Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!think!snorkelwacker!mit-eddie!bu.edu!dartvax!eleazar.dartmouth.edu!tga
From: tga@eleazar.dartmouth.edu (Greg Ames)
Newsgroups: comp.sys.mac.hardware
Subject: Why no VM on a 68K? (was: Re: Why 68000?)
Summary: Didn't Sun do it?
Keywords: MMU virtual memory Sys. 7.0 low-end
Message-ID: <19472@dartvax.Dartmouth.EDU>
Date: 15 Feb 90 22:26:00 GMT
References: <1990Feb11.154304.19943@smsc.sony.com> <3919@hub.UUCP> <10223@hoptoad.uucp> <1990Feb15.155556.5319@uncecs.edu>
Sender: news@dartvax.Dartmouth.EDU
Organization: Dartmouth College, Hanover, NH
Lines: 29

In article <1990Feb15.155556.5319@uncecs.edu> dlugose@uncecs.edu (Dan Dlugose) writes:
:Any new low end Mac will be bought by a lot of people who will want to
:upgrade it and do more a year or two later.
:
: [discussion of why the 68000 can't support virtual memory nuked
:  to save the net millions in phone costs! :-) ]
:
:     "The 68000 lacks the ability to restart an instruction following
:a memory fault, but the 68010 permits the instruction to be continued
:after the condition that caused the fault to be corrected" supporting
:virtual memory.  So I believe the minumum chip would be a 68010 AND
:MMU chip, which might use more power than a 68030 with its on board
:memory management.

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).

         Greg

--
Greg Ames, '90     |  tga@eleazar.Dartmouth.EDU
HB 1362            |  ...!{harvard,linus,inhp4,etc}!dartvax!eleazar!tga
Dartmouth College  |
Hanover NH, 03755  |          { This space available for rent! }