How do computers play chess?
In 1950 Claude Shannon proposed two basic strategies for restricting the number of possibilities to be considered. Both of these strategies, with minor modifications, are still used to date by competent and incompetent chessprograms alike. The so-called “Shannon type A strategy” considers all possible moves up to certain number of plies at which point some criteria is applied to choose the best possible of the moves considered based upon the positions attained at the end of the search. The idea is that, since it is not possible to try all the possible responses and counter-responses until the game is finished, the computer restricts the number of plies or depth of the search to a number that allows it to produce a reply in a reasonable amount of time. It is rather interesting to note that human chess players too, look ahead only a limited number of plies until some satisfactory position is achieved. Of course the computer needs some method to evaluate the positions reached after the
