All SCSI-II and SCSI-III wide drives are supposed to be backward
compatible, but may require a jumper to be set differently. I have
several adapters that convert the 80pin SCA drives to be able to use
both the 50pin, or 68pin cables. With SCSI, the slowest drive, or
device on the chain (cable) determines the maximum speed that the
chain can run at, so if you have slower SCSI-II, or SCSI-III wide
drives on a cable that also has a SCSI-I 50pin device, the faster
device will be slowed down to the max. speed of the slower device.
I have an over-clocked Amiga A4000 that can no longer use it's SCSI
controller, because of timing issues. But I have another RAM
expansion board that has a fast SCSI-II controller that I can use
instead of the SCSI controller on the Amiga accelerator, so I am
happier to keep the accelerator over-clocked at 60% faster operation
and give up the accelerator's built-in SCSI controller.
SCSI has much less CPU overhead than IDE, which can make direct speed
comparisons misleading, as all good operating systems are now Multi-
tasking, Multi-threaded, so when copying large files, or loading them
to RAM to run while also doing other things on your computer, using a
SCSI drive will allow a great deal more CPU resources for the other
tasks, where an IDE drive will not.
As most computers are far more powerful today than is needed for most
software, this is not an issue often. Back in the days of 30MHz CPU's
instead of 3.0GHz CPU's with multiple cores, using a SCSI drive could
make more of a difference. At least on an Amiga, which was one of the
first popular home computers that pioneered Multi-tasking. I remember
impressing Windows users by formatting up to 4 floppy disks at the
same time while playing a 4 voice music mod and using a high color
paint program all at the same time on a 7MHz computer that reacted
faster than their 286 systems running at 16MHz or 20MHz. Ahhh, the
good old days! SCSI was a great interface in it's day.
On Dec 10, 2011, at 4:54 PM, Barry Levine wrote:
Hi
One of the 8GB SCSI HD's on my 8600 G3 is failing. Checking around
eBay, I
see 68 pin SCSI HD's for sale; and one can purchase an adapter to go
to
the mac 50 pin cable.
I also noticed that there are many larger size 68 pin scsi HD's around
than the 50 pin - are these 68 pin drives a bit more recent than the
50
pin ones, and are they usable in my mac with the adapter?
thanks
Barry
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