Was wondering if Windows writes to and FLAGS somewhere in registry that the system was brought down prior into a hibernation mode, so that on boot from hibernation it knows then to read in the hiberfil.sys file to memory to restore back to the original desktop environment. Or if the Hiberfil.sys simply exists and is found by Windows at boot if it just finds this file and runs with it as knowing that the system was last brought down into a hibernation state.

 Only info I found on google search was talking about it writing memory to disk and then restoring on the next POWER up to the original environment that was saved. But it doesnt go into detail as to how Windows knows to bring it back up from Hibernation state -or- bring it up totally fresh boot.

Working on a laptop that hibernation is enabled and it works sometimes and doesnt work other times and while I should just reinstall 7 clean, I figured I'd play with this laptop a little further to better understand this process to PINPOINT the cause rather than just taking the easy way out of setting it back to a clean build state.

I feel that the registry may be troubled and so if there is a flag in the registry that should be set that is not, then upon boot of the laptop from hibernation, it will totally skip over loading the hiberfil.sys file and bringing the laptop back up to where it was prior to hibernation. If there is a registry location to inspect, I'd like to know its location in there to inspect it and SEE what I find.When hibernating, the Power Manager saves the compressed contents of memory to a hibernation file, hiberfil.sys, which is large enough to hold the uncompressed contents of memory, in the root directory of the system volume. Compression is used to minimize disk I/O and improve hibernation and resume-from-hibernation performance. When that finishes, it shuts off the computer. When the PC is turned back on a normal boot process occurs, except that Bootmgr checks for and detects a valid memory images stored in the hibernation file. if it contains saved system state, bootmgr will launch "Winresume" which reads the contents of the file into memory and then resumes execution at the point in memory recorded in the hibernation file.

Source: Windows Internals, Fifth EditionSweet!!!   

Thanks for all the info BC on this. So its a lower level boot manager that looks at the Hiberfil.sys and based on this decides to boot normally or boot from the hiberfil.sys then.

So on this laptop there may be an issue with the RAM writing to the HDD on shutdown, in which the hiberfil.sys file if corrupted for some reason or another could cause the boot manager to skip over the hiberfil.sys file and boot normally as is the random case here.

I am going to run memtest86 on this laptop since I already ran crystaldiskinfo on it and the HDD came up as healthy. Maybe the RAM is acting up somehow when performing the memory dump to disk into this hiberfil.sys file.

I'll be back to report my findings once I dig out that CD with memtest86 to run on it for a few passes.Well memtest86 came back with some red memory addresses. Removed 1 of the 2 sticks and tested and determined that the one stick seems to be troublesome. Going to see if it behaves on the single 2GB stick and order a replacement stick.

I bet that troubled stick was the cause of the hibernation issue with a scrambled dump or something. I also tested the laptop with going back and forth to hibernation and booting back up and it hasnt acted up yet since removing that 2nd stick that failed with memtest86.

Strange that that stick didnt cause any other stability issues.