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From: philip@pescadero.Stanford.EDU (Philip Machanick)
Newsgroups: comp.sys.mac.system
Subject: Re: Protected-mode snake oil
Message-ID: <1990Aug24.180757.3439@Neon.Stanford.EDU>
Date: 24 Aug 90 18:07:57 GMT
References: <33164@cup.portal.com> <1204.26c2fb48@waikato.ac.nz> <8919@ur-cc.UUCP>
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Reply-To: philip@pescadero.stanford.edu
Organization: Computer Science Department, Stanford University
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In article <33164@cup.portal.com>, ts@cup.portal.com (Tim W Smith) writes:
> The Callan Data Systems Unistar 200 I used to have had only
> a 68000 and supported an MMU quite well.  A whole bunch of
> other 68000 systems of the same vintage also supported
> MMUs quite well.
> 
There was a discussion of this on comp.arch a while back. I don't remember
the details, but it wasn't trivial. The problem is the 68000 doesn't
keep enough state to restart some instructions that may be interrupted
by a page fault. Some solutions included tricks like a second 68000 -
it didn't sound to me as if one could simply tack on an MMU and get paging,
the way you can with a 68020 (well, if assuming getting the software side
to work is simple...).

Philip Machanick
philip@pescadero.stanford.edu