Path: utzoo!utgpu!attcan!uunet!unisoft!hoptoad!tim
From: tim@hoptoad.uucp (Tim Maroney)
Newsgroups: comp.sys.mac
Subject: Re: When will MacOS get virtual memory?
Message-ID: <5537@hoptoad.uucp>
Date: 5 Oct 88 04:33:03 GMT
References: <5624@zodiac.UUCP> <76000290@p.cs.uiuc.edu> <1526@oakhill.UUCP>
Reply-To: tim@hoptoad.UUCP (Tim Maroney)
Organization: Eclectic Software, San Francisco
Lines: 23

C'mon, Tom, let's admit that the 68000 non-recoverable bus error is a serious
screw-up.  Just 'cause you work for Motorola doesn't mean you have to say
everything they did is perfect; a non-recoverable exception is a bad idea.
And it will still be a bad idea no matter how many Motorola employees say
there's nothing wrong with it.  Why'd you fix it if it wasn't broken?

On the other hand, the original message was also wrong.  So what that the 68000
can't be rigged for virtual memory without horrible external logic (I believe
the Sun-1 did something like that)?  It takes more than a CPU to do virtual
memory.  The Mac I motherboard (128K through SE versions) is not socketed for
a memory management chip or daughterboard, so just having a 68010 in there
would make no difference.  You still need a motherboard upgrade, either a
straight swap or an add-on that takes over the whole address bus.  Many
upgrades that take over the whole address bus clip on the 68000 and disable
it, replacing it with one on the add-on board for simplicity.  It would be
just as easy for the add-on board to have its own 68010.

There's no way the simple swap of a 68010 for the 68000 would make the Mac I
any more suited for virtual memory.  VM's a lot more than handling a bus fault.
-- 
Tim Maroney, Consultant, Eclectic Software, sun!hoptoad!tim
"The time is gone, the song is over.
 Thought I'd something more to say." - Roger Waters, Time