Boot Process and MBR

Boot Process:

There are two items in the computer: BIOS and CMOS. CMOS is the storage device that records various hardware parameters and is embedded on the motherboard, BIOS is a firmware written to the motherboard (firmware is a software program written to the hardware ). This BIOS is the first program that the computer system will take the initiative to run when it is started!

The BIOS can be used to set hardware devices in the computer. We use the hard disk as an example. The BIOS will obtain the hard disk that can be started based on the user's configuration, and read the MBR location of the first magnetic zone from the hard disk. MBR occupies 446bytes of hard disk capacity, where the boot loader is placed, and the next step is the work of the boot loader in MBR.

The purpose of the boot loader is to load the Kernel File. Because the boot loader is provided by the operating system during installation, it knows the file system format in the hard disk, therefore, you can read the kernel file, and then start the Kernel File!

Process description:
BIOS ==> MBR ==> Boot Loader ==> Kernel File

1. BIOS: Start the firmware that runs actively. You will know the first device that can be started.

2. MBR (Main Boot Record): The Main Boot Record block in the first magnetic zone of the first enable device, which contains the startup management program.

3. boot loader: the software that can read core files and run grub (for linux) is the most popular boot loader.

4. Core File: Start the operating system function.

MBR is located in the primary Boot Sector (that is, the first sector of the 0 head and 0 cylinder), with a total of 446 bytes.

Both BIOS and MBR are functions supported by hardware. As for Boot loader, the operating system is a set of software installed on MBR or Partition Boot Sector.

Main tasks of Boot loader:

1. Menu provided: users can choose different boot options, which is also an important feature of Multi-boot!

2. Load the core file: direct to the executable program section to start the operating system.

3. Transfer the function to other loaders.

The boot loader can be installed on the boot sector to implement the "Multi-Boot" function.

Attributes of Boot loader:

1. Each partition has its own boot sector)

2. The actual boot kernel files are stored in each partition.

3. boot loader only recognizes the boot kernel files in the system partition and other boot loaders.

If you want to install multiple boot times, you 'd better install Windows before installing Linux (of course, you can install a boot loader that identifies windows/linux)

During Linux installation, you can install the boot loader in the MBR or Partition boot Sector, and the Linux boot loader can be manually configured, therefore, you can add the Windows Startup option to the Linux boot loader.

During Windows installation, the installer overwrites the MBR and the startup sector of the partition, and does not allow us to select the menu.

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