Confused about what "Hibernate" does?

  Simsy 10:25 21 Apr 2009


Despite now being an experienced PC user I've never bothered with "Hibernate" before as I believed, (incorrectly I now know), that it's a "low power" state and was still using power.

When I shut off I REALLY want to shut off, and use no power at all, so I've always shut down...

I've recently been pointed towards it by a colleague, who always uses it, and told me that it does completely shut down, but boot up after is much quicker...

So I give it a try and sure enough it does shut down completely, quicker, and it starts up much quicker as well, approx 40 secs to get to the log-in screen compared with about 2.5 mins from a full shutdown...

That's good I think! I know, I'll try and make it even quicker by disabling the RAM test that the BIOS checks on bootup. But when I've "hibernated" and restart, there is no option to get into the BIOS to make changes!?

I'm confused! How can "Hibernate" mode affect entry into the BIOS?

My understanding is that when using "Hibernate" what happens is that the contents of RAM is copied onto the HDD, and a suitable flag is placed in the boot up gubbins, and then all is depowered.... When restarted from "Hibernate" this file is copied into RAM, instead of the "normal" bootup procedure. How can it be quicker for the HDD to have to read and copy 1 Gig from HDD into RAM, than the 500Mg or so from a "normal" bootup?

So that's 2 questions.

1 How is the BIOS entry affected?
2 Why quicker to restart from "Hibernate"

I's not a problem... I'm just curious!

And I have to go out now... I'll check for any responses later!




  Quiller. 10:40 21 Apr 2009

hibernation, have done for years.

The only time the computer fully starts is when I have a windows update, software install or I wan to enter the bios.

I thought that hibernation writes the data to the harddrive, so when you close down you use no power.

that is certainly the case with a laptop because I have seen the battery run completely flat, with no power plug in and still it boots from hibernation.

  Stuartli 10:45 21 Apr 2009

The difference, as has been obviously realised, is that putting a system into Hibernation Saves whatever is in use on the system at that time and it then shuts down completely.

However, in Standby, if power is lost than so, most likely, is any work being done.

I use Hibernation during the day when not at my system and do a proper Shutdown each night; I am aware that many laptop owners only use the Hibernation function, but a regular Shutdown is beneficial.

  Quiller. 10:46 21 Apr 2009

"Or Windows XP can detect when your batteries are running low, and then automatically put your computer in Hibernate mode to save your work before the battery fails. "

from click here

If it was stored in memory you would loose your work. When it is written to the cache of the hard drive it is stored and should start windows very fast.

Mine loads in around 30 seconds.

  OTT_Buzzard 10:50 21 Apr 2009

You're on the right lines with your assessment; hibernate essentially 'saves' your current work session in to an area of the hard drive. This does have a side effect though - when you access BIOS and make any changes, the computer is required to do a compelte restart. This clears out any work that you have saved in memory, therefore there would be no point in being able to access BIOS from hibernate mode.

It's quicker to start from hibernate because Windows is already loaded - it has to be in order to save your work session.

"How can it be quicker for the HDD to have to read and copy 1 Gig from HDD into RAM, than the 500Mg or so from a "normal" bootup?"

One way of looking at this is to ignore the use of RAM. When you run windows or any application, the data held in RAM isn't constant. It's permanently changing with information from pagefiles on your hard drive and fresh application instructions. RAM isn't directly loaded from the hard drive either, all information comes via the northbridge after instructions from the processor. The actual time for loading RAM is two parts of nothing.

Its worth noting that even PC's that are 'shut down' still use power. The only way to prevent this is to turn the PC off at the socket. Also, it really does your PC the world of good to reboot it from time to time. It clears out any unneeded data from your session and frees up hard drive space. If you use your PC heavily and don't reboot it for several days you'll find yourself slowing to a snails pace!

Anyway, that's a start and I'm sure other people will coment!

  dms_05 10:58 21 Apr 2009

From my point of view Hibernation stores the good, the bad and the ugly. With the passage of time the ugly becomes unacceptable. Starting from a true shutdown helps to clear out the rubbish that accumulates over time. I agree with Stuarti that use of Hibernation during the working day but then having a true shutdown overnight is an acceptable use of Hibarnation. I came to this conclusion after email problems - the cause was old authentication on my system due to never using a cold boot and forcing the email server and laptop to exchange information.

  interzone55 11:42 21 Apr 2009

OTT_Buzzard has explained this very well, but I'll add a few points that may or may not help.

When you hibernate the whole contents of memory & the page file are saved to the hard drive as an image file. This space is pre-allocated, so once you enable Hibernation a RAM sized area of your drive is lost for general use.

When you restart from Hibernation this image is then copied back to RAM and you start from where you left off.

This is so much quicker than a normal boot because during booting all the drivers are individually loaded & tested, all the services are individually loaded and tested, this takes way, way longer than simply copying a chunk of the hard drive to RAM.

As others have said, it's a good idea to do a proper shut down and re-boot every now & again to spring clean the system...

  Clapton is God 11:51 21 Apr 2009

Also note that in the seconds immediately before a PC goes into hibernation (from standby, for example), it momentarily powers itself and all peripherals back up again.

So, if you have any USB devices connected (such as a mouse) which are set to bring the PC out of standby, hibernation will fail because that momentary power up will, effectively, be sufficient for the mouse to bring the PC out of standby.

The solution is to ensure that USB devices (particularly the mouse) are NOT set to bring the PC out of standby.

  DieSse 16:25 21 Apr 2009

Hibernation, and switching off the computer are two separate and independant things.

You can choose Hibernate and put the computer into a low power "standby" mode - and when it wakes up, it'll reload the image from the hard drive.

But when the computer is hibernating, you can also switch it off. Then when you switch it back on, it'll boot up through the POST as normal - but then reload the hibernation image from the hard drive.

At least it will do that on my desktop system. I don't actually use it - but I have tested it. Possibly laptops may vary from this, though I can't see why they should.

  Stuartli 16:30 21 Apr 2009

My system is completely switched off in Hibernation mode.....:-)

  Simsy 17:25 21 Apr 2009

I understand most of what's been posted so far... but the clearest answer, for me, regarding why it's a quicker boot up has come from Alan14, (11:42 post)...

So that leaves the BIOS thing...
With regard to the answer from OTT_Buzzard, "there would be no point in being able to access BIOS from hibernate mode".. That may be so, but what I don't understand is...

How does the BIOS know that I am coming from "hibernate" mode. That doesn't become relevant until AFTER the POST, surely? So why is the POST different? In a dual boot situation I might want to boot into a Windows installation that isn't hibernating.

Am I missing something? Is my understanding of BIOS and POST wrong.

Thansk for all the input,



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