Author: Matthew Hull
Date: 09:48:36 08/27/02
Go up one level in this thread
On August 27, 2002 at 11:16:27, Robert Hyatt wrote: >On August 27, 2002 at 10:28:09, K. Burcham wrote: > >> >>I am not clear on these questions: >> >>1. when does a program write to hash? > >Whenever it completes searching at any particular node in the tree. It >tries to save the results of this search so that if the same position >arises elsewhere the search can be avoided. Basically one store per node >searched, except for the nodes where you get a hash hit to avoid a search, >since storing there would be pointless. > >>2. when does a program write to the hard drive? > >In my case, at three points: > >1. when it does book learning, which is 10 moves out of book. > >2. whenever it does "position learning" which happens when a search is >completely finished, a move is made, and the score is significantly worse >than expected. > >3. whenever it displays a PV, because this goes into the log file. >But it is _very_ rare. > > > >>3. when does a program write to ram separate from the hash? > >All the time. Updating scoring tables, temp variables, PV stuff, generating >moves and sticking them in a move list. Evaluating. You-name-it... > >>4. If a pc has 512 megs ram, If we set hash at 64 megs, what happens when hash >>gets full? > >Stuff starts getting replaced, even if it might be useful. > > >>5. lets say a program stays in book for 15 moves, is the program accessing only >>the hard drive to play book moves? Or Is this info moved to ram first and then >>the program plays the book from ram? > >Depends on the implementation. Some read the entire book in first. Others >(myself included) do not so that the book can be far larger than physical RAM. > > > >>6. In the middle game after book, I assume this is when the program starts to >>store info from analysis. during this period, what is being read/write to the >>hard drive before the hash is full? > > >For Crafty, it would mainly be log file info. > > >>7. In the middle game after book, what is being read/write to the hard drive >>after the hash is full. > > >same as above. > >>8. In the middle game after book, if we set the hash at 64 megs, and then this >>fills, will the program just use more of the ram, or will it store analysis >>directly to the hard drive? > > >Neither. It will just have to replace hash entries by overwriting them. > > >>9. what were programs doing with analysis before hash tables? did all this >>analysis set in ram? did the operating system manage this info as needed, and >>move the stored analysis to the hard drive as the ram filled? > > >They simply didn't have the hash tables. But this has been around since the >early 1960's as Richard Greenblatt was the first to mention the idea and he >used it in Mack Hack. > > > >>10. if we set up two identical computers, running same program on each. >>set up same test position on both. computer A with hash tables and computer B >>without hash tables. how do these two compare, what memory are they using and >>when. >> > > >The main point is that the program with hash tables will search deeper, faster. I found out just how important hash tables are with an experiment. Phalanx22 is a decent chess engine, but it is not as strong as Crafty on equal hardware. On a Duron 900mhz, Crafty beats Phalanx on average 7.5-2.5 at 1 minute/move over several matches. I put Crafty on a p90, which performs about 16 times slower on average, and Phalanx on the 900. But, I forgot to give Phalanx some hash tables, since the default tables are tiny. Crafty won the match 6-4! After I found the mistake and re-ran the match, Phalanx won 9-1. > > > > > >> >>In other words when exactly, will a hard drive speed increase also speed up a >>chess program and why? > >Hard drive speed is irrelevant until you start probing endgame tablebases. Then >that speed becomes very important. > >But otherwise, it can be ignored. > > > > >> >>some will say go study on the internet. i have at many sites. i cannot find >>answers to these type of questions. if you know a site that answers these >>questions, please let me know, i will go there and study. >>thanks >>kburcham
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