A compact disc or a CD is an optical storage device originally used for storing audio data. It was originally created in 1982, and until 1985, was only used for storing audio. Typically, they are 4.7 in (120 mm) in diameter and hold up to 750 megabytes. CDs today are also used for storing other digital information and are called CD-ROMs. In addition, CD-Rs and CD-RWs  allow consumers to write (and rewrite) their own information, usually with a personal computer. The DVD format was designed to be backward compatible with the CD format.