Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!pyramid!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.m68k
Subject: Re: Apollo/Sun 68000,68010,68020
Message-ID: <3560@cbmvax.UUCP>
Date: 31 Mar 88 16:04:42 GMT
References: <3b219db7.d858@apollo.uucp>
Organization: Commodore Technology, West Chester, PA
Lines: 33

in article <3b219db7.d858@apollo.uucp>, heinzl_c@apollo.uucp (Carl Heinzl) says:

> This is incorrect.  Apollo DN600 (do not confuse with DN660), 400 and 420
> are all 68000 based machines.  They use an arrangement of Dual 68000
> cpus to allow preemptive multitasking.  

It's not the preemptive multitasking that this is needed for...

> Basically, one of the processors
> does the error handling when a page fault is taken while the other
> preserve machine state (making it restartable).

yes, we have it here.  Page Fault.  As in, virtual memory.  When the CPU
tries to access memory that isn't in the system, it gets a page fault,
that memory is brought in from mass storage, and then the instruction is
either continued or restarted.  The 68000 certainly doesn't allow either
instruction continuation or restart, thus the two 68000 scheme.  On the
68010, they added instruction continuation, so eveything's cool at that
level on up.

>>Not that this implies that multi-tasking is impossible on the
>>68000.  The Amiga is a prime counter example.

The 68000 handles preemptive multi-tasking just fine.  It would work just
fine with an MMU, too.  But it's not going to allow any virtual happenings
without some serious black magic, like maybe a second 68000.  Fortunately
for anyone concerned these days, 68010s are available and pin compatible.

> Carl G. Heinzl  apollo.UUCP
> (617) 256-6600 x 7153
-- 
Dave Haynie  "The B2000 Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {ihnp4|uunet|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
		"I can't relax, 'cause I'm a Boinger!"