Path: utzoo!attcan!uunet!samsung!usc!petunia!news
From: rcfische@polyslo.CalPoly.EDU (Ray Fischer)
Newsgroups: comp.sys.mac.misc
Subject: Re: System Errors, MF --> Why???
Message-ID: <2661ada6.62fa@petunia.CalPoly.EDU>
Date: 28 May 90 23:00:54 GMT
References: <6364.266023a1@umiami.miami.edu>
Organization: Cal Poly State Univ,CSC Dept,San Luis Obispo,CA 93407
Lines: 34



gross@umiami.miami.edu writes ...
>A friend of mine and me were having another one of our "religious" conversations
>about the virtues of the Mac vs. <insert system here>. 
>1) Why did Apple decide to go with their version of multitasking instead of
>   "true" multitasking like even a lowly Amiga 500 can do (and I don't want
>   arguments that run like 'Well, if you do multitask on an A500, your system
>   will get real slow...I ain't talking performance..I want to know what 
>   why certain capabilities have been put into a machine)

Pre-emptive multitasking on the Mac would require a major rewrite of 
large chunks of the ROM code.  One example.  The menu manager saves
the screen under the menu on the stack.  With pre-emptive multitasking
the screen might change under the menu, thus invalidating the saved
screen contents.  Thus, the current menu manager wouldn't work too well.

The current cooperative multitasking does work passably well; most of
the shortcomings affect programmers more than users.

>2) Why does Apple allow these system errors to continue?  I can't believe
>   that after 6.0.5 versions of the OS that they haven't found a better
>   way to recover from various errors?  Is it because everything runs in
>   supervisor mode?  Can't Apple protect certain sections of memory?

Ever written a perfect program?  Neither have I.  Bugs exist.
Could it be made more robust?  Yes.  Memory protection would help, but
is not a trivial undertaking as it would require many modifications.
(how do you protect low memory globals anyway?)  It also wouldn't work 
on the Mac Plus, SE, or portable.


Ray Fischer
rcfische@polyslo.calpoly.edu