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Subject: Re: Bitboard engine speed difference on different processors

Author: Tony Werten

Date: 00:37:06 04/19/03

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On April 17, 2003 at 20:35:35, James Robertson wrote:

>Out of curiosity I tested just the move generation and basic board functions of
>my bitboard chess program on several different computers. My home computer is a
>Pentium 933mhz, and the other computers I used were Athlons in the 1.6ghz range.
>
>My program's move generator runs at roughly the same speed on both systems. I
>was surprised and tested using several different compilers (VC5, VC6, .NET,
>gcc), under Windows and under Linux. To compare more easily, I wrote a simple
>non-bitboard move generator and tested this on all of the machines. The speed
>differences scaled with the speed of the processors, which seemed logical.
>However, I still cannot explain why the bitboard functions are so much slower on
>the faster computers. The only difference I can see is that my home computer is
>a pentium and the others are athlons.
>
>It seems strange that this would make such a large difference. Can anyone give
>any reasons why? I used no assembly, just C/C++ code, with all the default
>compiler options on all tests.

I think it's because bitboards tend to fill up the caches, so memory becomes the
bottleneck.

With other approaches this doesn't happen, ( until you add the big stuff like
eval ) so all things stay in chache  wich makes it (almost) only processor
limited.

Tony

>
>Thanks,
>James



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