Hello Andrew!

  AB> The 160Mb/sec SCSI doesn't run at 160MHz because it is wider
    > than the 8 bits of the old sparcs...

That's one of the reasons, the other is double-transition clocking:
data is transferred on both the rising and falling edges (of the
clock?), effectively doubling the maximum possible throughput for any
given clock speed.

  AB> I think 160Mb/sec is ultra-wide ie. 32bits, so it would only
    > need to run at a sensible 40MHz.

The 'ultra' part of 'ultra, wide' refers to the clock speed.  The
'wide' part signifies a 16-bit wide bus.  My understanding of Ultra160
(I'm not rich enough to play with this stuff ;o) is that it's clocked
at 40 MHz.

   40 MHz x 2 transfers per clock x 2 bytes per transfer = 160 Mb/S

     ...theoretical peak, I imagine individual disks are still slow
enough not to saturate an Ultra160 bus.

  AB> Could you imagine trying to get reasonable propogation
    > characteristics at 160Mhz from unscreened ribbon cable?

No thanks! ;-)

Regards,
  - Andy Ball.