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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

Enabling Bus Mastering (DMA) Support

By default, ATAPI CD-ROM drives may operate in Programmed I/O (PIO) mode rather than DMA mode, which is also called Bus Mastering mode. The fact that PIO mode limits DTR to 16.7 MB/s versus the 33.3 or 66.7 MB/s DTR available with DMA is unimportant because no CD-ROM drive even approaches the DTR limit of PIO mode. What is important is that PIO mode causes much higher CPU utilization than DMA mode. A typical ATAPI CD-ROM drive operating in PIO mode may occupy 80% or more of the CPU when the drive is being accessed heavily, while the same drive operating under the same conditions in DMA mode may occupy only 1% to 5% of CPU time.

Accordingly, enabling DMA mode is usually a good idea, but doing so requires that the BIOS, operating system, chipset, and CD-ROM drive itself all support DMA mode. Most recent ATAPI CD-ROM drives support DMA mode. Most motherboards of late-model Pentium vintage or later also support DMA mode on their embedded ATAPI interfaces.

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Publisher Resources

ISBN: 059600513XErrata Page