Does Windows 10 support UTC as BIOS time?

Yep, I had success. Don't forget disabling the "internet update" for the time!

I used the way described in the ArchWiki using a QWORD on a 64bit Win10. The NTP is done on Arch and not on Windows, but the latter isnt getting booted so often anyway.

Here's the .reg file:

RealTimeIsUniversal.reg

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
     "RealTimeIsUniversal"=hex(b):01,00,00,00,00,00,00,00

From ArchWiki: UTC in Windows

Using regedit, add a DWORD value with hexadecimal value 1 to the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation\RealTimeIsUniversal
Alternatively, create a *.reg file (on the desktop) with the following content and double-click it to import it into registry:
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
 "RealTimeIsUniversal"=dword:00000001
If the above appears to have no affect, and a 64-bit variant of Windows is being used, using a QWORD value instead of a DWORD value may resolve the issue.

larkey

Posted 2015-09-20T19:27:41.297

Reputation: 1 590

Thank you, though this does not resolve the problem (it sounds like you've tried the same as me) it's helpful to know someone else has this working in Windows 10. – Dylan – 2015-09-20T23:33:24.480

@Dylan Yep. The only though I have (if you did it really the same) is that they might have deactivated this feature on the Home Editions or similar. Using Enterprise here. But otherwise I have no idea. – larkey – 2015-09-20T23:38:02.333

4DWORD works fine also in 64 bit mode home edition. Also: note that ntpd may refuse to change if the time difference is too large (which it may be in case windows 10 already started writing to the hardware clock - if so, run ntpd as root ntpd -q). – j-a – 2016-09-23T20:00:54.343

1@j-a I could imagine that DWORD works most of the time but that the actual value is a QWORD, so there might be problems using DWORD if something isn't initialized properly or such – larkey – 2016-09-23T20:19:53.203

7Why does internet update have to be disabled? – gamen – 2016-11-16T16:27:27.403

3@gamen Good question actually, but it seems that MS is using the internet time to sync with the hardware clock while ignoring the Registry setting, ie. setting the clock to your localtime while interpreting it as UTC. – larkey – 2016-11-16T18:57:54.937

9@larkey I thought I'd try it to see what happened, and it works so far - I'll re-post if this changes; multiple reboots, switching between OS:es. My system time is in UTC, the local time is UTC+1. Set Time Automatically and Adjust for daylight saving time automatically are On, Set zime zone automatically is Off, and the RealTimeIsUniversal registry key QWORD is set to 1. I'm on x86_64, Windows 10 Pro (Build 10586). It might also be worth mentioning that I'm not using a Microsoft time server. – gamen – 2016-11-17T11:48:32.070

the .reg file worked for me, Windows 10 Enterprise (64 bit, but with the DWORD key as posted). – Brian Minton – 2016-11-19T22:29:04.363

1I had to disable internet time updating but could reactivate it afterwards, and now it seems to work fine in either case – Tobias Kienzler – 2017-01-07T19:50:13.407

8Just a comment in the sense of an affirmation: I have the 64bit version of Win10 and the DWORD version did not work. The QWORD-way was the right one for me. I did not have to enable or disable any other option, btw. – henry – 2017-05-06T10:32:53.310

Does Windows 10 support UTC as BIOS time?

Answers