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Handling Discs and Data
4
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.