Chess opening book (computers)

Opening book is often used to describe the database of chess openings given to computer chess programs (and related games, such as computer shogi). Such programs are quite significantly enhanced through the provision of an electronic version of an opening book. This eliminates the need for the program to calculate the best lines during approximately the first ten moves of the game, where the positions are extremely open-ended and thus computationally expensive to evaluate. As a result, it places the computer in a stronger position using considerably less resources than if it had to calculate the moves itself.

On some occasions, a player might consider playing a strange move outside the opening book to force a computer to think for itself. While this may introduce a strategic weakness, a lot of the time, playing out of the book early may end up compromising one's own pawn structure, losing a tempo or allow the opponent to develop more effectively, as chess engines have become significantly more powerful over time to think more deeply or accurately than in the past.