A Compact Disc (also known as a CD) is an optical disc used to store digital data. It was developed to store music at the start, but later it also allowed to store other kinds of data. CD have been available since October 1982. In 2009, they are still the standard physical medium for commercial audio recordings.
Standard CDs have a diameter of 120 mm and can hold up to 80 minutes of audio (700 MB of data). The Mini CD has various diameters ranging from 60 to 80 mm; they are sometimes used for CD singles or device drivers, storing up to 24 minutes of audio.
The technology was later adapted and expanded to include data storage CD-ROM, write-once audio and data storage CD-R, rewritable media CD-RW, Video Compact Discs (VCD), Super Video Compact Discs (SVCD), PhotoCD, PictureCD, CD-i, and Enhanced CD.
CD-ROMs and CD-Rs remain widely used technologies in the computer industry. The CD and its extensions are successful: in 2004, worldwide sales of CD audio, CD-ROM, and CD-R reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide.
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