compact disc
Disk for storing digital information, about 12 cm/4.5 in across, mainly used for music, when it can have over an hour's playing time. A laser beam etches the compact disc with microscopic pits that carry a digital code representing the sounds; the pitted surface is then coated with aluminium. During playback, a laser beam reads the code and produces signals that are changed into near-exact replicas of the original sounds.
CD-ROM, or compact-disc read-only memory, is used to store written text, pictures, and video clips in addition to music. The disks are ideal for large works, such as catalogues and encyclopedias. CD-I, or Compact-Disc Interactive, is a form of CD-ROM used with a computerized reader, which responds intelligently to the user's instructions.
| Increasingly the dominance of the CD is being challenged by the development of alternative formats. The DVD has the same dimensions as a CD but can store over double the capacity of data. DVD drives are replacing CD-ROM drives in personal computers and as a medium for storing computer programs. Solid-state memory cards capable of exchanging data between PCs, digital cameras, PDAs, and MP3 music players are increasingly being used. |
