Spin Speed

The rate of spin of an original 1x CD-ROM drive varied, in order to achieve a constant data transfer rate of 150KB/s. Subsequent speed increases used the same CLV methods through approximately 10x speeds, depending upon the manufacturer. Most manufacturers then used CAV or partial CAV technology to increase maximum transfer speeds substantially, while improving minimum transfer speeds less dramatically. For instance, Plextor's (http://www.plextor.com) UltraPlex 40Max CAV drive achieves 40x transfer speeds at its fastest point, but only 17x at its slowest. You can expect similar speed disparities in other CAV drives, but less speed disparity in partial CAV drives.

TrueX drives, which use multiple laser beams rather than higher transfer rates to improve performance, generally use CLV operation, so they can achieve uniformly high transfer rates. As mentioned earlier, however, some of these drives don't work well under Linux, and some can damage CD-R or CD-RW media. Be sure to check with the manufacturer or on the comp.os.linux.hardware and comp.sys.ibm.pc.hardware.cdrom newsgroups about these details before buying one.

In years past, the fastest drives available typically used caddies (shown in Figure 7.5). These devices hold CDs in order to protect them and position them more precisely in the drive than can be done using a more typical tray-loading design. Ideally, you place each CD in its own caddy as soon as you get the CD, and don't remove it. You insert the caddy, complete with its passenger CD, into the drive when you want to read a data CD-ROM or listen to an audio CD. This procedure protects the CD from scratches and dirt, but can become expensive if you collect a large number of CDs. Today, caddies are rare, although a few recordable CD drives still use them.

Part II

Figure 7.5

A caddy's lid flips up to allow you to insert or remove a CD.

Figure 7.5

A caddy's lid flips up to allow you to insert or remove a CD.

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