Time Zone Information

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Time Zone Information

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Windows operating systems from Windows 98 forward store time zone information in the registry. Entries for each known time zone worldwide contain information such as the name, offset from GMT (UTC) and specific dates or formulas for calculating the dates that a transition from Standard Time to Daylight Saving Time (and back to Standard Time) are to occur. Not all time zones observe Daylight Saving Time.

ezAudit uses the operating system's stored time zone information to calculate time values for audit report records, specifically the "Event Time" (the actual time something occurred) and "Log Time" (log date and time that an event is scheduled to occur). When an audit report is created, ezAudit uses information from the selected station's configuration to read time zone information from the registry in order to correctly interpret the date and time information in the report.

What Changed in 2007?

Starting in the spring of 2007, daylight saving time (DST) start and end dates for the United States transitioned to comply with the Energy Policy Act of 2005. DST dates in the United States start three weeks earlier (2:00 A.M. on the second Sunday in March) and end one week later (2:00 A.M. on the first Sunday in November).

There have also been other related DST changes, time zone behavior, and settings for other parts of the world, some taking effect in 2007, while others went into effect after some versions of Microsoft operating systems went end-of-life.

How Do I Know if my Time Zone Information is Up-to-Date?

Determining whether your time zone information tables in the registry are correct and up-to-date may take a bit of effort, depending on the operating system you're using with ezAudit.

1.Windows Vista and later operating systems. If you're using any of these operating systems, the time zone information tables in the registry are up-to-date and should require no changes unless there are changes to time zone information after their respective product releases.
2.Windows XP. Microsoft offered an optional download that updated all time zone information. If you ran Windows Update and selected the Time Zone Update, the registry information is up-to-date. Users also had the option of downloading a manual update tool that provides the means to update a single time zone at a time.
3.Windows NT 4, Windows Me, Windows 98. Microsoft did not offer any updates for these operating systems. A number of companies provided free tools to update the time zone information in the registry, including dcsTools.com. Depending on which tool you used, the updated information may or may not include the means to deal with historical audit data - audit data files generated prior to 2007.

If you used a manual means to update a single time zone, the only time zone for which data created in 2007 and beyond will have correct times is the one you updated. Thus, if you are generating reports for stations that created data in time zones other than the one updated, the report times will be off, particularly in the range of dates between "old" DST dates and "new" DST dates.

Additionally, dates for 2006 and prior for all time zones will be off for the dates between "old" and "new" DST dates.

Manual inspection of the Windows registry to determine whether or not Dynamic DST information exists is probably the surest way to know if a PC is up-to-date. Instructions on how to perform this task are beyond the scope of this document.

What About Audit Data Generated Prior to 2007?

The introduction of new "spring forward" and "fall back" dates in many time zones in 2007 creates a problem for those who have a need to use the "old" time zone information - as ezAudit does.

To deal with the need to preserve previous time zone information, Microsoft introduced additional information for each time zone, stored in the registry as applicable. Called "Dyamic DST", in Windows XP and later operating systems additional information about prior years DST dates is available. In XP, this additional information is only available if you installed the Time Zone Update Microsoft offered.

If you are running Windows 98, Me, or NT4, Dynamic DST information will not be available unless you updated the time zone information with a third-party tool that includes the Dynamic DST updates. dcsTools.com made such a tool available.

If you are running an audit report for a date in 2006 or prior and do not have Dynamic DST information in the registry, the reported times will be an hour off in all days between the "old" and "new" DST switch dates. In the U.S., for instance, this means that 3 weeks of spring dates and 1 week of fall dates for all years prior to 2007 will be off one hour. It is highly recommended that for PC's running ezAudit, you install a complete time zone update package, whether it's from Microsoft (XP) or some other vendor who provides a complete update package.