Daylight-saving time (DST) will start three weeks earlier this year, on Sunday, March 11, and end one week later, on Sunday, Nov. 4, as a result of a bill passed by Congress last year. Most Windows and Mac computers require an operating system update to accommodate the new DST period.

Automatic updates (from Microsoft and Apple) are being supplied to computers running Windows XP (SP2), Mac 10.3 or Mac 10.4 -- unless those computers have been set to disallow automatic updating. The new Windows Vista does not need updating.

For information about manually updating these operating systems or updating older Windows and Mac systems, see http://www.cit.cornell.edu/computer/system/daylight.html.

Other networked devices, such as smartphones and PDAs, may also need updates to accommodate this change; look for instructions from the device's manufacturer.

Not updating a computer could result in problems in mid-March to early April and again in late October to early November each year when software and services that interact with the computer's clock are used. (That's because the computer will still be adjusting for the old DST period, which until this year began the first Sunday in April and ended the last Sunday in October).