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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.sys.apple2
Subject: Re: Multitasking on a II
Message-ID: <14729@smoke.brl.mil>
Date: 13 Dec 90 16:58:20 GMT
References: <14720@smoke.brl.mil> <10563@ucrmath.ucr.edu> <&RF^T6-@rpi.edu>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 42

In article <&RF^T6-@rpi.edu> floyd@pawl.rpi.edu (Patrick J Wetmore) writes:
>Bull. The apple iigs (curse its evil presence. I hate hate hate it. Infernal
>lousy piece of... growl snarl.) has no protected memory, and no virtualling
>hardware. Any machine can multitask, but without the proper memory 
>architecture the thing will be completely useless. Plus, the damnable
>thing is so slow. It plods.

Again, you shouldn't make pronouncements about these things if you
don't have the practical experience to back it up.  There is no MMU
in the Blit multitasking terminals either, but they multitask fine
and are FAR from "useless".  (Indeed, I use one as my primary user
interface to a Sun workstation, in preference to the Sun's famous
graphic windowing interface.)  As I type this in one window running
a news system interface, another window is running an alarm clock,
another has the "sam" bitmap mouse-driven text editor running in it,
another has a dynamic system load monitor (smoothly varying bar graph),
another has a screen-dump printer interface, and another has a pair
of "eyes" that always look toward the mouse cursor.  (Of course I
could have had different applications running; this happens to be what
I'm actually using at the moment.)  These windows appear to operate
SIMULTANEOUSLY, asynchronously, and without overlap interference
(unlike many windowing systems, the process associated with a window
need not take any action to redraw uncovered portions).  As a reminder,
the processor in Blit terminals is not significantly more powerful than
a 65816, and the other hardware is quite simple, with no use of timer
interrupts or memory management unit.  If the IIGS hardware had been
exploited by Apple to the extent that the Blit terminal hardware was
exploited by AT&T, we would have a wonderful user environment.
Instead, the mickey-mouse Macintosh notion of one active process at a
time (with the only multitasking provision the "desk accesories") must
have been foremost in the minds of the IIGS developers at Apple.

While it is true that GS/OS is not designed with multitasking in mind,
it also doesn't particularly get in the way.  A multitasking monitor
(meaning system module, not display) could use GS/OS for storage-
device access, for example.  At least the IIGS does use a centralized
memory manager, so that concurrent tasks can be loaded without
interference.  Since the 65816 architecture has an inherently limited
supply of direct-page memory, probably a multitasking monitor ought
to switch direct pages as part of task context.  IIGS multitasking is
eminently doable, but should be undertaken only by experienced OS
designers.