Computer extension of chess theory

Computers have played a role in extending the knowledge of chess. In 1986 Kenneth Thompson of AT&T Bell Laboratories reported a series of discoveries in basic endgames. By working backward from positions of checkmate, Thompson was able to build up an enormous number of variations showing every possible way of reaching the final ones. This has been possible with only the most elementary endgames, with no more than five pieces on the board. Thompson's research proved that certain conclusions that had remained unchallenged in endgame books for decades were untrue. For example, with best play on both sides, a king and queen can defeat a king and two bishops in 92.1 percent of the initial starting positions; this endgame had been regarded as a hopeless drawn situation. Also, a king and two bishops can defeat a king and lone knight in 91.8 percent of situations--despite human analysis that concluded the position was drawn. Thompson's research of some five-piece endgames required considering more than 121 million positions.

Because of their ability to store information, computers had become invaluable to professional players by the 1990s, particularly in the analysis of adjourned games. However, computers have severe limits. In the 1995 PCA championship, Kasparov won the 10th game with a heavily analyzed opening based on the sacrifice of a rook. According to his aides, the prepared idea was tested on a computer beforehand, and the program evaluated the variation as being in the opponent's favour until it had reached the end of Kasparov's lengthy analysis.

The availability of top-notch microcomputers poses a major problem for postal chess. A principal difference between over-the-board chess and all forms of correspondence chess is that in the latter players are permitted to analyze a position by moving the pieces and by consulting reference books. By the 1990s most serious postal players used a computer database containing thousands of games categorized by opening moves. However, if the use of computers is extended to finding the best moves in the middlegame or endgame, postal chess becomes computer chess. The International Correspondence Chess Federation said in 1993 that "the existence of chess computers is a reality and for correspondence chess the use of chess computers cannot be controlled."