After many years of development, optical disc technology, promising great strides in storage capacity and reliability as well as competition for magnetically based disk media, was made available commercially.

The introduction of data storage using optically based methods represented an exciting yet evolutionary step in mass storage technology. The excitement resulted from the numerous significant advantages that optical discs offer over traditional magnetic storage media; the emergence of the optical disc was, however, evolutionary in that the technology involved had a degree of overlap with the dominant magnetically based technology. Computers;external storage
CD-ROM technology[CD ROM technology]
Optical disc technology
[kw]Introduction of Optical Discs for Data Storage (1984)
[kw]Optical Discs for Data Storage, Introduction of (1984)
[kw]Discs for Data Storage, Introduction of Optical (1984)
[kw]Data Storage, Introduction of Optical Discs for (1984)
Computers;external storage
CD-ROM technology[CD ROM technology]
Optical disc technology
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[g]Europe;1984: Introduction of Optical Discs for Data Storage[05340]
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[g]United States;1984: Introduction of Optical Discs for Data Storage[05340]
[g]Japan;1984: Introduction of Optical Discs for Data Storage[05340]
[c]Science and technology;1984: Introduction of Optical Discs for Data Storage[05340]
[c]Computers and computer science;1984: Introduction of Optical Discs for Data Storage[05340]
[c]Inventions;1984: Introduction of Optical Discs for Data Storage[05340]

To understand the significance of the introduction of optical discs for data storage, it is thus helpful to compare and contrast optical discs with magnetic disks and tape. For years, virtually all computers used two types of data storage media: magnetic tape and magnetic disk. Magnetic tape consists of a continuous thin plastic ribbon coated with iron oxide. It is typically packaged in a plastic reel or in a smaller tape cartridge. A magnetic tape is mounted on a tape drive (similar in function to a tape recorder/player) that has a read/write head that creates or reads magnetized sections of iron oxide on the tape. When input is required from the tape, the read/write head detects magnetized spots of left or right orientation corresponding to the digit 0 or 1 (all computer information is encoded using the base-two numbering system known as binary) on the tape and converts the sequencing of these spots into electrical signals, which are then interpreted by the computer. When output to the tape is desired, the computer sends the proper sequence of electrical signals to the read/write head, which then magnetizes a stretch of tape. The use of a read/write head in some form is common to all the storage media considered in this article. The relevant feature for comparison to disk technology, both magnetic and optical, is the method of data access. Magnetic tape passes by the read/write head in the forward or reverse direction. Information can thus be accessed only in a sequential fashion.

The second and more common type of secondary data storage medium is the magnetic disk. It comes in two varieties: removable and fixed. The first of these, in the form of the floppy diskette, or floppy disk, long dominated the microcomputer media market. A floppy disk Floppy disks consists of a flexible circular piece of plastic coated with a magnetizable iron oxide. This thin platter, analogous to a phonograph record, is enclosed in a paper or plastic jacket for protection; cut into the jacket is a small oblong opening for access by the read/write head. The main advantage of floppy disks over fixed hard disks is their portability. The trade-off is in capacity and speed; fixed disks offer significantly more storage space, and the information that is stored on a hard disk can be accessed by a computer in about one-tenth the time it takes to access data on a floppy disk. Fixed disks, or hard disks, are similar to floppy disks in operation but differ in construction and performance. A fixed disk usually consists of one or more metal platters coated with the same magnetizable material used with floppy disks, but the fixed disk is sealed permanently in a cabinet in order to protect it from dust.

Information is written to or retrieved from floppy and fixed disks by a read/write head that skims over the surface of the spinning disk. Data are organized on the surface of the disk in concentric rings called tracks; the computer can access data rapidly by radially positioning the read/write head to the proper track and then reading or writing data along a track as the disk spins underneath. This is known as random access and is considerably faster than the sequential mode used for magnetic tape media. All optical discs for computer data storage use random access.

Although IBM experimented with optical disc storage in the mid-1960’s, it was not until the advent of the semiconductor laser that the idea became practical. In the late 1960’s, Sony Corporation and NV Philips, Inc., entered agreements on cooperative research in the optical disc arena. The first commercial product realized from this joint venture was the laser videodisc Laser videodiscs in the late 1970’s. The laser videodisc is analogous to the phonograph record (LP) in that information in this case, video rather than audio or computer data is recorded in a spiral track in analog, rather than digital, fashion. Information in analog form can take on any value, whereas digital information can be only one of two values: 1 or 0. The videodisc player used a laser stylus to play back prerecorded information.

The next commercial product to be launched from this merger was the compact disc (CD) in 1982. Videodisc technology Videodisc technology was adapted to store audio information in a digital format. The move to the digital format was not only pivotal in producing higher-quality sound but also meant that more sound could be embedded in a small, 12-centimeter platter than could be found on the analog tracks of a larger phonograph record. This product was highly successful, and CDs soon all but totally replaced LPs and prerecorded audiocassette tapes in consumers’ preferences.

The natural extension of this idea to the computer world emerged in 1984, when CD-ROMs were made commercially available. CD-ROM is an acronym for “compact disc read-only memory.” CD-ROMs presented computer data prerecorded on optical discs that users could read but not write to. Audio compact discs and CD-ROM disks are fabricated in the same manner. A high-power laser is used to burn pits in the recording-medium layer of a master disk. A computer retrieves information from the disk by reading the sequencing of “pit” and “land” (the space between the “pits”) areas using a lower-powered laser that is focused to a small spot on a single circular tract. As the disk spins at a speed of up to 3,600 revolutions per minute, the laser beam from the optical head shines on the pit and land regions, resulting in variations in the intensity of the reflected light. The reflected light is then captured by an optical system using lenses and focused onto an electrical device known as a photodetector. The photodetector detects the light intensity fluctuations and translates them into electrical signals, which, in turn, are translated into video, audio, or computer text by means of electrical circuitry.

Another significant event for computer data storage that took place in 1984 was the introduction of WORM optical discs. WORM optical discs WORM is an acronym for “write once, read many.” WORM drives allow the computer user to write to the optical disc once and read what was written many times, but the user cannot erase what has been written. Every time information is saved to the disk, it resides there permanently.

The ultimate goal for data storage was to merge the best characteristics of the optical and magnetic disk technologies that is, to create a fast, high-capacity disk on which a user could both read and write repeatedly. Such a goal was attained in 1988, when the first erasable optical discs became available. The achievement required a fusion of magnetic and optical physics and represented a remarkable feat in applied science. The erasable, or magneto-optical, disk Magneto-optical discs[Magnetooptical discs] is similar to the CD-ROM disk in construction but differs in the recording medium. Rather than burning pits in a metallic coating, the read/write head laser heats spots in the magneto-optical medium, and then a weak magnetic field is applied to magnetize the region of the spot. The direction of magnetization, analogous to the metal arrow in a compass, is either up or down (representing a 0 or a 1) and lies perpendicular to the plane of the platter.

To read data on a magneto-optical disc, the laser is run at lower power. When the laser beam is reflected off the magnetized regions, it experiences a change in its physical characteristics. This phenomenon, known in physics as the Kerr effect, is detectable by a special optical system. In the case of the magneto-optical medium, the change occurs in one direction if the magnetization is up (for example, representing a 1) and in another direction if the magnetization is down. Again, the sequencing of the transitions between up and down states corresponds to the sequencing of 1’s and 0’s in the binary words that constitute all computer data.

Advances in secondary storage technology for computer data followed the major trend that has characterized the short history of the computer industry miniaturization. This beneficial trend in hardware of packing more devices, circuits, and information in an ever-shrinking piece of silicon substrate proceeded at a rapid pace, as became evident particularly with the advent of the optical disc.

Conventional tape technology provided low capacity and long data-access times. Newer tape formats (such as VHS and DAT) improved on both measures. Floppy disks, while providing portability, are inferior in data storage capacity. Hard disks are faster than floppies and provide greater data storage capacity. None of the tape or magnetic disk technologies can, however, achieve the performance of optical media. CD-ROM, WORM, and magneto-optical discs offer portability and thus security (the disks are removable), reliability (there is no wear on the media, as access is accomplished by a laser that sits relatively far from the surface of the platter in comparison with the read/write head for a magnetic disk or tape), and significant storage capacity (a single CD can store as much as 275,000 pages of text), and all for considerably lower cost per bit of data than other storage formats.

One of the most compelling applications found for CD-ROMs was as a publishing medium. This type of optical disc found multiple uses in government and industries (ranging from insurance companies to national laboratories) where large data storage is needed. One of the first applications for CD-ROM was the publication of the twenty-volume Grolier’s Academic American Encyclopedia; the entire work resided on a mere 20 percent of the surface of a single disk.

CD-ROMs were soon put to use for pedagogical and entertainment purposes, and in the early 1990’s, the optical disc storage format of DVD (for “digital versatile disc” or “digital video disc”) was developed. Optical storage media had a direct impact as the world of entertainment and computing coalesced under the banner of interactive multimedia.

In 1989, NEXT, Inc., became the first manufacturer of personal computers to include a removable magneto-optical drive as standard equipment. Apple Computer also became a leader in the use of optical media for education. Computers;external storage
CD-ROM technology[CD ROM technology]
Optical disc technology

• Brand, Stewart. The Media Lab: Inventing the Future at MIT. New York: Viking Press, 1987. Popular presentation of the exciting research conducted in the futuristic media laboratory at MIT. Chapter 2 includes a short discussion of new media directly relevant to the development of optical discs for data storage. Successfully conveys the excitement and potential benefits of technologies based on interactive media.
• Buddine, Laura, and Elizabeth Young. The Brady Guide to CD-ROM. Englewood Cliffs, N.J.: Prentice Hall, 1987. A standard reference to the world of CD-ROM and optical technology. Provides discussions of the technology, applications, industry standards, and software. Very well written and accessible to general readers. Includes many figures and diagrams.
• Hecht, Jeff, and Dick Teresi. Laser: Supertool of the 1980’s. New York: Ticknor & Fields, 1982. In the same vein as the Brand volume cited above; presents all the glitter of the new technology of lasers. Includes some references to optical media, but this work appeared at the same time audio compact discs first came to market. Presents much discussion of current as well as potential laser applications.
• Kryder, Mark H. “Data-Storage Technologies for Advanced Computing.” Scientific American 243 (October, 1987): 116-125. Provides an excellent review of the state of the art in disk storage technology. Part of a dedicated issue on the topic of the next revolution in computers. Includes good discussion on the physics underlying magneto-optical disc technology, with superb diagrams and photographs.
• Lambert, Steve, and Suzanne Ropiequet, eds. The New Papyrus: CD-ROM. Bellevue, Wash.: Microsoft Press, 1986. Classic visionary work on what the future holds for this revolutionary medium. Includes descriptions of hardware and media, marketing advice, case studies, and tutorials on handling audio, video, and text.
• White, Robert M. “Disk-Storage Technology.” Scientific American 243 (August, 1980): 138-148. Reviews the state of the art in disk storage technology. Focuses primarily on explaining the physics behind magnetic disk technology, and so is directed toward readers with at least some high school physics background. Although somewhat dated, the article’s predictions about future developments were on target.

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