Belle (chess Machine)

Belle was the name of a chess computer and its associated software, developed by Joe Condon and Ken Thompson at Bell Labs in the 1970s and 1980s. Belle was the first computer built for the sole purpose of chess playing. The strongest computer chess system of its time, Belle achieved a USCF rating of 2250, and officially became the first master-level machine in 1983. It won the ACM North American Computer Chess Championships of 1978, 1980, 1981, 1982, and 1986. It also won the 1980 World Computer Chess Championship.

In its final incarnation, Belle was composed of a PDP-11/23 with a LSI-11 processor and many custom boards. There were three custom boards for move generation, four custom boards for position evaluation, and one board with custom microcode which controlled the whole thing. The computer also had one megabyte of commercial memory which was used for transposition tables. At the end of its career, Belle was donated to the Smithsonian Institution. The overall architecture of Belle was used for the initial designs of ChipTest, the progenitor of IBM Deep Blue.

In 1982, Belle was confiscated by the US State Department at Kennedy Airport when heading to the USSR to compete in a computer chess tournament; its shipping was considered to be an illegal transfer of advanced technology to a foreign country. It took over a month and a $600 fine to get Belle out of customs. Thompson learned that the reason for confiscation was the attached HP 2640 terminal which had internal VLSI memory and a microprocessor.

Ken Thompson used Belle extensively for pioneering research into chess endgame tablebase. In particular, he used Belle to exhaustively calculate tablebases to cover all four- and five-piece endgames, including KBBKN, KQPKQ, and KRPKR. Thompson then wrote the paper: “Retrograde Analysis of Certain Endgames” in 1986 to describe his efforts.