Students and faculty lost FAS network access across campus yesterday after an early-morning system upgrade went awry.

Network users were unable to check e-mail, surf the Internet or start machines connected to the network intermittently throughout the day. The network was stable by 5:20 p.m., according to FAS Network Operations.

Harvard Arts and Sciences Computer Services (HASCS) administrators said the campus-wide blackout was caused by a glitch in a network upgrade.

HASCS performed several upgrades between 4:30 and 7:30 a.m. yesterday, among them the installation of new software on its core switch, a central part of the network in the Science Center. According to HASCS Director Franklin M. Steen, the new software unexpectedly caused the switch to malfunction.

With the network fading in and out, e-mail was unavailable for much of the day. The shutdown also affected computers that are set up to look for the network as they boot up, including machines that run Microsoft Windows.

"This morning I woke up and tried to boot up my computer," said Thomas J. Mucha '03, who said he encountered a blank screen. "I thought it was my computer's fault."

Rick Osterberg '96, database applications specialist for HASCS, speculated that the intermittent connection to the network may have caused start-up problems that might not have occurred if the network were completely unavailable.

"The instabilities may have been of a nature that some traffic was getting through--but it wasn't a reliable communications stream," Osterberg said. "Sometimes an unreliable stream is worse than no stream at all."