option ROMs could be Legacy x86 & UEFI. If the Option ROM format is set to "UEFI Compatible" in the UEFI Setup, the DXE stage will load the newer UEFI Option ROM if one is present and the legacy Option ROM if one is not. UEFI can use legacy option ROMs when a Compatibility Support Module (CSM) is enabled. Note that when Secure Boot is enabled, execution of the Compatibility Support Module and legacy option ROMs is prohibited because legacy firmware drivers do not support authentication, which is a security hole. See also BIOS UEFI Booting Legacy Plug and Play PCI configuration space Read-only memory (ROM) Preboot eXecution Environment (PXE) References BIOS