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PC Hardware in a Nutshell, 3rd Edition by Barbara Fritchman Thompson, Robert Bruce Thompson

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ATA Versus SCSI

Relative to ATA, SCSI has the following advantages:

Performance

ATA drives, whether PATA or SATA, simply cannot compare to SCSI drives in performance under heavy load (although ATA drives may actually be a bit faster under light load because their simpler protocols impose minimum overhead). In our real-world testing, under very heavy disk access, the slowest SCSI drives we used were faster than the fastest ATA drives, particularly under Windows NT/2000/XP, Linux, and other multitasking operating systems. This held true across the board, even when we tested an elderly, midrange Seagate SCSI drive against the fastest of the current ATA drives. Although ATA may actually beat SCSI under light load, when disk activity starts to climb, SCSI is simply faster. Don’t let anyone convince you otherwise.

Tip

To verify our impression of SCSI versus ATA, we did an experiment in mid-2002. At that time, Barbara’s main workstation used a 7,200 RPM SCSI Seagate Barracuda drive. We built an identical system, but substituted a 7,200 RPM Seagate Barracuda ATA IV drive. During normal operation, performance of the two PCs was indistinguishable.

We then started an XCOPY operation that streamed gigabytes of data comprising hundreds of directories and thousands of files from a third system across our 100BaseT network to the hard drive of the ATA system. While that data was being copied, the ATA system was nearly unusable. Loading Word from the hard drive took literally a full minute, and opening ...

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