Thursday, March 07, 2013 10:42 PM
Does anyone know how WinPE 3.x/4.x is able to boot in UEFI And BIOS mode (using the same boot media)?
I would love to be able to do the same thing for my OS images. (non-MDT images)
Friday, March 08, 2013 8:11 AM
booting into UEFI or BIOS is more a bios setting then image settings.
if your bios supports it and you set it up correctly you can boot into uefi mode and your windows image or winpe will know you booted into UEFI.
sadly the settings are different for every brand of motherboard.
you shouldn't be needing a different image for bios and or uefi installations.
- Proposed As Answer by DCtheGeek Friday, March 08, 2013 2:41 PM
Monday, March 11, 2013 2:54 AMModerator
The boot up process for uEFI and BIOS are quite different.
BIOS machines don't understand the file systems on a disk, so they will first load a small program at an offset like the MBR, or in a specific location on the DVD. That program will then attempt to load the boomgr, bcd, and other associated files so it can load the rest of the operating system into memory and kick off into kernel mode. There are about 50 or so related/required files in Windows Vista and above. I won't list them here.
for uEFI machines, the firmware understands Fat32, so it will load the bootmgr.efi, bcd, and other associated files from the media.
There are several different ways to get to bootmgr and bootmgr.efi. PXE, USB, Hard Disk, CD (el-torito). But the other programs that run in real mode can continue running.
WinPE images directly from the ADK should support booting both BIOS and uEFI, it is up to you to copy all necessary files down to support both uEFI and BIOS booting. MDT should do that for you.
Keith Garner - Microsoft PM
- Proposed As Answer by Keith GarnerModerator Monday, March 11, 2013 2:54 AM
Thursday, March 28, 2013 10:16 PM
Thanks Keith, after doing some testing it appears that my image will work fine regardless of the firmware type on the target machine (as long as the partitions are setup correctly for each firmware type). But is there a way to have a single disk layout that supports booting from both legacy and UEFI?
The BCDBOOT /F ALL option seems to imply that this is possible. but not sure how the disk needs to be configured.
I hope my question makes sense. if not then let me know.
Friday, March 29, 2013 2:26 PM
If you're referring to the harddisk/ssd that you install Windows on, then the answer is no.
A system that's running in uEFI mode, will require the disk to converted to a GPT disk, Windows cannot boot in this scenario from a basic disk. The same goes the other way around, a system running in legacy BIOS mode, Windows cannot boot from a GPT disk.
You'll notice this behavior when you try to run the Windows Setup from a regular disk, you'll receive an error message when trying one of these two cases. Alternatively when trying to apply the bootmgr onto the disk and it detects this, it also will not be able to continue and create it.
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- Marked As Answer by Jay.lambert Friday, March 29, 2013 2:41 PM