• Contains low-level IO software

  • Nowadays, stored in Flash RAM - nonvolatile & can be updated

  • The newer standard is called UEFI

  • The first program that starts when booting up a computer

    1. Checks Main Memory capacity
    2. Check IO Device
    3. Scanning IO Bus to detect all devices attached
    4. Determine the Boot Device by trying out a list of devices stored in the CMOS. (Users can press keyboard shortcut - F12, F11, Esc, F8, F9 to enter a Boot Menu and choose the boot device manually)
    5. The Boot loader inside the boot device will carry out the next step

Boot Device

  • Storage device that contains Master Boot Record and the OS
  • Master Boot Record is read into Main Memory to start the Boot Loader

Boot loader

  1. Examines the partition table at the end of boot sector to determine which partition is active. Providing a menu for user to select which OS to boot
  2. When an OS is selected, boot loader loads in the corresponding Kernel into the Main Memory
  3. Kernel Booting will finish up on the booting of the OS
  • One common boot loader is Grub2


  • How Does Linux Boot Process Work?