In preparation for the Daylight Savings Time (DST) change on March 11th, IET would like to share some important information with you regarding the affect of Microsoft DST patches on your operating system. Microsoft patches for DST are not year specific; they make a blanket change for DST to occur on the second Sunday of March for all years. This may affect some applications that use time data from previous years. While this does not affect Microsoft's newest operating system, Vista, it affects all earlier Microsoft operating systems.

The Microsoft DST 2007 product team has confirmed that this is expected behavior, and writes:

"DST has never been 'year' specific. It doesn't modify the files on the system, just the filter you use to look at the time date stamp. This is because the OS only can track one set of DST rule sets at a time.  The reason it changes the previous years is because it is now using the new rule set.

Microsoft has released a time zone update for Microsoft Windows XP Service Pack 2 and Windows Server 2003 that automatically configures all these changes. The time zone update includes a new registry subkey that is named Dynamic DST. This subkey contains information about past or future changes in some time zones. This information is not used by versions of Windows that are earlier than Windows Vista. The information is provided for other programs that may use the information to predict or to compute future and past time zone information.

To date, time zone information has been stateless, that is there is only one rule in effect at a time, and ALL dates and times are interpreted by that rule - past, present and future. So that means if you have applied the 2007 rules to your desktop and go back and look at the third week in March 2006 (assuming US time zone) you will see it's DST when in fact it's not supposed to be.

Dynamic DST will help that in the future. But today, the OS and all apps interpret local time based on the TZI in the legacy key.  In thefuture apps will be able to leverage the dynamic keys. "If you should have any questions regarding this information, we encourage you to contact the Microsoft DST 2007 support line at: 800-642-7676 or join one of the following daily technical chat rooms:

http://www.microsoft.com/businesssolutions/chatroom.aspx

http://blogs.technet.com/dst2007/default.aspx

You may contact the IT Express help desk at ithelp@ucdavis.edu.

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IT Express consultants are available via telephone Monday-Friday from 7am until 9pm at 530-754-HELP. Walk-in service hours and other information about our services may be found at: http://itexpress.ucdavis.edu/

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