Path: utzoo!attcan!uunet!jarthur!elroy.jpl.nasa.gov!usc!zaphod.mps.ohio-state.edu!swrinde!emory!hubcap!sjl
From: sjl@myrias.com (Stuart Lomas)
Newsgroups: comp.parallel
Subject: SIMD vs MIMD programming (was Acceptable efficiency factors)
Message-ID: <9633@hubcap.clemson.edu>
Date: 11 Jul 90 13:02:20 GMT
Sender: fpst@hubcap.clemson.edu
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Approved: parallel@hubcap.clemson.edu

In article <9521@hubcap.clemson.edu> argosy!ian@decwrl.dec.com (Ian L. Kaplan) writes:
>  Perhaps the difference in the execution efficiency between the Intel
>cube (an MIMD machine) and the CM-2 (a SIMD machine) is due to the
>fact (not doubt hotly contested) that SIMD systems are easier to
>program. ...
>
>			...  SIMD systems can be programmed in
>_standard_ Fortran 90. MIMD systems can only be programmed in a
>language that contains extensions for synchronization.  The SIMD
>programmer need only consider machine architecture when it comes to
>making their program run more efficiently.  The MIMD programmer must
>consider the machine architecture or the program will not run
>deterministicly.  Full symbolic debugging can also be supported on a
>SIMD machine.  Has anyone done a symbolic debugger for a large scale
>MIMD system?
>
>  Of course I am biased.
>
>                       Ian Kaplan
>		       MasPar Computer Corp.
>		       ian@maspar.com
	
Most MIMD machines are indeed dificult to program. However, if the net
will forgive me an arguably commercial posting, I would like to
present a counter example. The machine in question is the SPS series
from Myrias Research Corporation, a large scale MIMD machine. Please
be warned that I work for Myrias Research.

Myrias machines are programmed in standard Fortran 77. To make a
program run in parallel, it is necessary to label the loops that can
be executed in parallel, by putting 'PAR' in front of the 'DO'. If you
don't do this, your program runs serially, but it still runs.

Programs on a Myrias machine run deterministicly, and the machine
architecture can be ignored except for efficiency considerations. (It
is possible to generate a race condition if you go through the I/O
system, but that is really stretching a point). If a program runs
correctly on N processors, it will run correctly on any other number
of processors provided there is enough memory.

All Myrias machines support full source-level symbolic debugging as a
standard feature.


Stuart Lomas				sjl@myrias.com or uunet!myrias!sjl
Myrias Research Corporation		phone: +1 403 428 1616
#900 10611 98 Ave, Edmonton, Alberta, Canada, T5K 2P7