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From: kraig@biostr.biostr.washington.edu (Kraig Eno)
Newsgroups: comp.sys.mac.system
Subject: Re: PPC, IAC, and True Multitasking (tm)
Message-ID: <6588@milton.u.washington.edu>
Date: 21 Aug 90 22:59:21 GMT
Sender: news@milton.u.washington.edu
Organization: University of Washington
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References:<1990Aug3.040513.14844@d.cs.okstate.edu> <2760@bridge2.ESD.3Com.COM> <13888@cbmvax.commodore.com> <3474@tellab5.tellabs.com>

In article <13888@cbmvax.commodore.com> valentin@cbmvax (Valentin Pepelea) 
writes:
>Actually, you either have pre-emptive multitasking, or you have nothing...
>An operating system has a pre-emptive scheduler, or it doesn't
>have one at all. There is no such thing as a cooperative scheduler. The
>term cooperative is used when there is an absence of a scheduler.

I agree with this definition of multitasking more than the others that have
been flying around here.  MultiFinder on a Mac just isn't doing multitasking
if any user process can hog the machine for an arbitray length of time.
The beauty of a multitasking machine is that several things can appear to
be going on at once -- whatever scheduling system is in use, you should be
able run compute-intensive jobs and continue with some unrelated task
without having to wait for them to finish.  "Cooperative" multitasking is
meaningless because most normal applications don't cooperate.

Two examples:
(1) If a HyperCard script starts in and you decide you don't want to wait,
you're stuck; with true multitasking, you should be able to just click on
another application window and do something else for a while.  HyperCard
shouldn't have to jump hoops to allow you to do this; with a multitasking
environment, the capability is inherent.

(2) Try using Word on a long doc and doing a lengthy Change command.  Word
is nice: it lets you go off and do something else in the middle.  But does
the Change command continue processing and eventually finish while you're
off reading netnews?  No way.

A workstation like the NeXT will do this sort of thing.  Now, I've never
used a window system on ANY Unix machine that is as responsive as
Multifinder, but the Mac is NOT multitasking.

Kraig Eno
kraig@biostr.washington.edu