A 120 mm metal disk on which there is a digital recording of audio information, providing high-quality recording and reproduction of music, speech, etc. The recording is protected by a layer of clear plastic. The information is permanently encoded in the form of a spiral track of minute pits impressed on one surface of the disk during manufacture; these impressions correspond to a changing sequence of bits. The CD is rotated at constant linear velocity (CLV) in a CD player; the rotation rate varies according to the radius of the track accessed. Data are retrieved from the rotating disk by means of a low-power laser focused on the track and modulated by the binary code impressed on the track. See also CD-RW.