--- Bill Pechter <pechter_at_pechter.dyndns.org> wrote:
> > Is that a SystemIII box with dual 68000 processors,
> >
> > -ethan
>
>
> Actually, it only had a single cpu. (10 mhz). Ran SysIII (UniPlus)
> SysV (microXelos -- which had it's root in UniPlus SysV), and Idris.
Mine has SysIII/UniPlus. Got all the docs and disks, too.
> The dual cpu stuff at the time was done by Sun (I think) and Masscomp
> (their 500 series stuff).
My apologies for not being clearer... IIRC, there are two 68000 CPU
chips in the box. One runs the OS, the other is part of the memory
management system. Since the 68000 itself (not the 68010 and up)
does not save enough information on a page fault trap to restart
instructions, the way I was told the Perkin-Elmer worked was to have
the other CPU kick in on a page fault, load the page, then somehow
automagically get the main CPU to resume without loss of information,
etc. Perhaps it holds off DTACK during a page fault, then releases
it when the page is ready to go; I don't know any technical details
and I never did anything with the kernel on it. I was just a user
then an admin. The hairiest thing we ever did to the box was to
replace a power supply and an HDA.
This sort of gyration was obviated by the 68010 since it _did_
fully support virtual memory. Old Suns went that way, as did
the NCR tower I have. I remember sticking in the '010 into
my Amiga 1000 for the 5% performance gain that came from the
two instruction cache/loop mode enhancement. Very few programs
after AmigaDOS 1.2 used the now-supervisor-mode MOVEcc instructions
and in any case, there was an OS patch to add a trap handler for
that (but I digress wildly).
We got the Perkin-Elmer because it was a) cheap b) 68000-based. I'm
happy to have rescued it at the end of its useful life eight years
ago.
-ethan
=====
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Received on Wed Oct 18 2000 - 13:44:25 BST