A CD-ROM (, compact disc read-only memory) is a pre-pressed optical compact disc that contains data. Computers can read—but not write to or erase—CD-ROMs, i.e. it is a type of read-only memory.
During the 1990s, CD-ROMs were popularly used to distribute software and data for computers and fifth generation video game consoles. Some CDs, called enhanced CDs, hold both computer data and audio with the latter capable of being played on a CD player, while data (such as software or digital video) is only usable on a computer (such as ISO 9660 format PC CD-ROMs).
The earliest theoretical work on optical disc storage was done by independent researchers in the United States including David Paul Gregg (1958) and James Russel (1965-1975). In particular, Gregg's patents were used as the basis of the LaserDisc specification that was co-developed between MCA and Phillips after MCA purchased Gregg's patents, as well as the company he founded, Gauss Electrophysics. The LaserDisc was the immediate precursor to the CD, with the primary difference being that the LaserDisc encoded information through an analog process whereas the CD used digital encoding.
Key work to digitize the optical disc was performed by Toshi Doi and Kees Schouhamer Immink during 1979-1980, who worked on a taskforce for Sony and Phillips. This was an extension of Compact Disc Digital Audio, and adapted the format to hold any form of digital data, with a storage capacity of 553 MiB. Sony and Philips created the technical standard that defines the format of a CD-ROM in 1983, in what came to be called the Yellow Book. One of a set of color-bound books that contain the technical specifications for all CD formats, the Yellow Book specifies a format for discs with a maximum capacity of 650 MiB. The CD-ROM was introduced by Denon and Sony at the first Japanese COMDEX computer show in 1985.
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