Belle Chess Machine by Peter Adams.

Belle Chess Machine

The first purpose built chess computer – Belle, was created by Ken Thompson and Joe Condon.
Before Deep Blue there was Belle — the first computer of its kind designed with the sole purpose of winning the game of chess. Belle was the product of Bell Labs researchers Ken Thompson (inventor the UNIX operating system) and Joe Condon. The pair created and developed several generations of the chess machine throughout the l970’s and 1980s. Belle was one of the strongest chess machines of its time. It achieved a USCF rating of 2250 and was the first machine to reach "master" level in 1983. The computer employed a “brute force” approach to play in which it evaluated the outcome of all possible moves several levels deep. This innovation ultimately earned it five ACM North American Computer Chess Championships as well as the winner title at the World Computer Chess Championship in 1980. Thompson's personal interest in chess generated a fair share of unintended publicity as Belle began to win high profile championships. The notoriety begged the question of whether or not Bell Labs should be building a chess champion – a topic Bell Labs senior management never took up with Thompson. However, that didn't stop Thompson's colleague Mike Lesk from making light of the issue by authoring a now infamous fake memo written on letterhead stolen from then AT&T Chairman John deButts.