If you have multiple versions of Windows installed, why do they all try to adjust the clock?

Raymond Chen


Commenter Martin notes that if you have multiple copies of Windows installed on your machine, then each one will try to adjust the clock when you enter or exit daylight saving time. “I cannot believe that this feature is a bug. Please could you comment this?”
This falls into a category of issue that I like to call “So what did you expect?” (This was the catch phrase of the old Call-A.P.P.L.E. magazine.)
If you have multiple operating systems installed on your machine, each one thinks that it has control of your computer. It’s not like there’s some standard cross-operating system mechanism for negotiating control of hardware resources. If you install CP/M and MINIX on your machine, each one is unaware of the presence of the other. CP/M doesn’t know how to mount MINIX file systems and update a configuration file to say “Hey, I updated the time, you don’t need to.”
And not that you would expect it to, either.
It’s like signing up for two housekeeping services and telling both of them to water the plants every Monday. And lo and behold, every Monday, the plants get double-watered. There’s no standard protocol for multiple housekeeping services to coordinate their activities; each housekeeping service assumes it’s responsible for cleaning your house.

Bonus reading: Why does Windows keep your BIOS clock on local time?

Raymond Chen
Raymond Chen

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