Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!intercon!amanda@intercon.com
From: amanda@intercon.com (Amanda Walker)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Need info on multitasking capabilities on the mac
Message-ID: <1574@intercon.com>
Date: 28 Nov 89 00:11:12 GMT
References: <6432@tank.uchicago.edu> <TIME.89Nov27154310@oxtrap.oxtrap.UUCP>
Sender: news@intercon.com
Reply-To: amanda@intercon.com (Amanda Walker)
Lines: 59

In article <TIME.89Nov27154310@oxtrap.oxtrap.UUCP>, time@oxtrap.oxtrap.UUCP
(Tim Endres) writes:
> True multitasking is just that: TRUE.

Sigh.  I guess it's that time of year again.

Try the following: go to a good university or scientific bookstore.
Pick up a good textbook on operating systems, and read through the sections
on multitasking.

Multitasking is an overall term that covers a variety of different techniques,
much in the same way that "virtual memory" does.  The term "multitasking"
simply means that a single processor is shared among several different programs
in order to gove the illusion that a computer is doing more than one thing
at once.  "True multitasking" doesn't mean anything, although many people
use it to mean "The kind of multitasking that I am used to on other machines,"
whatever that may be.  This makes its definition a political issue, not a
technical one.  In case you are unfamiliar with them, here are some simple
definitions of the major different types of multitasking:

Cooperative Multitasking:

    In this technique, control of the processor is given up explicitly by
    each task.  This is used by many real-time operating systems, internally
    within conventional UNIX kernels, most MS-DOS multitasking extensions,
    and MultiFinder.

Pre-emptive Multitasking:

    In this technique, control of the processor is switched from task to
    task my means of a hardware interrupt, thus preventing any single process
    from monopolizing the processor, at the expense of guaranteed response
    time.  This technique is used by most UNIX user process schedulers, the
    Commodore Amiga Operating System, and most "time-sharing" operating
    systems.

Either of these techniques can be used in conjunction with other processing
techniques, such as multiple independent address spaces (also called "protected
memory"), threads (multiple simultaneous logical processes within a single
address space), time-slicing, virtual memory, process swapping, or paging.

However, none of these has anything to do with whether or not the machine
"has true multitasking" or not.

For a Macintosh, MultiFinder does an excellent job of allocating time and
resources.  For an example, Try running a Mac binary on a heavily loaded
(or even lightly loaded :-)) A/UX system--it's pre-emptive, and it makes
everything equally slow.  Under MultiFinder, things stay generally pretty
quick, in comparison.  For most things, I'd actually rather use my Mac II
with MultiFinder than a Sun 3 with the same amount of memory running UNIX,
since  I get to control how slow it gets...

Complaining that "the Macintosh doesn't have the kind of multitasking
I think I want" is fine.  Complaining that it doesn't have "true multitasking"
just demonstrates ignorance.

Amanda Walker
InterCon Systems Corporation
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