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From: rgm@sandstorm.Berkeley.EDU (Robert Menke)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Why no VM on a 68K? (was: Re: Why 68000?)
Keywords: MMU virtual memory Sys. 7.0 low-end
Message-ID: <22145@pasteur.Berkeley.EDU>
Date: 16 Feb 90 00:31:18 GMT
References: <1990Feb11.154304.19943@smsc.sony.com> <3919@hub.UUCP> <10223@hoptoad.uucp> <1990Feb15.155556.5319@uncecs.edu> <19472@dartvax.Dartmouth.EDU>
Sender: news@pasteur.Berkeley.EDU
Reply-To: rgm@sandstorm.Berkeley.EDU (Robert Menke)
Organization: TEAM CS -- Making Tomorrow's Mistakes Today!
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In article <19472@dartvax.Dartmouth.EDU> tga@eleazar.dartmouth.edu
(Greg Ames) writes:

>And I may be going out on a limb saying this, but didn't the original
>Sun's (the 1/XX series) use a 68000 to run Unix and virtual memory?
>I was under the impression that they came out before the 68010.  If so,
>how did Sun do it?  The MMU could be implemented in custom hardware,
>but what about restarting instructions in mid-stream? (I was under
>the impression the 1/XX's used 68000's, the 2/XX's used 68010's, and
>the 3/XX's used 020's and, later, 030's).

I'm going out on a smaller limb by answering this, but I do know of a
method to implement VM with an original 68000.  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?

>GIVE COIN TO CHARON			|  Robert Menke
"So educated," giggles the voice in	|    rgm@OCF.berkeley.edu
your ear...				|    Robert.Menke@bmug.fidonet.org