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From: mcdonald@aries.scs.uiuc.edu (Doug McDonald)
Newsgroups: comp.lang.fortran,comp.lang.c
Subject: Re: Fortran vs. C for numerical work (SUMMARY)
Message-ID: <1990Nov30.145649.17688@ux1.cso.uiuc.edu>
Date: 30 Nov 90 14:56:49 GMT
References: <9458:Nov2721:51:5590@kramden.acf.nyu.edu> <2392:Nov2902:59:0590@kramden.acf.nyu.edu> <7339@lanl.gov>
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Organization: School of Chemical Sciences, Univ. of Illinois at Urbana-Champaign
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In article <7339@lanl.gov> ttw@lanl.gov (Tony Warnock) writes:
>
>
> 
>      Model        Multiplication Time     Memory Latency
> 
>      YMP          5  clock periods         18 clock periods
>      XMP          4  clock periods         14 clock periods
>      CRAY-1       6  clock periods         11 clock periods
> 
>      Compaq       25 clock periods         4  clock periods
>      Zenith      120 clock periods        30  clock periods
> 
>    The times on the PC-clones are approximate depending on the type
>    of variables being accessed and the sizes of the indices.
> 
I don't know what kind of Compaq or Zenith you are using, but 
on a 25 or 33 MHz 386 or 486 machine with a 3167 or 4167 floating
point unit the memory latency and FPU multiplication time are
roughly equal. The manuals of the compilers I use say that the
memory accesses slow computations down by up to a factor of two compared
to things on the FPU stack.

Doug McDonald