ERIC Identifier: ED303176
Publication Date: 1988-05-00
Author: Schamber, Linda
Source: ERIC Clearinghouse on
Information Resources Syracuse NY.
Optical Disk Formats: A Briefing. ERIC Digest.
The first optical disks that became commercially available, around 1982, were
compact audio disks. Since then, and during a particularly active marketing
period from 1984 to 1986, at least a dozen other optical formats have emerged or
are under development. The rapid proliferation of formats has led,
understandably, to some confusion. This digest will briefly describe the most
prominent formats (and their acronyms), and the contexts in which they are used.
Optical disks go by many names--OD, laser disk, and disc among them--all of
which are acceptable. At first glance, they bear some resemblance to floppy
disks: they may be about the same size, store information in digital form, and
be used with microcomputers. But where information is encoded on floppy disks in
the form of magnetic charges, it is encoded on optical disks in the form of
microscopic pits. These pits are created and read with laser (light) technology.
The optical disks that are sold are actually "pressed," or molded from a
glass master disk, in somewhat the same way as phonograph records. The copies
are composed of clear hard plastic with a reflective metal backing, and
protected by a tough lacquer. As the disk spins in the optical disk player
(reader, drive), a reader head projects a beam from a low-power laser through
the plastic onto the pitted data surface and interprets the reflected light.
Optical disk players can stand alone, like portable tape players, or be
connected to stereos, televisions, or microcomputers.
Optical disks lack the erasability and access speed of floppies, but these
disadvantages are offset by their huge storage capacity, higher level of
accuracy, and greater durability.
OPTICAL DISK FORMATS
Optical disk formats are described by capability, information form, and disk
size. The most familiar capabilities are: o Read Only Memory (ROM, RO):
permanent, unalterable storage,
currently the only firmly established format. o Write Once, Read Many (WORM,
WO): new data can be written to the
disk, but existing data cannot be altered or erased. The drive
head contains two lasers: one for reading, and a more powerful
laser for etching new data pits. WORM capability may reduce
storage capacity by a third. Both 5.25- and 12-inch versions were
marketed around 1985. o Interactive (I): stores information in any or all
with interactive programming that allows flexible access, animates
visuals, runs games, etc.; similar to the capabilities of
microcomputer software. o Erasable (E): information can be deleted and
format requires complex technology and is still being developed.
These capabilities may or may not be available on disks containing different
forms of information--audio, text or data, video or graphics, or a combination.
And various forms of information can be found on different sizes of disk, most
often 12 or 4.72 inches in diameter. Some 12-inch formats are: o Optical Digital
Data Disk (OD3, ODD): contains digitized information (bits), usually text,
sometimes images, and used primarily in business and research settings. The disk
may have ROM or WORM capabilities. o Video Disk (videodisc, laser video disk,
LV, reflective optical video disk): carries sound and moving images--movies--as
analog (continuous) signals. The disk itself may be silvery, reflecting colors
for a rainbow effect. o Digital Video Disk (digitally encoded video disk)
contains digital video, audio, and/or text. Still video is more common than
motion video because it is more economical to store and easier to access.
Digital motion video must be converted to analog signals for playing on standard
home televisions. The disk may also include some interactivity programming. o
Interactive Video Disk (IVD): stores 54,000 still frames or 30 minutes of
full-motion video with audio. A microcomputer interface allows IVD to gain some
interactive capability, although interactivity is hampered by the analog video
signal. This format has applications in education, business and industrial
training, public information terminals, and games and other entertainment.
Most compact disks (CDs) are 4.72 inches across; a few are 5.25 inches.
Audio, text, and still video are stored on CDs. The first two formats below are
the most commercially successful to date: o Compact Audio Disk (digital audio
disk; CD-audio): contains digital stereo audio signals, generally 75 minutes of
high-fidelity, static-free music. o Compact Disk-Read Only Memory (CD-ROM): has
tremendous storage capacity, used to store text databases such as bibliographic
indexes. One compact disk holds 550 MB of data, the equivalent of 1,500 floppy
disks. This amounts to 275,000 pages of information or 200 pounds of paper.
Audio or still video may be integrated with text. This format is marketed for
library, academic, and professional applications. o Compact Disk-Write Once,
Read Many (CD-WORM): often contains text or text with still images (see WORM).
Several 5.25-inch formats with write and possibly erase capabilities are also
The next wave of optical disk formats is
about to break. This year or next we are likely to see:
o HDTV Video Disk: a digital format that is readable by high-definition
television, with more than double the number of lines per screen.
o Compact Disk-Interactive (CD-I): a writable, very adaptable format that
will store text, multichannel audio at several quality levels, still or motion
video with low- or high-definition, and animated graphics. Signals may be all
digital or include some analog video. CD-I players can stand alone or link to
home entertainment systems. This disk and a similar product, compact disk video
(CD-video, CD-V), are targeted for mass-market education and entertainment.
o Digital Video Interactive (DVI): similar to CD-I, but a highly integrated
system that promises more. Compressed digital signals allow the storage capacity
of CD-ROM and more motion video than CD-I and IVD: up to an hour of video, with
multitrack audio. This disk also has the interactive graphics capabilities of a
microcomputer program. Applications include simulations, video paint, special
effects, sales tools, and scientific imaging. DVI's release is slated for 1990
o Compact Disk-Erasable Magneto Optic (CD-EMO): combines optic and magnetic
technologies in a format that is expected to be easily erasable and reusable for
10 years. Like WORM, EMO requires a drive head with separate read and write
lasers. In writing, heat from the laser works in conjunction with a change in
magnetic polarity to change the shape of the pit. The erasable disk should also
appear within two years.
With the exception of audio CD, CD-ROM, and video disk, the optical disk
formats described here are largely experimental: just released or about to be
released. And because the technology is so new, there are very few standards for
compatibility of hardware or software, or for encoding, accessing, or
integrating data in various forms. But these problems will disappear within the
next few years, with optical formats and optical systems that offer... o o
players o o o
different wavelengths or colors o o o
networks o o
organization o o ...just to name a few. The optical technologies industry is
moving so fast that the only way to keep up is to contact manufacturers
directly, and to read periodicals. CD-ROM REVIEW,
ELECTRONIC AND OPTICAL PUBLISHING REVIEW, OPTICAL INFORMATION SYSTEMS, DATABASE, and JOURNAL OF INFORMATION AND IMAGE MANAGEMENT all focus
on optical technologies; while BYTE MAGAZINE, INFORMATION TODAY, and PC WORLD
take a more general look at high-tech developments. Special issues of two
journals focus on CD-ROM for libraries: THE BULLETIN OF THE AMERICAN SOCIETY FOR
INFORMATION SCIENCE, 14(1), October-November 1987; and WILSON LIBRARY BULLETIN,
Becker, Karen A. (1987, July/August). CD-ROM: A
primer. C&RL NEWS, 48(7), 388-399.
Berg, Brian A. (1987, September-October). Critical considerations for WORM
software development. OPTICAL INFORMATION SYSTEMS, 7(5), 329-333.
Brewer, B. (1987, March-April). Multimedia media mastery. CD-ROM REVIEW, 2,
Brewer, B. (1987, April). Ready when you are, CD-I. PC WORLD, 5, 252-255.
Davies, David H. (1988, January). The CD-ROM medium. JOURNAL OF THE AMERICAN
SOCIETY OF INFORMATION SCIENCE. 39(1), 34-42.
Herther, Nancy K. (1988, January). The next CD evolution: Compact
Disk-Interactive (CD-I): An interview with Bert Gall." ONLINE, 12(1), 68-74.
Levine, R. (1987, February). Optical storage. DEC PROFESSIONAL, 6, 30-38.
RCA Laboratories (David Sarnoff Research Center). (1987, November-December).
New integrated video and graphics technology: Digital Video Interactive. OPTICAL
INFORMATION SYSTEMS, 7(6), 412-415.
Ropiequet, S. (ed.). (1987). CD-ROM VOLUME 2, OPTICAL PUBLISHING. Redmond,
WA: Microsoft Press, 1987.
Saffady, William. (1987, September-October). Optical disks at the 1987 AIIM
conference. OPTICAL INFORMATION SYSTEMS, 7(5), 321-328.