Path: utzoo!attcan!uunet!mcvax!hp4nl!phigate!philmds!leo
From: leo@philmds.UUCP (Leo de Wit)
Newsgroups: comp.sys.atari.st
Subject: Re: Multitasking on the ST
Message-ID: <1071@philmds.UUCP>
Date: 12 Aug 89 16:39:09 GMT
References: <8908021826.AA05333@ucbvax.Berkeley.EDU> <15627@watdragon.waterloo.edu> <652@opal.tubopal.UUCP> <471@tw-rnd.SanDiego.NCR.COM> <1066@philmds.UUCP> <482@tw-rnd.SanDiego.NCR.COM>
Reply-To: leo@philmds.UUCP (Leo de Wit)
Organization: Philips I&E DTS Eindhoven
Lines: 53

In article <482@tw-rnd.SanDiego.NCR.COM> johnl@tw-rnd.SanDiego.NCR.COM () writes:
|In article <1066@philmds.UUCP> leo@philmds.UUCP (Leo de Wit) writes:
   []
|>I think two issues are being confused here, the need for per process
|>memory protection, and the possible to run processes 'simultaneously'.
|>Why should memory protection be a hotter item when parallel processes
|>are involved?
|
|Because of the potential for a single user program to cause the termination
|of all the processes in the system.

This is equally well possible in the current 'one-process-running-at-a-time'
scheme. Note that there are already accessory-based editors, batch
modem transfer programs, TSR print spoolers for the ST right now.

|Consider: You are a user of the Spiffy multi-tasking-but-no-
|per-process-memory-protection Machine.  You fire up a ray-trace.
   [etc. good example left out]
|
|On a machine with memory protection (OK and resource tracking) the MMU will
|prevent corruption of other processes address space, and the nasty process can
|be removed from the system cleanly.

I think you'll need a bit more than just an MMU for a secure system.
S'pose your nasty process alters some system vector (applying patch 271
to SAFEDOS). A pity that the last bug was not yet removed... My point
is, that a MMU is a probably undispensable ingredient IN AN OTHERWISE
EXCELLENT SYSTEM.  That safe system (which undoubtedly will have a
notion of privileges, users) is what you should start with in the first
place.

B.T.W. what do you do when a thunderstorm is coming up, but your
raytracer has yet to finish its last hour of calculations? Use a TMU :-) ?

   []
|I'm all for system robustness for ANY system.  My point is that when you
|introduce multitasking, memory protection is more important due to the
|potential to disrupt other processes.

I heard this one before and I still won't believe it, unless a proper
argument is given.

|>[about VM]
|
|Sounds Good!  But now you're wandering into the area of virtual memory and
|that's not what our original discussion was about.  Thanks for the reply.

You bought an MMU but you don't want VM? Gee, that would be the first
reason I would buy an MMU for (and not for protection). As long as the
filesystems used are single-user, not write protectable, I don't care
much for safe core.

   Leo.