Windows – How are the initial boot files found in UEFI

bootuefiwindows 8

I was curious and poking around my Windows 8 system. Per Wikipedia's entry on UEFI

Boot loaders can also be automatically detected by the UEFI firmware, to enable booting from removable devices. Auto-detection relies on a standardized file path to the operating system loader, depending on the actual architecture to boot. Format of the file path is defined as EFI_SYSTEM_PARTITION/BOOT/BOOTMACHINE_TYPE_SHORT_NAME.EFI, e.g. /efi/BOOT/BOOTX64.EFI

I decided to mount my EFI system partition and check it out.

The only remotely relevant file I see is M:\boot\boot.sdi

In M:\boot there is also an en-us (which contains bootsect.exe.mui), fonts, resources folder as well as bcd, etfsboot.exe, and memtest.exe

Since there is no BOOT*.efi how does UEFI know where to find the boot files? Also the "boot" folder is lower cased and per Wiki it seems it should be "BOOT"

Best Answer

On UEFI System Partition paths begin with \EFI !

For example:

Z:\EFI\Boot\bootx64.efi

Z:\EFI\Microsoft\Boot\bootmgfw.efi

Z:\EFI\ubuntu\grubx64.efi

"\EFI\Boot" folder/directory stores the default fallback boot loader.

\EFI\'Company' - are also reserved names.

'Company' folder can have any structure (sub, sub-sub folders). The corresponding boot entry has the correct path to boot loader file, e.g. "\EFI\Microsoft\Boot\bootmgfw.efi"