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Collective Wisdom

Brian Hayes

The most powerful computer in the world, according to a recent ranking, is a machine called Janus, which has 9,216 Pentium Pro processors. That's a lot of Pentia, but it's a pretty puny number in comparison with the 20 million or more processors attached to the global Internet. If you have a big problem to solve, recruiting a few percent of the CPUs on the Net would gain you more raw power than any supercomputer on earth.

Of course the trick is to get all those millions of scattered machines working on your problem. The 9,216 Pentiums are all conveniently housed in a single room at the Sandia National Laboratory in Albuquerque. Setting them to work on the task of your choice is a simple matter; all you need is an account on the machine, a password, an allocation of CPU time, possibly a security clearance, and a little knowledge of programming in a specialized dialect of FORTRAN or C. Persuading the Internet to do your bidding is not so easy.

And yet it can be done. Consider the hunt for trophy-quality prime numbers. For two decades, the weapon of choice in this elite sport was a supercomputer—preferably the latest model from Cray Research. Beginning in 1979, the prime-number pursuit was dominated by David Slowinski and his colleagues at Cray (which is now a division of Silicon Graphics). The Cray team had to keep topping their own records, because they had so little competition elsewhere. In 1996, however, a new largest prime was found with an unpretentious desktop PC. The discoverer was a member of an Internet consortium who attacked the problem collectively with a few thousand computers. In August of 1997 another member of the same group found a still larger prime, which stands as the current record. Slowinski, being a good sport, offered one of his supercomputers to verify the discoveries.

The rise of cooperative-computing projects on the Internet is both a technical and a social phenomenon. On the technical side, the key requirement is to slice a problem into thousands of tiny pieces that can be solved independently, and then to reassemble the answers. The social or logistical challenge is to find all those widely dispersed computers and persuade their owners to make them available.

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