CD

A "small" injection-molded optical disc containing digitized information that has been recorded with a laser device and must be read on a laser device. The term "small" generally refers to a disc that is 8 cm or 12 cm (4.72 inches) in diameter as opposed to videodiscs that typically are much larger in diameter. Also, videodiscs usually are restricted to analog inputs from videotape whereas CDs rely on inputs from computer tape or other digitized platforms. Although there are several types of CDs for audio, television, and computer playback, the CD-Audio and CD-ROM discs have overwhelming shares of the market. For example, Kim (1994) discusses why CD-ROM discs are replacing floppy discs in a "ground swell." CD-ROM discs now hold approximately 680 Mb (i.e., 680 million characters) although compression techniques make it possible to record CDs from even larger computer files. Usually CDs have slower access speeds than magnetic hard drives, but speeds are improving and playback of video is now possible on both CD-ROM and CD-I players. Although the best known CDs once were those that contain only audio recordings, there is a rapidly growing market for various types of CDs that contain computer files and/or files that can be read on special devices connected to television sets. (See also Bar codes , CAV , CLV , Photo CD , Videodisc , Minidisc , CD-Stand Alone , Nintendo/SGI Cartridges , and Laserdisc )