Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!zaphod.mps.ohio-state.edu!usc!ucla-cs!ucla-se!PRICE@uclapp.physics.ucla.edu
From: price@uclapp.physics.ucla.edu (John Price)
Newsgroups: comp.sys.mac.system
Subject: Re: Apple HW & SW questions
Message-ID: <0094A13A.09CA3900@uclapp.physics.ucla.edu>
Date: 14 Jun 91 02:05:19 GMT
References: <1991Jun13.221640.11341@msuinfo.cl.msu.edu>
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Reply-To: price@uclapp.physics.ucla.edu (John Price)
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Organization: UCLA Particle Physics Research Group
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In article <1991Jun13.221640.11341@msuinfo.cl.msu.edu>, soeryant@frith.msu.edu (Herr Soeryantono             						      *) writes:
>I have often heard that the MacOS is not a TRUE MULTITASKING one.
>On the other hand UNIX is. Can someone explain the difference to
>me in layman's terms?

Since I'm a layman, those are the only terms I know.  :)  Here's how it was 
explained to me (I'm sure someone will correct me...):

The difference is in how you define multitasking.  To be very precise, no 
single processor can be truly multitasking, since it can only execute one 
instruction at a time.  A better word would be multischeduling.  It's sort 
of like eating and talking at the same time.  Yes, you can do it, but you 
can't do both simultaneously, and each task interferes with the other - 
either you talk slower, or you spit food all over the place.

The word multitasking is, however, firmly entrenched in the minds of people 
using computers, so we'll use that one.  Macs *can* multitask.  Case in 
point: Superclock.  While you sit there, typing away at your word 
processor, the time in the upper right of the screen changes every minute.

A more practical example: you can, given the right software, download a 
file with a modem, print out something on your printer, and play a game all 
at the same time, and that time will *still* change every minute.  Don't 
tell me it can't be done - I do this with a *Plus*!!!

Mac multitasking is, however, different than multitasking on other systems 
(Unix, VMS, etc.).  Those other, Brand X operating systems, use what's 
called preemptive multitasking.  The Mac uses cooperative multitasking.  
(Note to gurus: this is where I get fuzzy...)  In preemptive multitasking, 
the operating system dictates how much CPU time each process receives, 
allocated according to some algorithm defined by the person running the 
system.  In cooperative multitasking, the programs themselves determine how 
much CPU time they get.  

Preemptive multitasking is much easier for the application programmer, 
since {he|she|it} doesn't have to worry about resource allocation - the 
system software takes care of that.  However, the system itself, since it 
has to deal with all this, is much larger.  Cooperative multitasking, on 
the other hand, is much harder for the application programmer (how much 
harder I don't know), who must worry about resource allocation, but results 
in a smaller system file.

As to which is "better", it's sort of a silly argument.  If you're basing 
your computer buying decision on which system supports which kind of 
multitasking, instead of which applications you can run on the machine and 
how well those applications fit your needs, then you're missing the point.

           John Price * * * * price@uclapp.physics.ucla.edu
           Where there is no solution, there is no problem.