UEFI - About UEFI

Q: How does UEFI differ from BIOS?
A: The Basic Input/Output System (BIOS) served as the OS-firmware interface for the original PC-XT and PC-AT computers. This interface has been expanded over the years as the “PC clone” market has grown, but was never fully modernized as the market grew. UEFI defines a similar OS-firmware interface, known as “boot services” and “runtime services”, but is not specific to any processor architecture. BIOS is specific to the Intel x86 processor architecture, as it relies on the 16-bit “real mode” interface supported by x86 processors.

Q: Does UEFI completely replace a PC BIOS?
A: No. While UEFI uses a different interface for “boot services” and “runtime services”, some platform firmware must perform the functions BIOS uses for system configuration (a.k.a. “Power On Self Test” or “POST”) and Setup. UEFI does not specify how POST & Setup are implemented.

I'm not sure what I think about this. On one hand, Sun is not included (thus the OpenFirmware/OpenBoot compatibility seems missing)... It seems like it could make it easier to make a cross-hardware OS, but.... I dunno.