Startup and Init

• Bootstrapping
  • First thing that happens when you power on a system is a positive voltage (5v) is applied to the reset pin of the CPU
  • Two registers are initialized:
    • CS Register: Has the address of the stack
    • EIP Register: The current instruction to execute
  • Load the BIOS from ROM
    • Linux doesn’t use the BIOS after boot, it only uses device drivers loaded by the kernel
    • MSDOS used the BIOS to execute system calls
    • BIOS Steps:
      1. POST (Power on self test)
      2. ACPI - builds tables of devices with information regrading power. Can be used to decide when a system can power down a device or set it to a lower power level
      3. Hardware Initialisation
      • 3 ways to communicate with devices on a PC:
        1. IO port from CPU to the device for communication via a port address
        2. Map memory from the device to the address space of the computer and read/write to it
        3. Use interrupts
      4. Find a boot device by searching for a boot sector on each device.
      • First sector of a disk is the master boot record with contains the partition table and a boot loader (GRUB)