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Does hibernation use more power than a total shutdown?

The oft-given answer is no, but I can't help but wonder if that's a lie: hibernation seems to be an ACPI feature, and a completely different sleep state (S4) than, well, "off" (S5).

So, does hibernation use more power than shutdown?
If not, then why is it a different hardware state than shut down?

Edit:

I forgot to mention the last part of the question, sorry:
If so, then what makes it different from shutdown, from a hardware (not driver) perspective?
Shouldn't devices not be receiving power either way?
i.e. How does a device behave differently when it is "shut down" versus when it is hibernated?

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Modern PCs use power even when shutdown. –  Celeritas Mar 5 '13 at 18:31
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If you yanked the cord while it was in S4, it will still resume (from disk) once you give it power again and turn it on. The fact that most computers draw SOME power in both S4 and S5 has nothing to do with a difference between S4 and S5. :) –  Ƭᴇcʜιᴇ007 Mar 5 '13 at 19:03
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@techie007: Ahh, it's so confusing when you say S5 "dumps RAM", because a "dump" means writing contents to disk (crash dumps, core dumps, etc.), but when you said "dump" you meant discard, which confused the heck out of me. Okay, I see what you're saying now, but it still doesn't make sense: S5 is a state, not an action. It can't do anything, can it? The action is a transition, and it seems like going from S4 to S1 is equivalent to going from S5 to S1 -- either way, the system restores the contents of RAM and powers all devices back on, so what makes S4 use more power than S5? –  Mehrdad Mar 5 '13 at 19:12
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My computer will react to keyboard presses when in S4 (and will power up), it will not when in S5. So there is a behavioral difference. The OS doesn't care though; if you unplug/replug the PC, it will go to S5, but the system will restore itself just fine. –  avakar Mar 5 '13 at 22:16
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How in the world is this question "not constructive"? I don't see how these votes to close are justified... –  DragonLord Mar 5 '13 at 23:34

6 Answers 6

up vote 6 down vote accepted

It depends.

On some computers, S4 and S5 will use the same amount of power. I believe this is the more common scenario.

Some computers, however, can be configured to (for example) leave the network card powered up when in S4 but turn it off when in S5. In that scenario, power consumption will be higher in S4 than in S5.

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Can you provide any links to sources with more information? –  ruakh Mar 7 '13 at 18:58
    
@ruakh: see the "Deep Sleep Control" option, page 49 in ftp.dell.com/Manuals/all-products/esuprt_desktop/… –  Harry Johnston Mar 7 '13 at 20:40

According to this article hibernate is about the same as powering off:

Hibernate powers down your monitor to about 5 watts of energy and your PC to 2.3 watts—virtually the same as turning your PC off

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Who's monitor gets power from their PC? IDK about you but my monitor has get's power from a wall outlet. –  Kyle Mar 5 '13 at 18:56
    
@Kyle there must be a little bit because if you unplug the monitor from the PC then it gives a message like "no signal detected" so their must be power over that cable, even when the machine is shutdown. But I like your idea of getting power directly from the PC :P –  Celeritas Mar 5 '13 at 18:59
    
An easy test for you to do: take a VGA/DVI cable that isn't plugged into a computer and plug it into a monitor, it will do the same thing. The monitor has power from the wall and can sense when the metal pins are connected as it completes a circuit, in fact one of those pins is a ground. –  Kyle Mar 5 '13 at 19:08
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Once upon a time I had a power supply that included a switched plug for attaching your monitor, so it would power down automatically with the PC (this was from before the days of "green" monitors that would know when to shut down). Either way, in this case my monitor was being powered by the PC. Not the standard today, by any means... –  techturtle Mar 5 '13 at 19:15
    
A monitor that didn't take power from the PC wouldn't comply with the current VESA EDID or HDMI standards. For example, it wouldn't be able to supply identification data when unplugged, which is required by the standard. (See, for example, section 8.4.4 of the HDMI standard, version 1.3a) –  David Schwartz Mar 5 '13 at 20:24

When your computer hibernates, the contents of physical memory (RAM) are stored onto the hard drive and the computer is physically turned off. As a result, the system does not consume any more power than if it was shut down (but see exception below).

When you turn your computer back on, early in the boot process, the system will detect that it went into hibernation and will restore from the memory image on the hard drive. A system with legacy BIOS will likely go through POST as if it is starting up from a full shutdown. A system with UEFI will often be aware that the system had hibernated (having been notified so by the operating system) and bypass POST, instead proceeding directly to the bootloader.

Do not confuse sleep with hibernate. Sleep, or standby, mode places the computer into a low-power state to allow you to quickly resume your session. If power is lost, data may be lost as this is equivalent to a hard shutdown.

Newer versions of Windows support hybrid sleep, where the contents of physical memory are written to the hard drive as with hibernation, but the system remains in a low-power state rather than turning off altogether. This allows for quick resuming while preventing data loss should power be lost--the computer will simply load from the memory image stored on the hard drive.

On Windows, the file hiberfil.sys in the root of the system volume is used to reserve space for the contents of physical memory for hibernation.


Note, however, that if wake-on-LAN (WOL) is enabled, the system will keep the network adapter on to permit the system to resume automatically on a WOL message. Depending on BIOS configuration, the network adapter may or may not be on when the system is fully shut down, and it may be possible to configure WOL in the BIOS setup so that WOL is enabled in hibernate but not when fully shut down. Otherwise, there would be no power difference.

On some systems, and once again depending on BIOS configuration, there may indeed be a nontrivial difference between a full shutdown and hibernate. For example, a computer may keep USB ports powered in hibernation to permit resuming by pressing a key or moving the mouse. In any case, a power failure will not cause a system in hibernation to lose data.

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They have to be different sleep states because the transition rules are different (what happens when you hit a key or press the power button). So even if the power consumption was precisely the same, they'd still have to be different sleep states. The documentation for S4 says, "The system consumes the least power compared to all other sleep states."

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States and transitions are completely orthogonal though. What makes it an ACPI concept instead of an OS/driver concept? They could just make different transitions to the same state; what makes the states themselves different? –  Mehrdad Mar 5 '13 at 18:37
    
@Mehrdad: A state is defined by what happens when you're in that state, how you enter that state, and how you leave that state. If two things are left differently, then they are different states. –  David Schwartz Mar 5 '13 at 20:23
    
How are S4 and S5 left differently, from the hardware's perspective? –  Mehrdad Mar 5 '13 at 20:25
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On many systems, the BIOS attempts to resume as quickly as possible when leaving the S4 state (to meet rapid resume requirements). In order to do this, it has to be a different state. Otherwise, the BIOS would have no way to know which behavior to provide. (The OS can just check for a valid hibernation file, so it doesn't need a different hardware state. But the BIOS can't.) Also, some firmwares clear memory when leaving the S4 state to ensure a new OS instance can't steal information left in memory from the previous instance. (I don't understand why that's needed, but it is a fact.) –  David Schwartz Mar 5 '13 at 20:38
    
Ahh, +1 that explains a lot, thanks for the great info! –  Mehrdad Mar 5 '13 at 20:44

According to my knowledge, Hibernate saves your work to a file on your HDD and then turns off your PC as shutdown would do. So it's basically the same as power off.

I rarely shutdown my pc (only on occasions when i actually have to reboot in order to load some new files or when windows is acting crazy)

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Hibernation does use power. Its not the same as Shutdown but can be related closely to Sleep mode. When a computer goes into hibernate mode, it saves the contents in its RAM to the harddrive and goes to sleep.

Hibernation uses much less power than sleep mode.

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"It's not the same as shutdown"... well, that's basically what I said in my original question, where I said it's S4 instead of S5. The question is, well, how? Isn't everything turned off either way? What makes it different from shutdown? And yes, it uses power, but does it use more power than shutdown? (Why should it?) –  Mehrdad Mar 5 '13 at 18:48
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Accoding to Microsoft this is incorrect - hibernate stores the contents of the ram to disk AND THEN SHUTS DOWN THE PC, using no power while its off - windows.microsoft.com/en-us/windows7/… states "[hibernation] puts your open documents and programs on your hard disk, and then turns off your computer." –  davidgo Mar 5 '13 at 18:50
    
@davidgo: That's what everyone says, and that's why I asked this question: it seems to be an outright lie (though not a very wrong one) as far as I can see -- just look up ACPI states S4 and S5. –  Mehrdad Mar 5 '13 at 18:51
    
@davidgo Is correct. Sleep states (like S3) save RAM connects and go into low power mode, with enough power to keep the RAM live. Hibernation dumps to disk and shuts off, and requires no power to retain the state. –  Ƭᴇcʜιᴇ007 Mar 5 '13 at 19:04
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My reading on S4 vs S5 states all say the same thing - that the system is powered down after dumping memory to disk. Can you point to anything which implies otherwise that I can consider ? –  davidgo Mar 5 '13 at 19:10

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