Five years and 5 million networked PCs find no sign of extraterrestrials. They'll keep looking.Mulder and Scully made it look so easy. An alien hunt has been underway for more than five years using the world's largest\u00a0grid supercomputer\u00a0- 5 million Internet-linked PCs - as part of a project called SETI@Home. The project, run by the University of California Berkeley, harnesses unused CPU cycles to comb through deep-space radio noise, searching for signals from extraterrestrials.So after expending 2 million years of accumulated CPU time and analyzing 50T bytes of data - are we alone?"We still don't know the answer to the big question," says Dan Wertheimer, chief scientist for the SETI@ Home project and the director of the Search for Extra Terrestrial Intelligence (SETI) program at UC Berkeley. "We haven't bugged any aliens yet."But this wasn't a bummer to the world's top ET scientists, who congregated at Harvard University for last week's SETI Symposium. Dozens of astronomy Ph.D.s spent two days discussing strategies for detecting intelligent life in the universe."I'm optimistic that earthlings will find ETs in the long run," Wertheimer says, "But don't hold your breath."With the one-in-a-billion odds of a SETI@Home PC finding an alien radio signal, many volunteers have turned the project into a kind of PC hot-rodding contest, where users soup up their machines in a race to produce the most work units - the chunks of radio waves distributed by SETI@Home to clients. The SETI@Home software also has become a tool for testing and benchmarking computer performance among IT professionals and some server vendors.SETI@Home starts with Cornell University's Arecibo Observatory radio telescope in Puerto Rico - a dish three times the size of the new Olympic Stadium in Athens, Greece - which collects radio noise from distant stars. The data is recorded on tapes that are sent to Berkeley, where servers break them into chunks and make them available over the Internet. The 5 million PCs worldwide that have the SETI@Home screen-saver program installed can download chunks of signals and look for patterns in the noise. The processed work units are then sent back to Berkeley's SETI computer lab - a storage closet in the astronomy department where the servers are kept.SETI@Home's Web site\u00a0keeps a leader board for the top work-unit workhorses. Statistics show individual performances and SETI@Home groups, which include corporations such as Boeing, Sun, HP and Cisco, and organizations such as Ohio University, the University of Leeds in England and the Tempe, Ariz., Union High School District."It's hard to say whether the main motivation for people running the program has more to do with scientific goals or with the competition for work units," says David Anderson, director of the SETI@Home project, who wrote the screen-saver software. "The competitive aspect, having the fastest computer on the block, is probably the main driving force."Anderson says the most enthusiastic users tweak their computers' CPUs to squeeze out every megahertz of performance for processing work units.The technique known as "overclocking" is used by many of the leaders on the SETI@Home scoreboard - most notably Overclockers UK, a group of British PC enthusiasts that runs a Web site for building super-fast PCs. Enormous computer cooling fans, special gels that dissipate heat on a CPU's surface and water cooling systems are among the items\u00a0for sale.According to the group's Web site, Overclockers UK's SETI@ Home goal is "to wave the U.K. flag for all the world to see by reaching the top position and proving to the rest of the world that U.K. overclockers are indeed a force to be reckoned with."SETI@Home's Anderson cautions that overclocking a PC can produce erroneous results on work units. That's why all work units are sent out twice, and the results compared, to ensure there are no errors. If the results of a work-unit pair are out of sync, both work units are cancelled and sent out again.SETI@Home, at workSome IT folks who run SETI@Home use it at work because it makes a great tool for testing the performance of new machines.SETI@Home "is a very good [benchmark] of real server workloads," says Leon Parkhouse, director of technology at Drake Institute for Behavioral Medicine in Los Angeles. "If I'm putting together new systems and I want to know how quick they're going to run, I'll use SETI@Home."Parkhouse, who has an interest in astronomy and science, started using SETI@Home three years ago on old machines he brought home from work - some Digital Alpha servers and a few late-model Pentium machines. He runs four computers in his basement dedicated to SETI@Home.But Parkhouse doesn't use his main SETI@Home username on the work machines, however. "That would really affect my score," because the machines he runs at home are faster than most PCs in the office. He recently passed 5,000 work units, commonly seen as a milestone separating the curious user from dedicated enthusiast.Pushing the grid envelopeWith more than 70 teraflops of computer power, the SETI@ Home project is one of the largest examples of grid computing.Sun donated much of the hardware Anderson and his colleagues used to set up the grid system for distributing work units over the Internet."If someone were to write a history of grid computing, I think SETI@Home would be a big chapter," says Joerg Schwartz, senior program manager for external research at Sun."We thought the idea of introducing peer-to-peer computing - harvesting compute cycles otherwise not utilized for the advancement of science - was a good idea," Schwartz says. "The idea was new, and it inspired us to do a lot of things." Many of the architectural concepts behind Sun's JXTA programming language for peer-to-peer networking were inspired by SETI@ Home, he adds.Sun is also among the top 10 corporate work-unit producers, thanks to a large group of developers at Sun who use SETI@ Home as an every-day screen saver. Also, a few Sun computer labs, where benchmarking is done and operating systems are "burned in" to hardware, use SETI@Home to give machines a CPU workout."You have to run something," Schwartz says, "so you might as well run SETI@Home."The search for ET, and beyondSome might think one of the world's largest supercomputers could be put to better use. SETI@Home's Anderson is working on that too."There are a whole bunch of areas where unlimited computing power would let you do the kind of science you couldn't do before," Anderson says. New software developed by Anderson called Berkeley Open Infrastructure for Network Computing (BOINC) lets users choose from several projects for devoting unused CPU cycles. Among some of the projects in development for BOINC are a program that evaluates the behavior of black holes. Closer to Earth, Climateprediction.net will use BOINC to crunch data on world temperatures to more accurately predict the weather.But for those behind SETI@ Home, finding ET is still paramount. "We're just beginning to comb the cosmic haystack," SETI@ Home's chief scientist Wertheimer says."Sun does not have an official position" on the existence of aliens, Sun's Schwartz says. "But wouldn't it be terrible if we were the only intelligent life forms in all of the universe?"