Contribute
Register

Fix incorrect time in Windows + OSX dual boot

Joined
Mar 13, 2014
Messages
6
Motherboard
MSI Z87-G45 Gaming Motherboard
CPU
i7-4770K
Graphics
R9 270X
Classic Mac
512K, Apple, Classic, iMac, Plus
Mobile Phone
iOS
I just thought I'd give people an easy to find guide for this information. Hope the mods are alright with that, and that this doesn't violate any posting guidelines.

1. Why does this happen?


The simple explanation is; Windows uses Greenwhich time, and OSX uses Universal Time. It's as simple as that. Every time the other OS boots up - it changes around your BIOS settings in-order to 'correct' the CPU clock timer - which is essential for any computer to calculate things correctly.

2. What's the difference?

GMT

Windows is always defaulted to use GMT as the location to set the time and date. GMT stands for 'Greenwich Observatory'. This observatory broadcasts the current time of the world based on the calculations of where the Earth rotation is in relation to the prime meridian.

Because of the fact that GMT is outdated - it doesn't consider other factors that are important to calculating time - such as; where the earth is in relation to the sun. Because of this - GMT is pretty much an 'average' or an estimated guess as to what time it is where you live.

To quote the Greenwich website...

Over time, time zones became established based on GMT as being x number of hours ahead or behind GMT. Interestingly, the clock began at noon under GMT so noon was represented by zero hours.

UTC


As more sophisticated time pieces became available to scientists, the need for a new international time standard became apparent. Atomic clocks did not need to keep time based on average solar time at a particular location because they were very, very accurate. In addition, it became understood that due to the irregularity of the earth and the sun's movements, the exact time needed to be modified occasionally through the use of leap seconds. With this precise accuracy of time, UTC was born.


UTC, while based on zero degrees longitude, which passes through the Greenwich Observatory, is based on atomic time and includes leap seconds as they are added to our clock every so often. UTC was used beginning in the mid-twentieth century but became the official standard of world time on January 1, 1972.


UTC is 24-hour time, which begins at 0:00 at midnight. 12:00 is noon, 13:00 is 1 p.m., 14:00 is 2 p.m. and so on until 23:59, which is 11:59 p.m.


Time zones today are a certain number of hours or hours and minutes behind or ahead of UTC. UTC is also known as Zulu time in the airforce. When European Summer Time is not in effect, UTC matches the time zone of the United Kingdom.


Today, it is most appropriate to use and refer to time based on UTC and not on GMT.

3. How do I fix this?

It's quite simple really. All you need to do is set Windows to use UTC instead of GMT. To do this - we need to perform a simple registry edit. Go perform this - hold down the 'Windows' button, and at the same time press R (Win + R) this will bring up a new window titled 'RUN'

In this window type the command 'regedit'. UAC will popup asking for admin permission. Click accept and the registry editor will open. Now that were in regedit, navigate to...

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
Left click on 'TimeZoneInformation' and on the left it will display all the current values attributed to this registry key. On the left right click anywhere and choose 'Create new D-WORD'. You will now see a new entry at the bottom of the list.

Right click on this new entry and choose 'Modify'. Rename the key 'RealTimeIsUniversal' and change it's value to '1'. Click save, and now the entry should say 'RealTimeIsUniversal - 0x0000001' If it looks like that - then you're all done!

Reboot, and sync the windows clock - now your time settings will be universal (no pun intended :p ).

EDIT:

If you don't like fooling around with your registry, I've created a .reg file that will do all the work for you. All you need to do is download the attachment, extract it to where ever you want, and double click on 'Windows Universal time On'

If you want to switch back to GMT. Do the same, but instead - double click on the reg file named 'Windows Universal time Off' and that will remove the registry edits we made. :thumbup:

Anyways, hope this guide helps someone! Thanks for reading everyone!! It's greatly appreciated! I'm definitely looking forward to a good tenure on this very helpful forum. :)

View attachment Time Fix - Windows.zip


 
Joined
Mar 13, 2014
Messages
6
Motherboard
MSI Z87-G45 Gaming Motherboard
CPU
i7-4770K
Graphics
R9 270X
Classic Mac
512K, Apple, Classic, iMac, Plus
Mobile Phone
iOS
Also, if someone could show me how to remove the very distracting line spacing - I'd appreciate it alot! Thanks!
 

RehabMan

Moderator
Joined
May 3, 2012
Messages
191,123
Motherboard
Intel DH67BL
CPU
Core i7-2600K
Graphics
Intel HD 3000
Mac
MacBook Air
Mobile Phone
iOS
...
The simple explanation is; Windows uses Greenwhich time, and OSX uses Universal Time. It's as simple as that. Every time the other OS boots up - it changes around your BIOS settings in-order to 'correct' the CPU clock timer - which is essential for any computer to calculate things correctly.

...

Windows is always defaulted to use GMT as the location to set the time and date. GMT stands for 'Greenwich Observatory'. This observatory broadcasts the current time of the world based on the calculations of where the Earth rotation is in relation to the prime meridian.

Because of the fact that GMT is outdated - it doesn't consider other factors that are important to calculating time - such as; where the earth is in relation to the sun. Because of this - GMT is pretty much an 'average' or an estimated guess as to what time it is where you live.
...
Although the solution to fixing the time sync problems is correct (set RealTimeIsUniversal to 1 in the Windows registry), the explanation of the problem is incorrect.

There is a time maintained by the system board called the RTC (real time clock). This is the clock that is maintained by the small battery present on your motherboard. Windows expects this time to indicate local time, whereas OS X expects this time to represent UTC. For all practical purposes, GMT and UTC are the same and local times are a time relative to GMT/UTC. The RealTimeIsUniversal simply causes Windows to treat the BIOS/RTC time as UTC, just like OS X.

GMT: Greenwich Mean Time
UTC: Coordinated Universal Time

Think of UTC time as a way to represent the current time based on a standard location irrespective of local conventions (irrespective of local time, daylight savings time, etc).

See here for further descriptions:
http://en.wikipedia.org/wiki/Greenwich_Mean_Time
http://en.wikipedia.org/wiki/Coordinated_Universal_Time

Although many technical people think it is silly that by default Windows expects BIOS time to be local time, it is retained for backward compatibility and the 99.9% of people that don't dual boot and would be confused by BIOS showing UTC vs. Windows showing local time.
 
Joined
Feb 13, 2012
Messages
5
Motherboard
GA-Z87N-Wifi
CPU
i5 4690K
Graphics
MSI GTX 570 Twin Frozr iii
Mac
MacBook Pro
Classic Mac
Mobile Phone
iOS
Joined
Mar 13, 2014
Messages
6
Motherboard
MSI Z87-G45 Gaming Motherboard
CPU
i7-4770K
Graphics
R9 270X
Classic Mac
512K, Apple, Classic, iMac, Plus
Mobile Phone
iOS
Although the solution to fixing the time sync problems is correct (set RealTimeIsUniversal to 1 in the Windows registry), the explanation of the problem is incorrect.

There is a time maintained by the system board called the RTC (real time clock). This is the clock that is maintained by the small battery present on your motherboard. Windows expects this time to indicate local time, whereas OS X expects this time to represent UTC. For all practical purposes, GMT and UTC are the same and local times are a time relative to GMT/UTC. The RealTimeIsUniversal simply causes Windows to treat the BIOS/RTC time as UTC, just like OS X.

GMT: Greenwich Mean Time
UTC: Coordinated Universal Time

Think of UTC time as a way to represent the current based on a standard location irrespective of local conventions (irrespective of local time, daylight savings time, etc).

See here for further descriptions:
http://en.wikipedia.org/wiki/Greenwich_Mean_Time
http://en.wikipedia.org/wiki/Coordinated_Universal_Time

Although many technical people think it is silly that by default Windows expects BIOS time to be local time, it is retained for backward compatibility and the 99.9% of people that don't dual boot and would be confused by BIOS showing UTC vs. Windows showing local time.
Much better explaination - Thank you :thumbup:
 
Joined
Nov 4, 2010
Messages
29
Motherboard
na
CPU
na
Graphics
na
Mac
Classic Mac
Mobile Phone
maybe windows time is just fine, and apple time is the wrong way to do it?

So my question is, instead of fixing it in windows , how do i tell osx to that it should use the same time settings, that windows uses?

BTW Thanks for figuring out the issue in general!
 
Joined
Mar 24, 2016
Messages
1
Mac
Classic Mac
Mobile Phone
The registry addition worked for Windows 10.

Thanks!
 

slim.jim

Moderator
Joined
Dec 17, 2014
Messages
4,106
Motherboard
MSI Z97 Gaming 9 AC
CPU
i7-4790K
Graphics
GTX 970
Mac
MacBook Pro
Classic Mac
PowerBook
Mobile Phone
iOS
Joined
Jun 15, 2011
Messages
73
Motherboard
Gigabyte Z97X-UD3H
CPU
Intel Core i7-4790K
Graphics
Radeon HD 6870
Mac
MacBook Air
Classic Mac
Power Mac
Mobile Phone
iOS
Oh my goodness. I've only had this problem since Windows 7. Since I only use Windows for gaming, I've just put up with it, occasionally asking Windows to re-sync. I always thought it was just a Windows-being-stupid thing and didn't think it had to do with dual booting.

Thanks!
 
Top