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From: lim@iris.ucdavis.edu (Lloyd Lim)
Newsgroups: comp.sys.mac.misc
Subject: Re: System Errors, MF --> Why???
Message-ID: <7410@ucdavis.ucdavis.edu>
Date: 30 May 90 06:10:43 GMT
References: <6364.266023a1@umiami.miami.edu>
Sender: usenet@ucdavis.ucdavis.edu
Reply-To: lim@iris.ucdavis.edu (Lloyd Lim)
Organization: U.C. Davis - Department of Electrical Engineering and Computer Science
Lines: 81

In article <6364.266023a1@umiami.miami.edu> gross@umiami.miami.edu writes:
>[...] Apple is coming up with version 7 of their OS.  When
>are they going to make it stable enough so that the least little problem
>doesn't bring up those system error messages and crash your system.

Actually, it's not too bad right now.  As most developers know, if you are
running a debugger with MultiFinder and a System error occurs, you can exit
to the Finder without affecting other applications for most errors.  This
isn't totally reliable though.

>Here's the meat of the matter:  I and my friend would like to know two
>things from Apple and from other informed people:

These two questions are like asking something like:  Cars that run on methane
are better than cars that run on gasoline.  Why doesn't Ford start making all
their 1990 cars run on methane?  (Methane is just some example - I don't know
what fuels are good.)

>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)

Compatibility.  The Mac OS started out as non-multitasking system and there
are many things in it that need to be cleaned up before true multitasking
can take place.  Multitasking operating systems usually are written from the
ground up.  Actually, it's pretty impressive that they were able to pull off
the kind of multitasking that occurs with MultiFinder.  There's a lot of stuff
that goes on behind your back...

>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?

Most system errors occur when an application fails to handle some situation
correctly.  The first place to blame is the person who wrote the application.
The next best thing, like you said, is to have the OS recover from these
errors without affecting other applications.  The way everything is currently
set up, applications share some things so you can't be sure everything is ok
after an error.

The usual way to handle this is to isolate the OS and have applications access
the OS through routines.  Then you can run in supervisor mode for the OS and
user mode for applications and possibly have memory protection.  The newer
Systems seem to be heading this way but there is a lot of old stuff to clean
up (e.g. - low memory, direct access to the System heap).  Apple has managed
to push developers away from some bad practices already.  Not many applications
write directly to the screen these days, which makes MultiFinder and multiple
connected monitors of different bit depths possible.

Interestingly, when the Mac started out, it forced developers to access the OS
through routines (the Toolbox) more than any other computer.  The rules were
not as firm then but Apple has been making them firmer and life harder for
developers who don't follow them.  So far this has given the Mac remarkable
consistency between applications, the ability to run on very different
machines, and to have neat things like multiple screen desktops and
international Systems work for most applications.

Now the Mac is being compared to things like NeXT and OS/2 which were written
from the ground up.  The Mac has been heading that way for a while but it
takes time to push the software mass and there are other features Apple wants
to add also.  Look at how developers are worried over System 7.0.  I'd say you
probably won't see true multitasking until there is a low cost 68030 Mac and
developers have been pushed more in the right direction with more System
versions.  Maybe not until System 9.0 which might take about three years on the
bright side.  :-(

I don't mean to say the Mac is perfect, Apple knows what it's doing all
the time (Apple has done some pretty bone-headed things), and developers are
bad (we just need guidance and alternatives), but I thought I'd try to explain
how things were and why things don't happen now (as I see it that is, of course
you may disagree).  I too would like to see the day when my file transfer in
the background doesn't timeout when I'm looking at some menu in the
foreground application.

+++
Lloyd Lim     Internet: lim@iris.ucdavis.edu (128.120.57.20)
              Compuserve: 72647,660
              US Mail: 146 Lysle Leach Hall, U.C. Davis, Davis, CA 95616