A CD player has three major mechanical components : a drive motor, a lens system, and a tracking mechanism. The drive motor (also called spindle) rotates the disc between 200 and 500 revolutions per minute. The tracking mechanism moves the lens system along the spiral tracks in which information is encoded, and the lens reads the information using a laser beam, typically produced by a laser diode. The laser reads information by focusing a beam on the CD, which is reflected back to a sensor. The sensor detects changes in the beam, and interprets these changes to read the data. This data is processed, and eventually converted to sound using a digital-to-analog converter (DAC).
A subcode in an audio CD contains information on the total number of audio tracks, the running time on the CD, the running time of each track, and other information.