Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!oliveb!amiga!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: Multitasking -multiprocessing
Message-ID: <6539@cbmvax.UUCP>
Date: 7 Apr 89 20:30:06 GMT
References: <12479@louie.udel.EDU>
Organization: Commodore Technology, West Chester, PA
Lines: 57

in article <12479@louie.udel.EDU>, DAVEA%CERNVM.BITNET@cunyvm.cuny.edu (David Almond) says:

> Multitasking is the ability to perform more than one task at atime, usually 
> on one cpu whereas multiprocessing is the more complicated process of 
> spliting computation into chunks which are processed usually by a group of 
> cpus. 

So far, so good....

> In that the amiga has dedicated processers for graphics etc it is, to some 
> degree multitasking, but not in any sophisticated, scheduled sense. 

Do you write for BYTE, by any chance?  That's dead wrong, on every account.

The Amiga is FULLY multitasking, in the sense that the processor is time
sliced among many processes.  Much in the same vein as UNIX, OS/9, Aegis,
VMS, etc.

The fact that some work is offloaded to decicated auxiliary processors
should tell you that the Amiga does some multiprocessing.  In that the
bimmer can be drawing a line on the screen at the same time as the CPU is
calculating a square root.  This is, of course, not general multiprocessing
in that the bimmer is not a general purpose processor.  That's not really
a bad thing, though, depending on what you're after.  The bimmer in Agnus
can do many graphics operations considerably faster than a 68000 could,
so as long as you've got enough of those type of tasks scheduled, the 
bimmer + 68000 gets more work done than a general setup of two 68000s.

> The transputer is the classic multiprocessing machine so far.

Well, it's one.  The Transputer is designed to handle loosely coupled
multiprocessing.  Such a system has no definite limit on the number of
processors that could be employed, but it generally requires a decent
architecture, and an operating system smart enough to schedule tasks at
a corse grain, in order to be effective.  The architecture cleverness
is based on the fact that only 4 Transputers are ever directly connected.
So you resort to interconnection in large networks, maybe a modified
hypercube or something.  The corse grain in based on the fact that a
transfer between two processors will take longer than the entire run
time of a small task.  Finally, the main reason Transputers are used for
this type of multiprocessing is that they have on-chip support for serial
links.  It's nice, at the right price, but it's nothing that couldn't be
supported by external hardware and any other processor, at possibly even
higher transfer rates (examples -- Connection Machine, Intel Hypercubes).

Most of the other efforts are in tightly coupled multiprocessing.  The 
number of tightly coupled processors is limited by the bus architecture,
and rarely goes above 7 or 8.  However, the communication between processors
is instant.  It does require significant design considerations to work well.
Many new RISC chips have hooks for tight multiprocessing, including the
Motorola 88000 family, Motorola 68040, Apollo PRISM, and several others.

>             ............. Dave
-- 
Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
              Amiga -- It's not just a job, it's an obsession