-- Digging Deeper
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3 The original CD reading
and recording standard was the Constant Linear Velocity (CLV). CLV
kept the laser beam on a constant spiral motion around the CD for
either writing or reading. New CDRW drive come with new technology to
allow for faster recording speed. Three of the newer technologies are
the Zone-Constant Linear Velocity (Z-CLV), Partial Constant Angular
Velocity (P-CAV), and Buffer Underrun protection.
Z-CLV was developed by Sanyo to achieve a higher
recording speed. As the name implies, Zone, divides the CD into
three regions. CLV will record each region at a constant velocity.
For example, a 24x CDRW drive equipped with Z-CLV will burn Fig. 1
(Sanyo Z-CLV) Zone 1, the inner part of a CD, at 16x. When it moves
to Zone 2, it will write at 20x. Finally when it reaches Zone 3, it
will record at 24x.
P-CAV was developed by Yamaha to allow
for drives to record faster. In P-CAV, the CD is divided into two
regions. The inner part of the CD will be recorded using CLV
technology. When it reaches the second region, it will use its CAV
to achieve faster recording time. Notice that Constant Linear
Velocity keeps the CD spinning at the same speed as it moves toward
the outer part of the CD. Constant Angular Velocity keeps the motor
spinning at the same speed, thus as the laser beam moves toward the
outer part of the CD, the speed at which the CD spins increases.
Buffer Underrun errors occur when the
CDRW drive is not receiving any data to write. Thus it does not know
what to do, and terminates the recording process in an error.
Manufacturers have developed several solutions to this problem.
However the concept is the same for all of them. When the drive is
not receiving any data, it will enter a waiting state. In the
waiting state the drive will wait for data to be sent for
processing. Once data transmission resume, the drive will complete
the recording process. Fig. 3 and 4 show how Buffer Underrun occurs.
 
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