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CHESS is a war game with a difference: both sides can see behind enemy
lines, and know exactly how a piece may move. There are just six types of
chess piece: pawn, knight, bishop, rook, queen and king. In the starting
position of the game, the players put their pieces on the first two rows
(‘ranks’) of the square board, which has 64 squares. Pawns move forward
one square up the ‘files’, bishops move on diagonals, rooks forward and
sideways, the queen in all directions, and the king one square in any direction.

The knight move often confuses beginners – it is the only piece that
can jump over others, moving two squares forward, and one sideways. All
pieces can move backwards with the exception of the pawn, which moves only
forwards. The pawn also has other rules, such as promotion to another piece
if it reaches the end of the board. Pieces capture enemy pieces by occupying
the same square, removing the opposition from the board. Pawns capture only
diagonally.

A queen is the most powerful piece, because it can move any number of
squares in all directions. But it is not the most valuable – that is the
king, because the object of the game is to corner the king so it cannot
move. The game is a series of manoeuvres to produce this position – ‘checkmate’.

In any game, there are an enormous number of possible positions that
the players can create. It is not enough just to count the pieces on both
sides to say who is winning: the positions of the pieces are a critical
measure of advantage. Top players, called international masters and grandmasters,
have a deep knowledge of the variations in the opening phase of the game
(up to 20 moves by each side) At some point, however, the game will leave
the theory books, and then the players must use their experience and brilliance
to create strategic plans, open up and probe weaknesses, and spot opportunities
for tactical ‘coups’. It is this middle-phase of the game that presents
the main challenge for the chess programmers. If the computer cannot resolve
the position by reducing it to a series of tactical moves and captures,
it must find moves intended to lead to improvements in its game.

Some middle-game chess positions are so complex that chess journals
often subject them to months of analysis. Even the end-phase of the game,
where there are fewer pieces, can be extremely difficult to win where an
advantage is small. Chess games can also end as draws: fighting for a draw
in a bad position is often a feature of tournament games.

Players also play against the clock. Tournament rules vary, but a standard
rate of play is 40 moves in two hours (for each person). At this speed,
a computer has much less advantage than in the faster ‘speed’ chess, where
moves come every 10 seconds, or all moves must be made in five minutes.
In these fast conditions, computer programs are now good enough to smash
all comers.

The world’s top human player is Gary Kasparov of the Soviet Union. To
many, the idea that a machine could conquer Kasparov’s profound strategic
thinking is simply unbelievable. Yet Kasparov and his fellow grandmasters
are now decidedly uncommitted about chess computers: they have placed no
large wagers against the unthinkable.