(Written by me in 2011)

Discussion of the evolution of CD-ROM technology. An example of the how optical data storage was achieved in ancient history; through photography, CD-ROM, DVD, HD-DVD, Blu-Ray and Ancient Egyptian Holographics. The technical specifications of CD ROM and DVD format are discussed.

Figure 1: Ancient Egyptian Hieroglyphics represent early man's obsession of optical data storage

Optical recording was first done by humans over 30,000 years ago in the form of rock art [1], but it wasn't until recent times that more sophisticated techniques of using optical means to store information were used. In 1998 Günter Dreyer uncovered a tomb of Predynastic Egyptian ruler, and recovered three hundred clay labels inscribed with proto-hieroglyphs, dating to the Naqada III A period of the 33rd century B.C. [2]. These hieroglyphs represent an early sophisticated attempt by humans to store information for later retrieval. These early types of optical storage contrast with modern forms in that the ‘data’ could be directly perceived through human physiology without the need for advanced machinery and electric power. The data could theoretically be “stored” through mechanical means without light, but it was only the refraction of the light against the etched surface that enabled its “understanding”.

Photography as a Means of Optical Data Storage

Later on in 1800s, photography was the first real example of optical data storage in the modern sense. Photography used analog methods to store data. However, this approach led to a degradation of data, and is not useful for modern digital storage needs.

Figure 2: First camera: Data is stored when a silver
and chalk mixture is exposed to light

Evolution of the CD

In 20th century, it was found that light could be for digital storage of information too, which was possible due to the use of lasers (first used in 1959). It was in 1982 that the audio compact discs (CD) were seen by the public for the first time [3]. The disc technology, a collaborative development between Philips and Sony [4], consisted of clear polycarbonate material, coated with a reflective metal, and also containing a layer of clear lacquer for protection [5]. In this author’s opinion, the audio CD was simply an advanced intuitive development of the earlier “musical box” (which is itself an example of mechanical data storage); where lasers “strike” bits (on the disk) as do the music box’s pins to its metallic combs. The same could be said for the Gramophone record. If this is the case, then the development of CDs came along the ancestral line of audio storage technology, rather than the later magnetic storage means like floppy disks.

A further intuitive progression was the adoption of the audio CD to record any kind of binary data. This data CD was called a CD-ROM which consisted of small pits recorded in a spiral track starting at the center of the CD-ROM and working to the outer edge [6]. The CD-ROM could hold 680MB of data including error detection and correction codes. CD-ROM discs are identical in appearance to audio CDs, and data is stored and retrieved in a very similar manner (only differing from audio CDs in the standards used to store the data). In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed-Solomon error correction [7].

Figure 3: How a CD-ROM works

For the sake of categorizing such optical storage methods, this article will talk of the rainbow book colors, a set of color-bound books that contain the technical specifications for all CD and CD-ROM formats. Most optical storage technologies are defined according to the technical standards laid down in these books. The set of rainbow book colors consist of Red, Yellow, Orange, White, Blue, Beige, Green, Purple and scarlet; each representing some variation of the initial CD format. So when one talks of the initial audio CD format, the ancestor of the CD-ROM, one is only talking about the specifications mentioned by Philips and Sony in the “Red Book”. Further along the line came the “Orange Book” which explored CD-R and CD-RW. CD-ROMs technology was defined in a “Yellow book” which directly followed from the original “red book”. The main cause for these systematic definitions was the public standardization for these media. Experts felt the need to define the volume and file structures of the disks [8]. Therefore, it was often the case that the technological idea came first, and then a standard was proposed later. Standards outlined in the rainbow books may include: “Standards for testing the disk; usage context and storage technicalities; mechanical, physical and dimensional characteristics of the disk; recording characteristics, the format of the tracks; error –related characters; optical characteristics for reading the information”.

DVD Technology

In December 1995, the DVD specification was finalized as a result of two high-density optical storage standards, Multimedia Compact Disc and Super Density disc which were in development by two rival sets of companies. The two standards united (with slight modifications) due to the efforts of IBM’s president Lou Gerstner [9].

Figure 4: DVD as seen under an electon microscope

DVD is actually an umbrella name for three distinct ways in which data can be stored optically. DVD-ROM has data which can only be read and not written, DVD-R can be written once and then functions as a DVD-ROM, and DVD-RAM holds data that can be re-written multiple times. DVD uses a 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller spot on the media surface that is 1.32 µm for DVD while it was 2.11 µm for CD. Its capacity is at least 4.7 GB for single layer disks or 8.5 GB for dual layer disks [10].

The HD (High-Definition) DVD is based on the standard DVD format but can store six times as much data as its predecessor (Maximum capacity: 51 GB instead of 8.5 GB) [11]. The HD DVD standard was jointly developed by Toshiba and NEC [12]. On 19 November 2003, the DVD Forum voted to support HD DVD as the high definition successor of the standard DVD. At this meeting, they also renamed it HD DVD. HD DVD stands for “High Definition Digital Versatile Disc”. One significant development occurred in November 2006 with Microsoft’s release of an external add-on HD DVD drive for the Xbox 360 game console.

Blu-ray discs use a blue-violet laser to read and write data to and from the type of disc. Because of its shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red (650 nm) laser [13]. A dual layer Blu-ray Disc can store 50 GB, almost 6 times the size of a dual layer DVD at 8.5 GB. A recent development is to cover the disks with a clear polymer coating for scratch resistance. This solved the problem of Blu-ray discs placing the data recording layer close to the surface of the disc which led to data contamination [14]. At present, Blu-ray disc specification continues to develop. TDK have demonstrated the use of Quad-layer (100 GB) technology [15]. Furthermore TDK announced in August 2006 that they have created a working experimental Blu-ray Disc capable of holding 200 GB of data on a single side, using six 33 GB data layers [16]. Also, Ritek has revealed that they had successfully increased the capacity of the discs to 250 GB for Blu-ray compared to 150 GB for HD DVD using the same process. In Blu-ray data is retained for an estimated 30 years minimum can be rewritten over 100,000 times discs can be used and accessed like a removable hard disk.

HD DVD is currently in a “format war” with rival format Blu-ray Disc, to determine which of the two formats will become the leading carrier for high-definition content to consumers [14].

Holographics – the Future of Optical Data Storage

As the war rages between blu-ray and HD-DVD, a new technology is emerging which uses holographic images to store information at high density inside crystals or photopolymers. Holographic disks could be used to store data not only on the surface, but also in the actual volume of the disk. This three-dimensional approach enables “Bragg detuning” to be implemented so that a number of holographs can be superimposed on each other [17]. Maxell-USA website says: “…with uncompressed storage capacities achieving 1.6 Terabytes per disk and data rates as high as 120 MBP, holographic technology is a true breakthrough in optical media” [15]. In holographic technology, millions of bits can be stored in a single flash of light. This leads me to suspect that holographic technology could bridge the gap between optical technology and solid state technology.

Figure 5: Multi Layer Holographic Disk

As can be seen, the development and implementation of optical storage from hieroglyphics to holographic has been a slowly developing and non-linear approach for humans to exercise their need to store information.

REFERENCES

1. Zerzan, J. Title: www.primitivism.com. Retrieved on Sept. 21st 2008
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3. Nakajima, H, 1989. The conception and evolution of digital audio. Solid-State Circuits Conference, 1989. Digest of Technical Papers. 36th ISSCC. 1989 IEEE International. Pg. 60-62.
4. Gandal N. 2000. The Dynamics of Technological Adoption in Hardware/Software Systems: The Case of Compact Disc Players. The RAND Journal of Economics. 31(1), 43-61.
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6. Card J. J. 1991. CD-ROM Technology and the Teaching of Sociology. Teaching Sociology. 19(2), 255-259.
7. Vermuelen, B. 1989. Digital audio tape for data storage. Spectrum, IEEE. 26(10), 34-38.
8. ECMA, 2006. Data interchange on read-only 120 mm optical data disks (CD-ROM). Standard ECMA-130, 2nd Edition - June 1996.
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13. Uchida, S. 2003. Recent progress in high-power blue-violet lasers. IEEE Journal of Selected Topics in Quantum Electronics. 9(5), 1252- 1259.
14. Flaherty, N. 2004. Battle of the blues. IEE Review. 50(4): 48-50.
15. Williams, M. 2005. TDK develops 2X, 100GB Blu-ray Disc prototype. Macworld News. May 19, 2005 edition.
16. Block, R. 2006. TDK: Ok, we're done with the 200GB recordable Blu-Ray. Engadget. Apr 28th 2006.
17. Dhar, L. 1999. Recording media that exhibit high dynamic range for digital holographic data storage. Optics Letters 24: 487-489.