Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!jato!vsnyder
From: vsnyder@jato.jpl.nasa.gov (Van Snyder)
Newsgroups: comp.sys.atari.st
Subject: Re: Multitasking
Message-ID: <1991Feb16.011147.26767@jato.jpl.nasa.gov>
Date: 16 Feb 91 01:11:47 GMT
References: <1991Feb11.151210.4010@informatik.uni-erlangen.de> <1976@lee.SEAS.UCLA.EDU> <1991Feb14.133758.3687@doe.utoronto.ca> <1986@lee.SEAS.UCLA.EDU>
Reply-To: vsnyder@jato.Jpl.Nasa.Gov (Van Snyder)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 28

In article <1986@lee.SEAS.UCLA.EDU> plinio@turing.seas.ucla.edu (Plinio Barbeito/) writes:
>Not *all* of the CPU.  Even though you may not notice it, part of
>the CPU time has to be going to the taxman, simply because there's a
>timer interrupting the processor constantly, waking up the scheduler
>many times a second to check if it is time for another process to run.
>And this is the *efficient* way to do it.

It's most definitely NOT the efficient way to do it, if you have an adequate
clock.  The *efficient* way to do it is to give the process a time quantum,
set the clock to interrupt WHEN THAT QUANTUM HAS EXPIRED, and DON'T USE CLOCK
INTERRUPTS FOR ANYTHING ELSE.  What purpose is served by getting clock
interrupts every 10ms, only to discover that what you were doing is what you
wish to continue doing?  'Way back in '72, Madnick and Donovan described this
notion in their text "Operating Systems".  Petersen and Silberschatz did a good
job too.  I've not taught an operating systems class in over 6 years, but I've
been told that Tanenbaums book is excellent.  Better yet, get hold of Univac
1100 OS listings -- Univac hasn't gone OCO yet, so most any Unisys 1100 site
has them.

Sorry to keep harping on this.  I just can't understand why nowadays one
requires 196k to do 10% of what could be done in 90k 25 years ago.

Van.

-- 
vsnyder@jato.Jpl.Nasa.Gov
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