On Feb 10, 2004, at 12:09 pm, Peter da Silva wrote:
With ATA you have to deal with master-slave conflicts, cable-select that
doesn't, devices that only work right as master and devices that only work
right as slave, ATA-66, -100, -133, and crappy performance because ATA
doesn't support disconnect and tagging.
The key and pivotal advantage SCSI has over all forms of ATA (at least up to ATA133) is the fact that ATA requires huge amounts of CPU interrupts to process read and write commands. This slows EVERYTHING down while the computer loads or saves large files or volumes of data. SCSI on the other hand only requires a minimum of CPU interrupts in the same time frame and unless you are accessing a very fragmented data mass, or the app you are using decodes or executes files or data as it loads the file, the CPU impact is almost nothing so you can carry on with about 90% CPU cycles free for doing other things. I am pretty sure SerialATA, as used in the G5 and my only PC, has dramatically reduced the number of ATA interrupts requested in a set time frame but it is not as efficient as SCSI.
Yeh, I know Apple's SCSI was never particularly high performance but that's
Apple's problem, not anything specific to SCSI.
It's a shame PCI SCSI cards are such a crapper to get working in OS X as I'd far prefer to run my system from the U2W SCSI bus in my 9600, but can't.
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