18 Jan
2007
18 Jan
'07
8:39 a.m.
On 17 Jan 2007 at 22:55, Don North wrote:
A few years earlier Apollo Computer came out with
their first system
that employed a 68000 that implemented a full demand paged virtual
memory system. The trick they used was to have two separate 68000
processors, one for the user and the other to service page faults.
When it was determined that the user processor would fault, that
68000 was frozen mid-access, then the system 68000 would service the
fault, fix memory up, and then let the user 68000 continue. Actually
kind of an innovative approach at the time.
I recall hearing about that. One 68K ran a clock or so ahead of the
other. Sort of like navigating in the dark by sending someone with a
rope tied around him a few paces ahead of you. If he drops into a
pit, you can pull him out, step around the pit and keep going. My
impression is that it was a fairly expensive way to do things, but
there weren't a lot of microprocessor CPUs that could handle VM at
the time.
Cheers,
Chuck