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When I put my desktop computer in sleep mode I can simply wake it up by pressing a button on the keyboard. Easy! But whenever there's a power outage the computer needs to do a complete boot up to start up again, effectively loosing all my unsaved data.

It's as if it was previously shut down (as opposed to going to sleep mode), even though I had it put to sleep before the power outage. So it should be off already, but only in sleep mode, when the power is cut.

I also get the Windows Error Recovery screen on boot up and I can't wake it up by pressing a button on the keyboard. Instead, I have to press the power button.

Is this normal behavior? How can it "crash" when it's already powered off? Sleep mode doesn't use any power?! Or does it?...

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Sleep mode does use power, mostly to maintain the state of the RAM (memory). So when your computer loses power in sleep mode, the RAM becomes lost - in this context, this is the same as you pulling the plug from your computer while running.

There's another mode, hibernation, which effectively saves an "image" of your RAM's contents on the hard drive, and then completely powers off. Losing power in that mode will not cause a crash, obviously, but the start-up will be longer when compared to sleep mode.

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It's worth noting that there is (at least on Windows >=Vista) a "hybrid sleep", enabled by default. The main disadvantage of hibernation is it takes time to restore the previous state from disk. Hybrid sleep saves the current state to disk, but also keeps it in RAM at the same time - it uses the same amount of power as normal sleep, and resumes in the same amount of time, but won't lose the state if all power is lost (in which case it will restore the same way hibernation does). –  Bob Jun 8 '13 at 13:14
    
You're right! But... I thought I had the "hibernation" setup. I mean that's what I'm used to, and that's why I always make sure there is free space on my C disk. I'm not sure when this behavior started, power outage is rare in my area. But it can't be due to an upgrade from Vista Home Premium to Vista Ultimate?! I googled and found that I need "Hybrid Sleep" enabled. But I don't have that option! Why?... –  sammyg Jun 8 '13 at 13:16
    
@Bob You were a bit quicker than me. Yes, I also just found out about "Hybrid Sleep". But I am missing that option in the power settings. I'm not sure why... Is Hybrid Sleep available in Vista Ultimate? Does it have anything to do with editions and 64/32 bit versions? And is there no dedicated Hibernation-only mode in Windows Vista and newer versions of Windows? –  sammyg Jun 8 '13 at 13:21
    
@Bob Got it! There was no hiberfil.sys file on my system and Hibernation was disabled for some reason. Running powercfg /hibernate on solved that issue. Now I can once again get a power outage and still recover to the last working system state since the RAM data is being dumped to the disk drive (hiberfil.sys). And Hybrid Sleep means I can almost instantly recover the system state since it's being held in RAM as well as HDD, when power is not lost. Great! Thanks! –  sammyg Jun 9 '13 at 9:58
    
@Sammy Note that turning on Hybrid Sleep (it's in advanced power options, and usually on by default) removes "hibernate" from menus and causes the "sleep" option to save to disk. It doesn't add a new option to any menus. –  Bob Jun 9 '13 at 10:02

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