Author: Don Dailey
Date: 22:20:55 06/24/98
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On June 25, 1998 at 00:42:26, Bobby Ang wrote:
>I am merely a chess software user, so perhaps many of you here in the
>computer-chess club should excuse this ignorant question.
>
>The other day I was talking with the other admins in the ICC, and we were
>discussing the difference in the chess software being used there. One rather
>undiplomatic query I put to Tim McGrew (the computer-buster) was how he can
>differentiate between Fritz5 and Crafty. His answer was very intriguing:
>"Crafty is more prone to make meaningless pawn moves in the opening, but its
>search extensions seem to be better". When I pursued the matter further
>("search extensions? what's that!?) he replied : "I have seen Crafty announce a
>mate-in-28 in a blitz game".
>
>Wow! Impressive -- but this now leads me to another point: Don't search
>extensions require large hash tables? Which brings us to another question: but
>Fritz5 is a lot more hash-table size hungry than Crafty? shouldn't this be the
>other way around? And finally, if I am wrong, what are hash tables really used
>for?
>
>BOBBY ANG
Hi Bobby,
Search extensions have nothing to do with hash tables. It is just
another kind of selectivity, look deeper at moves that seem important.
When you play chess, you will often think ahead and come to some
position which you eventually come to understand pretty well. It
may, for instance, be an ending you know you can win. As you
examine other moves you may discover that you get to the same
exact position a different way simply by playing the same moves
in a different order. Since you already have figured out that
you can win this position, you do not have to figure it out again,
you simply remember it from before.
Chess programs do exactly the same thing with the hash tables.
They are remembering positions they have already seen and
evaluated. Since a computer can look at thousands of moves
every second, they can use quite a bit of memory remembering
all the positions they have seen (and what the score of each
one of them is.) Fritz is one of the fastest programs and
this is part of the reason it needs so much memory for its
hash tables.
- Don
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