Overview:Daylight saving time (DST), and "Summer Time" in much of Europe, is the practice of moving local time forward one hour in the spring and backwards in the autumn. These spring and fall shifts to DST are different between northern and southern hemispheres. The start of DST in the northern hemisphere is in March or April (depending on the country/continent), and ending in October or November. In the southern hemisphere, the changes are the opposite, with DST beginning in October and ending in March or April. Generally, DST is not observed in Asia and Africa, and parts of Central and South America.

Challenges introduced by changes to DST:Unless certain updates are applied to your computer, the time zone settings for your computer's system clock may be incorrect during this four-week period. In particular, you must make sure that both your Windows operating system and your calendar programs are updated.

Observance in Canada and the United States:In the United States, the Energy Policy Act (EPAct) of 2005 introduced changes to the start and end dates of DST, which began in 2007. Now, DST in North America is observed across most of the United States as well as Canada from the second Sunday in March through to the first Sunday in November. In 2008, DST across much of the United States and Canada began at 2:00AM (02:00) local time on March 9, several weeks earlier than in years prior to 2007. DST will end later than in years prior to 2007, at 2:00AM local time on November 2 in 2008. This results in a new DST period that is approximately three to four weeks longer than in previous years.

Observance in Europe:European Summer Time is observed across most of Europe from the last Sunday in March through the last Sunday in October. In 2008, European Summer Time began at 01.00 Greenwich Mean Time (GMT) on March 30, 2008, and will end at 01.00 GMT on October 26, 2008.

Do I have to update my computer?

As noted in this article, Microsoft strongly recommends that DST and time zone updates be installed on all affected systems, devices and applications to ensure consistency with current DST rules and time zone settings worldwide. Customers should review the product updates available and posted on this site and at http://support.microsoft.com/gp/dst_prodlist for the latest and updated information of Microsoft products affected by daylight saving time.

Home users: If you use Windows Vista or have Automatic Updates turned on, you may not be affected by the change in daylight saving time. If you want to confirm, please review the list of products affected.

IT professionals and IT managers: Here is a list of updates and products affected by DST and Time Zone changes.