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Date: Tue, 2 Oct 2007 12:34:58 -0400
From: Matthew Wozniski <godlygeek AT gmail DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Can cron cause computer to wake up from hibernate?
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On Tue, Oct 02, 2007 at 08:51:19AM -0700, Andrew DeFaria wrote:
> Danilo Turina wrote:
>> I then discovered that my network card was configured to wake up the PC 
>> when receiving certain kind of packets. Disabling that feature did the 
>> job.
> AFAICT that's not hibernation - that's sleep mode. There's a difference, 
...
> I use hibernate mode all the time. I once used it at work when we were 
> moving from one building to another. During that time the computer was not 
> even connected to the power source and indeed in a moving truck! When at 
> the new building I powered it on and it came back exactly to where I had 
> left it off prior to hibernating it.

Hibernation does involve swapping everything in memory to disk,
freezing the state of all processes, and powering down the system.
But, the system being powered down does not mean that no part of the
system is receiving power.  In fact, Wake On LAN technology is
designed to work on machines that are completely shut down - the only
caveat is that the motherboard reserves power for the network card,
and the network card scans for a particular magic packet addressed to
it.  If that packet shows up, the computer turns itself back on.

So, not only can this bring a computer out of sleep or hibernation, it
can bring a computer out of a shutdown, too, as long as the device is
still plugged in.

~Matt Wozniski

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