A modular BIOS update mechanism provides a standardized method to update options ROMs and to provide video and processor microcode upgrades in a computer system without requiring a complete replacement of the system BIOS. The MBU mechanism provides several advantages. First, new features and BIOS bugs from earlier release may be delivered to an installed base of end-user systems even if direct OEM support cannot be identified. Also, BIOS components may be provided as a validated set of revisions. With resort to a validation matrix, BIOS updates may be managed easily. The modular BIOS update is particularly useful in systems having several independent BIOS's stored within unitary firmware.