CAV VS CLV

7/12/97

Constant Angular Velocity (CAV) vs Constant Linear Velocity (CLV): These are two different techniques for storing data on rotating media. Many magnetic disks (some Macintosh floppies excepted), that are frequently randomly accessed, rotate at a constant speed (Constant Angular Velocity). Unless read/write speeds are adjusted to give greater density, this spreads data bits out over more space on outside tracks than interior tracks.

CDROMs on the other hand were originally designed to play music sequentially and are recorded at fixed data density -- Constant Linear Velocity. This requires the drive to vary its speed during read. While this results in more data stored per unit of surface area, it requires the drive to change rotation speed when moving to a different track. This results in lengthy seek times when CDROMs are read randomly since the drive must speed up or slow down. Some "Fast" CDROMs use CAV playback resulting in faster seeking, but in variable read rates -- slowest on the inner tracks where data is most likely to be recorded, and fastest on the outer tracks where data may well not be recorded. Quoted speeds for CAV CDROMs are for the faster outside tracks.

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