If  you installed Windows XP on a Mac using Bootcamp, chances are you’re going to have problems with your system time having offsets. You adjust the time setting on Mac and after booting on to Windows and going back to Mac, you find your time setting changed or offset (depending on which time zone you defined on XP).

Mac OS X Clock

Mac OS X Clock

This happens because Mac and Windows interpret the system time stored in the hardware differently. Windows assumes that the RTC (Real Time Clock) is the local time set by the user. Mac, on the other hand, assumes that the RTC is in UTC (Coordinated Universal Time).

To fix this problem, we can edit Windows’ registry setting to make it calculate its hardware time based on UTC.

1. Click Start>Run and type in “regedit” and click OK.
2. Navigate within the explorer to “HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation“.
3. With the TimeZoneInformation folder selected, right click on the space inside the folder and select New>DWORD Value.
4. Type in “RealTimeIsUniversal” (without quotes) and give it a value of “1”.

You may also download this registry fix (bootcamptime.reg) to automatically fix the problem. After downloading, double-click the file and allow it to merge with the registry.

Set the correct time in Windows, then on Mac. Do alternate reboots to check if time is already synchronized on both operating systems.

I’m not sure yet if this works on Vista and Windows 7. If you have tested it, please spread the info by commenting.

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