For the longest time I simply lived with the fact that my system clock didn’t behave properly in my Windows partition when I had BootCamp setup on the macbook. It didn’t matter what I did, I couldn’t seem to find a way to keep the clock properly synchronized.  The problem stems from how Apple decided to implement the system clock which is different from the way that most PC manufacturers do.

Apple’s hardware always returns time in UTC, most PCs update the system clock to local time and won’t require a conversion of that time so of course the default Windows settings aren’t really set up for BootCamp (though you’d think the BootCamp installer could correct this…)

The solution, as it turns out, is a simple registry key change to tell Windows that the system’s clock is using UTC time.  One value in one key, that’s all it takes:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlTimeZoneInformation] "RealTimeIsUniversal"=dword:00000001

BootcampUtcClockFix.reg

Another solution that I found over at superuser.com is to modify OS X to change the time at startup and at shutdown. To me, this seems like more of a hack than the “unsupported” registry key. Windows 7 has been working well under this configuration and has even successfully interpreted the daylight saving time change.