FOR A COUPLE of decades now, various people-including a few otherwise-brilliant IT pros-have been telling me that it's better to leave your PC running round the clock than to shut it off at night and boot it back up in the morning. If you never shut down your computer, the reasoning goes, you will save wear and tear on your components and extend the life of your machine. I've asked some top tech types at HP, Seagate, and other major companies, and nobody seems to know how this rumor was born. But they all agree on one thing: It's bogus.

"If you don't care at all about energy consumption or your carbon footprint, then there's no great downside to leaving your PC running," says Ken Bosley, a 12-year veteran of HP's Personal Systems Group who has spent years researching hard-drive reliability. "But you shouldn't waste energy to extend the life of a com¬puter by a very small amount."

Bosley discounts the notion that shutting down and starting up a computer puts undue stress on the components, noting that most systems are retired because of obsolescence, not because of hardware failure.

Always-on proponents cite hard-drive longevity in particular as a major reason never to shut down. But Sea gate staff engineer Billy Ruddock says, "Turning off the system is usually best to prolong hard-drive life." Unless you're talking about servers, most com¬puters' hard disks are simply not de¬signed for continuous operation. Besides, Ruddock notes, "Windows operating systems execute various important housekeeping tasks during shutdown and startup-another very good reason for turning off a system."