Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!wuarchive!mailrus!ncar!mephisto!mcnc!ecsvax.uncecs.edu!dlugose
From: dlugose@uncecs.edu (Dan Dlugose)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Why 68000?
Keywords: MMU virtual memory Sys. 7.0 low-end
Message-ID: <1990Feb15.155556.5319@uncecs.edu>
Date: 15 Feb 90 15:55:56 GMT
References: <1990Feb11.154304.19943@smsc.sony.com> <3919@hub.UUCP> <10223@hoptoad.uucp>
Organization: UNC Educational Computing Service
Lines: 19

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.

Previous articles compared the 68000 to the 68030.  I don't know if
someone has pointed out that since most people will sooner or later
want to use System 7.0 AND virtual memory, they will need something
beyond the 68000.  In these discussions a little knowledge is 
dangerous, but I gather that the 68000 cannot support memory
management in a way that will support System 7, since Steve Williams'
68030 Assembly Language Reference (Addison-Wesley) states on p. 8
     "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.

Dan Dlugose
UNC Educational Computing Service