4 Jul
2015
4 Jul
'15
12:43 p.m.
Mouse wrote:
I recall hearing of a company that build a machine
with two 68000s,
one
running one instruction behind the other. When the
leading processor
got a
page fault, hardware interrupted the lagging processor
(which had not
yet
encountered the faulting instruction) and there's
a dance where the
two
processors switch roles, allowing useful page faults.
I think Wicat Systems did this in their System 100 (early Unix
workstation) machines.
I very clearly remember that Tektronix got one of these systems for
evaluation back in the day when I worked there.
I went to a presentation when the machine was brought in by the local
distributor, and the presentation mentioned that there were two Motorola
68000 microprocessors in it "to make it more powerful" or some such
marketing BS.
When the Microprocessor Development Group got its hands on the machine,
immediately it was opened up, and on the CPU board were indeed two
Motorola 68000 chips sitting side-by-side. Some reverse-engineering was
done, and it was determined that these two CPUs worked together in some
way to provide way to provide demand paging.
We got lots of early Unix workstations for evaluation back in those
days. I remember the Wicat quite vividly, and I'm pretty sure this
was the machine, but it's possible it was some other Unix workstation
machine.
-Rick