Accurate Time In Windows

For many years Windows was just a lousy timekeeper, and had no support for leap seconds at all.

Support for leap second handling was only provided by 3rd party (non-Microsoft) software like

Only very current versions of Windows 10 and Windows Server 2019 can keep accurate time, and have some built-in support for leap seconds, which explicitly has to be enabled, though.

For details see these Microsoft blog articles:

2019-04-10 How NOT to test the Windows Time Service (Dan Cuomo, Microsoft)
https://techcommunity.microsoft.com/t5/Networking-Blog/How-NOT-to-test-the-Windows-Time-Service/ba-p/411592

2019-03-04 Windows Subsystem for Linux for testing Windows 10 PTP Client (Dan Cuomo, Microsoft)
https://techcommunity.microsoft.com/t5/Networking-Blog/Windows-Subsystem-for-Linux-for-testing-Windows-10-PTP-Client/ba-p/389181

2018-07-18 Top 10 Networking Features in Windows Server 2019: #10 Accurate Network Time (Dan Cuomo, Microsoft)
https://techcommunity.microsoft.com/t5/Networking-Blog/Top-10-Networking-Features-in-Windows-Server-2019-10-Accurate/ba-p/339739

2018-10-17 Leap Seconds for the IT Pro: What you need to know (Dan Cuomo, Microsoft)
https://techcommunity.microsoft.com/t5/Networking-Blog/Leap-Seconds-for-the-IT-Pro-What-you-need-to-know/ba-p/339811

2018-10-24 Leap Seconds for the AppDev: What you should know (Travis Luke, Daniel Havey, Microsoft)
https://techcommunity.microsoft.com/t5/Networking-Blog/Leap-Seconds-for-the-AppDev-What-you-should-know/ba-p/339813/

Further reading linked from the above:

2018-05-31: Acquiring high-resolution time stamps
https://docs.microsoft.com/en-us/windows/desktop/SysInfo/acquiring-high-resolution-time-stamps#resolution__precision__accuracy__and_stability

SDN/FeatureGuide/Validation Guide - RS5 - Dev - Leap Second.docx on GitHub
https://github.com/Microsoft/SDN/blob/master/FeatureGuide/Validation%20Guide%20-%20RS5%20-%20Dev%20-%20Leap%20Second.docx

— Martin Burnicki martin.burnicki@meinberg.de 2019-04-17