[rc5] Identical results, two CPUs

Tom Wheeler tomw at intelligraphics.com
Sat Jul 26 12:55:10 EDT 1997

On Sat, 26 Jul 1997 11:15:34 -0500, Mike Silbersack wrote:

>> Among other machines, I'm running the client on a P200/MMX and a
>> regular P200.  A coworker says there's "no way" these two machines can
>> be running at virtually identical speed, but they are - about 240Kk/s. 
>> Would anyone care to take a crack (ha ha) at explaining why they are
>> the same so my coworker and I can end this silliness?
>> Regards,
>> Tom Wheeler
>> tomw at intelligraphics.com
>Well, the Pentium MMX has an improved branch prediction unit and a larger
>internal cache, so it *should* be faster.  However, the possibility also
>exists that the motherboards/bios settings differ on these systems to a
>great enough extent that the MMX is being slowed down to the speed of the
>Pentium Classic.  Maybe if you check out the BIOS settings on the two
>computers you will find that the Pentium Classic is using more aggressive
>timings, has a larger external cache, or something else.

I can see the better branch prediction making a small difference.  I
don't think the larger L1 cache is relevant - I would hazard to guess
that the client is small enough to fit in the P200's cache (or mostly,

As for BIOS settings, the machines unfortunately have the AMI "Let's
give the user exactly no control over his machine" BIOS, so there's not
much I can even look at there, much less change.  Nevertheless, the
client is massively compute-bound anyway, so I can't think of any
changes to the BIOS that would make a difference.

Tom Wheeler
tomw at intelligraphics.com

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