Newsgroups: comp.sys.amiga.tech
Path: utzoo!utgpu!watserv1!maytag!maytag!himacdon
From: himacdon@maytag.uwaterloo.ca (Hamish Macdonald)
Subject: Re: Help --> How to prevent the visit from the dreaded guru
In-Reply-To: dave@cs.arizona.edu's message of 4 Jan 91 19:00:54 GMT
Message-ID: <1991Jan4.203339.8800@maytag.waterloo.edu>
Sender: daemon@maytag.waterloo.edu (Admin)
Organization: University of Waterloo, Waterloo, Ontario
References: <611@caslon.cs.arizona.edu>
Date: Fri, 4 Jan 91 20:33:39 GMT
Lines: 38

>>>>> In article <611@caslon.cs.arizona.edu>, 
>>>>> dave@cs.arizona.edu (Dave P. Schaumann) writes:

Dave> [...]
Dave> There is a solution to this.  It's called virtual memory.  It takes an MMU,
Dave> which is not available to the 68000.  However, the 68030 has one.  I think this
Dave> is something CBM should be seriously considering putting into their next major
Dave> release of Workbench.

Virtual memory does not provide protection between processes.  Virtual
memory provides a transparent way to address more memory than a
machine really has.  Memory mapping and memory protection mechanisms
(which are also provided by an MMU) provide the protection you are
referring to.

In addition, putting memory protection into AmigaDos is not as easy as
you imply.   It  will   break the  vast  majority  of   existing Amiga
programs.  All interprocess communication  in the Amiga  is done using
shared memory techniques.  Guidelines for writing programs in a manner
upwardly compatible with future memory protection  mechanisms have not
existed for a long time, and have not been religiously followed in any
case.

Almost  every "hot" game  written for   the Amiga would  fail to work,
since they  almost  all  go right to   the hardware, which    would be
disallowed in a protected AmigaDos.

In   summary, I agree that    it is true   that  memory protection  is
something  which the Amiga  needs, but it is not  that easy to achieve
(due to the  initial  design  decisions made in creating AmigaDos  (or
Exec, if you  prefer)) and in most  cases,  judicious selection of the
programs you run in your system should keep you out of trouble most of
the time.  If a program GURUs your machine, throw it away!

Hamish.
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himacdon@maytag.uwaterloo.ca                 watmath!maytag!himacdon