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