Flashback functionality without a functional CPU generally is accomplished using a separate microcontroller on the board which runs its own code separate from the BIOS. It shouldn't need any of the original BIOS code in-tact, since there's nothing to execute it anyway if there's no CPU installed. :)
phire|3 years ago
It would be smart to implement it as seperate chip, so it can work even with an empty SPI flash. Would also explain why it's only available on some motherboards.
But it wouldn't entirely surprise me if they managed to implement it as pure software inside an extra microcontroller core inside the chipset (or another chip). There are dozens of microcontrollers cores spread out over the various chips on the motherboard which might be abused for such purposes.