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From: amanda@mermaid.intercon.com (Amanda Walker)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Why no VM on a 68K? (was: Re: Why 68000?)
Message-ID: <1990Feb16.164414.6377@intercon.com>
Date: 16 Feb 90 16:44:14 GMT
References: <1990Feb11.154304.19943@smsc.sony.com> <3919@hub.UUCP> <10223@hoptoad.uucp> <1990Feb15.155556.5319@uncecs.edu> <19472@dartvax.Dartmouth.EDU> <22145@pasteur.Berkeley.EDU>
Sender: @intercon.com
Reply-To: amanda@mermaid.intercon.com (Amanda Walker)
Organization: InterCon Systems Corporation, Sterling, VA
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In article <22145@pasteur.Berkeley.EDU>, rgm@sandstorm.Berkeley.EDU (Robert
Menke) writes:
> What you do is have
> TWO processors, with one running just behind the other.  When the
> first one bus-faults, the secondary one is halted, the missing page is
> loaded in, and the secondary one switches places with the original
> primary one.  Not exactly sure if it was Sun who pulled this rabbit
> out of a hat or not, though.  Can anyone out there confirm?

[a moment while I search through my brain's backup tapes...]

I think it was Motorola themselves who first suggested this.  When the
68000 first came out, they issues a bunch of "application notes" showing
things like example memory interface circuitry, use of VPA, and so on.
One of these was an example of doing virtual memory with a two-processor
system.  When a page fault occured, processor A just went into a wait state,
processor B woke up, swapped in the page, and then woke up processor A
again.

Kind of a kluge, but it did work.  The 68010 was a big improvement.

Trivia quiz: anyone remember the 68012?

--
Amanda Walker
InterCon Systems Corporation

"Many of the truths we cling to depend greatly upon our own point of view."
	--Obi-Wan Kenobi in "Return of the Jedi"