Computer storage device developed from the technology of the audio compact disc. It consists of a plastic-coated metal disk, on which binary digital information is etched in the form of microscopic pits. This can then be read optically by passing a laser beam over the disk. CD-ROMs typically hold over 600 megabytes of data, and are used in distributing large amounts of text, graphics, audio, and video, such as encyclopedias, catalogues, technical manuals, and games.
Standard CD-ROMs cannot have information written onto them by computer, but must be manufactured from a master, although recordable CDs, called CD-R disks, have been developed for use as computer disks. A compact disc, CD-RW, that can be overwritten repeatedly by a computer has also been developed, but due to its relatively high unit cost the format has not become widely adopted.
The technology is being developed rapidly: a standard CD-ROM spins at between 240 and 1,170 rpm, but faster disks have been introduced that speed up data retrieval to many times the standard speed (a 52× speed CD-ROM drive spins the disc at 10,350 rpm). Research is being conducted into high-density CDs capable of storing many gigabytes of data, made possible by using multiple layers on the surface of the disk, and by using double-sided disks. The first commercial examples of this research include DVD players and DVD-ROM computer disks launched in 1997. The future of the format looks unsure with the growth in popularity of the Blu-ray disk and its 25 gigabytes capacity.
Quality in a Digital Age
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