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Well I recently read that when you hibernate the state is saved to the hard drive.

However this confused me...

When I hibernate my PC (or follow windows' new hybrid booting) and I turn it back on were it usually has HP (or any other OEM) it doesn't show information on entering the BIOS. (F1 - Setup ESC - Boot menu...)

My Question

How does the motherboard already know that the OS is in a hibernated state if it is from the HD. I believe the HD has not yet been launched yet so there could be no HD.

Hope it made sense

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    Incorrect: during sleep the PC is never fully turned off. During hibernation, all volatile information is stored to disk. You may unplug the PC, and even remove the battery from a laptop, but when power is restored, the previous Windows state is restored from disk (the information in hiberfil.sys.).
    – DrMoishe Pippik
    Dec 13, 2015 at 2:09
  • @DrMoishePippik sleep state saved to rqm; hibernation state saved to HD.
    – Racing121
    Dec 13, 2015 at 8:19
  • How do you think the motherboard is involved in the booting of an operating system? The bootloader has that job.
    – Vinayak
    Dec 13, 2015 at 8:37
  • As soon as windows starts, the bootloader, access the hdd to check it's settings, date and time from the HDD, my guess is that there must be a log file or something created, whenever you put your PC in hibernation mode, which the bootloader access and skips the screen. Although I haven't noticed something like this ever, so I will be trying it now and would answer here the results.
    – Hunter
    Dec 13, 2015 at 8:41
  • @Hunter the presence of hiberfil.sys in the partition where Windows is installed a dead giveaway of a hibernated state. The Windows bootloader could simply check for the presence of that file and perform some integrity checks and proceed to load that file into memory.
    – Vinayak
    Dec 13, 2015 at 8:50

1 Answer 1

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Exact way is implementation-dependent. In general BIOS while booting, based on chipset registers values and content of NVRAM, decide what boot path should be used to wake up platform. Note that while going to ACPI S4 (aka Hibernate or Suspend to Disk) system indicate it in different way to hardware then S5 (soft power off) or G3 (mechanical power off).

Why vendors prevent entering BIOS setup while waking up from S4 or S3 ?

I see at least 2 reasons:

  1. Entering BIOS setup, while waking up from S4, and changing some options may cause unrecoverable system crash.
  2. It is very hard to test all conditions that may happen. To cut platform cost vendor prevent entering BIOS while waking up from S4 (I assume same thing is in case of S3, but then additional reason is that OS context is in DRAM).

For example I found that for Intel 9 Series Chipset Family there is SPL_TYP bit filed in PM1_CNT register that keeps sleep state until reset by RTCRST# signal. So those value will be preserved, CMOS RAM will be cleared ie. by jumper or removing battery.

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