Knowledge Base

Computer BIOS and Windows NT Daylight Saving Time Settings

Article ID: 139452

Article Last Modified on 1/23/2007

Microsoft Windows NT Workstation 3.5
Microsoft Windows NT Workstation 3.51
Microsoft Windows NT Server 3.5
Microsoft Windows NT Server 3.51

This article was previously published under Q139452

SUMMARY

Some system BIOS adjust the computers built-in real-time clock to compensate for daylight saving time automatically. Windows NT can also be configured to adjust for daylight saving time. If both the BIOS and Windows NT adjust the close for daylight saving time, your clock will be one hour off.

MORE INFORMATION

Windows NT updates its internal date and time every hour by reading the CMOS on the motherboard. In-between the one hour intervals, Windows NT increments its own clock approximately every 10 milliseconds. Because Windows NT cannot detect when the system BIOS/CMOS (hardware level) adjusts the clock for daylight saving time, it may change the clock by one hour, just as the BIOS does. This causes your computer clock to be one hour ahead in the Spring or one hour behind in the Fall after both your computer's BIOS and Windows NT adjust the clock for daylight saving time.

If you encounter this problem, change your BIOS or Windows NT configuration so that only one adjusts for daylight savings.

NOTE: If you boot you computer under both Windows 95 and Windows NT, both operating systems will adjust for daylight saving time independently, also causing the clock to be off by an hour.

For more information on Windows NT daylight saving time implementation, please see the following article(s) in the Microsoft Knowledge Base:

ARTICLE-ID: 129574
TITLE : Time Stamp Changes with Daylight Savings

Additional query words: prodnt

Keywords: KB139452