From: S_JUFFA@iravcl.ira.uka.de (|S| Norbert Juffa)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: ULSI co-processor chips any good?
Date: 18 Aug 1992 18:23:46 GMT
Organization: University of Karlsruhe (FRG) - Informatik Rechnerabt.
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In <1992Aug15.234529.311@magnus.acs.ohio-state.edu> rjones@magnus.acs.ohio-state.edu writes:

> Anyone have any experience with ULSI co-processor chips. I'm looking at
> Cyrix, IIT, Intel and ULSI for my 386-33. I seem to recall a magazine
> test that compared these and the ULSI came out high. It didn't suffer
> from the accuracy problems of IIT or Cyrix, I believe. However, it
           ^^^^^^^^^^^^^^^^^^^^        ^^^^^

Hold it right there! While doing some research for an article on coprocessors
which I intend to post tomorrow, I have tested the IIT, ULSI, Intel, and Cyrix
coprocessors as well as the Intel RapidCAD and the i486. The Cyrix 83D87 and
387+ are the coprocessors with the highest degree of compatibility with the
Intel 387DX. The IIT does not support denormals for the extended precision
format and fails quite a few tests in the IEEETEST program. The ULSI does not
support rounding control, it always uses extended precision, and it fails a
few of the tests in IEEETEST. The Intel and Cyrix chips pass all these test
without a single failure. However, neither of the 387 'clones' is entirely
compatible with the Intel 387DX. Cyrix has documented existing differences
in a "Compatibility Report". Only the Intel 387DX can asynchronously with the
CPU, meaning that CPU and coprocessor run at a different clock rate. The 
coprocessors from Cyrix, ULSI, and IIT always run at the full speed of the
CPU even if you jumper your motherboard for asynchronous operation, so make
sure to get the right speed coprocessor for your CPU. Don't try to 'push' a
coprocessor above its stated maxmimum operating frequency, it may introduce
computational errors into the coprocessors results (I have had this happen to
myself). Of all coprocessors tested, the Cyrix 387+ had the most accurate
transcendental functions, followed by the Cyrix 83D87, the Intel 486, the
Intel RapidCAD, the IIT 3C87, and the ULSI 83C87. The maximum error for
the transcendental function on the ULSI is within the limits specified by
Intel though. As for performance the Cyrix offers the highest overall
benchmark performance of all 387 'clones', followed by the IIT, ULSI, and 
Intel 387DX. However, the performance difference in real applications is
hardly noticeable and well under 10%. Since the incompatiblities found in
the IIT and ULSI coprocessors are hardly an issue with regard to most or
even all applications, you might also go for the cheapest coprocessor
available. Hope this helps!


> -- 
>  < Ron Jones                   |    E-mail:       rj+@osu.edu   > 
>  < The Ohio State University   |    Office:      (614) 292-1665 >
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Norbert
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Norbert Juffa        email: S_JUFFA@IRAVCL.IRA.UKA.DE        Live and let live!