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The approximate process of system startup: power-on-->BIOS-->loader-->kernel image
It can be subdivided as follows:
Initialization of CPU
Read the first instruction from 0xfffff0 after the CPU is powered on and stabilized
CS：IP = 0xf000：fff0
The first instruction is a jump instruction
CPU initialization state is 16-bit real mode
CS: IP is a 16-bit register
Instruction pointer PC=16*CS+IP
The maximum address space is 1M
BIOS initialization process
Hardware self-test POST
Detect the presence and working status of key components such as memory and graphics cards in the system
Find and execute the BIOS of interface cards such as graphics cards to initialize the device
Execute the system's BIOS to perform system detection
Detect and configure Plug and Play devices installed in the system
Update Extended System Configuration Data ESCD in CMOS
Boot from a floppy disk, hard disk, or CD in the specified boot order
Master Boot Record MBR format
Startup code: 446 bytes
Check partition table correctness
Load and jump to the bootloader on disk
Hard disk partition table: 64 bytes
Describe partition status and location
Each partition description information occupies 16 bytes
End marker: 2 bytes (55AA)
Valid flags for the master boot record
Partition Boot Sector Format
Jump instruction: jump to the startup code
platform-specific code
File volume header: file system description information
Startup Code: Jump to Loader
End Mark: 55AA
Refinement of the loader
System startup specification
BIOS
Program for fixing the phone to the motherboard of the computer
Including system settings, self-checking procedures and system self-starting procedures
BIOS-MBR，BIOS-GPT，PXE
UEFA
interface standard
Consistent OS startup services on all platforms