Why can't my machine hibernate? And how's that different than Stand-by?

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Summary: Hibernate and standby are ways to save power when you're not using your computer. Each has pros and cons. Hibernation, at least, must be enabled.

It's not a step so much as an option that probably just needs to be turned on.

We'll do that, and while we're at it we'll explain the difference between standby and hibernate.

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First the setting.

In Control Panel, open Power Options:

Click on the Hibernate tab:

I'm guessing that Enable Hibernation isn't checked on your machine. Check it, click OK and you should be set. It might require a reboot before taking effect.

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So what is hibernation anyway? And how does it differ from standby?

Over-simplifying just a bit:

Hibernation writes a complete image of your computer's RAM memory to the hard drive, and then completely powers down your machine. When you reboot after hibernating, the boot loader then simply reloads the memory image into RAM, reinitializes some hardware, and you're good to go.

The key is simply that the entire state of what your machine is doing at any point in time is almost completely contained in your system's RAM. So the theory is that simply saving and restoring your RAM (along with a few other details, perhaps) should be enough to completely save and restore what you were doing across a complete shutdown of your computer.

If you look closely at the second dialog image above, you'll see that it says "Disk space required to hibernate: 2,048 meg." That's the amount of RAM installed in this machine, and thus that's how much space is required to save the RAM on disk. That image, by the way, is written to the hidden file "hiberfil.sys" in the root of your boot drive which is always present to reserve that space if you have hibernation turned on. One way that people free up that disk space is to turn off hibernation.

Standby does not write your RAM memory image to disk. Standby instead turns all your hardware off except your RAM. Thus resuming from standby is often faster than resuming from hibernation, as the memory image does not have to be loaded from disk - it's still in memory.

The downside to standby, of course, is that your machine is not completely off. Some power is still required to maintain RAM. I've also seen some devices, particularly network cards, wake up periodically while on standby.

If the machine's battery drops too low while it's on standby, Windows will either put the machine in hibernate, if that's enabled, or attempt to cleanly shut down so as not to lose any work in progress.

Both standby and hibernate have been problematic at times in the past. Sometimes devices won't come back up properly after one or the other, or sometimes the machine won't resume at all. Standby in particular requires not only Windows support, but cooperation between the computer's BIOS and the various device drivers that may be impacted by a loss or partial loss of power.

The good news it that for the most part, standby and hibernate tend to work relatively well on current computers.

Related:

• Ask Leo! - Why does my network not work after resuming from standby?

• Ask Leo! - Should I turn my computer off at night?

• Ask Leo! - Why do so many tech support solutions start with "reboot" or "turn it off"?