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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.sys.apple2
Subject: Re: Multitasking on a II
Message-ID: <14730@smoke.brl.mil>
Date: 13 Dec 90 17:18:22 GMT
References: <&RF^T6-@rpi.edu> <10063@darkstar.ucsc.edu> <7TF^W^=@rpi.edu>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 43

In article <7TF^W^=@rpi.edu> floyd@pawl.rpi.edu (Patrick J Wetmore) writes:
>>	I believe that the original IBM PC can run Xenix...
>Yah, you can run it fine, until a poitner gets screwed and zaps something
>in another processes memory. Then you get crashes. If it worked just fine,
>we wouldn't have MMUs, would we?

MMUs serve several purposes, interprocess protection being merely one
of them, and relatively unimportant at that in a single-user (albeit
multitasking) environment.  There have been many implementations of
UNIX, UNIX-like, and other multitasking operating systems without use
of an MMU; I believe "MiniUNIX" was described in the 1978 BSTJ UNIX
special issue, and Whitesmiths' Idris was another such system from
roughly the same time frame.  While it is convenient to have an amok
task aborted without adverse effect on other concurrent tasks or the
OS kernel, it is certainly not necessary under normal situations.  My
normal working environment is a fully-protected UNIX system that would
abort tasks that attempt to use pointers out of their own address
space, and I almost never see a task aborted for that reason.

Without an MMU, the main difference in operation is that relocation
must be provided as task images are loaded into memory for execution
(except if position-independent code is involved, but normally that
imposes too stiff a speed penalty and requires cooperating compilers).
The IIGS already does this, in ROM no less.

>The GS is not a profitable machine. There are much better machines
>much more geared towards multitasking. I shudder to think of UNIX on the
>plodding beast. The GS is overpriced and overrated.

While I would never recommend a IIGS for multitasking, since at present
there isn't very much support along those lines, it's not particularly
slow.  Mine is easily a match for typical IBM PC clones for significant
applications that I happen to care about.

I don't know who it would be that is "overrating" the IIGS.  Apple
surely doesn't, the software industry in general doesn't, and the IIGS
is seldom mentioned favorably (or at all!) in computing publications.
Most experienced IIGS developers seem to think that its capabilities
are UNDERrated.

I second the motion for the fellow who suggested that if you don't
like your (free) IIGS you quit whining about it here.  Particularly
since you don't know what you're talking about.