From: AAAI Technical Report WS-97-04. Compilation copyright © 1997, AAAI (www.aaai.org). All rights reserved. The Historical Development of ComputerChess and its Impact on Artificial Intelligence David Heath and Derek Allum Faculty of Science and Computing, University of Luton, Park Square, Luton LU1 3JU United Kingdom [email protected] [email protected] The minimaxalgorithm was first applied in a Abstract computer chess context in the landmark paper of Shannon.He also introduced the classification of In this paper we review the historical chess playing programsinto either type A or B. developmentof computerchess and discuss its Type A are those that search by ’brute force’ impacton the conceptof intelligence. Withthe alone, while type B programs try and use some adventof electronic computersafter the Second considerable selectivity in deciding which World War, interest in computer chess was branches of the gametree require searching. stimulated by the seminal papers of Shannon (1950) and Turing(1953). Theinfluential paper Alpha-beta pruning was first formulated by of Shannonintroduced the classification of chess McCarthy at the Dartmouth Summer Research playingprograms into either type A(brute force) Conference on Artificial Intelligence in 1956. or type B (selective). Turing’s paper (1953) However,at this stage no formal specification of highlighted the importanceof only evaluating it was given, but it was implemented in game ’dead positions’ which have no outstanding playing programs of the late 1950s. Papers by captures. Thebrute force search methodis the Knuth and Moore (1975) and Newborn (1977) most popular approach to solving the chess have analysed the efficiency of the methodand it problem today. Search enhancements and has been proved that the algorithm returns pruningtechniques developed since that era have exactly the same moveas that obtained by full ensuredthe continuingpopularity of the type A method.Alpha-beta pruning remainsa standard minimaxingor, alternatively, a moveof the same technique. Other important developmentsare value. surveyed. A popular benchmark test for The success of type A ’brute force’ programs determiningintelligence is the Turingtest. In the using exhaustive search, minimaxingand alpha- case of a computerprogram playing chess the beta pruning, transposition tables and other movesare generatedalgorithmically using rules search enhancements has had the unfortunate that have been programmedinto the software by effect of minimising interest in the development a humanmind. Akey question in the artificial of type B programs. The work of Simon and intelligence debate is to what extent computer Chase (1973) established that most humansonly bytes aided by an arithmetic processingunit can be claimedto ’think’. consider a handful of plausible moves. The power and ability of the chess grandmaster resides in his ability to select the correct subset Introduction of movesto examine. With the advent of computersafter the end of the In contrast the brute force programssearch the Second World War, interest in the development entire spectrum of initial movesdiverging from of chess playing programswas stimulated by two some given position referred to as the root. seminal papers in this area. The paper by These initial movesfan out, generating a game Shannon(1950) remains even to this day to be tree which grows exponentially with depth. central importance while the paper by Turing Apart from the work of Botvinnik et.al in recent (I 953)is equallyinfluential. years, there has been no significant progress in developing a type B strategy program which 63 would reduce the initial span of the search tree. The first significant chess playing program The successful development of algorithms that was by Bernstein (1957) and ran on an IBM704 introduced selectivity into the search engine, so computer, capable of performing approximately that the program followed similar lines of 42,000 operations per second. This was not a thought to those of a chess grandmaster, would ’brute force’ programas it only selected the best considerably reduce the amount of searching seven movesfor consideration using heuristics required. based on chess lore. Compared to the Turing’s paper (1953) highlighted the sophisticated brute force programs of today importance of only evaluating ’dead positions’ which generate the full span of moves at the which have no outstanding captures. It is from root, this is a very limited range of moves. this paper the term ’Turing dead’ is taken. Most The Bernstein program was built around the chess programs search to a quiescent position strategy of working to a plan. As it was (Turing dead) and then evaluate the position as incapable of doing a full width search due to function of the material balance and other time considerations, it selected its quota of seven features. This evaluation function encapsulates movesfor deeper analysis by seeking the answer chess-specific knowledgetypically relating to to eight questions. Once the moves were pawnstructures and king safety. selected, they were analysed to a search depth of 4 ply. The potential replies by the opponentwere History also selected on the basis of seeking answers to the sameset of questions. The historical evolution of computer chess Bernstein’s program played at a very programming techniques and knowledge can be elementary level and the first programto attain conveniently discussed in three broad eras. Each any recognisable standard of play was that of era is characterised by its own particular Greenblatt (1968). For a number of years this developments, some of which can be directly remained the most proficient chess program and linked to increased processor power, the played at an Elo strength of approximately 1500. availability of new hardware devices and others It had carefully chosen quiesence rules to aid to algorithmic advances. tactical strength and wasalso the first programto The boundary between each era is not always use transposition tables to reduce the search precise as it is sometimes not easy to draw a space. However, the Greenblatt program also clear dividing line across a time continuum.Any used an initial selection process to minimizethe such process is artificial. However,these broad size of the game-tree as the computing hardware historical eras are (Donskoy and Schaeffer of that era was incapable of achieving the 1990): computing speeds of today. Again this program, (i) 1st era (1950 - c1975) because of its selectivity at the root node, falls into the first era. (ii) 2ndera(c1975-c1985) The first programto achieve full width search (iii) 3rd era (c1985 onwards) and make ’brute force’ appear a viable possibility was Chess 4.5. This program was The first pioneering era as stated above runs developed for entry into the ACM1973 from 1950-c1975.Here there is a definite point Computer Chess contest by Slate and Atkin, at which this history commences,marked by the using the experience they had gained in publication of Shannon’spaper and the advent of programming earlier selective search chess electronic computers. These computers, although programs. The techniques used by Slate and originally regarded as revolutionary and Atkin (1977) are still in use today although they powerful, had but a fraction of the computing have been refined and improved over the years. power of the current generation of These standard techniques initiated what maybe microprocessors. Indeed hardware limitations classed as the second technology era giving rise characterise the first era of computer chess to programstypically searching to a fixed depth development, requiring highly selective as fast as possible and then resolving the horizon techniques in order to produce moves in an problemby extending checks at the cutoff depth acceptable time. The earliest programs were, and considering captures only in a quiescence therefore, Shannontype B. search. 64 The second era of computer chess also saw Move Ordering Techniques more emphasis placed on the development of Theprevious section has outlined the historical dedicated chess hardware. Typical of such developmentof computerchess. The transition developments was Ken Thompson’s chess to ShannonB type programsto ShannonA is not machine Belle which won the ACMNorth American Computer Chess Championship in solely attributable to increasedcomputing power. It also partly arose out of increased 1978. The special purpose hardwareincreased the speed of Belle enabling it to analyse 30 understandingof the alpha-beta algorithmwhich million positions in 3 minutes and search was subjected to deep analysis by Knuthand exhaustively to 8 or 9 ply in middlegame Moore(1975). Other techniques for increasing positions. It also had an extensiveopening book. the efficiency of the search and pruning Belle won the 3rd World Computer Chess mechanismsalso becamemore prominentat the beginningof the secondera. Championshipin 1983, achieving a rating of Producinga cutoff as soonas possiblewith the over 2200 in 1980and wasthe first programto receive a Masterrating. It was for Belle that alpha-beta algorithm considerably reduces the Thompsondevised his first end gamedatabase, size of the search tree. Consequently, move ordering is an important aspect of achieving solving the KQKRproblem and hence partially removingthe perceivedweakness at that time of maximumspeed since, if we knowthe best move computersin endgamepositions. in a certain situation producingit early rather In 1975 Hyatt commencedwork on Blitz than late, will havebeneficial