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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0110:  Removable Media
      9  IV  CD-ROM

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CLV vs. CAV
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CD-ROM Formats
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Other Performance Factors

Some other factors to be aware of in determining the overall performance of the CD-ROM drive or that of seek time, latency, an access time. Seek time refers to the amount of time that it takes to move the read heads to a specific part of the disk to perform a read.

Of course this amount of time is determined by how far the heads are from the point they need to be moved to. Therefore seek times are usually reported as the average time it takes to move the heads for a typical random read.

The latency of the CD-ROM drive refers to the time it takes for the proper block of data to be moved underneath the read head once the read head has been moved to its proper location.

This means that a CAV drive would have better latency on the inside of the disk than on the outside. CLV drives on the other hand have the best latency times on the outside of the disk.

The most important performance factor of any CD-ROM drive is its access time. Access time is a measurement of the amount of time it takes from the start of a random read until the data starts to be read from the disk.

Access time is a composite metric composed of the speed change time (for CLV drives), the seek time, and latency of the drive.

Unfortunately, there's no easy mathematical formula that you can plop these three values into and determine a drive's access time.

This is due in part to the fact that these three factors can be done in parallel.

[spacer]CD-ROM Access Time

Older CD-ROM drives had pathetic access times of over 300 milliseconds, whereas newer drives have come down to 100 milliseconds or less.



Previous Topic/Section
CLV vs. CAV
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CD-ROM Formats
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