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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.micro.atari16,net.micro.amiga,net.micro.68k
Subject: Re: 68000 Memory Managment
Message-ID: <7072@utzoo.UUCP>
Date: Tue, 26-Aug-86 16:03:06 EDT
Article-I.D.: utzoo.7072
Posted: Tue Aug 26 16:03:06 1986
Date-Received: Tue, 26-Aug-86 16:03:06 EDT
References: <508@elmgate.UUCP>
Organization: U of Toronto Zoology
Lines: 18
Keywords: 68000 atari amiga 68k mmu

> If memory serves me correct the 68000 can not restart/resume a bus faulted
> instruction.  So regardless of what mkind of MMU you try to hang on it, it
> can not overcome this problem.

That's right.  On the other hand, being unable to restart a faulted
instruction (in the general case) only means you can't do demand paging,
or similar schemes where you want to pretend memory is always there when
it sometimes isn't.  The inability to do this is a wart, but it does not
preclude doing useful things like running Unix.  This message is being
typed on a PDP-11/44 running V7, which doesn't do virtual memory but is
still a fine system if you don't want to run huge programs.  The MMU on
the 44 can actually do demand paging, although it's not clear that it's
worthwhile given various complications, but V7 doesn't use it that way.
Relocation and protection is all you need to run a multiprogramming system
simply and well.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,decvax,pyramid}!utzoo!henry