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From: eric@chronon.UUCP (Eric Black)
Newsgroups: net.micro.amiga
Subject: Re: How to prevent system death from errors in user code?
Message-ID: <281@chronon.chronon.UUCP>
Date: Tue, 3-Jun-86 17:59:48 EDT
Article-I.D.: chronon.281
Posted: Tue Jun  3 17:59:48 1986
Date-Received: Thu, 5-Jun-86 07:29:46 EDT
References: <8605310909.AA00952@pavepaws> <1265@utcs.uucp>
Reply-To: eric@chronon.UUCP (Eric Black)
Organization: Chronon Computer Corp., Mtn. View, CA
Lines: 30

In article <1265@utcs.uucp> wagner@utcs.UUCP (Michael Wagner) writes:
>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.

Explain to me how these techniques are not "Memory Management".  Reminder:
MMU stands for "Memory Management Unit", NOT "Memory Mapping Unit".
You are confused by the fact that the current spate of single-chip
solutions to some memory management problems all seem to have logical
address mapping (whether virtual or not).  Ignoring the advantages
that address mapping will give (e.g. easier implementation of shared
code!), the protection capability of an MMU does not stem primarily
from allowing or not allowing addressability; rather, it is the
ability to permit or deny particular types of access to specific ranges
of addresses (whether those addresses get mapped before going to the
RAM chips or not).

Sound like what you were talking about?  Do you think that mainframes
which implemented memory keys and the like did it "on-chip"?
-- 
Eric Black   "Garbage In, Gospel Out"
UUCP:        {sun,pyramid,hplabs,amdcad}!chronon!eric