Glossary of Computer Chess Terms

This glossary is my attempt to list done terms that are commonly used in the Computer Chess field. The glossary will cover the following areas


As you can see this is a huge under-taking and the project may never be finished. Currently, there are still many empty placeholder entries and even the existing entries are still devoid of external links. Perhaps you might like to help by suggesting new entries , definitions or external links? Send me an email at



Used to enable one Chess engine based on one protocol to run in another GUI/protocol. For example there are Winboard to Chessbase adaptors, UCI to winboard adaptors, winboard to auto232 adaptors, 

Related Pages : My adaptors Faq. ,Winboard to ChessPartner adaptor

Aegon Man versus Machine tournament
A Man verus Machine team event held in the 1990s. A group of as many 50 humans of differing strengths played the best computers of the time in a Swiss tourney (computers can only be matched versus humans and vice versa).. Discontinued after the 12th Edition in 1997.   In 1996, the computer team won 162.5 to 137.5 for the first time, though the top scorer was generally human. Many GMs like Yasser Seriwan and John Van der Wiel achieved their anti-comp reputation by winning Aegon tourneys.

Related Pages :   Coverage of Aegon 96 from point of view of Chesssystem Tal  : Rebel at Aegon
Alpha beta
Pure Alpha Beta algothrim is proven to be safe and gives the same score as min-max searches but are more efficient, the better your move ordering is. It relies on keeping two scores alpha and beta levels which represent respectively the best score achievable so far, and the worse score that your opponent can force on you.Moves that cause a score higher than beta , "fail high" and force a beta-cutoff. Other re-findments of the basic alpha-beta include Principal variant searche [PVS] and Aspirant Search.

Related pages: Bruce Moreland explains , Paul Verhelst explains , Dr Walker explains

A Computer Chess communication protocol by Christian Donninger. Supported by most commercial programs . Auto232 allows you to automatically conduct chess matches between two programs using a null cable. 2 Winboard to Auto232 adaptors by Eberhard Boerger (only for 2 computers) and Rémi Coulom (for connecting a non-winboard engine to Winboard via auto232 on the same computer) allow Winboard chess engines to work with auto232 enabled programs as well.

Related Pages : Gambitsoft, Eberhard Boerger Auto232 player adaptor . Rémi Coulom auto232 player adaptor



A mainframe that won the 1980 Computer chess championships. Led by Ken Thompson from Bell labs. Also the first computer to achieve a US master's title.
Another open source Chess program designed to be easily readable by Colin Frayn and Dann Corbit Related Pages : Beowulf Homepage
Book learning
A method for chess programs to avoid bad opening moves in their book.No standard method, though most do results learning (based on win/loss ratios) and position (the average of the resulting score from the best n moves once out of book.) In addition, aggressive book learning involves repeating lines that have won in the past as opposed to just avoiding bad lines.
Branching factor
Normally the number of legal moves [typically 36] in each position. This affects how much longer it takes for the chess program to search one more ply compared to the last ply. Pure Min-max programs have a branching factor of 36, while safe alpha beta pruning cuts it down to about 6. Modern Chess programs which use various tricks like null move pruning are able to achieve branching factors of 3 or less.



The Chess format used by Chessbase to store games. CBH is the newer format used by Chessbase 6.0 and higher. CBF files are also read by the free Chessbase light.
Chess 4.7
The "Chess x" series was one of the strongest chess programs in the 70s. World Chess Champion 1978. Most remembered for losing to IM David Levy with the score of 3 losses and one draw in 1978. See David Levy's bet
Chess engine
The Chess playing portion of a Chess program. Chess engines that are Winboard compatiable can run in graphical interfaces that support the Winboard protocol.
Chess Academy
A commercial Chess database.Like many commercial Chess databases it supports the use of Winboard Chess engines.
Chess Assistant
A commercial Chess database.Like many commercial Chess databases it supports the use of Winboard Chess engines as well as UCI and a host of other Chess programs including Rebel Tiger,Zarkov,Genius.Also supports the playing of Chess in ICC.There is also a free light version available.
A commercial Chess database. Chessbase is one of the most popular Chess database's in the world and supports analysis with top Chess programs like Fritz,Junior,HIARCS,Nimzo and Tiger
Chess Genius
Famous Chess  program by Richard Lang. Richard Lang's programs (for micros) dominated the computer chess scenes in the 80s and early 90s. In 1994, Chess Genius 2 beat Kasparov in a 25 minute game at the Intel Speed Grand Prix.
A free PGN viewer by Mark van der Leek with some database capabilities and other useful functions [eg exporting of positions in HTML,RTF,EPD formats]. Supports the import of Winboard Chess engines for playing and Crafty for analysis.
A commercial Chess database by Lokasoft. Like other Chess databases, it supports the use of Winboard Chess engines. You can use it to connect to all types of Chess servers.
A popular commercial Chess program by Ubi Soft. The latest version Chessmaster8000 supports Winboard compatible Chess engines.
Conspiracy Number Search
Search the CCC archives for this.
Claude Shannon
Father of Computer chess. The article Programming a computer for playing chess published in 1950 was the first article ever on computer chess in 1950. Suprising modern it includes the understanding that a Evaluation function should be applied only in Quiescience positions. The term Shannon Type A Strategy and Shannon Type B Strategy was introduced here.
Computer Chess problems suites
A series of Chess positions usually in EPD used to test the strenght of Chess programs.The number of positions in each test suite vary, and some are able to calculate a "rating" based on the correct answers scored.It is unknown how accurate such tests are. Some famous ones include the Aemis,Covax,LCT, Nolot, Bratko-Kopec , Win at Chess
A strong, free source Chess engine by Dr Robert Hyatt. Crafty is also Winboard compatiable.
Related pages: My Crafty FAQ section , Download Crafty , Crafty help
Cray Blitz
One of the most successful chess systems of the 1980s. Written by Robert Hyatt it was based on his earlier program Blitz, but converted (as the name suggests) to run on Cray supercomputers, then the most powerful machines available. The freeware engine Crafty is a direct descendent.
Cray Blitz won two consecutive World Computer Chess Championships in 1983 and 1986 and won the (ACM) North American Computer Chess Championship in 1984.



David Levy
A famous bet made by IM David Levy in 1968 that no computer could beat him in a match in the next 10 years. He won (the wager was a year's wages circa 1968) in 1978 by beating Chess 4.7 3.5-1.5. He won a second bet in 1984 by beating Cray Blitz 4-0 in 1984 but declined to take any further bets. He was right, in 1989, he was crushed in an exhibitation match with Deep Thought 4-0.
Deep Blue
Descended from Deep thought. Brain child of Hsu and Campbell. Name was changed from Deep Thought to Deep Blue to reflect sponsorship by IBM. Lost a match to Gary Kasparov the reigning World Champion in 1996 by 2-4. It however became the first computer to beat a reigning World champion at standard time controls by winning the first Game. Retired after win over Kasparov in 1997.

Deep Blue versus Kasparov 1997
Often refered to as "Deeper Blue" this souped up version of Deep Blue beat Gary Kasparov by 3.5-2.5 in 1997. Kasparov won the first game comfortably. But in the by now infamous second games Deep Blue outplayed Kasparov on the White side of ruy lopez, but a disheartened Kasparov resigned in a drawn position. Kasparov dominated the rest of the games but managed to score only draws. With the score tied at 2.5-2.5, in the last and final game , Kasparov made an elementary opening error by transposing moves (or was that strategy?), and lost quickly.

Related Pages :

Deep Fritz versus Kramnik
A 6 game match, termed "Brains in Baharin", where Deep Fritz a leading computer PC program played Vladmir Kramnik (who had defeated Kasparov in a world champion match earlier)to a tie. Kramnik comprehensively outplayed and beat Fritz in games 2 and 3, by keeping the position simple. In game 5, Kramnik blundered and lost. In game 6, Kramnik quickly overplayed Fritz to achieve a good position, but overplayed his hand with a speculative sacrifice. The computer defended well and Kramnik had to resign. Later (shades of Game 2 Kasparov verus Deep Blue 1997] it was found that there was perhaps a drawing resource Kramnik had failed to see when he resigned.

Related Pages :

Deep Thought
Predecessor of Deep Blue .World Computer Chess champion in 1989. First computer to seriously challenge human supremancy. Shared first place in US open 1988. It victims included Bent Larsen, Robert Byrne and David Bronstein in exhibition and tournament play. Lost to Kasparov 2-0 in 1989 exhibition match. The name "Deep Thought" is a reference to The Hitch-hiker's guide to the Galaxy".



Edwards tablebase
Another form of tablebases by Steven J Edward .Like Nalimov tablebases, are based on distance to mate. Supported by older versions of Crafty.
Popular tool used to calculate ratings by Dr Frank Schubert.
Endgame tablebase Database of stored endgame positions. Allows Chess programs that can access them to play such endgame perfectly. There are various formats, the most popular currently are the ones by Eugene Nalimov.
Extended Futility pruning

See also Futility pruning

EPD [Extended Position Description]
Like FEN it is used to represent Chess positions. However it includes other attributes such as "am" [avoid move] and "bm" [best move] used by Chess programs, particularly in Chess problem suites.



Fail High
When a move is found at a node to exceed beta. Beta is the worse score (from your point of view) that your opponent can force on you. If a reply move scores equal to or greater than beta then this move is so good (from your point of view) that the opponent's last move becomes bad, and the opponent would have never played it and let this situation arise, hence searching other moves in this position (node) is pointless - That is we have a Beta cutoff. Note: Generally a good thing.
Fail Low
When all moves searched at a node are below alpha. Alpha is the best score you can achieve, but if all moves return a score lower then alpha, and this is the root position, you are in trouble. That is, the position is worse then you thought in the first place.
FEN [Forsyth-Edwards Notation]
A standard used to represent positions in Chess. See also EPD
Futility pruning
See also Extended futility pruning
Fredkin Prize
The prize, established at Carnegie Mellon University 17 years ago by Professor Edward Fredkin, was designed to encourage research in computer chess. A prize of $5,000 was awarded to Belle, the first chess program to attain a Master's rating in 1983, and a $10,000 prize was given to Hitech, the system that achieved Grandmaster status in 1988.
A top commercial Chessbase program written by Frans Morsch. Fritz is one of the strongest and most popular Chess programs and it will be challenging Kramnik to a Human versus Comuter Chess match in 2002. Experimental versions of Fritz usually plays under the name Quest.



A Chess program with source available by Bruce Moreland
The first original Chess program installed with Xboard/Winboard. Currently up to version 5.0.


Harvard Cup
blah blah
Hash tables
See Transposition table
Horizon effect 

blah blah


ICS [Internet Chess Servers]
Generic name for places where humans and computer programs can connect with telenet,a Chess client or even just with a browser to play Chess online. Not to be confused with ICC [Internet Chess Club altough it used to be called ICS a long time ago before it became commercial]. The most well known Chess servers are [formerly FICS] and ICC [Internet Chess Club].
International Chess Computer Association [ICCA]
The international body that holds the WCC [World Computer Chess tournaments] and WMCC [World Microcomputer Chess tournament]. The ICCA also publishes the quarterly ICJA [formerly ICCA] journal
Iterative deepening 
A process whereby the chess program searchs up to depth 1, then depth 2, then depth 3... rather then searching to depth N immediately. It provides you with a simple means of interrupting a search when you run out of time,. It is also efficent because the transposition tables can speed up searches to higher depths becuase they are already filled with used information from earlier searches. Not to be confused with Internal Iterative deepening.


Strong commercial Chessbase Chess program by Amir Ban and Shay Bushinsky. Deep Junior is the 2001 World Microcomputer Chess Champion [multi-processor]



The first official computer chess champion in 1974. From the Soviet Union.



Lazy Evalution
The idea is certain evalutation terms are very expensive to calculate, so if you find after calculating the value of simpler evaluation terms and material and adding the maximum score from the expensive evalution term, the value is still too low to affect the search, you can save time by not calculating the exact value of the more expensive term.



A search algothrim based on the idea that the first player will always try to maximise the score , while the second player will always minimise the score. Extremely in-efficent compared to safe alpha-beta, the number of nodes that needs to be searched is equal to W D where W= number of moves searched per positions and D = depth achieved.


Nalimov tablebases
Currently the most popular endgame tablebases by Eugene Nalimov.Nalimov tablebases may be compressed and are supported by Crafty,Fritz and others. Based on DTM [Distance to mate]. 3-4-5 and some 6 men tablebase are available for download.
Nolot suite
A extremely tough set of problems by Pierre Nolot who claimed that no computer could find the correct move under tournament controls. Brought to the attention of the computer chess community in 1994. This test suite is well known because some of the key moves have proven to be correct after hours and days of analyis by Deep Thought II (extremly unusual many test suites are too easy, or there are many winning moves).

Related Pages : Bruce Moreland's Nolot page including EPD for download, Googlegroup thread of Deep Thought's Analysis

Null move
Null move is considered to be one of the most important search heuristic found in the 90s. It based on the idea that in most positions, if you could "pass" or give your opponent's two moves in a row, and still obtain a "good" position, you must have a very good position (too good actually, beta cutoff) to start with. A null move is hence done, by "passing" (i.e not making a move) and doing a normal search on that position. However unlike a normal search, you do it with reduced depth search(this is where the speedup comes from ) . If this special reduced search is found to be above beta , you stop searching that node just as if you were doing a normal search. How much shallower you search is denoted by convention to R. . Doing null move R=2 (the safest) means that if you were intending to search to depth 4, you would do a search of 4-2=2 more ply instead. The main weakness of Null move comes from zugzwang positions where the right to move is actually a disadvantage , hence most chess engines turn off null move when in a endgame.



Opening book
Collection of opening lines used by the Chess program. Such opening lines are usually generated from a collection of Grandmaster games and/or hand tuned.


PGN [Portable Game Notation]
Standard format used to store move list of Chess games in ASCII format.
PGN extract

A half move. For example in the game 1 e4 e6 2. Nf3 Nc6 3. Bb5 there are 5 plies in total. Standard convention used generally to indicate how far a computer has seen (exception Junior). E.g Crafty searched this position to 10 ply.
A program is said to be "pondering" if it "thinks" on it's opponent's time. This is usually done by assuming the predicted opponent's move is played and analysing from there. There are other ways to generate "ponder moves" of course.
Principal variation
A predicted line that lies between alpha and beta. In other words, the program's best guess of what the best line is



Quiescent search
An extended part of the Chess program's search to reduce the horizon effect problem. Generally this involves extending the search in a limited way with perhaps only a subset of moves [captures,passed pawn pushes,forks] until a "quiescent" or quiet/stable position is reached before the Evaluation function is called.



"Limited razoring" ,See also futility pruning and Extended futility pruning



SAN [Standard Algebraic Notation ]
In almost all cases, exactly the same as normal "short" Algebraic Notation, except that standard English representation of pieces [B=Bishop,N=Knight,Q=Queen etc] as opposed to say German is used.
SCID [Shane's chess information database]
A free, fully featured Chess database by Shane Hudson.Supports the use of Winboard Chess engines.
A top commercial program by Stefan Meyer-Kahlen. Shredder is the 2001 World Microcomputer Chess Champion [Single processor] as well as the 9th and current World Computer Chess Champion. Shredder is available in it's own interface Shredder 5 and in a Chessbase version .
A free source Chess program by Gian-Carlo Pascutto. Sjeng plays not only normal Chess but Chess variants like suicide and losers Chess.
SMP stands for symmetric multi-processing. Chess programs that are SMP ready benefit from being run by Computer with multiprocessors. Examples include Crafty,Fritz, Junior, Shredder, Diep. Sometimes the tag "deep" is used to indicate that a Chess program is SMP ready.
A rating list maintained by the Swedish Computer Chess association. Ratings are calculated based on thousands of computer versus computer matches.
Static evalution
The Static evaluation of a position usually refers to the score an engine gives to a position without doing any search. That is, it calls it's evalution function immediately. The more accurate the result, the better.


Transposition table
Positions stored in memory by the Chess program to help speed up search. The size of the transposition table is usually adjustable by the user.
TSCP [Tom Kerrigan's Simple Chess program]
A simple Chess program for which the source is available. Written by Tom Kerrigan.
Thompson tablebase
Another form of tablebases by Ken Thompson. Unlike the Nalimov and Edwards tablebases, Thompson tablebases are based on distance to conversion. Not supported by many Chess programs.



UCI [Universal Chess interface]
Another Chess communication protocol by Rudolf Huber and Stefan Meyer-Kahlen. Similar to Winboard protocol in that the protocol is open, but no free graphical user interface exists.Currently supported by only a few Chess engines including Yace,Pepito,Anmon, Dragon etc.





WAC (Win at Chess)
A collection of 300 Chess problems from the book "Win at Chess". Used by many programmers to test the tactical ability of Chess programs altough most are fairly easy. Top programs routinely get 280 or more out of 300 at 5 second per move.

Related Pages :

A free graphical interface by Tim Mann that allows users to log onto Chess servers.Also serves as a front end interface for many Chess engines. See also Chess Engines, Xboard. [Related pages Why use Winboard?]
Winboard communication protocol
The protocol is a set of commands that the Chess engine has to recognise to work in Winboard. Extremely popular the protocol is supported by more than 100 available Chess engines and many graphical user interfaces like Chessmaster, Chessbase,Chess assistant. There are 2 levels of the protocol.



The Unix version of Winboard. Functionally similar, except that it is possible to display a move list in Xboard. See also Winboard




Used by Winboard/Xboard to allow Winboard Chess engines to run on online Chess Servers.