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Possible Duplicate:
how does reboot work ?

In the spectrum of questions asked on this site, this may well be one of the more mundane. But I've been wondering recently just HOW a restart or reboot command works on a computer. The question being along the lines of: If a computer is turned off, what is the mechanism that's turning it back on? That is to say, in the course of a reboot, the computer is turned off. At that point, it seems, something must remain on in order for the command to start up again to be issued and acknowledged.

I'm not sure why it hasn't occurred to me to ask this question before.

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marked as duplicate by BloodPhilia, Shinrai, MaQleod, Not Kyle stop stalking me, studiohack Mar 17 '11 at 15:10

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Nice whitepaper on this – Moab Mar 17 '11 at 16:08
up vote 1 down vote accepted

The short answer is that a plugged in computer is never truly "off." For example, a shut down computer can be awoken, with the proper settings, by a "magic packet" (yes it's really called that) sent to the MAC address of its NIC.

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