PC Boot Sequence

This collection of pages describes how a PC boots.  “Booting” is the process of loading and starting the operating system, the fundamental piece of software that in turn loads your applications.

The boot sequence consists of these steps:

  1. Initiating the boot sequence. Power on Reset or Other
  2. Basic Input Output System (BIOS) Power On Self Test  (POST). The POST tests and initializes the hardware.
  3. BIOS Boot. The BIOS Boot routine selects a boot device and boots it. If booting the hard disk, it reads the MBR into memory.
  4. Master Boot Record (MBR). The MBR selects the active partition and reads the PBR from that partition.
  5. Partition Boot Record (PBR). The PBR loads the next stage of the boot loader into memory.
  6. Boot Loader. The boot loader reads the kernel and selected drivers into memory. The details depend on the OS being loaded.
  7. Kernel Initialization. The kernel initializes internal state and other data structures to begin normal operation.
  8. System Process Initialization. Once the kernel is initialized it begins dispatching processes. The initial process continues the system initialization.
  9. Login. Part of system initialization is to start the mechanism to allow users to log in.
  10. User Process Startup. Once a user logs on, additional processing occurs to initialize the user’s desired configuration.

For more details go here.

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