In order to program a computer to play chess, you need knowledge of chess techniques and strategies -- just knowing how the pieces move isn't enough. People play chess by strategizing and recognizing patterns of play. Computers use both algorithms (step-by-step instructions) and heuristics (trial-and-error problem solving). Specifically, a system that incorporates the minimax algorithm and the alpha-beta pruning technique.
The minimax algorithm allows the computer to search through every possible move as well as the opponent's possible responses. The "minimax" part comes from the computer's need to figure out the best and worst moves (both its own and its opponent's) after each turn. Alpha-beta pruning means that the computer creates two "trees." Tree A considers every possible chess move to a certain extent. Then it "prunes" Tree A to create tree B, which further explores the moves that look the best. As you might imagine, today's computers can do this with amazing speed -- far faster than any human ever could.
By the 1960s, computer chess programs were good enough to beat amateurs. In 1967, MIT professor and chess player Richard Greenblatt created the Mac Hack IV chess program, and the computer using it became the first to beat a person in a chess tournament. It wasn't a chess master, though. In 1968, International Chess Master David Levy bet that no computer could beat him at chess in 10 years, and that if he did win, it would be another ten after that before a computer beat him.
Levy won the bet, but in 1989, it finally happened. Deep Thought, initially created by programmers at Carnegie Mellon University, beat Levy. In 1997, Deep Blue -- predecessor to Deep Thought -- beat Gary Kasparov, a Chess Grandmaster (the highest level you can attain in the FIDE, the world chess organization) and reigning World Champion. Since then, there have been more computer victories, but as one computer science professor put it, "the science is done" [source: New York Times]. We've taken computer-vs.-human chess as far as it can go -- but there are plenty of other games to dominate.