There was also the scenario where the CPU was 64 bit but the EFI was 32 bit.
Booting a 32 bit OS was fine, but 64 bit OS' generally came with a 64 bit bootloader, so you had to do a special song and dance to load a 32 bit bootloader with a 64 bit OS.
Booting a 32 bit OS was fine, but 64 bit OS' generally came with a 64 bit bootloader, so you had to do a special song and dance to load a 32 bit bootloader with a 64 bit OS.