Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!van-bc!mdavcr!ewm
From: ewm@mdavcr.UUCP (Eric W. Mitchell)
Newsgroups: comp.sys.mac.system
Subject: Re: PPC, IAC, and True Multitasking (tm)
Message-ID: <964@mdavcr.UUCP>
Date: 24 Aug 90 18:03:58 GMT
References: <3474@tellab5.tellabs.com> <6588@milton.u.washington.edu> <44150@apple.Apple.COM>
Organization: MacDonald Dettwiler, 13800 Commerce Parkway, Richmond, BC, Canada  V6V 2J3
Lines: 48

In article <44150@apple.Apple.COM> daveo@Apple.COM (David M. O'Rourke) writes:
>  There are several example of multitasking system that aren't pre-emptive.
>Lots of early computer OS's did the context switch off of some/all system
>calls or other non-preemptive mech.  I've yet to find an OS book that doesn't
>mention co-operative multi-tasking as a scheduling mech.

Agreed.  You are on the nose with this one.


>  Multi-tasking _STRICTLY_ defined is the running of more than one process
>at a time.  Well to do that you need a CPU for each process.  So any single
>CPU system is not a multi-tasking system.  Or when ever you get n+1 processes
>going on an n-processor system then you no longer have a multi-tasking
>system.

Ummm, not quite.  I think you are confusing *multi-tasking* with
*multi-processing*.  A _LOOSE_ definition of a *multi-tasking* system
is that it has multiple processes *active* at the same time, with each
making progress toward completion.  A *multi-processing* system is one
that has multiple processors executing code simultaneously.  Note that
a multi-processing system is not necessarily multi-tasking.  The system
may be designed so that that all processors execute code from a single
program - as with a single-tasking *parallel processing* system.  On the
other hand, not all multi-processing systems are parrallel processing.  A
multi-processing system does not necessarily execute sections of the
same program on different processors at the same time, whereas a
parallel processing system does.

* Whew!!! *


>Therefore multi-finder is a multi-tasking extension of the Macintosh OS.  Just
>because the scheduling method doesn't do it the way most bigger OS's do it
>doesn't remove the ability.
>
>  There is more than one way to multi-task a system, and there will always be
>debate regarding which way is best.

Bravo.


>daveo@apple.com                                               David M. O'Rourke


Eric

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