Microsoft is bringing support for leap seconds — yes, that one extra second — to Windows, starting with Windows 10 Redstone 5 and Windows Server 2019. With the upcoming updates for Windows 10, Microsoft’s operating system now deals with leap seconds in a way that is incredibly accurate, UTC-compliant, and traceable.
Leap seconds typically occur every 18 months, resulting in one extra second. The extra leap second occurs to adjust with the earth’s slowed down rotation, and an extra second is added to UTC in order to keep it in-sync with mean solar time. To deal with the extra second more appropriately, Windows 10 will now display that extra second, instead of directly jumping to the next one, making it the world’s first OS to have full support for leap seconds. It’s quite difficult to explain in words, but the following GIF will help make it less confusing:
Right now, Windows 10 directly jumps from 16:59:59 to 17:00:00 without a leap second, but it will now include 16:59:60 when there is an actual leap second. That one extra second is quite important for time accuracy, especially with increased demand for higher accuracy time from government regulations, according to Microsoft. The company says it will not include an option for leap second smearing where the extra second would be split up into smaller units and added throughout the day as it will prevent the OS from meeting accuracy requirements.
Microsoft is delivering a number of other improvements in Windows Server 2019 to provide better time accuracy, including a new Precision Time Control, time synchronization method, and more. Microsoft has detailed all of the new improvements in a technical blog post here, and you can read about all the improvements coming with future versions of Windows 10 if you happen to care about such improvements.