After I bricked a brand new motherboard in flashing a modded BIOS obtained in this forum I'm trying to better understand BIOS (I keep a tiny hope that I can recover my motherboard!) As far as I understand a BIOS file contains 2 main blocks: boot sector block main BIOS code block (a main BIOS image) The boot sector block contains critical BIOS codes, including memory detection and recovery codes for you to flash a new BIOS image if the original BIOS image is corrupted. When the system powers on, the boot sector code executes first. Once it is completed, the main BIOS code will continue with system initialization and bootup. These days, the BIOS resides in a SPI Flash EEPROM chip soldered directly on the motherboard. The size of the EEPROM can vary. Mine is (was) 32MB. Now questions: The original BIOS file for my mobo is 4MB in size and is stored in a 32MB EEPROM. Does anybody know what else resides in the SPI Flash EEPROM? In a BIOS file is the boot sector block mentionned above always the same size? At which address in the code does it start? I tend to believe that it is at the end of the BIOS file but need confirmation. In case of a DUAL CPU board are there 2 different EEPROM which each contains the BIOS for each CPU or one EEPROM for both BIOSes of each CPU or a single EEPROM containing a single BIOS for both CPUs? Thank you for sharing your knowledge.