Your questions: What’s all this about the Leap Second, and how does it affect the Microsoft Windows OS and other products?

First off, Happy Canada Day. (eh? 😉

Lots of talk today about the ‘Leap second bug’ that caused various site and software crashes (see this post via CNET)…

“The addition of a leap second to the Coordinated Universal Time at midnight Greenwich Mean Time last night appears to have caused site disruptions for a handful of popular Web sites and software platforms.

“The adjustment, which was made by International Earth Rotation and Reference Systems Service, was necessary to keep atomic clocks in line with the Earth’s ever-changing speed of rotation. Dozens of leap seconds have been added since their introduction in 1972.”

Once again, The Extra Second was too much for some sites. Sounds like a new James Patterson crime novel. Or perhaps a new thriller from our own Mark Russinovich… I prefer his writing more these days anyway.

As I noted a couple of years ago, you’ll find more documenting the impact of a leap second in Microsoft Knowledge Base (KB) article 909614, How the Windows Time service treats a leap second (as Michael Kaplan noted in his most excellent post)… 

“In short, W32Time does not account for a leap second being dependent on the NTP server. Most applications and services may be unaffected, but sysadmins and IT professionals should know that the leap second is not addressed until the next time sync following the official addition/ subtraction of the leap second.  Consumers really have nothing to worry about save questioning whether or not the time is accurate as broadcast during Dick Clark’s New Year’s Rockin’ Eve when the crystal ball drops in Times Square.

“Info on syncing clocks to absolute time, please see KB 816042, How to configure an authoritative time server in Windows Server 2003, and KB 884776, How to configure the Windows Time service against a large time offset.

“General information on the Windows Time Service is also available in the team blog at  More articles/ information in which you may be interested:

IIRC, the concept of a leap second is actually in question, and an ITU working group is evaluating whether or not the process of adding/subtracting leap seconds should be discontinued.


Tags: Microsoft, Daylight Saving Time, Daylight Savings Time, leap second, DST.

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