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From: wagner@utcs.uucp (Michael Wagner)
Newsgroups: net.micro.amiga
Subject: Re: How to prevent system death from errors in user code?
Message-ID: <1265@utcs.uucp>
Date: Mon, 2-Jun-86 04:08:57 EDT
Article-I.D.: utcs.1265
Posted: Mon Jun  2 04:08:57 1986
Date-Received: Mon, 2-Jun-86 04:47:43 EDT
References: <8605310909.AA00952@pavepaws>
Reply-To: wagner@utcs.UUCP (Michael Wagner)
Organization: University of Toronto Computing Services, general purpose UNIX
Lines: 20
Summary: 

In article <8605310909.AA00952@pavepaws> dillon@PAVEPAWS.BERKELEY.EDU (Matt Dillon) writes:
>
>	Unfortunetly, since the Amiga does not have an MMU, an error in
>a user program is more likely to overwrite vital system storage (or other
>user programs).  
>					-Matt
>
Lots of people seem to think that MMUs are the only way of solving
such problems.  Protection against bad stores has existed in mainframe
architecture much longer than virtual memory has.  Memory keys,
supervisory modes, 'safe area' registers (which have a proper name I 
can't remember right now) are all attempts to close up the worst holes.
MMUs solve the problem to a much greater extent, because you can't even
address the memory you shouldn't be touching.

Unfortunately, the Amiga doesn't seem to implement any of these.
There is a supervisory mode, but it doesn't deal with storage protection,
unless you add logic off-chip to do it.  Too bad AMIGA didn't.

Michael Wagner (wagner@utcs)