Did Deep Blue win because of a software bug?

A few days back I watched the famous documentary ‘Game Over: Kasparov and the Machine‘. The IBM supercomputer Deep Blue defeated Kasparov at chess, a feat nobody thought was possible back then. Garry Kasparov was the ‘Classical’ World Chess Champion at the time (the FIDE champion was Anatoly Karpov).

Game Over: Kasparov and the Machine

The documentary is based on the epic 1997 rematch between Kasparov and Deep Blue. In fact, the first round of games happened in 1996 which ended with Kasparov winning 4-2. After much tweaks to the Deep Blue engine, IBM challenged for a rematch in 1997, which Kasparov accepted.

Deep Blue computer
Deep Blue

Kasparov won the first game after 45 moves. The turning point of the series was the second game. In the 37th move, Deep Blue played Be4!? which caught Kasparov off guard. After a few more moves Kasparov resigned and claimed that Be4 was not a move possibly considered as good by a machine and accused IBM of cheating. IBM fired back saying that Deep Blue wasn’t a regular chess program and if anyone thought it would play like a normal chess computer would do, that would be a big mistake.

Kasparov making a move against Deep Blue
Kasparov making a move against Deep Blue

Kasparov requested IBM to provide the game logs to check how Deep Blue concluded that Be4 was the best move, to which IBM did not comply. This would be fair during the series, as the logs would reveal the thinking pattern of Deep Blue which would lead to an unfair advantage to Kasparov. However, they could have at least released the logs later on. Several studies that followed concluded that a software bug helped Deep Blue win, i.e. it had chosen a random move in a seemingly dead-lock situation.

To make things worse, it was soon revealed that Kasparov could have drawn the game with a perpetual check. Critics claim that Kasparov had met with a mental breakdown after hearing this, which led to his defeat in the 6th game, after three more draws (3, 4, 5), thus making Deep Blue the winner of the series.

Kasparov resigning in Game 6
Kasparov resigning in Game 6

Deep Blue was retired soon after this match and no further development followed. Just like they retired sending people to the moon after the first successful attempt in 1969. The computers have become faster and more efficient by now and there exist dozens of popular chess engines like Deep Fritz, Rybka and Shredder. It’s not clear whether these actually exceed the power of Deep Blue.

‘Game Over: Kasparov and the Machine’ is an exciting documentary, featuring Kasparov himself and the actual scientists who built the Deep Blue. You can watch it in Youtube. Also, an annotated version of the second game can be found here.