Relative to the SCSI bus, this is better than the internal bus
which gave 9-10 MB/sec.
Is it the bus speed that is limiting the drive performance? The
SCSI controller card is capable of 40MB/sec.
Yep.
with all due respect, wrongo, keebler! the system bus is 50mhz, but the
pci bus is only 33mhz. but neither of these are the limitation you are
seeing. the pci bus is 32 bits wide, so multiply 32 bits times 33mhz
and divide by 8 (bits per byte) and you find that the pci bus is capable
of a maximum transfer of 132 megaBYTES per second. in practice, you may
only get a sustained transfer rate of a little more than half that, but
still it is way faster than any other link in the chain. the REAL
limiting factor is the sustained internal transfer rate of the drives,
themselves. older drives can be as low as 5mb/sec or even less. a few
years ago, i paid top dollar for a scsi drive with a sustained internal
transfer rate of 28mb/sec. still way below the maximum of the interface
card OR the pci bus. now, brandy new drives can give sustained internal
transfer rates approaching 60mb/sec. the brandy new maxtor 300gb SATA
drive i just installed in my G5 can manage 58mb/sec. lots of people get
suckered into believing that they only need to buy a new controller
card, and they will automatically get blazing speed. the truth is that
the drives themselves are almost always the limiting factor. with a
scsi ultra 160 interface, you can only achieve that rarefied 160mb/sec
rate if you have a half-dozen or so drives in a raid configuration.
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