Macintosh IIfx: NuBus/SCSI Speed


I'm a little confused about SCSI data transfer. Several sources say that
the speed of the SCSI port on a Macintosh IIfx is between 1.4MB and 4.0MB
per second. I know that synchronous mode is needed to obtain the higher
rates, but if a drive is only rated at 13 kilobytes per second with an
access time of 11.9 milliseconds, how do I get rates of 2 or 3 megabytes
per second?

Also, if the NuBus slots are rated at 10MB per second, wouldn't I gain by
using these slots?

It's not the access time of the drive that matters, but rather the
sustained transfer rate. Any SCSI hard drive that can sustain transfer
rates above 1.25MBps will operate faster on a Macintosh IIfx compared to
any other Macintosh system. None of Apple's present drives take advantage
of this potential.

If a SCSI card was designed to operate with NuBus it would limited to 10MB
per second, which is faster than the Macintosh IIfx's 3MB per second spec,
but much faster that any of our other drives, at this point.


Published Date: Feb 18, 2012