PC Boot Sequence

The boot sequence consists of these steps:

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

Links to information on booting other types of systems may be found here.

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