http://git.savannah.gnu.org/cgit/grub.git/tree/util/grub.d/10_windows.in
This looks like BIOS bootloader recognition with two distinctions:
Windows NT/2000/XP (loader)
Windows Vista/7 (loader)
http://git.savannah.gnu.org/cgit/grub.git/tree/util/grub.d/30_os-prober.in
This might be the one for EFI, but I can't tell how it distinguishes
between them.
Windows\ Vista*|Windows\ 7*|Windows\ Server\ 2008*)
--
Chris Murphy