compact disc

compact disc (CD), a small plastic disc used for the storage of digital data. As originally developed for audio systems, the sound signal is sampled at a rate of 44,100 times a second, then each sample is measured and digitally encoded on the 4 3/4 in (12 cm) disc as a series of microscopic pits on an otherwise polished surface. The disc is covered with a transparent coating so that it can be read by a laser beam. Since nothing touches the encoded portion, the CD is not worn out by the playing process. Introduced in 1982, the CD offered other advantages over the phonograph record and recording tape—smaller size, greater dynamic range, extremely low distortion—and met with rapid consumer acceptance; the CD became the music carrier of choice by 1991, when sales exceeded those of audiocassettes.

Other CD formats include CD-ROM [ C ompact D isc- R ead O nly M emory], a form of CD that is read (but not written to) by computer using a CD-ROM drive and that can contain computer programs and digitized text, sound, photographs, and video; CD-R [ C ompact D isc- R ecordable] and CD-RW [ C ompact D isc- R e W ritable], which can be written to one time and multiple times, respectively. Interactive CDs (CD-I, CDTV, and other formats) can store video, audio, and data. Photo CD is a format that holds digitized photographs and sound. There are also CD-ROMs that require special players with built-in microcomputers.

Other optical disk formats include digital versatile (or video) discs and videodiscs. A digital versatile disk (DVD) holds far more information than a CD. DVD players are backward compatible to existing technologies, so they can also play a CD (or CD-ROM), but a CD player cannot be used with a DVD (or DVD-ROM). The videodisc , or laser disk system, uses 12-in. (30-cm) disks for video recording. Its technology, unlike that of the CD, is an analog system that uses a laser to read a variable-width track, much like a conventional phonograph record.

compact disc (CD) Disc used for high-quality digital sound reproduction. It is a plastic disc with a shiny metal layer and a transparent protective plastic coating. The sound signal consists of millions of minute pits, pressed into one side of the metal. On replay, a narrow laser beam is reflected from the rotating disc's surface. A sensor detects changes in the beam, and forms an electrical signal of pulses. This is processed and decoded to form a sound signal that can be amplified for reproduction on loudspeakers. See also CD-ROM

com·pact disc (also com·pact disk) (abbr.: CD) • n. a small plastic disc on which music or other digital information is stored, and from which the information can be read using reflected laser light.See also CD-ROM.