the key 

physically shifted the carriage to print an alternative character. 

See also Caps Lock key. 

Shift-PrtSc n. See Print Screen key. 

shift register n. A circuit in which all bits are shifted one 

position at each clock cycle. It can be either linear (a bit is 

inserted at one end and “lost” at the other during each 

cycle) or it can be cyclic or looped (the “lost” bit is 

inserted back at the beginning). See also register, shift. 

Shockwave n. A format for multimedia audio and video 

files within HTML documents, created by Macromedia, 

which markets a family of Shockwave servers and plug-in 

programs for Web browsers. See also HTML. 

shopping cart n. In e-commerce programs, a file in 

which an online customer stores information on potential 

purchases until ready to order. Usually represented on

short card sideband 

screen with a drawing of a shopping cart, the virtual shopping 

cart provides a recognizable point of reference to users 

new to the e-commerce experience. See also e-commerce. 

short card n. A printed circuit board that is half as long 

as a standard-size circuit board. Also called: half-card. See 

also printed circuit board. 

short-circuit evaluation n. A form of expression evaluation 

that guarantees that Boolean expressions will be evaluated 

only far enough to determine their value. See also 

AND, Boolean operator, OR. 

shortcut n. In Windows 9x, Windows XP, Windows NT 

4, and Windows 2000, an icon on the desktop that a user 

can double-click to immediately access a program, a text 

or data file, or a Web page. See also symbolic link. 

shortcut key n. See accelerator. 

short-haul adj. Of or pertaining to a communications 

device that transmits a signal over a communications line 

for a distance less than approximately 20 miles. Compare 

long-haul. 

short message service n. Service for wireless phones 

that allows users to send and receive brief messages consisting 

of text and numbers. Acronym: SMS. 

shout vb. To use ALL CAPITAL LETTERS for emphasis 

in e-mail or a newsgroup article. Excessive shouting is 

considered a violation of netiquette. A word can be more 

acceptably emphasized by placing it between *asterisks* 

or _underscores_. See also netiquette. 

shovelware n. A commercially sold CD-ROM containing 

a miscellaneous assortment of software, graphic images, 

text, or other data that could otherwise be obtained at little 

or no cost, such as freeware or shareware from the Internet 

and BBSs or public-domain clip art. See also BBS (definition 

1), freeware, shareware. 

ShowSounds n. In Windows 9x and Windows NT 4, a 

global flag that instructs application programs to provide 

some kind of visual indication that the program is generating 

a sound in order to alert users with hearing impairments 

or those in a noisy location such as a factory floor. 

shredder n. An application designed to completely 

destroy digital data so it cannot be reconstructed with file 

recovery software. 

shrinkwrap agreement n. A contract or license in or on 

a software box or package that sets forth conditions for 

use of the software. Typically, a shrinkwrap agreement 

479 

states that a user accepts the terms of the agreement when 

he or she opens the box. A shrinkwrap agreement is a print 

version of an End-User License Agreement. Also called: 

box-top license. See also End-User License Agreement. 

Compare clickwrap agreement. 

shrink-wrapped adj. Boxed and sealed in clear plastic 

film for commercial distribution. Use of the term implies a 

final version of a product as opposed to a beta version. See 

also beta1 . 

SHS virus n. Any of a class of viruses that infect a user’s 

system by hiding in files with an .shs extension. These 

viruses typically spread through e-mail attachments. A 

widely distributed e-mail warning cautions readers to 

beware of the “SHS virus,” but no one specific virus by 

that name exists. 

SHTML n. Short for server-parsed HTML. Hypertext 

Markup Language (HTML) text that contains embedded 

server-side include commands. SHTML documents are 

fully read, parsed, and modified by the server before being 

passed to the browser. See also HTML, server-side include. 

S-HTTP or SHTTP n. Acronym for Secure Hypertext 

Transfer Protocol. An extension to HTTP that supports 

various encryption and authentication measures to keep all 

transactions secure from end to end. S-HTTP is designed 

to ensure the security of individual transmissions over the 

Internet and has been approved as a standard by the Internet 

Engineering Task Force (IETF). S-HTTP should not 

be confused with HTTPS, a Netscape-developed technology 

based on SSL (Secure Sockets Layer). HTTPS is also 

designed to ensure secure transmissions, but does so 

between communicating computers rather than on a message-by-message 

basis. Also called: Secure HTTP. See 

also SSL. 

shut down vb. To close a program or an operating system 

in a manner ensuring that no data is lost. 

sibling n. A process or node in a data tree that is 

descended from the same immediate ancestor(s) as other 

processes or nodes. See also generation (definition 2), 

node (definition 3). 

sideband n. The upper or lower portion of a modulated 

carrier wave. One portion can be processed while the other 

is used to carry separate data, a technique that doubles the 

amount of information that can be carried over a single 

line. See the illustration. 

S

S 

sidebar sign bit 

F0Sgn14.eps 

Sideband. 

Upper sideband 

Lower sideband 

sidebar n. A block of text placed to the side of the main 

body of text in a document, often set off by a border or 

other graphic element. 

side-by-side execution n. The ability to install and use 

multiple versions of an assembly in isolation at the same 

time. This can occur on the same machine, or in the same 

process or application domain. Side-by-side execution can 

apply to applications and components as well as the components 

of the .NET Framework. Allowing assemblies to 

run side-by-side is essential to support robust versioning 

in the common language runtime. 

side effect n. Any change of state caused by a subroutine, 

such as a routine that reads a value from a file and 

advances the current file position. 

side head n. A heading placed in the margin of a printed 

document and top-aligned with the body text, rather than 

being vertically aligned with text, as is a normal head. 

sieve of Eratosthenes n. An algorithm for finding prime 

numbers. It is often used as a benchmark in testing the 

speed of a computer or programming language. See also 

benchmark1 . 

.sig n. A file extension for a signature file for e-mail or 

Internet newsgroup use. The contents of this file are automatically 

appended to e-mail correspondence or newsgroup 

articles by their respective client software. See also 

signature file (definition 1). 

SIG n. Acronym for special interest group. An e-mail 

online discussion group or a group of users who meet and 

share information, especially one of the groups supported 

by the Association for Computing Machinery (ACM), 

such as SIGGRAPH for computer graphics. 

SIGGRAPH n. Short for Special Interest Group on Computer 

Graphics, a part of the Association for Computing 

Machinery (ACM). 

sigmoid function n. A kind of S-shaped mathematical 

function arising in many dynamical systems, including 

neural networks, because it is the solution to a first-order 

differential equation. It typically maps a real value, which 

may be arbitrarily large in magnitude (positive or nega- 

480 

tive), to another real value, which lies within some narrow 

range. The sigmoid function, in neural network computation 

literature, is also sometimes referred to as the logistic 

function. The reason for its prevalence is that it is thought 

to resemble the probability that a true neuron generates as 

an action potential in response to particular input and output. 

See also artificial intelligence, neural network. 

sign n. The character used to indicate a positive or negative 

number. In assembly-level programming, the sign is 

indicated by the sign bit accompanying the number. See 

also sign bit. 

signal n. 1. Any electrical quantity, such as voltage, current, 

or frequency, that can be used to transmit information. 

2. A beep or tone from a computer’s speaker or a 

prompt displayed on screen that tells a user that the computer 

is ready to receive input. 

signal converter n. A device or circuit that converts a 

signal from one form to another, such as analog to digital, 

or pulse code modulation to frequency modulation. 

signal-to-noise ratio n. The amount of power, measured in 

decibels, by which the signal exceeds the amount of channel 

noise at the same point in transmission. Abbreviation: S/N. 

See also noise (definition 2). 

signature n. 1. A sequence of data used for identification, 

such as text appended to an e-mail message or a fax. 2. A 

unique number built into hardware or software for authentication 

purposes. 

signature block n. A block of text that an e-mail client or 

a newsreader automatically places at the end of every message 

or article before the message or article is transmitted. 

Signature blocks typically contain the name, e-mail 

address, and affiliation of the person who created the message 

or article. 

signature file n. 1. A file that contains information 

inserted by a user and automatically appended to e-mail 

correspondence or newsgroup articles by client software. 

A signature file typically contains the name or nickname 

of the user and might include such information as the 

user’s e-mail address, Web page, company, or job title. 

2. A file that updates an antivirus program so that the program 

recognizes signatures of new viruses and removes 

the viruses from the user’s computer. See also antivirus 

program, virus signature. 

sign bit n. The most significant, or leftmost, bit of a number 

field, usually set to 1 if the number is negative.

sign extension SIMD 

sign extension n. See sign bit. 

significand n. See mantissa. 

significant digits n. The sequence from the first nonzero 

digit to the last digit in a number (the last nonzero digit in 

an integer), used to express the number’s precision (for 

example, 12,300 has three significant digits, and 

0.000120300 has six). See also floating-point notation. 

sign off vb. See log off. 

sign on vb. See log on. 

sign propagation n. See sign bit. 

SIIA n. Acronym for Software & Information Industry 

Association. A nonprofit trade association representing 

over 1200 high-tech companies worldwide and charged 

with watching over the interests of the software and digital 

content industry. The SIIA was formed in 1999 when the 

Software Publishers Association (SPA) merged with the 

Information Industry Association (IIA). The SIIA focuses 

on three areas: providing information and forums in which 

to distribute information to the high-tech industry; protection 

in the form of an antipiracy program geared to help 

members enforce their copyrights; and promotion and 

education. 

silica gel n. A desiccant (moisture-absorbing substance) 

often packaged with optical or electronic equipment. 

silicon n. A semiconductor used in many devices, especially 

microchips. Silicon, with atomic number 14 and 

atomic weight 28, is the second most common element in 

nature. Compare silicone. 

Silicon Alley n. The Manhattan, New York, metropolitan 

area. Originally the term referred to the area of Manhattan 

below 41st Street, which had a heavy concentration of 

technology companies, but it now includes the entire 

island, reflecting the number of businesses involved in 

computer technology in that area. The name was inspired 

by Silicon Valley, the area of northern California that is 

home to many technology firms. See also Silicon Valley. 

silicon chip n. An integrated circuit that uses silicon as 

its semiconductor material. 

silicon-controlled rectifier n. A semiconductor rectifier 

whose conductance can be controlled by a gate signal. 

Acronym: SCR. See also gate (definition 1), rectifier. 

silicon dioxide n. An insulator used to form thin insulating 

layers in some types of semiconductors; also the primary 

component of glass. 

481 

silicone n. A polymer in which silicon and oxygen are 

major components. Silicone is an excellent electrical insulator 

and conducts heat well. Compare silicon. 

silicon foundry n. A factory or machine used to create 

wafers of crystalline silicon. 

silicon on insulator n. See SOI. 

silicon-on-sapphire n. A method of fabricating semiconductors 

in which the semiconductor devices are formed in 

a thin single layer of silicon that has been grown on an 

insulating substrate of synthetic sapphire. Acronym: SOS. 

Silicon Valley n. The region of California south of San 

Francisco Bay, otherwise known as the Santa Clara Valley, 

roughly extending from Palo Alto to San Jose. Silicon Valley 

is a major center of electronics and computer research, 

development, and manufacturing. See the illustration. 

San 

Francisco 

F0Sgn15.eps 

Silicon Valley. 

Palo Alto 

Silicon 

Valley 

San Jose 

Silicorn Valley n. Clusters of high-tech companies headquartered 

in small cities in the Midwestern United States, 

particularly in areas of rural Iowa. 

SIM n. See Society for Information Management. 

SIM card n. Short for Subscriber Identity Module card. 

A smart card designed for use with GSM (Global System 

for Mobile Communications) mobile phones. SIM cards 

contain chips that store a subscriber’s personal identifier 

(SIM PIN), billing information, and data (names, phone 

numbers). See also Global System for Mobile Communications, 

smart card (definition 2). 

SIMD n. Acronym for single-instruction, multiple-data 

stream processing. A category of parallel-processor computer 

architecture in which one instruction processor 

fetches instructions and distributes orders to several other 

processors. See the illustration. See also parallel processing. 

Compare MIMD. 

S

S 

SIMM single-precision 

Instruction 

processor 

F0Sgn16.eps 

SIMD. 

D 1 D 2 D 3 D n 

SIMM n. Acronym for single inline memory module. A 

small circuit board designed to accommodate surfacemount 

memory chips. 

Simple API for XML n. See SAX. 

Simple Authentication and Security Layer n. See 

SASL. 

Simple Control Protocol n. See SCP. 

Simple Mail Transfer Protocol n. A TCP/IP protocol for 

sending messages from one computer to another on a network. 

This protocol is used on the Internet to route e-mail. 

Acronym: SMTP. See also communications protocol, 

TCP/IP. Compare CCITT X series, Post Office Protocol. 

Simple Network Management Protocol n. See SNMP. 

Simple Object Access Protocol n. See SOAP. 

simplex n. Communication that takes place only from 

sender to receiver. Compare duplex2 (definition 1), halfduplex2 

. 

simplex transmission n. See simplex. 

SIMULA n. Short for simulation language. A general-purpose 

programming language based on ALGOL 60, with 

special features designed to aid the description and simulation 

of active processes. Visual C++ is based on aspects 

of this language. 

simulation n. The imitation of a physical process or an 

object by a program that causes a computer to respond 

mathematically to data and changing conditions as though 

it were the process or object itself. See also emulator, 

modeling (definition 1). 

simultaneous access n. See parallel access. 

simultaneous processing n. 1. True multiple-processor 

operation in which more than one task can be processed at 

a time. See also multiprocessing, parallel processing. 

2. Loosely, concurrent operation in which more than one 

task is processed by dividing processor time among the 

tasks. See also concurrent, multitasking. 

482 

sine wave n. A uniform, periodic wave often generated 

by an object that vibrates at a single frequency. See the 

illustration. Compare square wave. 

Amplitude 

Data 

processors 

F0Sgn17.eps 

Sine wave. 

Time 

single attachment station n. An FDDI node that connects 

to the primary ring through a concentrator. Compare 

dual attachment station. 

single-board adj. Of or pertaining to a computer that 

occupies only one circuit board, usually with no capacity 

for additional boards. 

single-density adj. Of or pertaining to a disk that is certified 

only for use with frequency modulation (FM) recording. 

A single-density disk can store much less data than a 

disk using modified FM encoding or run-length limited 

encoding. See also modified frequency modulation encoding, 


Single Image Random Dot Stereogram n. See autostereogram. 

Single Image Stereograms n. See autostereogram. 

single inline memory module n. See SIMM. 

single inline package n. See SIP. 

single inline pinned package n. See SIP. 

single-instruction, multiple-data stream 

processing n. See SIMD. 

single-line digital subscriber line n. See SDSL. 

single-precision adj. Of or pertaining to a floating-point 

number having the least precision among two or more

single-sided skyscraper 

options commonly offered by a programming language, 

such as single-precision versus double-precision. See also 

floating-point notation, precision (definition 2). Compare 

double-precision. 

single-sided adj. Of or pertaining to a floppy disk in 

which data can be stored on only one side. 

single sign-on n. A system enabling a user to enter one 

name and password to log on to different computer systems 

or Web sites. Single sign-on is also available for 

enterprise systems so a user with a domain account can 

log on to a network once, using a password or smart card, 

and thereby gain access to any computer in the domain. 

See also domain, smart card (definition 1). 

single step vb. To execute a program one step at a time, 

usually within the context of a debugger. See also debugger. 

single switch device n. An assistive computer technology 

for people with mobility impairments. A single switch 

device allows users to interact with a computer by using 

slight body movements. 

single threading n. 1. Within a program, the running of a 

single process at a time. 2. A condition in which each leaf 

node of a tree data structure contains a pointer to its parent. 

See also node (definition 3), pointer (definition 1), 

threading. 

single-user computer n. A computer designed for use by 

a single individual; a personal computer. Compare multiuser 

system. 

sink n. A device or part of a device that receives something 

from another device. See also data sink, heat sink. 

SIP n. Acronym for single inline package. A type of housing 

for an electronic component in which all leads (connections) 

protrude from one side of the package. Also 

called: single inline pinned package. Compare DIP. 

SIPP n. Acronym for single inline pinned package. See SIP. 

SIR n. See Serial Infrared. 

SirCam worm n. A malicious worm that combines fast 

infection with the potential to deliver multiple malicious 

payloads. SirCam spreads through multiple means, both 

by mailing infected personal files from a compromised 

disk to other potential victims and through Windows network 

shares on unprotected machines. One time in 20 Sir- 

Cam deletes the contents of the infected drive, and one 

time in 50 it fills all free space on the disk with trash data. 

483 

SirCam was discovered in mid-2001 and has reappeared 

regularly since that time. 

SIRDS n. Acronym for Single Image Random Dot 

Stereogram. See autostereogram. 

SIS n. Acronym for Single Image Stereogram. See 

autostereogram. 

.sit n. The file extension for a Macintosh file compressed 

with StuffIt. See also StuffIt. 

site n. See Web site. 

site license n. A purchase agreement for using multiple 

copies of the same software at a business or an institution, 

usually at a volume discount. 

size box n. A control in the upper right corner of the 

frame of a window on the Macintosh screen. When the 

user clicks the size box, the window toggles between the 

size the user has set for it by dragging and the maximum 

size. Compare Maximize button. 

skew n. The difference between what is and what should 

be—for example, the misalignment of a page that prevents 

accurate reproduction, or the difference between input and 

output when circuits do not respond evenly to a propagated 

signal. 

skin n. An alternative graphical interface for an operating 

system (OS) or a software program. A skin customizes the 

look of the OS or program but does not affect its functionality. 

Programs that allow the use of skins usually make 

standards available for the creation and distribution of new 

skins. See also graphical user interface. 

skin mode n. An operational state of various media players, 

including RealPlayer, Winamp, and Windows Media 

Player, in which the user interface is customized and displayed 

as a skin. Often some features of the player are not 

accessible in skin mode. Skin mode was called compact 

mode in Windows Media Player 7. See also full mode. 

Skutch box n. A slang term for a device manufactured by 

Skutch Electronics, Inc., that simulates the functioning of 

a telephone line with a good connection. Telephone line 

simulators are used to test telecommunications systems 

and devices. 

skyscraper n. One of several larger formats for online 

ads developed to replace traditional banner ads on the 

Internet. See avalanche ad. 

S

S 

slave slotted-ring network 

slave n. Any device, including a computer, that is controlled 

by another computer, referred to as the master. See 

also master/slave arrangement. 

sleep1 n. 1. In a multiprocessing environment, a temporary 

state of suspension during which a process remains in 

memory so that some event, such as an interrupt or a call 

from another process, can “awaken” it. 2. In programming, 

a state of suspension caused by a loop statement that creates 

an intentional delay. 

sleep2 vb. To suspend operation without terminating. 

sleep mode n. A power management mode that shuts 

down all unnecessary computer operations to save energy 

after it has received no input or other activity for a specified 

period of time. A computer in sleep mode usually 

awakens when it receives an input signal from a user or a 

network, such as a keyboard entry or an incoming call 

through a modem. Many battery-powered devices, including 

portable computers, support sleep mode. See also 

green PC, sleep1 (definition 1), Suspend command. 

sleeve n. See disk envelope. 

slice n. See time slice. 

SLIP n. Acronym for Serial Line Internet Protocol. A data 

link protocol that allows transmission of TCP/IP data packets 

over dial-up telephone connections, thus enabling a 

computer or a LAN (local area network) to be connected to 

the Internet or some other network. It is an older, less secure 

protocol than the PPP (Point-to-Point Protocol) and does 

not support dynamic allocation of IP addresses. A newer 

form of SLIP, known as CSLIP (Compressed SLIP), optimizes 

transmission of long documents by compressing 

header information. See also data link, IP. Compare PPP. 

SLIP emulator n. Software that mimics a SLIP connection 

in UNIX shell accounts that do not offer a direct SLIP 

connection. Many Internet service providers (ISPs) are 

UNIX based and offer shell accounts to users for Internet 

access. Like a SLIP connection, the SLIP emulator allows 

the user to avoid dealing with the ISP’s UNIX environment 

directly when accessing the Internet and to use Internet 

applications such as graphical Web browsers. See also 

ISP, shell account, SLIP. 

slot n. 1. See expansion slot. 2. An integrated circuit 

mounting connector designed to connect a microprocessor 

with a PC’s data bus. Currently, only newer models of 

484 

Intel’s Pentium family employ this. See also Pentium, Slot 

1, Slot 2. 

Slot 1 n. A receptacle on a PC motherboard designed to 

hold a Pentium II microprocessor. The microprocessor, 

which is encased in Intel’s Single Edge Contact (SEC) 

packaging, slides into the slot on the motherboard. Slot 1 

includes 242 electrical contact points and communicates 

with the chip’s L2 cache at half of the PC’s clock speed. 

Slot 1 replaced socket 7 and socket 8 in Intel architectures, 

but has been superceded by Slot 2 in newer model Pentiums. 

See also L2 cache, motherboard, Pentium. Compare 

Slot 2, socket 7, socket 8. 

Slot 2 n. A receptacle on a PC motherboard designed to 

hold Intel microprocessors beginning with the Pentium II 

Xeon and including the Pentium III microprocessor. Like 

Slot 1, Slot 2 is encased in Intel’s Single Edge Contact 

packaging, so it slides easily into the slot on the motherboard. 

It includes 330 electrical contact points and is 

slightly wider than Slot 1. It also supports communication 

between the CPU and the L2 cache at the full clock speed 

of the PC. See also L2 cache, motherboard, Pentium. 

Compare Slot 1. 

slot mask n. A type of mask used in cathode ray tube 

(CRT) monitors in which a thin sheet of metal perforated 

with elliptical holes is used to ensure that the electron beam 

for a particular color (red, green, or blue) strikes only the 

phosphor (of the corresponding color) that it is intended to 

illuminate. The elliptical—lozenge-shaped—holes in a slot 

mask place it between a shadow mask, which is based on 

round openings, and an aperture grill, which is based on 

vertical strips of metal. Slot masks were introduced by NEC 

in its CromaClear technology. See also CRT, mask (definition 

2). Compare aperture grill, shadow mask. 

slot pitch n. The distance, measured horizontally, between 

phosphor dots of the same color on a cathode ray tube 

(CRT) display based on slot mask technology. Although the 

measurements are based on different methods of applying 

phosphor to the screen surface, slot pitch is comparable to 

dot pitch, the measurement used with CRTs based on 

shadow mask technology. See also CRT, mask (definition 

2), slot mask. Compare dot pitch, stripe pitch. 

slotted-ring network n. A ring network allowing data to 

be transmitted between data stations in one direction. A 

slotted-ring network transfers data in predefined time slots 

(fixed-length portions of a data frame) in the transmission

SlowKeys SmartSuite 

stream over one transmission medium. See also data 

frame, ring network. Compare token ring network. 

SlowKeys n. An accessibility feature built into Macintosh 

computers and available for DOS and Windows that 

allows the user to add a delay to the keyboard so that a key 

must be held down for a certain amount of time before it is 

accepted. This feature facilitates the use of the keyboard 

by individuals with poor motor control who might accidentally 

bump keys when moving around the keyboard. 

SLSI n. See super-large-scale integration. 

Small Business Server n. A software application developed 

by Microsoft Corporation to increase the efficiency 

of Web-based services for small businesses with 50 or 

fewer personal computers. Small Business Server provides 

shared Internet access, features for building Web-based 

customer management and customer communications 

tools, and additional features that increase productivity by 

streamlining employee access to files and applications 

over the Web. 

small caps n. A font of capital letters that are smaller 

than the standard capital letters in that typeface. 

Small Computer System Interface n. See SCSI. 

small model n. A memory model of the Intel 80x86 processor 

family that allows only 64 kilobytes (KB) for code 

and 64 KB for data. See also memory model. 

Small Office/Home Office n. See SOHO. 

small-scale integration n. A concentration of fewer than 

10 components on a single chip. Acronym: SSI. See also 

integrated circuit. 

Smalltalk n. An object-oriented language and development 

system developed at Xerox Palo Alto Research Center 

(PARC) in 1980. Smalltalk pioneered many language 

and user interface concepts that are now widely used in 

other environments, such as the concept of an object that 

contains data and routines and on-screen icons that the 

user can choose to make the computer perform certain 

tasks. See also object-oriented programming. 

smart adj. A synonym for intelligent. See intelligence. 

smart cable n. See intelligent cable. 

smart card n. 1. In computers and electronics, a circuit 

board with built-in logic or firmware that gives it some 

kind of independent decision-making ability. 2. In banking 

and finance, a credit card that contains an integrated cir- 

485 

cuit that gives it a limited amount of intelligence and 

memory. 

smart card reader n. A device that is installed in computers 

to enable the use of smart cards for enhanced security 

features. See also smart card (definition 2). 

smart device n. An electronic device capable of being 

networked and remotely controlled in a smart home. 

Smart devices can include appliances, lighting, heating 

and cooling systems, entertainment systems, and security 

systems. See also home automation, home network (definition 

1), smart home. 

smart home n. A home or building wired for networking 

and home automation. In a smart home, occupants control 

smart devices programmatically or on command using a 

home-networking communications protocol. Also called: 

automated home, digital home, e-home, Internet home, 

networked home, smart house, wired home. See also home 

automation, home network (definition 1). 

smart house n. See smart home. 

smart linkage n. A feature of programming languages 

that guarantees that routines will always be called with 

correct parameter types. See also link (definition 1). 

smartphone n. A hybrid between a wireless telephone and 

a personal digital assistant (PDA). Smartphones integrate 

wireless telephones with many of the personal organizational 

functions of PDAs, such as calendar, calculator, database, 

e-mail, wireless Web access, note taking, and other 

programs common to lightweight palm-style computers. 

Smartphones may rely on a stylus, keypad, or both for data 

entry or may use voice recognition technology. See also 

cell, palmtop, PDA, pen computer, wireless phone. 

smart quotes n. In word processors, a function that automatically 

converts the ditto marks (") produced by most 

computer keyboards to the inverted commas (“ and ”) used 

in typeset text. 

SmartSuite n. A suite of business application programs 

sold by Lotus Development. Lotus SmartSuite includes six 

programs: Lotus 1-2-3 spreadsheet, Lotus WordPro word 

processor, Lotus Approach database, Lotus Freelance 

Graphics presentation software, Lotus Organizer timemanagement 

software, and Lotus FastSite Internet/intranet 

publishing tool. SmartSuite Millennium Edition 9.7 supports 

collaboration, Web publishing, use of Internet/intranet 

resources, and customizable document and project 

organizers. SmartSuite competes with Microsoft Office 

and WordPerfect Office. 

S

S 

SMART system SNA 

SMART system n. Short for self-monitoring analysis 

and reporting technology system. A system by which 

technology is used to monitor and predict device performance 

and reliability. A SMART system employs various 

diagnostic tests to detect problems with devices, with the 

object of increasing productivity and protecting data. 

smart terminal n. A terminal that contains a microprocessor 

and random access memory (RAM) and that does 

some rudimentary processing without intervention from 

the host computer. Compare dumb terminal. 

SMB n. Acronym for Server Message Block. A filesharing 

protocol designed to allow networked computers 

to transparently access files that reside on remote systems 

over a variety of networks. The SMB protocol defines a 

series of commands that pass information between computers. 

SMB uses four message types: session control, file, 

printer, and message. See also LAN Manager, NetBIOS, 

Samba. 

SMDS n. Acronym for Switched Multimegabit Data Services. 

A very high-speed, connectionless, packet-switched 

data transport service that connects LANs (local area networks) 

and WANs (wide area networks). 

SMIL n. Acronym for Synchronized Multimedia Integration 

Language. A markup language that enables separate 

elements, including audio, video, text, and still images, to 

be accessed separately and then integrated and played 

back as a synchronized multimedia presentation. Based on 

XML (eXtensible Markup Language), SMIL allows Web 

authors to define the objects in the presentation, describe 

their locations onscreen, and determine when they will be 

played back. The language is based on statements that can 

be entered with a text editor and was developed under the 

auspices of the World Wide Web Consortium (W3C). See 

also markup language, XML. 

smiley n. See emoticon. 

S/MIME n. Acronym for Secure/Multipurpose Internet 

Mail Extensions. An Internet e-mail security-oriented protocol 

that adds public key encryption and support for digital 

signatures to the widely used MIME e-mail protocol. 

See also public key encryption. 

SMIS n. Acronym for Society for Management Information 

Systems. See Society for Information Management. 

486 

smoke test n. The testing of a piece of hardware after 

assembly or repairs by turning it on. The device fails the 

test if it produces smoke, explodes, or has some other 

unexpected violent or dramatic reaction, even if it appears 

to work. 

smooth vb. 1. To eliminate irregularities in statistical data 

by some process such as continuous averaging or by 

removing random (irrelevant) values. 2. In graphics, to 

remove jagged edges from a figure or line. See also antialiasing. 

SMP n. Acronym for symmetric multiprocessing. A computer 

architecture in which multiple processors share the 

same memory, which contains one copy of the operating 

system, one copy of any applications that are in use, and 

one copy of the data. Because the operating system 

divides the workload into tasks and assigns those tasks to 

whichever processors are free, SMP reduces transaction 

time. See also architecture, multiprocessing. 

SMP server n. Short for symmetric multiprocessing 

server. A computer that is designed with the SMP architecture 

to improve its performance as a server in client/ 

server applications. See also SMP. 

SMS n. See Systems Management Server. 

SMS n. See short message service. 

SMT n. See surface-mount technology. 

SMTP n. See Simple Mail Transfer Protocol. 

smurf attack n. A form of denial-of-service attack on an 

Internet server that sends simultaneous echo request packets 

(“ping” packets) to one or more broadcast IP addresses 

(such as an IRC server), each of which in turn relays the 

request to as many as 255 individual host computers, with 

the address of the attack’s victim as the forged (spoofed) 

source address. When the hosts return echo packets to the 

apparent source of the request, the volume of the 

responses is enough to disable the network. See also 

denial of service attack, spoofing. 

SNA n. Acronym for Systems Network Architecture. A 

network model devised by IBM to enable IBM products, 

including mainframes, terminals, and peripherals, to communicate 

and exchange data. SNA started out as a fivelayer 

model and was later extended with two additional 

layers to correspond more closely to the ISO/OSI refer-

snail mail SOAP 

ence model. More recently, the SNA model was modified 

to include minicomputers and microcomputers in a specification 

known as APPC (Advanced Program to Program 

Communications). See the illustration. See also APPC. 

Compare ISO/OSI reference model. 

SNA 

Function 

management 

Data flow 

control 

Transmission 

control 

Path 

control 

Data-link 

control 

ISO Open Systems 

Interconnection 

Application 

Presentation 

Session 

Transport 

Network 

Data-link 

Physical 

F0Sgn18.eps 

SNA. Comparable (not compatible) layers in the SNA and 

ISO/OSI architechures. 

snail mail n. A popular phrase on the Internet for referring 

to mail services provided by the U.S. Postal Service 

and similar agencies in other countries. The term has its 

origins in the fact that regular postal mail is slow compared 

with e-mail. 

snap-in n. 1. See plug-in. 2. A software component that 

provides system administration and system management 

capability within the framework of the Microsoft Management 

Console (MMC) for Windows NT, Windows 2000, 

and Windows XP. A snap-in (also capitalized as Snap-In) 

is a COM object that represents one unit of management 

behavior, the smallest extension available through the 

MMC. There are two types of snap-ins: stand-alone (not 

reliant on any other snap-in) and extension (invoked by a 

parent snap-in). Multiple snap-ins can be combined to create 

larger management tools. 

487 

snapshot n. A copy of main memory or video memory at 

a given instant, sent to the printer or hard disk. Also 

called: snapshot dump. See also screen dump. 

snapshot program n. A program that performs a trace 

by taking a snapshot of certain chunks of memory at 

specified times. 

.snd n. A file extension for a type of interchangeable 

sound file format used on Sun, NeXT, and Silicon Graphics 

computers, consisting of raw audio data preceded by a 

text identifier. 

sneaker n. An individual employed by a company or 

organization to test their security by breaking into the 

employer’s network. Information gathered by the sneaker 

can be used to repair network security weaknesses. See 

also tiger team. 

sneakernet n. Transfer of data between computers that 

are not networked together. The files must be written onto 

floppy disks on the source machine, and a person must 

physically transport the disks to the destination machine. 

sniffer n. See packet sniffer. 

SNMP n. Acronym for Simple Network Management 

Protocol. The network management protocol of TCP/IP. 

In SNMP, agents, which can be hardware as well as software, 

monitor the activity in the various devices on the 

network and report to the network console workstation. 

Control information about each device is maintained in a 

structure known as a management information block. See 

also agent (definition 4), TCP/IP. 

SNOBOL n. Acronym for String-Oriented Symbolic Language. 

A string- and text-processing language developed 

between 1962 and 1967 by Ralph Griswold, David Farber, 

and I. Polonsky at AT&T Bell Laboratories. See also string. 

snow n. 1. In television, temporary distortion of a displayed 

image caused by interference, usually in a weak 

signal, that takes the form of random white spots. 2. In 

computer displays, a specific type of distortion characterized 

by the blinking on and off of random pixels that 

occurs when the microprocessor and the display hardware 

interfere with each other by attempting to use the computer’s 

video memory at the same time. 

SOAP n. Acronym for Simple Object Access Protocol. A 

simple, XML-based protocol for exchanging structured 

and type information on the Web. The protocol contains 

S

S 

SOC softmodem 

no application or transport semantics, which makes it 

highly modular and extensible. 

SOC n. Acronym for system on a chip. A chip integrating 

computer, microprocessors, and all necessary support 

components in a single unit. SOC technology is used in 

firewalls, gateways, specialized servers, and interactive 

devices like Web pads and vending machines. 

social engineering n. The practice of penetrating system 

security by tricking individuals into divulging passwords 

and information about network vulnerabilities. Often done 

by calling the individual on phone and pretending to be 

another employee of company with a computer-related 

question. 

Society for Information Management n. A professional 

society based in Chicago for information systems 

executives, formerly the Society for Management Information 

Systems. Acronym: SIM. 

Society for Management Information Systems n. See 

Society for Information Management. 

socket n. 1. An identifier for a particular service on a 

particular node on a network. The socket consists of a 

node address and a port number, which identifies the service. 

For example, port 80 on an Internet node indicates a 

Web server. See also port number, sockets API. 2. The 

receptacle part of a connector, which receives a plug. See 

also female connector. 3. A receptacle on a PC motherboard 

into which a microprocessor is plugged. A socketmounted 

microprocessor, such as the Pentium, connects 

to the motherboard through numerous pins on the underside. 

Newer Intel microprocessors, such as the Pentium II 

and later, plug into the motherboard through an edge connector 

along the side of the chip. See also socket 4, socket 

5, socket 7, socket 8. Compare Slot 1, Slot 2. 

socket 4 n. A 5-volt mounting socket on a PC motherboard 

designed to hold a Pentium microprocessor operating 

at 60 MHz or 66 MHz. Socket 4 includes openings for 

273 pins. See also Pentium, socket (definition 3). Compare 

Slot 1, Slot 2, socket 5, socket 7, socket 8. 

socket 5 n. A 3.3-volt mounting socket on a PC motherboard 

designed to hold a Pentium microprocessor operating 

at the following speeds: 75, 90, 100, 120, 133, 150, 

166, 180, and 200 MHz. Socket 5 includes openings for 

320 pins. It has been superceded by socket 7, socket 8, slot 

1, and slot 2. See also Pentium, socket (definition 3). Compare 

Slot 1, Slot 2, socket 4, socket 7, socket 8. 

488 

socket 7 n. A mounting socket on a PC motherboard 

designed to hold a microprocessor operating at the following 

speeds: 150, 166, 180, 200, 210, and 233 MHz. Socket 

7 includes openings for 321 pins and operates at two voltages, 

2.5 volts at the core and 3.3 volts input/output. It is 

used with the Pentium MMX chip and competitive microprocessor 

chips from other manufacturers, such as AMD 

and Cyrix. See also MMX, Pentium, socket (definition 3). 

Compare Slot 1, Slot 2, socket 4, socket 5, socket 8. 

socket 8 n. A 2.5-volt mounting socket on a PC motherboard 

designed to hold a Pentium Pro microprocessor. 

Socket 8 has openings for 387 pins. See also Pentium, 

socket (definition 3). Compare Slot 1, Slot 2, socket 4, 

socket 5, socket 7. 

sockets API n. An application programming interface 

implemented to create and use sockets in client/server networking. 

The most common sockets API is the University 

of California at Berkeley UNIX/BSD implementation 

(Berkeley Sockets API), which is the basis for Winsock. 

See also socket (definition 1). 

soc. newsgroups n. Usenet newsgroups that are part of 

the soc. hierarchy and have the prefix soc. These newsgroups 

are devoted to discussions of current events and 

social issues. Soc. newsgroups are one of the seven original 

Usenet newsgroup hierarchies. The other six are 

comp., misc., news., rec., sci., and talk. See also newsgroup, 

traditional newsgroup hierarchy, Usenet. 

soft adj. 1. In computing, temporary or changeable. For 

example, a soft error is a problem from which the system 

can recover, and a soft patch is a temporary program fix that 

holds only while the program is running. Compare hard 

(definition 1). 2. In electronics, characterized by magnetic 

materials that do not retain their magnetism when a magnetic 

field is removed. Compare hard (definition 2). 

soft boot n. See warm boot. 

soft copy n. The temporary images presented on a computer 

display screen. Compare hard copy. 

soft error n. An error from which a program or operating 

system is able to recover. Compare hard error. 

soft font n. See downloadable font. 

soft hyphen n. See hyphen. 

soft link n. See symbolic link. 

softmodem n. See software-based modem.

soft patch software piracy 

soft patch n. A fix or modification performed only while 

the code being patched is loaded into memory, so that the 

executable or object file is not modified in any way. See 

also patch1 . 

soft return n. A line break inserted in a document by a 

word processor when the next word in the current line of 

text would cause the line to overflow into the margin—a 

movable line break. See also wordwrap. Compare hard 

return. 

soft-sectored disk n. A disk, especially a floppy disk, 

whose sectors have been marked with recorded data marks 

rather than punched holes. See also index hole. Compare 

hard-sectored disk. 

software n. Computer programs; instructions that make 

hardware work. Two main types of software are system 

software (operating systems), which controls the workings 

of the computer, and applications, such as word processing 

programs, spreadsheets, and databases, which perform 

the tasks for which people use computers. Two additional 

categories, which are neither system nor application software 

but contain elements of both, are network software, 

which enables groups of computers to communicate, and 

language software, which provides programmers with the 

tools they need to write programs. In addition to these 

task-based categories, several types of software are 

described based on their method of distribution. These 

include packaged software (canned programs), sold primarily 

through retail outlets; freeware and public domain 

software, which are distributed free of charge; shareware, 

which is also distributed free of charge, although users are 

requested to pay a small registration fee for continued use 

of the program; and vaporware, software that is announced 

by a company or individuals but either never makes it to 

market or is very late. See also application, canned software, 

freeware, network software, operating system, 

shareware, system software, vaporware. Compare firmware, 

hardware, liveware. 

Software & Information Industry Association n. See 

SIIA. 

software-based modem n. A modem that uses a general-purpose, 

reprogrammable digital signal processor 

chip and RAM-based program memory rather than a dedicated 

chip with the modem functions burned into the silicon. 

A software-based modem can be reconfigured to 

update and change the modem’s features and functions. 

489 

software bloat n. A software condition caused by the 

addition of excessive number of possibly unnecessary 

features and functions as new versions of the software 

are released. Software bloat is generally assumed to 

result in long loading times and inordinate resource 

(memory and storage) requirements. See also bloatware, 

creeping featurism. 

software conversion n. Changing or moving a program 

designed to run on one computer to run on another. Usually 

this involves detailed (professional) work on the program 

itself. 

software-dependent adj. Of, pertaining to, or being a 

computer or device that is tied to a particular program or 

set of programs developed for it. 

software development kit n. See developer’s kit. 

software engineer n. 1. In general, one who works at the 

code level with software. Although such engineering can 

be considered to encompass everything from software 

design to management and testing, the term is generally 

considered more or less synonymous with programmer— 

one who actually writes the code. 2. See developer. 

software engineering n. The design and development of 

software. See also programming. 

software handshake n. A handshake that consists of signals 

transmitted over the same wires used to transfer the 

data, as in modem-to-modem communications over telephone 

lines, rather than signals transmitted over special 

wires. See also handshake. 

software house n. An organization that develops and 

supports software for its customers. 

software IC n. See software integrated circuit. 

software integrated circuit n. An existing software 

module that can be designed into a program, much as an 

integrated circuit can be designed into a logic board. 

Abbreviation: software IC. See also abstract data type, 

module (definition 1), object-oriented programming. 

software interrupt n. A program-generated interrupt that 

stops current processing in order to request a service provided 

by an interrupt handler (a separate set of instructions 

designed to perform the task required). Also called: trap. 

software package n. A program sold to the public, 

ready to run and containing all necessary components and 

documentation. 

software piracy n. See piracy. 

S

S 

software portability sort algorithm 

software portability n. See portable (definition 1). 

software program n. See application. 

software protection n. See copy protection. 

software publisher n. A business engaged in the development 

and distribution of computer software. 

Software Publishers Association n. See SIIA. 

software publishing n. The design, development, and 

distribution of noncustom software packages. 

software rot n. See dead code. 

software stack n. See stack. 

software suite n. See suite (definition 1). 

software tools n. Programs, utilities, libraries, and other 

aids, such as editors, compilers, and debuggers, that can 

be used to develop programs. 

SOHO n. Acronym for Small Office/Home Office, a 

term used for home-based and small businesses. The 

fast-growing SOHO market has sparked a concomitant 

expansion in computer software and hardware products 

designed specifically to meet the needs of self-employed 

individuals or small businesses. See also distributed 

workplace, telecommuter. 

SOI n. Acronym for silicon on insulator. A method used in 

the construction of microprocessors in which the chip’s 

transistors—the tiny circuits that conduct electrical 

charges—are built on a layer of silicon placed on top of a 

layer of insulating material, such as glass. SOI construction 

improves speed at the same time it reduces the 

amount of power required by the microprocessor. 

solar cell n. A photoelectric device that produces electrical 

power when exposed to light. Also called: photovoltaic 

cell. 

Solaris n. A distributed UNIX-based computing environment 

created by Sun Microsystems, Inc., widely used as a 

server operating system. Versions of Solaris exist for 

SPARC computers, 386 and higher Intel platforms, and 

the PowerPC. 

solenoid n. An electromagnetic device that converts electrical 

energy to mechanical movement, typically consisting 

of an electromagnet with a movable rod through the 

center. 

solid ink n. Ink manufactured in the form of solid sticks 

resembling crayons, for use in solid-ink printers. See also 

solid-ink printer. 

490 

solid-ink printer n. A computer printer using solid ink 

sticks. The ink sticks are heated until they melt, and the 

molten ink is sprayed onto the page, where it cools and 

solidifies. See also solid ink. 

solid model n. A geometric shape or construction that has 

continuity in length, width, and depth and is treated by a 

program as if it had both surface and internal substance. 

Compare surface modeling, wire-frame model. 

solid-state device n. A circuit component whose properties 

depend on the electrical or magnetic characteristics of 

a solid substance (as opposed to a gas or vacuum). Transistors, 

diodes, and integrated circuits are solid-state 

devices. 

solid-state disk drive n. A mass storage device that 

holds data in RAM rather than in magnetic storage. See 

also magnetic storage, RAM. 

solid-state memory n. Computer memory that stores 

information in solid-state devices. 

solid-state relay n. A relay that depends on solid-state 

components, rather than mechanical components, to open 

and close a circuit. 

SOM n. 1. Acronym for System Object Model. A language-independent 

architecture from IBM that implements 

the CORBA standard. See also CORBA, OMA. 

2. Acronym for self-organizing map. A form of neural 

network in which neurons and their connections are added 

automatically as needed to develop the desired mapping 

from input to output. 

SONET n. Acronym for Synchronous Optical Network. A 

high-speed network that provides a standard interface for 

communications carriers to connect networks based on 

fiberoptic cable. SONET is designed to handle multiple 

data types (voice, video, and so on). It transmits at a base 

rate of 51.84 Mbps, but multiples of this base rate go as 

high as 2.488 Gbps (gigabits per second). 

sort vb. To organize data, typically a set of records, in a 

particular order. Programs and programming algorithms 

for sorting vary in performance and application. See also 

bubble sort, distributive sort, insertion sort, merge sort, 

quicksort, Shell sort. 

sort algorithm n. An algorithm that puts a collection of 

data elements into some sequenced order, sometimes 

based on one or more key values in each element. See also 

algorithm, bubble sort, distributive sort, insertion sort, 

merge sort, quicksort, Shell sort.

sorter source program 

sorter n. A program or routine that sorts data. See also sort. 

sort field n. See sort key. 

sort key n. A field (commonly called a key) whose 

entries are sorted to produce a desired arrangement of the 

records containing the field. See also field (definition 1), 

primary key, secondary key. 

SOS n. See silicon-on-sapphire. 

Sound Blaster n. 1. A family of sound cards manufactured 

by Creative Technology or its subsidiary, Creative 

Labs. See also sound card. 2. A de facto standard set by 

the family of sound cards developed by Creative Technologies 

and its subsidiaries. Many other manufacturers also 

make Sound Blaster–compatible products. 

sound board n. See sound card. 

sound buffer n. A region of memory used to store the bit 

image of a sequence of sounds to be sent to a computer’s 

speaker(s). 

sound card n. A type of expansion board on PC-compatible 

computers that allows the playback and recording 

of sound, such as from a WAV or MIDI file or a music 

CD-ROM. Most PCs sold at retail include a sound card. 

Also called: sound board. See also expansion board, 

MIDI, WAV. 

sound clip n. A file that contains a short audio item, usually 

an excerpt from a longer recording. 

sound editor n. A program that allows the user to create 

and manipulate sound files. 

sound generator n. A chip or chip-level circuit that can 

produce electronic signals that can drive a speaker and 

synthesize sound. 

sound hood n. A five-sided box, lined with soundproofing 

material, that is placed over a loud printer to muffle 

its noise. 

SoundSentry n. An optional Windows feature that 

instructs Windows to produce a visual cue such as a screen 

flash or a blinking title bar whenever a system beep 

occurs. SoundSentry is designed for users with hearing 

impairments or users who operate a computer in a noisy 

environment. 

source n. 1. In information processing, a disk, file, document, 

or other collection of information from which data 

is taken or moved. Compare destination. 2. In a FET, the 

electrode toward which charge carriers (electrons or holes) 

move from the source under control of the gate. See also 

491 

CMOS (definition 1), drain (definition 1), FET, gate (definition 

2), MOSFET, NMOS, PMOS. 

source code n. Human-readable program statements written 

by a programmer or developer in a high-level or assembly 

language that are not directly readable by a computer. 

Source code needs to be compiled into object code before it 

can be executed by a computer. Compare object code. 

source code control system n. A tool designed to track 

changes made to source code files. Changes are documented 

in such a way that previous versions of the files can 

be retrieved. Source code control is used in software development, 

particularly in situations involving concurrent 

development and multiple user access to source code files. 

source computer n. 1. A computer on which a program 

is compiled. Compare object computer. 2. A computer 

from which data is transferred to another computer. 

source data n. The original data on which a computer 

application is based. 

source data acquisition n. The process of sensing, as 

with a bar code reader or other scanning device, or receiving 

source data. See also source data. 

source data capture n. See source data acquisition. 

source directory n. During a file copy operation, the 

directory in which the original versions of the files are 

located. 

source disk n. Any disk from which data will be read, as 

during a copy operation or when an application is loaded 

from a disk into memory. Compare target disk. 

source document n. The original document from which 

data is taken. 

source drive n. The disk drive from which files are being 

copied during a copy operation. 

source file n. 1. A file that contains source code. See also 

source code. 2. A file that contains the data that a program 

will process and store in a destination file. 3. In MS-DOS 

and Windows commands that involve the copying of data 

or program instructions, the file containing the data or 

instructions that are copied. 

source language n. The programming language in 

which the source code for a program is written. See also 

programming language, source code. 

source program n. The source code version of a program. 

See also source code. Compare executable program. 

S

S 

source statement special character 

source statement n. A single statement in the source 

code of a program. See also source code, statement. 

SPA n. See SIIA. 

spacebar n. The long key occupying much of the bottom 

row of most keyboards that sends a space character to the 

computer. 

space character n. A character that is entered by pressing 

the Spacebar on the keyboard and that typically 

appears on the screen as a blank space. 

space-division multiplexing n. The first automated form 

of communications multiplexing, which replaced the 

human-operated switchboard. Space-division multiplexing 

was replaced by frequency-division multiplexing (FDM), 

which was in turn replaced by time-division multiplexing 

(TDM). Acronym: SDM. See also FDM, multiplexing, 

time-division multiplexing. 

spaghetti code n. Code that results in convoluted program 

flow, usually because of excessive or inappropriate 

use of GOTO or JUMP statements. See also GOTO statement, 

jump instruction. 

spam1 vb. To distribute unwanted, unrequested mail 

widely on the Internet by posting a message to too many 

recipients or too many newsgroups. The act of distributing 

such mail, known as spamming, angers most Internet users 

and has been known to invite retaliation, often in the form 

of return spamming that can flood and possibly disable the 

electronic mailbox of the original spammer. 

spam2 n. 1. An unsolicited e-mail message sent to many 

recipients at one time, or a news article posted simultaneously 

to many newsgroups. Spam is the electronic 

equivalent of junk mail. In most cases, the content of a 

spam message or article is not relevant to the topic of the 

newsgroup or the interests of the recipient; spam is an 

abuse of the Internet in order to distribute a message to a 

huge number of people at minimal cost. 2. An unsolicited 

e-mail message from a business or individual that seeks to 

sell the recipient something. Also called: UCE, unsolicited 

commercial e-mail. 

spam blocking n. See address munging. 

spambot n. A program or device that automatically posts 

large amounts of repetitive or otherwise inappropriate 

material to newsgroups on the Internet. See also bot (definition 

3), robopost, spam1 . 

spamdexter n. An individual who lures users to spamrelated 

Web sites by loading the site with hundreds of hid- 

492 

den copies of popular keywords, even if those words have 

no relation to the Web site. Because the keywords appear 

so many times, the spamdexter’s site will appear near the 

top of search result and indexing lists. The term spamdexter 

was created by combining the words spam and index. 

Also called: keyword stuffing. 

span n. See range. 

SPARC n. Short for Scalable Processor Architecture. A 

RISC (reduced instruction set computing) microprocessor 

specification from Sun Microsystems, Inc. See also RISC. 

sparse array n. An array (arrangement of items) in which 

many of the entries are identical, commonly zero. It is not 

possible to define precisely when an array is sparse, but it 

is clear that at some point, usually when about one-third of 

the array consists of identical entries, it becomes worthwhile 

to redefine the array. See also array. 

sparse infector n. A type of virus or other malicious 

code that delivers its payload only when certain predetermined 

conditions are met. A sparse infector might hide on 

an infected computer until a certain date or until a certain 

number of files or applications have been run. By restricting 

their active phases to only certain situations, sparse 

infectors are more likely to avoid detection. 

spatial data management n. The representation of data 

as a collection of objects in space, particularly as icons on 

a screen, in order to make the data easier to comprehend 

and manipulate. 

spatial digitizer n. A three-dimensional scanner most 

often used in medical and geographical work. Compare 

optical scanner. 

speaker dependent recognition n. A type of automatic 

speech recognition (ASR) in which the computer system 

becomes accustomed to the voice and accent of a specific 

speaker, allowing a larger vocabulary can be recognized. 

See also ASR, speaker independent recognition. 

speaker independent recognition n. A type of automatic 

speech recognition (ASR) in which the computer 

system will respond to commands from any speaker. 

Because the system does not adjust to the nuances of a 

specific voice, only a limited vocabulary is possible. See 

also ASR, speaker dependent recognition. 

spec n. See specification. 

special character n. Any character that is not alphabetic, 

numeric, or the space character (for example, a

special interest group spoiler 

punctuation character). See also reserved character, wildcard 

character. 

special interest group n. See SIG. 

special-purpose language n. A programming language 

whose syntax and semantics are best suited for a given 

field or approach. See also Prolog. 

specification n. 1. A detailed description of something. 

2. In relation to computer hardware, an item of information 

about the computer’s components, capabilities, and 

features. 3. In relation to software, a description of the 

operating environment and proposed features of a new 

program. 4. In information processing, a description of the 

data records, programs, and procedures involved in a particular 

task. Also called: spec. 

spectral color n. In video, the hue represented by a single 

wavelength in the visible spectrum. See also color model. 

spectral response n. In relation to sensing devices, the 

relationship between the device’s sensitivity and the frequency 

of the detected energy. 

spectrum n. The range of frequencies of a particular type 

of radiation. See also electromagnetic spectrum. 

Speech API n. See SAPI. 

Speech Application Programming Interface n. See 

SAPI. 

speech recognition n. See voice recognition. 

Speech Recognition API n. See SRAPI. 

Speech Recognition Application Programming 

Interface n. See SRAPI. 

speech synthesis n. The ability of a computer to produce 

“spoken” words. Speech synthesis is produced either 

by splicing together prerecorded words or by programming 

the computer to produce the sounds that make up 

spoken words. See also artificial intelligence, neural network, 

synthesizer. 

spelling checker n. An application that employs a diskbased 

dictionary to check for misspellings in a document. 

Also called: spell checker. 

spew vb. On the Internet, to post an excessive number of 

e-mail messages or newsgroup articles. 

spider n. An automated program that searches the Internet 

for new Web documents and indexes their addresses 

and content-related information in a database, which can 

be examined for matches by a search engine. Spiders are 

generally considered to be a type of bot, or Internet robot. 

493 

Also called: crawler. See also bot (definition 3), search 

engine (definition 2). 

spike n. A transient electrical signal of very short duration 

and usually high amplitude. Compare surge. 

spindle n. 1. An axle for mounting a disk or reel of magnetic 

tape. 2. Any drive included within the chassis of a 

laptop or other portable computer. A laptop including a 

floppy disk drive and a hard drive would be considered a 

two-spindle machine. 

spintronics n. An emerging field of study in electronics 

and physics that is based on the ability to detect and control 

the spin of electrons in magnetic materials. Using 

spintronics, it might eventually be possible to produce 

small, fast electronic devices, including transistors, memory 

devices, and quantum computers. 

Spirale virus n. See Hybris virus. 

splash screen n. A screen containing graphics, animation, 

or other attention-getting elements that appears while 

a program is loading or as an introductory page to a Web 

site. A splash screen used with an application typically 

contains a logo, version information, author credits, or a 

copyright notice, and it appears when a user opens a program 

and disappears when loading is complete. A splash 

screen used on a Web site serves as a front door, typically 

loading before any content-related pages. 

spline n. In computer graphics, a curve calculated by a 

mathematical function that connects separate points with a 

high degree of smoothness. See the illustration. See also 

Bézier curve. 

F0Sgn19.eps 

Spline. 

split screen n. A display method in which a program can 

divide the display area into two or more sections, which 

can contain different files or show different parts of the 

same file. 

spoiler n. A post to a newsgroup or mailing list that 

reveals what is intended to be a surprise, such as a plot 

twist in a film or television episode or the solution to a 

S

S 

spoofing SRAPI 

game. The subject line should contain the word spoiler, 

but netiquette requires that the sender further protect readers 

who do not or cannot scan posts for subject lines in 

advance by encrypting the post, putting one or more 

screenfuls of white space above the text, or both. See also 

netiquette. 

spoofing n. The practice of making a transmission appear 

to come from an authorized user. For example, in IP 

spoofing, a transmission is given the IP address of an 

authorized user in order to obtain access to a computer or 

network. See also IP address. 

spool vb. To store a data document in a queue, where it 

awaits its turn to be printed. See also print spooler. 

spot n. A “composite dot” produced through the halftone 

creation process on a PostScript printer that consists of a 

group of dots arranged in a pattern reflecting the gray level 

of a particular pixel. See also gray scale, halftone. Compare 

dot (definition 2). 

spot color n. A method of handling color in a document 

in which a particular color of ink is specified and each 

page having elements in that color is printed as a separate 

layer. The printer then prints one layer for each spot color 

in the document. See also color model, color separation 

(definition 1), PANTONE MATCHING SYSTEM. Compare 

process color. 

spot function n. The PostScript procedure used to create 

a given type of screen in a halftone. See also halftone, 

PostScript, spot. 

SPP n. See scalable parallel processing. 

spraycan n. An artist’s tool in Paintbrush or another graphics 

application for applying a pattern of dots to an image. 

spreadsheet program n. An application commonly used 

for budgets, forecasting, and other finance-related tasks 

that organizes data values using cells, where the relationships 

between cells are defined by formulas. A change to 

one cell produces changes to related cells. Spreadsheet 

programs usually provide graphing capabilities for output 

and a variety of formatting options for text, numeric values, 

and graph features. See also cell (definition 1). 

spread spectrum adj. Of or pertaining to a system of 

secure radio communication in which the content of a 

transmission is broken into split-second pieces, which 

are transmitted over separate frequencies. When a 

receiver identifies a spread spectrum signal, it reassembles 

it to its original form. Spread spectrum was invented 

494 

by the actress Hedy Lamarr in 1940, but it was not used 

until 1962. 

Springboard n. Handspring Inc.’s expansion platform for 

its line of Visor handheld personal digital assistants. The 

term describes both the 68-pin Springboard socket incorporated 

into the Visor, as well as a series of add-on 

Springboard modules that fit into the socket. Add-on modules 

include features such as multimedia, games, e-books, 

additional memory storage, and a wireless phone module. 

See also Visor. 

sprite n. In computer graphics, a small image that can be 

moved on the screen independently of other images in the 

background. Sprites are widely used in animation 

sequences and video games. See also object (definition 3). 

sprocket feed n. A paper feed in which pins engage 

holes in the paper to move it through a printer. Pin feed 

and tractor feed are both sprocket feeds. See also paper 

feed, pin feed, tractor feed. 

SPX n. 1. Acronym for Sequenced Packet Exchange. The 

transport level (ISO/OSI level 4) protocol used by Novell 

NetWare. SPX uses IPX to transfer the packets, but SPX 

ensures that messages are complete. See also ISO/OSI reference 

model. Compare IPX. 2. Acronym for simplex. See 

simplex. 

SQL n. See structured query language. 

square wave n. A blocklike waveform that is generated 

by a source that changes instantly between alternate states, 

usually at a single frequency. See the illustration. Compare 

sine wave. 

Amplitude 

F0Sgn20.eps 

Square wave. 

Time 

SRAM n. See static RAM. 

SRAPI n. Acronym for Speech Recognition Application 

Programming Interface. A cross-platform application programming 

interface for speech recognition and text-tospeech 

functions supported by a consortium of developers 

including Novell, IBM, Intel, and Philips Dictation Sys-

SSA standard 

tems. See also application programming interface, speech 

recognition. 

SSA n. Acronym for Serial Storage Architecture. An interface 

specification from IBM in which devices are arranged 

in a ring topology. In SSA, which is compatible with SCSI 

devices, data can be transferred at up to 20 megabytes per 

second in each direction. See also SCSI device. 

SSD n. Acronym for solid-state disk. See solid-state disk 

drive. 

SSE n. Short for Streaming SIMD Extensions. A set of 70 

new instructions implemented in Intel’s Pentium III 

microprocessor. SSE, more formally called Internet SSE 

(ISSE), uses SIMD (single-instruction, multiple-data) 

operations to accelerate floating point calculations. 

Designed to improve performance in visual areas such as 

real-time 3-D and graphics rendering, SSE also provides 

support for development of such applications as real-time 

video and speech recognition. See also SIMD. 

SSI n. 1. See small-scale integration. 2. See server-side 

include. 

SSL n. Acronym for Secure Sockets Layer. A protocol 

developed by Netscape Communications Corporation for 

ensuring security and privacy in Internet communications. 

SSL supports authentication of client, server, or both, as 

well as encryption during a communications session. While 

primary purpose of SSL is to enable secure electronic financial 

transactions on the World Wide Web, it is designed to 

work with other Internet services as well. This technology, 

which uses public key encryption, is incorporated into the 

Netscape Navigator Web browser and Netscape’s commerce 

servers. See also commerce server, open standard, 

public key encryption, PCT. Compare S-HTTP. 

SSO n. See single sign-on. 

ST506 interface n. The hardware signal specification 

developed by Seagate Technologies for hard-disk-drive 

controllers and connectors. The ST506/412 version of this 

interface has become a de facto standard. 

stack n. A region of reserved memory in which programs 

store status data such as procedure and function call 

addresses, passed parameters, and sometimes local variables. 

See also pop, push (definition 1). Compare heap 


stacking order n. The order in which layers in a digital 

graphic file are arranged. Foreground elements are typi- 

495 

cally stacked on top of background elements. Changes in 

stacking order can affect the way the final graphic is seen 

by the viewer. See also layering. 

stack pointer n. A register that contains the current 

address of the top element of the stack. See also pointer 

(definition 1), stack. 

stackware n. A HyperCard application consisting of a 

HyperCard data stack and HyperCard programming. See 

also HyperCard. 

staging web n. A local Web site maintained on a file system 

or local Web server that currently cannot be browsed 

by site visitors. These Web sites allow authors and workgroups 

to make changes or updates to Web sites before 

they are published. 

staging Web server n. A Web server where you publish 

and test your Web site before putting it on a production 

server. A staging Web server cannot be browsed by an 

Internet or intranet audience. 

stairstepping n. A rough outline like the steps of a stair 

in a graphic line or curve that should be smooth. Also 

called: aliasing, jaggies. 

stale link n. A hyperlink to an HTML document that has 

been deleted or moved, rendering the hyperlink useless. 

See also HTML document, hyperlink. 

stale pointer bug n. See aliasing bug. 

stand-alone or standalone adj. Of, pertaining to, or 

being a device that does not require support from another 

device or system, for example, a computer that is not connected 

to a network. 

standard n. 1. A de jure technical guideline advocated by 

a recognized noncommercial or government organization 

that is used to establish uniformity in an area of hardware 

or software development. The standard is the result of a 

formal process, based on specifications drafted by a cooperative 

group or committee after an intensive study of 

existing methods, approaches, and technological trends 

and developments. The proposed standard is later ratified 

or approved by a recognized organization and adopted 

over time by consensus as products based on the standard 

become increasingly prevalent in the market. Standards of 

this type are numerous, including the ASCII character set, 

the RS-232-C standard, the SCSI interface, and ANSIstandard 

programming languages, such as C and FOR- 

TRAN. See also ANSI, convention, RS-232-C standard, 

S

S 

standard ASCII start page 

SCSI. 2. A de facto technical guideline for hardware or 

software development that occurs when a product or philosophy 

is developed by a single company and, through 

success and imitation, becomes so widely used that deviation 

from the norm causes compatibility problems or limits 

marketability. This type of highly informal standard 

setting is exemplified by Hayes-compatible modems and 

IBM PC–compatible computers. See also compatibility 


standard ASCII n. The set of characters assigned to 

ASCII (American Standard Code for Information Interchange) 

values between decimal 0 and 127 (hexadecimal 

00 through 7F). These characters include most found on a 

standard keyboard, including the letters A–Z (uppercase 

and lowercase), numerals (0 through 9), and some special 

characters, such as colons and parentheses. Standard 

ASCII has for years been used as a near-universal “common 

language” in the PC environment for enabling different 

programs to exchange information reliably. See also 

ASCII. Compare Extended ASCII. 

standard deviation n. In statistics, a measure of the dispersion 

of a group of measurements relative to the mean 

(average) of that group. Each score’s difference from the 

mean is squared, and the standard deviation is defined as 

the square root of the average of these squared values. 

standard disclaimer n. A phrase placed in an e-mail 

message or news article that is intended to replace the 

statement required by some businesses and institutions 

that the contents of the message or article do not necessarily 

represent the opinions or policies of the organization 

from whose e-mail system the message originated. 

standard function n. A function that is always available 

within a particular programming language. See also function 


Standard Generalized Markup Language n. See 

SGML. 

standby n. A state in which your computer consumes less 

power when it is idle but remains available for immediate 

use. While your computer is on standby, information in 

computer memory is not saved on your hard disk. If there is 

an interruption in power, the information in memory is lost. 

star n. See *. 

star bus n. A network topology in which nodes connect to 

hubs in a star pattern, but the hubs are connected by a bus 

trunk. Star bus is a combination of star and bus topologies. 

496 

star-dot-star or star dot star n. A file specification (*.*) 

using the asterisk wildcard, which means “any combination 

of file name and extension” in operating systems such 

as MS-DOS. See also *.*, asterisk, wildcard character. 

star network n. A LAN (local area network) in which 

each device (node) is connected to a central computer in a 

star-shaped configuration (topology); commonly, a network 

consisting of a central computer (the hub) surrounded 

by terminals. See the illustration. Compare bus 

network, ring network. 

Node 1 

Node 2 

F0Sgn21.eps 

Star network. 

Hub 

Node 3 

Node 5 

Node 4 

start bit n. In asynchronous transmission, the bit (actually, 

a timing signal) that represents the beginning of a 

character. See also asynchronous transmission. Compare 

parity bit, stop bit. 

Start button n. In Microsoft Windows 9x and Windows 

NT 4 and later, the control on the desktop task bar that 

opens the main menu. 

starting point n. A World Wide Web document designed 

to help users begin navigating the Web. A starting point 

often contains tools such as search engines and hyperlinks 

to selected Web sites. See also hyperlink, search engine 

(definition 2), World Wide Web. 

star topology n. A network configuration based on a 

central hub, from which nodes radiate in a star-shaped pattern. 

See also topology. 

start page n. See home page (definition 2).

start/stop transmission stationery2 stationery 

start/stop transmission n. See asynchronous 

transmission. 

startup n. See boot1 . 

startup application n. On the Macintosh, the application 

that takes control of the system when the computer is 

turned on. 

STARTUP.CMD n. A special-purpose batch file stored in 

the root directory of the startup disk in OS/2—the OS/2 

equivalent of an MS-DOS AUTOEXEC.BAT file. 

startup disk n. See system disk. 

startup ROM n. The bootstrap instructions coded into a 

computer’s ROM (read-only memory) and executed at 

startup. The startup ROM routines enable a computer to 

check itself and its devices (such as the keyboard and disk 

drives), prepare itself for operation, and run a short program 

to load an operating-system loader program. See 

also boot1 , power-on self test. 

startup screen n. A text or graphics display that appears 

on the screen when a program is started (run). Startup 

screens usually contain information about the software’s 

version and often contain a product or corporate logo. 

star-wired ring n. A network topology in which hubs and 

nodes connect to a central hub in typical star fashion, but 

the connections within the central hub form a ring. Starwired 

ring is a combination of star and ring topologies. 

state n. See status. 

stateful adj. Of or pertaining to a system or process that 

monitors all details of the state of an activity in which it 

participates. For example, stateful handling of messages 

takes account of their content. Compare stateless. 

stateless adj. Of or pertaining to a system or process that 

participates in an activity without monitoring all details of 

its state. For example, stateless handling of messages 

might take account of only their sources and destinations 

but not their content. Compare stateful. 

statement n. The smallest executable entity within a programming 

language. 

state-of-the-art adj. Up to date; at the forefront of current 

hardware or software technology. 

static1 adj. In information processing, fixed or predetermined. 

For example, a static memory buffer remains 

invariant in size throughout program execution. The opposite 

condition is dynamic, or ever-changing. 

497 

static2 n. In communications, a crackling noise caused 

by electrical interference with a transmitted signal. See 

also noise (definition 2). 

static allocation n. Apportionment of memory that 

occurs once, usually when the program starts. The memory 

remains allocated during the program’s execution and 

is not deallocated until the program is finished. See also 

allocate, deallocate. Compare dynamic allocation. 

static binding n. Binding (converting symbolic 

addresses in the program to storage-related addresses) that 

occurs during program compilation or linkage. Also 

called: early binding. Compare dynamic binding. 

static buffer n. A secondary sound buffer that contains 

an entire sound; these buffers are convenient because the 

entire sound can be written once to the buffer. See also 

streaming buffer. 

static electricity n. An electrical charge accumulated in 

an object. Although generally harmless to humans, the 

discharge of static electricity through an electronic circuit 

can cause severe damage to the circuit. 

static RAM n. A form of semiconductor memory (RAM) 

based on the logic circuit known as a flip-flop, which 

retains information as long as there is enough power to run 

the device. Static RAMs are usually reserved for use in 

caches. Acronym: SRAM. See also cache, RAM, synchronous 

burst static RAM. Compare dynamic RAM. 

static routing n. Routing based on a fixed forwarding 

path. Unlike dynamic routing, static routing does not 

adjust to changing network conditions. Compare dynamic 

routing. 

static Web page n. Web page that displays the same 

content to all viewers. Usually written in hypertext 

markup language (HTML), a static Web page displays 

content that changes only if the HTML code is altered. See 

also dynamic Web page. 

station n. 1. In the IEEE 802.11 wireless LAN specification, 

a single, often mobile, node. 2. See workstation. 

stationery1 adj. Describing a type of document that, 

when opened by the user, is duplicated by the system; the 

copy is opened for the user’s modification while the original 

document remains intact. Stationery documents can be 

used as document templates or boilerplates. See also boilerplate, 

template (definition 5). 

stationery2 n. A stationery document. See also 

stationery1 . 

S

S 

statistical multiplexer storage area network 

statistical multiplexer n. A multiplexing device that 

adds intelligence to time-division multiplexing by using 

buffering (temporary storage) and a microprocessor to combine 

transmission streams into a single signal and to allocate 

available bandwidth dynamically. Also called: stat 

mux. See also dynamic allocation, multiplexing, timedivision 

multiplexing. 

statistics n. The branch of mathematics that deals with 

the relationships among groups of measurements and with 

the relevance of similarities and differences in those relationships. 

See also binomial distribution, Monte Carlo 

method, probability, regression analysis, standard deviation, 

stochastic. 

stat mux n. See statistical multiplexer. 

status n. The condition at a particular time of any of 

numerous elements of computing—a device, a communications 

channel, a network station, a program, a bit, or 

other element—used to report on or to control computer 

operations. 

status bar n. In Windows 9x and Windows NT 4 and 

later, a space at the bottom of many program windows that 

contains a short text message about the current condition 

of the program. Some programs also display an explanation 

of the currently selected menu command in the status 

bar. See the illustration. 

F0Sgn22.eps 

Status bar. 

status codes n. Strings of digits or other characters that 

indicate the success or failure of some attempted action. 

Status codes were commonly used to report the results of 

early computer programs, but most software today uses 

words or graphics. Internet users, especially those with 

UNIX shell accounts, are likely to encounter status codes 

while using the Web or FTP. See also HTTP status codes. 

steganography n. A “hide-in-plain-sight” technique for 

concealing information by embedding a message within 

an innocuous cover message. In steganography, bits of 

unnecessary data within an image, sound, text, or even a 

blank file are replaced with bits of invisible information. 

The term steganography comes from the Greek for “covered 

writing” and has traditionally included any method of 

secret communication that conceals the existence of the 

message. Because steganography cannot be detected by 

decryption software, it is often used to replace or supplement 

encryption. 

498 

step-frame n. The process of capturing video images one 

frame at a time. This process is used by computers that are 

too slow to capture analog video images in real time. 

stepper motor n. A mechanical device that rotates only a 

fixed distance each time it receives an electrical pulse. A 

stepper motor is part of a disk drive. 

step-rate time n. The time required to move a disk actuator 

arm from one track to the next. See also actuator, 

stepper motor. 

stereogram n. See autostereogram. 

sticky adj. In reference to a Web site, properties such as 

targeted content or services that increase the amount of 

time users choose to spend at the site and increase user’s 

desire to return to the site repeatedly. 

StickyKeys n. An accessibility feature built into Macintosh 

and Windows computers that causes modifier keys 

such as Shift, Control, or Alt to “stay on” after they are 

pressed, eliminating the need to press multiple keys simultaneously. 

This feature facilitates the use of modifier keys 

by users who are unable to hold down one key while 

pressing another. 

stochastic adj. Based on random occurrences. For example, 

a stochastic model describes a system by taking into 

account chance events as well as planned events. 

stop bit n. In asynchronous transmission, a bit that signals 

the end of a character. In early electromechanical 

teleprinters, the stop bit provided time for the receiving 

mechanism to coast back to the idle position and, 

depending on the mechanism, had a duration of 1, 1.5, or 

2 data bits. See also asynchronous transmission. Compare 

parity bit, start bit. 

Stop error n. A serious error that affects the operating 

system and that could place data at risk. The operating 

system generates an obvious message, a screen with the 

Stop error, rather than continuing on and possibly corrupting 

data. Also called: blue screen error, fatal system error. 

See also Blue Screen of Death. 

storage n. In computing, any device in or on which information 

can be kept. Microcomputers have two main types 

of storage: random access memory (RAM) and disk drives 

and other external storage media. Other types of storage 

include read-only memory (ROM) and buffers. 

storage area network n. A high-speed network that provides 

a direct connection between servers and storage, 

including shared storage, clusters, and disaster-recovery

storage device streaming buffer 

devices. A storage area network, or SAN, includes components 

such as hubs and routers that are also used in local 

area networks (LANs), but it differs in being something of a 

“subnetwork” dedicated to providing a high-speed connection 

between storage elements and servers. Most SANs rely 

on fiber-channel connections that deliver speeds up to 1000 

Mbps and can support up to 128 devices. SANs are implemented 

to provide the scalability, speed, and manageability 

required in environments that demand high data availability. 

Acronym: SAN. Also called: system area network. 

storage device n. An apparatus for recording computer 

data in permanent or semipermanent form. When a distinction 

is made between primary (main) storage devices 

and secondary (auxiliary) storage devices, the former 

refers to random access memory (RAM) and the latter 

refers to disk drives and other external devices. 

storage location n. The position at which a particular 

item can be found—either an addressed location or a 

uniquely identified location on a disk, tape, or similar 

medium. 

storage media n. The various types of physical material 

on which data bits are written and stored, such as floppy 

disks, hard disks, tape, and optical discs. 

storage tube n. See direct view storage tube. 

store-and-forward n. A method of delivering transmissions 

in which messages are held temporarily by an intermediary 

before being sent on to their destination. Store 

and forward is used by some switches in delivering packets 

to their destinations. Compare cut-through switch. 

stored procedure n. A precompiled collection of SQL 

statements and optional control-of-flow statements stored 

under a name and processed as a unit. They are stored in 

an SQL database and can be run with one call from an 

application. 

stored program concept n. A system architecture 

scheme, credited largely to the mathematician John von 

Neumann, in which both programs and data are in directaccess 

storage (random access memory, or RAM), thereby 

allowing code and data to be treated interchangeably. See 

also von Neumann architecture. 

storefront n. See virtual storefront. 

storm n. On a network, a sudden, excessive burst of traffic. 

Storms are often responsible for network outages. 

STP n. Acronym for shielded twisted pair. A cable consisting 

of one or more twisted pairs of wires and a sheath 

499 

of foil and copper braid. The twists protect the pairs from 

interference by each other, and the shielding protects the 

pairs from interference from outside. Therefore, STP 

cable can be used for high-speed transmission over long 

distances. See also twisted-pair cable. Compare UTP. 

straight-line code n. Program code that follows a direct 

sequence of statements rather than skipping ahead or 

jumping back via transfer statements such as GOTO and 

JUMP. See also GOTO statement, jump instruction. Compare 


stream1 n. Any data transmission, such as the movement 

of a file between disk and memory, that occurs in a continuous 

flow. Manipulating a data stream is a programming 

task. Consumers, however, are likely to encounter references 

to streams and streaming in connection to the Internet, 

which has increased reliance on stream techniques to 

enable users (even those with slower equipment) to access 

large multimedia files—especially those containing audio 

and video components—and to display or play them 

before all the data has been transferred. 

stream2 vb. To transfer data continuously, beginning to 

end, in a steady flow. Many aspects of computing rely on 

the ability to stream data: file input and output, for example, 

and communications. If necessary, an application 

receiving a stream must be able to save the information to 

a buffer in order to prevent loss of data. On the Internet, 

streaming enables users to begin accessing and using a file 

before it has been transmitted in its entirety. 

stream cipher n. A method for encrypting a data 

sequence of unlimited length using a key of fixed length. 

See also key (definition 3). Compare block cipher. 

streaming n. 1. On the Internet, the process of delivering 

information, especially multimedia sound or video, in a 

steady flow that the recipient can access as the file is being 

transmitted. 2. In magnetic tape storage devices, a lowcost 

technique to control the motion of the tape by removing 

tape buffers. Although streaming tape compromises 

start/stop performance, it achieves highly reliable storage 

and retrieval of data, and is useful when a steady supply of 

data is required by a particular application or computer. 

streaming buffer n. A small sound buffer that can play 

lengthy sounds because the application dynamically loads 

audio data into the buffer as it plays. For example, an 

application could use a buffer that can hold 3 seconds of 

audio data to play a 2-minute sound. A streaming buffer 

requires much less memory than a static buffer. See also 

static buffer. 

S

S 

Streaming Server StrongARM 

Streaming Server n. A server technology designed by 

Apple Computer to send streaming QuickTime media files 

over the Internet. Built on RTP and RTSP standard Internet 

protocols, Streaming Server can set up a QuickTime 

streaming media Web broadcasting station capable of 

streaming digital videos and music files to more than 3000 

users via the Internet. Streaming Server may be used with 

Mac OS X and other UNIX-based operating systems. Also 

called: Darwin Streaming Server, QuickTime Streaming 

Server. 

streaming tape n. See tape (definition 1). 

stream interface device driver n. A user-level DLL that 

controls devices connected to a Windows CE–based platform. 

A stream interface device driver presents the services 

of a hardware device to applications by exposing 

Win32 stream interface functions. Stream interface drivers 

also can control devices built into a Windows CE–based 

platform, depending on the software architecture for the 

drivers. Also called: installable device driver. 

stream-oriented file n. A file used to store a fairly continuous 

series of bits, bytes, or other small, structurally 

uniform units. 

street price n. The actual retail or mail-order price of a 

consumer hardware or software product. In most cases, the 

street price is somewhat lower than the “suggested retail 

price.” 

stress test n. A test of a software or hardware system’s 

functional limits, performed by subjecting the system to 

extreme conditions, such as peak volumes of data or 

extremes in temperature. 

strikethrough n. One or more lines drawn through a 

selected range of text, usually to show deletion or the 

intent to delete. See the illustration. 

F0Sgn23.eps 

Strikethrough. 

string n. A data structure composed of a sequence of 

characters usually representing human-readable text. 

string variable n. An arbitrary name assigned by the programmer 

to a string of alphanumeric characters and used 

to reference that entire string. See also string. 

500 

stripe vb. See disk striping. 

stripe pitch n. The distance, measured horizontally, 

between bands of phosphor that are the same color on a 

cathode ray tube (CRT) display based on aperture grill 

technology. Although the measurements are based on different 

methods of applying phosphor to the screen surface, 

stripe pitch is comparable to dot pitch, the measurement 

used with CRTs based on shadow mask technology. See 

also aperture grill, CRT, mask (definition 2). Compare dot 

pitch, slot pitch. 

striping n. A means of protecting data on a network by 

spreading it across multiple disks. In the most commonly 

used approach, striping is combined with parity (error-correcting 

information) to ensure that if some portion of the 

data is lost, it can be reconstructed. Striping is implemented 

in RAID security. See also RAID. Compare disk 

mirroring. 

strobe n. A timing signal that initiates and coordinates 

the passage of data, typically through an input/output (I/O) 

device interface, such as a keyboard or printer. 

stroke n. 1. In data entry, a keystroke—a signal to the 

computer that a key has been pressed. 2. In typography, a 

line representing part of a letter. 3. In paint programs, a 

“swipe” of the brush made with the mouse or keyboard in 

creating a graphic. 4. In display technology, a line created 

as a vector (a path between two coordinates) on a vector 

graphics display (as opposed to a line of pixels drawn dot 

by dot on a raster graphics display). 

stroke font n. A font printed by drawing a combination 

of lines rather than by filling a shape, as with an outline 

font. Compare outline font. 

stroke weight n. The width, or thickness, of the lines 

(strokes) that make up a character. See also font. 

stroke writer n. In video, a display unit that draws characters 

and graphic images as sets of strokes—lines or 

curves connecting points—rather than as sets of dots, as 

on a typical raster-scan monitor. See also vector graphics. 

StrongARM n. The architecture underlying Intel’s lowpower, 

high-performance SA microprocessors. StrongARM 

is based on the 32-bit RISC architecture licensed 

by ARM Limited. StrongARM-based SA microprocessors 

support a number of platforms, including Windows CE 

and Java, and are designed for use in four primary areas:

strong name submenu 

smart portable devices, such as cellular phones and handheld 

computers; Internet access devices, such as set-top 

boxes; networking devices, such as switches and routers; 

and embedded controls, such as entertainment devices and 

automation equipment. See also ARM. 

strong name n. A name that consists of an assembly’s 

identity: its simple text name, version number, and often 

the culture information strengthened by a public key and a 

digital signature generated over the assembly. Assemblies 

with the same strong name are expected to be identical. 

strong typing n. A characteristic of a programming language 

that does not allow the program to change the data 

type of a variable during program execution. See also data 

type, variable. Compare weak typing. 

structure n. 1. The design and composition of a program, 

including program flow, hierarchy, and modularity. 2. A 

collection of data elements. See also data structure. 

structured graphics n. See object-oriented graphics. 

structured programming n. Programming that produces 

programs with clean flow, clear design, and a degree 

of modularity or hierarchical structure. See also modular 

programming, object-oriented programming. Compare 


structured query language n. A database sublanguage 

used in querying, updating, and managing relational 

databases—the de facto standard for database products. 

Acronym: SQL. 

structured walkthrough n. 1. A meeting of programmers 

working on different aspects of a software development 

project, in which the programmers attempt to 

coordinate the various segments of the overall project. 

The goals, requirements, and components of the project 

are systematically reviewed in order to minimize the error 

rate of the software under development. 2. A method for 

examining a computer system, including its design and 

implementation, in a systematic fashion. 

STT n. See Secure Transaction Technology. 

stub n. A routine that contains no executable code and 

that generally consists of comments describing what will 

eventually be there; it is used as a placeholder for a routine 

to be written later. Also called: dummy routine. See also 

top-down programming. 

StuffIt n. A file compression program originally written 

for the Apple Macintosh, used for storing a file on one or 

501 

more disks. Originally shareware, StuffIt is now a commercial 

product for Macs and PCs that supports multiple 

compression techniques and allows file viewing. StuffIt 

files can be uncompressed using a freeware program, 

StuffIt Expander. 

style sheet n. 1. A file of instructions used to apply character, 

paragraph, and page layout formats in word processing 

and desktop publishing. 2. A text file containing code 

to apply semantics such as page layout specifications to an 

HTML document. See also HTML document, semantics 


stylus n. A pointing device, similar to a pen, used to 

make selections, usually by tapping, and to enter information 

on the touch-sensitive surface. 

subclass n. A class in object-oriented programming that 

is derived from, and inherits its attributes and methods 

from, another class known as a superclass. Compare 

superclass. 

subcommand n. A command in a submenu (a menu that 

appears when a user selects an option in a higher-level 

menu). 

subdirectory n. A directory (logical grouping of related 

files) within another directory. 

subdomain n. A domain, often representing an administrative 

or other organizational subgroup within a secondlevel 

domain. See also domain. 

subform n. A form contained within another form or a 

report. 

subject drift n. See topic drift. 

subject tree n. A type of World Wide Web index that is 

organized by subject categories, many of which are broken 

down into subcategories, or “branches.” An example of a 

World Wide Web subject tree is Yahoo! See also Yahoo! 

submarining n. A phenomenon that occurs when some 

part of a screen display moves more quickly than the 

screen can show. The object (such as the mouse pointer) 

disappears from the screen and reappears where it comes 

to rest, just as a submarine resurfaces after a dive. Submarining 

is especially a problem with the slowly responding 

passive-matrix LCD displays on many laptop computers. 

submenu n. A menu that appears as the result of the 

selection of an item on another, higher-level menu. 

S

S 

subnet SuperDrive 

subnet n. 1. In general, a network that forms part of a 

larger network. 2. In terms of the ISO/OSI reference 

model, the subnet comprises the layers below the transport 

layer—that is, the network, data link, and physical layers. 

subnet mask n. See address mask. 

subnetting n. The division of a network into subnets to 

improve network security and performance. See also subnet 

(definition 1). Compare supernetting. 

subnetwork n. A network that is part of another, larger 

network. 

subnotebook n. A class of portable computer that is 

smaller in size and lighter in weight than a full-sized laptop. 

Subnotebooks feature a reduced-sized keyboard and 

screen and often use an external floppy drive to save space 

and weight. Despite their size, subnotebooks retain all the 

functions of a full-sized portable computer. 

subportable n. See subnotebook. 

subprogram n. A term used in some languages for routine 

(procedure or function) because the structure and syntax 

of a subprogram closely model those of a program. See 

also program, routine. 

subreport n. A report contained within another report. 

subroutine n. A common term for routine, likely to be 

used in reference to shorter, general, frequently called routines. 

See also procedure, routine. 

subschema n. The definition of a user view of the database 

(in CODASYL/DBTG systems only), roughly equivalent 

to the external schema of an ANSI/X3/SPARC 

database management system or to a view in a relational 

database management system. See also schema. 

subscribe vb. 1. To add a newsgroup to the list of such 

groups from which a user receives all new articles. 2. To 

add a name to a LISTSERV distribution list. See also 

LISTSERV. 

Subscriber Identity Module card n. See SIM card. 

subscript n. 1. One or more characters printed slightly 

below the baseline of surrounding text. See also baseline. 

Compare superscript. 2. In programming, one or more 

numbers or variables that identify the location of an element 

in an array. See also array, index (definition 2). 

subscription site n. E-commerce Web site that provides 

information or services to customers who pay a subscription 

fee. 

502 

substrate n. The inactive supporting material used in a 

manufacturing process. In circuit boards, it is the base to 

which the traces (foil areas) are attached. In tapes and 

disks, it is the material on which the magnetic particles are 

fused. 

substring n. A sequential section of a string. See also 

string. 

subtransaction n. See nested transaction. 

subtree n. Any node within a tree, along with any selection 

of connected descendant nodes. See also node (definition 

3), tree. 

subweb n. A named subdirectory of the root Web site that 

is a complete FrontPage-based Web site. Each subweb can 

have independent administration, authoring, and browsing 

permissions from the root Web site and other subwebs. 

suitcase n. A file on Macintosh computers that contains 

one or more fonts or desk accessories. In early versions of 

the operating system, such files are indicated with the icon 

of a suitcase. See also font suitcase. 

suite n. 1. A set of application programs sold as a package, 

usually at a lower price than that of the individual 

applications sold separately. A suite for office work, for 

example, might contain a word processing program, a 

spreadsheet, a database management program, and a communications 

program. 2. See protocol suite. 

summarize vb. To post the results of a survey or vote in 

short form to a newsgroup or mailing list after collecting 

the results by e-mail. 

SunOS n. Short for Sun Operating System. A variety of 

the UNIX operating system used on workstations from 

Sun Microsystems, Inc. 

superclass n. A class in object-oriented programming 

from which another class—a subclass—is derived. The 

subclass inherits its attributes and methods from the superclass. 

Compare subclass. 

supercomputer n. A large, extremely fast, and expensive 

computer used for complex or sophisticated calculations. 

See also computer. 

superconductor n. A substance that has no resistance to 

the flow of electricity. 

SuperDrive n. An Apple 3.5-inch disk drive that can read 

and write in both Apple Macintosh (400K and 800K) and 

MS-DOS/Windows (720K and 1.44-MB) formats.

super-large-scale integration surface modeling 

super-large-scale integration n. A reference to the density 

with which components (transistors and other elements) 

are packed onto an integrated circuit and to the fineness of 

the connections between them. The actual number of components 

is nonspecific, but generally considered to be in of 

50,000 to 100,000 range. Acronym: SLSI. See also integrated 

circuit. Compare large-scale integration, mediumscale 

integration, small-scale integration, ultra-large-scale 

integration, very-large-scale integration. 

superminicomputer n. See computer. 

supernetting n. The aggregation of multiple network 

addresses of the same class into a single block. See also 

classless interdomain routing, IP address classes. Compare 

subnetting. 

superpipelining n. A method of preprocessing used by 

some microprocessors in which two or more of a microprocessor’s 

execution stages (fetch, decode, execute, and 

write-back) are divided into two or more pipelined stages, 

resulting in higher performance. See also DECchip 21064, 

pipelining (definition 1). 

superscalar adj. Of, pertaining to, or being a microprocessor 

architecture that enables the microprocessor to execute 

multiple instructions per clock cycle. See also CISC, 

RISC. 

superscript n. A character printed slightly above the surrounding 

text, usually in smaller type. Compare subscript 


superserver n. A network server with especially high 

capabilities for speed and data storage. See also server 


superstitial n. An Internet ad format that downloads in 

the background while a user is viewing a Web page and 

then plays in a pop-up window when triggered by a mouse 

click or a break in surfing. Because the superstitial doesn’t 

appear until it has completely downloaded and temporarily 

cached itself on the user’s system, attention-getting 

effects like animation, sound, and large graphics can be 

used without slowing down the ad. Unicast developed the 

“polite cache and play” technology used with the superstitial 

ad format. 

supertwist display n. A form of passive-matrix liquid 

crystal displays (LCDs) that rotates polarized light as it 

passes through liquid crystal molecules in which the top 

and bottom orientations of the molecules causes them to 

twist 180 to 270 degrees. This technology is used to 

503 

improve contrast and widen the screen’s viewing angle. 

Supertwist displays, also known as supertwist nematic displays, 

are widely used and are less expensive than activematrix 

displays. Different forms of supertwist displays 

include DSTN (double supertwist nematic), which is 

based on two supertwist layers with opposite twist directions, 

and CSTN (color supertwist nematic), which produces 

wide-angle, high-quality color. Nematic refers to 

microscopic threadlike bodies characteristic of the liquid 

crystals used in these displays. Supertwist displays are 

widely used in cellular telephones and other devices that 

may be used in low-light environments. Also called: color 

supertwist nematic display, CSTN, double supertwist 

nematic, DSTN, twisted nematic display. See also twisted 

nematic display. 

superuser n. A UNIX user account with root (i.e., unrestricted) 

access privileges, usually that of a system administrator. 

See also root account, system administrator, user 

account. 

super VAR n. Short for super value-added reseller. A 

large value-added reseller. See also value-added reseller. 

Super VGA n. See SVGA. 

supervisor n. 1. See operating system. 2. A metaoperating 

system under which several operating systems are 

active. See also metaoperating system. 

supervisor state n. The most privileged of the modes in 

which a Motorola 680x0 microprocessor can operate. 

Every operation of which the microprocessor is capable 

can be executed in the supervisor state. See also privileged 

mode. Compare user state. 

support1 n. Assistance, such as technical advice provided 

to customers. 

support2 vb. To work with another program or product; 

for example, an application might support file transfers 

from another program. 

surf vb. To browse among collections of information on 

the Internet, in newsgroups, in Gopherspace, and especially 

on the World Wide Web. As in channel surfing 

while watching television, users ride the wave of what 

interests them, jumping from topic to topic or from one 

Internet site to another. Also called: cruise. 

surface modeling n. A display method used by some 

CAD programs that gives on-screen constructions the 

appearance of solidity. See also CAD. Compare solid 

model, wire-frame model. 

S

S 

surface-mount technology swarm intelligence 

surface-mount technology n. A method of manufacturing 

printed circuit boards in which chips are fixed directly 

to the surface of the board instead of being soldered into 

holes predrilled to hold them. Its advantages are compactness, 

resistance to vibration, and the capacity for dense 

interconnections on both sides of the board. Acronym: 

SMT. Compare DIP, leadless chip carrier, pin grid array. 

surge n. A sudden—and possibly damaging—increase in 

line voltage. See also surge protector, voltage regulator. 

Compare power failure, spike. 

surge protector n. A device that prevents surges from 

reaching a computer or other kinds of electronic equipment. 

Also called: surge suppressor. See also surge, transient 

suppressor. 

surge suppressor n. See surge protector. 

suspend vb. To halt a process temporarily. See also sleep2 . 

Suspend command n. A power management feature of 

Windows 9x and Windows NT 4 and later for portable 

computers. Clicking on the Suspend command in the Start 

menu allows the user to temporarily suspend operations of 

the machine (enter “Suspend mode”) without turning the 

power off, saving battery power without having to restart 

applications or reload data. 

suspend mode n. See sleep mode. 

sustained transfer rate n. A measure of the speed at 

which data can be transferred to a storage device such as a 

disk or a tape. The sustained transfer rate is the data transfer 

speed that can be kept up by the device for an extended 

period of time. 

SVC n. Acronym for switched virtual circuit. A logical 

connection between two nodes on a packet-switching network 

that is established only when data is to be transmitted. 

See also node (definition 1), packet switching. 

Compare PVC. 

SVG n. Acronym for Scalable Vector Graphics. An XMLbased 

language for device-independent description of twodimensional 

graphics. SVG images maintain their appearance 

when printed or when viewed with different screen 

sizes and resolutions. SVG is a recommendation of the 

World Wide Web Consortium (W3C). 

SVGA n. Acronym for Super Video Graphics Array. A 

video standard established by the Video Electronics Standards 

Association (VESA) in 1989 to provide high-resolution 

color display on IBM-compatible computers. 

504 

Although SVGA is a standard, compatibility problems can 

occur with the video BIOS. See also BIOS, video adapter. 

S-video connector n. A hardware interface for video 

devices that handles chrominance (color) and luminance 

(black and white) separately. An S-video connector is 

capable of providing a sharper image than those achieved 

with systems using RCA-type, or composite, connectors. 

S/WAN n. See secure wide area network. 

swap vb. 1. To exchange one item for another, as in swapping 

floppy disks in and out of a single drive. 2. To move 

segments of programs or data between memory and disk 

storage. See also virtual memory. 

swap file n. A hidden file on the hard drive that Windows 

uses to hold parts of programs and data files that do not fit 

in memory. The operating system moves data from the 

swap file to memory as needed and moves data out of 

memory to the swap file to make room for new data. The 

swap file is a form of virtual memory. See also memory, 

virtual memory. 

swap-on-the-fly n. In Linux, a process which allows swap 

space to be added as needed. Swap-on-the-fly allows a 

swap file to be created at any time on any available disk, 

and active only until the system is shut down. 

swapping n. 1. A technique for enabling an operating 

system, and therefore a computer, to address—roughly, 

have available—more memory than is physically present 

in the system. Swapping in this sense (as opposed to swapping 

disks in and out of a drive, for example) involves 

moving blocks of information in units known as pages 

between memory and disk as they are needed during the 

execution of the application. Swapping is supported by 

operating systems such as Windows NT and later, Windows 

9x and later, OS/2, and Linux. 2. A technique for 

moving entire processes in and out of main memory. 3. In 

programming, the process of exchanging two values—for 

example, exchanging values between two variables. See 

also page (definition 2), swap, swap file, virtual memory. 

swap space n. See swap file. 

swarm intelligence n. An emerging subfield of artificial 

intelligence that relies on the collective knowledge 

of relatively simple particles or agents. Based loosely on 

the principles of social insect colonies, it seeks to apply 

the collective intelligence of fragmented agents or 

groups. It emphasizes distributedness, direct or indirect 

interactions, flexibility, and robustness. Successful appli-

Swatch symbol font 

cations of its principles have been evidenced in communications 

networks, and robotics. See also artificial 

intelligence, robotics. 

Swatch n. Short for Simple Watcher. A UNIX log monitoring 

and alarm program. Swatch filters system log data 

as specified by the user, forwarding only important data. 

Swatch also looks for patterns of changes made in the log 

file and alerts the user to system problems as they occur. 

swim n. A condition in which images slowly move about 

the positions they are supposed to occupy on screen. 

SWING set n. A library of Java GUIs that run uniformly 

on any native platform that supports the Java Virtual 

Machine (JVM). Swing Set components have largely supplanted 

Sun Microsystems’s Abstract Window Toolkit. 

See also Abstract Window Toolkit, graphical user interface, 

Java Virtual Machine. 

switch n. 1. A circuit element that has two states: on and 

off. 2. A control device that allows the user to choose one 

of two or more possible states. 3. In communications, a 

computer or electromechanical device that controls routing 

and operation of a signal path. 4. In networking, a 

device capable of forwarding packets directly to the ports 

associated with particular network addresses. See also 

bridge, multilayer, router. 5. In operating systems such as 

MS-DOS, an argument used to control the execution of a 

command or an application, typically starting with a slash 

character (/). 

switch box n. An enclosure that contains a selector 

switch. When a user selects a switch setting, the signal 

passing through the box may be directed either from a 

single input to one of multiple outputs, or from the 

selected input to a single output. Switch boxes are often 

used to connect multiple peripherals, such as printers, to 

a single port. 

switched configuration n. A communications link in 

which a signal moves from the origin to a switch that 

routes the signal to one of several possible destinations. 

Compare point-to-point configuration. 

switched Ethernet n. An Ethernet network run through 

a high-speed switch instead of an Ethernet hub. A 

switched Ethernet involves dedicated bandwidth of 10 

Mbps between stations rather than a shared medium. See 

also Ethernet (definition 1), switch (definition 3). 

switched line n. A standard dial-up telephone connection; 

the type of line established when a call is routed 

through a switching station. Compare leased line. 

505 

Switched Multimegabit Data Services n. See SMDS. 

switched network n. A communications network that 

uses switching to establish a connection between parties, 

such as the dial-up telephone system. 

Switched T1 n. A circuit-switched form of T1 communications. 

See also T1. 

switched virtual circuit n. See SVC. 

Switcher n. A special Macintosh utility that allowed 

more than one program to be resident in memory at one 

time. Switcher was made obsolete by MultiFinder. See 

also MultiFinder. 

switching n. A communications method that uses temporary 

rather than permanent connections to establish a link 

or to route information between two parties. In the dial-up 

telephone network, for example, a caller’s line goes to a 

switching center, where the actual connection is made to 

the called party. In computer networks, message switching 

and packet switching allow any two parties to exchange 

information. In both instances, messages are routed 

(switched) through intermediary stations that together 

serve to connect the sender and the receiver. 

switching hub n. A central device (switch) that connects 

separate communication lines in a network and routes 

messages and packets among the computers on the network. 

The switch functions as a hub, or PBX, for the network. 

See also hub, packet (definition 1), PBX, switch 

(definition 3), switched Ethernet, switched network. 

switching speed n. In a packet-switching telecommunications 

technology, such as ATM, the speed at which data 

packets are sent through the network. Switching speed is 

generally measured in kilobits or megabits per second. See 

also ATM (definition 1), packet switching. 

SYLK file n. Short for symbolic linkfile. A file constructed 

with a proprietary Microsoft format, used primarily 

for exchanging spreadsheet data in such a way that 

formatting information and intercellular data value relationships 

are preserved. 

symbol n. In programming, a name that represents a register, 

an absolute value, or a memory address (relative or 

absolute). See also identifier, operator (definition 1). 

symbol font n. A special font or typeface that replaces 

the characters normally accessible from the keyboard with 

alternative characters used as symbols, such as scientific, 

linguistic, or foreign-alphabet characters. 

S

S 

symbolic address Synchronous Digital Hierarchy 

symbolic address n. A memory address that can be 

referred to in a program by name rather than by number. 

symbolic coding n. The expression of an algorithm in 

words, decimal numbers, and symbols rather than in 

binary numbers, so that a person can read and understand 

it. Symbolic coding is used in high-level programming 

languages. See also algorithm, high-level language. 

symbolic language n. A computer language that uses 

symbols such as keywords, variables, and operators to 

form instructions. All computer languages except machine 

language are symbolic. 

symbolic link n. A disk directory entry that takes the 

place of a directory entry for a file but is actually a reference 

to a file in a different directory. Also called: alias, 

shortcut, soft link, symlink. 

symbolic logic n. A representation of the laws of reasoning, 

so named because symbols rather than natural-language 

expressions are used to state propositions and 

relationships. See also logic. 

symbol set n. Any collection of symbols legitimized by a 

data-coding system, such as extended ASCII, or a programming 

language. 

symbol table n. A list of all identifiers encountered when 

a program is compiled (or assembled), their locations in 

the program, and their attributes, such as variable, routine, 

and so on. See also compile, identifier, linker, module 

(definition 1), object code. 

symlink n. See symbolic link. 

symmetric digital subscriber line n. See SDSL. 

symmetric multiprocessing n. See SMP. 

symmetric multiprocessing server n. See SMP server. 

SYN n. Short for synchronous idle character. A character 

used in synchronous (timed) communications that enables 

the sending and receiving devices to maintain the same 

timing. Also called: sync character. 

sync character n. See SYN. 

syncDRAM n. See SDRAM. 

synchronization n. 1. In networking, a communications 

transmission in which multibyte packets of data are sent 

and received at a fixed rate. See also packet (definition 1). 

2. In networking, the matching of timing between computers 

on the network. All of the computers are generally 

assigned identical times to facilitate and coordinate com- 

506 

munications. 3. In a computer, the matching of timing 

between components of the computer so that all are coordinated. 

For instance, operations performed by the operating 

system are generally synchronized with the signals of 

the machine’s internal clock. See also clock (definition 1), 

operating system. 4. In application or database files, version 

comparisons of copies of the files to ensure they contain 

the same data. 5. In multimedia, precise real-time 

processing. Audio and video are transmitted over a network 

in synchronization so that they can be played back 

together without delayed responses. See also real-time. 

6. In handheld computing, the process of updating or backing 

up the data on a handheld computer to the linked software 

applications on a desktop computer. Data changes 

made on the desktop computer may also be copied to the 

handheld during synchronization. See also partnership. 

synchronization signal n. See sync signal. 

synchronize vb. To cause to occur at the same time. 

Synchronized Multimedia Integration Language n. 

See SMIL. 

synchronous adj. Occurring at the same time. In computer 

transmissions, a reference to activity governed by a 

clock or by synchronized timing. 

synchronous burst static RAM n. A type of static 

RAM that is synchronized with the system clock. Synchronous 

burst static RAM is used in a computer’s L2 

cache, where frequently accessed information is stored 

for fast retrieval by the CPU. Synchronous burst static 

RAM is faster than asynchronous static RAM but is limited 

to a maximum bus speed of 66 MHz. Computers 

running at faster speeds can use another form of cache 

memory known as pipeline burst static RAM. Also 

called: sync SRAM. See also L2 cache, static RAM. 

Compare asynchronous static RAM, dynamic RAM, 

pipeline burst static RAM. 

synchronous communications n. Computer-to-computer 

communications in which transmissions are synchronized 

by timing between the sending and receiving 

machines. 

Synchronous Data Link Control n. See SDLC. 

Synchronous Digital Hierarchy n. An ITU recommendation 

implemented in Europe and similar in most 

respects to the SONET standard used in North America 

and Japan. See also SONET.

synchronous DRAM sysop 

synchronous DRAM n. See SDRAM. 

synchronous graphics RAM n. A form of dynamic 

RAM optimized for the high-speed, high-volume data 

transfers required by 3D graphics, video, and other memory-intensive 

applications. Used primarily on video 

accelerator cards, synchronous graphics RAM makes use 

of burst operations and includes features such as block 

writes that increase efficiency in retrieving and writing 

graphics data to the screen. Acronym: SGRAM. See also 

block, mask. 

synchronous idle character n. See SYN. 

synchronous operation n. 1. Any procedure under the 

control of a clock or timing mechanism. Compare asynchronous 

operation. 2. In communications and bus operation, 

data transfer accompanied by clock pulses either 

embedded in the data stream or provided simultaneously 

on a separate line. 

synchronous operation n. 1. Two or more processes that 

depend on the occurrences of specific events such as common 

timing signals. 2. A data transmission method in 

which there is constant time between successive bits, characters, 

or events. The timing is achieved by the sharing of 

a single clock. Each end of the transmission synchronizes 

itself with the use of clocks and information sent along 

with the transmitted data. Characters are spaced by time 

and not by start and stop bits. 3. A function call that blocks 

execution of a process until it returns. See also asynchronous 

operation. 

Synchronous Optical Network n. See SONET. 

synchronous protocol n. A set of guidelines developed 

to standardize synchronous communications between 

computers, usually based on either bit stream transmission 

or recognized character codes. Examples include the character-oriented 

binary synchronous (BISYNC) protocol 

and the bit-oriented High-level Data Link Control 

(HDLC) and Synchronous Data Link Control (SDLC) 

protocols. See also BISYNC, HDLC, SDLC. 

synchronous transmission n. Data transfer in which 

information is transmitted in blocks (frames) of bits separated 

by equal time intervals. Compare asynchronous 

transmission. 

synchronous UART n. A universal asynchronous 

receiver/transmitter (UART) that supports synchronous 

serial transmission, where the sender and receiver share a 

timing signal. See also UART. 

507 

sync signal n. Short for synchronization signal. The part 

of a raster-display video signal that denotes the end of 

each scan line (the horizontal sync signal) and the end of 

the last scan line (the vertical sync signal). 

sync SRAM n. See synchronous burst static RAM. 

SYN flood n. A method of overwhelming a host computer 

on a network, especially the Internet, by sending the host a 

high volume of SYN (synchronization) packets requesting 

a connection, but never responding to the acknowledgement 

packets returned by the host. A SYN flood is a form 

of denial of service attack. See also denial of service 

attack. Compare Ping of Death. 

synonym n. 1. A word that is an equivalent of another 

word. When used in reference to data input, for example, 

the verbs type and keyboard are synonyms. 2. In hashing, 

one of two distinct keys that produce the same hash 

address. See also hash2 . 

syntax n. The grammar of a language; the rules governing 

the structure and content of statements. See also logic, 

programming language, syntax error. Compare semantics 


syntax checker n. A program for identifying errors in 

syntax for a programming language. See also syntax, syntax 

error. 

syntax error n. An error resulting from a statement that 

violates one or more of the grammatical rules of a language 

and is thus not “legal.” See also logic, semantics 

(definition 1), syntax. 

synthesis n. The combining of separate elements to form 

a coherent whole, or the result of such a combining (for 

example, combining digital pulses to replicate a sound, or 

combining digitized words to synthesize human speech). 

See also speech synthesis. 

synthesizer n. A computer peripheral, chip, or standalone 

system that generates sound from digital instructions 

rather than through manipulation of physical equipment 

or recorded sound. See also MIDI. 

.sys n. A file extension for system configuration files. 

sysadmin n. The usual logon name or e-mail address for 

the system administrator of a UNIX-based system. See 

also system administrator. 

sysgen n. See system generation. 

sysop n. Short for system operator. The overseer of a bulletin 

board system (BBS) or a small multiuser computer 

system. 

S

S 

Sys Req key System Request key 

Sys Req key n. Short for System Request key. A key on 

some IBM and compatible keyboards that is intended to 

provide the same function as the Sys Req key on an IBM 

mainframe computer terminal: to reset the keyboard or to 

change from one session to another. 

system n. Any collection of component elements that 

work together to perform a task. Examples are a hardware 

system consisting of a microprocessor, its allied chips and 

circuitry, input and output devices, and peripheral devices; 

an operating system consisting of a set of programs and 

data files; or a database management system used to process 

specific kinds of information. 

system administrator n. The person responsible for 

administering use of a multiuser computer system, communications 

system, or both. A system administrator performs 

such duties as assigning user accounts and 

passwords, establishing security access levels, allocating 

storage space, and watching for unauthorized access to 

prevent virus or Trojan horse programs from entering the 

system. Also called: sysadmin. See also superuser, Trojan 

horse, virus. Compare sysop. 

system area network n. See storage area network. 

system board n. See motherboard. 

system clock n. See clock (definition 1). 

system console n. The control center of a computer system, 

primarily with reference to mainframe and minicomputers. 

In networked or distributed systems, one 

workstation is designated as the system administrator’s; 

this workstation is analogous to the LAN system console. 

See also console, LAN. 

system conversion n. Changing from one operating system 

to another—for example, from Windows 98 to Windows 

2000, UNIX, or OS/2. 

system development n. The process of defining, designing, 

testing, and implementing a new system. 

system disk n. A disk that contains an operating system 

and can be used to boot a computer. Also called: startup 

disk. See also boot2 , operating system. 

system error n. A software condition that renders the 

operating system incapable of continuing to function normally. 

This type of error usually requires rebooting the 

system. 

system failure n. The inability of a computer to continue 

functioning, usually caused by software rather than 

hardware. 

508 

System file n. A resource file on the Macintosh that contains 

the resources needed by the operating system, such 

as fonts, icons, and default dialog boxes. 

System folder n. The Macintosh file folder (directory) 

that contains the System file and other vital files, such as 

Finder, device drivers, INIT files, and control panel files. 

See also control panel, Finder, INIT, System file. 

system font n. On the Macintosh and in some PC applications, 

the font used by the computer for on-screen text, 

such as menu titles and items (but not on-screen text 

within a word processor or other application). See also 

font. 

system generation n. The process of configuring and 

installing system software for a particular set of hardware 

components. Complex operating systems such as UNIX 

are shipped with device drivers and utilities that are often 

not relevant to a particular hardware configuration; putting 

together only the necessary components, as well as specifying 

important system characteristics, is part of the system 

generation process. Also called: sysgen. 

system heap n. See heap (definition 1). 

system.ini n. In Windows 3.x, the initialization file used 

to store the hardware configuration information necessary 

to run the Windows operating environment. The system.ini 

file was replaced by the registry database in Windows 

9x and in Windows NT. See also ini file. 

system life cycle n. An information system’s useful life. 

At the end of a system’s life cycle it is not feasible to 

repair or expand it, so it must be replaced. 

system memory n. See memory. 

System Object Model n. See SOM (definition 1). 

system on a chip n. See SOC. 

system operator n. See sysop. 

system prompt n. See prompt (definition 1). 

system recovery n. Processing that takes place after a 

system failure in order to restore a system to normal operation. 

System recovery takes place after the operating system 

is initiated. It sometimes requires that tasks in process 

during the failure be backed out of and that structures in 

memory during the failure be reconstructed. 

System Registry n. See registry. 

system replacement n. See replacement strategy. 

System Request key n. See Sys Req key.

system resource System V 

system resource n. On the Macintosh, any of numerous 

routines, definitions, and data fragments that are stored in 

the Macintosh System file, such as floating-point arithmetic 

routines, font definitions, and peripheral drivers. See 

also resource (definition 2). 

systems analysis n. The examination of a system or 

problem with the goal of either improving an existing system 

or designing and implementing a new one. As a science, 

systems analysis is related to cybernetics, a branch 

of engineering that studies the behavior of systems. 

systems analyst n. A person who works on designing 

and developing systems. Systems analysts generally combine 

technical, managerial, and human-relations activities 

in order to complete their analyses. 

Systems Application Architecture n. See SAA. 

systems integration n. The development of a computer 

system for a particular customer by combining products 

from different original equipment manufacturers (OEMs). 

Systems Management Server n. A Microsoft Back- 

Office component that provides services for centralized 

network management. Acronym: SMS. 

509 

Systems Network Architecture n. See SNA. 

system software n. The collection of programs and data 

that make up and relate to the operating system. Compare 

application. 

systems programming n. The development or maintenance 

of programs designed to execute as part of an operating 

system, such as I/O routines, user interfaces, 

command-line interpreters, and task-scheduling and memory 

management routines. 

system support n. The provision of services and material 

resources for the use, maintenance, and improvement 

of an implemented system. 

system timer n. See clock (definition 1). 

system unit n. See console. 

System V n. A version of the UNIX system provided by 

AT&T and others. It is both a standard (principally controlled 

by AT&T) and a set of commercial products. See 

also UNIX. 

S

T 

T prefix See tera-. 

T1 or T-1 n. A high-speed communications line that can 

handle digital communications and Internet access at the 

rate 1.544 Mbps (megabits per second). Although originally 

designed by AT&T to carry multiple voice calls over standard 

twisted-pair telephone wiring, this high-bandwidth 

telephone line can also transmit text and images. T1 speed 

is attained through multiplexing 24 separate 64 Kbps channels 

into a single data stream. T1 lines are commonly used 

by larger organizations for Internet connectivity. Also 

called: T-1 carrier. See also T-carrier. Compare fractional 

T1, T2, T3, T4. 

T.120 standard n. A family of International Telecommunications 

Union (ITU) specifications for multipoint data 

communications services within computer applications, 

such as conferencing and multipoint file transfer. 

T2 or T-2 n. A T-carrier that can handle 6.312 Mbps 

(megabits per second) or 96 voice channels. See also 

T-carrier. Compare T1, T3, T4. 







TA n. See terminal adapter. 

tab character n. A character used to align lines and columns 

on screen and in print. Although a tab is visually 

indistinguishable from a series of blank spaces in most 

programs, the tab character and the space character are 

different to a computer. A tab is a single character and 

therefore can be added, deleted, or overtyped with a single 

keystroke. The ASCII coding scheme includes two codes 

for tab characters: a horizontal tab for spacing across the 

screen or page and a vertical tab for spacing down the 

screen or page. See also Tab key. 

Tab key n. A key, often labeled with both a left-pointing 

and a right-pointing arrow, that traditionally (as in word 

processing) is used to insert tab characters into a docu- 

T 

510 

ment. In other applications, such as menu-driven programs, 

the Tab key is often used to move the on-screen 

highlight from place to place. Many database and spreadsheet 

programs allow the user to press the Tab key to move 

around within a record or between cells. The word tab is 

short for “tabulator,” which was the name given to this key 

on typewriters, where it was used in creating tables. See 

also tab character. 

table n. 1. In programming, a data structure usually consisting 

of a list of entries, each entry being identified by a 

unique key and containing a set of related values. A table 

is often implemented as an array of records, a linked list, 

or (in more primitive languages) several arrays of different 

data types, all using a common indexing scheme. See also 

array, list, record1 . 2. In relational databases, a data structure 

characterized by rows and columns, with data occupying 

or potentially occupying each cell formed by a rowcolumn 

intersection. The table is the underlying structure 

of a relation. See also relational database. 3. In word processing, 

desktop publishing, and in HTML documents, a 

block of text formatted in aligned rows and columns. 

table lookup n. The process of using a known value to 

search for data in a previously constructed table of values— 

for example, using a purchase price to search a tax table for 

the appropriate sales tax. See also lookup. 

tablet n. See graphics tablet. 

Tablet PC n. A touch-sensitive computer screen tablet 

designed by Microsoft for the entry of handwritten text 

using a stylus or digital pen. The Tablet PC runs Windows 

applications and can function as a primary personal computer 

as well as a note-taking device. 

tabulate vb. 1. To total a row or column of numbers. 

2. To arrange information in table form. 

TACACS n. Acronym for Terminal Access Controller 

Access Control System. A network access technique in 

which users log into a single centralized server that contains 

a database of authorized accounts. After the access 

server authenticates the user, it forwards the login information 

to the data server requested by the user. See also 

authentication, server (definition 2).

tag tape tree 

tag n. 1. In programming, one or more characters containing 

information about a file, record type, or other structure. 

2. In certain types of data files, a key or an address 

that identifies a record and its storage location in another 

file. See also tag sort. 3. In markup languages such as 

SGML and HTML, a code that identifies an element in a 

document, such as a heading or a paragraph, for the purposes 

of formatting, indexing, and linking information in 

the document. In both SGML and HTML, a tag is generally 

a pair of angle brackets that contain one or more letters 

and numbers. Usually one pair of angle brackets is 

placed before an element, and another pair is placed after, 

to indicate where the element begins and ends. For example, 

in HTML, hello world indicates that the 

phrase “hello world” should be italicized. See also , element, 

emotag, HTML, SGML. 4. An early-generation raster 

graphics format used for Macintosh Ready, Set, Go 

programs and Letraset’s ImageStudio. See also raster 

graphics. 

Tagged Image File Format n. See TIFF. 

tag sort n. A sort performed on one or several key fields 

for the purpose of establishing the order of their associated 

records. Also called: key sort. 

tag switching n. A multilayer Internet switching technology 

developed by Cisco Systems that integrates routing 

and switching. 

talk1 n. The UNIX command that, when followed by 

another user’s name and address, is used to generate a 

request for a synchronous chat session on the Internet. See 

also chat1 (definition 1). 

talk2 vb. See chat2 . 

talker n. An Internet-based synchronous communication 

mechanism most commonly used to support multiuser 

chat functions. Such systems typically provide specific 

commands for movement through separate rooms, or chat 

areas, and allow users to communicate with other users in 

real time through text messages, indicate simple gestures, 

use a bulletin board system (BBS) for posting comments, 

and send internal e-mail. See also BBS (definition 1), 

chat1 (definition 1). 

talk. newsgroups n. Usenet newsgroups that are part of 

the talk. hierarchy and have the prefix talk. as part of their 

names. These newsgroups are devoted to debate and discussion 

of controversial topics. Talk. newsgroups are one 

of the seven original Usenet newsgroup hierarchies. The 

511 

other six are comp., misc., news., rec., sci., and soc. See 

also newsgroup, traditional newsgroup hierarchy, Usenet. 

tandem processors n. Multiple processors wired so 

that the failure of one processor transfers central processing 

unit (CPU) operation to another processor. Using tandem 

processors is part of the strategy for implementing 

fault-tolerant computer systems. See also central processing 

unit. 

TANSTAAFL n. Acronym for There ain’t no such thing as 

a free lunch. An expression used on the Internet in e-mail, 

chat sessions, mailing lists, newsgroups, and other online 

forums; derived from The Moon Is a Harsh Mistress, a 

science-fiction classic by Robert A. Heinlein. See also 

chat1 (definition 1), e-mail1 (definition 1), mailing list, 

newsgroup. 

tap1 n. A device that can be attached to an Ethernet bus to 

enable a computer to be connected. 

tap2 vb. To use a stylus to quickly touch a device screen 

to perform an activity. Tapping is analogous to clicking 

with a mouse. 

tap and hold vb. To hold a stylus on a device screen to 

open a pop-up or shortcut menu. Analogous to right-clicking 

with a mouse. 

tape n. 1. A thin strip of polyester film coated with magnetic 

material that permits the recording of data. Because 

tape is a continuous length of data storage material and 

because the read/write head cannot “jump” to a desired 

point on the tape without the tape first being advanced to 

that point, tape must be read or written sequentially, not 

randomly (as can be done on a floppy disk or a hard disk). 

2. A storage medium consisting of a thin strip of paper 

used to store information in the form of sequences of 

punched holes, chemical impregnation, or magnetic ink 

imprinting. 

tape cartridge n. A module that resembles an audio cassette 

and contains magnetic tape that can be written on and 

read from by a tape drive. Tape cartridges are primarily 

used to back up hard disks. See also tape (definition 1). 

tape drive n. A device for reading and writing tapes. See 

also tape (definition 1). 

tape dump n. The process of simply printing the data 

contained on a tape cartridge without performing any 

report formatting. See also tape cartridge. 

tape tree n. A means of audiotape distribution, used in 

Usenet music newsgroups and mailing lists, in which a 

T

T 

TAPI Tcl/Tk 

recording is copied and sent to a number of branch participants, 

who in turn send copies to their children, or leaves. 

See also branch (definition 1), child (definition 2), leaf, 

tree structure. Compare vine. 

TAPI n. Acronym for Telephony Application Programming 

Interface. In the Windows Open Systems Architecture 

(WOSA), a programming interface that gives Windows client 

applications access to a server’s voice services. TAPI 

facilitates interoperability between personal computers and 

telephone equipment. Also called: Telephony API. See also 

application programming interface, WOSA. Compare 

TSAPI. 

.tar n. The file extension that identifies uncompressed 

UNIX archives in the format produced by the tar program. 

tar1 n. Acronym for tape archive. A UNIX utility for 

making a single file out of a set of files that a user wishes 

to store together. The resulting file has the extension .tar. 

Unlike PKZIP, tar does not compress files, so compress or 

gzip is usually run on the .tar file to produce a file with 

extensions .tar.gz or .tar.Z. See also compress1 , gzip, 

PKZIP. Compare untar1 . 

tar2 vb. To make a single file out of a set of files using the 

tar utility. See also compress2 , PKZIP. Compare untar2 . 

target n. Loosely, the objective of a computer command 

or operation. Examples are a computer that is to run a program 

translated for its use, a “foreign” language (for 

another computer) into which a program is to be translated, 

or a group of people for whom a particular product 

is designed. In MS-DOS usage, the target is often the disk 

referred to by prompts in a copy operation (for example, 

“insert target diskette”). In terms of the SCSI (small computer 

system interface) connection, the target is the device 

that receives commands. See also SCSI, target computer, 

target disk, target language. 

target computer n. The computer that receives data 

from a communications device, a hardware add-in, or a 

software package. 

target disk n. The disk to which data is to be written, as 

in a copy operation. See also target. Compare source disk. 

target language n. The language into which source code 

is compiled or assembled. See also assembler, compiler 

(definition 2), cross-compiler. 

task n. A stand-alone application or a subprogram that is 

run as an independent entity. 

512 

taskbar n. A graphic toolbar used in Windows 9x, Windows 

CE, Windows NT, and Windows 2000 to select, via 

the mouse, one of a number of active applications. See 

also task button, toolbar. 

task button n. In Windows 9x, Windows CE, Windows 

NT, and Windows 2000, a button that appears on the taskbar 

on the screen when an application is run. By clicking 

on the button, the user can switch from another application 

to the application corresponding to the button. See also 

taskbar. 

task management n. The operating-system process of 

tracking the progress of and providing necessary resources 

for separate tasks that are running on a computer, especially 

in a multitasking environment. 

task swapping n. The process of switching from one 

application to another by saving the data for the application 

presently running in the foreground to a storage 

device and loading the other application. See also 

foreground2 (definition 2), task, task switching. 

task switching n. The act of moving from one program 

to another without shutting down the first program. Task 

switching is a single act, as compared to multitasking, in 

which the central processing unit rapidly switches back 

and forth between two or more programs. See also task, 

task swapping. Compare multitasking. 

TB n. See terabyte. 

T-carrier n. A long-distance, digital communications line 

provided by a common carrier. Multiplexers at either end 

merge several voice channels and digital data streams for 

transmission and separate them when received. T-carrier 

service, introduced by AT&T in 1993, is defined at several 

capacity levels: T1, T2, T3, and T4. In addition to voice 

communication, T-carriers are used for Internet connectivity. 

See also T1, T2, T3, T4. 

TCB n. Acronym for Trusted Computing Base. The complete 

set of security mechanisms that create security on a 

network. The TCB includes all the hardware, software, 

and firmware components that are responsible for system 

security. 

Tcl/Tk n. Acronym for Tool Command Language/Tool 

Kit. A programming system that includes a scripting language 

(Tcl) and a graphical user interface toolkit (Tk). 

The Tcl language issues commands to interactive programs, 

such as text editors, debuggers, and shells, which

TCM telecommunications closet 

tie together complex data structures into scripts. See also 

graphical user interface, script, scripting language. 

TCM n. See trellis-coded modulation. 

TCO n. See total cost of ownership. 

TCP n. Acronym for Transmission Control Protocol. The 

protocol within TCP/IP that governs the breakup of data 

messages into packets to be sent via IP (Internet Protocol), 

and the reassembly and verification of the complete messages 

from packets received by IP. A connection-oriented, 

reliable protocol (reliable in the sense of ensuring errorfree 

delivery), TCP corresponds to the transport layer in 

the ISO/OSI reference model. See also ISO/OSI reference 

model, packet, TCP/IP. Compare UDP. 

TCP/IP n. Acronym for Transmission Control Protocol/ 

Internet Protocol. A protocol suite (or set of protocols) 

developed by the U.S. Department of Defense for communications 

over interconnected, sometimes dissimilar, networks. 

It is built into the UNIX system and has become 

the de facto standard for data transmission over networks, 

including the Internet. 

TCP/IP reference model n. A networking model 

designed around the concept of internetworking—the 

exchange of information among different networks, often 

built on different architectures. The TCP/IP reference 

model, often called the Internet reference model, consists 

of four layers, the most distinctive of which is the internetwork 

that deals with routing messages and that has no 

equivalent in the ISO/OSI reference model or the SNA 

model. Compare ISO/OSI reference model, SNA. 

TCP/IP stack n. The set of TCP/IP protocols. See also 

protocol stack, TCP/IP. 

TDM n. See time-division multiplexing. 

TDMA n. Short for Time Division Multiple Access. A 

multiplexing technology used to divide a single cellular 

phone channel into multiple subchannels. TDMA works 

by allocating separate time slots to each user. It is implemented 

in D-AMPS (Digital Advanced Mobile Phone Service), 

which relies on TDMA to divide each of the 30 

analog AMPS channels into 3 separate subchannels, and 

GSM (Global System for Mobile Communications). See 

also D-AMPS, Global System for Mobile Communications. 

Compare AMPS, FDMA. 

team Web site n. See SharePoint team Web site. 

Teardrop attack n. An Internet-based attack that breaks 

a message into a series of IP fragments with overlapping 

offset fields. When these fragments are reassembled at 

513 

their destination, the fields don’t match, causing the system 

to hang, reboot, or crash. 

tearing n. A visual artifact produced when the screen 

refresh rate is out of sync with an application’s frame rate. 

The top portion of one frame is displayed at the same time 

as the bottom portion of another frame, with a discernible 

tear between the two partial images. 

tear-off adj. Capable of being dragged from an original 

position in a graphical user interface and placed where the 

user desires. For example, many graphics applications feature 

tear-off menus of tool palettes that can be dragged to 

locations other than the menu bar. 

techie n. A technically oriented person. Typically, a 

techie is the person on whom a user calls when something 

breaks or the user cannot understand a technical problem. 

A techie may be an engineer or a technician, but not all 

engineers are techies. See also guru. 

technical author n. See tech writer. 

technobabble n. Language that includes incomprehensible 

technical terms and jargon. In ordinary conversation, 

many of the words in this dictionary might be considered 

technobabble. 

technology n. The application of science and engineering 

to the development of machines and procedures in 

order to enhance or improve human conditions, or at 

least to improve human efficiency in some respect. See 

also high tech. 

technophile n. Someone who is enthusiastic about 

emerging technology. Compare computerphile. 

technophobe n. A person who is afraid of or dislikes 

technological advances, especially computers. See also 

Luddite. Compare technophile. 

tech writer n. Short for technical writer. One who 

writes the documentation material for a hardware or software 

product. Also called: technical author. See also 

documentation. 

telco n. Short for telephone company. A term generally 

used in reference to a telephone company’s provision of 

Internet services. 

telecom closet n. See wiring closet. 

telecommunications n. The transmission and reception 

of information of any type, including data, television pictures, 

sound, and facsimiles, using electrical or optical signals 

sent over wires or fibers or through the air. 

telecommunications closet n. See wiring closet. 

T

T 

telecommute template 

telecommute vb. To work in one location (often at 

home) and communicate with a main office at a different 

location through a personal computer equipped with a 

modem and communications software. 

telecommuter n. A member of the workforce who conducts 

business outside the traditional office setting, collaborating 

with business associates and colleagues through 

communications and computer technologies. Some workers 

telecommute full-time; others part-time. The telecommuting 

ranks include self-employed home workers, smallbusiness 

entrepreneurs, and employees of large corporations 

or organizations. See also distributed workplace, 

SOHO. 

teleconferencing n. The use of audio, video, or computer 

equipment linked through a communications system to 

enable geographically separated individuals to participate in 

a meeting or discussion. See also video conferencing. 

telecopy vb. See fax. 

telematics n. In communications technology, the linking 

of computers and telecommunications. Telematics technology 

is becoming standard in the automotive industry, 

with dashboard navigation systems, roadside assistance, 

entertainment, Internet, and cellular services available in 

vehicles. 

telephony n. Telephone technology—voice, fax, or 

modem transmissions based on either the conversion of 

sound into electrical signals or wireless communication 

via radio waves. 

Telephony API n. See TAPI. 

telephony device n. A mechanism designed to translate 

sound into electrical signals, transmit them, and then convert 

them back to sound. 

Telephony Service Provider n. A modem driver that 

enables access to vendor-specific equipment through a 

standard device driver interface. Acronym: TSP. See also 

Telephony Service Provider Interface. 

Telephony Service Provider Interface n. The external 

interface of a service provider to be implemented by vendors 

of telephony equipment. A telephony service provider 

accesses vendor-specific equipment through a 

standard device driver interface. Installing a service provider 

allows Windows CE–based applications that use elements 

of telephony to access the corresponding telephony 

equipment. Acronym: TSPI. See also Telephony Service 

Provider. 

514 

teleprocess vb. To use a terminal or computer and communications 

equipment to access computers and computer 

files located elsewhere. Teleprocess is a term originated by 

IBM. See also distributed processing, remote access. 

teleprocessing monitor n. See TP monitor. 

Telescript n. A communications-oriented programming 

language, released in 1994 by General Magic, that was 

designed to address the need for cross-platform, networkindependent 

messaging and abstraction of complex network 

protocols. See also communications protocol. 

teletext n. All-text information broadcast by a television 

station to a subscriber’s television set. 

Teletype n. The Teletype Corporation, developer of the 

teletypewriter (TTY) and various other printers used with 

computers and communications systems. See also TTY. 

teletype mode n. A mode of operation in which a computer 

or an application limits its actions to those characteristic 

of a teletypewriter (TTY). On the display, for 

example, teletype mode means that only alphanumeric 

characters can be shown, and they are simply “typed” on 

the screen, one letter after the other, and cannot be placed 

in any desired position. See also Teletype, TTY. 

teletypewriter n. See TTY. 

teleworker n. A businessperson who substitutes information 

technologies for work-related travel. Teleworkers 

include home-based and small business workers who use 

computer and communications technologies to interact 

with customers and/or colleagues. See also distributed 

workplace, SOHO. 

telnet1 n. 1. A client program that implements the Telnet 

protocol. 2. A protocol in the TCP/IP suite that enables 

individuals to log on to and use a remote computer as if 

they were sitting at a terminal directly connected to the 

machine. 

telnet2 vb. To access a remote computer over the Internet 

using the Telnet protocol. See also telnet1 . 

Telnet n. A protocol that enables an Internet user to log 

on to and enter commands on a remote computer linked to 

the Internet, as if the user were using a text-based terminal 

directly attached to that computer. Telnet is part of the 

TCP/IP suite of protocols. 

template n. 1. In an application package, an overlay for 

the keyboard that identifies special keys and key combinations. 

2. In image processing, a pattern that can be used to 

identify or match a scanned image. 3. In spreadsheet pro-

temporary file terminal server 

grams, a predesigned spreadsheet that contains formulas, 

labels, and other elements. 4. In MS-DOS, a small portion 

of memory that holds the most recently typed MS-DOS 

command. 5. In word processing and desktop publishing 

programs, a predesigned document that contains formatting 

and, in many cases, generic text. 

temporary file n. A file created either in memory or on 

disk, by the operating system or some other program, to 

be used during a session and then discarded. Also called: 

temp file. See also scratch1 . 

temporary storage n. A region in memory or on a storage 

device that is temporarily allocated for use in storing intermediate 

data in a computational, sorting, or transfer operation. 

ten’s complement n. A number in the base-10 system 

that is the true complement of another number and is 

derived either by subtracting each digit from 1 less than 

the base and adding 1 to the result or by subtracting each 

number from the next higher power of the base. For example, 

the ten’s complement of 25 is 75, and it can be derived 

either by subtracting each digit from 9, which is 1 less 

than the base (9 – 2 = 7, 9 – 5 = 4) and then adding 1 (74 + 

1 = 75) or by subtracting 25 from the next higher power of 

10, which is 100 (100 – 25 = 75). See also complement. 

Compare nine’s complement. 

tera- prefix A prefix meaning 1012 : 1 trillion in the American 

numbering system, 1 million million in British 

numbering. Abbreviation: T. See also terabyte. 

terabyte n. A measurement used for high-capacity data 

storage. One terabyte equals 240 , or 1,099,511,627,776, 

bytes, although it is commonly interpreted as simply one 

trillion bytes. Abbreviation: TB. 

teraflops n. One trillion floating-point operations 

(FLOPS) per second. Teraflops serves as a benchmark for 

larger computers that measures the number of floatingpoint 

operations they can perform in a set amount of time. 

Also called: TFLOPS. See also FLOPS. 

terminal n. 1. In networking, a device consisting of a video 

adapter, a monitor, and a keyboard. The adapter and monitor 

and, sometimes, the keyboard are typically combined in 

a single unit. A terminal does little or no computer processing 

on its own; instead, it is connected to a computer with a 

communications link over a cable. Terminals are used primarily 

in multiuser systems and today are not often found 

on single-user personal computers. See also dumb terminal, 

smart terminal, terminal emulation. 2. In electronics, a point 

that can be physically linked to something else, usually by a 

wire, to form an electrical connection. 

515 

Terminal n. An application that provides command-line 

access to the Mac OS X UNIX core. The Terminal command-line 

environment allows UNIX functions from 

within Mac OS X. 

Terminal Access Controller Access Control System 

n. See TACACS. 

terminal adapter n. The correct name for an ISDN 

modem, which connects a PC to an ISDN line but does not 

modulate or demodulate signals as a typical modem does. 

terminal emulation n. The imitation of a terminal by 

using software that conforms to a standard, such as the 

ANSI standard for terminal emulation. Terminal-emulation 

software is used to make a microcomputer act as if it 

were a particular type of terminal while it is communicating 

with another computer, such as a mainframe. See also 

VT-52, VT-100, VT-200. 

terminal server n. In a LAN (local area network), a computer 

or a controller that allows terminals, microcomputers, 

and other devices to connect to a network or host 

computer, or to devices attached to that particular computer. 

See the illustration. See also controller, LAN, 

microcomputer, terminal. 

Network 

computer 

F0Tgn01.eps 

Terminal server. 

Terminal 

server 

Terminals 

T

T 

terminal session text-only file 

terminal session n. The period of time spent actively 

using a terminal. See also session. 

terminal strip n. A usually long and narrow assembly 

containing one or more electrical connectors. Commonly, 

terminal strips consist of screws on which bare wires are 

wrapped before the screws are tightened; for example, 

some consumer-grade stereo receiver/amplifiers incorporate 

a set of terminal strips on the rear panel for attaching 

speaker wires to the unit. 

terminate vb. 1. With reference to software, to end a process 

or program. Abnormal termination occurs in response 

to user intervention or because of a hardware or software 

error. 2. With reference to hardware, to install a plug, jack, 

or other connector at the end of a wire or cable. 

terminate-and-stay-resident program n. See TSR. 

terminator n. 1. A character that indicates the end of a 

string, such as the null character in an ASCIIZ string. See 

also ASCII, ASCIIZ string. 2. An item of hardware that 

must be installed in the last device in a daisy chain or bus 

network, such as Ethernet or SCSI. The terminator caps the 

end of a cable in a bus network in order to keep signals from 

bouncing back along the line. See also terminator cap. 

terminator cap n. A special connector that must be 

attached to each end of an Ethernet bus. If one or both 

terminator caps are missing, the Ethernet network will 

not work. 

ternary adj. In programming, of, pertaining to, or characteristic 

of an element with three possible values, a condition 

that has three possible states, or a base-3 number 

system. Compare binary1 , unary. 

tessellate vb. To break an image into small, square 

regions for processing or output. 

test vb. To check program correctness by trying out various 

sequences and input values. See also debug, test data. 

test automation software n. A program that automatically 

enters a predetermined set of characters or user commands 

in order to test new or modified versions of 

software applications. 

test data n. A set of values used to test proper functioning 

of a program. Reasons for choosing particular test data 

include verifying known output (anticipated output) and 

pushing boundary conditions that might cause the program 

to fail. 

test post n. A newsgroup article that contains no actual 

message but is used simply as a means of checking the 

connection. See also article, newsgroup. 

516 

TeX or TEX n. A text-formatting software system created 

by mathematician and computer scientist Donald Knuth 

for producing typeset-quality scientific, mathematical, or 

other complex technical documents from plain ASCII text 

input. Implementations of TeX for UNIX systems, MS- 

DOS and Windows, and the Apple Macintosh are available 

free over the Internet (ftp://ftp.tex.ac.uk/tex-archive/) 

or in commercial distributions (which often include 

enhancements). Commands in the input file produce format 

elements and special symbols; for example, 

${\pi}r^2$ produces the expression pr2 . TeX is extensible 

through macros, and macro files are available for a wide 

variety of applications. See also LaTeX1 . 

Texas Instruments Graphics Architecture n. See 

TIGA. 

texel n. A single element in a texture. When a texture 

has been applied to an object, the texels rarely correspond 

to pixels on the screen. Applications can use texture 

filtering to control how texels are sampled and 

interpolated to pixels. 

text n. 1. Data that consists of characters representing the 

words and symbols of human speech; usually, characters 

coded according to the ASCII standard, which assigns 

numeric values to numbers, letters, and certain symbols. 

2. In word processing and desktop publishing, the main 

portion of a document, as opposed to headlines, tables, 

figures, footnotes, and other elements. 

text box n. In a dialog box or HTML form, a box in 

which the user may enter text. 

TextEdit n. A standard set of routines in the Macintosh 

operating system that are available to programs for controlling 

the way text is displayed. See also Toolbox. 

text editor n. See editor. 

text entry n. The inputting of text characters by means of 

a keyboard. 

text file n. A file composed of text characters. A text file 

can be a word-processing file or a “plain” ASCII file 

encoded in a format practically all computers can use. See 

also ASCII file, text (definition 1). 

text mode n. A display mode in which the monitor can 

display letters, numbers, and other text characters but no 

graphical images or WYSIWYG (“what-you-see-is-whatyou-get”) 

character formatting (italics, superscript, and so 

on). Also called: alphanumeric mode, character mode. 

Compare graphics mode. 

text-only file n. See ASCII file.

text-to-speech thimble 

text-to-speech n. The conversion of text-based data into 

voice output by speech synthesis devices to allow users to 

gain access to information by telephone or to allow blind 

or illiterate people to use computers. 

Text-to-Speech n. See TTS (definition 1). 

texture n. In computer graphics, shading or other 

attributes added to the “surface” of a graphical image to 

give it the illusion of a physical substance. For example, a 

surface could be made to appear reflective to simulate metal 

or glass, or a scanned image of wood grain could be applied 

to a shape intended to simulate an object made of wood. 

texture mapping n. In 3-D graphics, the process of adding 

detail to an object by creating a picture or a pattern 

that can be “wrapped” around the object. For example, a 

texture map of stones might be wrapped around a pyramid 

shape to create a realistic image. Texture mapping can also 

account for changes in perspective as the picture is 

wrapped around the shape. The technique is valued in 3-D 

graphics because it enables creation of detailed images 

without the performance degradation that can result from 

the computation required to manipulate images created 

with large numbers of polygons. 

TFLOPS n. See teraflops. 

TFT n. Acronym for thin film transistor. A transistor created 

using thin film methodology. See also active matrix 

display, thin film, transistor. 

TFT display n. See active matrix display. 

TFT LCD n. Acronym for thin film transistor liquid crystal 

display. See active matrix display. 

TFTP n. See Trivial File Transfer Protocol. 

TGA n. 1. Short for Targa. A raster graphics file format 

from Truevision, Inc., that handles 16-, 24-, and 32-bit 

color. See also 16-bit color, 24-bit color, 32-bit color, raster 

graphics, video graphics board. 2. The brand name of a 

series of high-resolution video graphics boards. 

theme n. 1. A set of visual elements that provide a unified 

look for your computer desktop. A theme determines the 

look of the various graphic elements of your desktop, such 

as the windows, icons, fonts, colors, and the background 

and screen saver pictures. It can also define sounds associated 

with events, such as opening or closing a program. 

2. A set of coordinated graphic elements applied to a document 

or Web page, or across all pages in a Web site. 

Themes can consist of designs and color schemes for 

fonts, link bars, and other page elements. 

517 

The Microsoft Network n. See MSN. 

thermal printer n. A nonimpact printer that uses heat to 

generate an image on specially treated paper. The printer 

uses pins to produce an image, but rather than striking the 

pins against a ribbon to mark the paper as does a wire-pin 

dot-matrix printer, it heats the pins and brings them into 

gentle contact with the paper. The special coating on the 

paper discolors when it is heated. 

thermal transfer printer n. See thermal wax-transfer 

printer. 

thermal wax printer n. See thermal wax-transfer printer. 

thermal wax-transfer printer n. A special type of nonimpact 

printer that uses heat to melt colored wax onto 

paper to create an image. Like a standard thermal printer, 

it uses pins to apply the heat. Rather than making contact 

with coated paper, however, the pins touch a wide ribbon 

saturated with different colored waxes. The wax melts 

under the pins and adheres to the paper. 

thesaurus n. 1. A book of words and their synonyms. 

2. In microcomputer applications, both a file of synonyms 

stored on disk and the program used to search the file. 

The World—Public Access UNIX n. One of the oldest 

public access Internet service providers, based in Boston. 

In 1990, The World began offering full dial-up Internet 

access to the public. Other services include World Wide 

Web access, Usenet, SLIP/PPP support, telnet, FTP, IRC, 

Gopher, and e-mail. In 1995, The World began supporting 

local dial-up access via UUNET. See also ISP. 

thick Ethernet n. See 10Base5. 

thick film adj. A term describing a method used in the 

manufacture of integrated circuits. Thick film technology 

uses a stencil-like technique called photosilkscreening to 

deposit multiple layers of special inks or pastes on a 

ceramic substrate. The inks or pastes can be conducting, 

insulating, or resistive. The passive components (wires, 

resistors, and capacitors) of the integrated circuits are 

formed by depositing a series of films of different characteristics 

and patterns. Compare thin film. 

ThickNet n. See 10Base5. 

ThickWire n. See 10Base5. 

thimble n. A type element, similar to a daisy wheel, that 

bears a full character set, with each character on a separate 

type bar. As with a daisy wheel, the spokes, or type bars, 

radiate out from a central hub. On a thimble print element, 

T

T 

thimble printer three-dimensional array 

however, each type bar is bent 90 degrees at its halfway 

point, so the type bars stick straight up with the type facing 

away from the hub. See also thimble printer. Compare 

daisy wheel, daisy-wheel printer. 

thimble printer n. A printer that uses a thimble print element, 

best known in a line of printers from NEC. Because 

these printers use fully formed characters like those on a 

typewriter, they generate letter-quality output that is indistinguishable 

from that of a typewriter. This includes the 

slight impression created by the type hitting the paper hard 

through the ribbon, which distinguishes this type of printout 

from that of laser printers. See also thimble. Compare 

daisy-wheel printer. 

thin client n. A software layer of a small client for a centrally 

managed, network terminal. The thin client allows 

the user access to server-hosted applications and data. 

thin Ethernet n. See 10Base2. 

thin film adj. A method used in the fabrication of integrated 

circuits. Thin film technology operates on the same 

basic principles as thick film technology. Rather than 

using inks or pastes, however, thin film technology uses 

metals and metal oxides that are “evaporated” and then 

deposited on the substrate in the desired pattern to form 

the integrated circuit’s passive components (wires, resistors, 

and capacitors). See also molecular beam epitaxy. 

Compare thick film. 

thin film transistor n. See TFT. 

ThinNet n. See 10Base2. 

thin server n. A client/server architecture in which most 

of an application is run on the client machine, which is 

called a fat client, with occasional data operations on a 

remote server. Such a configuration yields good client performance, 

but complicates administrative tasks, such as 

software upgrades. See also client/server architecture, fat 

client, thin client. Compare fat server. 

thin space n. An amount of horizontal space in a font, 

equal to one-quarter the point size of the font. For example, 

a thin space in a 12-point font is 3 points wide. See 

also point1 (definition 1). Compare em space, en space, 

fixed space. 

thin system n. See thin server. 

ThinWire n. See 10Base2. 

Third Generation n. See 3G. 

518 

third-generation computer n. Any of the computers 

produced from the mid-1960s to the 1970s that were based 

on integrated circuits rather than on separately wired transistors. 

See also computer. 

third-generation language n. See 3GL. 

third normal form n. See normal form (definition 1). 

third-party1 adj. In computer console games, a game 

made for a specific console by a company other than the 

console manufacturer. 

third party2 n. A company that manufactures and sells 

accessories or peripherals for use with a major manufacturer’s 

computer or peripheral, usually without any 

involvement from the major manufacturer. 

thrashing n. The state of a virtual memory system that is 

spending almost all its time swapping pages in and out of 

memory rather than executing applications. See also swap 

(definition 2), virtual memory. 

thread n. 1. In programming, a process that is part of a 

larger process or program. 2. In a tree data structure, a 

pointer that identifies the parent node and is used to facilitate 

traversal of the tree. 3. In electronic mail and Internet 

newsgroups, a series of messages and replies related to a 

specific topic. 

threaded discussion n. In a newsgroup or other online 

forum, a series of messages or articles in which replies to 

an article are nested directly under it, instead of the articles 

being arranged in chronological or alphabetical order. 

See also newsgroup, thread (definition 3). 

threaded newsreader n. A newsreader that displays 

posts in newsgroups as threads. Replies to a post appear 

directly after the original post, rather than in chronological 

or any other order. See also newsreader, post, thread (definition 

3). 

threaded tree n. A tree in which the leaf (end) nodes 

contain pointers to some of the nodes from which they 

arise. The pointers facilitate searching the tree for information. 

See also thread (definition 2). 

threading n. A technique used by certain interpretive languages, 

such as many Forth implementations, to speed 

execution. The references to other support routines in each 

threaded support routine, such as a predefined word in 

Forth, are replaced by pointers to those routines. See also 

Forth, thread (definition 1). 

three-dimensional array n. An ordered arrangement of 

information in which three numbers (integers) are used to

three-dimensional model tick 

locate a particular item. A three-dimensional array treats 

data as if it were laid out in rows, columns, and layers. See 

also 3-D array, array, two-dimensional array. 

three-dimensional model n. A computer simulation of a 

physical object in which length, width, and depth are real 

attributes—a model, with x-, y-, and z-axes, that can be 

rotated for viewing from different angles. 

three-finger salute n. Slang term for a warm, or soft, 

boot, in which the Ctrl, Alt, and Delete keys are pressed 

simultaneously to restart a computer without first turning 

off the power. Also called: Vulcan death grip. See also 

warm boot. 

three-nines availability n. The availability of a system 

99.9% of the time. Three-nines availability equates to 

approximately 526 minutes of downtime in a standard 

365-day year. See also high availability. 

three-point editing n. In digital video editing, a feature 

that simplifies the process of placing new video within a 

sequence by assisting in calculating edit points. To make 

an edit, in and out points must be defined in the video clip 

to be added and in the sequence into which the clip is to be 

inserted. The user provides any three of these edit points 

and the editing software determines the fourth. 

three-tier client/server n. A client/server architecture 

in which software systems are structured into three tiers or 

layers: the user interface layer, the business logic layer, 

and the database layer. Layers may have one or more components. 

For example, there can be one or more user interfaces 

in the top tier, each user interface may communicate 

with more than one application in the middle tier at the 

same time, and the applications in the middle tier may use 

more than one database at a time. Components in a tier 

may run on a computer that is separate from the other 

tiers, communicating with the other components over a 

network. See also client/server architecture. Compare twotier 

client/server. 

throbber n. An animated icon that moves while an application 

is completing a task, such as a browser loading a 

Web page. Throbbers serve to reassure the user that the 

application is still working on the task and has not frozen. 

Web browsers and some other applications come with a 

throbber icon. In some cases, the user can replace the original 

throbber with a customized icon of the user’s choice. 

throttle control n. A device that enables the user of a 

flight simulator or game to control simulated engine 

power. The throttle control is used along with a joystick 

519 

(which controls the simulated ailerons and elevators) and 

possibly a rudder control. 

throughput n. 1. The data transfer rate of a network, measured 

as the number of bits per second transmitted. 2. A 

measure of the data processing rate in a computer system. 

throughput test n. See bandwidth test. 

thumb n. See elevator. 

thumbnail n. A miniature version of an image or electronic 

version of a page that is generally used to allow 

quick browsing through multiple images or pages. For 

example, Web pages often contain thumbnails of images 

(which can be loaded much more quickly by the Web 

browser than the full-size image). Many of these thumbnails 

can be clicked on to load the complete version of the 

image. 

thumbwheel n. A wheel embedded in a case so that only 

a portion of the outside rim is revealed. When rolled with 

the thumb, the wheel can control an on-screen element 

such as a pointer or a cursor. Thumbwheels are used with 

three-dimensional joysticks and trackballs to control the 

depth aspect of the pointer or cursor. See also joystick, relative 

pointing device, trackball. 

thunk1 n. Code that enables 16-bit code to call 32-bit 

code, and vice versa. There are three different types of 

thunk: a flat thunk relies on a thunk compiler to allow 32bit 

code to call a 16-bit DLL and 16-bit code to call a 32bit 

DLL; a generic thunk enables a 16-bit application to 

load and call a 32-bit DLL; and a universal thunk allows 

32-bit code to load and call a 16-bit DLL. All thunks are 

Windows-based, but the type of thunk used depends on the 

Windows version. 

thunk2 vb. To call 32-bit code from 16-bit code, or vice 

versa. Thunking involves, in large part, the translation to 

and from 16-bit segment offset memory addressing and 

32-bit flat, or linear, memory addressing. See also address 

space, flat address space, segmented address space. 

TIA n. Acronym for thanks in advance. On the Internet, a 

popular sign-off to a request of some sort. Also 

called: aTdHvAaNnKcSe. 

tick n. 1. A regular, rapidly recurring signal emitted by a 

clocking circuit; also, the interrupt generated by this signal. 

2. In some microcomputer systems, notably Macintosh, 

one sixtieth of a second, the basic time unit used by 

the internal clock that is accessible by programs. 

T

T 

tiebreaker time out 

tiebreaker n. A circuit that arbitrates competing circuits 

and resolves bottlenecks by giving priority to one circuit at 

a time. 

tie line n. A private line leased from a communications 

carrier and often used to link two or more points in an 

organization. 

Tier 1 n. An Internet Network Access Point that provides 

access to and interconnection among major national and 

international network backbone providers, such as MCI 

WorldCom, Sprint, BBN, and IBM. See also Network 

Access Point. Compare Tier 2. 

Tier 2 n. A regional Internet Network interchange location 

where local ISPs exchange data. By using a Tier 2 

exchange point, ISPs in the same area can move data 

between their users without the need to transport that data 

over long distances. For example, if a user in Singapore 

connects to a Web site in the same city through a local Tier 

2 exchange point, it is not necessary to move the data 

through a major Network Access Point, or NAP, in Japan 

or North America. Tier 2 locations generally have much 

smaller capacities than the national and international Tier 

1 NAPs. See also Network Access Point. Compare Tier 1. 

.tif or .tiff n. The file extension that identifies bitmap 

images in Tagged Image File Format (TIFF). See also 

TIFF. 

TIFF or TIF n. Acronym for Tagged Image File Format or 

Tag Image File Format. A standard file format commonly 

used for scanning, storage, and interchange of gray-scale 

graphic images. TIFF may be the only format available for 

older programs (such as older versions of MacPaint), but 

most modern programs are able to save images in a variety 

of other formats, such as GIF or JPEG. See also gray 

scale. Compare GIF, JPEG. 

TIFF JPEG n. Acronym for Tagged Image File Format 

JPEG. A means of saving photographic images compressed 

according to the JPEG (Joint Photographic 

Experts Group) standard. TIFF JPEG saves more information 

about an image than does the lower-end JFIF (JPEG 

File Interchange Format), but TIFF JPEG files are limited 

in portability because of differences in implementation 

among applications. See also JFIF, JPEG. 

TIGA n. Acronym for Texas Instruments Graphics Architecture. 

A video adapter architecture based on the Texas 

Instruments 340x0 graphics processor. 

tiger team n. A group of users, programmers, or hackers 

who are charged with finding flaws in networks, applica- 

520 

tions, or security procedures. Tiger teams may be hired 

or may be composed of volunteers, and may have a single, 

short-term goal or may be used for a number of 

investigative purposes over a longer period of time. The 

term “tiger team” was originally used by the military to 

describe infiltration groups, and was first used in the 

computer industry to refer to hackers hired to expose 

flaws in network security. 

tightly coupled adj. 1. Refers to two computing processes 

whose successful completion and individual performance 

rates are highly interdependent. 2. Of, pertaining 

to, or characteristic of a relationship of interdependency 

between computers, as in multiprocessing. 

tile vb. 1. In computer-graphics programming, to fill adjacent 

blocks of pixels on the screen with a design or pattern 

without allowing any blocks to overlap. 2. To fill the space 

on a monitor or within a smaller area with multiple copies 

of the same graphic image. 3. In an environment with multiple 

windows, to rearrange and resize all open windows so 

that they appear fully on the screen without any overlap. 

time and date n. In computing, the timekeeping and 

datekeeping functions maintained by the computer’s operating 

system, used most visibly as a means of “stamping” 

files with the date and time of creation or last revision. 

time and date stamp n. See time stamp. 

time bomb n. 1. A feature often built into evaluation or 

beta versions of software that renders the software unusable 

after a certain period of time. With some evaluation 

versions of software containing time bombs, users are 

given codes or registration numbers after purchasing the 

software that will deactivate the time bomb. 2. See logic 

bomb. 3. See Year 2000 problem. 

Time Division Multiple Access n. See TDMA. 

time-division multiplexing n. A form of multiplexing in 

which transmission time is broken into segments, each of 

which carries one element of one signal. Acronym: TDM. 

See also statistical multiplexer. Compare FDM. 

time horizon to failure n. See event horizon. 

time out or timeout or time-out n. An event that indicates 

that a predetermined amount of time has elapsed 

without some other expected event taking place. The timeout 

event is used to interrupt the process that had been 

waiting for the other expected event. For example, a dialup 

remote system might allow the user 60 seconds to log 

in after making a connection. If the user fails to enter a

timer tiny model 

valid login name and password within this time, the computer 

breaks the connection, thus protecting itself against 

crackers as well as freeing a phone line that may have 

gone dead. 

timer n. A register (high-speed memory circuit) or a special 

circuit, chip, or software routine used to measure time 

intervals. A timer is not the same as the system clock, 

although its pulses can be derived from the system clock 

frequency. See also time and date. Compare clock (definition 

1), clock/calendar. 

time server n. A computer that periodically synchronizes 

the time on all computers within a network. This ensures 

that the time used by network services and local functions 

remains accurate. 

time-sharing or timesharing n. 1. The use of a computer 

system by more than one individual at the same time. 

Time-sharing runs separate programs concurrently by 

interleaving portions of processing time allotted to each 

program (user). See also quantum (definition 2), time 

slice. 2. A method, used primarily in the 1960s and 1970s, 

for sharing the capabilities (and cost) of a computer, such 

as a mainframe. Time-sharing allowed different clients to 

“rent” time on a large computer and pay for only the portion 

of time they used. 

time shifting n. A method of dealing with programs with 

Year 2000 problems that entails modifying the date either 

in data with which a program works (program encapsulation) 

or in the input/output logic of the program (data 

encapsulation). In both cases, the date is moved back in 

time to process the input, and forward in time to the correct 

date to produce output. See also encapsulation. 

time slice n. A brief period of time during which a particular 

task is given control of the microprocessor in a 

time-sharing multitasking environment. See also multitasking, 

preemptive multitasking. Compare quantum (definition 

2). 

time-slice multitasking n. See preemptive multitasking. 

timestamp n. A certification by a trusted third party 

specifying that a particular message existed at a specific 

time and date. In a digital context, trusted third parties 

generate a trusted timestamp for a particular message by 

having a timestamping service append a time value to a 

message and then digitally signing the result. See also digital 

signature, service. 

time stamp n. A time signature that is added by a program 

or system to files, e-mail messages, or Web pages. A 

521 

time stamp indicates the time and usually the date when a 

file or Web page was created or last modified or when an 

e-mail message was sent or received. Most time stamps 

are created by programs and are based on the time kept by 

the system clock of a computer on which the program 

resides. Commercial time stamp services are available on 

the Web or by e-mail, and offer proof of posting certificates 

to corroborate the time and date a message was sent. 

Also called: date and time stamp, date stamp, time and 

date stamp. 

time-synchronization service n. A program used to 

ensure that all systems on a network use a common time. 

Time-synchronization services on the Internet typically 

update real-time clocks to Universal Time Coordinate 

(UTC) using Network Time Protocol (NTP). Windows 

Time Synchronization Service (Win32Time) is a timesynchronization 

service. See also clock (definition 2), Network 

Time Protocol, Universal Time Coordinate. 

Time to Live n. A header field for a packet sent over the 

Internet indicating how long the packet should be held. 

Acronym: TTL. See also header (definition 2), packet (definition 

1). 

timing attack n. An attack on a cryptographic system 

that exploits the fact that different cryptographic operations 

take slightly different amounts of time to process. 

The attacker exploits these slight time differences by carefully 

measuring the amount of time required to perform 

private key operations. Taking these measurements from a 

vulnerable system can reveal the entire secret key. Cryptographic 

tokens, network-based cryptosystems, and other 

applications where attackers can make reasonably accurate 

timing measurements are potentially at risk from this 

form of attack. 

timing signals n. 1. Any of several types of signals used 

to coordinate activities within a computer system. 2. A 

signal used to coordinate data transfer operations. 

Tinkerbell program n. A program used to monitor network 

traffic and alert security administrators when connections 

are made from a predetermined list of sites and 

individuals. A Tinkerbell program acts as a low-level 

security reporting feature. 

tiny model n. A memory model in the Intel 80x86 processor 

family. The tiny model allows a combined total of only 

64 kilobytes (KB) for code and for data. See also 8086, 

memory model. 

T

T 

title bar token ring network 

title bar n. In a graphical user interface, a horizontal 

space at the top of a window that contains the name of the 

window. Most title bars also contain boxes or buttons for 

closing and resizing the window. Clicking on the title bar 

allows the user to move the entire window. 

TLA n. Acronym for three-letter acronym. An ironic term, 

usually used in jest on the Internet in e-mail, newsgroups, 

and other online forums, referring to the large number of 

acronyms in computer terminology, particularly those 

consisting of three letters. 

TLD n. See top-level domain. 

TLS n. Acronym for Transport Layer Security. A standard 

protocol that is used to provide secure Web communications 

on the Internet or intranets. It enables clients to 

authenticate servers or, optionally, servers to authenticate 

clients. It also provides a secure channel by encrypting 

communications. TLS is the latest and a more secure version 

of the SSL protocol. See also authentication, communications 

protocol, SSL. 

TMS34010 n. See 34010, 34020. 

TN display n. See twisted nematic display. 

TOF n. See top-of-file. 

toggle1 n. An electronic device with two states or a program 

option that can be turned on or off using the same 

action, such as a mouse click. 

toggle2 vb. To switch back and forth between two states. 

For example, the Num Lock key on an IBM-style keyboard 

toggles the numeric keypad between numbers and 

cursor movement. 

ToggleKeys n. A feature of Windows 9x and Windows 

NT 4 that sounds high and low beeps when one of the toggle 

keys (Caps Lock, Num Lock, or Scroll Lock) is turned 

on or off. See also typematic. Compare BounceKeys, 

FilterKeys, MouseKeys, ShowSounds, SoundSentry, 

StickyKeys. 

token n. 1. A unique structured data object or message 

that circulates continuously among the nodes of a token 

ring and describes the current state of the network. Before 

any node can send a message, it must first wait to control 

the token. See also token bus network, token passing, 

token ring network. 2. Any nonreducible textual element 

in data that is being parsed—for example, the use in a program 

of a variable name, a reserved word, or an operator. 

Storing tokens as short codes shortens program files and 

speeds execution. See also Basic, parse. 

522 

token bus n. The IEEE 802.4 specification for tokenpassing 

networks based on a bus or tree topology. Token 

bus networks were designed primarily for manufacturing 

but the specification also corresponds to the ARCnet 

architecture used for LANs. 

token bus network n. A LAN (local area network) 

formed in a bus topology (stations connected to a single, 

shared data highway) that uses token passing as a means 

of regulating traffic on the line. On a token bus network, a 

token governing the right to transmit is passed from one 

station to another, and each station holds the token for a 

brief time, during which it alone can transmit information. 

The token is transferred in order of priority from an 

“upstream” station to the next “downstream” station, 

which might or might not be the next station on the bus. In 

essence, the token “circles” through the network in a logical 

ring rather than a physical one. Token bus networks are 

defined in the IEEE 802.4 standards. See also bus network, 

IEEE 802 standards, token passing. Compare token 

ring network. 

token passing n. A method of controlling network 

access through the use of a special signal, called a token, 

that determines which station is allowed to transmit. The 

token, which is actually a short message or a small packet, 

is passed from station to station around the network. Only 

the station with the token can transmit information. See 

also token bus network, token ring network. Compare collision 

detection, contention, CSMA/CD. 

token ring n. Spelled with lowercase t and r, the IEEE 

specification 802.5 for token ring networks. See also token 

ring network. 

Token Ring n. See Token Ring network. 

token ring network n. A LAN (local area network) 

formed in a ring (closed loop) topology that uses token 

passing as a means of regulating traffic on the line. On a 

token ring network, a token governing the right to transmit 

is passed from one station to the next in a physical circle. 

If a station has information to transmit, it “seizes” the 

token, marks it as being in use, and inserts the information. 

The “busy” token, plus message, is then passed 

around the circle, copied when it arrives at its destination, 

and eventually returned to the sender. The sender removes 

the attached message and then passes the freed token to 

the next station in line. Token ring networks are defined in 

the IEEE 802.5 standards. See also IEEE 802 standards, 

ring network, token passing. Compare token bus network.

Token Ring network ToolTips 

Token Ring network n. A token-passing, ring-shaped 

local area network (LAN) developed by IBM that operates 

at 4 megabits (4 million bits) per second. With standard 

telephone wiring, the Token Ring network can connect up 

to 72 devices; with shielded twisted-pair (STP) wiring, the 

network supports up to 260 devices. Although it is based 

on a ring (closed loop) topology, the Token Ring network 

uses star-shaped clusters of up to eight workstations connected 

to a wiring concentrator (Multistation Access Unit, 

or MSAU), which, in turn, is connected to the main ring. 

The Token Ring network is designed to accommodate 

microcomputers, minicomputers, and mainframes; it follows 

the IEEE 802.5 standards for token ring networks. 

See the illustration. See also ring network, STP, token 

passing. 

MSAU 

MSAU 

MSAU 

MSAU 

Token ring 

F0Tgn02.eps 

Token Ring network. An IBM Token Ring configuration with 

MSAUs. 

tone n. 1. A particular tint of a color. Also called: shade, 

value. See also brightness, color model. 2. One sound or 

signal of a particular frequency. 

523 

tone compression n. In digital graphics, the compression 

of the complete color range of an image to the narrower 

range of the chosen output device. Allowing for 

tone compression in scanning and graphics editing may 

improve the quality of the final printed image. 

toner n. Powdered pigment that is used in office copiers 

and in laser, LED, and LCD printers. See also electrophotographic 

printers. 

toner cartridge n. A disposable container that holds 

toner for a laser printer or other page printer. Some types 

of toner cartridge contain toner only; however, the most 

popular printer engines pack all expendables, including 

toner and the photosensitive drum, in a single cartridge. 

Toner cartridges are interchangeable among printers that 

use the same engine. 

toolbar n. In an application in a graphical user interface, a 

row, column, or block of on-screen buttons or icons. When 

these buttons or icons are clicked on with the mouse, macros 

or certain functions of the application are activated. 

For example, word processors often feature toolbars with 

buttons for changing text to italic, boldface, and other 

styles. Toolbars often can be customized by the user and 

usually can be moved around on the screen according to 

the user’s preference. See the illustration. See also graphical 

user interface. Compare menu bar, palette (definition 

1), taskbar, title bar. 

F0Tgn03.eps 

Toolbar. 

toolbox n. A set of predefined (and usually precompiled) 

routines a programmer can use in writing a program for a 

particular machine, environment, or application. Also 

called: toolkit. See also library (definition 1). 

Toolbox n. A set of routines stored mostly in the readonly 

memory of a Macintosh that provides application 

programmers with the tools needed to support the graphical 

interface characteristic of the computer. Also 

called: User Interface Toolbox. 

Tool Command Language/Tool Kit n. See Tcl/Tk. 

toolkit n. See toolbox. 

ToolTips n. Brief descriptions of the names of buttons and 

boxes on toolbars and in the toolbox. A ToolTip is displayed 

when the mouse pointer rests on the button or 

combo box. See also ScreenTips. 

T

T 

top-down design tower 

top-down design n. A program design methodology that 

starts with defining program functionality at the highest 

level (a series of tasks) and then breaks down each task 

into lower-level tasks, and so on. See also bottom-up programming, 

top-down programming. Compare bottom-up 

design. 

top-down programming n. An approach to programming 

that implements a program in top-down fashion. Typically, 

this is done by writing a main body with calls to several 

major routines (implemented as stubs). Each routine is 

then coded, calling other, lower-level, routines (also done 

initially as stubs). See also bottom-up design, stub, topdown 

design. Compare bottom-up programming. 

topic drift n. The tendency of an online discussion to 

move from its original subject to other related or unrelated 

subjects. For example, someone in a conference devoted to 

television may ask about a news program; then somebody 

else may say something about a story on that program 

about food poisoning, which leads somebody else to start 

a general discussion on the advantages of organic fruits 

and vegetables. 

topic group n. An online discussion area for participants 

with a common interest in a particular subject. 

top-level domain n. In the domain-name system of Internet 

addresses or DNS hierarchy, any of the broadest category 

of names, under which all domain names fit. Toplevel 

domains for sites in the United States include .com, 

.edu, .gov, .net, and .org. See also DNS (definition 1), 

major geographic domain. 

top-of-file n. 1. The beginning of a file. 2. A symbol 

used by a program to mark the beginning of a file—the 

first character in the file or, in an indexed (ordered) 

database, the first indexed record. Acronym: TOF. See 

also beginning-of-file. 

topology n. The configuration or layout of a network 

formed by the connections between devices on a LAN 

(local area network) or between two or more LANs. See 

also bus network, LAN, ring network, star network, token 

ring network, tree network. 

top posting n. In e-mail and newsgroup discussions, 

placing new material before material quoted from earlier 

posts rather than after. Because top-posted messages are 

read out of chronological order, top-posting is considered 

an undesirable practice. 

524 

total bypass n. A communications network that uses satellite 

transmission to bypass both local and long-distance 

telephone links. 

total cost of ownership n. Specifically, the cost of owning, 

operating, and maintaining a single PC; more generally, 

the cost to businesses and organizations of setting up 

and maintaining complex and far-reaching networked 

computer systems. Total cost of ownership includes the 

up-front costs of hardware and software added to later 

costs of installation, personnel training, technical support, 

upgrades, and repairs. Industry initiatives designed to 

lower the total cost of ownership include centralized network 

management and administration, as well as hardware 

solutions in the form of network-based computers 

with or without local storage and expansion capability. 

Acronym: TCO. 

touch pad n. A variety of graphics tablet that uses pressure 

sensors, rather than the electromagnetics used in 

more expensive high-resolution tablets, to track the position 

of a device on its surface. See also absolute pointing 

device, graphics tablet. 

touch screen n. A computer screen designed or modified 

to recognize the location of a touch on its surface. By 

touching the screen, the user can make a selection or move 

a cursor. The simplest type of touch screen is made up of a 

grid of sensing lines, which determine the location of a 

touch by matching vertical and horizontal contacts. 

Another, more accurate type uses an electrically charged 

surface and sensors around the outer edges of the screen to 

detect the amount of electrical disruption and pinpoint 

exactly where contact has been made. A third type has 

infrared light-emitting diodes (LEDs) and sensors around 

the outer edges of the screen. These LEDs and sensors create 

an invisible infrared grid, which the user’s finger interrupts, 

in front of the screen. Compare light pen. 

touch-sensitive display n. See touch screen. 

touch-sensitive tablet n. See touch pad. 

touch tone dialing n. The signaling system used in telephones 

with touch-tone keypads, in which each digit is 

associated with two specific frequencies. During dialing, 

these frequencies—for example, 1336 Hz and 697 Hz for 

the number 2—are transmitted to the telephone company. 

Also called: DTMF, Dual Tone Multiple Frequency. 

tower n. A microcomputer system in which the cabinet 

for the central processing unit (CPU) is tall, narrow, and

TP tracked change 

deep rather than short, wide, and deep. The motherboard is 

usually vertical, and the disk drives are often perpendicular 

to the motherboard. A tower cabinet is at least 24 

inches tall. See the illustration. See also cabinet, microcomputer, 

motherboard. Compare minitower. 

F0Tgn04.eps 

Tower. 

TP n. See transaction processing. 

TPC n. See Transaction Processing Council. 

TPC-D n. Acronym for Transaction Processing Council 

Benchmark D. A benchmark standard that addresses a 

broad range of decision support applications working with 

complex data structures. See also Transaction Processing 

Council. 

TPI n. See tracks per inch. 

TP monitor n. Short for teleprocessing monitor or transaction 

processing monitor. A program that controls the 

transfer of data between terminals (or clients) and a mainframe 

(or one or more servers) so as to provide a consistent 

environment for one or more online transaction 

processing (OLTP) applications. A TP monitor may also 

control the appearance of the screen displays and check 

input data for proper format. See also client (definition 3), 

mainframe computer, OLTP, server (definition 1). 

trace vb. To execute a program in such a way that the 

sequence of statements being executed can be observed. 

See also debugger, single step. 

traceroute n. A utility that shows the route a packet takes 

through a network to arrive at a remote host. A traceroute 

also reports the IP addresses of all intermediate hosts or 

routers and the time required for the packet to reach each 

of them. See also IP address, packet. 

525 

track 1 n. One of numerous circular data storage areas on 

a floppy disk or a hard drive, comparable to a groove on a 

record but not spiral. Tracks, composed of sectors, are 

recorded on a disk by an operating system during a disk 

format operation. On other storage media, such as tape, a 

track runs parallel to the edge of the medium. See the 

illustration. 

F0Tgn05.eps 

Track 1 . The storage areas on a floppy disk or hard drive. 

track2 vb. 1. To follow a path. 2. In data management, to 

follow the flow of information through a manual or an 

automated system. 3. In data storage and retrieval, to follow 

and read from a recording channel on a disk or a magnetic 

tape. 4. In computer graphics, to cause a displayed 

symbol, such as a pointer, to match on the screen the 

movements of a mouse or another pointing device. 

trackball n. A pointing device that consists of a ball resting 

on two rollers at right angles to each other, which 

translate the ball’s motion into vertical and horizontal 

movement on the screen. A trackball also typically has 

one or more buttons to initiate other actions. A trackball’s 

housing is stationary; its ball is rolled with the hand. See 

the illustration. Compare mechanical mouse. 

F0Tgn06.eps 

Trackball. 

Tracks 

tracked change n. A mark that shows where a deletion, 

insertion, or other editing change has been made in a 

document. 

T

T 

trackpad Transact-SQL 

trackpad n. A pointing device consisting of a small, flat 

pad that is sensitive to touch. Users move the mouse cursor 

on screen by touching the trackpad and moving their 

fingers across the trackpad’s surface. Such devices are 

most commonly installed on laptop computers. See also 

pointing device. 

tracks per inch n. The density with which concentric 

tracks (data storage rings) are recorded or can be recorded 

in an inch of radius on a disk. The greater the density (the 

more tracks per inch), the more information a disk can 

hold. Acronym: TPI. 

tractor feed n. A method of feeding paper through a 

printer using pins mounted on rotating belts. The pins 

engage holes near the edges of continuous-form paper and 

either push or pull the paper through. See also continuousform 

paper. Compare pin feed. 

trademark n. A word, phrase, symbol, or design (or some 

combination thereof) used to identify a proprietary product, 

often accompanied by the symbol TM or ® . 

trade show n. A multivendor sales event or exposition 

that showcases companies’ products. The computer industry 

has a number of trade shows every year, including 

COMDEX. 

traditional newsgroup hierarchy n. The seven standard 

newsgroup categories in Usenet: comp., misc., news., rec., 

sci., soc., and talk. Newsgroups can be added within the 

traditional hierarchy only following a formal voting process. 

See also comp. newsgroups, misc. newsgroups, 

newsgroup, news. newsgroups, rec. newsgroups, Request 

for Discussion, sci. newsgroups, soc. newsgroups, talk. 

newsgroups, Usenet. Compare alt. newsgroups. 

traffic n. The load carried by a communications link or 

channel. 

traffic management n. See ITM. 

traffic shaping n. A technique for allocating bandwidth 

and preventing packet loss by enforcing prioritization policies 

on the transmission of data over a network. Also 

called: bandwidth shaping. See also bandwidth management, 

bandwidth reservation, token passing. 

trailer n. Information, typically occupying several bytes, at 

the tail end of a block (section) of transmitted data and often 

containing a checksum or other error-checking data useful 

for confirming the accuracy and status of the transmission. 

See also checksum. Compare header (definition 2). 

526 

trailer label n. 1. A small block of information used in 

tape processing that marks the end of a file or the end of the 

tape and that can contain other information, such as the 

number of records in the file or files on the tape. Compare 

header label. 2. A label used in communications data 

frames that follows the data and might contain an end-ofmessage 

mark, a checksum, and some synchronization bits. 

trailing edge n. The latter part of an electronic signal. 

When a digital signal switches from on to off, the transition 

is the trailing edge of the signal. 

train1 n. A sequence of items or events, such as a digital 

pulse train consisting of transmitted binary signals. 

train2 vb. To teach an end user how to use a software or 

hardware product. 

transaction n. A discrete activity within a computer system, 

such as an entry of a customer order or an update of 

an inventory item. Transactions are usually associated 

with database management, order entry, and other online 

systems. 

transactional e-mail n. A form of Web-based marketing 

in which goods and services are sold to consumers directly 

from an e-mail message. Unlike traditional e-mail marketing 

that requires the e-mail recipient to visit the seller’s Web 

site, transactional e-mail allows an entire sales transaction 

to be completed from within the marketing e-mail. To take 

advantage of transactional e-mail buying options, the recipient 

must view the e-mail message in HTML format. 

transaction file n. A file that contains the details of 

transactions, such as items and prices on invoices. It is 

used to update a master database file. See also transaction. 

Compare master file. 

transaction log n. See change file. 

transaction processing n. A processing method in 

which transactions are executed immediately after they 

are received by the system. Acronym: TP. See also transaction. 


Transaction Processing Council n. A group of hardware 

and software vendors with the goal of publishing 

benchmark standards. Acronym: TPC. 

transaction processing monitor n. See TP monitor. 

Transaction Tracking System n. See TTS (definition 2). 

Transact-SQL n. A query language. Transact-SQL is 

sophisticated SQL dialect loaded with additional features 

beyond what is defined in the ANSI SQL 92 Standard. 

Also called: T-SQL, TSQL.

transceiver transistor 

transceiver n. Short for transmitter/receiver. A device 

that can both transmit and receive signals. On LANs (local 

area networks), a transceiver is the device that connects a 

computer to the network and that converts signals to and 

from parallel and serial form. 

transceiver cable n. A cable that is used to connect a 

host adapter within a computer to a LAN (local area network). 

See also AUI cable, LAN. 

transducer n. A device that converts one form of energy 

into another. Electronic transducers either convert electric 

energy to another form of energy or convert nonelectric to 

electric energy. 

transfer1 n. 1. The movement of data from one location 

to another. 2. The passing of program control from one 

portion of code to another. 

transfer2 vb. To move data from one place to another, 

especially within a single computer. Compare transmit. 

transfer rate n. The rate at which a circuit or a communications 

channel transfers information from source to destination, 

as over a network or to and from a disk drive. 

Transfer rate is measured in units of information per unit 

of time—for example, bits per second or characters per 

second—and can be measured either as a raw rate, which 

is the maximum transfer speed, or as an average rate, 

which includes gaps between blocks of data as part of the 

transmission time. 

transfer statement n. A statement in a programming 

language that transfers the flow of execution to another 

location in the program. See also branch instruction, 

CALL statement, GOTO statement, jump instruction. 

transfer time n. The time elapsed between the start of a 

data transfer operation and its completion. 

F0Tgn07.eps 

Transistor. 

527 

transform vb. 1. To change the appearance or format of 

data without altering its content; that is, to encode information 

according to predefined rules. 2. In mathematics 

and computer graphics, to alter the position, size, or nature 

of an object by moving it to another location (translation), 

making it larger or smaller (scaling), turning it (rotation), 

changing its description from one type of coordinate system 

to another, and so on. 

transformer n. A device used to change the voltage of an 

alternating current signal or to change the impedance of an 

alternating current circuit. 

transient adj. 1. Fleeting, temporary, or unpredictable. 

2. Of or pertaining to the region of memory used for programs, 

such as applications, that are read from disk storage 

and that reside in memory temporarily until they are 

replaced by other programs. In this context, transient can 

also refer to the programs themselves. 3. In electronics, of 

or pertaining to a short-lived, abnormal, and unpredictable 

increase in power supply, such as a voltage spike or surge. 

Transient time is the interval during which a change in 

current or voltage is building up or decaying. 

transient suppressor n. A circuit designed to reduce or 

eliminate unwanted electrical signals or voltages. 

transistor n. Short for transfer resistor. A solid-state circuit 

component, usually with three leads, in which a voltage 

or a current controls the flow of another current. The 

transistor can serve many functions, including those of 

amplifier, switch, and oscillator, and is a fundamental 

component of almost all modern electronics. See the illustration. 

See also base (definition 3), FET, NPN transistor, 


Emitter 

Base 

Collector 

Emitter Base Collector 

T

T 

transistor-transistor logic transport layer 

transistor-transistor logic n. A type of bipolar circuit 

design that utilizes transistors connected to each other 

either directly or through resistors. Transistor-transistor 

logic offers high speed and good noise immunity and is 

used in many digital circuits. A large number of transistortransistor 

logic gates can be fabricated on a single integrated 

circuit. Acronym: TTL. 

transitive trust n. The standard type of trust relationship 

between Windows domains in a domain tree or forest. 

When a domain joins an existing forest or domain tree, a 

transitive trust is automatically established. Transitive 

trusts are always two-way relationships. This series of 

trusts, between parent and child domains in a domain tree 

and between root domains of domain trees in a forest, 

allows all domains in a forest to trust each other for the 

purposes of authentication. For example, if domain A 

trusts domain B and domain B trusts domain C, then 

domain A trusts domain C. See also domain, forest, oneway 

trust, two-way trust. 

translate vb. 1. In programming, to convert a program 

from one language to another. Translation is performed by 

special programs such as compilers, assemblers, and interpreters. 

2. In computer graphics, to move an image in the 

“space” represented on the display, without turning (rotating) 

the image. 

translated file n. A file containing data that has been 

changed from binary (8-bit) format to ASCII (7-bit) format. 

BinHex and uuencode both translate binary files into 

ASCII. Such translation is necessary to transmit data 

through systems (such as e-mail) that may not preserve the 

eighth bit of each byte. A translated file must be decoded 

to its binary form before being used. See also BinHex, 

uuencode. 

translator n. A program that translates one language or 

data format into another. 

transmission channel n. See channel. 

Transmission Control Protocol n. See TCP. 

Transmission Control Protocol/Internet Protocol 

n. See TCP/IP. 

transmit vb. To send information over a communications 

line or a circuit. Computer transmissions can take place in 

the following ways: asynchronous (variable timing) or 

synchronous (exact timing); serial (essentially, bit by bit) 

or parallel (byte by byte; a group of bits at once); duplex 

or full-duplex (simultaneous two-way communication), 

half-duplex (two-way communication in one direction at a 

528 

time), or simplex (one-way communication only); and 

burst (intermittent transmission of blocks of information). 

Compare transfer2 . 

Transmit Data n. See TXD. 

transmitter n. Any circuit or electronic device designed 

to send electrically encoded data to another location. 

transparency n. The quality that defines how much light 

passes through an object’s pixels. If an object is 100 percent 

transparent, light passes through it completely and 

renders the object invisible; in other words, you can see 

through the object. 

transparency scanner n. See scanner. 

transparent adj. 1. In computer use, of, pertaining to, or 

characteristic of a device, function, or part of a program 

that works so smoothly and easily that it is invisible to the 

user. For example, the ability of one application to use 

files created by another is transparent if the user encounters 

no difficulty in opening, reading, or using the second 

program’s files or does not even know the use is occurring. 

2. In communications, of, pertaining to, or characteristic 

of a mode of transmission in which data can include any 

characters, including device-control characters, without 

the possibility of misinterpretation by the receiving station. 

For example, the receiving station will not end a 

transparent transmission until it receives a character in the 

data that indicates end of transmission. Thus, there is no 

danger of the receiving station ending communications 

prematurely. 3. In computer graphics, of, pertaining to, or 

characteristic of the lack of color in a particular region of 

an image so that the background color of the display 

shows through. 

transponder n. A transceiver in a communications satellite 

that receives a signal from an earth station and retransmits 

it on a different frequency to one or more other earth 

stations. 

transportable computer n. See portable computer. 

transport layer n. The fourth of the seven layers in the 

International Organization for Standardization’s Open 

Systems Interconnection (OSI) reference model for standardizing 

computer-to-computer communications. The 

transport layer is one level above the network layer and is 

responsible for both quality of service and accurate delivery 

of information. Among the tasks performed on this 

layer are error detection and correction. See the illustration. 

See also ISO/OSI reference model.

Transport Layer Security tree view 

ISO/OSI Layer 

Application 


Presentation 

Session 

Transport 

Network 

Data-link 

Physical 

F0Tgn08.eps 

Transport layer. 

ISO/OSI MODEL 

Focus 




conversion 









Transport Layer Security n. See TLS. 

transpose1 n. The result of rotating a matrix. 

transpose2 vb. 1. To reverse, as the order of the letters h 

and t in hte, in correcting the spelling of the; or reversing 

two wires in a circuit. 2. In mathematics and spreadsheets, 

to rotate a matrix (a rectangular array of numbers) about a 

diagonal axis. 

transputer n. Short for transistor computer. A complete 

computer on a single chip, including RAM and an 

FPU, designed as a building block for parallel computing 

systems. 

trap1 n. See interrupt. 

trap2 vb. 1. To intercept an action or event before it 

occurs, usually in order to do something else. Trapping is 

commonly used by debuggers to allow interruption of program 

execution at a given spot. See also interrupt, interrupt 

handler. 2. To slightly overlap adjacent colors in 

preparing material for printing. Page layout and prepress 

programs trap color to prevent gaps between colors caused 

by minor variations in registration during printing. 

trapdoor n. See back door. 

trap handler n. See interrupt handler. 

Trash n. An icon on the screen in the Macintosh Finder, 

resembling a garbage can. To delete a file or eject a diskette, 

the user drags the icon for the file or diskette to the 

Trash. However, until the user shuts down the system or 

529 

chooses the menu option “Empty Trash,” a file in the 

Trash is not actually deleted; the user can retrieve it by 

double-clicking the Trash icon and dragging the file’s icon 

out of the resulting window. Compare Recycle Bin. 

traverse vb. In programming, to access in a particular 

order all of the nodes of a tree or similar data structure. 

tree n. A data structure containing zero or more nodes 

that are linked together in a hierarchical fashion. If there 

are any nodes, one node is the root; each node except the 

root is the child of one and only one other node; and each 

node has zero or more nodes as children. See also child 

(definition 2), graph, leaf, node (definition 3), parent/child 

(definition 2), root. 

tree network n. A topology for a local area network 

(LAN) in which one machine is connected to one or more 

other machines, each of which is connected to one or more 

others, and so on, so that the structure formed by the network 

resembles that of a tree. See the illustration. See also 

bus network, distributed network, ring network, star network, 

token ring network, topology. 

F0Tgn09.eps 

Tree network. 

tree search n. A search procedure performed on a tree 

data structure. At each step of the search, a tree search is 

able to determine, by the value in a particular node, which 

branches of the tree to eliminate, without searching those 

branches themselves. See also branch (definition 1), tree 

structure. 

tree structure n. Any structure that has the essential 

organizational properties of a tree. See also tree. 

tree view n. A hierarchical representation of the folders, 

files, disk drives, and other resources connected to a computer 

or network. For example, Windows Explorer uses a 

tree view to display the resources that are attached to a 

computer or a network. See also resource. 

T

T 

trellis-coded modulation troll 

trellis-coded modulation n. An enhanced form of 

quadrature amplitude modulation that is used by modems 

that operate at or above 9,600 bps (bits per second). Trelliscoded 

modulation encodes information as unique sets of 

bits associated with changes in both the phase and amplitude 

of the carrier, as well as using extra signal points for 

error-checking bits. Acronym: TCM. See also quadrature 

amplitude modulation. 

trendline n. A graphic representation of trends in data 

series, such as a line sloping upward to represent increased 

sales over a period of months. Trendlines are used for the 

study of problems of prediction. Also called: regression 

analysis. 

triage1 n. The process of prioritizing projects or elements 

of a project (such as bug fixes) to ensure that available 

resources are assigned in the most effective, time-efficient, 

and cost-efficient manner. Traditionally, triage has 

referred to the prioritization of treatment to the wounded 

during wartime or medical disaster situations. More 

recently, the term also refers to anticipating and preventing 

computer system crashes brought on by the Year 2000 

(Y2K) problem. See also Year 2000 Problem. 

triage2 vb. To identify and prioritize the elements of a 

project or problem to order them in a way that makes best 

use of labor, funds, and other resources. 

tri-band phone n. A wireless phone designed for international 

travel. Tri-band phones broadcast on the personal 

communication service (PCS) frequency used in North 

America as well as PCS frequencies used in other regions 

of the world. 

trichromatic adj. Of, pertaining to, or characteristic of a 

system that uses three colors (red, green, and blue in computer 

graphics) to create all other colors. See also color 

model. 

trigger1 n. 1. In a database, an action that causes a procedure 

to be carried out automatically when a user attempts 

to modify data. A trigger can instruct the database system 

to take a specific action, depending on the particular 

change attempted. Incorrect, unwanted, or unauthorized 

changes can thereby be prevented, helping to maintain the 

integrity of the database. 2. A function built into a virus or 

worm that controls the release of a malicious payload or 

similar event. The trigger may be activated at a predetermined 

time or date or in response to a user-initiated event, 

such as opening a specific program or file. In some cases, 

530 

the trigger may reset itself repeatedly until the virus is 

neutralized. 

trigger2 vb. To activate a function or program, such as the 

release of a virus payload, in response to a specific event, 

date, or time. 

trigonometry n. The branch of mathematics dealing with 

arcs and angles, expressed in functions (for example, sine 

and cosine) that show relationships—for example, 

between two sides of a right triangle or between two complementary 

angles. 

trilinear filtering n. A technique used in 3-D computer 

game rendering and other digital animation applications 

that produces the illusion of depth of field by making distant 

objects less distinct and detailed than nearer objects. 

tri-mode phone n. A wireless phone that broadcasts on 

1900 MHz personal communication service (PCS), 800 

MHz digital cellular networks, and 800 MHz analog 

networks. 

triple-pass scanner n. A color scanner that performs 

one scanning pass on an image for each of the three primary 

colors of light (red, green, and blue). See also color 

scanner. 

tristimulus values n. In color graphics, the varying 

amounts of three colors, such as red, blue, and green, that 

are combined to produce another color. See also color, 

color model. 

Trivial File Transfer Protocol n. A simplified version of 

File Transfer Protocol (FTP) that provides basic file transfer 

with no user authentication and is often used to download 

the initial files needed to begin an installation process. 

Acronym: TFTP. See also communications protocol. 

troff n. Short for typesetting run off. A UNIX text formatter 

often used to format man pages. See also man pages, 

RUNOFF. Compare TeX. 

Trojan horse n. A destructive program disguised as a 

game, utility, or application. When run, a Trojan horse 

does something harmful to the computer system while 

appearing to do something useful. See also virus, worm. 

troll vb. To post a message in a newsgroup or other online 

conference in the hopes that somebody else will consider 

the original message so outrageous that it demands a 

heated reply. A classic example of trolling is an article in 

favor of torturing cats posted in a pet lovers’ newsgroup. 

See also YHBT.

troubleshoot TTFN 

troubleshoot vb. To isolate the source of a problem in a 

program, computer system, or network and remedy it. 

troubleshooter n. A person trained and hired to find and 

resolve problems or breakdowns in machinery and technical 

equipment or systems. Troubleshooters often work as 

short-term consultants or freelancers because many organizations 

and businesses regard troubleshooting as a shortterm 

effort or possibly an exceptional—unplanned—part 

of a project or system. See also troubleshoot. 

trouble ticket n. A report of a problem with a particular 

device or system that is tracked through the workflow process. 

Originally written on paper, electronic trouble tickets 

are featured by many workflow and help-desk applications. 

See also help desk (definition 2), workflow application. 

True BASIC n. A version of Basic created in 1983 by 

John Kemeny and Thomas Kurtz, the creators of the original 

Basic, to standardize and modernize the language. 

True BASIC is a compiled, structured version of Basic 

that does not require line numbers. True BASIC includes 

advanced control structures that make structured programming 

possible. See also Basic, structured programming. 

true color n. See 24-bit color. 

true complement n. See complement. 

TrueType n. An outline font technology introduced by 

Apple Computer, Inc., in 1991 and by Microsoft Corporation 

in 1992 as a means of including high-grade fonts 

within the Macintosh and Windows operating systems. 

TrueType is a WYSIWYG font technology, which means 

that the printed output of TrueType fonts is identical to 

what appears on the screen. See also bitmapped font, outline 

font, PostScript. 

TrueType Open version 2 n. See OpenType. 

truncate vb. To cut off the beginning or end of a series of 

characters or numbers; specifically, to eliminate one or 

more of the least significant (typically rightmost) digits. In 

truncation, numbers are simply eliminated, unlike rounding, 

in which the rightmost digit might be incremented to 

preserve accuracy. Compare round. 

trunk n. 1. In communications, a channel connecting two 

switching stations. A trunk usually carries a large number 

of calls at the same time. 2. In networking, the cable forming 

the main communications path on a network. On a bus 

network, the single cable to which all nodes connect. See 

also backbone. 

trunking n. See link aggregation. 

531 

Trusted Computing Base n. See TCB. 

trust relationship n. A logical relationship established 

between domains to allow pass-through authentication, in 

which a trusting domain honors the logon authentications 

of a trusted domain. User accounts and global groups 

defined in a trusted domain can be given rights and permissions 

in a trusting domain, even though the user 

accounts or groups don’t exist in the trusting domain’s 

directory. See also authentication, domain, group, permission, 

user account. 

truth table n. A table showing the value of a Boolean 

expression for each of the possible combinations of variable 

values in the expression. See also AND, Boolean 

operator, exclusive OR, NOT, OR. 

try n. A keyword used in the Java programming language 

to define a block of statements that may throw a Java language 

exception. If an exception is thrown, an optional 

“catch” block can handle specific exceptions thrown 

within the “try” block. Also, an optional “finally” block 

will be executed regardless of whether an exception is 

thrown. See also block, catch, exception, finally. 

TSAPI n. Acronym for Telephony Services Application 

Programming Interface. The set of standards for the interface 

between a large telephone system and a computer network 

server, developed by Novell and AT&T and 

supported by many telephone equipment manufacturers 

and software developers. Compare TAPI. 

TSP n. See Telephony Service Provider. 

TSPI n. See Telephony Service Provider Interface. 

T-SQL or TSQL n. See Transact-SQL. 

TSR n. Acronym for terminate-and-stay-resident. A program 

that remains loaded in memory even when it is not 

running, so that it can be quickly invoked for a specific 

task performed while another program is operating. Typically, 

these programs are used with operating systems that 

are not multitasking, such as MS-DOS. See also hot key. 

TSV n. Filename extension, short for tab separated values, 

assigned to text files containing tabular (row and column) 

data of the type stored in database fields. As the name 

indicates, individual data entries are separated by tabs. 

Compare CSV (definition 3). 

TTFN n. Acronym for Ta ta for now. An expression sometimes 

used in Internet discussion groups, such as Internet 

Relay Chat (IRC), to signal a participant’s temporary 

departure from the group. See also IRC. 

T

T 

TTL Tux 

TTL n. See Time to Live, transistor-transistor logic. 

TTS n. 1. Acronym for Text-to-Speech. The process of 

converting digital text into speech output. TTS is used 

extensively in fax, e-mail, and other services for the blind, 

and for telephone-based informational and financial services. 

2. Acronym for Transaction Tracking System. A 

feature developed to protect databases from corruption 

caused by incomplete transactions. TTS monitors 

attempted transactions and in the event of a hardware or 

software failure, TTS will cancel the update and back out 

to maintain database integrity. 

TTY n. Acronym for teletypewriter. A device for lowspeed 

communications over a telephone line, consisting of 

a keyboard that sends a character code for each keystroke 

and a printer that prints characters as their codes are 

received. The simplest video display interface behaves 

like a TTY. See also KSR terminal, teletype mode. 

tunnel vb. To encapsulate or wrap a packet or a message 

from one protocol in the packet for another. The wrapped 

packet is then transmitted over a network via the protocol 

of the wrapper. This method of packet transmission is used 

to avoid protocol restrictions. See also communications 

protocol, packet (definition 2). 

tunneling n. A method of transmission over internetworks 

based on differing protocols. In tunneling, a packet 

based on one protocol is wrapped, or encapsulated, in a 

second packet based on whatever differing protocol is 

needed in order for it to travel over an intermediary network. 

In effect, the second wrapper “insulates” the original 

packet and creates the illusion of a tunnel through 

which the wrapped packet travels across the intermediary 

network. In real-life terms, tunneling is comparable to 

“encapsulating” a present (the original packet) in a box 

(the secondary wrapper) for delivery through the postal 

system. 

tunnel server n. A server or router that terminates tunnels 

and forwards traffic to the hosts on the target network. 

See also host, router, server, tunnel. 

tuple n. In a database table (relation), a set of related values, 

one for each attribute (column). A tuple is stored as a 

row in a relational database management system. It is the 

analog of a record in a nonrelational file. See also relation. 

Turing machine n. 1. A theoretical model created by 

British mathematician Alan Turing in 1936 that is considered 

the prototype for digital computers. Described in a 

paper (“On Computable Numbers with an Application to 

532 

the Entscheidungsproblem”) published in the Proceedings 

of the London Mathematical Society, the Turing machine 

was a logical device that could scan one square at a time 

(either blank or containing a symbol) on a paper tape. 

Depending on the symbol read from a particular square, 

the machine would change its status and/or move the tape 

backward or forward to erase a symbol or to print a new 

one. See also status. 2. A computer that can successfully 

mimic human intelligence in the Turing test. 

Turing test n. A test of machine intelligence proposed by 

Alan Turing, British mathematician and developer of the 

Turing machine. In the Turing test, also known as the Imitation 

Game, a person uses any series of questions to interrogate 

two unseen respondents, a human and a computer, 

to try to determine which is the computer. 

turnaround time n. 1. The elapsed time between submission 

and completion of a job. 2. In communications, the 

time required to reverse the direction of transmission in 

half-duplex communication mode. See also half-duplex 

transmission. 

turnkey system n. A finished system, complete with all 

necessary hardware and documentation and with software 

installed and ready to be used. 

turnpike effect n. The communications equivalent of 

gridlock; a reference to bottlenecks caused by heavy traffic 

over a communications system or network. 

turtle n. A small on-screen shape, usually a triangle or a 

turtle shape, that acts as a drawing tool in graphics. A turtle 

is a friendly, easily manipulated tool designed for children 

learning to use computers. It takes its name from a 

mechanical, dome-shaped turtle that was developed for the 

Logo language and moved about the floor in response to 

Logo commands, raising and lowering a pen to draw lines. 

turtle graphics n. A simple graphics environment, 

present in Logo and other languages, in which a turtle is 

manipulated by simple commands. Some versions display 

the turtle and its track on screen; others use electromechanical 

turtles that write on paper. 

tutorial n. A teaching aid designed to help people learn to 

use a product or procedure. In computer applications, a 

tutorial might be presented in either a book or a manual or 

as an interactive disk-based series of lessons provided 

with the program package. 

Tux n. The mascot of the Linux operating system. Tux is a 

rotund cartoonish penquin and the Tux image is available 

for use by any provider of Linux products or services. The

TV tuner card two-out-of-five code 

name Tux is both short for tuxedo, in reference to a penguin’s 

appearance, and an acronym for Torvalds’s UniX, 

after Linus Torvalds, the creator of the Linux operating 

system. 

TV tuner card n. A PCI card that allows a computer to 

receive television programming and display it on the computer’s 

monitor. See also PCI card. 

TWAIN n. The de facto standard interface between software 

applications and image-capturing devices such as 

scanners. Nearly all scanners contain a TWAIN driver, but 

only TWAIN-compatible software can use the technology. 

The TWAIN specification was developed by the TWAIN 

Working Group, a consortium of industry vendors formed 

in 1992. The name is thought by some to be an acronym 

for the phrase “technology without an interesting name,” 

although the TWAIN Working Group maintains the name 

is not an acronym. Others attribute the name to the quote 

“Ne’er the twain shall meet,” because the TWAIN driver 

and the application receiving the image are separated. See 

also scanner. 

tweak vb. To make final small changes to improve hardware 

or software performance; to fine-tune a nearly complete 

product. 

tween vb. In a graphics program, to calculate intermediary 

shapes during the metamorphosis of one shape into 

another. 

twinaxial adj. Having two coaxial cables contained in a 

single insulated jacket. See also coaxial cable. 

twip n. A unit of measure used in typesetting and desktop 

publishing, equal to one-twentieth of a printer’s point, or 

1/1440th of an inch. See also point1 (definition 1). 

twisted nematic display n. A type of passive-matrix liquid 

crystal display (LCD) in which the glass sheets enclosing 

nematic liquid crystal material are treated in such a 

way that the crystal molecules twist 90 degrees between 

top and bottom—in other words, the orientation at the bottom 

of the crystal is perpendicular to the orientation at the 

top. When an electrical charge is applied selectively to 

these crystals, they become temporarily untwisted and 

block the passage of polarized light. This blockage is what 

produces the dark pixels on an LCD display. The nematic 

part of the description refers to microscopic threadlike 

bodies that characterize the type of liquid crystals used in 

these displays. Also called: TN display. 

twisted-pair cable n. A cable made of two separately 

insulated strands of wire twisted together. It is used to 

533 

reduce signal interference introduced by a strong radio 

source such as a nearby cable. One of the wires in the pair 

carries the sensitive signal, and the other wire is grounded. 

twisted-pair wiring n. Wiring consisting of two insulated 

strands of copper twisted around one another to form a 

cable. Twisted-pair wiring comes in two forms, unshielded 

twisted pair (UTP) and shielded twisted pair (STP), the 

latter named for an extra protective sheath wrapped 

around each insulated pair of wires. Twisted-pair wiring 

can consist of a single pair of wires or, in thicker cables, 

two, four, or more pairs of wires. Twisted-pair wiring is 

typical of telephone cabling. Compare coaxial cable, 

fiberoptic cable. 

two-digit date storage n. A limitation in many computer 

systems and programs that store the year portion of 

a date as two digits instead of four. This practice in programming 

dates from the earliest days of computers when 

space on punch cards and memory in the computer were 

very limited, and many programmers used a two-digit 

year in date fields to economize on space or memory 

requirements. 

two-digit shortcut n. The practice of using two digits to 

indicate the year in a program, particularly those written in 

programming languages or running on systems that have 

the capability to work with a four-digit year (hence the 

term shortcut). 

two-dimensional adj. Existing in reference to two measures, 

such as height and width—for example, a twodimensional 

model drawn with reference to an x-axis and 

a y-axis, or a two-dimensional array of numbers placed in 

rows and columns. See also Cartesian coordinates. 

two-dimensional array n. An ordered arrangement of 

information in which the location of any item is described 

by two numbers (integers) identifying its position in a particular 

row and column of a matrix. 

two-dimensional model n. A computer simulation of a 

physical object in which length and width are real 

attributes but depth is not; a model with x- and y-axes. 

Compare three-dimensional model. 

two-nines availability n. The availability of a system 

99% of the time. Two-nines availability equates to approximately 

87.6 hours of downtime in a standard 365-day 

year. See also high availability. 

two-out-of-five code n. An error-sensitive code for data 

transmission that stores each of the ten decimal digits (0 

through 9) as a set of five binary digits: either two of the 

T

T 

two’s complement type font 

digits are 1s and the other three digits are 0s or two of 

the digits are 0s and the other three digits are 1s. 

two’s complement n. A number in the base-2 system 

(binary system) that is the true complement of another 

number. A two’s complement is usually derived by reversing 

the digits in a binary number (changing 1s to 0s and 0s 

to 1s) and adding 1 to the result. When two’s complements 

are used to represent negative numbers, the most significant 

(leftmost) digit is always 1. See also complement. 

two-tier client/server n. A client/business logic layer 

and the database layer. Fourth-generation languages 

(4GL) have helped to popularize the two-tier client/server 

architecture. Compare three-tier client/server. 

two-way trust n. A type of trust relationship in which 

both of the domains in the relationship trust each other. In 

a two-way trust relationship, each domain has established 

a one-way trust with the other domain. For example, 

domain A trusts domain B and domain B trusts domain A. 

Two-way trusts can be transitive or nontransitive. All twoway 

trusts between Windows domains in the same domain 

tree or forest are transitive. See also domain, forest, oneway 

trust, transitive trust. 

TXD n. Short for Transmit (tx) Data. A line used to carry 

transmitted data from one device to another, as from computer 

to modem; in RS-232-C connections, pin 2. See also 

RS-232-C standard. Compare RXD. 

.txt n. A file extension that identifies ASCII text files. In 

most cases, a document with a .txt extension does not 

include any formatting commands, so it is readable in any 

text editor or word processing program. See also ASCII. 

Tymnet n. A public data network available in over 100 

countries, with links to some online services and Internet 

service providers. 

type1 n. 1. In programming, the nature of a variable—for 

example, integer, real number, text character, or floatingpoint 

number. Data types in programs are declared by the 

programmer and determine the range of values a variable 

can take as well as the operations that can be performed on 

it. See also data type. 2. In printing, the characters that 

make up printed text, the design of a set of characters 

(typeface), or, more loosely, the complete set of characters 

in a given size and style (font). See also font, typeface. 

type2 vb. To enter information by means of the keyboard. 

Type I PC Card n. See PC Card. 

Type II PC Card n. See PC Card. 

534 

Type III PC Card n. See PC Card. 

type-ahead buffer n. See keyboard buffer. 

type-ahead capability n. The ability of a computer program 

to gather incoming keystrokes in a temporary memory 

reservoir (buffer) before displaying them on the screen. 

This capability ensures that keystrokes are not lost if they 

are typed faster than the program can display them. 

type ball n. A small ball mounted on the print head of a 

printer or a typewriter (for example, the IBM Selectric) 

that bears all the characters in the character set on its surface. 

The ball rotates to align the correct character with the 

paper and with an inked or carbon ribbon before striking 

against the paper. See the illustration. 

F0Tgn10.eps 

Type ball. 

type checking n. The process performed by a compiler 

or interpreter to make sure that when a variable is used, 

it is treated as having the same data type as it was 

declared to have. See also compiler (definition 2), data 

type, interpreter. 

type declaration n. A declaration in a program that specifies 

the characteristics of a new data type, usually by 

combining more primitive existing data types. 

typeface n. A specific, named design of a set of printed 

characters, such as Helvetica Bold Oblique, that has a 

specified obliqueness (degree of slant) and stroke weight 

(thickness of line). A typeface is not the same as a font, 

which is a specific size of a specific typeface, such as 12point 

Helvetica Bold Oblique. Nor is a typeface the same 

as a typeface family, which is a group of related typefaces, 

such as the Helvetica family including Helvetica, Helvetica 

Bold, Helvetica Oblique, and Helvetica Bold Oblique. 

See also font. 

type font n. See font.

typematic typosquatter 

typematic adj. The keyboard feature that repeats a keystroke 

when a key is held down longer than usual. Also 

called: auto-key, auto-repeat. See also repeat key, Repeat- 

Keys. 

typeover mode n. See overwrite mode. 

type size n. The size of printed characters, usually measured 

in points (a point is approximately 1 /72 inch). See 

also point1 (definition 1). 

type style n. 1. The obliqueness, or degree of slant, of a 

typeface. 2. Loosely, the overall design of a typeface or a 

typeface family. 3. One of the variant forms of a type character, 

including roman, bold, italic, and bold italic. 

535 

typography n. 1. The art of font design and typesetting. 

See also computer typesetting, font. 2. The conversion of 

unformatted text into camera-ready type, suitable for 

printing. See also camera-ready. 

typosquatter n. A form of cybersquatter that takes 

advantage of typographical errors to snare Web surfers. 

The typosquatter registers variations of popular trademarked 

domain names that contain the most likely spelling 

errors (for example: JCPenny). A user who makes a 

mistake typing in a Web site address will be taken to the 

typosquatter’s site, which typically is loaded with banner 

and pop-up ads. The typosquatter is paid by the number of 

users who see the ads. See also cybersquatter. 

T

U 

u- prefix A letter sometimes substituted for the Greek letter 

µ (mu), meaning micro, used as a prefix in measurements 

denoting one millionth, or 10-6 . See also micro- 


UA n. See user agent. 

UART n. Acronym for universal asynchronous receivertransmitter. 

A module, usually composed of a single integrated 

circuit, that contains both the receiving and transmitting 

circuits required for asynchronous serial 

communication. A UART is the most common type of circuit 

used in personal computer modems. Compare USRT. 

ubiquitous computing n. A term coined by Mark Wieser 

(1988) at the Xerox PARC Computer Science Lab to 

describe a computing environment so pervasive in daily life 

that it’s invisible to the user. Household appliances such as 

VCRs and microwave ovens are contemporary low-level 

examples of ubiquitous computing. In the future, prognosticators 

say, computers will be so embedded in all facets of 

life—so ubiquitous—that their presence will fade into the 

background. Ubiquitous computing is considered to be the 

third stage in the evolution of computing technology, after 

the mainframe and the personal computer. Acronym: UC. 

UC n. See ubiquitous computing. 

UCAID n. Acronym for University Corporation for 

Advanced Internet Development. An organization created 

to provide guidance in advanced networking development 

within the university community. UCAID is responsible 

for the development of the Abilene fiber-optic backbone 

network that will interconnect over 150 universities into 

the Internet2 project. 

UCE n. Acronym for unsolicited commercial e-mail. 

See spam. 

UCITA n. Acronym for Uniform Computer Information 

Transactions Act. Legislation proposed or enacted in several 

states that will set legal standards and control systems 

for dealing with computer information. UCITA is a model 

law intended as an amendment to the Uniform Commercial 

Code to cover new technology-related issues. One of 

U 

536 

UCITA’s main provisions is a standard for mass market 

software shrinkwrap and clickwrap agreements. See also 

clickwrap agreement, shrinkwrap agreement. 

UCSD p-system n. A portable operating system and 

development environment that was developed by Kenneth 

Bowles at the University of California at San Diego. The 

system was based on a simulated, 16-bit, stack-oriented 

“pseudomachine.” The development environment included 

a text editor and compilers for several languages, such as 

FORTRAN and Pascal. Programs written for a p-system 

were more portable than programs compiled to machine 

language. See also bytecode, pseudomachine, p-system, 

virtual machine. 

UDDI n. Acronym for Universal Description, Discovery, 

and Integration. A platform-independent framework functioning 

like a directory (similar to a telephone book) that 

provides a way to locate and register Web services on the 

Internet. The UDDI specification calls for three elements: 

white pages, which provide business contact information; 

yellow pages, which organize Web services into categories 

(for example, credit card authorization services); and 

green pages, which provide detailed technical information 

about individual services. The UDDI also contains an 

operational registry, which is available today. 

UDP n. Acronym for User Datagram Protocol. The connectionless 

protocol within TCP/IP that corresponds to the 

transport layer in the ISO/OSI reference model. UDP converts 

data messages generated by an application into packets 

to be sent via IP, but it is “unreliable” because it does 

not establish a path between sender and receiver before 

transmitting and does not verify that messages have been 

delivered correctly. UDP is more efficient than TCP, so it is 

used for various purposes, including SNMP; the reliability 

depends on the application that generates the message. See 

also communications protocol, ISO/OSI reference model, 

packet, SNMP, TCP/IP. Compare IP, TCP. 

UDT n. Acronym for uniform data transfer. The service 

used in the OLE extensions to Windows that allows two

UI UNC 

applications to exchange data without either program 

knowing the internal structure of the other. 

UI n. See user interface. 

UKnet n. 1. The University of Kentucky’s campus network. 

2. In the United Kingdom, an Internet service provider 

(ISP) based at the University of Kent. See also ISP. 

ULSI n. See ultra-large-scale integration. 

UltimateTV n. A television digital recording technology 

developed by Microsoft. UltimateTV can record up to 35 

hours of DIRECTV broadcasts. Because the television 

signal is recording on UltimateTV’s hard drive, viewers 

can pause a live show, rewind scenes, and watch previously 

shown parts of the show in slow or fast motion while 

UltimateTV records the remainder of the show live. 

Ultra DMA/33 n. A data transfer protocol, based on direct 

memory access, for transferring data between a hard drive 

and a computer’s RAM. Ultra DMA/33 improves ATA/IDE 

performance, doubles burst transfer rates to 33 megabytes 

per second, and increases data transfer integrity. See also 

ATA, direct memory access, IDE (definition 1). 

ultrafiche n. Microfiche with very high density. The 

image in ultrafiche is reduced at least 90 times from its 

original size. See also microfiche. 

ultra-large-scale integration n. The highest currently 

possible density at which components (transistors and 

other elements) are packed onto an integrated circuit. 

“Ultra-large-scale” is generally applied to component densities 

of 1,000,000 or greater. Acronym: ULSI. See also 

integrated circuit. Compare large-scale integration, 

medium-scale integration, small-scale integration, superlarge-scale 

integration, very-large-scale integration. 

ultralight computer n. See portable computer. 

UltraSCSI n. An extension of the SCSI-2 standard that 

doubles the transfer speed of Fast-SCSI to allow a transfer 

rate of 20 megabytes per second (MBps) on an 8-bit connection 

and 40 MBps on a 16-bit connection. See also 

SCSI, SCSI-2. 

Ultra Wide SCSI n. See UltraSCSI. 

UMA n. 1. Acronym for upper memory area. The portion 

of DOS memory between the first 640K and 1 MB. Compare 

high memory area. 2. Acronym for Uniform Memory 

Architecture. See SMP. 

UMB n. Acronym for upper memory block. A block of 

memory in the UMA (upper memory area) that can be 

537 

used for device drivers or TSRs. A UMB is allocated and 

managed by special memory manager programs such as 

EMM386.EXE. See also device driver, TSR, UMA (definition 

1). 

UML n. Acronym for Unified Modeling Language. A language 

developed by Grady Booch, Ivar Jacobson, and Jim 

Rumbaugh of Rational Software that can be used for specifying, 

building, and documenting software and non-software 

systems, such as business models. UML notation 

provides a common foundation for object-oriented design 

by providing descriptions of modeling concepts including 

object class, associations, interface, and responsibility. 

The UML standard is supported by software developers 

and vendors and overseen by the Object Management 

Group (OMG). 

UMTS n. Acronym for Universal Mobile Telecommunications 

System. Third-generation wireless communications 

standard developed to provide a consistent set of 

packet-based voice, text, video, and multimedia capabilities 

to users in any communications environment worldwide. 

When UMTS reaches full implementation, users 

will be able maintain computer and phone Internet connections 

from anywhere in the world. 

unary adj. Of, pertaining to, or characteristic of a mathematical 

operation with a single operand (object); monadic. 

Compare dyadic. 

unary operator n. An operator that takes only one operand 

—for example, unary minus (as in –2.5). See also operator. 

Compare binary operator. 

unbuffered adj. Of, pertaining to, or characteristic of 

something that does not store data characters in memory 

but instead processes them as they are received. See also 

buffer2 . 

unbundle vb. To separate the items of a composite sales 

package; for example, to sell components of a software 

package separately rather than as a package. Compare 

bundle. 

unbundled adj. Not included as part of a complete hardware/software 

package; the term particularly applies to a 

product that was previously bundled, as opposed to one 

that has always been sold separately. 

UNC n. Acronym for Universal Naming Convention or, 

sometimes, Uniform Naming Convention. The system of 

naming files among computers on a network so that a file 

on a given computer will have the same pathname when 

accessed from any of the other computers on the network. 

U

U 

uncompress unified messaging 

For example, if the directory c:\path1\path2\...pathn on 

computer servern is shared under the name pathdirs, a 

user on another computer would open \\servern\pathdirs\filename.ext 

to access the file c:\path1\path2\...pathn\ 

filename.ext on servern. See also URL, virtual path. 

uncompress vb. To restore the contents of a compressed 

file to its original form. Also called: decompress. Compare 

compress2 . 

unconditional branch n. A transfer of execution to 

another line of code in a program without a check for some 

condition being true or false. The transfer always takes 

place whenever such an instruction is encountered. See also 

branch (definition 2). Compare conditional branch. 

undelete1 n. The act of restoring deleted information. An 

undelete is comparable to (and usually included as part of) 

an undo command; it is more restricted, however, in that 

“undo” reverses any previous act, but undelete reverses 

only a deletion. Undelete generally refers only to excised 

text or deleted files. See also undo. 

undelete2 vb. 1. To restore deleted information, usually 

the last item deleted. 2. In file storage, to restore a file’s 

storage information so that a deleted file becomes available 

for access again. Also called: unerase. See also file 

recovery. 

undeliverable adj. Not able to be delivered to an intended 

recipient. If an e-mail message is undeliverable, it is 

returned to the sender with information added by the mail 

server explaining the problem; for example, the e-mail 

address may be incorrect, or the recipient’s mailbox may 

be full. 

undercolor separation n. In the CMYK color model, the 

process of converting equal quantities of cyan, magenta, 

and yellow to equivalent gray levels, which are then 

printed in black ink. This produces grays that are clearer 

and sharper than those produced by mixing colored inks. 

See also CMY, CMYK, color model. 

underflow n. A condition in which a mathematical calculation 

produces a result too near to zero to be represented 

by the range of binary digits available to the computer for 

holding that value in the specified precision. See also precision 

(definition 2), single-precision. 

underline vb. To format a selection of text so that the text 

is printed with a line slightly below it. 

Undernet n. An international network of Internet Relay 

Chat (IRC) servers created in 1992 as an alternative to the 

538 

larger and more chaotic main IRC network. For information 

about connecting to Undernet, see http://www.undernet.org. 

See also IRC. 

underscore n. An underline character often used to 

emphasize a letter or a word; on nongraphics displays, 

generally used to indicate italic characters. 

undo vb. To reverse the last action—for example, to undo 

a deletion, thus restoring deleted text to a document. Many 

application programs enable the user both to undo and to 

redo an action. See also undelete (definition 1). 

undock vb. 1. To detach a laptop or other portable computer 

from a docking station. See also docking station, 

laptop. 2. To move a toolbar from the edge of a window so 

that the toolbar becomes its own free-floating window. See 

also toolbar. 

unerase n. See undelete1 . 

unfold adj. See inline (definition 1). 

unhandled exception n. An error condition that an 

application does not internally resolve. When an unhandled 

exception occurs, the operating system terminates the 

application that caused the error. 

Unibus n. A bus architecture introduced by Digital Equipment 

Corporation in 1970. 

unicast vb. To transmit between a single sender and a single 

receiver over a network. A two-way, point-to-point 

transmission, unicast is typical of network communications. 

Compare anycasting, narrowcast. 

Unicode n. A 16-bit character encoding standard developed 

by the Unicode Consortium between 1988 and 1991. 

By using 2 bytes to represent each character, Unicode 

enables almost all the written languages of the world to be 

represented using a single character set. (By contrast, 8-bit 

ASCII is not capable of representing all the combinations 

of letters and diacritical marks that are used just with the 

Roman alphabet.) Approximately 39,000 of the 65,536 

possible Unicode character codes have been assigned to 

date, 21,000 of them being used for Chinese ideographs. 

The remaining combinations are open for expansion. 

Compare ASCII. 

unified messaging n. The integration of various communications 

technologies such as voicemail, fax, and e-mail 

into a single service. Unified messaging is designed to be 

a time-saving tool to provide users with a single package 

with which they can receive, organize, and respond to 

messages in a variety of media.

Unified Modeling Language United States of America Standards Institute 

Unified Modeling Language n. See UML. 

Uniform Computer Information Transactions 

Act n. See UCITA. 

Uniform Data Transfer n. See UDT. 

Uniform Memory Access n. See SMP. 

Uniform Naming Convention n. See UNC. 

Uniform Resource Citation n. A description of an 

object on the World Wide Web, consisting of pairs of 

attributes and their values, such as the Uniform Resource 

Identifiers (URIs) of associated resources, author names, 

publisher names, dates, and prices. Acronym: URC. 

Uniform Resource Identifier n. A character string used 

to identify a resource (such as a file) from anywhere on the 

Internet by type and location. The set of Uniform 

Resource Identifiers includes Uniform Resource Names 

(URNs) and Uniform Resource Locators (URLs). Acronym: 

URI. See also relative URL, Uniform Resource 

Name, URL. 

Uniform Resource Locator n. See URL. 

Uniform Resource Name n. A scheme for uniquely 

identifying resources that might be available on the Internet 

by name, without regard to where they are located. The 

specifications for the format of Uniform Resource Names 

are still under development by the Internet Engineering 

Task Force (IETF). They include all Uniform Resource 

Identifiers (URIs) having the schemes urn:, fpi:, and path:; 

that is, those that are not Uniform Resource Locators 

(URLs). Acronym: URN. See also IETF, Uniform 

Resource Identifier, URL. 

UniForum n. 1. The International Association of Open 

System Professionals, an organization of UNIX users and 

administrators. 2. A series of UNIX trade shows sponsored 

by UniForum and managed by Softbank COMDEX, 

Inc. See also COMDEX. 

Unimodem n. 1. The universal modem driver, provided 

with Windows CE, that translates Telephony Service Provider 

Interface (TSPI) calls into AT commands and sends 

the commands to a virtual device driver that talks to the 

modem. 2. A universal modem that supports standard 

modem AT commands. Windows CE currently supports 

only PCMCIA modems. 

uninstall vb. To remove software completely from a system, 

including the elimination of files and components 

539 

residing in system locations such as the registry in Windows 

9x, Windows NT, or Windows 2000. Some applications 

have built-in uninstall utilities, and in other cases a 

separate uninstall program can be used. Also called: 

deinstall. 

uninterruptible power supply n. See UPS. 

union n. 1. In set theory, the smallest combination of two 

sets that contains all elements of both sets. 2. In logic, an 

inclusive OR operation—that is, the result, C, of any union 

of A and B is true (1) except when A and B are both false 

(0). See the table. 3. In programming, a structure that can 

be used to store different types of variables (such as integer, 

character, or Boolean). 4. In database management, a 

relational operator. Given two relations (tables), A and B, 

that are union-compatible (contain the same number of 

fields, with corresponding fields containing the same 

types of values), A UNION B builds a new relation containing 

those tuples (records) that appear either in A or in 

B or in both. Compare difference, intersect. 

Table U.1 A Truth Table Showing the Results of Unions. 

A OR B = C 

1 1 1 

1 0 1 

0 1 1 

0 0 0 

union-compatible adj. In database management, of, pertaining 

to, or characteristic of two relations (tables) that 

are of the same order (have the same number of attributes) 

and whose corresponding attributes are based on the same 

domain (the set of acceptable values). 

unipolar adj. Having one state. In electronics, a unipolar 

device or signal is one in which the same voltage polarity 

(positive or negative) is used to represent binary states— 

on/off or true/false. Compare bipolar. 

unique user n. An individual visitor to a Web site. Tracking 

unique users is important in ascertaining the success of 

a given Web site because it indicates how many different 

visitors access the site, as opposed to the number of hits— 

visits by the same or different individuals—the site receives. 

Also called: unique visitor. 

unique visitor n. See unique user. 

United States of America Standards Institute n. The 

former name of the American National Standards Institute. 

See also ANSI. 

U

U 

unit position unmanaged code 

unit position n. The “one’s place” in a multiple-digit 

number—for example, the 3 in the number 473. 

UNIVAC I n. Short for Universal Automatic Calculator I. 

The first commercially available electronic computer, 

designed by J. Presper Eckert and John Mauchly, also the 

inventors of ENIAC (generally considered the first fully 

electronic computer). UNIVAC I was the first computer to 

handle both numeric and textual information. 

universal asynchronous receiver-transmitter n. See 

UART. 

Universal Description, Discovery, and Integration n. 

See UDDI. 

Universal Mobile Telecommunications System n. See 

UMTS. 

Universal Naming Convention n. See UNC. 

Universal Plug and Play n. See UPnP. 

Universal Plug and Play Forum n. See UPnP Forum. 

Universal Plug and Play networking n. See UPnP networking. 

Universal Product Code n. See UPC. 

Universal Resource Locator n. See URL. 

universal serial bus n. See USB. 

Universal Server n. 1. Software from Oracle Corporation 

that supplies information from its database in a variety of 

forms, such as text, sound, and video, in response to 

HTTP requests. 2. Database software from Informix that 

works with snap-in software modules to handle user needs 

for specific data types and ways of processing. 

universal synchronous receiver-transmitter n. See 

USRT. 

Universal Time Coordinate n. For all practical purposes, 

the same as Greenwich Mean Time, which is used for the 

synchronization of computers on the Internet. Acronym: 

UTC. Also called: coordinated universal time format. 

University Corporation for Advanced Internet 

Development n. See UCAID. 

UNIX n. A multiuser, multitasking operating system. 

Originally developed by Ken Thompson and Dennis 

Ritchie at AT&T Bell Laboratories from 1969 through 

1973 for use on minicomputers, UNIX has evolved into a 

complex, powerful operating system that, because it is 

540 

written in the C language, is more portable—that is, less 

machine-specific—than many other operating systems. 

UNIX has been released in a wide variety of versions, or 

flavors, including System V (developed by AT&T for 

commercial release; many current flavors on based on it), 

BSD UNIX (freeware developed at the University of California 

Berkeley, which has spun off many related flavors), 

AIX (a version of System V adapted by IBM to run on 

RISC-based workstations), A/UX (a graphical version for 

the Macintosh), Linux (a newer version that runs on the 

Intel chip), and SunOS (based on BSD UNIX and available 

on Sun workstations). Many flavors of UNIX are 

available free. With some flavors, the source code is also 

free, making it an instrumental part of the open source 

movement. UNIX is widely used as a network operating 

system, especially in conjunction with the Internet. See 

also BSD UNIX, Linux, open source, System V. 

UNIX shell account n. A shell account providing 

command-line access to a UNIX system. See also shell 

account. 

UNIX shell scripts n. Sequences of UNIX commands 

stored as files that can be run as programs. In MS-DOS, 

batch (.bat) files provide similar capabilities. See also 

batch file, shell1 , shell script. 

UNIX-to-UNIX Copy n. See UUCP. 

UNIX wizard n. A particularly expert and helpful UNIX 

programmer. Some companies actually use this phrase as a 

job title. The newsgroup comp.unix.wizards provides 

answers to many user questions. 

unknown host n. A response to a request for a connection 

to a server that indicates that the network is unable to 

find the specified address. See also server (definition 1). 

unknown recipients n. A response to an e-mail message 

that indicates that the mail server is unable to identify one 

or more of the destination addresses. 

unload vb. 1. To remove a storage medium, such as a tape 

or disk, from its drive. 2. To remove software from system 

memory. See also memory. 

unmanaged code n. Code that is executed directly by the 

operating system, outside of the common language runtime 

environment. Unmanaged code must provide its own 

garbage collection, type checking, security support, and so 

on, unlike managed code, which receives these services

unmoderated upload1 upload 

from the common language runtime. See also managed 

code. 

unmoderated adj. Of, pertaining to, or characteristic of a 

newsgroup or mailing list in which all articles or messages 

received by the server are automatically available or distributed 

to all subscribers. Compare moderated. 

unmount vb. To remove a disk or tape from active use. 

Compare mount. 

unpack vb. To restore packed data to its original format. 

Compare pack. 

unpopulated board n. A circuit board whose sockets are 

empty. Compare fully populated board. 

unread adj. 1. Of, pertaining to, or being an article in a 

newsgroup that a user has not yet received. Newsreader 

client programs distinguish between “read” and “unread” 

articles for each user and download only unread articles 

from the server. 2. Of, pertaining to, or being an e-mail 

message that a user has received but has not yet opened in 

an e-mail program. 

unrecoverable error n. A fatal error—one that a program 

is unable to recover from without the use of external 

recovery techniques. Compare recoverable error. 

unreliable protocol n. A communications protocol that 

makes a “best effort” attempt to deliver a transmission but 

does not provide for verifying that the transmission arrives 

without error. 

unroll adj. See inline (definition 1). 

unset vb. To make the value of a bit position equal to 0. 

Compare set (definition 1). 

unshielded cable n. Cable that is not surrounded with a 

metal shield. If the wires in an unshielded cable are not at 

least twisted around each other in pairs, the signals they 

carry have no protection from interference by external 

electromagnetic fields. Consequently, unshielded cable 

should be used only over very short distances. Compare 

coaxial cable, ribbon cable, twisted-pair cable, UTP. 

unshielded twisted pair n. See UTP. 

unshielded twisted-pair wiring n. See UTP. 

unsolicited commercial e-mail n. See spam. 

unsubscribe vb. 1. In a newsreader client program, to 

remove a newsgroup from the list of newsgroups to which 

541 

one subscribes. See also newsgroup. 2. To remove oneself 

as a recipient on a mailing list. See also mailing list. 

untar1 n. A utility, available for systems in addition to 

UNIX, for separating the individual files out of an archive 

assembled using the UNIX tar program. Compare tar1 . 

untar2 vb. To separate the individual files out of an archive 

assembled with the UNIX tar program. Compare tar2 . 

unzip vb. To uncompress an archive file that has been compressed 

by a program such as compress, gzip, or PKZIP. 

up adj. Functioning and available for use; used in describing 

computers, printers, communications lines on networks, 

and other such hardware. 

UPC n. Acronym for Universal Product Code. A system of 

numbering commercial products using bar codes. A UPC 

consists of 12 digits: a number system character, a five-digit 

number assigned to the manufacturer, a five-digit product 

code assigned by the manufacturer, and a modulo 10 check 

digit. See also bar code. 

update1 n. A new release of an existing software product. 

A software update usually adds relatively minor new features 

to a product or corrects errors (bugs) found after the 

program was released. Updates are generally indicated by 

small changes in software version numbers, such as 4.0b 

from 4.0. See also version number. Compare release1 . 

update2 vb. To change a system or a data file to make it 

more current. 

update query n. A database query that changes a set of 

records according to search conditions or criteria. 

upflow n. In the data warehousing process, the stage during 

which stored information is checked for completeness, 

summarized, and readied for distribution. See also data 

warehouse2 . Compare downflow, inflow, metaflow. 

upgrade1 n. The new or enhanced version of a product. 

upgrade2 vb. To change to a newer, usually more powerful 

or sophisticated version. 

uplink n. The transmission link from an earth station to a 

communications satellite. 

upload1 n. 1. In communications, the process of transferring 

a copy of a file from a local computer to a remote 

computer by means of a modem or network. 2. The copy 

of the file that is being or has been transferred. 

U

U 

upload2 upload 

URN 

upload2 vb. To transfer a copy of a file from a local computer 

to a remote computer. Compare download. 

UPnP n. Acronym for Universal Plug and Play. A 

Microsoft initiative which prompted the creation of the 

UPnP Forum for interconnecting computers, appliances, 

networks, and services. UPnP extends conventional Plug 

and Play to include devices connected to networks. It 

allows peripheral devices to discover and connect to other 

devices and to enumerate the characteristics of those 

devices. UPnP is intended to be an element of home networking, 

in which PCs, appliances, and the services they 

provide are linked together. 

UPnP Device Architecture n. A specification developed 

by the Universal Plug and Play (UPnP) Forum that defines 

the structure of UPnP networking. The UPnP Device 

Architecture, formerly known as the DCP Framework, 

provides information about discovery, description, control, 

eventing, and presentation in a UPnP network. See also 

UPnP networking. 

UPnP Forum n. A consortium of companies and individuals 

that oversees Universal Plug and Play (UPnP) specifications, 

protocols, logos, sample implementations, test 

suites, white papers, and other UPnP-related efforts. See 

also UPnP, UPnP Device Architecture, UPnP networking. 

UPnP networking n. The peer-to-peer networking of 

intelligent machines, appliances, wireless devices, computers, 

and other devices according to the Universal Plug and 

Play (UPnP) Device Architecture. UPnP networking uses 

control points, devices, services, and protocols including 

GENA, SOAP, SSDP, standard TCP/IP, and other Internet 

protocols. See also UPnP Device Architecture. 

uppercase adj. Of, pertaining to, or characterized by capital 

letters. Compare lowercase. 

upper memory area n. See UMA (definition 1). 

upper memory block n. See UMB. 

UPS n. Acronym for uninterruptible power supply. A 

device, connected between a computer (or other electronic 

equipment) and a power source (usually an outlet receptacle), 

that ensures that electrical flow to the computer is not 

interrupted because of a blackout and, in most cases, protects 

the computer against potentially damaging events, 

such as power surges and brownouts. All UPS units are 

equipped with a battery and a loss-of-power sensor; if the 

sensor detects a loss of power, it switches over to the battery 

so that the user has time to save his or her work and 

shut off the computer. See also blackout, brownout. 

542 

upstream1 n. The direction in which information is delivered 

from a client to a (Web) server. Compare 

downstream1 . 

upstream2 adj. 1. The location of a server in relation to 

another server. Compare downstream2 (definition 1). 

2. The direction in which data moves from an individual 

computer to the remote network. With certain communications 

technologies, such as ADSL, cable modems, and 

high-speed 56-Kbps modems, data flows upstream more 

slowly than downstream. For example, a 56-Kbps modem 

can deliver data at a 56-Kbps maximum only downstream; 

upstream, it delivers data at either 28.8 or 33.6 Kbps. 

Compare downstream2 (definition 2). 

uptime n. The amount or percentage of time a computer 

system or associated hardware is functioning and available 

for use. Compare downtime. 

upward-compatible adj. Of, pertaining to, or characteristic 

of a computer product, especially software, designed to 

perform adequately with other products that are expected 

to become widely used in the foreseeable future. The use 

of standards and conventions makes upward compatibility 

easier to achieve. 

urban legend n. A widely distributed story that remains 

in circulation in spite of the fact that it is not true. Many 

urban legends have been floating around the Internet and 

other online services for years, including the request for 

cards for the sick boy in England (he’s long since recovered 

and grown up), the cookie or cake recipe that cost 

$250 (it’s a myth), and the Good Times or Penpal Greetings 

virus, which will infect your computer when you read 

an e-mail message (it does not exist). See also Good 

Times virus. 

URC n. See Uniform Resource Citation. 

URI n. See Uniform Resource Identifier. 

URL n. Acronym for Uniform Resource Locator. An 

address for a resource on the Internet. URLs are used by 

Web browsers to locate Internet resources. A URL specifies 

the protocol to be used in accessing the resource (such 

as http: for a World Wide Web page or ftp: for an FTP 

site), the name of the server on which the resource resides 

(such as //www.whitehouse.gov), and, optionally, the path 

to a resource (such as an HTML document or a file on that 

server). See also FTP1 (definition 1), HTML, HTTP, path 

(definition 1), server (definition 2), virtual path (definition 

1), Web browser. 

URN n. See Uniform Resource Name.

usable user-initiated update 

usable adj. Of, pertaining to, or characteristic of the ease 

and adaptability with which a product can be applied to 

the performance of the work for which it is designed. A 

high degree of usability implies ease of learning, flexibility, 

freedom from bugs, and good design that does not 

involve unnecessarily complicated procedures. 

usage analysis n. Data collected to evaluate how a Web 

site is being used, such as visitor user names, how often 

each page was visited, and the types of Web browsers used. 

USB n. Acronym for universal serial bus. A serial bus 

with a data transfer rate of 12 megabits per second (Mbps) 

for connecting peripherals to a microcomputer. USB can 

connect up to 127 peripherals, such as external CD-ROM 

drives, printers, modems, mice, and keyboards, to the system 

through a single, general-purpose port. This is accomplished 

by daisy chaining peripherals together. USB is 

designed to support the ability to automatically add and 

configure new devices and the ability to add such devices 

without having to shut down and restart the system (hot 

plugging). USB was developed by Intel, Compaq, DEC, 

IBM, Microsoft, NEC, and Northern Telecom. It competes 

with DEC’s ACCESS.bus for lower-speed applications. 

See also bus, daisy chain, hot plugging, input/output port, 

peripheral. Compare ACCESS.bus. 

U.S. Department of Defense n. The military branch of 

the United States government. The Department of Defense 

developed ARPANET, the origin of today’s Internet and 

MILNET, through its Advanced Research Projects 

Agency (ARPA). See also ARPANET, Internet, MILNET. 

Usenet or UseNet or USENET n. A worldwide network 

of UNIX systems that has a decentralized administration 

and is used as a bulletin board system by special-interest 

discussion groups. Usenet, which is considered part of the 

Internet (although Usenet predates it), is comprised of 

thousands of newsgroups, each devoted to a particular 

topic. Users can post messages and read messages from 

others in these newsgroups in a manner similar to users on 

dial-in BBSs. Usenet was originally implemented using 

UUCP (UNIX-to-UNIX Copy) software and telephone 

connections; that method remains important, although 

more modern methods, such as NNTP and network connections, 

are more commonly used. See also BBS (definition 

1), newsgroup, newsreader, NNTP, UUCP. 

Usenet User List n. A list maintained by the Massachusetts 

Institute of Technology that contains the name and 

e-mail address of everyone who has posted to the Usenet. 

See also Usenet. 

543 

user account n. On a secure or multiuser computer system, 

an established means for an individual to gain access 

to the system and its resources. Usually created by the system’s 

administrator, a user account consists of information 

about the user, such as password, rights, and permissions. 

See also group1 , logon, user profile. 

user agent n. In the terminology established by the ISO/ 

OSI reference model for LANs (local area networks), a 

program that helps a client connect with a server. Acronym: 

UA. See also agent (definition 3), ISO/OSI reference 

model, LAN. 

user control n. In ASP.NET: A server control that is 

authored declaratively using the same syntax as an 

ASP.NET page and is saved as a text file with an .ascx 

extension. User controls allow page functionality to be 

partitioned and reused. Upon first request, the page framework 

parses a user control into a class that derives from 

System.Web.UI.UserControl and compiles that class into 

an assembly, which it reuses on subsequent requests. User 

controls are easy to develop due to their page-style authoring 

and deployment without prior compilation. In Windows 

Forms: A composite control that provides consistent 

behavior and user interface within or across applications. 

The user control can be local to one application or added 

to a library and compiled into a DLL for use by multiple 

applications. 

User Datagram Protocol n. See UDP. 

user-defined data type n. A data type defined in a program. 

User-defined data types are usually combinations of 

data types defined by the programming language being 

used and are often used to create data structures. See also 

data structure, data type. 

user-defined function key n. See keyboard enhancer, 

programmable function key. 

user-friendly adj. Easy to learn and easy to use. 

user group n. A group of people drawn together by interest 

in the same computer system or software. User groups, 

some of which are large and influential organizations, provide 

support for newcomers and a forum where members 

can exchange ideas and information. 

user-initiated update n. An operating system update 

mechanism, provided by the dial-up boot loader, which is 

designed to be used by remote users and field technicians. 

The operating system image is downloaded using a 

modem connection. See also automatic update, factory 

update. 

U

U 

user interface UUCP 

user interface n. The portion of a program with which a 

user interacts. Types of user interfaces, or UIs, include 

command-line interfaces, menu-driven interfaces, and 

graphical user interfaces. Acronym: UI. 

User Interface Toolbox n. See Toolbox. 

username n. The name by which a user is identified to a 

computer system or network. During the logon process, 

the user must enter the username and the correct password. 

If the system or network is connected to the Internet, 

the username generally corresponds to the leftmost 

part of the user’s e-mail address (the portion preceding the 

@ sign, as in username@company.com). See also e-mail 

address, logon. 

user name n. The name by which a person is known and 

addressed on a communications network. See also alias 


user profile n. A computer-based record maintained 

about an authorized user of a multiuser computer system. 

A user profile is needed for security and other reasons; it 

can contain such information as the person’s access 

restrictions, mailbox location, type of terminal, and so on. 

See also user account. 

user state n. The least privileged of the modes in which 

a Motorola 680x0 microprocessor can operate. This is the 

mode in which application programs are run. See also 

68000. Compare supervisor state. 

USnail n. 1. Slang for the United States Postal Service. 

USnail, a term used on the Internet, is a reference to how 

slow the postal service is in comparison to e-mail. 2. Mail 

delivered by the United States Postal Service. See also 

snail mail. 

/usr n. A directory in a computer system that contains 

subdirectories owned or maintained by individual users of 

the computer system. These subdirectories can contain 

files and additional subdirectories. Typically, /usr directories 

are used in UNIX systems and can be found on many 

FTP sites. See also FTP site. 

USRT n. Acronym for universal synchronous receivertransmitter. 

A module, usually composed of a single integrated 

circuit, that contains both the receiving and transmitting 

circuits required for synchronous serial 

communication. Compare UART. 

UTC n. See Universal Time Coordinate. 

544 

UTF-8 n. Acronym for UCS Transformation Format 8. A 

character set for protocols evolving beyond the use of 

ASCII. The UTF-8 protocol provides for support of 

extended ASCII characters and translation of UCS-2, an 

international 16-bit Unicode character set. UTF-8 enables 

a far greater range of names than can be achieved using 

ASCII or extended ASCII encoding for character data. See 

also ASCII, Unicode. 

utility n. A program designed to perform a particular 

function; the term usually refers to software that solves 

narrowly focused problems or those related to computer 

system management. See also application. 

utility program n. A program designed to perform maintenance 

work on the system or on system components (for 

example, a storage backup program, disk and file recovery 

program, or resource editor). 

UTP n. Acronym for unshielded twisted pair. A cable 

containing one or more twisted pairs of wires without 

additional shielding. UTP is more flexible and takes up 

less space than shielded twisted-pair (STP) cable but has 

less bandwidth. See the illustration. See also twisted-pair 

cable. Compare STP. 

F0Ugn01.eps 

UTP. 

.uu n. The file extension for a binary file that has been 

translated into ASCII format using uuencode. Also 

called: .uud. See also ASCII, binary file, uuencode1 . 

Compare .uue. 

UUCP n. Acronym for UNIX-to-UNIX Copy. A set of 

software programs that facilitates transmission of information 

between UNIX systems using serial data connec-

.uud uupc 

tions, primarily the public switched telephone network. 

See also uupc. 

.uud n. See .uu. 

uudecode1 n. A UNIX program that converts a uuencoded 

file back into its original binary format. This program 

(along with uuencode) allows binary data, such as 

images or executable code, to be disseminated through 

e-mail or newsgroups. Compare uuencode1 . 

uudecode2 vb. To transform a uuencoded file back into 

its binary original using the uudecode program. Compare 

uuencode2 . 

.uue n. The file extension for a file that has been decoded 

from ASCII format back into binary format using uudecode. 

See also ASCII, binary file, uudecode1 . 

uuencode1 n. A UNIX program that converts a binary 

file, in which all 8 bits of every byte are significant, into 

printable 7-bit ASCII characters without loss of information. 

This program (along with uudecode) allows binary 

data, such as images or executable code, to be disseminated 

through e-mail or newsgroups. A file thus encoded 

545 

is one-third again as long as the original. Compare 

uudecode1 . 

uuencode2 vb. To transform a binary file into printable 

7-bit ASCII text using the uuencode program. Compare 

uudecode2 . 

UUID n. Acronym for universally unique identifier. A 

128-bit value that uniquely identifies objects such as OLE 

servers, interfaces, manager entry-point vectors, and client 

objects. Universally unique identifiers are used in crossprocess 

communication, such as remote procedure calling 

(RPC) and OLE. Also called: GUID. 

uupc n. The version of UUCP for IBM PCs and PCcompatibles 

running DOS, Windows, or OS/2. This version 

is a collection of programs for copying files to, logging 

in to, and running programs on remote networked 

computers. See also UUCP. 

U

V 

V.120 n. The ITU-T (formerly CCITT) standard that 

governs serial communications over ISDN lines. Data is 

encapsulated using a protocol similar to the Lightweight 

Directory Access Protocol (LDAP), and more than one 

connection may be multiplexed on a communications 

channel. See also communications channel, communications 

protocol, International Telecommunications Union, 

ISDN, Lightweight Directory Access Protocol, multiplexing, 

standard (definition 1), V series. 

V20, V30 n. NEC microprocessors that were slight 

improvements on Intel’s 8088 and 8086, using the same 

command sets but different microcode. 

V.2x, V.3x, V.4x, V.5x series n. See V series. 

V.32terbo n. A modem protocol developed by AT&T for 

19,200-bps modems, with fallback to the speeds supported 

by the ITU-T (formerly CCITT) V.32 standard. 

This protocol is proprietary to AT&T and was not adopted 

by CCITT or ITU-T. In the V series, V.34 takes the place 

of V.32terbo. See also International Telecommunications 

Union, V series. 

V.34 n. Data transmission standard that provides for up 

to 28,800 bits per second (bps) communications over 

telephone lines. It defines a full-duplex (two-way) modulation 

technique and includes error-correcting and negotiation. 

See also bits per second, full-duplex, modulation 

standards, V.90. 

V.42 n. The ITU-T (formerly CCITT) recommendation 

specifying procedures for error correction in data communications 

equipment (DCEs) designed for asynchronousto-synchronous 

conversion. See also V series. 

V.42bis n. The ITU-T (formerly CCITT) recommendation 

specifying procedures for data compression in datacircuit 

terminating equipment utilizing error-correction 

operations. See also V series. 

V86 mode n. See virtual real mode. 

V.90 n. Data transmission standard that provides for up to 

56,000 bits per second (bps) communications over telephone 

lines. The transmission speed from the client-side 

V 

546 

modem for uploads is 33,600 bps. The transmission speed 

for downloads from the host-side modem such as an Internet 

service provider (ISP) or a corporate network is up to 

56,000 bps, with an average speed of 40,000 to 50,000 

bps. When the host-side modem does not support this 

standard, the alternative is V.34. See also bits per second, 

client, host, ISP, modem, modulation standards, V.34. 

VAB n. See voice answer back. 

VAC n. See volts alternating current. 

vacuum tube n. A set of metal electrodes and intervening 

metal grids, contained in a glass or metal tube from which 

all gas has been removed. Voltages on the grids control 

electrical currents between the electrodes. Formerly used 

for amplification and switching in electronic circuits, vacuum 

tubes are now used in applications such as cathoderay 

tubes and those requiring very high power levels. A 

vacuum tube is known as a valve in Great Britain. 

validation server controls n. A set of server controls, 

included with ASP.NET, that verify user input. The input 

is checked as it comes from HTML server controls and 

Web server controls (for example, a Web page form) 

against programmer-defined requirements. Validation controls 

perform input checking in server code. If the user is 

working with a browser that supports DHTML, the validation 

controls can also perform validation using client 

script. See also ASP.NET server control, HTML server 

control, Web server control. 

validation suite n. A set of tests that measures compliance 

with a standard, especially a standard definition of a 

programming language. See also standard (definition 1). 

valid date interval n. A span of time during which a 

computer will maintain the correct date. For many PCs, 

the valid date interval is 1980 forward. 

validity check n. The process of analyzing data to determine 

whether it conforms to predetermined completeness 

and consistency parameters. 

value n. A quantity assigned to an element such as a variable, 

symbol, or label. See tone (definition 1).

value-added network VCACHE 

value-added network n. A communications network 

that offers additional services, such as message routing, 

resource management, and conversion facilities, for computers 

communicating at different speeds or using different 

protocols. Acronym: VAN. 

value-added reseller n. A company that buys hardware 

and software and resells it to the public with added services, 

such as user support. Acronym: VAR. 

value list n. A list of values used by some application, 

such as a database, as a search string or as values for a filtered 

query. See also filter (definition 1), query (definition 

1), search string. 

value type n. A data type that is represented by the type’s 

actual value. If a value type is assigned to a variable, that 

variable is given a fresh copy of the value. (This is in contrast 

to a reference type, where assignment does not create 

a copy.) Value types are usually created on a method’s 

stack frame, rather than in the garbage-collected heap. A 

value type can be boxed, which is a process that creates a 

corresponding reference type. See also reference type. 

valve n. See electron tube, vacuum tube. 

vampire tap n. A type of transceiver used on Ethernet 

networks that is equipped with sharp metal prongs that 

pierce the insulation on thicknet cable to make contact 

with the copper core over which signals travel. 

VAN n. See value-added network. 

vanilla adj. See plain vanilla. 

vaporware n. Software that has been announced but not 

released to customers. The term implies sarcastically that 

the product exists only in the minds of the marketing 

department. Compare freeware, shareware. 

VAR n. See value-added reseller. 

variable n. In programming, a named storage location 

capable of containing data that can be modified during 

program execution. See also data structure, data type, global 

variable, local variable. Compare constant. 

variable expression n. An expression that depends on 

the value of at least one variable and, hence, must be evaluated 

during program execution. See also run time (definition 

1), variable. Compare constant expression. 

variable-length field n. In a record, a field that can vary 

in length according to how much data it contains. See also 

field (definition 1). 

547 

variable-length record n. A record that can vary in 

length because it contains variable-length fields, certain 

fields only under certain conditions, or both of these. See 

also variable-length field. 

VAX n. Acronym for virtual address extension. A family 

of 32-bit minicomputers introduced by Digital Equipment 

Corporation in 1978. The VAX, like the later 68000 

microprocessor, has a flat address space and a large 

instruction set. The VAX was highly favored within the 

hacker community but has been superseded by microprocessors 

and RISC workstations. See also flat address space, 

instruction set, microprocessor, minicomputer, RISC. 

VBA n. See Visual Basic for Applications. 

vBNS n. Short for very high-speed Backbone Network 

Service. A network connecting several supercomputer 

centers and reserved for high-performance, high-bandwidth 

scientific applications requiring massive computing 

power. The vBNS was developed by the National Science 

Foundation and MCI Telecommunications. It began operation 

in 1995, reaching speeds of 2.4 Gbps, using MCI’s 

network of advanced switching and fiberoptic transmission 

technologies. Later, vBNS expanded to provide backbone 

services for Internet2. 

VBScript n. See Visual Basic, Scripting Edition. 

VBS/VBSWG virus n. Acronym for Visual Basic Script/ 

Visual Basic Script Worm Generator virus. Any virus 

created using the VBSWG virus creation toolkit. The tools 

available in VBSWG worm kit allow individuals to write 

viruses without having significant computer knowledge. 

Homepage and the Anna Kournikova virus are examples 

of VBS/VBSWG viruses. 

VBX n. Short for Visual Basic custom control. A software 

module that, when called by a Visual Basic application, 

produces a control that adds some desired feature to the 

application. A VBX is a separate executable file, usually 

written in C, that is dynamically linked to the application 

at run time and can be used by other applications, including 

some applications not developed in Visual Basic. 

Although VBX technology was developed by Microsoft, 

most VBXs have been written by third-party developers. 

VBXs are still in use, but the technology has been superseded 

by OCXs and ActiveX controls. See also control 

(definition 2), Visual Basic. Compare ActiveX controls, 

dynamic-link library, OCX. 

VCACHE n. The disk caching software used with VFAT 

driver in Windows 9x. VCACHE uses 32-bit code, runs in 

V

V 

vCalendar vector display 

protected mode, and automatically allocates space in RAM 

rather than requiring the user to reserve space for the cache. 

See also cache, driver, protected mode, RAM, VFAT. 

vCalendar n. A specification defining the format for 

applications to exchange scheduling information. The 

vCalendar specification is based on existing industry standards, 

including international standards for representing 

dates and times, and permits the exchange of schedules 

and “to-do” lists of the sort users commonly enter into 

personal calendars. Like the companion vCard specification 

for electronic business cards, it was created by the 

versit consortium founded by Apple, AT&T, IBM, and 

Siemens. Handed off to the Internet Mail Consortium 

(IMC) in 1996, vCalendar is supported by numerous hardware 

and software vendors. See also vCard. 

vCard n. A specification for creating an electronic business 

card (or personal-information card) and for the card 

itself. Designed to be exchanged through applications 

such as e-mail and teleconferencing, a vCard includes 

information such as name, address, telephone and fax 

number(s), and e-mail address. It can also include timezone, 

geographic location, and multimedia data such as 

photographs, company logos, and sound clips. Based on 

the ITU’s X.500 directory services specification, vCard 

was developed by versit, a consortium whose principal 

members include Apple, AT&T, IBM, and Siemens. The 

specification is under the guidance of the Internet Mail 

consortium Version 3.0 of the vCard specification has 

been approved as a proposed standard by the IETF. A 

companion specification known as vCalendar supports 

electronic exchange of scheduling information. See also 

vCalendar, X series. 

V-chip n. Electronic chip for installation in a television, 

VCR, cable box, or stand-alone device to provide adults 

with the ability to block programming they deem inappropriate. 

Intended to provide parents with a means of controlling 

the programming viewed by children, the V-chip allows 

adults to screen programs based on a rating level transmitted 

in the portion of the TV signal known as the vertical 

blanking interval (the same portion that carries closed captioning 

information). When programs exceed the chosen 

level, the V-chip signals the television, which then displays 

an “unauthorized to receive” message on a blank screen. 

VCOMM n. The communications device driver in Windows 

9x that provides the interface between Windowsbased 

applications and drivers on one side, and port drivers 

and modems on the other. See also driver. 

548 

VCPI n. See Virtual Control Program Interface. 

VCR-style mechanism n. 1. A user interface for playing 

movie files that has controls similar to those on a videocassette 

recorder (VCR). 2. A type of motorized docking 

mechanism in which a laptop or notebook computer is 

physically locked into place by the docking station. The 

advantage to a VCR-style mechanism is that it provides an 

electrically consistent, secure bus connection. See also 

docking mechanism, docking station, laptop, portable 

computer. 

VDD n. Acronym for virtual display device driver. See virtual 


VDL n. Acronym for Vienna Definition Language. A metalanguage, 

containing both a syntactic and a semantic 

metalanguage, used to define other languages. See also 

metalanguage. 

VDM n. See video display metafile. 

VDSL n. Short for very-high-speed digital subscriber line. 

The high-speed version of the xDSL (digital subscriber 

line) communication technologies, all of which operate 

over existing phone lines. VDSL can deliver up to 52 

Mbps downstream, but it is effective only within about 

4500 to 5000 feet of the central exchange. The data delivery 

rate is, in fact, related to the distance the signal must 

travel. To attain a rate of 52 Mbps, for example, the subscriber 

must be within 1000 feet of the exchange office. At 

a distance of 3000 feet, the data rate drops to about 26 

Mbps; and at 5000 feet, the data rate drops to about 13 

Mbps. See also central office, xDSL. 

VDT n. Acronym for video display terminal. A terminal 

that includes a CRT (cathode-ray tube) and keyboard. See 

also CRT. 

VDU n. Acronym for video display unit. A computer 

monitor. See also monitor. 

vector n. 1. In mathematics and physics, a variable that has 

both distance and direction. Compare scalar. 2. In computer 

graphics, a line drawn in a certain direction from a starting 

point to an endpoint, both of whose locations are identified 

by the computer using x-y-coordinates on a grid. Vectors are 

used in the output of some graphics programs instead of 

groups of dots (on paper) or pixels (on screen). See also 

vector graphics. 3. In data structures, a one-dimensional 

array—a set of items arranged in a single column or row. 

See also array, matrix. 

vector display n. A CRT (cathode-ray tube), commonly 

used in oscilloscopes and DVST (direct view storage

vector font vertical retrace 

tube) displays, that allows the electron beam to be arbitrarily 

deflected, based on x-y-coordinate signals. For 

example, to draw a line on a vector display, the video 

adapter sends signals to the X and Y yokes to move the 

electron beam over the path of the line; there is no background 

composed of scan lines, so the line drawn on the 

screen is not constructed of pixels. See also CRT, yoke. 

Compare raster display. 

vector font n. A font in which the characters are drawn 

using arrangements of line segments rather than arrangements 

of bits. See also font. Compare bitmapped font. 

vector graphics n. Images generated from mathematical 

descriptions that determine the position, length, and direction 

in which lines are drawn. Objects are created as collections 

of lines rather than as patterns of individual dots 

or pixels. Compare raster graphics. 

Vector Markup Language n. See VML. 

vector table n. See dispatch table. 

Velocity Engine n. A component of Apple’s Macintosh 

G4 processor that processes data in 128-bit chunks. The 

Velocity Engine is capable of over one gigaflop of floating-point 

operations per second. 

Venn diagram n. A type of diagram, used to express the 

result of operations on sets, in which a rectangle represents 

the universe and circles inside the rectangle represent sets of 

objects. Relationships between sets are indicated by the 

positions of the circles in relation to one another. The Venn 

diagram is named after John Venn (1834–1923), an English 

logician at Cambridge University. See the illustration. 

Numbers 

Fibonacci 

numbers 

Odd 

numbers 

Prime 

numbers 

>2 

F0VgnF0Vgn01.eps 

Venn diagram. 

verbose adj. Displaying messages as English text rather 

than as concise (but cryptic) codes. 

verify vb. To confirm either that a result is correct or that a 

procedure or sequence of operations has been performed. 

549 

Veronica n. Acronym for very easy rodent-oriented Netwide 

index to computerized archives. An Internet service 

developed at the University of Nevada that searches for 

Gopher archives by keywords. Users can enter Boolean 

operators, such as AND, OR, and XOR, to help narrow or 

expand their search. If any matching archives are found, 

they are listed on a new Gopher menu. See also Boolean 

operator, Gopher. Compare Archie, Jughead. 

version n. A particular issue or release of a hardware 

product or software title. 

version control n. The process of maintaining a database 

of all the source code and related files in a software 

development project to keep track of changes made during 

the project. 

version number n. A number assigned by a software 

developer to identify a particular program at a particular 

stage, before and after public release. Successive public 

releases of a program are assigned increasingly higher 

numbers. Version numbers usually include decimal fractions. 

Major changes are generally marked by a change in 

the whole number, whereas for minor changes only the 

number after the decimal point increases. 

verso adj. The publishing term for a left-hand page, 

which is always even-numbered. Compare recto. 

vertex n. The highest point of a curve, the point where a 

curve ends, or the point where two line segments meet in a 

polygon or freeform. 

vertical application n. A specialized application 

designed to meet the unique needs of a particular business 

or industry—for example, an application to keep track of 

billing, tips, and inventory in a restaurant. 

vertical bandwidth n. The rate at which a display screen 

is refreshed entirely, expressed in hertz (Hz). The vertical 

bandwidth of display systems ranges from 45 Hz to over 100 

Hz. Also called: vertical scan rate, vertical sync, V-sync. 

vertical blanking interval n. The time required for the 

electron beam in a raster-scan display to perform a vertical 

retrace. See also blanking, vertical retrace. 

vertical recording n. See perpendicular recording. 

vertical redundancy check n. See VRC. 

vertical retrace n. On raster-scan displays, the movement 

of the electron beam from the lower right corner back 

to the upper left corner of the screen after the beam has 

completed a full sweep of the screen. See also blanking, 

vertical blanking interval. Compare horizontal retrace. 

V

V 

vertical scan rate V.FC 

vertical scan rate n. See vertical bandwidth. 

vertical scrolling n. Movement up or down in a displayed 

document. See also scroll bar. 

vertical sync n. See vertical bandwidth. 

vertical sync signal n. The part of a video signal to a 

raster display that denotes the end of the last scan line at 

the bottom of the display. 

very-high-level language n. See 4GL. 

very-high-rate digital subscriber line n. See VDSL. 

very-high-speed integrated circuit n. An integrated circuit 

that performs operations, usually logic operations, at a 

very high speed. Acronym: VHSIC. 

Very Large Database n. A database system containing 

volumes of data hundreds of gigabytes, or even terabytes, 

in size. A Very Large Database must often support 

thousands of users and tables with billions of rows 

of data, must often be able to operate across several different 

platforms and operating systems, and must often 

be able to work with many different software applications. 

Acronym: VLDB. See also data warehouse. 

Very Large Memory n. A memory system designed to 

handle the huge data blocks associated with a Very Large 

Database. Very Large Memory uses 64-bit RISC technology 

to allow the use of addressable main memory and file 

sizes larger than 2 gigabytes (GB) and to cache as much as 

14 GB of memory. Acronym: VLM. See also RISC, Very 

Large Database. 

very-large-scale integration n. A reference to the density 

with which transistors and other elements are packed 

in an integrated circuit and to the thinness of the connections 

between them. Very-large-scale integration is generally 

considered to encompass the range from 5000 to 

50,000 components. Acronym: VLSI. See also integrated 

circuit. Compare large-scale integration, medium-scale 

integration, small-scale integration, super-large-scale integration, 

ultra-large-scale integration. 

Very Long Instruction Word n. See VLIW. 

very-low-frequency electromagnetic radiation n. See 

VLF radiation. 

VESA1 adj. Having VL bus expansion slots. Also 

called: VLB. See also expansion slot, VL bus. Compare 

VESA/EISA, VESA/ISA. 

VESA2 n. Acronym for Video Electronics Standards 

Association. An organization of hardware manufacturers 

550 

and vendors dedicated to drafting and improving standards 

for video and multimedia devices. Standards developed by 

VESA include the Display Data Channel (DDC), Display 

Power Management Signaling (DPMS), and VESA local 

bus (VL bus). See also DDC, DPMS, VL bus. 

VESA DDC n. See DDC. 

VESA Display Data Channel n. See DDC. 

VESA Display Power Management Signaling n. See 

DPMS. 

VESA/EISA adj. Having both EISA and VL bus expansion 

slots. See also EISA, expansion slot, VESA2 , VL bus. 

Compare VESA1 , VESA/ISA. 

VESA/ISA adj. Having both ISA and VL bus expansion 

slots. See also expansion slot, ISA, VESA2 , VL bus. Compare 

VESA1 , VESA/EISA. 

VESA local bus n. See VL bus. 

vesicular film n. A coating for optical discs that facilitates 

erasing and rewriting. The surface is marked by small 

bumps, which can be flattened and thereby erased, rather 

than by the pits used in standard CD-ROM discs. 

V.everything n. A marketing term used by some modem 

manufacturers to describe modems that comply with both 

the ITU-T (formerly CCITT) V.34 standard and the various 

proprietary protocols that were used before the standard 

was adopted, such as V.Fast Class. A V.everything 

modem should be compatible with any other modem that 

operates at the same speed. See also V.Fast Class, V series. 

V.Fast Class n. A de facto modulation standard for 

modems implemented by Rockwell International prior to 

approval of the V.34 protocol, which is the standard. 

Although both V.Fast Class and V.34 are capable of 28.8- 

Kbps transmission, V.Fast Class modems cannot communicate 

with V.34 modems without an upgrade. Acronym: 

V.FC. See also V series. 

VFAT n. Acronym for Virtual File Allocation Table. The 

file system driver software used under the Windows 9x 

Installable File System Manager (IFS) for accessing disks. 

VFAT is compatible with MS-DOS disks but runs more 

efficiently. VFAT uses 32-bit code, runs in protected 

mode, uses VCACHE for disk caching, and supports long 

filenames. See also Installable File System Manager, long 

filenames, protected mode, VCACHE, Windows. Compare 

file allocation table. 

V.FC n. See V.Fast Class.

VGA video display terminal 

VGA n. Acronym for Video Graphics Adapter. A video 

adapter that duplicates all the video modes of the EGA 

(Enhanced Graphics Adapter) and adds several more. See 

also video adapter. Compare EGA. 

VHLL n. Acronym for very-high-level language. See 4GL. 

VHSIC n. See very-high-speed integrated circuit. 

vi1 n. Short for visual. The first full-screen text editor 

under UNIX. The vi editor offers many powerful but not 

very intuitive keyboard commands. It is still in use on 

UNIX systems, despite the existence of other editors such 

as Emacs. See also editor, UNIX. 

vi2 vb. To edit a file using the vi editor. See also vi1 . 

VIA n. See Virtual Interface Architecture. 

VI Architecture n. See Virtual Interface Architecture. 

video adj. Of or pertaining to the visual component of a 

television signal. In relation to computers, video refers to 

the rendering of text and graphics images on displays. 

Compare audio. 

video accelerator n. See graphics engine (definition 1). 

video adapter n. The electronic components that generate 

the video signal sent through a cable to a video display. 

The video adapter is usually located on the computer’s 

main system board or on an expansion board, but it is 

sometimes built into the terminal. Also called: video 

adapter board, video board, video card, video controller, 

video display adapter. 

video adapter board n. See video adapter. 

video board n. See video adapter. 

video buffer n. The memory on a video adapter that is 

used to store data to be shown on the display. When the 

video adapter is in a character mode, this data is in the 

form of ASCII character and attribute codes; when it is in 

a graphics mode, the data defines each pixel. See also bit 

image, bit plane, color bits, pixel image. 

video capture board n. See video capture device. 

video capture card n. See video capture device. 

video capture device n. An expansion board that converts 

analog video signals to digital form and stores them 

in a computer’s hard disk or other mass storage device. 

Some video capture devices are also capable of converting 

digital video to analog video for use in a VCR. Also 

called: video capture board, video capture card. See also 

expansion board. 

551 

video card n. See video adapter. 

video clip n. A file that contains a short video item, usually 

an excerpt from a longer recording. 

video compression n. Reduction of the size of files containing 

video images stored in digital form. If no compression 

were done, 24-bit color video at 640 x 480 pixels 

would occupy almost one megabyte per frame, or over a 

gigabyte per minute. Video compression can, however, be 

lossy without affecting the perceived quality of the image. 

See also lossy compression, Motion JPEG, MPEG. 

video conferencing n. Teleconferencing in which video 

images are transmitted among the various geographically 

separated participants in a meeting. Originally done using 

analog video and satellite links, today video conferencing 

uses compressed digital images transmitted over wide area 

networks or the Internet. A 56K communications channel 

supports freeze-frame video; with a 1.544-Mbps (T1) 

channel, full-motion video can be used. See also 56K, 

desktop conferencing, freeze-frame video, full-motion 

video, T1, teleconferencing. Compare data conferencing. 

video controller n. See video adapter. 

video digitizer n. A device used in computer graphics 

that uses a video camera, rather than a scan head, to capture 

a video image and then stores it in memory with the 

aid of a special-purpose circuit board. See also digitize. 

Compare digital camera. 

videodisc n. An optical disc used to store video images 

and associated audio information. See also CD-ROM. 

video display n. Any device capable of displaying, but 

not printing, text or graphics output from a computer. 

video display adapter n. See video adapter. 

video display board n. A video adapter implementation 

using an expansion board rather than the computer’s main 

system board. See also video adapter. 

video display card n. See video display board. 

video display metafile n. A file containing video display 

information for the transport of images from one system to 

another. Acronym: VDM. 

video display page n. A portion of a computer’s video 

buffer that holds one complete screen image. If the buffer 

can hold more than one page, or frame, screen updates can 

be completed more rapidly because an unseen page can be 

filled while another is being displayed. 

video display terminal n. See VDT. 

V

V 

video display tube vine 

video display tube n. See CRT. 

video display unit n. See monitor. 

video DRAM n. See video RAM. 

video driver n. Software that provides the interface 

between the video adapter hardware and other programs, 

including the operating system. The user can access the 

video driver to specify the resolution and color-bit depth 

of images on the monitor during the setup process. See 

also driver, monitor, video adapter. 

video editor n. A device or program used to modify the 

contents of a video file. 

Video Electronics Standards Association n. See 

VESA2 . 

video game n. See computer game. 

Video Graphics Adapter or Video Graphics Array 

n. See VGA. 

video graphics board n. A video adapter that generates 

video signals for displaying graphical images on a video 

screen. 

video look-up table n. See color look-up table. 

video memory n. Memory from which a display image is 

created, located in the video adapter or video subsystem. 

If both the video processor and the central processing unit 

(CPU) have access to video memory, images are produced 

by the CPU’s modification of video memory. Video circuitry 

normally has priority over the processor when both 

attempt to read or write to a video memory location, so 

updating video memory is often slower than accessing 

main memory. See also video RAM. 

video mode n. The manner in which a computer’s video 

adapter and monitor display on-screen images. The most 

common modes are text (character) mode and graphics 

mode. In text mode, characters include letters, numbers, 

and some symbols, none of which are “drawn” on screen 

dot by dot. In contrast, graphics mode produces all screen 

images, whether text or art, as patterns of pixels (dots) that 

are drawn one pixel at a time. 

videophone n. A device equipped with camera and 

screen, as well as a microphone and speaker, capable of 

transmitting and receiving video signals as well as voice 

over a telephone line. Using conventional telephone lines, 

a videophone can transmit only freeze-frame video. See 

also freeze-frame video. 

video port n. A cable connector or port on a computer 

that outputs video signals to a monitor. 

552 

video RAM n. A special type of dynamic RAM (DRAM) 

used in high-speed video applications. Video RAM uses 

separate pins for the processor and the video circuitry, 

providing the video circuitry with a back door to the 

video RAM. The video circuitry can access the video 

RAM serially (bit by bit), which is more appropriate for 

transferring pixels to the screen than is the parallel 

access provided by conventional DRAM. Acronym: 

VRAM. See also dynamic RAM. 

video server n. A server designed to deliver digital 

video-on-demand and other broadband interactive services 

to the public over a wide area network. 

video signal n. The signal sent from a video adapter or 

other video source to a raster display. The signal can 

include horizontal and vertical synchronization signals, as 

well as image information. See also composite video display, 

RGB monitor. 

video terminal n. See terminal (definition 1). 

videotex n. An interactive information retrieval service 

designed to be accessed by subscribers over telephone 

lines. Information can be displayed on a home television 

screen or a videotex terminal. Subscribers use keypads to 

choose from menus and to request specific screens, or 

pages. Also called: videotext. 

videotext n. See videotex. 

Vienna Definition Language n. See VDL. 

view1 n. 1. The display of data or an image from a given 

perspective or location. 2. In relational database management 

systems, a logical table created through the specification 

of one or more relational operations on one or more 

tables. A view is equivalent to a divided relation in the relational 

model. See also relational database, relational model. 

view2 vb. To cause an application to display information 

on a computer screen. 

viewer n. An application that displays or otherwise outputs 

a file in the same way as the application that created 

the file. An example of a viewer is a program to 

display the images stored in GIF or JPEG files. See also 

GIF, JPEG. 

viewport n. In computer graphics, a view of a document 

or an image. A viewport is similar to the view in a window, 

but usually only part of the document or graphical 

image is visible. Compare window. 

vine n. A means of distributing audiotape copies that is 

similar to a tape tree. Because vine tapes are digital in for-

Vines Virtual Interface Architecture 

mat, there is no degradation of sound quality as tapes are 

copied down the vine from one participant to the next. 

Compare tape tree. 

Vines n. A UNIX-based networking operating system 

from Banyan Systems. 

viral marketing n. A marketing concept that relies on 

computer users to distribute marketing materials, possibly 

without even being aware of their participation. Viral marketing 

is often tied in with free e-mail accounts or other 

free online services, from which users pass along advertisements 

with every message they send. 

virgule n. The forward slash (/) character. Compare 

backslash. 

virtual adj. Of or pertaining to a device, service, or sensory 

input that is perceived to be what it is not in actuality, 

usually as more “real” or concrete than it actually is. 

virtual 8086 mode n. See virtual real mode. 

virtual 86 mode n. See virtual real mode. 

virtual address n. In a virtual memory system, the 

address that the application uses to reference memory. The 

memory management unit (MMU) translates this address 

into a physical address before the memory is actually read 

or written to. See also physical address, virtual memory. 

Compare real address. 

virtual channel n. In Asynchronous Transfer Mode 

(ATM), the path taken by data sent from one sender to one 

receiver. See also ATM (definition 1), virtual path (definition 

2). 

virtual circuit n. A connection between communicating 

computers that provides the computers with what appears 

to be a direct link but can actually involve routing data 

over a defined but longer path. 

virtual community n. See online community. 

Virtual Control Program Interface n. A specification 

for MS-DOS programs to allow access to extended memory 

under a multitasking environment (for example, Windows) 

for 386 and higher-level processors. Acronym: 

VCPI. See also 80386DX, extended memory, multitasking. 

Compare protected mode. 

virtual desktop n. A desktop enhancement tool that provides 

access to the desktop when it is covered by open 

windows or that expands the size of the working desktop. 

See also desktop. 

virtual device n. A device that can be referenced but that 

does not physically exist. Virtual-memory addressing, for 

553 

example, uses magnetic disk storage to simulate memory 

larger than that physically available. 

virtual device driver n. Software in Windows 9x that 

manages a hardware or software system resource. If a 

resource retains information from one access to the next 

that affects the way it behaves when accessed (for example, 

a disk controller with its status information and buffers), 

a virtual device driver must exist for it. Virtual device 

drivers are described using three-letter abbreviations 

beginning with V and ending with D; the middle letter 

indicates the type of device, such as D for a display, P for a 

printer, T for a timer, and x when the type of device is not 

under discussion. Acronym: VxD. See also device driver. 

virtual disk n. See RAM disk. 

virtual display device driver n. See virtual device driver. 

Virtual File Allocation Table n. See VFAT. 

virtual hosting n. A form of hosting that provides a Web 

server, communication, and other services to customers 

for their own Web sites. In addition to hardware, software, 

and communication, virtual hosting can include assistance 

with domain name registration, e-mail addresses, and 

other Web-related issues. See also host, hosting. 

virtual image n. An image that is stored in computer 

memory but is too large to be shown in its entirety on the 

screen. Scrolling and panning are used to bring unseen 

portions of the image into view. See also virtual screen. 

virtual-image file n. A file that specifies the material to 

be recorded onto a CD-ROM. A virtual-image file generally 

contains pointers to files that are distributed across a 

hard disk rather than gathered in one area. Since a complete 

copy of the material is not assembled, problems 

may occur in writing the CD-ROM due to delays in 

assembling the material from a scattered group of files. 

See also CD-ROM. Compare physical-image file. 

Virtual Interface Architecture n. An interface specification 

that defines a standard low-latency, high-bandwidth 

means of communication between clusters of servers in a 

System Area Network (SAN). Developed by Compaq, 

Intel, Microsoft, and more than 100 industry groups, the 

Virtual Interface Architecture is processor and operating 

system independent. By reducing the time required for 

message-passing between applications and the network, it 

seeks to reduce overhead and thus deliver enterprise-level 

scalability for mission-critical applications. Acronym: 

VIA. Also called: VI Architecture. See also cluster, System 

Area Network. 

V

V 

virtual LAN virtual route 

virtual LAN n. Short for virtual local area network. A 

local area network consisting of groups of hosts that are 

on physically different segments but that communicate as 

though they were on the same wire. See also LAN. 

virtual machine n. Software that mimics the performance 

of a hardware device, such as a program that allows 

applications written for an Intel processor to be run on a 

Motorola chip. Acronym: VM. 

virtual memory n. Memory that appears to an application 

to be larger and more uniform than it is. Virtual memory 

may be partially simulated by secondary storage such as a 

hard disk. Applications access memory through virtual 

addresses, which are translated (mapped) by special hardware 

and software onto physical addresses. Acronym: VM. 

Also called: disk memory. See also paging, segmentation. 

virtual monitor n. An enhanced monitor viewing system 

for visually impaired users that uses a virtual-reality headset 

to move enlarged text across the screen in a direction 

opposite to head motion. See also virtual reality. 

virtual name space n. The set of all hierarchical 

sequences of names that can be used by an application to 

locate objects. One such sequence of names defines a path 

through the virtual name space, regardless of whether the 

hierarchy of names reflects the actual arrangement of 

objects around the system. For example, the virtual name 

space of a Web server consists of all possible URLs on the 

network on which it runs. See also URL. 

virtual network n. A part of a network that appears to a 

user to be a network of its own. For example, an Internet 

service provider can set up multiple domains on a single 

HTTP server so that each one can be addressed with its 

company’s registered domain name. See also domain 

name, HTTP server (definition 1), ISP. 

virtual path n. 1. A sequence of names that is used to 

locate a file and that has the same form as a pathname in 

the file system but is not necessarily the actual sequence of 

directory names under which the file is located. The part 

of a URL that follows the server name is a virtual path. 

For example, if the directory c:\bar\sinister\forces\distance 

on the server miles is shared on the local area network 

at foo.com under the name \\miles\baz and contains 

the file elena.html, that file may be returned by a Web 

request for http://miles.foo.com/baz/elena.html. 2. In 

Asynchronous Transfer Mode (ATM), a set of virtual 

channels that are switched together as a unit through the 

network. See also ATM (definition 1), virtual channel. 

554 

virtual peripheral n. A peripheral that can be referenced 

but does not physically exist. For example, an application 

might treat a serial port through which data is being transmitted 

as a printer, but the device receiving the data might 

be another computer instead. 

virtual printer n. A feature in many operating systems 

that allows printer output to be saved to a file until a 

printer becomes available. 

virtual printer device driver n. See virtual device driver. 

virtual private network n. 1. Nodes on a public network 

such as the Internet that communicate among themselves 

using encryption technology so that their messages are as 

safe from being intercepted and understood by unauthorized 

users as if the nodes were connected by private lines. 2. A 

WAN (wide area network) formed of permanent virtual circuits 

(PVCs) on another network, especially a network 

using technologies such as ATM or frame relay. Acronym: 

VPN. See also ATM (definition 1), frame relay, PVC. 

virtual reality n. A simulated 3-D environment that a 

user can experience and manipulate as if it were physical. 

The user sees the environment on display screens, possibly 

mounted in a special pair of goggles. Special input 

devices, such as gloves or suits fitted with motion sensors, 

detect the user’s actions. Acronym: VR. 

Virtual Reality Modeling Language n. See VRML. 

virtual real mode n. A feature of the Intel 80386 (SX and 

DX) and later microprocessors that allows them to emulate 

several 8086 (real-mode) environments at the same 

time. The microprocessor provides a set of virtual registers 

and virtual memory space to each virtual 8086 environment. 

A program running in a virtual 8086 

environment is completely protected from other virtual 

8086 environments in the system and behaves as if it had 

control of the entire system. Also called: V86 mode, virtual 

8086 mode, virtual 86 mode. See also real mode. 

virtual root n. The root directory that a user sees when 

connected to an Internet server, such as an HTTP or FTP 

server. The virtual root is actually a pointer to the physical 

root directory, which may be in a different location, such 

as on another server. The advantages of using a virtual 

root include being able to create a simple URL for the 

Internet site and to move the root directory without affecting 

the URL. Also called: v-root. See also pointer (definition 

1), root directory, server (definition 2), URL. 

virtual route n. See virtual circuit.

virtual screen Visual C++ 

virtual screen n. An image area that extends beyond the 

dimensions of the physical screen on the monitor, allowing 

manipulation of large documents or of multiple documents 

that lie partially outside the normal screen view. See 

also monitor. 

virtual server n. A virtual machine that resides on an 

HTTP server but has the appearance to the user of being a 

separate HTTP server. Several virtual servers can reside 

on one HTTP server, each capable of running its own programs 

and each with individualized access to input and 

peripheral devices. Each virtual server has its own domain 

name and IP address and appears to the user as an individual 

Web site. Some Internet service providers use virtual 

servers for those clients who want to use their own domain 

names. See also domain name, HTTP server (definition 2), 

IP address. 

virtual storefront n. A company’s point of presence on 

the Web, providing opportunities for online sales. Also 

called: electronic storefront. 

virtual terminal n. See terminal emulation. 

virtual timer device driver n. See virtual device driver. 

virtual world n. 1. A 3-D modeled environment, often 

created in VRML, where a user can interact with the 

viewer to change variables. See also viewer, VRML. 2. An 

electronic environment that has no basis in the physical 

world. Multiuser dungeons (MUDs), talkers, and chat 

rooms are often considered virtual worlds. See also chat1 (definition 1), MUD, talker. 

virus n. An intrusive program that infects computer files 

by inserting in those files copies of itself. The copies are 

usually executed when the file is loaded into memory, 

allowing the virus to infect still other files, and so on. 

Viruses often have damaging side effects—sometimes 

intentionally, sometimes not. For example, some viruses 

can destroy a computer’s hard disk or take up memory 

space that could otherwise be used by programs. See also 

Good Times virus, Trojan horse, worm. 

virus signature n. A portion of unique computer code 

contained in a virus. Antivirus programs search for known 

virus signatures to identify infected programs and files. 

See also virus. 

visible page n. In computer graphics, the image that is 

being displayed on the screen. Screen images are written 

into display memory in sections called pages, each of 

which contains one screen display. 

555 

Visio n. A software application offered by Microsoft that 

allows users to create diagrams and visual presentations in 

electronic form. Visio enables users to share ideas and 

concepts visually by using diagrams to augment written 

material in documents or by expanding visual elements in 

a public presentation. Microsoft acquired the Visio application 

in 1999, when it purchased Visio Corporation. 

visit n. A session during which a person views one or 

more pages in a particular Web site. 

visitor n. A person who views a Web page or Web site. 

Visor n. A product line of handheld personal digital assistants 

(PDAs) developed by Handspring Corporation. Features 

include an address list, an appointments calendar, a 

to-do list, and memos. Visor also features a 68-pin Springboard 

socket that allows plug-ins of additional devices 

offered by Handspring. See also Springboard. 

Visual Basic n. A trademarked name owned by 

Microsoft Corporation for a high-level, visual-programming 

version of Basic. Visual Basic was designed for 

building Windows-based applications. See also Basic, 

Visual Basic for Applications, Visual Basic, Scripting Edition, 

visual programming. 

Visual Basic Editor n. An environment in which you 

write new and edit existing Visual Basic for Applications 

code and procedures. The Visual Basic Editor contains a 

complete debugging toolset for finding syntax, run-time, 

and logic problems in your code. 

Visual Basic for Applications n. A macro-language 

version of Visual Basic that is used to program many 

Windows 9x applications and is included with several 

Microsoft applications. Acronym: VBA. See also macro 

language, Visual Basic. 

Visual Basic Script n. See Visual Basic, Scripting Edition. 

Visual Basic, Scripting Edition n. A subset of the Visual 

Basic programming language, optimized for Web-related 

programming. As with JavaScript, code for Visual Basic, 

Scripting Edition is embedded in HTML documents. This 

version is included with the Internet Explorer Web browser. 

Also called: VBScript, Visual Basic Script. See also Visual 

Basic for Applications. 

Visual C++ n. A Microsoft application development system 

for the programming language C++ that runs under 

MS-DOS and Windows. Visual C++ is a visual programming 

environment. See also visual programming. Compare 

Visual Basic, Visual J++. 

V

V 

Visual Café VML 

Visual Café n. The Java-based suite of software development 

tools from Symantec Corporation. Visual Café is 

available in several product packages. The Standard Edition, 

intended for beginning Java programmers, includes 

an integrated editor, debugger, and compiler, as well as a 

JavaBean library, wizards, and utilities. The Professional 

Edition provides a larger library of JavaBeans and more 

sophisticated tools for development and debugging. The 

Database Edition, as the name indicates, adds support for 

database functionality. The Enterprise Suite provides a 

high-end environment for development of enterprise applications. 

See also Java. 

Visual FoxPro Database and Command Language 

n. A Microsoft product for developing database applications 

that includes a rich object-oriented programming 

language derived from the Xbase language. 

Visual InterDev n. Microsoft’s integrated development 

environment for Web applications. Visual InterDev 

includes tools for end-to-end (design through deployment) 

development, as well as integrated tools for database programming 

and design. The first version of Microsoft 

Visual InterDev was released in 1997. 

visual interface n. See graphical user interface. 

visualization n. A feature of an application that displays 

data in the form of a video image. For example, some 

databases can interpret and show data in the form of a twoor 

three-dimensional model. 

Visual J++ n. Microsoft’s Java visual programming environment, 

which can be used to create applets and applications 

in the Java language. See also applet, Java, Java 

applet, visual programming. 

visual programming n. A method of programming using 

a programming environment or language in which basic 

program components can be selected through menu 

choices, buttons, icons, and other predetermined methods. 

Visual SourceSafe n. A project-oriented version control 

system designed by Microsoft to manage software and 

Web site development. Visual SourceSafe stores files in a 

secure repository that provides easy access to authorized 

users and tracks all changes made to files. Visual Source- 

Safe works with any type of file produced by any development 

language, authoring tool, or application. 

Visual Studio n. Microsoft’s suite of software development 

tools for rapid development of business applications 

and components. Visual Studio is provided in two editions. 

The Professional Edition, for professional programmers, 

includes the Visual Basic and Visual C++ 

556 

languages, Visual FoxPro for database development, 

Visual InterDev for Web development, and Visual J++ for 

Java development. The Enterprise Edition, for enterpriselevel 

development, also includes Visual SourceSafe (a 

team-based source code control system) and the Developer 

Edition of Microsoft BackOffice Server. 

Visual Studio .NET n. A development environment for 

creating XML Web services and applications on the 

Microsoft .NET platform. See also .NET, .NET My 

Services. 

VLAN n. See virtual LAN. 

VLB1 adj. See VESA1 . 

VLB2 n. See VL bus. 

VL bus n. Short for VESA local bus. A type of local bus 

architecture introduced by the Video Electronics Standards 

Association. The VL bus specification allows up to 

three VL bus slots to be built into a PC motherboard and 

allows for bus mastering (wherein intelligent adapter cards 

can do some processing independently of the CPU). A VL 

bus slot consists of a standard connector plus an additional 

16-bit Micro Channel Architecture connector and must be 

built into the motherboard by the manufacturer. Standard 

connectors cannot simply be converted to VL bus slots. A 

non–VL bus adapter card can be used in a VL bus slot, but 

it cannot use the local bus and so performs as it normally 

would in a non–VL bus slot. Also called: VL local bus. 

See also local bus, PCI local bus. 

VLF radiation n. Short for very-low-frequency radiation. 

Electromagnetic radiation (radio) at frequencies within the 

range of approximately 300 Hz to 30,000 Hz (30 kHz). 

Computer monitors emit this type of radiation. A voluntary 

standard, MPR II, regulates the amount of VLF radiation 

that a monitor can emit. See also MPR II. 

VLIW n. Acronym for Very Long Instruction Word. An 

architecture that combines many simple instructions into a 

single long instruction word that uses different registers. 

VL local bus n. See VL bus. 

VLSI n. See very-large-scale integration. 

VM n. Acronym for Virtual Machine. An operating system 

for IBM mainframes that provides virtual-machine 

capability. VM was developed by IBM customers and later 

taken over by IBM itself under the name OS/VM. See also 

virtual machine, virtual memory. 

VML n. Acronym for Vector Markup Language. An 

XML-based specification for the exchange, editing, and

VoATM VoIP 

delivery of 2-D vector graphics on the Web. An application 

of XML (Extensible Markup Language), VML uses 

XML tags and Cascading Style Sheets to create and place 

vector graphics, such as circles and squares, in an XML or 

HTML document, such as a Web page. These graphics, 

which are rendered in the native operating system, can 

include color and are editable in a variety of graphics programs. 

See also Cascading Style Sheets, XML. 

VoATM n. Short for Voice over Asynchronous Transfer 

Mode. The transmission of voice and other telephony over 

an ATM network. See also ATM, VoFR, VoIP. 

VoFR n. Short for Voice over Frame Relay. Voice transmission 

over a frame relay network. See also frame relay, 

VoATM, VoIP. 

voice answer back n. The use of sound-recorded messages 

by a computer in responding to commands or queries. 

Acronym: VAB. 

voice-capable modem n. A modem that can support 

voice messaging applications along with its data-handling 

functions. 

voice chat n. A feature offered by Internet service providers 

(ISPs) that allows users to converse with each other 

directly through an Internet connection. See also Internet 

telephone. 

voice coil n. A device that moves a disk drive actuator 

arm using electromagnetism. It works more quickly than a 

stepper motor. See also actuator. Compare stepper motor. 

voice-grade channel n. A communications channel, 

such as a telephone line, with an audio bandwidth of 300 

to 3000 Hz, suitable for carrying speech. A voice-grade 

channel can also be used for transmitting facsimile, analog, 

and digital information at rates up to 33 kilobits per 

second (Kbps). 

voice input n. Spoken instructions that a computer translates 

into executable commands using speech recognition 

technology or that are embedded into documents with the 

aid of a microphone. See also speech recognition. 

voice mail n. A system that records and stores telephone 

messages in a computer’s memory. Unlike a simple 

answering machine, a voice mail system has separate 

mailboxes for multiple users, each of whom can copy, 

store, or redistribute messages. 

voice messaging n. A system that sends and receives 

messages in the form of sound recordings. 

557 

voice modem n. A modulation/demodulation device that 

supports a switch to change between telephony and data 

transmission modes. Such a device might contain a builtin 

loudspeaker and microphone for voice communication, 

but more often it uses the computer’s sound card. See also 

modem, sound card, telephony. 

voice navigation n. The use of spoken commands to control 

a Web browser. Voice navigation is a feature of some 

plug-in applications that embellish Web browsers to allow 

the user to navigate the Web by means of his or her voice. 

See also Web browser. 

voice-net n. A term used on the Internet to refer to the 

telephone system, often preceding the user’s telephone 

number in an e-mail signature. 

voice output n. See speech synthesis. 

Voice over Asynchronous Transfer Mode n. See 

VoATM. 

Voice over Frame Relay n. See VoFR. 

Voice over IP n. See VoIP. 

voice recognition n. The capability of a computer to 

understand the spoken word for the purpose of receiving 

commands and data input from the speaker. Systems that 

can recognize limited vocabularies as spoken by specific 

individuals have been developed, but developing a system 

that deals with a variety of speech patterns and accents, as 

well as with the various ways in which a request or a statement 

can be made, is more difficult, although advances are 

being made in this area. Also called: speech recognition. 

See also artificial intelligence, dictation software, neural 

network. 

voice synthesis n. See speech synthesis. 

VoIP n. Acronym for Voice over IP. The use of the Internet 

Protocol (IP) for transmitting voice communications. 

VoIP delivers digitized audio in packet form and can be 

used for transmitting over intranets, extranets, and the 

Internet. It is essentially an inexpensive alternative to traditional 

telephone communication over the circuitswitched 

Public Switched Telephone Network (PSTN). 

VoIP covers computer-to-computer, computer-to-telephone, 

and telephone-based communications. For the sake 

of compatibility and interoperability, a group called the 

VoIP Forum promotes product development based on the 

ITU-T H.323 standard for transmission of multimedia 

over the Internet. Also called: Internet telephony. See also 

H.323. 

V

V 

volatile memory V series 

volatile memory n. 1. Memory, such as RAM, that loses 

its data when the power is shut off. Compare nonvolatile 

memory. 2. Memory used by a program that can change 

independently of the program, such as memory shared by 

another program or by an interrupt service routine. 

volt n. The unit used to measure potential difference or 

electromotive force. One volt is defined as the potential 

across which 1 coulomb of charge will do 1 joule of work, 

or the potential generated by 1 ampere of current flowing 

through 1 ohm of resistance. See also electromotive force. 

voltage n. See electromotive force. 

voltage regulator n. A circuit or circuit component that 

maintains a constant output voltage despite variations in 

input voltage. 

volts alternating current n. The measure of the peak-topeak 

voltage swing of an electrical signal. Acronym: VAC. 

volume n. 1. A disk or tape that stores computer data. 

Sometimes, large hard disks are divided into several volumes, 

each of which is treated as a separate disk. 2. The 

loudness of an audio signal. 

volume label n. A name for a disk or tape. MS-DOS systems, 

which seldom use disk names except in directory 

listings, use the term volume label. Apple Macintosh systems, 

which often refer to disks by name, use the term volume 

name. 

volume name n. See volume label. 

volume reference number n. See volume serial number. 

volume serial number n. The optional identifying volume 

number of a disk or tape. MS-DOS systems use the 

term volume serial number. Apple Macintosh systems use 

the term volume reference number. A volume serial number 

is not the same as a volume label or volume name. 

Compare volume label. 

VON n. Acronym for voice on the net. A broad category of 

hardware and software technology for real-time voice and 

video transmission over the Internet. The term was coined 

by Jeff Pulver, who formed a group called the VON Coalition, 

which opposes regulation of VON technology and 

promotes VON to the public. 

von Neumann architecture n. The most common structure 

for computer systems, attributed to the mathematician 

John von Neumann. It uses the concept of a program that 

can be permanently stored in a computer and manipulated 

or made self-modifying through machine-based instructions. 

Sequential processing is characteristic of von Neu- 

558 

mann architecture. Parallel architectures have evolved to 

improve on the encumbrances of sequential instructions. 

See also parallel computer. 

von Neumann bottleneck n. Competition between data 

and instructions for CPU time. Mathematician John von 

Neumann was the first to show that a computer based on 

architecture linking a single processor with memory will 

actually spend more time retrieving data from memory 

than processing it. The bottleneck arises when the processor 

has to trade off between executing a large number of 

instructions per second and reading in a large amount of 

data in the same time. See also CPU. 

VPD n. Acronym for virtual printer device driver. See virtual 


VPN n. See virtual private network. 

VR n. See virtual reality. 

VRAM n. See video RAM. 

VRC n. Acronym for vertical redundancy check. A 

method for checking the accuracy of transmitted data. 

VRC generates an extra bit (parity bit) for each character 

transmitted. The parity bit indicates whether the character 

contains an odd or an even number of 1 bits. If its value 

does not match the type of the character, that character is 

assumed to be incorrectly transmitted. See also parity. 

Compare LRC. 

VRML n. Acronym for Virtual Reality Modeling Language. 

A scene description language for creating 3-D interactive 

Web graphics similar to those found in some video 

games, allowing the user to “move around” within a graphic 

image and interact with objects. VRML, a subset of Silicon 

Graphics’ Inventor File Format (ASCII), was created by 

Mark Pesce and Tony Parisi in 1994. VRML files can be 

created in a text editor, although CAD packages, modeling 

and animation packages, and VRML authoring software are 

the tools preferred by most VRML authors. VRML files 

reside on an HTTP server; links to these files can be embedded 

in HTML documents, or users can access the VRML 

files directly. To view VRML Web pages, users need a 

VRML-enabled browser or a VRML plug-in for Internet 

Explorer or Netscape Navigator. See also 3-D graphic, 

HTML document, HTTP server (definition 1). 

v-root n. See virtual root. 

V series n. The series of ITU-T (formerly CCITT) recommendations 

relating to modems and modem communications 

over the public phone system, including signaling, 

coding, and circuit characteristics. See the table.

V-sync VxD 

Table V.1 Recommendations in the V Series for Modem Communications. 

Recommendation 

Number What It Covers 

V.17 14,000-bps two-wire modems used for facsimile applications 

V.21 300-bps modems used with dial-up lines; full-duplex transmission; not the same as Bell 103 (in 

North America) 

V.22 1200-bps modems used with dial-up and leased lines; full-duplex transmission; not the same as 

Bell 212A (in North America) 

V.22bis 2400-bps modems used with dial-up and leased lines; full-duplex transmission 

V.23 600/1200-bps synchronous or asynchronous modems used with dial-up and leased lines; halfduplex 

transmission 

V.26 2400-bps modems used with four-wire leased lines; full-duplex transmission 

V.26bis 1200/2400-bps modems used with dial-up lines; full-duplex transmission 

V.26ter 2400-bps modems used with dial-up and two-wire leased lines; DPSK modulation; fallback to 1200 

bps; echo canceling to remove phone-line echo; full-duplex transmission 

V.27 4800-bps modems used with leased lines; manual equalizer; full-duplex transmission 

V.27bis 2400/4800-bps modems used with leased lines; automatic equalizer; full-duplex transmission 

V.27ter 2400/4800-bps modems used with dial-up lines; full-duplex transmission 

V.29 9600-bps modems used with point-to-point leased circuits; half-duplex transmission or full-duplex 

transmission 

V.32 9600-bps modems used with dial-up lines; echo canceling to remove phone-line echo; full-duplex 

transmission 

V.32bis 4800/7200/9600/12,000/14,400-bps modems used with dial-up lines; echo canceling; full-duplex 

transmission 

V.33 12,000/14,400-bps modems used with four-wire leased lines; synchronous; QAM modulation; 

time-division multiplexing; full-duplex transmission 

V.34 28,800-bps modems; full-duplex transmission 

V.35 Group band modems, which combine the bandwidth of more than one telephone circuit 

V.54 Operation of loop test devices in modems 

V.56 Network transmission model for evaluating modem performance over standard voice-grade telephone 

connections 

V.56bis Network transmission model for evaluating modem performance over two-wire voice-grade 

connections 

V.56ter Network transmission model for evaluating modem performance over two-wire, 4-kilohertz duplex 

modems 

V.61 4800-bps modems operating at voice plus data rate or 14,000-bps modems operating at data-only 

rate over standard switched telephone circuits or on point-to-point, two-wire phone circuits 

V-sync n. See vertical bandwidth. 

VT-52, VT-100, VT-200 n. A popular set of control codes 

used in terminals with those model numbers that were 

originally manufactured by Digital Equipment Corporation. 

Appropriate software can enable a microcomputer to 

use these codes to emulate such terminals. 

559 

VTD n. Acronym for virtual timer device driver. See virtual 


Vulcan death grip n. A warm boot by pressing the 

Alt+Crl+Delete keys. The name is a reference from Star 

Trek. See also three-finger salute, warm boot. 

VxD n. See virtual device driver. 

V

W 

w3 n. See World Wide Web. 

W3 n. See World Wide Web. 

W3C n. Abbreviation for the World Wide Web Consortium, 

a standards body based in the United States, Europe, and 

Japan. The W3C is dedicated (in part) to encouraging the 

development of open Web standards, such as the HTML and 

XML document markup languages, to promote interoperability 

and assist the Web in achieving its potential. 

wafer n. A thin, flat piece of semiconductor crystal used 

in the fabrication of integrated circuits. Various etching, 

doping, and layering techniques are used to create the 

circuit components on the surface of the wafer. Usually 

multiple identical circuits are formed on a single wafer, 

which is then cut into sections. Each integrated circuit 

then has leads attached and is packaged in a holder. See 

also integrated circuit, semiconductor. 

wafer-scale integration n. The fabrication on a single 

wafer of different microcircuits that are then connected to 

form a single circuit the full size of the wafer. See also wafer. 

WAI n. Acronym for Web Accessibility Initiative. A set of 

guidelines released by the World Wide Web Consortium 

(W3C) in May 1999. The WAI is intended to promote Web 

accessibility for users with disabilities by setting Web 

design and compatibility guidelines that help assure Web 

access and usability for all users. See also accessibility. 

WAIS n. Acronym for Wide Area Information Server. A 

UNIX-based document search and retrieval system on the 

Internet that can be used to search over 400 WAIS libraries, 

such as Project Gutenberg, for indexed files that match keywords 

entered by the user. WAIS can also be used on an 

individual Web site such as a search engine. WAIS, developed 

by Thinking Machines Corporation, Apple Computer, 

and Dow Jones, uses the Z39.50 standard to process natural 

language queries. The list of documents returned by WAIS 

often contains numerous false matches. Users need a WAIS 

client to use a WAIS server. See also natural language 

query, Project Gutenberg, search engine, Z39.50 standard. 

WAIS client n. The program needed for accessing the 

WAIS (Wide Area Information Server) system to search 

W 

560 

its databases. A WAIS client program must be installed on 

a user’s own machine or accessed from a computer with 

such a program already installed. Many freeware and 

shareware WAIS programs for various operating systems, 

including UNIX, MS-DOS, OS/2, and Windows, are 

available for download on the Internet. To look for documents 

in a WAIS database, the user selects the database(s) 

to search and types a query containing keywords to search 

for. The WAIS client sends this query to the server, communicating 

with the server via the Z39.50 protocol. The 

server processes the request using indexes and returns a 

list of document headlines matching the query to the client. 

The user can then choose which document to retrieve, 

send that request to the server, and receive the complete 

document in return. See also WAIS. 

WAIS database n. See WAIS. 

waisindex n. 1. A UNIX utility for building an index to 

text files for access using WAIS (Wide Area Information 

Server) query software. 2. A URL for accessing WAIS. The 

URL takes the form wais://hostport/database[? search]. 

WAIS library n. A WAIS (Wide Area Information Server) 

database. A WAIS library is a comprehensive collection of 

online documents on a specific topic—for example, 

Project Gutenberg’s collection of public-domain literary 

and historical texts available over the Internet, and the 

Dow Jones Information Service collection of business and 

financial information products. Because the hundreds of 

WAIS free libraries currently accessible are updated and 

maintained by volunteers, the quality of topic coverage is 

uneven. See also WAIS, WAIS client, Project Gutenberg. 

WAIS server or waisserver n. See WAIS. 

wait state n. A processing cycle of the microprocessor 

during which it only waits for data from an input/output 

device or from memory. While a single wait state is not 

humanly perceptible, the cumulative effect of wait states is 

to slow system performance. See also zero wait state. 

wallet n. In electronic commerce, a software program that 

contains a user’s address and credit card information for 

use in paying for online purchases. When the wallet is 

opened at the electronic checkout, it identifies the user to

wallpaper wave table synthesis 

the merchant’s server and allows the user to authorize the 

appropriate debit to a credit card. 

wallpaper n. In a graphical user interface such as Windows, 

a pattern or picture in the screen background that can 

be chosen by the user. See also graphical user interface. 

WAN n. Acronym for wide area network. A geographically 

widespread network, one that relies on communications 

capabilities to link the various network segments. A 

WAN can be one large network, or it can consist of a number 

of linked LANs (local area networks). 

wand n. Any pen-shaped device used for data entry, such 

as a graphics tablet’s stylus or, most commonly, the scanning 

instrument used with many bar code readers. See also 

optical scanner, scan head. Compare stylus. 

wanderer n. A person who frequently uses the World 

Wide Web. Many of these people make indexes of what 

they find. 

WAP n. See Wireless Application Protocol. 

war dialer n. A computer program that calls a range of 

phone numbers to identify those numbers that make a connection 

to a computer modem. War dialers are typically 

used by hackers to search for vulnerable computers and, 

once a connection is made, the war dialers may automatically 

probe the computer for potential weaknesses. Early 

war dialer programs called demon dialers were used to 

crack telephone systems in the 1970s and 1980s. 

warez n. Illegal copies of computer software distributed 

through the Internet and other online channels, such as bulletin 

boards and FTP servers. The spelling is part of the tendency 

among some online groups to use odd symbols and 

intentional misspellings. Compare freeware, shareware. 

warm boot n. The restarting of a running computer without 

first turning off the power. Also called: soft boot, 

three-finger salute, vulcan death grip, warm start. 

warm start n. See warm boot. 

warp vb. Sometimes used by computer game developers 

to describe the need to completely redraw a screen within 

a game. For example, moving through a door or advancing 

to a higher level would require a complete screen overhaul. 

See also computer game. 

watchdog n. A hardware device (usually a timer or driver) 

used to monitor continuing system health and functionality 

through communications with the system software using a 

dedicated device driver. 

561 

watermark n. A semitransparent image often used for 

letters and business cards. In currency, a watermark is visible 

when you hold a bill up to the light. 

watt n. The unit of power equal to the expenditure of 1 

joule of energy in 1 second. The power of an electrical circuit 

is a function of the potential across the circuit and the 

current flowing through the circuit. If E = potential, I = 

current, and R = resistance, power in watts can be calculated 

as I x E, I2 x R, or E2 /R. 

.wav n. The file extension that identifies sound files stored 

in waveform (WAV) audio format. See also WAV. 

WAV n. A file format in which Windows stores sounds as 

waveforms. Such files have the extension .wav. Depending 

on the sampling frequency, on whether the sound is monaural 

or stereo, and on whether 8 or 16 bits are used for 

each sample, one minute of sound can occupy as little as 

644 kilobytes or as much as 27 megabytes of storage. See 

also sampling, waveform. 

wave n. 1. Any disturbance or change that has an oscillatory, 

periodic nature, for example, a light or sound wave. 

See also waveform. 2. In electronics, the time-amplitude 

profile of an electrical signal. 

wave division multiplexing n. See dense wavelength 

division multiplexing. 

waveform n. The manner in which a wave’s amplitude 

changes over time. See also period, phase, wavelength. 

wavelength n. The distance between successive peaks or 

troughs in a periodic signal that is propagated through 

space. Wavelength is symbolized by the Greek letter lambda 

and can be calculated as speed divided by frequency. 

wavelet n. A mathematical function that varies over a 

limited extent of time. Wavelets are coming into increasing 

use for analyzing signals (such as sound). They have 

limited duration and sudden changes in frequency and 

amplitude rather than the infinite duration and constant 

amplitude and frequency of the sine and cosine functions. 

Compare Fourier transform. 

wave table synthesis or wavetable synthesis n. A 

method of producing sound, especially music, through a 

PC. Wave table synthesis is based on use of a wave table, 

which is a collection of digitized sound samples taken 

from recordings of actual instruments. These samples are 

typically stored on a sound card and are edited and mixed 

together to produce music. Wave table synthesis produces 

W

W 

WBEM Web cam 

higher quality audio output than FM (frequency modulation) 

techniques. 

WBEM n. Acronym for Web-Based Enterprise Management. 

A protocol that links a Web browser directly to a 

device or an application that monitors a network. See also 

communications protocol. 

WDEF n. See window definition function. 

WDL n. See Windows Driver Library. 

WDM n. See dense wavelength division multiplexing, 

Windows Driver Model. 

weak typing n. A characteristic of a programming language 

that allows the program to change the data type of a 

variable during program execution. See also data type, 

variable. Compare strong typing. 

wearable computer n. A portable personal computer 

that its user wears like eyeglasses, clothing, or a wristwatch 

but which, unlike those items, is interactive, 

responds to commands, and carries out instructions. A 

wearable computer may be used like a conventional computer 

for data collection, storage, and retrieval, but without 

tying the user to a stationary location while operating 

the computer. The earliest wearable computers were 

clandestine devices used in the mid-1960s to predict the 

performance of roulette wheels. Today, wearable computers 

are used for such applications as inventory and 

express package tracking. 

web n. A set of interlinked documents in a hypertext system. 

The user enters the web through a home page. See 

also World Wide Web. 

Web n. See World Wide Web. 

Web Accessibility Initiative n. See WAI. 

Web address n. See URL. 

Web application n. A set of clients and servers that 

cooperate to provide the solution to a problem. 

Web architect n. An individual who analyzes the purpose 

of a Web site and forms a plan for assembling and 

integrating the hardware, software, and other technical 

resources necessary to make the site function properly. 

Web author n. A person who creates content for the 

World Wide Web. A Web author might be a writer who 

produces text for a designer to include in a Web page, or a 

Web designer who writes the text and also adds graphic 

elements and prepares the HTML code. 

562 

Web-Based Enterprise Management n. See WBEM. 

Web browser n. Software that lets a user view HTML 

documents and access files and software related to those 

documents. Originally developed to allow users to view or 

browse documents on the World Wide Web, Web browsers 

can blur the distinction between local and remote resources 

for the user by also providing access to documents on a 

network, an intranet, or the local hard drive. Web browser 

software is built on the concept of hyperlinks, which allow 

users to point and click with a mouse in order to jump from 

document to document in whatever order they desire. Most 

Web browsers are also capable of downloading and transferring 

files, providing access to newsgroups, displaying 

graphics embedded in the document, playing audio and 

video files associated with the document, and executing 

small programs, such as Java applets or ActiveX controls 

included by programmers in the documents. Helper applications 

or plug-ins are required by some Web browsers to 

accomplish one or more of these tasks. Also called: 

browser. See also ActiveX control, helper application, 

hyperlink, Internet Explorer, Java applet, Lynx, Mosaic, 

Netscape Navigator, plug-in. 

Web bug n. A small, nearly undetectable graphic that 

links to a Web page and is embedded in a document for 

use as an eavesdropping device. A Web bug usually takes 

the form of a 1-by-1-pixel transparent GIF file, so it is 

nearly invisible. This file is placed in a Web page, 

Microsoft Word file, or other document that users will 

access. The application in which the document is opened 

immediately links to the Web to download and display the 

embedded graphic. Information about the user, including 

IP address, browser, referrer, and time viewed, is passed to 

the author of the file when the application retrieves the 

invisible graphic information. 

Webby Award n. Award bestowed annually by the International 

Academy of Digital Arts and Sciences to Web 

sites. The academy bestows awards to Web sites in more 

than 20 categories, which include technical achievement, 

humor, and best community site. 

Web cam or webcam n. A video camera whose output 

appears on a Web page, usually updated on a regular and 

frequent schedule. Web cams are used to display weather 

and traffic conditions, to allow customers and other users 

to observe current activities at the site owner’s business or 

home (for example, at a day care center), for promotional 

purposes, and as a form of “gee whiz, look at this!” entertainment.

webcast1 webcast 

webographics 

webcast1 n. Live or delayed audio or video programming 

delivered to users over the Web. Downloading these broadcasts 

requires a user to have the appropriate video or audio 

application, such as RealPlayer. The necessary application 

is usually available from the webcaster without cost. 

webcast2 vb. To produce and disseminate Web-based 

audio, video, and text programming. 

webcaster n. A company or organization that produces 

and disseminates Web-based audio, video, and text programming. 

webcasting n. Popular term for broadcasting information 

via the World Wide Web, using push and pull technologies 

to move selected information from a server to a client. An 

emergent technology in 1997, webcasting was developed 

to provide users with customized content—for example, 

sports, news, stocks, and weather—that can be updated 

both regularly and automatically. Webcasting gives users 

the ability to specify the type of content they want to see, 

and it gives content providers a means of delivering such 

information directly to the user’s desktop. Also called: 

netcasting. See also pull, push (definition 2). 

Web clipping n. A Web service that delivers brief snippets 

of information to handheld Web-enabled devices, such as 

wireless phones and personal digital assistants. Rather than 

opening a Web site and browsing for information, Web 

clipping allows a customer to request specific types of 

information from a service. The Web clipping service then 

downloads the information to the handheld device. 

web CLUT n. See browser CLUT. 

Web container n. A container that implements the Web 

component contract of Sun Microsystems’s Java 2 Platform 

Enterprise Edition (J2EE) network architecture. This 

contract specifies a run time environment for Web components 

that includes security, concurrency, life cycle management, 

transaction, deployment, and other services. 

Provided by a Web or J2EE server, a Web container provides 

the same services as a JavaServer Pages (JSP) container 

and provides a federated view of the J2EE platform 

APIs. See also API, container, J2EE, JSP container, servlet 

container. 

Web cramming n. A common form of fraud in which 

Internet Service Providers (ISPs) add charges to the 

monthly bill for fictitious services or for services the customer 

had been told were free. 

WebCrawler n. A World Wide Web search engine operated 

by America Online. See also search engine. 

563 

WebDAV n. Short for Web Distributed Authoring and 

Versioning. A set of extensions to the HTTP protocol that 

allows users to collaboratively edit, publish, and manage 

resources on the World Wide Web. WebDAV-enabled additions 

to HTTP include document writing, editing, and publishing 

tools and search, storage, and file sharing options. 

Web development n. The design and coding of World 

Wide Web pages. 

Web directory n. A list of Web sites, giving the URL and 

a description of each. See also URL. 

Web Distributed Authoring and Versioning n. See 

WebDAV. 

Web Forms n. The ASP.NET page framework, which 

consists of programmable Web pages (called Web Forms 

pages) that contain reusable server controls. See also 

ASP.NET server control. 

Web hosting n. See hosting. 

Web index n. A Web site intended to enable a user to 

locate other resources on the Web. The Web index may 

include a search facility or may merely contain individual 

hyperlinks to the resources indexed. 

Weblication n. Slang for Web application. See Web 

application. 

Weblog or weblog or web log n. A Web site that has 

regularly updated content reflecting the interests of the 

site’s host. Often, but not always, the content is in journal 

form, has highlights of news and information from 

other Web sites, and is presented from a personal point of 

view. On some sites, the Weblog is a collaboration 

between visitors to the site. The high-tech-oriented 

Slashdot.org is frequently cited as being among the bestknown 

Weblogs. 

Webmaster or webmaster n. A person responsible for 

creating and maintaining a World Wide Web site. A Webmaster 

is often responsible for responding to e-mail, 

ensuring the site is operating properly, creating and updating 

Web pages, and maintaining the overall structure and 

design of the site. Also called: webmistress, webweaver. 

webmistress n. See Webmaster. 

webographics n. Demographics of Web users specifically 

focusing on surfing and online shopping habits and 

on other related information, such as connection method, 

browser, and platform. 

W

W 

WebPad WebTV 

WebPad n. A class of wireless Internet appliances offering 

full Internet and personal digital assistant (PDA) functions. 

A WebPad features a larger LCD screen than other handheld 

communications devices and resembles a tablet. 

Web page n. A document on the World Wide Web. A Web 

page consists of an HTML file, with associated files for 

graphics and scripts, in a particular directory on a particular 

machine (and thus identifiable by a URL). Usually a Web 

page contains links to other Web pages. See also URL. 

Web page embedding n. Embedding a digital streaming 

media player directly onto a Web page using HTML code. 

Rather than displaying a hyperlink to the media file, Web 

page embedding uses browser plug-ins to present the media 

player as a visual element in the layout of the Web page. 

Web phone n. See Internet telephone. 

Web Presence Provider n. A Web hosting and Internet 

service provider who manages the Web server hardware 

and software required to make a Web site available on the 

Internet. Acronym: WPP. 

Web rage n. 1. Anger or frustration related to the use or 

operation of the Internet. 2. An intemperate, rude, or angry 

posting on the Internet; a flame. 3. The latest fad to gain 

popularity among Web users. 

websafe palette n. See browser CLUT. 

Web server n. See HTTP server. 

Web server control n. An ASP.NET server control that 

belongs to the System.Web.UI.WebControls namespace. 

Web server controls are richer and more abstract than 

HTML server controls. A Web server control has an 

prefix on an ASP.NET page. See also 

ASP.NET server control, HTML server control, 

namespace. 

Web services n. A modular collection of Web protocol– 

based applications that can be mixed and matched to 

provide business functionality through an Internet connection. 

Web services can be used over the Internet or an 

intranet to create products, business processes, and B2B 

interactions. Web services use standard Internet protocols 

such as HTTP, XML, and SOAP to provide connectivity 

and interoperability between companies. 

Web Services Description Language n. See WSDL. 

Web site n. A group of related HTML documents and 

associated files, scripts, and databases that is served up by 

564 

an HTTP server on the World Wide Web. The HTML documents 

in a Web site generally cover one or more related 

topics and are interconnected through hyperlinks. Most 

Web sites have a home page as their starting point, which 

frequently functions as a table of contents for the site. 

Many large organizations, such as corporations, will have 

one or more HTTP servers dedicated to a single Web site. 

However, an HTTP server can also serve several small 

Web sites, such as those owned by individuals. Users need 

a Web browser and an Internet connection to access a Web 

site. See also home page, HTML, HTTP server (definition 

1), Web browser. 

Web Storage System n. The storage component of 

Exchange 2000 Server and SharePoint Portal servers, 

which integrates Web server, database, file system, and 

workgroup functionality. The Web Storage System lets 

you store and share many types of data in a single integrated 

system. Acronym: WSS. 

Web switch n. A network device—a switch—designed to 

optimize Web traffic routing by using the information 

embedded in HTTP requests to route the requests to the 

most appropriate servers, no matter where they are 

located. Web switches are intended to address issues of 

speed, scalability, and performance for high-volume Web 

sites. See also switch. 

Web terminal n. A system containing a central processing 

unit (CPU), RAM, a high-speed modem or other means of 

connecting to the Internet, and powerful video graphics, but 

no hard disk, intended to be used solely as a client to the 

World Wide Web rather than as a general-purpose computer. 

Also called: network computer. 

Web-to-host n. A service that allows remote users to 

access programs and data on legacy or mainframe systems 

through a Web browser. Web-to-host packages typically 

include a combination of services such as emulation support, 

legacy access, centralized management, host services, 

and security options, with some degree of customization 

possible. See also legacy system, mainframe computer. 

WebTV n. A system that provides consumers with the 

ability to access the Web as well as send and receive 

e-mail on a television by means of a set-top box equipped 

with a modem. Users must have an ISP (Internet service 

provider) and subscribe to the WebTV Network. Developed 

by WebTV Networks, WebTV was purchased by 

Microsoft in 1996.

webweaver Whistler 

webweaver n. See Webmaster. 

webzine n. An electronic publication distributed primarily 

through the World Wide Web, rather than as an ink-onpaper 

magazine. See also e-zine. 

weighted code n. A data representation code in which 

each bit position has a specified inherent value, which 

might or might not be included in the interpretation of the 

data, depending on whether the bit is on or off. 

weighted fair queuing n. A technique used to improve 

quality of service that prioritizes each session flow passing 

through a network device. With weighted fair queuing, 

high-bandwidth traffic is given a smaller proportion of 

network capacity than low-bandwidth traffic. Acronym: 

WFQ. Compare fair queuing. 

welcome page n. See home page. 

WELL n. Acronym for Whole Earth ’Lectronic Link. A 

conferencing system based in San Francisco, California, 

that is accessible through the Internet and through dial-up 

access points in many major cities. The WELL attracts 

many computer professionals, along with other people 

who enjoy participating in one of the Internet’s most successful 

virtual communities. Because of the number of 

journalists and other prominent people who participate in 

the WELL, it has substantial influence beyond its own relatively 

small number of subscribers. 

well-behaved adj. 1. Of, pertaining to, or characteristic of 

a program that performs properly even when given 

extreme or erroneous input values. 2. Obeying the rules of 

a particular programming environment. 

well-formed n. An XML or HTML document that follows 

all the rules of syntax outlined in the protocol’s specification. 

A well-formed XML or HTML document can be 

read by all Web browsers without difficulty. 

well-mannered adj. See well-behaved. 

WEP n. Acronym for Wired Equivalent Privacy. An 

encryption algorithm system included as part of the 

802.11 standard, developed by the Institute of Electrical 

and Electronics Engineers as a security measure to protect 

wireless LANs from casual eavesdropping. WEP uses a 

shared secret key to encrypt packets before transmission 

between wireless LAN devices and monitors packets in 

565 

transit to detect attempts at modification. WEP offers both 

40-bit and 128-bit hardware-based encryption options. 

wetware n. Slang for human beings—part of the environment 

that also includes hardware and software. Also 

called: liveware. 

WFC n. See Windows Foundation Classes. 

WFQ n. See weighted fair queuing. 

whatis n. 1. A UNIX utility for obtaining a summary of a 

keyword’s documentation. See also man pages. 2. An 

Archie command for locating software whose description 

contains desired words. 

What You See Before You Get It adj. See WYSBYGI. 

What You See Is What You Get adj. See WYSIWYG. 

wheel printer n. See daisy-wheel printer. 

Whetstone n. A benchmark test that attempts to measure 

the speed and efficiency with which a computer carries out 

floating-point operations. The result of the test is given in 

units called whetstones. The Whetstone benchmark has 

fallen out of favor because it produces inconsistent results 

compared with other benchmarks such as the Dhrystone 

and the sieve of Eratosthenes. See also benchmark1 , Dhrystone, 

sieve of Eratosthenes. 

WHIRLWIND n. A digital computer using vacuum tubes, 

developed at the Massachusetts Institute of Technology in 

the 1940s and used during the 1950s. The innovations 

introduced with WHIRLWIND included CRT displays 

and real-time processing. WHIRLWIND project members 

included Kenneth H. Olsen, who founded Digital Equipment 

Corporation in 1957. See also CRT, real-time, vacuum 

tube. 

Whistler n. The code name for Microsoft Windows XP 

that was used during its development cycle. New visual 

and operational features are designed to make Windows 

XP easy for the home user to operate. Features include 

real-time voice, video and application sharing, enhanced 

mobility, added support for digital photos and video, and 

download and playback of high-quality audio and video 

content. Like Microsoft Windows 2000, Windows XP was 

developed from Windows NT, consolidating consumer 

and business operating systems into a single code base. 

W

W 

whiteboard wildcard character 

whiteboard n. Software that allows multiple users across 

a network to work together on a document that is simultaneously 

displayed on all the users’ screens, as though they 

are all gathered around a physical whiteboard. 

Whiteboard n. Microsoft NetMeeting feature that opens a 

separate window in which multiple users can simultaneously 

review, create, and update graphic information. 

The Whiteboard is object-oriented, not pixel-oriented, 

allowing participants to manipulate the contents by clicking 

and dragging with the mouse. In addition, they can use a 

remote pointer or highlighting tool to point out specific 

contents or sections of shared pages. The NetMeeting 

Whiteboard is T.126 compliant and is interoperable with 

other T.126-compatible whiteboards. 

white box n. A nonbranded PC assembled by a reseller, 

potentially including components from a number of manufacturers. 

The name refers to the typical color of the shipping 

carton, a box unadorned by brand name or logo. 

white box testing n. A method of testing software that is 

based on knowledge of how the software is intended to 

function. Unlike black box testing, which focuses on how 

the software functions without reference to how it is 

designed, white box testing relies on detailed knowledge 

of the program code itself and is intended to find flaws 

and/or errors in its design and specification. Also 

called: glass box testing. Compare black box testing. 

white hat n. A hacker who operates without malicious 

intent. A white hat will not break into a system with the 

intention of doing damage. White hats may be employed 

to provide security against other hackers. See also hacker. 

Compare black hat. 

white noise n. Noise that contains components at all frequencies, 

at least within the frequency band of interest. It 

is called “white” by analogy to white light, which contains 

light at all the visible frequencies. In the audible spectrum, 

white noise is a hiss or a roar, such as that produced when 

a television set is tuned to a channel over which no station 

is broadcasting. 

white pages n. See DIB (definition 2). 

white space n. The areas of blank space on a page that can 

be used in a design for balance, contrast, and visual appeal. 

566 

whois n. 1. An Internet service, provided by some 

domains, that enables a user to find e-mail addresses and 

other information for users listed in a database at that 

domain. 2. A UNIX command to access the whois service. 

3. A command that displays a list of all users logged onto 

a Novell network. 

whois client n. A program (such as the UNIX whois command) 

that enables a user to access databases of usernames, 

e-mail addresses, and other information. See also whois 


whois server n. Software that provides the usernames and 

e-mail addresses from a database (often listing people who 

have accounts at an Internet domain) to users who request 

the information using whois clients. See also whois (definition 

1). 

Whole Earth ’Lectronic Link n. See WELL. 

whole number n. A number without a fractional component—for 

example, 1 or 173; an integer. 

WID n. Acronym for Wireless Information Device. 

Smart phone or other handheld wireless device capable 

of multiple communications functions, including e-mail 

and Internet access. 

Wide Area Information Server n. See WAIS. 

wide area network n. See WAN. 

wideband transmission n. See broadband network. 

Wide SCSI n. A form of the SCSI-2 interface that can 

transfer data 16 bits at a time at up to 20 megabytes per 

second. The Wide SCSI connector has 68 pins. Also 

called: Wide SCSI-2. See also SCSI, SCSI-2. Compare 

Fast SCSI, Fast/Wide SCSI. 

Wide SCSI-2 n. See Wide SCSI. 

widow n. A last line of a paragraph, shorter than a full 

line, appearing at the top of a page. A widow is considered 

visually undesirable on the printed page. Compare orphan. 

wildcard character n. A keyboard character that can be 

used to represent one or many characters. The asterisk (*), 

for example, typically represents one or more characters, 

and the question mark (?) typically represents a single character. 

Wildcard characters are often used in operating systems 

as a means of specifying more than one file by name.

WIMP Windows 

WIMP n. Acronym for Windows, Icons, Mouse, and 

Pointers. A graphical user interface (GUI) such as those 

provided by the Apple Macintosh and Microsoft Windows 

operating systems. WIMP is usually said to stand for Windows, 

Icons, Mouse, and Pointers, but the acronym is 

sometimes spelled out as either Windows, Icons, Menus, 

and Pointers or Windows, Icons, Mouse, and Pull-down 

menus. The WIMP interface was invented at the Xerox 

Palo Alto Research Center (PARC), where it was first used 

in the Alto computer in the early 1970s. See also graphical 


Win32 n. The application programming interface in Windows 

95 and Windows NT that enables applications to use 

the 32-bit instructions available on 80386 and higher processors. 

Although Windows 95 and Windows NT support 

16-bit 80x86 instructions as well, Win32 offers greatly 

improved performance. See also 16-bit machine, 32-bit 

machine, 80386DX, 8086, application programming interface, 

central processing unit, Win32s. 

Win32 Driver Model n. See Windows Driver Model. 

Win32s n. A subset of the Win32 application programming 

interface that works under Windows 3.x. By including 

the Win32s software, which is distributed as freeware, 

an application can gain in performance from using the 32bit 

instructions available on 80386 and higher processors 

while running on Windows 3.x. See also 32-bit machine, 

80386DX, central processing unit, Win32. 

Winchester disk n. An early IBM name for a hard disk. 

The term is derived from IBM’s internal code name for its 

first hard disk, which stored 30 megabytes (MB) and had a 

30-millisecond access time, reminding its inventors of a 

Winchester .30-caliber rifle known as a “.30-.30.” 

window n. In applications and graphical interfaces, a portion 

of the screen that can contain its own document or 

message. In window-based programs, the screen can be 

divided into several windows, each of which has its own 

boundaries and can contain a different document (or 

another view into the same document). 

window definition function n. A resource associated 

with a window in a Macintosh application. The Macintosh 

Window Manager calls this function to perform 

567 

such actions as drawing and resizing the window. Also 

called: WDEF. 

windowing n. An approach to remediation (correction of 

problems) or simply user convenience in which two-digit 

years are interpreted in relation to a window of time. Logical 

procedures based on windowing thus enable software 

to correctly produce accurate four-digit years. In windowing, 

the century is determined by presuming that the year 

falls within a 100-year span. So if the window ranges from 

1995 to 2094, any year that is 95 or greater is presumed to 

be in the twentieth century (19xx), while any number less 

than 95 is presumed to be in the twenty-first century 

(20xx). Fixed windowing presupposes that a window 

always starts with the same date, or pivot year. Moving 

windowing permits a user or another system to specify the 

pivot year when the program is installed or started. Sliding 

windowing is calculated every time a program runs and 

can be based on a predetermined span of time, called a 

slider, that can be added to the current date to produce the 

pivot year for the window. Potential differences in windows 

require analysis whenever importing or exporting 

data between systems. Also called: logic fix. See also 

pivot year. 

windowing environment n. An operating system or 

shell that presents the user with specially delineated 

areas of the screen called windows. Windowing environments 

typically allow windows to be resized and moved 

around on the display. The Macintosh Finder, Windows, 

and the OS/2 Presentation Manager are all examples of 

windowing environments. See also graphical user interface, 

window. 

window random access memory n. See WRAM. 

Windows n. An operating system introduced by 

Microsoft Corporation in 1983. Windows is a multitasking 

graphical user interface environment that runs on MS- 

DOS–based computers (Windows 3.x. and Windows for 

Workgroups), and as a self-contained operating system for 

desktop computers (Windows 9x and Windows Me), 

workstations (Windows NT Workstation, Windows 2000 

Professional), and network servers (Windows NT Server, 

Windows NT Enterprise Edition, Windows 2000 Server, 

and Windows 2000 Advanced Server). The most recent 

W

W 

Windows 95 Windows 2000 Datacenter Server 

versions of Windows are Windows XP Home (home and 

entertainment use) and Professional (advanced computing, 

businesses, and large organizations). The next generation 

of Windows server products will be the Windows Server 

2003 family. Windows provides a standard graphical interface 

based on drop-down menus, windowed regions on the 

screen, and a pointing device such as a mouse. 

Windows 95 n. An operating system with a graphical 

user interface for 80386 and higher processors, released 

by Microsoft Corporation in 1995. Intended to replace 

Windows 3.11, Windows for Workgroups 3.11, and MS- 

DOS, Windows 95 is a complete operating system, rather 

than a shell that requires MS-DOS, as does Windows 3.x. 

For backward compatibility, Windows 95 can run MS-DOS 

software. Under Windows 95, filenames can be up to 255 

characters long and may include dots and spaces. Windows 

95 supports the Plug and Play method for installing and 

configuring hardware and can access Windows, NetWare, 

and UNIX networks. The minimum configuration for Windows 

95 is an 80386 processor with 4 MB of RAM, but an 

i486 or higher processor with at least 8 MB of RAM is 

recommended. Internet functionality is provided in large 

part in Windows 95 by Microsoft Internet Explorer. See 

also MS-DOS, NetWare, Plug and Play, Windows. 

Windows 98 n. An operating system with a graphical 

user interface for i486 and higher processors, released by 

Microsoft Corporation in 1998. Building upon Windows 

95, Windows 98 features an improved interface and more 

robust functionality. With the Active Desktop, Windows 

98 integrates Internet connectivity even more closely, 

allowing users to access remote files in the same way they 

would access files on their hard drives. Hardware support 

includes USB, IEEE 1394, AGP ports, television tuner 

cards, DVD drives, multiple modems, and multiple monitors. 

Windows 98, Second Edition, released in 1999, 

builds on the features in the initial release and offers home 

networking and improved maintenance features. See also 

Windows, Windows 95. 

Windows 9x n. The architecture upon which Windows 

95 and Windows 98 were built. See also Windows 95, 

Windows 98. 

Windows 2000 n. A Microsoft operating system, the 

successor to Windows NT, designed for business rather 

than consumer use. Like its predecessor, Windows 2000 is 

a multithreaded, multitasking 32-bit operating system. 

568 

Implemented in desktop and several server versions, Windows 

2000 focuses overall on improved ease of use, networking, 

management, reliability, scalability, and security. 

See the table. 

Table W.1 ATA Specifications. 

Version Designed For Features 

Windows 

2000 

Professional 

Windows 

2000 Server 

Windows 

2000 

Advanced 

Server 

Windows 

2000 

Datacenter 

Server 

Business desktop Improvements in: 

Ease of use; security, 

performance, 

and reliability; support 

for mobile 

Small to mediumsized 

deployments— 

workgroups, branch 

offices, departmental 

application, file, 

print servers 

Mid-range departmental 

and application 

deployments 

computing 

Two-way symmetric 

multiprocessing 

(SMP); ActiveDirectory;management 

tools; 

Kerberos and PKI 

security; COM+; 

Windows Terminal 

Support; improved 

Internet services 

Windows 2000 

Server features, 

plus four-way 

SMP; load balancing; 

clustering; 

high-performance 

sorting; 64-GB 

physical memory 

Large operations— Windows 2000 

data warehouses, Advanced Server 

online transaction- features, plus 16processing 

(OLTP), way SMP 

science and engineering 

simulations, enterprise 

solutions 

Windows 2000 Advanced Server n. Microsoft’s network 

server for larger organizations. Designed to replace 

Windows NT 4 Enterprise Edition, it supports up to fourway 

SMP, large physical memories, and database-intensive 

work. It integrates clustering and load balancing support. 

See also SMP, Windows. 

Windows 2000 Datacenter Server n. Microsoft’s network 

server for larger organizations. Considered the most

Windows 2000 Professional Windows Image Acquisition 

powerful and functional server operating system ever 

offered by Microsoft, it supports up to 16-way SMP and 

up to 64 GB of physical memory (depending on system 

architecture). Like Windows 2000 Advanced Server, it 

provides both clustering and load balancing services as 

standard features. It is optimized for large data warehouses, 

econometric analysis, large-scale simulations in 

science and engineering, OLTP, and server consolidation 

projects. See also OLTP, SMP, Windows. 

Windows 2000 Professional n. Microsoft’s mainstream 

desktop operating system for businesses of all sizes. 

Designed to replace Windows NT Workstation 4, which 

many people are using today as the standard business 

desktop, Windows 2000 Professional builds upon the 

interface and kernel in NT 4. It also includes improved 

security, state-of-the-art features for mobile users, industrial-strength 

reliability, and better performance. 

Windows 2000 Server n. Microsoft’s network server 

for small to medium businesses. Designed to replace 

Windows NT 4 Server, Windows 2000 Server offers 

improved functionality and supports new systems with up 

to two-way symmetric multiprocessing (SMP). 

Windows application n. A software application designed 

for use with the Microsoft Windows environment. 

Windows-based accelerator n. A type of super VGA 

(SVGA) video adapter designed specifically to run Windows 

and Windows-based applications more quickly. A 

Windows-based accelerator achieves performance 

improvements over a standard SVGA video adapter with 

the help of special routines built into the adapter’s readonly 

memory. These routines relieve the Windows operating 

system of some of the video-related duties it must perform 

on a nonaccelerated system. Also called: Windowsbased 

accelerator card. See also SVGA. 

Windows CE n. A small operating system from Microsoft 

designed for use with handheld and palm-size PCs and in 

embedded systems, such as the AutoPC. Windows CE, 

which has a user interface that is similar to Windows 9x 

and Windows NT, includes scaled-down versions of several 

Microsoft applications, including Excel, Word, Internet 

Explorer, Schedule+, and an e-mail client. See also 

handheld PC. 

Windows CE Services n. A set of technologies that 

makes Windows CE–based devices Web enabled. It provides 

the functionality to deliver Web content information 

569 

to Windows CE–based devices from a wireless network or 

by desktop synchronization. 

Windows Distributed interNet Applications 

Architecture n. See Windows DNA. 

Windows DNA n. Short for Microsoft Windows Distributed 

interNet Applications Architecture. A framework 

introduced in 1997 as a means of integrating client/server 

and Web technologies in the creation of scalable, multitier 

applications delivered over an enterprise network. Windows 

DNA is based on a number of technologies, among 

them COM (Component Object Model), ActiveX, and 

dynamic HTML. 

Windows Driver Library n. A collection of hardware 

device drivers for a Microsoft Windows operating system 

that were not included in the original Windows package. 

Acronym: WDL. See also driver. 

Windows Driver Model n. A 32-bit layered architecture 

for device and bus drivers that allows for drivers that can 

be used by both Windows NT and Windows 98. It provides 

common input/output services understood by both 

operating systems and supports Plug and Play, USB (Universal 

Serial Bus), IEEE 1394 bus, and various devices, 

including input, communication, imaging, and DVD. 

Acronym: WDM. Also called: Win32 Driver Model. 

Windows Explorer n. A utility in Windows that enables 

the user to locate and open files and folders. Windows 

Explorer resembles the File Manager of Windows 3.1. The 

user can select folders from a list displayed on the left side 

of the screen and access files in a selected folder from a 

list displayed on the right side of the screen. 

Windows Forms n. A rich Windows client library for 

building Windows client applications. 

Windows Foundation Classes n. A Java class library 

for developing Java applications to run in the Windows 

environment. Designed by Microsoft to make it easy to 

write code for the Windows platform using the powerful 

Java programming language, the Windows Foundation 

Classes represent an object-oriented framework that 

encapsulates and unifies the Microsoft Win32 API and 

Dynamic HTML programming models. This framework 

enables developers to link Java code directly to Windows 

APIs. Acronym: WFC. See also Java, Java Foundation 

Classes. 

Windows Image Acquisition n. A device-driver interface 

that supports still digital cameras and low-end and 

W

W 

Windows IP Configuration Windows Media Technologies 

high-end scanners and allows retrieving of still images 

from IEEE 1394-based DV camcorders and USB-based 

Web cams. Acronym: WIA. 

Windows IP Configuration n. See Winipcfg. 

Windows Management Instrumentation n. A management 

infrastructure in Windows that supports monitoring 

and controlling system resources through a common set of 

interfaces and provides a logically organized, consistent 

model of Windows operation, configuration, and status. 

Acronym: WMI. See also resource. 

Windows Me n. Released in 2000, the Windows Millennium 

Edition (Windows Me) operating system designed 

for home users as an upgrade from Windows 95 or Windows 

98. Windows Me offers an improved home user 

experience including making it easier for users to share 

and manipulate digital photos, music, and videos, 

enhanced home networking capabilities, a rich Internet 

experience with support for broadband connections, different 

Internet communication tools, and online gaming. 

Windows Media Audio n. A digital audio coding scheme 

developed by Microsoft that is used in distributing recorded 

music, usually over the Internet. Windows Media Audio 

shrinks the size of the audio file by a factor of 20 to 24 without 

seriously degrading the quality (CD-recording level) of 

the sound. Windows Media Audio files are given the file 

extension .wma and can be created with Windows Media 

Tools and played with the Windows Media Player. Acronym: 

WMA. See also Windows Media Technologies. Compare 

MP3, RealAudio, Secure Digital Music Initiative. 

Windows Media Encoder n. A Windows Media technology 

that compresses live or prerecorded audio and video 

into a Windows Media stream, which can either be distributed 

immediately or saved as a Windows Media file for 

later distribution. The technology allows content developers 

to convert both live and prerecorded audio, video, and 

computer screen images to Windows Media Format for 

live and on-demand delivery. Windows Media Encoder 

also can save a stream as a Windows Media file and convert 

a file into Windows Media Format. Windows Media 

Encoder can distribute a stream via HTTP protocol. Also 

called: (if context is clear) Encoder, the encoder, the 

encoder engine. 

Windows Media Player n. A client/control that receives 

a stream from a Windows Media server or local content 

for playback. It can run as a stand-alone client executable 

program. Windows Media Player can also be embedded in 

570 

a Web page, a C++ program, or a Microsoft Visual Basic 

program that uses the client ActiveX control. 

Windows Media server n. A server on which Windows 

Media Services has been installed. 

Windows Media Services n. A digital media platform 

that runs on a server, such as Windows 2000, to support 

streaming media, such as video and audio. 

Windows Media Technologies n. Microsoft technologies 

for the creation, delivery, and playing of streaming 

audio and video over a network, including both intranets 

and the Internet. Windows Media Technologies, downloadable 

from the Microsoft Web site, support both live 

and on-demand (delivered from storage) content and are 

based on files delivered in Advanced Streaming Format 

(ASF). Three major components—Windows Media Tools, 

Windows Media Services, and Windows Media Player— 

comprise Windows Media Technologies. See the table. 

See also Advanced Streaming Format. Compare Real- 

System G2. 

Table W.2 ATA Specifications. 

Component Purpose Features 

Windows 

Media Tools 

Windows 

Media Services 

Content creation ASF authoring and 

editing tools, 

including tools for 

converting files 

from other formats 

(WAV, AVI, 

MPEG, and MP3) 

to ASF. 

Content delivery Tools for real-time 

and on-demand 

content delivery, 

administration 

tools, and Windows 

Media 

Rights Manager 

for piracy control. 

Windows Content playback ASF player for 

Media Player for 

audio, audio plus 

PC platforms, 

still images, and 

Windows Media 

full-motion video. 

Player for Macin- 

Also supports 

tosh, Windows 

other multimedia 

Media Player for 

data, including 

UNIX 

RealAudio.

Windows Media Tools win.ini 

Windows Media Tools n. See Windows Media Technologies. 

Windows Messenger n. See .NET Messenger Service. 

Windows Metafile Format n. A graphics file format 

used by Windows to store vector graphics in order to 

exchange graphics information between applications and 

to store information between sessions. Acronym: WMF. 

See also vector graphics. 

Windows Movie Maker n. Software from Microsoft for 

capturing, editing, and arranging audio and video source 

material to create movies. Acronym: WMM. 

Windows NT n. An operating system released by 

Microsoft Corporation in 1993. The Windows NT operating 

system, sometimes referred to as simply NT, is the 

high-end member of a family of operating systems from 

Microsoft. It is a completely self-contained operating system 

with a built-in graphical user interface. Windows NT 

is a 32-bit, preemptive multitasking operating system that 

features networking, symmetric multiprocessing, multithreading, 

and security. It is a portable operating system 

that can run on a variety of hardware platforms including 

those based on the Intel 80386, i486, and Pentium microprocessors 

and MIPS microprocessors; it can also run on 

multiprocessor computers. Windows NT supports up to 4 

gigabytes of virtual memory and can run MS-DOS, 

POSIX, and OS/2 (character-mode) applications. See also 

MS-DOS, operating system, OS/2, POSIX, Windows. 

Windows NT Advanced Server n. A superset of Windows 

NT that provides centralized, domain-based network 

management and security. Windows NT Advanced Server 

also offers advanced hard disk fault-tolerance features, 

such as mirroring and additional connectivity. See also 

Windows NT. 

Windows NT Embedded n. A version of the Microsoft 

Windows NT operating system designed for devices and 

other products that have embedded systems. Windows 

NT Embedded, released in 1999, targets devices in the 

midrange to high end of the embedded device industry, 

including high-speed copiers, patient monitors, private 

branch exchanges (PBXs), and point-of-sale terminals. 

Windows NT Embedded features include headless operation 

(with no keyboard, mouse, or display devices 

needed), diskless operation, and remote management 

infrastructure. See also embedded system, Windows NT. 

Windows Open Services Architecture n. See WOSA. 

571 

Windows Open System Architecture n. See WOSA. 

Windows Script Host n. The language-independent 

scripting host for Microsoft Windows platforms. Windows 

Script Host is a tool that allows users to run VBScript, 

JScript, or any other scripting language to automate common 

tasks and to create macros and logon scripts. 

Windows Server 2003 n. The next generation of Windows 

servers. Built on Windows 2000, the Windows 

Server 2003 family includes the functionality, dependability, 

scalability, and security options to serve as the computing 

foundation for businesses of all sizes. The flexible 

computing architecture, built on industry standards, allows 

businesses to create robust and innovative applications, 

improve collaboration across the organization, and connect 

securely with customers. 

Windows Sockets n. See Winsock. 

Windows terminal n. A thin-client solution from 

Microsoft, designed to enable terminals and minimally 

configured computers to display Windows applications 

even if they are not, in themselves, capable of running 

Windows software. Windows terminals work in conjunction 

with Windows NT Server, Terminal Server edition. 

See also thin client. 

Windows XP n. A member of the Microsoft Windows 

family of operating systems. Windows XP was released in 

2001 in two versions: Windows XP Home Edition for 

home use and Windows XP Professional for advanced 

home computing, businesses, and larger organizations. 

Windows XP features a new visual design that simplifies 

navigation and search capabilities, improved file management, 

additional media and Web publishing capabilities, 

an improved system for device discovery and installation, 

and advanced features for mobile computing. 

WinG n. Short for Windows Games. An application programming 

interface for games in the Windows 9x environment. 

Under WinG, games can access the video frame 

buffer directly for increased speed. See also application 

programming interface, buffer1 , frame buffer. 

WinHEC n. Short for Microsoft Windows Hardware 

Engineering Conference. Annual meeting of the computer 

hardware industry featuring forums, seminars, exhibits, 

and educational sessions for developers, technical managers, 

engineers, and product planners who use the 

Microsoft Windows family of operating systems. 

win.ini n. In Windows 3.x and MS-DOS, the initialization 

file used to pass the program configuration information 

W

W 

Winipcfg Wireless Services server component 

necessary to run the Windows operating environment. The 

win.ini file has been supplanted by the registry database in 

Windows 95 and later and Windows NT and later. See also 

configuration file, ini file, registry. 

Winipcfg n. Short for Windows IP Configuration. A Windows 

9x utility that enables users to access information 

about their TCP/IP (Transmission Control Protocol/Internet 

Protocol) and network adapter card settings. Running the 

Winipcfg program (winipcfg.exe) opens the IP Configuration 

window, which reveals the physical address, IP 

address, subnet mask, and default gateway settings of the 

primary TCP/IP adapter (or settings of multiple adapters if 

more than one is installed). This information is also helpful 

for troubleshooting. See also TCP/IP. 

WINS n. Acronym for Windows Internet Naming Service. 

A Windows NT Server method for associating a computer’s 

host name with its address. Also called: INS, Internet 

Naming Service. Compare DNS (definition 1). 

Winsock n. Short for Windows Sockets. An application 

programming interface standard for software that provides 

a TCP/IP interface under Windows. The Winsock standard 

developed out of a Birds of a Feather (BOF) discussion 

that arose among software vendors at a UNIX conference 

in 1991; it has gained the general support of software 

developers, including Microsoft. See also application programming 

interface, BOF, socket (definition 1), sockets 

API, TCP/IP. 

Wintel adj. Of, pertaining to, or characteristic of a computer 

that uses the Microsoft Windows operating system 

and an Intel central processing unit (CPU). See also 

Windows. 

wired adj. 1. Of, pertaining to, or characteristic of an electronic 

circuit or hardware grouping in which the configuration 

is determined by the physical interconnection of the 

components (as opposed to being programmable in software 

or alterable by a switch). See also hardwired (definition 

1). 2. Knowledgeable about Internet resources, 

systems, and culture. 3. Having access to the Internet. 

Wired Equivalent Privacy n. See WEP. 

wired home n. See smart home. 

wire-frame model n. In computer graphics applications 

such as CAD programs, a representation of a threedimensional 

object using separate lines that resemble 

strands of wire joined to create a model. Compare solid 

model, surface modeling. 

572 

wireless adj. Of, pertaining to, or characteristic of communications 

that take place without the use of interconnecting 

wires or cables, such as by radio, microwave, or 

infrared light. 

Wireless Application Protocol n. A specification for a 

global standard for enabling digital cellular phones and 

other wireless devices to access Internet and other information 

services. The Wireless Application Protocol, or 

WAP, is supported by an organization known as WAP 

Forum, which includes such members as Motorola, Nokia, 

L. M. Ericsson, and Unwired Planet. The goal of the 

forum is to create an open standard that works with different 

wireless technologies. Acronym: WAP. 

wireless communication n. Communication between a 

computer and another computer or device without wires. 

The form of wireless communication provided as part of the 

Windows operating system uses infrared light to transmit 

files. Radio frequencies, as used by cellular and cordless 

telephones, are another form of wireless communication. 

See also infrared, infrared device, infrared port. 

Wireless Information Device n. See WID. 

wireless Internet n. Version of the Internet designed for 

use on wireless phones and handheld devices with small 

display screens, limited memory, and slower data transmission 

speeds than a personal computer. Most wireless Internet 

sites offer content as basic text with limited graphics. 

wireless LAN n. A LAN (local area network) that sends 

and receives data via radio, infrared optical signaling, or 

some other technology that does not require a physical 

connection between individual nodes and the hub. Wireless 

LANs are often used in office or factory settings 

where a user must carry a portable computer from place to 

place. Also called: WLAN. 

Wireless Markup Language n. See WML. 

Wireless Multimedia Forum n. See WMF (definition 2). 

wireless phone n. Telephone that operates by means of 

radio waves without a wire connection. A base station 

(cell tower) relays the phone’s signal to a wireless carrier’s 

network, where it is transmitted to another wireless phone 

or to a wired telephone network. 

Wireless Services server component n. A component 

that allows a content provider or carrier to configure and 

schedule any number of information acquisition/encoding/ 

transmission components to create a data stream to be transmitted 

by a carrier to a device. The server component builds

Wireless Transaction Protocol word processor 

on an open architecture to allow new server components to 

be installed in any part of the stream at any time. 

Wireless Transaction Protocol n. A lightweight 

request/reply transaction protocol for devices with limited 

resources over networks with low to medium bandwidth. 

It is not called the Wireless Transport Protocol or the 

Wireless Transfer Protocol. Acronym: WTP. 

Wireless Transport Layer Security n. See WTLS. 

wire-pin printer n. See dot-matrix printer. 

wire-wrapped circuits n. Circuits constructed on perforated 

boards using wire instead of the metal traces found 

on printed circuit boards. The stripped ends of insulated 

wires are wrapped around the long pins of special wirewrapped 

integrated circuit sockets. Wire-wrapped circuits 

are generally handmade, one-of-a-kind devices used for 

prototyping and research in electrical engineering. Compare 

printed circuit board. 

wiring closet n. A room or location in a building where 

telecommunications and/or networking equipment such as 

hubs, switches, and routers are installed. Also called: data 

closet, telecom closet, telecommunications closet. 

wizard n. 1. Someone who is adept at making computers 

perform their “magic.” A wizard is an outstanding and creative 

programmer or a power user. Compare guru, UNIX 

wizard. 2. A participant in a multiuser dungeon (MUD) 

who has permission to control the domain, even to delete 

other players’ characters. See also MUD. 3. An interactive 

help utility within an application that guides the user 

through each step of a particular task, such as starting up a 

word processing document in the correct format for a business 

letter. 

wizzywig n. See WYSIWYG. 

WLAN n. See wireless LAN. 

WMA n. Acronym for Windows Media Audio. See Windows 

Media Audio. 

.wmf n. A file extension that identifies a vector image 

encoded as a Microsoft Windows Metafile. 

WMF n. 1. See Windows Metafile Format. 2. Acronym for 

Wireless Multimedia Forum. A consortium of technology 

companies formed to promote open standards for wireless 

streaming products. WMF members include Cisco Systems, 

Intel, and the Walt Disney Internet Group. See also ISMA. 

WMI n. See Windows Management Instrumentation. 

573 

WML n. Acronym for Wireless Markup Language. A 

markup language developed for Web sites that are 

accessed with microbrowsers on Wireless Application 

Protocol (WAP)–enabled devices. A Web site written with 

WML would be viewable on handheld devices with small 

screens, such as cell phones. See also markup language, 

microbrowser, Wireless Application Protocol. 

WMLScript n. A scripting language derived from the 

JavaScript language for use in the development of Wireless 

Markup Language (WML). 

WMM n. See Windows Movie Maker. 

word n. The native unit of storage on a particular machine. 

A word is the largest amount of data that can be handled by 

the microprocessor in one operation and also, as a rule, is 

the width of the main data bus. Word sizes of 16 bits and 

32 bits are the most common. Compare byte, octet. 

Word n. Microsoft’s word processing software, available 

for the Windows and Macintosh platforms. In addition to 

extensive editing, formatting, and customization features, 

Word provides such tools as automatic text completion and 

correction. The most recent version, Word 2002 (part of 

Office XP) adds Web functionality—for example, the ability 

to save documents in HTML format. The first version, 

Microsoft Word for MS-DOS 1.00, was introduced in 1983. 

word-addressable processor n. A processor that cannot 

access an individual byte of memory but can access a 

larger unit. In order to perform operations on an individual 

byte, the processor must read and write memory in the 

larger unit. See also central processing unit. 

WordPerfect Office n. A suite of business application 

programs from Corel Corporation. The basic (Standard 

Edition) WordPerfect Office suite includes the WordPerfect 

word processor, Quattro Pro spreadsheet, Corel Presentations 

presentation software, CorelCENTRAL 

personal information manager, Microsoft Visual Basic for 

Applications scripting tools, and Trellix Web publisher. A 

home and small-business package, the Voice-Powered Edition, 

adds speech recognition and publishing products; a 

business and corporate package, the Professional Edition, 

adds database and Internet tools to all of the preceding. 

word processing n. The act of entering and editing text 

with a word processor. Acronym: WP. 

word processor n. An application program for creating 

and manipulating text-based documents. A word processor 

is the electronic equivalent of paper, pen, typewriter, eraser, 

and, most likely, dictionary and thesaurus. Depending on 

W

W 

wordwrap WORM 

the program and the equipment in use, word processors can 

display documents either in text mode (using highlighting, 

underlining, or color to represent italics, boldfacing, and 

other such formatting) or in graphics mode (in which formatting 

and, sometimes, a variety of fonts appear on the 

screen as they will on the printed page). All word processors 

offer at least limited facilities for document formatting, 

such as font changes, page layout, paragraph indentation, 

and the like. Some word processors can also check spelling, 

find synonyms, incorporate graphics created with another 

program, align mathematical formulas, create and print 

form letters, perform calculations, display documents in 

multiple on-screen windows, and enable users to record 

macros that simplify difficult or repetitive operations. Compare 

editor, line editor. 

wordwrap or word wrap n. The ability of a word processing 

program or a text-editing program to break lines 

of text automatically to stay within the page margins or 

window boundaries of a document without the user having 

to do so with carriage returns, as is typically necessary 

when using a typewriter. See also hard return, soft return. 

workaround n. A tactic for accomplishing a task despite a 

bug or other inadequacy in software or hardware without 

actually fixing the underlying problem. See also kludge. 

workbook n. In a spreadsheet program, a file containing a 

number of related worksheets. See also worksheet. 

workflow application n. A set of programs that aids in 

the tracking and management of all the activities in a 

project from start to finish. 

workgroup n. A group of users working on a common 

project and sharing computer files, typically over a LAN 

(local area network). See also groupware. 

workgroup computing n. A method of working electronically 

in which various individuals on the same project 

share resources and access to files using a network 

arrangement, such as a local area network, enabling them 

to coordinate their separate tasks. This is accomplished 

through using software designed for workgroup computing. 

See also groupware. 

Workplace Shell n. The graphical user interface of OS/2. 

Like the Mac OS and Windows 95, the Workplace Shell is 

document-centric. Document files are displayed as icons; 

clicking an icon starts the corresponding application, and 

the user can print a document by dragging the document’s 

icon to a printer icon. The Workplace Shell uses the graphical 

functions of Presentation Manager. Acronym: WPS. 

574 

worksheet n. In a spreadsheet program, a page organized 

into rows and columns appearing on screen and used for 

constructing a single table. 

workstation n. 1. A combination of input, output, and 

computing hardware that can be used for work by an individual. 

2. A powerful stand-alone computer of the sort 

used in computer-aided design and other applications 

requiring a high-end, usually expensive, machine with 

considerable calculating or graphics capability. 3. A 

microcomputer or terminal connected to a network. 

World Wide Web n. The total set of interlinked hypertext 

documents residing on HTTP servers all around the world. 

Documents on the World Wide Web, called pages or Web 

pages, are written in HTML (Hypertext Markup Language), 

identified by URLs (Uniform Resource Locators) 

that specify the particular machine and pathname by 

which a file can be accessed, and transmitted from server 

to end user under HTTP (Hypertext Transfer Protocol). 

Codes, called tags, embedded in an HTML document 

associate particular words and images in the document 

with URLs so that a user can access another file, which 

may be halfway around the world, at the press of a key or 

the click of a mouse. These files may contain text (in a 

variety of fonts and styles), graphics images, movie files, 

and sounds as well as Java applets, ActiveX controls, or 

other small embedded software programs that execute 

when the user activates them by clicking a link. A user visiting 

a Web page also may be able to download files from 

an FTP site and send messages to other users via e-mail 

by using links on the Web page. The World Wide Web was 

developed by Timothy Berners-Lee in 1989 for the European 

Laboratory for Particle Physics, or Conseil Européen 

pour le Recherche Nucléaire, in French (CERN). Acronym: 

WWW. Also called: w3 , W3, Web. See also ActiveX 

controls, HTML, HTTP, HTTP server (definition 2), Java 

applet, URL. 

World Wide Web Consortium n. See W3C. 

worm n. A program that propagates itself across computers, 

usually by creating copies of itself in each computer’s 

memory. A worm might duplicate itself in one computer 

so often that it causes the computer to crash. Sometimes 

written in separate segments, a worm is introduced surreptitiously 

into a host system either as a prank or with the 

intent of damaging or destroying information. See also 

bacterium, Internet Worm, Trojan horse, virus. 

WORM n. Acronym for write once, read many. A type of 

optical disc that can be read and reread but cannot be

WOSA write protect 

altered after it has been recorded. WORMs are highcapacity 

storage devices. Because they cannot be erased 

and rerecorded, they are suited to storing archives and 

other large bodies of unchanging information. See also 

compact disc. 

WOSA n. Acronym for Windows Open Services Architecture, 

also known as Windows Open System Architecture. 

A set of application programming interfaces from 

Microsoft that is intended to enable Windows-based applications 

from different vendors to communicate with each 

other, such as over a network. The interfaces within the 

WOSA standard include Open Database Connectivity 

(ODBC), the Messaging Application Programming Interface 

(MAPI), the Telephony Application Programming 

Interface (TAPI), Windows Sockets (Winsock), and 

Microsoft Remote Procedure Calls (RPC). See also 

MAPI, ODBC, remote procedure call, TAPI, Winsock. 

.wp n. A file extension used to identify files formatted for 

the WordPerfect word processor. 

WP n. See word processing. 

WPS n. See Workplace Shell. 

WRAM n. Acronym for window random access memory. 

A type of RAM used in video adapters. Like video RAM 

(VRAM), WRAM allows the screen to be repainted while 

a graphical image is being written, but WRAM is faster. 

Compare video RAM. 

wrap around vb. To continue movement, as with the cursor 

or a search operation, to the beginning or to a new 

starting point rather than stopping when the end of a series 

is reached. For example, the screen cursor might wrap 

around to the first column of the next line rather than stopping 

when it reaches the last column of the current line. 

Likewise, a program starting a search or replace operation 

in the middle of a document might be instructed to wrap 

around to the beginning rather than stop when it reaches 

the end of the document. 

wrapper n. In the Java programming language, an 

object that encapsulates and delegates to another object 

with the aim of altering its behavior or interface. See 

also Java, object. 

.wri n. The file format that identifies document files in the 

Microsoft Write format. 

wrist support n. A device placed in front of a computer 

keyboard to support the wrists in an ergonomically neutral 

position, thereby safeguarding against repetitive strain inju- 

575 

ries, such as carpal tunnel syndrome. Also called: wrist rest. 

See also carpal tunnel syndrome, repetitive strain injury. 

write1 n. A transfer of information to a storage device, 

such as a disk, or to an output device, such as a monitor or 

a printer. For example, a disk write means that information 

is transferred from memory to storage on disk. See also 

output1 . Compare read1 . 

write2 vb. To transfer information either to a storage 

device, such as a disk, or to an output device, such as a 

monitor or a printer. Writing is the means by which a computer 

provides the results of processing. A computer can 

also be said to write to the screen when it displays information 

on the monitor. See also output1 . Compare read1 . 

write access n. A privilege on a computer system that 

allows a user to save, change, or delete stored data. Write 

access is usually set by the system administrator for a networked 

or server system and by the owner of the computer 

for a stand-alone machine. See also access privileges. 

write-back cache n. A type of cache with the following 

feature: when changes are made to cached data, they are not 

simultaneously made to the original data as well. Instead, 

the changed data is marked, and the original data is updated 

when the cached data is deallocated. A write-back cache 

can perform more quickly than a write-through cache. But 

in some contexts, differences between cached and original 

data could lead to problems, and write-through caches must 

be used. See also cache. Compare write-through cache. 

write-behind cache n. A form of temporary storage in 

which data is held, or cached, for a short time in memory 

before being written on disk for permanent storage. Caching 

improves system performance in general by reducing 

the number of times the computer must go through the relatively 

slow process of reading from and writing to disk. 

See also CPU cache, disk cache. 

write cache n. See write-behind cache. 

write error n. An error encountered while a computer is 

in the process of transferring information from memory to 

storage or to another output device. Compare read error. 

write mode n. In computer operation, the state in which a 

program can write (record) information in a file. In write 

mode, the program is permitted to make changes to existing 

information. Compare read-only. 

write protect vb. To prevent the writing (recording) of 

information, usually on a disk. Either a floppy disk or an 

individual file on a floppy disk or a hard disk can be 

W

W 

write-protect notch WYSIWYG 

write protected (though not necessarily infallibly). See 

also write-protect notch. 

write-protect notch n. A small opening in the jacket of a 

floppy disk that can be used to make the disk unwritable. 

On a 5.25-inch floppy disk, the write-protect notch is a 

rectangular hole on the edge of the disk jacket. When this 

notch is covered, a computer can read from the disk but 

cannot record new information on it. On 3.5-inch microfloppy 

disks that are enclosed in plastic shells, the writeprotect 

notch is an opening in a corner. When the sliding 

tab in this opening is moved to uncover a small hole, the 

disk is protected and cannot be written to. Also called: 

write-protect tab. See also write2 . 

write-protect tab n. See write-protect notch. 

write-through cache n. A type of cache in which 

changes made to cached data are simultaneously made in 

the original copy, rather than being marked for later updating. 

A write-through cache, though not as fast as a writeback 

cache, is needed in situations where problems would 

occur if both the original and cached data did not match. 

Compare write-back cache. 

.wrl n. File extension required for saving all Virtual Reality 

Modeling Language (VRML) documents; for example, 

cube.wrl. See also VRML. 

WSDL n. Acronym for Web Services Description Language. 

An XML format developed to allow for better 

interoperability among Web services and development 

tools. WSDL describes network services as collections of 

communication endpoints capable of exchanging messages 

and is extensible to allow description of endpoints 

576 

and their messages regardless of what message formats or 

network protocols are used to communicate. 

WSS n. See Web Storage System. 

WTLS n. Acronym for Wireless Transport Layer Security. 

A security protocol that provides encryption and authentication 

services for the Wireless Application Protocol 

(WAP). The WTLS layer uses data integrity, authentication, 

and encryption mechanisms to provide end-to-end 

security and privacy for wireless transactions. WTLS is 

based on Transport Layer Security (TLS), a Secure Socket 

Layer equivalent used with Internet applications. See also 

Wireless Application Protocol. 

WWW n. See World Wide Web. 

WYSBYGI adj. Acronym for What You See Before You 

Get It. Providing a preview of the effects of the changes the 

user has selected before the changes are finally applied. For 

example, a dialog box in a word processing program might 

display a sample of the font a user has chosen before the 

font is actually changed in the document. The user can cancel 

any changes after previewing them, and the document 

will be unaffected. See also WYSIWYG. 

WYSIWYG adj. Acronym for What You See Is What You 

Get, pronounced “wizzywig.” Allowing a user to view a 

document as it will appear in the final product, and to 

directly edit the text, graphics, or other elements within 

that view. A WYSIWYG language is often easier to use 

than a markup language, which provides no immediate 

visual feedback regarding the changes being made. Compare 

markup language.

X10 n. A popular communications protocol for powerline 

carrier (PLC) systems that uses existing electrical wiring 

in a home or building for home networking. X10 uses RF 

signals to communicate between transmitters and receivers. 

See also home automation, home network, powerline 

carrier system. 

X.200 n. See X series. 

X.25 n. A recommendation published by the ITU-T (formerly 

CCITT) international communications standards 

organization that defines the connection between a terminal 

and a packet-switching network. X.25 incorporates 

three definitions: the electrical connection between the terminal 

and the network, the transmission or link-access 

protocol, and the implementation of virtual circuits 

between network users. Taken together, these definitions 

specify a synchronous, full-duplex terminal-to-network 

connection. Packet format, error control, and other features 

are equivalent to portions of the HDLC (High-level 

Data Link Control) protocol defined by the International 

Organization for Standardization (ISO). See also CCITT 

X series, HDLC, packet switching, virtual circuit. 

X3D n. Acronym for 3D XML. An XML-based 3-D 

graphics specification incorporating the behavior capabilities 

of the Virtual Reality Modeling Language (VRML). 

X3D is compatible with existing VRML content and tools 

and supports full integration with other XML-based technologies. 

The X3D specification was developed and 

administered by the Web 3D Consortium. 






x86 n. Any computer based on an 8086, 80286, 80386, 

80486, or Pentium microprocessor. 

x-axis n. The horizontal reference line on a grid, chart, or 

graph that has horizontal and vertical dimensions. See also 


X 

577 

Xbase n. A generic name for a family of database languages 

based on dBASE, a copyrighted product of the 

Ashton-Tate Corporation. Xbase languages have since 

developed characteristics of their own and are now only 

partly compatible with the dBASE family. Xbase primarily 

refers to three different file types (.dbf, .dbt, and 

.ndx). Also called: xBase, xbase, XBase. 

Xbox n. A video game console developed by Microsoft 

Corporation and released in 2001. Powered by an Intel 

733-MHz processor, the Xbox delivers increased graphics 

capability over previously released game consoles and 

provides extensive storage capacity for gaming information. 

Peripherals plug into four game controller ports. An 

Ethernet port enables online gaming via a broadband connection. 

See also computer game, console game, GameCube, 

PlayStation. Compare Dreamcast. 

X button n. See close button. 

XCMD n. Short for external command. An external code 

resource used in HyperCard, a hypermedia program developed 

for the Macintosh. See also HyperCard, XFCN. 

X Consortium n. The body, composed of several hardware 

firms, that governed the standards for the X Window 

System. The Open Group’s X Project Team now has 

responsibility for the X Window System. See also X 


xDSL n. An umbrella term for all of the digital subscriber 

line (DSL) technologies, which use a variety of modulation 

schemes to pack data onto copper wires. The x is a 

placeholder for the first or first two letters of a member 

technology, which might be ADSL, HDSL, IDSL, 

RADSL, or SDSL. See also DSL. 

XENIX n. A version of UNIX that was originally adapted 

by Microsoft for Intel-based personal computers. Although 

it has been sold by many vendors, including Microsoft, 

Intel, and the Santa Cruz Operation (SCO), it has become 

principally identified with SCO. See also UNIX. 

xerography n. See electrophotography. 

Xerox Network System n. See XNS. 

X

X 

Xerox PARC XML-RPC 

Xerox PARC n. Short for Xerox Palo Alto Research Center. 

Xerox’s research and development facility in Palo Alto, 

California. Xerox PARC is the birthplace of such innovations 

as the local area network (LAN), the laser printer, and 

the graphical user interface (GUI). 

XFCN n. Short for external function. An external code 

resource that returns a value after it has completed executing. 

XFCNs are used in HyperCard, a hypermedia program 

developed for the Macintosh. See also HyperCard, XCMD. 

XFDL n. Short for Extensible Forms Description Language, 

a document description language introduced and 

submitted to the World Wide Web Committee in 1998 by 

the Canadian Internet forms company UWI.Com. XFDL 

is an XML-based language for describing complex forms, 

such as legal and government documents. It is designed to 

allow for interactivity yet remain consistent with Internet 

standards. 

XGA n. See Extended Graphics Array. 

x-height n. In typography, the height of the lowercase 

letter x in a particular font. The x-height thus represents 

the height of the body only of a lowercase letter, excluding 

ascenders (such as the top of the letter b) and 

descenders (such as the tail on the letter g). See also 

ascender, descender. 

XHTML n. Short for Extensible Hypertext Markup Language. 

A markup language incorporating elements of 

HTML and XML. Web sites designed using XHTML can 

be more readily displayed on handheld computers and 

digital phones equipped with microbrowsers. XHTML 

was released for comments by the World Wide Web Consortium 

(W3C) in September 1999. See also HTML, 

microbrowser, XML. 

XIP n. See execute in place. 

XLANG n. A derivative XML language that describes the 

logical sequencing of business processes, as well as the 

implementation of the business process by using various 

application services. 

XLink n. An XML language that provides a set of 

attributes that are used to create links between resources. 

XLink provides complex extended linking, link behavior, 

and management capabilities. XLink is able to describe 

links that connect sets of resources, point to multiple targets, 

or serve multiple roles within an XML document. 

578 

XLL n. Acronym for eXtensible Linking Language. Broad 

term intended to denote the family of XML linking/pointing/ 

addressing languages, which include XLink, XPointer, and 

XPath. 

XMI n. 1. Acronym for XML Metadata Interchange Format. 

An object-based model for exchanging program data 

across the Internet. XMI is sponsored by IBM, Unisys, and 

others and was submitted as a proposed standard to the 

Object Management Group (OMG); it is now one of 

OMG’s recommended technologies. XMI is designed to 

allow for storing and sharing programming information 

and exchanging data among tools, applications, and storage 

locations through a network or the Internet so that software 

developers can collaborate on applications, even if they are 

not all using the same development tools. 2. As XMI bus, 

a 64-bit parallel bus supported on certain DEC and Alpha- 

Server processors. An XMI bus is capable of transferring 

data, exclusive of addressing overhead, at 100 Mbps. 

XML n. Acronym for eXtensible Markup Language, a 

condensed form of SGML (Standard Generalized Markup 

Language). XML lets Web developers and designers create 

customized tags that offer greater flexibility in organizing 

and presenting information than is possible with the 

older HTML document coding system. XML is defined as 

a language standard published by the W3C and supported 

by the industry. See also SGML. 

XML attribute n. Information added to a tag to provide 

more information about the tag, such as <ingredient 

quantity=“2”units=“cups”>flour</ingredient>. 

XML element n. Information delimited by a start tag 

and an end tag in an eXtensible Markup Language 

(XML) document. An example would be <Lastname> 

Davalio</LastName>. 

XML entities n. Combinations of characters and symbols 

that replace other characters when an XML document is 

parsed, usually those that have other meanings in XML. 

For example, < represents the < symbol, which 

is also the opening bracket for a tag. 

XML Metadata Interchange Format n. See XMI (definition 

1). 

XML-RPC n. Acronym for eXtensible Markup Language- 

Remote Procedure Call. A set of XML-based implementations 

that allows cross-platform and cross-programming 

language procedure calls over the Internet. XML-RPC

XML Schema XSD 

permits complex data structures to be transmitted, processed, 

and returned between different operating systems 

running in different environments. 

XML Schema n. A specification providing a common 

base for data description and validation in XML environments. 

XML schema replaces Document Type Definition 

(DTD) by defining a greater set of data types with more 

explicit data descriptions. XML schema has been developed 

as an open, vendor-neutral format to enhance information 

exchange and e-commerce over the Internet. It is 

also a standard for the description and encoding of data. 

XML Schema Description Language n. See XSDL. 

XML stylesheet n. Contains formatting rules that are 

applied to an XML file referencing the stylesheet. The 

standard set of rules for XML stylesheets is the Extensible 

Stylesheet Language (XSL). See also XSL. 

XML Web services n. Units of application logic providing 

data and services to other applications. Applications 

access XML Web services via standard Web protocols and 

data formats such as HTTP, XML, and SOAP, independent 

of how each XML Web service is implemented. XML 

Web services combine the best aspects of componentbased 

development and the Web and are a cornerstone of 

the Microsoft .NET programming model. 

Xmodem n. A file transfer protocol used in asynchronous 

communications that transfers information in blocks of 

128 bytes. 

Xmodem 1K n. A version of the Xmodem file transfer 

protocol designed for larger, longer-distance file transfers. 

Xmodem 1K transmits information in 1-kilobyte (1024byte) 

blocks and uses a more reliable form of error checking. 

See also Xmodem. 

Xmodem-CRC n. An enhanced version of the Xmodem 

file transfer protocol that incorporates a 2-byte cyclical 

redundancy check (CRC) to detect transmission errors. 

See also CRC. 

XMS n. See extended memory specification. 

XMT n. Short for transmit. A signal used in serial 


XNS n. Acronym for Xerox Network System. A set of 

protocols assigned to five numbered layers (0 through 4) 

that form a suite designed to handle packaging and delivery 

of network transmissions. 

579 

XON/XOFF n. An asynchronous communications protocol 

in which the receiving device or computer uses special 

characters to control the flow of data from the transmitting 

device or computer. When the receiving computer cannot 

continue to receive data, it transmits an XOFF control 

character that tells the sender to stop transmitting; when 

transmission can resume, the computer signals the sender 

with an XON character. Also called: software handshake. 

See also handshake. 

XOR n. See exclusive OR. 

XOR encryption n. Short for Exclusive-OR encryption. 

A simple encryption scheme using the “exclusive-or” concept, 

in which a decision is based on only one of two conditions 

being met. Using a provided key, XOR encryption 

performs an exclusive-or process on each byte of data to 

be encrypted. Because XOR encryption is not a strong 

security tool used alone, it is typically used as an additional 

level of security for Internet transmission of sensitive 

information. 

XPath n. An XML language for addressing items in an 

XML document by specifying a path through the document 

structure. XPath is used by XPointer and XSLT to 

locate and identify XML document data. XPath is also 

considered a query language complement to XQuery. 

XPath is more supported than XQuery even though there 

is no approved standard yet for either. See also XPointer. 

XPointer n. An XML language used to locate data within 

an XML document based on data property descriptions, 

such as attributes, location, and content. XPointer references 

the internal structure of a document, allowing links 

to be made to occurrences of a word, character set, content 

attribute, or other element, rather than to a specific point 

within the document. See also XPath. 

XQuery n. Short for eXtensible Query Language. 

Designed to be a functional query language that is broadly 

applicable to a variety of XML data types derived from 

Quilt, XPath, and XQL. Both Ipedo and Software AG 

implement their own versions of the W3C’s proposed 

specification for the XQuery language. Also called: XML 

Query, XQL. 

XSD n. Acronym for eXtensible Schema Definition. A 

prefix used by convention to indicate a W3C schema 

namespace. 

X

X 

XSDL X Window System 

XSDL n. Acronym for XML Schema Description Language. 

A World Wide Web Consortium (W3C) recommendation 

for representing XML structure. XSDL is 

capable of describing complex XML-based data structures, 

and provides options not available with Document Type 

Definitions (DTDs), including namespace support, XML 

datatypes, and improved extensibility and data type support. 

X series n. A set of recommendations adopted by the 

International Telecommunication Union Telecommunication 

Standardization Sector (ITU-T), formerly the CCITT, 

and International Organization for Standardization (ISO) 

for standardizing equipment and protocols used in both 

public access and private computer networks. See the table. 

Table X.1 Recommendations in X Series for Network 

Communications. 

Recommendation 

Number What It Covers 

X.25 Interface required to connect a computer 

to a packet-switched network 

such as the Internet 

X.75 Protocols for connecting two public 

data networks 

X.200 Seven-layer set of protocols known 

as the ISO/OSI reference model for 

standardizing computer-to-computer 

connections 

X.400 Format at the ISO/OSI application 

layer for e-mail messages over various 

network transports, including Ethernet, 

X.25, and TCP/IP. Gateways must 

be used to translate e-mail messages 

between the X.400 and Internet 

formats 

X.445 Asynchronous Protocol Specification, 

which governs the transmission of 

X.400 messages over dial-up telephone 

lines 

X.500 Protocols for client/server systems 

that maintain and access directories of 

users and resources in X.400 form 

X.509 Digital certificates 

XSL n. Acronym for Extensible Stylesheet Language. A 

World Wide Web Consortium (W3C) standard stylesheet 

580 

language for XML documents. XSL determines how data 

in an XML document is displayed on the Web. XSL controls 

what data will be displayed, in what format, and in 

what type size and style. XSL contains two major extensions: 

XSL Transformations (XSLT), a language used to 

convert XML documents to HTML or other document 

types, and XSL Formatting Objects (XSL-FO), a language 

for specifying formatting semantics. See also 

XSL-FO, XSLT. 

XSL-FO n. Acronym for Extensible Stylesheet Language 

Formatting Objects. An XML-based markup language for 

specifying formatting semantics. XSL-FO allows format 

and style information to be applied to an XML document 

and can be used with XSLT to produce source documents. 

See also XSL. 

XSLT n. Acronym for Extensible Stylesheet Language 

Transformations. A language used in transforming an existing 

XML document into a restructured XML document. 

Formalized as a W3C Recommendation in 1999, XSLT is 

primarily intended for use as part of XSL. XSL describes 

the styling of a document in terms of XSLT transformations 

into an XML document. See also XML, XSL. 

X terminal n. An intelligent display device, connected to 

an Ethernet network, that performs operations on request 

from client applications in an X Window System. See also 

Ethernet (definition 1), X Window System. 

XT keyboard n. See PC/XT keyboard. 

XUL n. A standards-based interface description language 

that provides a standard way to exchange data describing a 

program’s user interface. XUL balances simplicity, flexibility, 

and ease of use with precise layout control. XUL 

was developed by Netscape and Mozilla and is used with 

XML, CSS, DOM, and HTML. 

X Windows n. See X Window System. 

X Window System n. A nonproprietary standardized set 

of display-handling routines, developed at MIT. Most 

often encountered on UNIX workstations, the X Window 

System is independent of hardware and operating system. 

An X Window System client calls on the server, which is 

located on the user’s workstation, to provide a window in 

which the client can generate a display of text or graphics. 

Also called: X Windows. See also X Consortium.

X-Y display x-y-z coordinate system 

X-Y display n. See vector display. 

x-y matrix n. An arrangement of rows and columns with a 

horizontal (x) axis and a vertical (y) axis. 

x-y plotter n. See plotter. 

581 

x-y-z coordinate system n. A three-dimensional system 

of Cartesian coordinates that includes a third (z) axis running 

perpendicular to the horizontal (x) and vertical (y) 

axes. The x-y-z coordinate system is used in computer 

graphics for creating models with length, breadth, and 

depth. See the illustration. See also Cartesian coordinates. 

y 

z 

F0Xgn01.eps 

x-y-z coordinate system. 

x 

X

Y 

Y2K n. See Year 2000 problem. 

Y2K BIOS patch card n. An ISA board that ensures that 

system calls to the BIOS return the correct year. The BIOS 

patch card checks the date the BIOS gets from the real-time 

clock and sends the correct date to whichever application 

or process requested it. While a BIOS patch card proved 

effective for most situations once the year 2000 was 

reached, some applications and processes that work directly 

with the real-time clock (not an advisable practice) actually 

received the wrong date on non-Year-2000-compliant PCs. 

Y2K BIOS test n. See BIOS test. 

Y2K bug n. See Year 2000 problem. 

Y2K-compliant adj. See Year 2000 compliant. 

Y2K computer bug n. See Year 2000 problem. 

Y2K ready adj. See Year 2000 compliant. 

Yahoo! n. The first major online Web-based directory 

and search engine for Internet resources, which can be 

found at http://www.yahoo.com. See also search engine 


Yahoo! Mail n. A popular Web-based e-mail service provided 

for free by Yahoo! Inc. Compare Hotmail. 

Yahoo! Messenger n. A popular instant-messaging application 

provided for free by Yahoo! Inc. on a variety of operating 

systems. See also instant messaging. Compare AIM, 

ICQ, .NET Messenger Service. 

Yanoff list n. The informal name of the Internet services 

list created and maintained by Scott Yanoff. The Yanoff list 

was one of the earliest directories of Internet services and 

resources. It is located at http://www.spectracom.com/islist/. 

y-axis n. The vertical reference line on a grid, chart, or 

graph that has horizontal and vertical dimensions. See also 


YB n. See yottabyte. 

Year 2000 compliant adj. The criteria for this varied 

among companies and organizations; however, a general 

Y 

582 

theme was that software or hardware would make the transition 

from 1999 to 2000 without producing errors. For a 

PC, the general thinking was that if the real-time clock 

passed a Year 2000 BIOS test, it was Year 2000 compliant. 

However, testing the computing environment from end to 

end, considering the readiness of the operating systems, 

applications, custom code, data, and system interfaces, 

was also strongly recommended. 

Year 2000 Information and Readiness Disclosure Act 

n. A U.S. statute enacted in October 1998 that required 

U.S. companies to publicly disclose how they were 

attempting to make their systems or products ready for the 

year 2000. Many companies made this information available 

on the World Wide Web. 

Year 2000 problem n. Prior to January 1, 2000, a potential 

software problem stemming from the use of two digits 

(99) rather than four (1999) as year indicators in computer 

programs. Such programs assumed that 19 preceded every 

year value, and so could potentially fail or produce incorrect 

calculations by interpreting the year 2000 (00) as an 

earlier date than 19xx when the year rolled over into a new 

century. The use of two-digit year indicators was prevalent 

in, though not limited to, older programs that had been 

written when a saving of two bytes (digits) per year value 

was significant in terms of computer memory. Because the 

use of two-digit year indicators was widespread, companies, 

governments, and other organizations took measures 

on a large scale to prevent the Year 2000 problem from 

affecting their computing systems. In the end, however, 

the problem—luckily—proved largely uneventful. 

Year 2000 ready adj. See Year 2000 compliant. 

Year 2000 rollover n. The moment when the year in a 

computer system changed from 1999 to 2000. Also 

called: date rollover, millennium transition, rollover, Year 

2000 transition. 

Year 2000 time problem n. See Year 2000 problem. 

Year 2000 transition n. See Year 2000 rollover.

Yellow Pages YYYY 

Yellow Pages n. 1. The former name of a UNIX utility, 

provided by SunSoft (Sun Microsystems system software), 

that maintains a central database of names and 

locations of the resources on a network. The Yellow Pages 

enables processes on any node to locate resources by 

name. This utility is now known formally as NIS (Network 

Information Service). 2. InterNIC Registration Services’ 

database of domain names and their IP addresses. 

See also domain name, IP address. 3. Any of several Internet 

business directory services. Some are print publications, 

some are strictly electronic, and some are both. 

Yes/No data type n. A data type used to define database 

fields that will contain only one of two values, such as Yes 

or No and True or False. Null values are not allowed. See 

also boolean. 

Yettie n. Short for Young, Entrepreneurial Tech-based 

Twenty-something or Young, Entrepreneurial Technocrat. 

A person who works in a technology or Internet-related 

field and who embraces technological change and opportunity. 

Yettie is intended to be a successor to the older term 

“yuppie.” 

YHBT n. Acronym for you have been trolled. An expression 

used in e-mail and newsgroups to indicate that the 

receiver has taken a deliberately set bait. See also troll. 

YHL n. Acronym for you have lost. An expression used in 

e-mail and newsgroups, often following YHBT. See also 

YHBT. 

Ymodem n. A variation of the Xmodem file transfer protocol 

that includes the following enhancements: the ability 

to transfer information in 1-kilobyte (1024-byte) blocks, 

the ability to send multiple files (batch file transmission), 

cyclical redundancy checking (CRC), and the ability to 

abort transfer by transmitting two CAN (cancel) characters 

in a row. See also CRC, Xmodem. 

yocto- prefix A metric prefix meaning 10 –24 (one septillionth 

in the U.S. system). 

yoke n. The part of a CRT (cathode-ray tube) that deflects 

the electron beam, causing it to strike a specific area on 

the screen. Also called: deflection coils. See also CRT. 

yotta- prefix A metric prefix meaning 1024 (one septillion 

in the U.S. system). 

yottabyte n. A unit of measure equal to 280 bytes, or 

approximately 1 septillion (1024 ) bytes. When calculated as 

a multiple of 1000 zettabytes (the next highest unit of measure), 

a yottabyte is 1,000,000,000,000,000,000,000,000 

bytes; when calculated as 1024 zettabytes, a yottabyte is 

1,208,925,819,614,629,174,706,176 bytes. The prefix 

yotta- is meant to sound like the Greek letter iota. 

Abbreviation: YB. 

YY n. The form in which the year part of a date is stored in 

some, mostly older, computer systems. Before 2000, the 

possibility existed that computers that used a 2-digit date 

would incorrectly interpret the year 2000 (year 00) as the 

year 1900 and disrupt the computer’s operation. 

YYYY n. Symbolic of providing fully distinguished dates, 

including 4-digit years. Using 4-digit years was an important 

step in many Year 2000 remediation programs—especially 

those focused on data. 

583 Y

Z 

.z n. The file extension identifying a UNIX file compressed 

using the gzip or compact utility. See also gzip. 

.Z n. The file extension for UNIX files that have been 

compressed using the compress utility. See also 

compress1 . 

Z39.50 standard n. A specification for a query language 

based on SQL (structured query language). It is used by 

WAIS, among other Internet services, to search for files 

through the use of keywords and is widely used for remote 

access to library catalogs. See also structured query language, 

WAIS. 

Z80 n. An 8-bit microprocessor from Zilog, a company 

founded by former Intel engineers. The Z80 has a 16-bit 

address bus, yielding a 64-kilobyte addressable memory 

space, and an 8-bit data bus. A descendant of the Intel 

8080, it was the favored processor in the days of the CP/M 

operating system. One of the most popular computers of 

the early 1980s, the Radio Shack TRS-80, was based on 

this chip. See also CP/M. 

zap vb. 1. To erase permanently. For example, to zap a file 

means to remove it without hope of retrieval. 2. To damage 

a device, usually by discharging static electricity 

through it. 

z-axis n. The third axis in a three-dimensional coordinate 

system, used in computer graphics to represent depth. See 

also Cartesian coordinates, x-y-z coordinate system. 

ZB n. See zettabyte. 

zepto- prefix A metric prefix meaning 10 –21 (one sextillionth 

in the American system). 

zero1 n. The arithmetic symbol (0) representing no 

magnitude. 

Z 

584 

zero2 vb. To fill or replace with zeros (for example, to 

zero a specified portion of memory, a field, or some other 

limited structure). 

zero divide n. A division operation in which the divisor is 

zero. Division by zero is mathematically undefined, is not 

allowed in a program, and is considered a bug. 

zero flag n. A flag (bit) in a microprocessor that is set 

(turned on), typically in a flag register, when the result of 

an operation is zero. See also flag (definition 1). 

zero-insertion-force socket n. See ZIF socket. 

zero-length string n. A string that contains no characters. 

You can use a zero-length string to indicate that you know 

there’s no value for a field. You enter a zero-length string 

by typing two double quotation marks with no space 

between them (""). 

zero out vb. To set a variable value or a series of bits to zero. 

zero suppression n. The elimination of leading (nonsignificant) 

zeros in a number. For example, zero suppression 

would truncate 000123.456 to 123.456. See also significant 

digits. 

zero wait state n. The condition of random access memory 

(RAM) that is fast enough to respond to the processor 

without requiring wait states. See also wait state. 

zetta- prefix A metric prefix meaning 1021 (one sextillion 

in the American system). 

zettabyte n. A unit of measure equal to 270 bytes, or one 

sextillion (1021 ) bytes. When calculated as a multiple of 1000 

exabytes (the next highest unit of measure), a zettabyte is 

1,000,000,000,000,000,000,000 bytes; when calculated as 

1024 exabytes, a zettabyte is 1,180,591,620,717,411,303,424

z-fold paper Zip drive 

bytes. The prefix (zetta-) is meant to sound like the Greek letter 

zeta. Abbreviation: ZB. 

z-fold paper n. See fanfold paper. 

ZIF socket n. Short for zero-insertion-force socket. A 

kind of socket for integrated circuits that can be opened 

with a lever or screw, allowing the chip to be placed in the 

socket without the application of pressure. The lever or 

screw of the socket is then closed, causing the socket contacts 

to grip the chip’s pins. ZIF sockets facilitate frequent 

insertion and removal of chips, but they take up more 

space and are more expensive than conventional sockets. 

F0Zgn01.eps 

Zip drive. 

585 

zinc-air battery n. Non rechargeable battery that is relatively 

inexpensive, offers extended battery life, and contains 

none of the harsh chemicals or metals found in 

conventional nickel metal cadmium (NiCad), nickel metal 

hydride (NiMH), or lithium ion (Li-ion) batteries. 

.zip n. A file extension that identifies a compressed 

archive file encoded in ZIP format, as by PKZIP. See also 

compressed file, PKZIP. 

Zip drive n. A disk drive developed by Iomega that uses 

3.5-inch removable disks (Zip disks) capable of storing 100 

megabytes of data. See the illustration. See also disk drive. 

Z

Z 

Zmodem ZV port 

Zmodem n. An enhancement of the Xmodem file transfer 

protocol that handles larger data transfers with less error. 

Zmodem includes a feature called checkpoint restart, 

which resumes transmission at the point of interruption, 

rather than at the beginning, if the communications link is 

broken during data transfer. See also Xmodem. 

zombie n. A computer that has become the unwilling host 

of a DDoS (distributed denial of services) attack program 

and that is controlled by remote signals from the attacker. 

To create a zombie, a hacker utilizes security vulnerabilities 

to crack a Web, mail, news, or application server and 

plant hidden DDoS tools such as Trinoo and Tribal Flood 

Network. Later, at a signal from the attacker, the server 

becomes a zombie that will participate in a coordinated 

attack on other servers. See also DDoS, hacker. 

zone n. 1. On a LAN (local area network), a subgroup of 

users within a larger group of interconnected networks. 

2. In Macintosh programming, a portion of memory that is 

allocated and reallocated by the memory manager facility 

as memory is requested and released by applications and 

by other parts of the operating system. See also heap (definition 

1). 

zone header n. On the Apple Macintosh, a header at the 

beginning of a block of memory that contains information 

needed by the memory management facility in order to use 

that memory block effectively. See also header (definition 2). 

zone transfer n. The process whereby a secondary DNS 

server obtains information about a zone or domain from 

the primary server. See also zone (definition 1). 

.zoo n. The file extension that identifies compressed 

archive files created with the zoo file compression utility. 

See also zoo210. 

zoo210 n. Version 2.1 of zoo, a program for creating 

compressed archive files (whose names have the extension 

.zoo). The algorithm for zoo210 is based on that of 

LHARC. Implementations of zoo210 are available for 

UNIX and Intel systems. See also archive file, LHARC. 

zoom vb. To enlarge a selected portion of a graphical 

image or document to fill a window or the screen. Zooming 

is a feature of many programs, including drawing, 

586 

word processing, and spreadsheet programs, that allows 

the user to select a small part of the screen, zoom it, and 

make changes to the enlarged portion at a finer level of 

detail. See also window. 

zoom box n. A control in the upper right corner of the 

frame of a window on the Macintosh screen. When the 

user clicks on the zoom box, the window toggles between 

the maximum size and the size the user has set for it by 

dragging. See also window. Compare Maximize button. 

zoomed video port n. See ZV port. 

zoo virus n. A virus that is kept in an isolated environment 

for the benefit of anti-virus research and training. 

Zoo viruses are not found outside the labs of anti-virus 

companies. 

Zope n. An open source application server for publishing 

objects on the Internet. Zope provides tools to integrate 

data and content from multiple sources into complete Web 

applications and can be used in conjunction with XML- 

RPC to form a system for remotely scriptable Web objects. 

Zope runs on UNIX, Windows NT and later, and most 

other major operating systems. See also XML-RPC. 

z-order n. 1. The order in which objects are drawn on top 

of one another onscreen to simulate depth (the third dimension) 

in conjunction with the x and y (height and width) 

coordinates. 2. The visual layering of windows or controls 

on a form along the z-axis (depth). The z-order determines 

which controls are in front of other controls. Each window 

or control has a unique position in the z-order. 

Zulu time n. Slang for Greenwich Mean Time. 

ZV port n. Short for zoomed video port. Port available on 

many portable computers as an inexpensive multimedia 

alternative to traditional video input. The ZV port allows 

data to flow uninterrupted from source to destination without 

need for buffering. Zoomed video was adopted by the 

Personal Computer Memory Card International Association 

(PCMCIA) to enable high transfer rates for portable 

computers, connected video cameras, and other multimedia 

devices.

ANSI Character Set 

Character 

Appendix endix A 

Common Character Sets 

Unicode Value 

(Hex) 

ANSI code 

(decimal) Description 

NUL 0000 0 Null 

SOH 0001 1 Start of heading 

STX 0002 2 Start of text 

ETX 0003 3 End of text 

EOT 0004 4 End of transmission 

ENQ 0005 5 Enquiry 

ACK 0006 6 Acknowledge 

BEL 0007 7 Bell 

BS 0008 8 Backspace 

HT 0009 9 Horizontal tabulation 

LF 000A 10 Line feed 

VT 000B 11 Vertical tabulation 

FF 000C 12 Form feed 

CR 000D 13 Carriage return 

SO 000E 14 Shift out 

SI 000F 15 Shift in 

DLE 0010 16 Data link escape 

DC1 0011 17 Device control 1 




NAK 0015 21 Negative acknowledge 

SYN 0016 22 Synchronous idle 

ETB 0017 23 End of transmission block 

CAN 0018 24 Cancel 

EM 0019 25 End of medium 

SUB 001A 26 Substitute 

ESC 001B 27 Escape 

FS 001C 28 File separator 

GS 001D 29 Group separator 

RS 001E 30 Record separator 

US 001F 31 Unit separator 

SP 0020 32 Space 

! 0021 33 Exclamation point 

" 0022 34 Quotation mark 

587

Appendix A: Common Character Sets 

ANSI Character Set continued 

Character 

Unicode Value 

(Hex) 

ANSI code 


# 0023 35 Number sign 

$ 0024 36 Dollar sign 

% 0025 37 Percent 

& 0026 38 Ampersand 

‘ 0027 39 Apostrophe 

( 0028 40 Left parenthesis 

) 0029 41 Right parenthesis 

* 002A 42 Asterisk 

+ 002B 43 Plus sign 

, 002C 44 Comma 

- 002D 45 Hyphen 

. 002E 46 Full stop 

/ 002F 47 Solidus 

0 0030 48 Digit zero 

1 0031 49 Digit one 

2 0032 50 Digit two 

3 0033 51 Digit three 

4 0034 52 Digit four 

5 0035 53 Digit five 

6 0036 54 Digit six 

7 0037 55 Digit seven 

8 0038 56 Digit eight 

9 0039 57 Digit nine 

: 003A 58 Colon 

; 003B 59 Semicolon 

< 003C 60 Less-than sign 

= 003D 61 Equals sign 

> 003E 62 Greater-than sign 

? 003F 63 Question mark 

@ 0040 64 Commercial at 

A 0041 65 Latin capital letter A 

B 0042 66 Latin capital letter B 

C 0043 67 Latin capital letter C 

D 0044 68 Latin capital letter D 

E 0045 69 Latin capital letter E 

F 0046 70 Latin capital letter F 

G 0047 71 Latin capital letter G 

H 0048 72 Latin capital letter H 

I 0049 73 Latin capital letter I 

J 004A 74 Latin capital letter J 

K 004B 75 Latin capital letter K 

L 004C 76 Latin capital letter L 

M 004D 77 Latin capital letter M 

N 004E 78 Latin capital letter N 

O 004F 79 Latin capital letter O 

588


Character 

Unicode Value 

(Hex) 

ANSI code 


P 0050 80 Latin capital letter P 

Q 0051 81 Latin capital letter Q 

R 0052 82 Latin capital letter R 

S 0053 83 Latin capital letter S 

T 0054 84 Latin capital letter T 

U 0055 85 Latin capital letter U 

V 0056 86 Latin capital letter V 

W 0057 87 Latin capital letter W 

X 0058 88 Latin capital letter X 

Y 0059 89 Latin capital letter Y 

Z 005A 90 Latin capital letter Z 

[ 005B 91 Left square bracket 

\ 005C 92 Reverse solidus 

] 005D 93 Right square bracket 

^ 005E 94 Circumflex accent 

_ 005F 95 Low line 

` 0060 96 Grave accent 

a 0061 97 Latin small letter a 

b 0062 98 Latin small letter b 

c 0063 99 Latin small letter c 

d 0064 100 Latin small letter d 

e 0065 101 Latin small letter e 

f 0066 102 Latin small letter f 

g 0067 103 Latin small letter g 

h 0068 104 Latin small letter h 

i 0069 105 Latin small letter i 

j 006A 106 Latin small letter j 

k 006B 107 Latin small letter k 

l 006C 108 Latin small letter l 

m 006D 109 Latin small letter m 

n 006E 110 Latin small letter n 

o 006F 111 Latin small letter o 

p 0070 112 Latin small letter p 

q 0071 113 Latin small letter q 

r 0072 114 Latin small letter r 

s 0073 115 Latin small letter s 

t 0074 116 Latin small letter t 

u 0075 117 Latin small letter u 

v 0076 118 Latin small letter v 

w 0077 119 Latin small letter w 

x 0078 120 Latin small letter x 

y 0079 121 Latin small letter y 

z 007A 122 Latin small letter z 

{ 007B 123 Left curly bracket 

| 007C 124 Vertical line 

589 

Appendix A: Common Character Sets



Character 

Unicode Value 

(Hex) 

ANSI code 


} 007D 125 Right curly bracket 

~ 007E 126 Tilde 

DEL 007F 127 Delete 

0080 128 Reserved 




IND 0084 132 Index 

NEL 0085 133 Next line 

SSA 0086 134 Start of selected area 

ESA 0087 135 End of selected area 

0088 136 Character tabulation set 

0089 137 Character tabulation with justification 

008A 138 Line tabulation set 

PLD 008B 139 Partial line down 

PLU 008C 140 Partial line up 

008D 141 Reverse line feed 

SS2 008E 142 Single shift two 

SS3 008F 143 Single shift three 

DCS 0090 144 Device control string 

PU1 0091 145 Private use one 

PU2 0092 146 Private use two 

STS 0093 147 Set transmit state 

CCH 0094 148 Cancel character 

MW 0095 149 Message waiting 

0096 150 Start of guarded area 

0097 151 End of guarded area 

0098 152 Start of string 


009A 154 Single character introducer 

CSI 009B 155 Control sequence introducer 

ST 009C 156 String terminator 

OSC 009D 157 Operating system command 

PM 009E 158 Privacy message 

APC 009F 158 Application program command 

00A0 160 No-break space 

¡ 00A1 161 Inverted exclamation mark 

¢ 00A2 162 Cent sign 

£ 00A3 163 Pound sign 

¤ 00A4 164 Currency sign 

¥ 00A5 165 Yen sign 

¦ 00A6 166 Broken bar 

§ 00A7 167 Section sign 

¨ 00A8 168 Diaeresis 

590


Character 

Unicode Value 

(Hex) 

ANSI code 


591 


© 00A9 169 Copyright sign 

ª 00AA 170 Feminine ordinal indicator 

« 00AB 171 Left-pointing double angle quotation mark 

¬ 00AC 172 Not sign 

- 00AD 173 Soft hyphen 

® 00AE 174 Registered sign 

¯ 00AF 175 Macron 

° 00B0 176 Degree sign 

± 00B1 177 Plus-minus sign 

² 00B2 178 Superscript two 

³ 00B3 179 Superscript three 

´ 00B4 180 Acute accent 

µ 00B5 181 Micro sign 

00B6 182 Pilcrow sign 

· 00B7 183 Middle dot 

¸ 00B8 184 Cedilla 

¹ 00B9 185 Superscript one 

º 00BA 186 Masculine ordinal indicator 

» 00BB 187 Right-pointing double angle quotation mark 

¼ 00BC 188 Vulgar fraction one quarter 

½ 00BD 189 Vulgar fraction one half 

¾ 00BE 190 Vulgar fraction three quarters 

¿ 00BF 191 Inverted question mark 

À 00C0 192 Latin capital letter A with grave 

Á 00C1 193 Latin capital letter A with acute 

Â 00C2 194 Latin capital letter A with circumflex 

Ã 00C3 195 Latin capital letter A with tilde 

Ä 00C4 196 Latin capital letter A with diaeresis 

Å 00C5 197 Latin capital letter A with ring above 

Æ 00C6 198 Latin capital ligature AE 

Ç 00C7 199 Latin capital letter C with cedilla 

È 00C8 200 Latin capital letter E with grave 

É 00C9 201 Latin capital letter E with acute 

Ê 00CA 202 Latin capital letter E with circumflex 

Ë 00CB 203 Latin capital letter E with diaeresis 

Ì 00CC 204 Latin capital letter I with grave 

Í 00CD 205 Latin capital letter I with acute 

Î 00CE 206 Latin capital letter I with circumflex 

Ï 00CF 207 Latin capital letter I with diaeresis 

Ð 00D0 208 Latin capital letter ETH 

Ñ 00D1 209 Latin capital letter N with tilde 

Ò 00D2 210 Latin capital letter O with grave 

Ó 00D3 211 Latin capital letter O with acute 

Ô 00D4 212 Latin capital letter O with circumflex



Character 

Unicode Value 

(Hex) 

ANSI code 


Õ 00D5 213 Latin capital letter O with tilde 

Ö 00D6 214 Latin capital letter O with diaeresis 

× 00D7 215 Multiplication sign 

Ø 00D8 216 Latin capital letter O with stroke 

Ù 00D9 217 Latin capital letter U with grave 

Ú 00DA 218 Latin capital letter U with acute 

Û 00DB 219 Latin capital letter U with circumflex 

Ü 00DC 220 Latin capital letter U with diaeresis 

Ý 00DD 221 Latin capital letter Y with acute 

Þ 00DE 222 Latin capital letter thorn 

ß 00DF 223 Latin small letter sharp s 

à 00E0 224 Latin small letter a with grave 

á 00E1 225 Latin small letter a with acute 

â 00E2 226 Latin small letter a with circumflex 

ã 00E3 227 Latin small letter a with tilde 

ä 00E4 228 Latin small letter a with diaeresis 

å 00E5 229 Latin small letter a with ring above 

æ 00E6 230 Latin small ligature ae 

ç 00E7 231 Latin small letter c with cedilla 

è 00E8 232 Latin small letter e with grave 

é 00E9 233 Latin small letter e with acute 

ê 00EA 234 Latin small letter e with circumflex 

ë 00EB 235 Latin small letter e with diaeresis 

ì 00EC 236 Latin small letter i with grave 

í 00ED 237 Latin small letter i with acute 

î 00EE 238 Latin small letter i with circumflex 

ï 00EF 239 Latin small letter i with diaeresis 

ð 00F0 240 Latin small letter eth 

ñ 00F1 241 Latin small letter n with tilde 

ò 00F2 242 Latin small letter o with grave 

ó 00F3 243 Latin small letter o with acute 

ô 00F4 244 Latin small letter o with circumflex 

õ 00F5 245 Latin small letter o with tilde 

ö 00F6 246 Latin small letter o with diaeresis 

÷ 00F7 247 Division sign 

ø 00F8 248 Latin small letter o with stroke 

ù 00F9 249 Latin small letter u with grave 

ú 00FA 250 Latin small letter u with acute 

û 00FB 251 Latin small letter u with circumflex 

ü 00FC 252 Latin small letter u with diaeresis 

ý 00FD 253 Latin small letter y with acute 

þ 00FE 254 Latin small letter thorn 

ÿ 00FF 255 Latin small letter y with diaeresis 

592

Apple Macintosh Extended Character Set 

APPA3.eps 

593 


Zapf 

ASCII Hex Times New York Courier Dingbats Symbol


Apple Macintosh Extended Character Set continued 

Zapf 

ASCII Hex Times New York Courier Dingbats Symbol 

APPA4.eps 

594


APPA5.eps 

595 


Zapf 

ASCII Hex Times New York Courier Dingbats Symbol



Zapf 

ASCII Hex Times New York Courier Dingbats Symbol 

APPA6.eps 

596

IBM Extended Character Set 

APPA7.eps 

597 


Dec Hex Char Dec Hex Char Dec Hex Char Dec Hex Char


IBM Extended Character Set continued 

Dec Hex Char Dec Hex Char Dec Hex Char Dec Hex Char 

APPA8.eps 

598

EBCDIC Character Set 

599 


Dec Hex Name Character Meaning 

0 00 NUL Null 

1 01 SOH Start of heading 

2 02 STX Start of text 

3 03 ETX End of text 

4 04 SEL Select 

5 05 HT Horizontal tab 

6 06 RNL Required new line 

7 07 DEL Delete 

8 08 GE Graphic escape 

9 09 SPS Superscript 

10 0A RPT Repeat 

11 0B VT Vertical tab 

12 0C FF Form feed 

13 0D CR Carriage return 

14 0E SO Shift out 

15 0F SI Shift in 

16 10 DLE Data length escape 

17 11 DC1 Device control 1 



20 14 RES/ENP Restore/enable presentation 

21 15 NL New line 

22 16 BS Backspace 

23 17 POC Program-operator communication 

24 18 CAN Cancel 

25 19 EM End of medium 

26 1A UBS Unit backspace 

27 1B CU1 Customer use 1 

28 1C IFS Interchange file separator 

29 1D IGS Interchange group separator 

30 1E IRS Interchange record separator 

31 1F IUS/ITB Interchange unit separator/intermediate transmission 

block 

32 20 DS Digit select 

33 21 SOS Start of significance 

34 22 FS Field separator 

35 23 WUS Word underscore 

36 24 BYP/INP Bypass/inhibit presentation 

37 25 LF Line feed 

38 26 ETB End of transmission block 

39 27 ESC Escape 

40 28 SA Set attribute 

41 29 SFE Start field extended


EBCDIC Character Set continued 


42 2A SM/SW Set mode/switch 

43 2B CSP Control sequence prefix 

44 2C MFA Modify field attribute 

45 2D ENQ Enquiry 

46 2E ACK Acknowledge 

47 2F BEL Bell 

48 30 (not assigned) 


50 32 SYN Synchronous idle 

51 33 IR Index return 

52 34 PP Presentation position 

53 35 TRN Transparent 

54 36 NBS Numeric backspace 

55 37 EOT End of transmission 

56 38 SBS Subscript 

57 39 IT Indent tab 

58 3A RFF Required form feed 

59 3B CU3 Customer use 3 

60 3C DC4 Device control 4 

61 3D NAK Negative acknowledge 

62 3E (not assigned) 

63 3F SUB Substitute 

64 40 SP Space 

65 41 RSP Required space 









74 4A ¢ 

75 4B . 

76 4C < 

77 4D ( 

78 4E + 

79 4F | Logical OR 

80 50 & 







600






90 5A ! 

91 5B $ 

92 5C * 

93 5D ) 

94 5E ; 

95 5F ¬ Logical NOT 

96 60 – 

97 61 / 









106 6A ¦ Broken pipe 

107 6B , 

108 6C % 

109 6D _ 

110 6E > 

111 6F ? 










121 79 ` Grave accent 

122 7A : 

123 7B # 

124 7C @ 

125 7D ' 

126 7E = 

127 7F " 


129 81 a 

130 82 b 

131 83 c 

601 





132 84 d 

133 85 e 

134 86 f 

135 87 g 

136 88 h 

137 89 i 

138 8A (not assigned) 

139 8B (not assigned) 

140 8C (not assigned) 

141 8D (not assigned) 


143 8F (not assigned) 


145 91 j 

146 92 k 

147 93 l 

148 94 m 

149 95 n 

150 96 o 

151 97 p 

152 98 q 

153 99 r 

154 9A (not assigned) 

155 9B (not assigned) 

156 9C (not assigned) 

157 9D (not assigned) 


159 9F (not assigned) 

160 A0 (not assigned) 

161 A1 ~ 

162 A2 s 

163 A3 t 

164 A4 u 

165 A5 v 

166 A6 w 

167 A7 x 

168 A8 y 

169 A9 z 

170 AA (not assigned) 

171 AB (not assigned) 

172 AC (not assigned) 

173 AD (not assigned) 

174 AE (not assigned) 

175 AF (not assigned) 

602



176 B0 (not assigned) 










186 BA (not assigned) 

187 BB (not assigned) 

188 BC (not assigned) 

189 BD (not assigned) 

190 BE (not assigned) 

191 BF (not assigned) 

192 C0 { Opening brace 

193 C1 A 

194 C2 B 

195 C3 C 

196 C4 D 

197 C5 E 

198 C6 F 

199 C7 G 

200 C8 H 

201 C9 I 

202 CA SHY Syllable hyphen 

203 CB (not assigned) 

204 CC (not assigned) 

205 CD (not assigned) 

206 CE (not assigned) 

207 CF (not assigned) 

208 D0 } Closing brace 

209 D1 J 

210 D2 K 

211 D3 L 

212 D4 M 

213 D5 N 

214 D6 O 

215 D7 P 

216 D8 Q 

217 D9 R 

218 DA (not assigned) 

219 DB (not assigned) 

603 





220 DC (not assigned) 

221 DD (not assigned) 

222 DE (not assigned) 

223 DF (not assigned) 

224 E0 \ Reverse slash 

225 E1 NSP Numeric space 

226 E2 S 

227 E3 T 

228 E4 U 

229 E5 V 

230 E6 W 

231 E7 X 

232 E8 Y 

233 E9 Z 

234 EA (not assigned) 

235 EB (not assigned) 

236 EC (not assigned) 

237 ED (not assigned) 

238 EE (not assigned) 

239 EF (not assigned) 

240 F0 0 

241 F1 1 

242 F2 2 

243 F3 3 

244 F4 4 

245 F5 5 

246 F6 6 

247 F7 7 

248 F8 8 

249 F9 9 

250 FA (not assigned) 

251 FB (not assigned) 

252 FC (not assigned) 

253 FD (not assigned) 

254 FE (not assigned) 

255 FF EO Eight ones 

604

Common File Extensions 

Appendix B 

File Extension Type of File 

.0 File containing information on hard disk compressed with DoubleSpace. 

.123 Spreadsheet file in Lotus 123. 

.4th Source file in Forth. 

.a Source file in Macintosh Assembly. 

.ad Screensaver file in After Dark. 

.ada Source file in Ada. 

.ai Vector graphic file in Adobe Illustrator. 

.aif See .aiff. 

.aifc See .aiff. 

.aiff Audio file in the Apple Audio Interchange Format originally used on Apple and Silicon Graphics 

(SGI) computers. 

.ani 1. Animated cursor file in Microsoft Windows 9x and Windows NT. 

2. Animation file. 

.aol File related to America Online. 

.aps Source file in Microsoft Visual C++. 

.arc Archive file compressed with ARC. 

.arj Archive file compressed with ARJ. 

.asc 1. ASCII text file. 

2. File encrypted with PGP (Pretty Good Privacy). 

.asf File in Microsoft Advanced Streaming Format. 

.asm Source file in Assembler. 

.asp File in Active Server Page format, generally found on the World Wide Web. 

.atm File in Adobe Type Manager. 

.au Sound file, generally on UNIX systems or the World Wide Web. 

.avi Audio visual interleaved data file in the Microsoft RIFF format. 

.bac See .bak. 

.bak Backup file. 

.bas Source file in Basic. 

.bat Batch program file. 

.bfc Briefcase file in Microsoft Windows 9x. 

.bin 1. Archive file compressed with MacBinary. 

2. Binary file. 

.bk See .bak. 

605

Appendix B: Common File Extensions 

Common File Extensions continued 


.bmk Bookmarked file. 

.bmp Raster graphics file stored in bitmap format. 

.box Mailbox file in Lotus Notes. 

.c Source file in C. 

.c++ Source file in C++. 

.cab Microsoft cabinet file—multiple files compressed into one and extractable with the extract.exe 

utility. 

.cas Comma-delimited ASCII text file. 

.cb Clean boot file in Microsoft Windows. 

.cbl Source file in Cobol. 

.cca E-mail message in Lotus cc:mail. 

.cda CD audio track. 

.cdf 1. File in Microsoft Channel Definition Format. 

2. File in Common Data Format. 

.cdi File in Phillips Compact Disk Interactive format. 

.cdr Vector graphics file in CorelDraw. 

.cgi File containing Common Gateway Interface scripts, generally for use on the World Wide Web. 

.cgm Vector graphics file in Computer Graphics Metafile format. 

.chk Portions of unidentifiable files saved in Windows by the Disk Defragmentor or ScanDisk utilities. 

.chm File containing compiled HTML. 

.cil Microsoft Clip Gallery download package. 

.class Class file in Java. 

.clp Temporary file created by Microsoft Windows Clipboard utility. 

.cmd Command file in Windows NT, OS/2, MS-DOS, and CP/M. 

.cmf File in Corel Metafile. 

.cob Source file in Cobol. 

.com Command file or program. 

.cpl Control Panel file in Microsoft Windows 9x. 

.cpp Source file in C++. 

.crt Certificate file. 

.css Cascading Style Sheet file, generally used in conjunction with Web sites. 

.csv Comma-delimited text file. 

.ct Graphics file in Paint Shop Pro. 

.cur Cursor file in Windows. 

.cxx Source file in C++. 

.dat Data file. 

.dbf Database in dBASE and FoxPro. 

.dcr Multimedia file in Macromedia Shockwave. 

.dib Graphics file in Device Independent Bitmap format. 

.dif File in Data Interchange Format. 

.dll Dynamic-link library file. 

606



.doc 1. Document file in Microsoft Word. 

2. In the past, document file in Adobe FrameMaker or WordStar. 

3. Document file formatted for a word processor. 

.dos MS-DOS–related files in Microsoft Windows 9x. 

.dot Document template in Microsoft Word. 

.drv Device driver. 

.dtd Document Type Definition file in SGML or XML. 

.dtp Document file in Microsoft Publisher or PublishIt! 

.dv Video file. 

.dvi Document file in TEX Device Independent File format. 

.emf File in Enhanced Windows Metafile format. 

.eml Mail message in Microsoft Outlook Express. 

.eps Encapsulated PostScript file. 

.exe Executable program or file. 

.F Source file in Fortran. 

.F77 Source file in Fortran 77. 

.F90 Source file in Fortran 90. 

.fax Fax file in many Fax programs. 

.fdf File in Adobe Acrobat Forms. 

.fla Movie file in Macromedia Flash. 

.fli Animation file in AutoDesk FLIC file. 

.flf Device driver in OS/2. 

.fm Document file in Adobe FrameMaker. 

.fon System font file in Windows. 

.for Source file in Fortran. 

.fp File in FileMaker Pro. 

.fpt See .fp. 

.frm Document file in Adobe FrameMaker. 

.gid Index file in Windows 9x. 

.gif Raster image file in GIF format. 

.giff See .gif. 

.gtar UNIX archive file compressed in GNU tar utility. 

.gz UNIX archive file compressed by gzip. 

.gzip See .gz. 

.h Header file. 

.hdf File in Hierarchical Data Format. 

.hex File encoded with Macintosh BinHex utility. 

.hlp Help file in Microsoft Windows. 

.hqx File encoded with BinHex utility. 

.htm See .html. 

.html HTML file, most commonly used as a Web page. 

607 

Appendix B: Common File Extensions




.ico Icon file in Microsoft Windows 9x. 

.iff 1. Image or sound file in IFF format. 

2. Data file on Amiga systems. 

.image Image file in Macintosh Disk Image format. 

.inf Device information file, which contains scripts used to control hardware operations. 

.ini In MS-DOS and Windows 3.x, an initialization file, which contains user preferences and startup 

information about an application program. 

.ins File containing InstallShield install script. 

.isu File containing InstallShield uninstall script. 

.jas Image file in JAS format. 

.jav See .java. 

.java Source file in Java. 

.jff See .jpg. 

.jfif See .jpg. 

.jpe See .jpg. 

.jpeg See .jpg. 

.jpg Graphic image file encoded in the JPEG File Interchange Format. 

.js Source file in JavaScript. 

.l Source file in LISP. 

.latex Text file in LaTeX. 

.lha Archive file compressed with LZH. 

.lib Library file in many programming languages. 

.lnk Shortcut file in Windows 9x and Windows NT 4. 

.log Log file. 

.lsp Source file in LISP. 

.lzh See .lha. 

.mac Image file in MacPaint. 

.mak Project file in Microsoft Visual Basic or Microsoft Visual C++. 

.man Manual page in UNIX. 

.mbox Mailbox file in BSD UNIX. 

.mbx 1. Address file in Microsoft Outlook. 

2. Mailbox file in Eudora. 

.mcw Document file in Microsoft Word for the Macintosh. 

.mdb Database in Microsoft Access. 

.mic Image file in Microsoft Image Composer. 

.mid Music file in MIDI format. 

.midi See .mid. 

.mime File encoded in MIME format. 

.moov Video file in Apple QuickTime. 

.mov See .moov. 

.movie See .moov. 

608


609 



.mp2 Audio file compressed and encoded according to the MPEG Audio Layer-2 standard. 

.mp3 Audio file compressed and encoded according to the MPEG Audio Layer-3 standard. 

.mpe See .mpg. 

.mpeg See .mpg. 

.mpg Compressed video and audio file in MPEG format. 

.mpp 1. Graphics file in CAD format. 

2. File in Microsoft Project. 

.msg E-mail message in Microsoft Outlook. 

.ncb File in Microsoft Developer Studio. 

.ncf Command file in Novell NetWare. 

.ncf Temporary file created by Microsoft Windows Clipboard utility. 

.net Network configuration file. 

.newsrc Setup file for UNIX-based newsreaders. 

.nlb Data file in Oracle 7. 

.nlm Module file in Novell NetWare. 

.nsf Database in Lotus Notes. 

.nws News message file in Microsoft Outlook Express. 

.obd File in Microsoft Office Binder. 

.ocx Microsoft OLE control. 

.ole Microsoft OLE object. 

.opt See .ncb. 

.p Source file in Pascal. 

.p65 Document file in PageMaker 6.5. 

.pab Address book file in Microsoft Outlook. 

.pcd Image file in Kodak Photo-CD. 

.pcl File in Hewlett-Packard Printer Control Language. 

.pcx Bitmapped image file in PC Paintbrush. 

.pdf Document file encoded in Adobe Portable Document Format. 

.pgp File encrypted in PGP (Pretty Good Privacy). 

.pic 1. Image file in PC Paint format. 

2. See .pict. 

.pict Image file in the Macintosh PICT. 

.pl 1. Source file in Perl. 

2. Source file in Prolog. 

.png Bitmap image file in PNG format. 

.pps 1. Image file in Paint Shop Pro. 

2. Slide show file in Microsoft PowerPoint. 

.ppt Presentation file in Microsoft PowerPoint. 

.prc Text or program file for 3Com PalmPilot. 

.prg File in Microsoft FoxPro, Ashton-Tate dBase, or CA Clipper. 

.ps PostScript printer file.




.psd Image file in Adobe PhotoShop. 

.pst Personal File Folder file in Microsoft Outlook. 

.pub Document file in Ventura Publisher, Adobe PageMaker, or Microsoft Publisher. 

.pwd Document file in Microsoft Pocket Word for handheld and palm-size computers. 

.pwl Password file in Microsoft Windows 9x. 

.pxl Spreadsheet file in Microsoft Pocket Excel for handheld and palm-size computers. 

.qic Backup file in Microsoft Backup. 

.qif See .qti. 

.qt See .qtm. 

.qti Image file in Apple QuickTime. 

.qtif See .qti. 

.qtm Movie file in Apple QuickTime. 

.qts See .qti. 

.qtx See .qti. 

.qxd Document file in QuarkXPress. 

.ra Sound file in RealAudio. 

.ram Metafile in RealAudio. 

.ras Raster image bitmap on Sun systems. 

.rast See .ras. 

.raw Bitmap file in RAW format. 

.rdf Resource Description Framework file in XML. 

.rgb See .raw. 

.rif Bitmap file in RIFF format. 

.riff See .rif. 

.rle Bitmap file in RLE compression scheme. 

.rm Video file in RealAudio. 

.rtf Document file in Rich Text Format. 

.s 1. Source file in Assembler. 

2. Source file in Scheme. 

.sam Document file in Lotus Ami Professional. 

.sav 1. Saved file in many games. 

2. Saved backup file. 

.scc File in Microsoft SourceSafe. 

.scd File in Microsoft Schedule+. 

.scr Screensaver file in Microsoft Windows. 

.sea Self-extracting Macintosh archive file compressed with StuffIt. 

.set File set in Microsoft Backup. 

.sgm File in SGML. 

.sgml See .sgm. 

.shtml 1. File in HTML format that has SSI (server side includes). 

2. Secure file in HTML. 

610


611 



.sig Signature file for e-mail or Internet newsgroup use. 

.sit Macintosh archive file compressed with StuffIt. 

.sm Source file in Smalltalk. 

.snd 1. Interchangeable sound file format used on Sun, NeXT, and Silicon Graphics computers, consisting 

of raw audio data preceded by a text identifier. 

2. Sound resource file on the Macintosh. 

.spl File in Macromedia Shockwave Flash. 

.sql Query or report file in SQL. 

.stm See .shtml. 

.sun Raster graphics file in Sun systems. 

.swa Audio file in Macromedia Shockwave. 

.swf File in Macromedia Shockwave Flash. 

.swp Swap file in Microsoft Windows. 

.sys System configuration file. 

.tar Uncompressed UNIX archive in tar format. 

.taz UNIX archive file in Gzip or tar format. 

.tcl Source file in TCL. 

.tga Bitmap file in Targa format. 

.tif Bitmap images in TIFF format. 

.tiff See .tif. 

.tmp Temporary file in Windows. 

.tsv Tab separated values file. 

.ttf TrueType font file. 

.txt ASCII text file. 

.udf Database file in Microsoft Windows NT. 

.uri File containing list of URIs. 

.url Shortcut file on the Internet for a URL. 

.uu See .uud. 

.uud Binary file that has been translated into ASCII format using uuencode. 

.uue File that has been decoded from ASCII format back into binary format using uudecode. 

.vbx Custom control in Microsoft Visual Basic. 

.vda See .tga. 

.vp Document file in Ventura Publisher. 

.vrm 1. See .vrml. 

2. Source file in Visual ReXX. 

.vrml A 3-D graphics file in VRML. 

.vst Bitmap image file in Targa. 

.vxd Virtual device driver in Microsoft Windows. 

.wab E-mail file in Microsoft Outlook Express. 

.wav Sound file stored in waveform (WAV) audio format. 

.wmf Vector image file encoded as a Microsoft Windows Metafile.




.wp Document file in Corel WordPerfect. 

.wp6 Document file in Corel WordPerfect 6.x. 

.wpd See .wp. 

.wpg Graphic file in Corel WordPerfect. 

.wps Document file in Microsoft Works. 

.wri Document file in Microsoft Write. 

.xls Spreadsheet file in Microsoft Excel. 

.z UNIX file archive compressed with gzip. 

.Z UNIX file archive compressed with compress utility. 

.zip Archive file compressed in ZIP format with PKZIP or WinZip. 

.zoo Archive file compressed with zoo. 

612

Appendix C 

Instant Messaging Emoticons 

and Acronyms 

Instant messaging, chat, and other Internet communications 

formats have led to a variety of shorthand indicators 

and clarifiers meant to enhance the user experience. 

Emotags 

Emotags were first used in e-mail and newsgroups to clarify 

a message for the reader. Typically, emotags consist of 

a word or words in brackets or parentheses, such as 

, and appear right after or both before and after the 

text they refer to. 

Smileys 

Text Meaning 

:-) smile 

(-: left-handed smile 

:o) smile with a large nose (or clown smiley) 

:) smile with no nose 

:-> smirk (or wry smile) 

:-} wry smile (or leer) 

:-t unsmiley 

:*) just clowning around (or inebriated) 

:-)))) extreme happiness (or sarcastic happiness) 

:-D very happy (or laughing) 

(-D laughing hard 

:-) :-) :-) loud guffaw 

:'-) laughing and crying 

%-) amused (and possibly confused) 

:-/ chagrined (or skeptical) 

:-I indifferent 

:~) touched (or ill with a cold) 

613 

Smileys 

The most common emoticons are faces and expressions 

composed of standard keyboard punctuation marks and 

symbols, and which are viewed sideways. These are 

known as “smileys” in reference to the first emoticons, 

which represented a smile, such as: : - ). Smileys are indicators 

of the emotional “tone of voice” intended by the 

writer.

Appendix C: Instant Messaging Emoticons and Acronyms 

Smileys continued 

Text Meaning 

(:-( sad (or bald and sad) 

:-( frown (or unhappy) 

:-c very unhappy 

:-(((( extremely unhappy (or sarcastic unhappiness) 

:-< forlorn 

>:-( annoyed 

:-[ pouting 

(:-& or %-( angry 

>:-< very angry 

~ :-( very angry (or fuming mad) 

%-( or :/) not amused 

:-| expressionless 

:-| or :-( have an ordinary day 

:-e disappointed 

:-X lips are sealed (or not saying a word) 

:-v talking 

:-I hmmm 

:-8( condescending stare 

:-O shouting (or shocked) 

:-@ screaming 

:,-( or :'-( crying 

~:-o baby 

]:-)> devilish 

):-) impish 

;-> lewd 

:-x kiss 

:-* ready for a kiss (or just ate something sour) 

8-] wow 

:-J tongue-in-cheek 

:-& tongue-tied (or biting tongue) 

:-p no way! (or nyah nyah) 

;-) wink 

'-) one-eyed wink 

:-7 wry statement (or tongue-in-cheek) 

:-| :-| déjà vu 

?-( sorry, I don’t know what went wrong (or black eye) 

:-C that’s unbelievable! (or incredible!) 

B-D serves you right 

:-B drooling 

:-*) drunk 

614


Text Meaning 

:-9 licking lips 

|-p yuck! 

:-b sticking out tongue 

-]:-)[- impressed 

8-I or 8-| in suspense 

|:-| excessively rigid 

:-] obnoxious 

|-) bored (or asleep) 

|-I asleep 

Iô snoring 

|-O yawning 

:-" whistling (or pursing lips) 

:-s incoherent statement 

:-# just said the wrong thing (or braces) 

:-! foot in mouth 

:-() or :-D big mouth 

(:-$ or :-(*) ill 

(:~) or :-') ill with a cold 

:-R ill with the flu 

%+| or %+{ lost a fight 

X-( unconscious (or dead) 

) big nose 

&:-) curly hair (or girl smiley) 

#:-) matted hair 

8-) wearing glasses 

8:-) glasses on forehead (or little girl, or hair in curlers) 

B-) wearing horn-rimmed glasses (or sunglasses) 

B-] wearing cool sunglasses 

O:-) angel 

&8-| nerd 

c:-) or (:-) bald 

:-{ has a moustache 

:-)} or :-)# has a beard 

:-Q or :-I smoker 

:-d~ heavy smoker 

:-? pipe smoker 


615



Text Meaning 

:-/I no smoking 

:-) X wearing a bow tie 

{(:-) wearing a toupee 

:-{} lipstick 

[:-) stereo headphones 

d :-o hats off 

~:-( has been flamed (or is on fire) 

~~:-( has been flamed repeatedly 

) Cheshire cat 

(:-I egghead 

3:-o cow 

[: |] robot 

M-) see no evil 

:X) hear no evil 

:-M speak no evil 

*8((: strange 

O+ female 

O-> male 

||*( handshake offered 

||*) handshake accepted 

– a rose 

@––>–– a long-stemmed rose 

@== atomic bomb 

Alternate (Japanese) Smileys 

Alternate smileys, which do not require users to tilt their 

heads sideways, were developed by Internet users in Japan 

Alternate Smileys 

Text Meaning 

(^_^) male smiley 

(^.^) female smiley 

(^L^) or (^(^) happy 

(-_-) secret smile 

(ô^) laughing out loud 

(^_^;) laughing to cover nervousness 

(^_^)/ waving hello 

(;_;)/ waving good-bye 

(^_~) or (^_-) winking 

(*ô^*) or (*^.^*) exciting 

\(^_^)/ joyful 

(;_;) or (~~>.._ excuse me? 

(*^_^*) blushing (or shy) 

(^_^;;;) embarrassed (or in a cold sweat) 

(?_?) confused (or wondering) 

(!_!) or (o_o) shocked 

(*_*) frightened (or in love) 

(=_=)~ sleepy 

(u_u) sleeping 

(@_@) stunned 

'\=o-o=/' wearing glasses 

m(_)m humble bow of thanks or apology 


617 

and are becoming more common worldwide. Some versions 

of these emoticons leave out the ( ) brackets around 

the faces.


Acronyms and Shorthand 

The first emotional indicators in newsgroups and e-mail 

were acronyms designed to give readers clues to the attitude 

and intent of the sender. Acronyms also quickly 

Acronyms 

Text Meaning 

AAMOF as a matter of fact 

AAR at any rate 

ADN any day now 

AFAIK as far as I know 

AFK away from keyboard 

AFKBRB away from keyboard, be right back 

ASAP as soon as possible 

A/S/L age/sex/location 

B2W back to work 

B4N (or BFN) bye for now 

BAK back at keyboard 

BBL be back later 

BBS be back soon 

BCNU be seeing you 

BF (or B/F) boyfriend 

BMN but maybe not 

BRB be right back 

BTDT been there, done that 

BTDTBTT been there, done that, bought the tape 

BTDTGTTS been there, done that, got the t-shirt 

BTDTGTTSAWIO been there, done that, got the t-shirt, and wore it out 

BTW by the way 

BYKT but you knew that 

CIO cut it out 

CMIIW correct me if I’m wrong 

CU (or CYA) see you 

CUL (or CUL8R) see you later 

DIY do it yourself 

DYJHIW don’t you just hate it when 

EAK eating at keyboard 

EOL end of lecture 

EOM end of message 

F2F (or FTF) face to face 

FAPP for all practical purposes 

618 

developed as keyboarding shortcuts. Use of acronyms is 

particularly prevalent in instant messaging, primarily to 

maintain the pace of real-time conversation.

Acronyms continued 

Text Meaning 

FOFL (or FOTFL) falling on the floor laughing 

FTR for the record 

FWIW for what it’s worth 

FYA for your amusement 

FYEO for your eyes only 

FYI for your information 

g (or ) grin 

G (or ) big grin 

G2G (or GTG) got to go 

GAL get a life 

GD&H grinning, ducking, and hiding 

GD&R grinning, ducking, and running 

GD&RVVF grinning, ducking, and running, very, very fast 

GF (or G/F) girlfriend 

GG gotta go (or good game) 

GIWIST gee, I wish I said that 

GMTA great minds think alike 

GoAT go away, troll 

HAK hugs and kisses 

HAGD have a great day 

HAND have a nice day 

HEH a courtesy laugh 

HHOS ha-ha, only serious 

HTH hope this helps (or hope that helps) 

IAE in any event 

HW homework (or hardware) 

IANAL I am not a lawyer 

IC I see 

ICBW I could be wrong (or it could be worse) 

IDTS I don’t think so 

IINM if I’m not mistaken 

IIRC if I recall correctly 

IIUC if I understand correctly 

IMCO in my considered opinion 

IME in my experience 

IMHO in my humble opinion 

IMNSHO in my not-so-humble opinion 

IMO in my opinion 


619



Text Meaning 

IOW in other words 

IRL in real life 

ISTM it seems to me 

ISWYM I see what you mean 

ITRW in the real world 

J (or ) joking 

JC just chillin’ 

JIC just in case 

JK (or J/K) just kidding (or that was a joke) 

JTYWTK just thought you wanted to know 

JW just wondering 

K okay 

KWIM know what I mean? 

L (or ) laughing 

L8R later 

LJBF let’s just be friends 

LOL laughing out loud 

LTNS long time no see 

MHBFY my heart bleeds for you 

MHOTY my hat’s off to you 

MOTAS member of the appropriate sex 

MOTD message of the day 

MYOB mind your own business 

NBD no big deal 

NBIF no basis in fact 

NOYB none of your business 

NP no problem 

NRN no response necessary (or no reply necessary) 

OIC oh, I see 

OM oh my (or old man, as in husband) 

OOI out of interest 

OOTB out of the box 

OTL out to lunch 

OTOH on the other hand 

OTTH on the third hand 

PAW parents are watching 

PC politically correct 

PDA public display of affection 

PEST please excuse slow typing 

620


Text Meaning 

PI (or PIC) politically incorrect 

PKB (or P/K/B) pot, kettle, black (or pot calling the kettle black) 

PMBI pardon my butting in 

PMFJI pardon me for jumping in 

POS parent over shoulder (or parents over shoulder) 

POV point of view 

PPL people 

PTB powers that be 

R (or r) are 

REHI re-hello (following a short time away) (or hi again) 

RFC request for comment 

RL real life 

ROTFL rolling on the floor laughing 

ROTFLOL rolling on the floor laughing out loud 

RSN real soon now 

S (or ) smile 

SCNR sorry, could not resist 

SITD still in the dark 

SOP standard operating procedure 

SPMD some people may differ 

SUP what’s up? 

TBE to be expected 

THX (or TX) thanks 

TIA thanks in advance 

TANJ there ain’t no justice 

TIC tongue-in-cheek 

TPHB the pointy-haired boss 

TPTB the powers that be 

TTBOMK to the best of my knowledge 

TTFN ta-ta for now 

TTYL talk to you later 

TVM thanks very much 

TVMIA thanks very much in advance 

TYVMIA thank you very much in advance 

U you 

UW you’re welcome 

VBG (or ) very big grin 

WB welcome back 

WCD what’s cookin’ doc? 


621



Text Meaning 

WHBT we have been trolled 

WOA work of art 

WRT with regard to (or with respect to) 

WTG way to go 

WTH what the heck? 

Y (or ) yawning 

YHBT you have been told (or you have been trolled) 

YHBW you have been warned 

YHGMTPOTG you have greatly misinterpreted the purpose of this group 

YHM you have mail 

YMMV your mileage may vary 

YOYO you’re on your own 

YWSYLS you win some, you lose some 

622

Appendix D 

Internet Domains 

Top-Level Domains: Organizational 

Domain Type of Organization 

.aero Air-transport industry 

.biz Businesses 

.com Commercial 

.coop Cooperatives 

.edu Educational 

.gov Nonmilitary agency, United States federal government 

.info Unrestricted use 

.int International organization 

.mil United States military 

.museum Museums 

.name Individuals 

.net Network provider 

.org Nonprofit organization 

.pro Professional workers 

Top-Level Domains: Geographic 

Domain Country/Region 

.ac Ascension Island 

.ad Andorra 

.ae United Arab Emirates 

.af Afghanistan 

.ag Antigua and Barbuda 

.ai Anguilla 

.al Albania 

.am Armenia 

.an Netherlands Antilles 

.ao Angola 

.aq Antarctica 

.ar Argentina 

623

Appendix D: Internet Domains 

Top-Level Domains: Geographic continued 


.as American Samoa 

.at Austria 

.au Australia 

.aw Aruba 

.az Azerbaijan 

.ba Bosnia and Herzegovina 

.bb Barbados 

.bd Bangladesh 

.be Belgium 

.bf Burkina Faso 

.bg Bulgaria 

.bh Bahrain 

.bi Burundi 

.bj Benin 

.bm Bermuda 

.bn Brunei 

.bo Bolivia 

.br Brazil 

.bs Bahamas, The 

.bt Bhutan 

.bv Bouvet Island 

.bw Botswana 

.by Belarus 

.bz Belize 

.ca Canada 

.cc Cocos (Keeling) Islands 

.cd Congo (DRC) 

.cf Central African Republic 

.cg Congo 

.ch Switzerland 

.ci Côte d‘Ivoire 

.ck Cook Islands 

.cl Chile 

.cm Cameroon 

.cn China 

.co Colombia 

.cr Costa Rica 

.cs Serbia and Montenegro 

.cu Cuba 

.cv Cape Verde 

.cx Christmas Island 

624



.cy Cyprus 

.cz Czech Republic 

.de Germany 

.dj Djibouti 

.dk Denmark 

.dm Dominica 

.do Dominican Republic 

.dz Algeria 

.ec Ecuador 

.ee Estonia 

.eg Egypt 

.er Eritrea 

.es Spain 

.et Ethiopia 

.fi Finland 

.fj Fiji Islands 

.fk Falkland Islands (Islas Malvinas) 

.fm Micronesia 

.fo Faroe Islands 

.fr France 

.ga Gabon 

.gd Grenada 

.ge Georgia 

.gf French Guiana 

.gg Guernsey 

.gh Ghana 

.gi Gibraltar 

.gl Greenland 

.gm Gambia, The 

.gn Guinea 

.gp Guadeloupe 

.gq Equatorial Guinea 

.gr Greece 

.gs South Georgia and the South Sandwich Islands 

.gt Guatemala 

.gu Guam 

.gw Guinea-Bissau 

.gy Guyana 

.hk Hong Kong SAR 

.hm Heard Island and McDonald Islands 

625 

Appendix D: Internet Domains




.hn Honduras 

.hr Croatia 

.ht Haiti 

.hu Hungary 

.id Indonesia 

.ie Ireland 

.il Israel 

.im Man, Isle of 

.in India 

.io British Indian Ocean Territory 

.iq Iraq 

.ir Iran 

.is Iceland 

.it Italy 

.je Jersey 

.jm Jamaica 

.jo Jordan 

.jp Japan 

.ke Kenya 

.kg Kyrgzstan 

.kh Cambodia 

.ki Kiribati 

.km Comoros 

.kn St. Kitts and Nevis 

.kp North Korea 

.kr Korea 

.kw Kuwait 

.ky Cayman Islands 

.kz Kazakhstan 

.la Laos 

.lb Lebanon 

.lc St. Lucia 

.li Liechtenstein 

.lk Sri Lanka 

.lr Liberia 

.ls Lesotho 

.lt Lithuania 

.lu Luxembourg 

.lv Latvia 

.ly Libya 

626



.ma Morocco 

.mc Monaco 

.md Moldova 

.mg Madagascar 

.mh Marshall Islands 

.mk Macedonia, Former Yugoslav Republic of 

.ml Mali 

.mm Myanmar 

.mn Mongolia 

.mo Macau SAR 

.mp Northern Mariana Islands 

.mq Martinique 

.mr Mauritania 

.ms Montserrat 

.mt Malta 

.mu Mauritius 

.mv Maldives 

.mw Malawi 

.mx Mexico 

.my Malaysia 

.mz Mozambique 

.na Namibia 

.nc New Caledonia 

.ne Niger 

.nf Norfolk Island 

.ng Nigeria 

.ni Nicaragua 

.nl Netherlands, The 

.no Norway 

.np Nepal 

.nr Nauru 

.nu Niue 

.nz New Zealand 

.om Oman 

.pa Panama 

.pe Peru 

.pf French Polynesia 

.pg Papua New Guinea 

.ph Philippines 

.pk Pakistan 

627 





.pl Poland 

.pm St. Pierre and Miquelon 

.pn Pitcairn Islands 

.pr Puerto Rico 

.ps Palestinian Authority 

.pt Portugal 

.pw Palau 

.py Paraguay 

.qa Qatar 

.re Reunion 

.ro Romania 

.ru Russia 

.rw Rwanda 

.sa Saudi Arabia 

.sb Solomon Islands 

.sc Seychelles 

.sd Sudan 

.se Sweden 

.sg Singapore 

.sh St. Helena 

.si Slovenia 

.sj Svalbard and Jan Mayen 

.sk Slovakia 

.sl Sierra Leone 

.sm San Marino 

.sn Senegal 

.so Somalia 

.sr Suriname 

.st São Tomé and Príncipe 

.sv El Salvador 

.sy Syria 

.sz Swaziland 

.tc Turks and Caicos Islands 

.td Chad 

.tf French Southern and Antarctic Lands 

.tg Togo 

.th Thailand 

.tj Tajikistan 

.tk Tokelau 

628



.tm Turkmenistan 

.tn Tunisia 

.to Tonga 

.tp East Timor 

.tr Turkey 

.tt Trinidad and Tobago 

.tv Tuvalu 

.tw Taiwan 

.tz Tanzania 

.ua Ukraine 

.ug Uganda 

.uk United Kingdom 

.um U.S. Minor Outlying Islands 

.us United States 

.uy Uruguay 

.uz Uzbekistan 

.va Vatican City 

.vc St. Vincent and the Grenadines 

.ve Venezuela 

.vg Virgin Islands, British 

.vi Virgin Islands 

.vn Vietnam 

.vu Vanuatu 

.wf Wallis and Futuna 

.ws Samoa 

.ye Yemen 

.yt Mayotte 

.za South Africa 

.zm Zambia 

.zw Zimbabwe 

629 


Numeric Equivalents 

Decimal 

(Base 10) 

Hexadecimal 

(Base 16) 

Appendix E 

Octal 

(Base 8) 

Binary 

(Base 2) 

1 01 01 00000001 

2 02 02 00000010 

3 03 03 00000011 

4 04 04 00000100 

5 05 05 00000101 

6 06 06 00000110 

7 07 07 00000111 

8 08 10 00001000 

9 09 11 00001001 

10 0A 12 00001010 

11 0B 13 00001011 

12 0C 14 00001100 

13 0D 15 00001101 

14 0E 16 00001110 

15 0F 17 00001111 

16 10 20 00010000 

17 11 21 00010001 

18 12 22 00010010 

19 13 23 00010011 

20 14 24 00010100 

21 15 25 00010101 

22 16 26 00010110 

23 17 27 00010111 

24 18 30 00011000 

25 19 31 00011001 

26 1A 32 00011010 

27 1B 33 00011011 

28 1C 34 00011100 

29 1D 35 00011101 

30 1E 36 00011110 

31 1F 37 00011111 

32 20 40 00100000 

631

Appendix E: Numeric Equivalents 

Numeric Equivalents continued 

Decimal 

(Base 10) 

Hexadecimal 

(Base 16) 

Octal 

(Base 8) 

Binary 

(Base 2) 

33 21 41 00100001 

34 22 42 00100010 

35 23 43 00100011 

36 24 44 00100100 

37 25 45 00100101 

38 26 46 00100110 

39 27 47 00100111 

40 28 50 00101000 

41 29 51 00101001 

42 2A 52 00101010 

43 2B 53 00101011 

44 2C 54 00101100 

45 2D 55 00101101 

46 2E 56 00101110 

47 2F 57 00101111 

48 30 60 00110000 

49 31 61 00110001 

50 32 62 00110010 

51 33 63 00110011 

52 34 64 00110100 

53 35 65 00110101 

54 36 66 00110110 

55 37 67 00110111 

56 38 70 00111001 

57 39 71 00111000 

58 3A 72 00111010 

59 3B 73 00111011 

60 3C 74 00111100 

61 3D 75 00111101 

62 3E 76 00111110 

63 3F 77 00111111 

64 40 100 01000000 

65 41 101 01000001 

66 42 102 01000010 

67 43 103 01000011 

68 44 104 01000100 

69 45 105 01000101 

70 46 106 01000110 

71 47 107 01000111 

632


Decimal 

(Base 10) 

Hexadecimal 

(Base 16) 

Octal 

(Base 8) 

Binary 

(Base 2) 

72 48 110 01001000 

73 49 111 01001001 

74 4A 112 01001010 

75 4B 113 01001011 

76 4C 114 01001100 

77 4D 115 01001101 

78 4E 116 01001110 

79 4F 117 01001111 

80 50 120 01010000 

81 51 121 01010001 

82 52 122 01010010 

83 53 123 01010011 

84 54 124 01010100 

85 55 125 01010101 

86 56 126 01010110 

87 57 127 01010111 

88 58 130 01011000 

89 59 131 01011001 

90 5A 132 01011010 

91 5B 133 01011011 

92 5C 134 01011100 

93 5D 135 01011101 

94 5E 136 01011110 

95 5F 137 01011111 

96 60 140 01100000 

97 61 141 01100001 

98 62 142 01100010 

99 63 143 01100011 

100 64 144 01100100 

101 65 145 01100101 

102 66 146 01100110 

103 67 147 01100111 

104 68 150 01101000 

105 69 151 01101001 

106 6A 152 01101010 

107 6B 153 01101011 

108 6C 154 01101100 

109 6D 155 01101101 

110 6E 156 01101110 

111 6F 157 01101111 

633 

Appendix E: Numeric Equivalents



Decimal 

(Base 10) 

Hexadecimal 

(Base 16) 

Octal 

(Base 8) 

Binary 

(Base 2) 

112 70 160 01110000 

113 71 161 01110001 

114 72 162 01110010 

115 73 163 01110011 

116 74 164 01110100 

117 75 165 01110101 

118 76 166 01110110 

119 77 167 01110111 

120 78 170 01111000 

121 79 171 01111001 

122 7A 172 01111010 

123 7B 173 01111011 

124 7C 174 01111100 

125 7D 175 01111101 

126 7E 176 01111110 

127 7F 177 01111111 

128 80 200 10000000 

129 81 201 10000001 

130 82 202 10000010 

131 83 203 10000011 

132 84 204 10000100 

133 85 205 10000101 

134 86 206 10000110 

135 87 207 10000111 

136 88 210 10001000 

137 89 211 10001001 

138 8A 212 10001010 

139 8B 213 10001011 

140 8C 214 10001100 

141 8D 215 10001101 

142 8E 216 10001110 

143 8F 217 10001111 

144 90 220 10010000 

145 91 221 10010001 

146 92 222 10010010 

147 93 223 10010011 

148 94 224 10010100 

149 95 225 10010101 

150 96 226 10010110 

634


Decimal 

(Base 10) 

Hexadecimal 

(Base 16) 

Octal 

(Base 8) 

Binary 

(Base 2) 

151 97 227 10010111 

152 98 230 10011000 

153 99 231 10011001 

154 9A 232 10011010 

155 9B 233 10011011 

156 9C 234 10011100 

157 9D 235 10011101 

158 9E 236 10011110 

159 9F 237 10011111 

160 A0 240 10100000 

161 A1 241 10100001 

162 A2 242 10100010 

163 A3 243 10100011 

164 A4 244 10100100 

165 A5 245 10100101 

166 A6 246 10100110 

167 A7 247 10100111 

168 A8 250 10101000 

169 A9 251 10101001 

170 AA 252 10101010 

171 AB 253 10101011 

172 AC 254 10101100 

173 AD 255 10101101 

174 AE 256 10101110 

175 AF 257 10101111 

176 B0 260 10110000 

177 B1 261 10110001 

178 B2 262 10110010 

179 B3 263 10110011 

180 B4 264 10110100 

181 B5 265 10110101 

182 B6 266 10110110 

183 B7 267 10110111 

184 B8 270 10111000 

185 B9 271 10111001 

186 BA 272 10111010 

187 BB 273 10111011 

188 BC 274 10111100 

189 BD 275 10111101 

190 BE 276 10111110 

635 




Decimal 

(Base 10) 

Hexadecimal 

(Base 16) 

Octal 

(Base 8) 

Binary 

(Base 2) 

191 BF 277 10111111 

192 C0 300 11000000 

193 C1 301 11000001 

194 C2 302 11000010 

195 C3 303 11000011 

196 C4 304 11000100 

197 C5 305 11000101 

198 C6 306 11000110 

199 C7 307 11000111 

200 C8 310 11001000 

201 C9 311 11001001 

202 CA 312 11001010 

203 CB 313 11001011 

204 CC 314 11001100 

205 CD 315 11001101 

206 CE 316 11001110 

207 CF 317 11001111 

208 D0 320 11010000 

209 D1 321 11010001 

210 D2 322 11010010 

211 D3 323 11010011 

212 D4 324 11010100 

213 D5 325 11010101 

214 D6 326 11010110 

215 D7 327 11010111 

216 D8 330 11011000 

217 D9 331 11011001 

218 DA 332 11011010 

219 DB 333 11011011 

220 DC 334 11011100 

221 DD 335 11011101 

222 DE 336 11011110 

223 DF 337 11011111 

224 E0 340 11100000 

225 E1 341 11100001 

226 E2 342 11100010 

227 E3 343 11100011 

228 E4 344 11100100 

229 E5 345 11100101 

636


Decimal 

(Base 10) 

Hexadecimal 

(Base 16) 

Octal 

(Base 8) 

Binary 

(Base 2) 

230 E6 346 11100110 

231 E7 347 11100111 

232 E8 350 11101000 

233 E9 351 11101001 

234 EA 352 11101010 

235 EB 353 11101011 

236 EC 354 11101100 

237 ED 355 11101101 

238 EE 356 11101110 

239 EF 357 11101111 

240 F0 360 11110000 

241 F1 361 11110001 

242 F2 362 11110010 

243 F3 363 11110011 

244 F4 364 11110100 

245 F5 365 11110101 

246 F6 366 11110110 

247 F7 367 11110111 

248 F8 370 11111000 

249 F9 371 11111001 

250 FA 372 11111010 

251 FB 373 11111011 

252 FC 374 11111100 

253 FD 375 11111101 

254 FE 376 11111110 

255 FF 377 11111111 

637

Microsoft Computer Dictionary, Fifth Edition eBook - ASSA ABLOY ...

Create successful ePaper yourself

Delete template?

Save as template?