In 1966 and 1967, MIT programmer Richard Greenblatt - working with Donald Eastlake - wrote a chess program called Mac Hack VI for a DEC PDP-6. In 1967 it became the first computer program to play in a human chess tournament, the first to be issued a chess rating by the United States Chess Federation, and the first to beat a human opponent in rated tournament play. The Computer History Museum records that it earned a rating around 1400, the level of a good high-school player.
Mac Hack VI is also tied to a famous philosophical jab. The MIT philosopher Hubert Dreyfus had argued that no computer could play even decent chess. In 1967, a group at MIT organized by Seymour Papert arranged for Dreyfus to play the program. Dreyfus lost, and the game was circulated as a pointed rebuttal to his skepticism about artificial intelligence.
Greenblatt and his collaborators described the system in “The Greenblatt Chess Program,” presented at the 1967 Fall Joint Computer Conference. The program leaned on Shannon’s selective “Type B” approach, using heuristics to focus its search rather than examining every move, and it set the template for the rated, tournament-playing chess machines that culminated three decades later in Deep Blue.