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[ The PC Guide | Systems and Components Reference Guide | CD-ROM Drives | CD-ROM Performance and Reliability ]

System CD-ROM Caching

Since the CD-ROM drive is a much slower device than the system memory, there is a major performance hit whenever data must be read from the drive itself. Caching refers generally to the use of a small faster store of recently-used data that can be used to fill subsequent requests for the same information while sparing the system from having to re-read it from a slow device. Caching a CD-ROM drive means using a piece of main system memory to hold recently-used data from the CD-ROM in this manner. This is exactly the same as how hard disk caching is done.

Most good operating systems will cache CD-ROM accesses automatically as part of their file system setup, although you can often control how the cache works and how much memory is devoted to it. If you hardly ever use your CD-ROM you may want to reduce the amount of memory set aside for CD-ROM caching, and if you use it a lot you may want to increase the size. Also, slower CD-ROM devices generally need more caching than faster ones, for obvious reasons. Remember that as with hard disk caching, spending too much memory on CD-ROM caching will quickly move you to a point of diminishing returns.

Interestingly, there are products that will cache CD-ROM accesses to the hard disk. This can be advantageous because CD-ROM drives are as much as ten times slower than hard disks (although they are both thousands of times slower than system memory). Caching the CD-ROM to system memory will give much better performance than caching it to the hard disk, but your PC probably has only about 32 MB or so of system memory but gigabytes of hard disk, so you can make the disk-based CD cache much larger. You generally will only want to bother with products like these if you do a lot of CD work.

Tip: A simple and free "caching" procedure for CD-based materials you use a great deal: copy them to a directory on a hard disk volume and use them there instead. Most games do this with some portion of their data for performance reasons.

Next: Drive Quality and Reliability Issues

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