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When we power off windows using hibernate mode, system will completely power down; according to Wikipedia:

"Hibernation saves electrical power. After hibernating, the hardware is completely powered down like a regular shutdown"

And we can boot it up using keyboard, mouse or through LAN; accouring to Microsoft FAQ:

You might be able to wake your computer by pressing any key on the keyboard, clicking a mouse button, or opening the lid on a laptop ... You can also wake some computers by turning them on remotely over a network.

So my question is this, How windows boot up when system is completely powered down by these methods? there is nothing on RAM so how can even windows control the system?

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    Your PSU will always keep the motherboard powered. The hibernate function saves everything to hard disk and then powers down as normal. But a small function is enabled. A keyboard (and other devices if your BIOS supports, say, WOL) monitor (in basic terms) is waiting for a key to be pressed which will turn the machine back on again. This is where such things as S1 and S3 power states come in. You could even have the computer wake up at a predetermined time of day - through your BIOS! – Kinnectus Jun 15 '14 at 22:11
  • So why it doesn't happen when we shutdown? so wikipedia's article is wrong and need to be edited? – Amirreza Nasiri Jun 15 '14 at 22:31
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    Yes, already fixed that. Hibernation ends up with same device power state as when standard shutdown is applied. Some basic electronic modules still function - depending on the construction and functionalities designed by manufacturer. To completely shut the computer down you have to completely unplug it's power sources or, in case of some desktop PC-s, use the power switch on the PSU. – Michał Sacharewicz Jun 16 '14 at 0:03
  • Now its OK to understand :). so windows fully shutdown and only it's motherboard which have been changed by windows, is handle this. is it true? if so, can you post an answer so I can accept it. – Amirreza Nasiri Jun 16 '14 at 0:07
  • The main difference between hibernate and shutdown is that hibernate keeps your session saved to disk so when you resume all your programs will be where you left them. Depending on motherboard function: hibernate can be woken from almost all wake features, where shutdown (from what I've experienced) is the power button, preset time or WOL. – Kinnectus Jun 16 '14 at 6:39
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The Wikipedia article was imprecise, and I already fixed that.

It's true that hibernation ends up with exactly the same device power state as when regular shutdown is applied. But while that state is called a "shut down", in modern computers some basic electronic modules still function. It's the motherboard that decides what to do, once it gets in that state - according to it's construction and features designed by manufacturer.

These features are eg. powering up by WakeOnLAN, keyboard shortcut, mouse move or time-preset launch. Or even pressing the front power button, which is not a real circuit breaker like in "the old times", but just an electronic, low-power "sensor" that, when pressed, allows that inner electronic module to know you want to power the rest of modules on.

To completely shut the computer (motherboard) down, you still have to completely unplug it's power sources or, in case of some desktop PC-s, use the power switch on the PSU.

Mind though, that RAM is truly powered down when in hibernation state. It's content gets stored on the hard drive right before shutdown and then gets recovered when you start computer again.

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There is often a setting under Power Management in the BIOS that allows for the PC to wake up via mouse/keyboard activity. This is similar to how Wake-on-LAN works.

To answer your question; The BIOS is responsible for bringing the PC out of the hibernation state, not Windows. Once Windows boots, it then goes about doing whatever it needs to do to get back to the pre-hibernation state.

  • So windows change BIOS settings? because it's not happening on shutdown. – Amirreza Nasiri Jun 15 '14 at 22:27
  • As @BigChris mentioned in his comment; when you hibernate your computer it powers down into a different S state than it would from a normal shutdown. – Michael Frank Jun 15 '14 at 22:35

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