Marion Tinsley has been the world's top-rated checkers player for decades, but No. 2 is breathing down his neck. Well, not exactly breathing; No. 2 is a computer, after all.

Equipped with a checker-playing program named Chinook, the computer has fought Tinsley to six straight draws in a 30-game match to determine the world's best player.Tinsley says he is. But the 67-year-old retired math teacher admits his opponent is getting better every day.

Chinook's creator says it's only a matter of time before the computer wins.

"In one small area - games - we're now on the threshold of demonstrating that machines are superior to humans," says Jonathan Schaeffer, the Canadian computer scientist who designed the software program.

The computer's secret: Its memory stores 250 billion checkers moves. That's every position possible with eight men or fewer on the board, and Chinook learns half a billion more moves every day.

"No human can even begin to match that," Tinsley says. "It's like playing a library."

If there is anyone who can give Chinook a run, it is Tinsley. He was declared world champion at age 28 and has lost only nine times in 36 years. He surrendered his title in 1992 and was named grand master emeritus.

He also defeated an earlier version of Chinook at a London tournament in 1992, losing only two games.

But Chinook's database is five times larger now. It can analyze 12 million plays a minute and has not lost a match in 125 games.

The rematch is being held at Boston's Computer Museum, where Tinsley sits at one end of a green felt table and a computer monitor sits at the other. Spectators watch the action on two large-screen TVs.

The winner gets $8,000 and recognition from the International Checkers Hall of Fame and British Draughts Federation as the "man-vs.-machine world checkers champion." That was a compromise to appease those who do not believe a computer should have a shot at the world championship.

So far, the computer has been playing flawlessly.

The competition has implications far beyond the game of checkers. It means computers can consider opportunities and consequences and make reasoned choices, just like humans.

"Real life is extraordinarily complex, so if you want to make a machine that can do something complex, you have to start with something simple like checkers," Schaeffer says.

The software uses a $500,000 supercomputer built by Silicon Graphics Inc., based in Mountain View, Calif., which is sponsoring the tournament to showcase its equipment. The company created the special effects for the movies "Jurassic Park" and "Forrest Gump."

As government and corporate demand for supercomputers dwindles, more and more of the powerful technology is being used for entertainment, from virtual reality to special effects to checkers, says Marvin Minsky, professor of computer science at the Massachusetts Institute of Technology.

"What's wrong with computers now is, they don't have common sense knowledge," Minsky says, "and that's what the entertainment people are doing, adding common sense."