Deep Blue versus Garry Kasparov was a pair of famous six-game human–computer chess matches, in the format of machine and humans, versus a human. In this format, on the machine side a team of chess experts and programmers manually alter engineering between the games.
The second game began with the Open Catalan Opening. Kasparov played in what could be called a preemptive style blocking all Deep Blue’s development tries. The game lasted for 73 moves but eventually Deep Blue’s operator had to resign the game for the computer in a position where both players had a bishop but Kasparov had three pawns against Deep Blue’s one.
The fifth game was the turning point in the match. During the game, Kasparov, playing Black, chose a different opening, the Four Knights Game, from the Sicilian Defence he had played in games one and three and came on top. This was particularly embarrassing for the Deep Blue team, because they had declined Kasparov’s draw offer after the 23rd move. This was the only game in the match that Black won.
In the end of the sixth game, Deep Blue’s pieces were crammed into its queen side corner, almost completely unable to defend its king. Kasparov’s next move would probably have been 44.Qe7 to exchange the queens. That would have allowed his pawn, which was about to promote, to advance.
Deep Blue’s 44th move in this game puzzled Kasparov, and he attributed it to “superior intelligence”. Allegedly, the move was a result of a bug in which Deep Blue, unable to determine a desirable move, resorted to a fail-safe. Nate Silver proposes that Kasparov “concluded that the counterintuitive play must be a sign of superior intelligence”, leading him to lose the second game.
In this game Kasparov accused IBM of cheating, a claim repeated in the documentary Game Over: Kasparov and the Machine. Kasparov eventually resigned, although post-game analysis indicates that the game could have been drawn. The game started with the Ruy Lopez opening Smyslov Defence variation.
At the time it was reported that Kasparov missed the fact that after 45…Qe3 46.Qxd6 Re8, Black (Kasparov) can force a draw by perpetual check (threefold repetition). His friends told him so the next morning. They suggested 47.h4 h5!, a position after which the black queen can perpetually check White. This is possible because Deep Blue moved 44.Kf1 instead of an alternate move of its king. Regarding the end of game 2 and 44.Kf1 in particular, chess journalist Mig Greengard in the Game Over film states, “It turns out, that the position in, here at the end is actually a draw, and that, one of Deep Blue’s final moves was a terrible error, because Deep Blue has two choices here. It can move its king here or move its king over here. It picked the wrong place to step.” Another in that film, four-time US champion Yasser Seirawan, then concludes that, “The computer had left its king a little un-defended. And Garry could have threatened a perpetual check, not a win but a perpetual check.”
The third game was interesting because Kasparov chose to use an irregular opening, the Mieses Opening. He believed that by playing an esoteric opening, the computer would get out of its opening book and play the opening worse than it would have done using the book. Although this is nowadays a common tactic, it was a relatively new idea at the time. Despite this anti-computer tactic, the game was eventually drawn.
In this game Kasparov played the Caro-Kann Defence. Later on he had time problems and had to play in a hurry, as both players had two hours for the first 40 moves and Kasparov was approaching his time limit. The sub-optimal moves he played in a hurry may have cost him the victory.
Before the sixth match the overall score was even: 2½–2½. As in game 4, Kasparov played the Caro-Kann Defence. He then allowed Deep Blue to commit a knightsacrifice which wrecked his defences and forced him to resign in fewer than twenty moves.