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From: dailey@frith.uucp (Chris Dailey)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Help --> How to prevent the visit from the dreaded guru
Message-ID: <1991Jan5.200226.19718@msuinfo.cl.msu.edu>
Date: 5 Jan 91 20:02:26 GMT
References: <611@caslon.cs.arizona.edu> <1991Jan4.203339.8800@maytag.waterloo.edu>
Sender: news@msuinfo.cl.msu.edu
Organization: Michigan State University
Lines: 74

In article <1991Jan4.203339.8800@maytag.waterloo.edu> himacdon@maytag.uwaterloo.ca (Hamish Macdonald) writes:
>>>>>> 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.

I think there is a bright young PhD student trying to get his degree by
putting VM into the AmigaOS.  This does not, however, imply memory
protection.  See below.

>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.  [...]

>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.

I don't care much about existing programs.  If the Amiga could provide
a more stable development environment, so we know that, when the
equivalent of Unix's reference through NULL pointer or the many other
things that cause a reboot on the Amiga as is, does not mean that the
machine needs to be rebooted.  This would speed up development and allow
programmers to write more correct programs that will make everybody's
lives easier.  I know if the SunOS machines that our schools had to be
rebooted every time one of these problems happened (instead of the usual
core dump or whatever) noone would finish programs in time!

>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

Even fake memory protection would due for many of us.  How about a
command like "run such and such a program so it doesn't touch anything
other than the OS".  It gets its own space, tucked away from the rest of
the system?

>(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!

It's not just running programs, it's developing!  Native development is
where it's at right now, and if that is made more difficult on the Amiga
then people will be more likely to develop for some other machine, and
maybe port it over to the Amiga some other time.

I don't mean to sound like a downer.  I'm sure Commodore would love to
see this sort of thing implemented, too.  It's a definite minus, but it
won't keep me from buying an A3000 later this year.  (A war in the
Persian Gulf might, but this wouldn't.)

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

--
Chris Dailey   dailey@(frith.egr|cpsin.cps).msu.edu
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