Handling Discs and Data

Partial CAV (Constant Angular Velocity)

The CLV (Constant Linear Velocity) method is generally used to write data on a CD-R disc. In writing by the CLV method, the disc rotation speed is adjusted to keep the data writing speed (data transfer rate) constant at any part of the disc.

In contrast, the CAV method (Constant Angular Velocity) method exercises control so as to keep the disc rotation speed constant. The CAV method makes it possible to substantially increase the maximum data transfer rate with a minimum increase in the load to the drive, and for this advantage, it is adopted today for most play-only CD-ROM drives.

Since a CD is formatted so that it has an even data recording density at all of its parts, the amount of data recorded in a track increases as the read/write head moves outward on the disc. For the CAV method, therefore, data is transferred at a higher rate when it is written in tracks at the outer radius of the disc.

To achieve up to 12X-speed writing, the CRW-70 drive employs the Partial CAV method, which is a combination of the CAV method used for writing in inner tracks and the CLV method used for writing in outer tracks. The Partial CAV method controls the disc rotation speed so that the CRW-70 drive starts writing at 8X speed in inner tracks, increases the speed to 12X as the read/write head moves outward, and holds the speed at 12X in outer tracks.

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