I found the Windows 7850 installation in one of my netbook boot into BSOD 0x0000007f, even the recovery environment boot into BSOD with the same error code. Moved the drive to another computer, same results. I can't confirm whether the installation broken, or there is a super timebomb in this build that not detected.

INACCESIBLE_BOOT_MEDIA.
Try on another drive.

INACCESIBLE_BOOT_DEVICE is 0x7e, not 0x7f.
I tried to burn the winre.wim to a CD and boot from that without problems, so it's not the timebomb issue.

Well...
I always got INACCESIBLE_BOOT_MEDIA with 7f...

It's me made a mistake that INACCESSIBLE_BOOT_DEVICE is 0x7b instead of 0x7e or 0x7f.
http://msdn.microsoft.com/en-us/library ... 85%29.aspx

Probably a controller driver. Easy way is to try Legacy/IDE mode and see what happens. If that doesn't work you could have a damaged partition table.

I can't remember what build 7850 you're talking about, but it is most likely a driver error. Had similar error in a virtual machine once. Think it had to do with the driver not supporting CDs/DVDs on a SATA drive. Using IDE or the IDE mode worked fine.

Although you probably checked Google already, might it be a "You try to over clock the speed of your computer's processor (for example, you set a 150 MhZ processor to run at 187 MhZ" error? http://support.microsoft.com/kb/137539

The error went away after I did a chkdsk of 7850's volume under XP.
Might be some weird bug in 7850 NTFS driver instead of any hardware issue.

Did you actually try going in to the BIOS setup and enabling legacy/IDE mode?

The BIOS of this netbook does not support AHCI at all, only IDE mode.
It's clear that the issue is not about the inaccessible boot device at all.

It clearly is since 7f at INACCESSIBLE_BOOT_DEVICE is a bugcheck showing the device itself could not be mounted.

INACCESSIBLE_BOOT_DEVICE is 7b instead of 7f.
bugcheck 0x7f is UNEXPECTED_KERNEL_MODE_TRAP.

Pardon my error, I assumed you referenced the wrong code assuming you had this running on said system before. Obviously this is not the case.
In that case all you can do is test hardware and update otherwise there's some piece of hardware the system does not like.