*Windows time zones*
Windows stores time zone information in two locations in the registry.
The first location is the time zone database in the following registry
subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones
The time zone database contains the configuration data for all time
zones in Windows. Windows and other applications use the data to
calculate local times.
The second location for time zone information is the following registry
subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation
Control sets in Windows store system configuration information such as
drivers and services. The TimeZoneInformation registry subkey in the
current control set contains the configuration data for the time zone
that Windows is currently using. Windows copies this information from
the time zone database when the time zone is selected.
_When the time zone information is changed, both locations in the
registry must be updated_. The database must be updated to make sure
that Windows and other applications have the most accurate time zone
information available. Additionally, the TimeZoneInformation registry
subkey in the current control set must be reloaded to make sure that the
time zone information is the same as the information that is in the time
zone database. We recommend that you update the time zone database
first. Then, reload the TimeZoneInformation registry key. This procedure
forces Windows to read the updated information in the database. The two
methods that are explained in this article use this approach.
[end quote]
John