pefo at opsycon.se
Tue Jun 13 16:06:06 UTC 2006
On Tuesday 13 June 2006 14:23, Rick Kelly wrote:
> Johnny Billquist said:
> >> There's actually a cheesy way to do demand paging with microprocessors
> >> that don't support demand paging (such as the original 68000--another
> >> "16 bit" machine). The way to do this is to run two processors in
> >> parallel but skewed by one instruction. If the first one does a bad
> >> memory fetch, then the second one will not have fetched the instruction
> >> causing the fault so contains restartable machine state. Masscomp sold
> >> a machine like this once.
> >Didn't the first Apollos do this?
> And also the Sun 1.
IIRC it was simpler than that. When the first cpu caused a 'miss' it was put
in wait and cpu 2 handled the pagein and then released cpu 1. Keeping the two
cpus synched, one instruction apart would have been too complicated if not
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