Unlike hard disks, which record data on a series of concentric tracks, CDs have only one track that spirals from the center of the CD out to the edge, much like a vinyl LP. Because the portions of the track toward the center are shorter than those toward the edge, moving data under the head at a constant rate requires spinning the disc faster as the head moves from the center, where there is less data per revolution, to the edge, where there is more. If an audio CD spun at some compromise constant rate, the audio would sound like the Addams Family’s Lurch when the CD was playing the inner portion of the track, and like Alvin the chipmunk when it was playing the outer.
The solution is to change the disc rotation rate as the heads progress from the inner to the outer portions of the track. When you play an audio CD in a CD player (or in your computer’s CD-ROM drive), the drive speeds up and slows down according to what portion of the track the heads are currently reading. This technology, shown in Figure 10-1, is called Constant Linear Velocity (CLV).
Figure 10-1. CLV technology, which spins a disc at a constantly varying speed to keep the data rate identical regardless of what part of the disc is being read (image courtesy of Ahead Software)
All audio CD players use CLV. CLV is a good choice for audio for two reasons. First, the drive only need ...