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From: GEOMAGIC@kcgl1.eng.ohio-state.edu (Daniel OConnell)
Newsgroups: comp.sys.dec
Subject: Re: Question regarding DS3100 Floating Point
Message-ID: <4221@quanta.eng.ohio-state.edu>
Date: 14 Feb 90 07:40:31 GMT
References: <Feb.12.10.17.01.1990.23389@paul.rutgers.edu> <119@hammer.UUCP> <9711@batcomputer.tn.cornell.edu> <3566@rti.UUCP>
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(Steve Thompson) writes:
> In article <119@hammer.UUCP> jockc@idsila.com (Jock Cooper) writes:
> >I have this ray tracing toy that runs faster on our MicroVax
> >(has FP coprocessor) than on my DECstation 3100. Does the 3100
> >have a Floating Point chip or what? Or is it an option?
>
> Well, I have two main applications that I run on a VAXstation 3100 and
> a DECstation 3100, using the SAME source code in both cases (it's
> fortran). They are a Monte Carlo and a Molecular Dynamics simulation
> of a fluid stucture. The MC code is 10% faster on the VAXstation than
> on the DECstation, and the MD code is 4 times faster on the DECstation.

>Differences this great on programs whose style of computing is probably
>reasonably similar (compared to programs using lots of strings or packed
<decimal) suggest either machine memory differences (that one of the
>machines is running out of memory and either paging to death or not
>able to create a large enough temporary store to achieve the maximum
<effect) or compiler differences (at least one of the programs has a
>code sequence that one or the other compiler isn't able to optimize).

>My guess (since the DECstation is generally considered to be faster)
>is that is that either the DECstation memory is underconfigured or
>the compiler isn't as intelligent as the VMS compiler.

>Comments?

>						Bruce C. Wright

I have used both (VAX3100 and DEC3100) and a DEC5400. If you have
enough memory (sometimes a big if) the DEC3100 is 4 times faster
executing a number crunching program, period! Otherwise, which
system swaps faster?! (Ugh).

If you don't use full F77 optimization on the DEC3100 (-O2), it
compiles faster than the VAX3100 fortran compiler. Such code runs
~50% slower however. When you use full optimization you had better
have LOTS of memory. I had a 2000 line main program that sent F77
into swap oblivion on a 16M DEC3100 and barely cleared through
the 32M 5400 without swapping. Took 10 minutes vs 13 seconds for
default (-O1) optimization. Some crunching benchmarks for your info.

Let a VAX8550 = 1.0 (higher numbers will indicated how much faster)
      DEC3100 = 2.0
      DEC5400 = 2.5
      CRAY-YMP = 5.0 (scalar)

P.S. Ultrix sucks, but it sucks fast.

Dan O'Connell
geomagic@geo1s.mps.ohio-state.edu