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PC Hardware in a Nutshell, 3rd Edition
book

PC Hardware in a Nutshell, 3rd Edition

by Robert Bruce Thompson, Barbara Fritchman Thompson
July 2003
Beginner to intermediate content levelBeginner to intermediate
874 pages
38h 13m
English
O'Reilly Media, Inc.
Content preview from PC Hardware in a Nutshell, 3rd Edition

DVD-ROM Speed

Like CD drives, DVD drives use the “X-factor” to specify throughput. Confusingly, DVD “X” doesn’t mean the same thing as CD “X”. A 1X CD drive transfers data at 150 KB/s (0.146 MB/s), but a 1X DVD drive transfers data at 11.08 million bits/sec (1.321 MB/s), or about nine times the 1X CD rate. In theory, then, the X-rating for a DVD drive when playing a CD disc would be about nine times its DVD rating. In practice, that’s not the case. Early-model DVD-ROM drives typically provide 20X to 32X max CD performance. Current DVD-ROM drives generally provide 40X to 48X max CD performance. DVD throughput faster than 1X is unimportant for DVD-Video, which always plays at 1X, but does provide faster and smoother searching. High throughput is more important if you use the drive to read DVD-ROM discs for playing games or for accessing DVD-ROM data.

Early DVD-ROM drives used CLV, spinning the disc more slowly on outer tracks and faster near the center, to maintain the constant data rate needed for DVD-Video. Current DVD-ROM drives use CAV, spinning the disc at a constant speed and using a buffer to maintain a constant data rate for sequential applications such as DVD-Video. A sure sign that a drive is CAV is if it lists “max” in its speed rating.

Tip

The actual throughput of a DVD-ROM drive depends on the type of disc it is reading. For example, a 16X drive may provide 16X max on single-layer discs, but only 10X max on double-layer discs.

As with CD drives, average access time is often ...

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Publisher Resources

ISBN: 059600513XErrata Page