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From: rhyde@hubbell.ucr.edu (randy hyde)
Newsgroups: comp.sys.mac.system
Subject: Re: Apple HW & SW questions
Message-ID: <15284@ucrmath.ucr.edu>
Date: 14 Jun 91 16:05:37 GMT
References: <1991Jun13.221640.11341@msuinfo.cl.msu.edu> <4123@ux.acs.umn.edu> <15262@ucrmath.ucr.edu> <1991Jun14.143348.28875@eng.umd.edu>
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Reply-To: rhyde@hubbell.ucr.edu (randy hyde)
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>> A program is pre-empted whenever it asks for use input

NO IT IS NOT!  It voluntarily gives up the CPU by calling the O/S (or toolbox,
or whatever you want to call it).  This is what multiprogramming is all about.
Processes keep the cpu until they: (a) quit.  (b) Perform some I/O. or (c)
explicitly give up the cpu.  This is exactly how the current Mac O/S operates
(unless Apple has dramatically changed things since I last looked at it.
Preemption means you can stop a process at any point (via interrupts).  Either
by a timer, a higher priority job showing up in the ready queue (which
generally
occurs on an I/O complete interrupt), etc.
*** Randy Hyde

Lets not propogate errors here folks....
You can correct me if I'm wrong, but please read up on the subject first.
Reference:  The Dinosaur Book.