James O'Neill's Blog

March 18, 2007

On Time-zones…

Filed under: How to,Windows 2003 Server,Windows Vista,Windows XP — jamesone111 @ 10:26 pm

Spring is here, Spring is here … I think the loveliest time of the year is the spring, yes I do, don’t you ? course you do.

Actually when I look at the weather it’s doesn’t look like spring. But unlike Tom Lehrer, the one thing that makes spring complete for me is the changing of the clocks. All of Europe changes it’s clocks on the last Sunday of March and October. The UK keeps pondering if we should move onto the same time as most of Europe who are an hour ahead of us – the argument for being that the 30 million people who live in the Southern half of England would save Energy and reduce their risk of accidents. The argument against being 5 million Scots would have to go to work in the dark.

I got thrown a question which I didn’t know the answer to –  At what time does Windows  change its time forward an hour on the 25th March 2007 in the UK.

“2AM” I thought… but then does that mean jumping from 1 to 2 or from 2 to 3 ? And going back does it jump from  2 to 1 or from 3 to 2 ? Rather than give the direct answer (the former in both cases) here’s how you check.

The Time Zone information is stored in the registry under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones (which you can export and re-import if needed) . However the critical bits are stored as block of Hex, and it’s not immediately clear how to decode it, instead there is a downloadable tool called TzEdit which lets you view the settings and check for yourself.

 

 

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This post originally appeared on my technet blog.

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