Grid computing reaches new prime

An effort in which hundreds of people donate their computers' unused processing power has uncovered the largest prime number so far known.

The number, with more than 6.3 million digits, is the sixth so far uncovered by the Great Internet Mersenne Prime Search (GIMPS). Two years ago, the group discovered the previous record holder, a comparative lightweight with only about 4 million digits.

A computer run by Michael Shafer, a 26-year-old at Michigan State University found the number, the GIMPS organizers said. The machine - a Dell with a 2GHz Pentium processor - was one of 211,000 run by about 60,000 volunteers involved in the project.

The prime number search, a conceptual cousin to the SETI@home quest to detect alien communications in radio telescope signals, is at one end of a spectrum of technology for pooling computing resources.

The GIMPS effort involves loosely linked machines that only need to check in to a central server occasionally, an idea often called distributed computing. But as resources get more formally attached to the pool, the technology takes on labels such as grid computing and utility computing.

Utility computing, a major effort under way at companies such as IBM, Hewlett-Packard and Sun Microsystems, has clear business applications, such as tapping into more computing power during times of peak demand. Distributed and grid computing have been of interest chiefly to the academic community, but it's becoming increasingly useful for commercial applications such as pharmaceutical research.

The GIMPS infrastructure is provided by Entropia, a company that sells distributed computing software. The GIMPS servers oversee the work done by the network of PCs, which collectively perform 9 trillion calculations per second.

A prime number is evenly divisible only by itself and the number one. Prime numbers have fascinated mathematicians for centuries, though the largest ones are chiefly of academic interest.

Mersenne primes are a particular variety named after Marin Mersenne, a French monk born in 1588 who investigated a particular type of prime number: 2 to the power of "p" minus one, in which "p" is an ordinary prime number.

In the number announced Tuesday, p is 20,996,011 - the 40th Mersenne prime found so far.

The actual digits can be downloaded from Wolfram Research's MathWorld site. True enthusiasts can buy posters with all the digits printed - as well as magnifying glasses to read them.

Stephen Shankland writes for CNET News.com