The beauty of OpenFirmware is that it is extended with Forth, which is extremely compact (so could fit on small PROMs in the computer and fcode for addon cards)

The beauty of OpenFirmware is that it is extended with Forth, which is extremely compact (so could fit on small PROMs in the computer and fcode for addon cards). If you are designing a PCI card, you can write a bit of fcode that will run on SPARC and PowerPC for instance to expose opaque RAID volumes as bootable disks. Keep in mind the PC BIOS was and is a complete tire fire, and uses something like this https://en.wikipedia.org/wiki/Option_ROM https://en.wikipedia.org/wiki/Option_ROM to approximate support for the above. UEFI is a bit of improvement but massive and obtuse in comparison to OpenFirmware.