A compact disc [sometimes spelled disk] (CD) is a small,
portable, round medium made of molded polymer (close in size to
the floppy disk) for electronically recording, storing, and
playing back audio, video, text, and other information in
digital form. Tape cartridges and CDs generally replaced the
phonograph record for playing back music. At home, CDs have
tended to replace the tape cartridge although the latter is
still widely used in cars and portable playback devices.
Initially, CDs were read-only, but newer technology allows users
to record as well. CDs will probably continue to be popular for
music recording and playback. A newer technology, the digital
versatile disc (DVD), stores much more in the same space and is
used for playing back movies. Some variations of the CD include: