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Where do Windows 2000 and Windows NT store time zone information?
John Savill
June 14, 1999
2 Min Read
A. From the Control Panel Date/Time applet, select the Time Zonetab to set the local country and its associated time difference. You can select the same tab to enable daylight saving.
Changing these settings updates the registry values under the HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlTimeZoneInformation key. I’ve listed the most useful time-zone values below.
ActiveTimeBias | This value is the current time difference from Greenwich Mean Time (GMT) in minutes and is the difference for GMT. For example, if you’re 1 hour ahead, GMT is 1 hour behind. The value would be ffffffc4, which is hexadecimal for -60. |
Bias | This value is the normal time difference from GMT, excluding daylight saving in minutes. The value is the difference for GMT, so if you’re 3 hours ahead (e.g., if you live in Moscow), the Bias would be ffffff4c, which is hex for 180. If you’re 2 hours behind GMT (e.g., if you're on a boat in the mid-Atlantic Ocean), GMT is 2 hours ahead, so the value is 120. |
DaylightBias | This value is the time difference used for daylight saving for GMT. If you're 1 hour ahead, the value is ffffffc4, which is hex for -60. Notice that the ActiveTimeBias is the sum of Bias and DaylightBias in daylight saving months, which is the same as Bias for standard months. |
DaylightName | The OS uses this name during daylight saving months. |
StandardName | The OS uses this name during non-daylight saving months. |
DaylightStart | This value tells the computer when to start daylight mode. |
StandardStart | This value tells the computer when to start standard mode. |
DisableAutoDaylightTimeSet | This value exists only if you clear the checkbox for the option Automatically adjust clock for daylight saving and if you set the value to 1. |
Using the Microsoft Windows 2000 Resource Kit or the Microsoft Windows NT Resource Kit reg.exe utility, you can use the following command to query these values from the command line:
C:>reg query hklmsystemcurrentcontrolsetcontroltimezoneinformationbias
REG_DWORD bias 0
C:>reg query hklmsystemcurrentcontrolsetcontroltimezoneinformationdaylightname
REG_SZ daylightname GMT Daylight TimeAbout the Author
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