Introduced in 1982, the Compact Disc (CD) is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage (CD-R), rewritable media (CD-RW), Video Compact Discs (VCD), Super Video Compact Discs (SVCD), PhotoCD, PictureCD, CD-i, and Enhanced CD.
Standard CDs can hold up to 80 minutes of uncompressed audio. CD-ROMs and CD-Rs remain widely used technologies in the computer industry. However, Compact Discs are increasingly being replaced or supplemented by other forms of digital distribution and storage, such as downloading and flash drives, with audio CD sales dropping nearly 50% from their peak in 2000.
Red Book (CD standard) The logical format of an audio CD (officially Compact Disc Digital Audio or CD-DA) is described in a document produced by the format's joint creators, Sony and Philips in 1980. The document is known colloquially as the "Red Book" after the color of its cover. The format is a two-channel 16-bit PCM encoding at a 44.1 kHz sampling rate per channel. Four-channel sound is an allowable option within the Red Book format, but has never been implemented. Monaural audio has no existing standard on a Red Book CD; mono-source material is usually presented as two identical channels on a 'stereo' track.
For more information on Compact Discs, please see the Compact Disc Article on Wikipedia.