The bug in daylight savings time

A new law that extends daylight savings time (DST) by four weeks means programmers will once again need to check their software code for potential problems in handling a calendar adjustment.

The measure, approved as part of energy legislation this summer, would shift the start of DST from April back to March--and move its end from October to November--most likely beginning in 2007. Those extra four weeks will save energy--the equivalent of 100,000 barrels of oil a day, according to legislators backing the change. But it may also trip up applications and gadgets programmed to automatically handle DST hours based on the schedule the United States has kept for nearly two decades.

Summer time changes, observed in patchwork fashion around the world, have always been an annoyance for programmers and systems administrators: Online support groups are full of work-arounds and suggestions for DST-related glitches.

Many applications rely on the operating system to maintain an accurate clock, meaning Micro-soft will play a critical role in keeping the world's computers running on time. Peter Houston, Microsoft's senior director of servicing strategy, says the company "will make sure that Windows handles the transition smoothly."

"Smoothly" doesn't necessarily mean flawlessly, however. Microsoft's support website contains dozens of articles related to DST hiccups, varying from minor oddities to broad problems (some multiprocessor computers running Windows NT 4.0 have trouble adjusting to DST).

Still, no one in the software industry is expecting Y2K-buglike chaos and expense. Research firms Gartner and Forrester Research are not studying the impact of a DST schedule change, while several major vendors have said the effects would be slight.