Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!mcvax!hp4nl!philmds!nlgvax!hans
From: hans@nlgvax.UUCP (Hans Zuidam)
Newsgroups: comp.sys.amiga
Subject: Re: Multitasking -multiprocessing
Message-ID: <232@nlgvax.UUCP>
Date: 7 Apr 89 15:58:13 GMT
References: <12479@louie.udel.EDU> <6531@cbmvax.UUCP>
Reply-To: hans@nlgvax.UUCP (Hans Zuidam)
Organization: Philips Research Geldrop
Lines: 40

There's some confusion on multi-tasking and multi-processsing.
The definitions below are derived from Burroughs terminology which
are clean enough (for me at least ;-)).

Multi-Tasking:
     The abillity to run another second task while a first task
     is waiting for resource to become available. Thus you split
     a single *physical* CPU in multiple *virual* CPUs. A resource
     might be the block of data the first one is reading from a disk.

Multi-Processing:
    The abillity to run multiple tasks *at the same time* on a number
    of *physical* CPUs.

A task is defined as a unit of work. It is a single stream of
instructions which are executed from beginning to end. Thus there is no
parallelism within a task. An amount of work submitted to the machine
is called a job. Within a job you can have multiple, concurrently
running tasks. A program is *not* equal to a task.

It follows that splitting a single task into pieces and running each
piece on a separate processor is wrong terminology. That is: you split
a job into several tasks which can then run in parallel.

Of course with the disaperance of batch systems the distinction between
jobs and tasks has disappeared also. But for clean discussion it is
often useful to fall back on the old (from around '65 or so!)
definitions.

So when your Amiga program builds a copper list and fires it off, you
end up with three things: your program which I would call a job, the
actual running 68000 code which is one task and the copper list which
is the other task.

							Hans
-- 
Hans Zuidam                                    E-Mail: hans@pcg.philips.nl
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