The traditional x86 hardware init scheme is to run x86 machine code from ROM's on the expansion cards. This of course limits the cards to only being used in machines that can execute x86 machine code.

Open Firmware replaces this with Forth code on the card and a Forth interpreter. This is how PowerPC Macs and Sun Sparc hardware would load card drivers.

EFI's driver functionality is pretty much the same as Open Firmware, except it uses an EFI Byte Code (EBC) as it's language.