Garry Kasparov still cannot come to grips entirely with Deep Blue. The fourth game saw the world champion overcome early difficulties to reach a winning endgame, only to let it slip at the critical moment.

The second draw of the match leaves it tied at 2-2 with two to play. Deep Blue's speed of response gives it an extra edge because it leaves Kasparov less time to reflect. Both sides have to make their first 40 moves in two hours thinking time. When Kasparov goes in for a long think at an early stage, as he did today, he finds he has to make his last few moves in a hurry as he strives to reach the first "time control" on the 40th move.

Consequently, errors creep into his play. The champion feels he missed a win in the time trouble phase. Deep Blue, naturally, just keeps churning out the moves and keeping the pressure on. Kasparov is tiring.

When questioned by commentator Maurice Ashley about a winning possibility near the end of the game, Kasparov replied: "I was tired and I could not figure it out."

Murray Campbell said of the machine: "It knew it was a little behind but it never saw a clear win (for Kasparov)."

Kasparov has obviously developed a healthy respect for Deep Blue, admitting that he "did not have any great aspirations with black," which implies he would have been satisfied with a draw when he sat down at 3 p.m. By 4p.m., when he stood badly, a draw seemed a long way off, but a pawn sacrifice from Kasparov changed the character of the position and Deep Blue did not react well.

At one point, Deep Blue had five "isolated pawns," a chess term for pawns that are not adjacent other pawns which can be used for protection. Kasparov looked really confident, and Deep Blue might have been worried because one of its handlers, Feng-hsiung Hsu started typing commands into it. This visibly amused the champion. Later it was explained that Feng was restarting the computer.

Kasparov was a pawn in arrears, but his two remaining pawns were united, and could support each other's advance. However, just as the Grandmasters were preparing to bury Deep Blue, it came up with a fantastic defense, and Kasparov's pawns were going nowhere. One of Deep Blue's pawns hovered over the queening square, and when another started to roll, Kasparov had seen enough and offered a draw.

--IM Malcolm Pein, London Chess Centre