OS boot process
①Activate CPU.
The activated CPU reads the boot program in the memory ROM, sets the IR as the first instruction of the BIOS (bootloader, basic input and output system), and registers the BIOS interrupt program entry address (build Interrupt vector table, subsequent power-on self-test needs to use interrupt calling and other functions) and prepare to start executing BIOS instructions.
②Hardware self-test.
After starting the BIOS program, first perform a hardware self-test to check whether the hardware is faulty.
a. If there is a fault, the motherboard will beep with different meanings and the startup will be aborted.
b. If there is no fault, the screen will display the CPU, memory, hard disk, etc. information.
③ Load the hard disk with OS.
BIOS reads the Boot Sequence (through the boot sequence saved in CMOS, or through interaction with the user), and hands control to the storage device with the first boot sequence, and then the CPU Load the contents of the boot sector of the storage device into memory.
④Load the master boot record MBR.
Tell the CPU which primary partition of the hard disk to go to find the operating system.
⑤CPU scans the hard disk partition table in the MBR,
and loads the hard disk active partition.
MBR contains the hard disk partition table, which uses specific identifiers to distinguish active partitions and inactive partitions.
The CPU scans the hard disk partition table and then identifies the hard disk partition (active partition) containing the operating system.
After the CPU finds the active partition of the hard disk, it starts to load the active partition of the hard disk and hands control to the active partition.
⑥Load the partition boot record PBR.
Read the first sector of the active partition, which is called the partition boot record (PBR).
Find and activate the partition root directory for The program that boots the operating system (boot manager).
⑦ Load the startup manager.
The partition boot record searches for the boot manager in the active partition and loads the boot manager.
⑧Load the operating system.
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