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Firmware Boot Process

Part of series osdev |

General Steps:

  • Click the power button on
  • CPU load instruction from firmware chip on the motherboard and execute it
  • Firmware code does initialize and tests system hardware.
  • Firmware start bootloader and give the next step to the boot loader.

Two famous firmware:

  • BIOS firmware
  • UEFI firmware

BIOS firmware:

  • Frequently is stored in ROM
  • Initializes and tests system hardware
  • Bases on user predefined prioritized boot device, BIOS try to check each device in order to see if it is bootable by trying to load MBR.
  • From valid MBR, BIOS loads boot loader and give next step to it.


  • Special type of boot sector
  • The very beginning of the partitioned hard disk

UEFI firmware

  • Designed to replace BIOS firmware
  • Initializes and tests system hardware.
  • UEFI, or user let UEFI knows which boot loader is used. Not dependent on disk and MBR.
  • Boot loader of UEFI is stored in the EFI system partition of the hard drive GPT partition type.

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Tags: linux | firmware | boot |