Define constant linear velocity and explain how it applies to CD standards?

Constant angular velocity of a rotating disk means that, given a stationary base reference line and a zero line on the disk, both extending from the center of rotation to the outside edge of the disk, the periodic change in angle between the two lines remains a constant. Such a disk will have constant angular velocity (CAV) if its rate of rotation or revolutions per minute (RPM) remains constant.

While it would be technically possible to have the linear velocity of the disk remain constant by gradually decreasing the speed of rotation as the player head moves across the disk (because the outer paths are longer than the inner ones), this would make things more complicated both for the recording and playback machines, and therefore more expensive.

The paths of information on a CD (or DVD) are analogous to the grooves on an LP recording. The recording and playback heads move across the disk (CD or LP) as it rotates. Actually, of course, there is only one spiral path or groove; on an LP, it goes from the outside edge toward the center; on a CD/DVD, it goes in the opposite direction. In deciding on the parameters for the LP and CD, engineers had to involve the amount of data to be recorded and the spacing required to record that data versus the size of the disk, the speed of rotation, the data capacity of the disk material, and the sensitivity of both the recording and playback heads. ---- The above answer defines Constant Angular Velocity (CAV), not Constant Linear Velocity. The following is the definition to Constant Linear Velocity (CLV): "Constant Linear Velocity (CLV) is a CD-ROM (Compact Disc - Read Only Memory) format in which the spacing of data is consistent on the CD, but the speed of the disc varies on whether the data being read is near the cent or the edge of the disc." During CLV, in order to create the effect of constant speed as the CD turns, the CD drive uses a mechanism that slows down the disc when the laser beam is near the center of the disc, and speeds up the disc when the laser beam is near the outer edge. Thus, the beam is over a sector for the same amount of time, no matter where the sector is.