BIOS is not dependent on the form factor (ATX) of the motherboard. BIOS are chips with information on how to run certain hardware, these are usually American Megatrends, Award, or Phoenix.
AMD is not a motherboard, it is a company. "Advanced Micro Devices" - they manufacture CPU chips, motherboard chipsets and motherboards. All are used by Wintel type PCs (Windows, Linux, FreeBSD.)