Iphone 4.0 - Background timer

It seems that an NSTimer created in the开发者_JS百科 background stalls till the app is brought back into foreground. How does the Iphone default Clock app's timer work then?

Thanks!

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There's a real time clock in hardware, and the operating system will interface with it. It exposes the clock via a C API which is likely what the Clock app is using.

Plus, Apple has no limitation on what they can do in the background with their applications like we third party devs do.