Analyze the functions and working principles of the Linux Master Boot Record (MBR)

Title: Analysis of the role and principle of Linux MBR

In the computer field, MBR (Master Boot Record) is a very important concept, especially for Linux operations to users of the system. The MBR is usually stored in the first sector of the disk and contains important information such as the boot loader and partition table, which determine how the computer boots and loads the operating system. This article will analyze the function and principle of Linux MBR in detail, and provide specific code examples to help readers better understand.

1. The role of MBR
   The main function of MBR is to load the boot loader (Boot Loader) when the computer starts, and the boot loader is responsible for loading the operating system kernel. When the computer starts, the BIOS reads the first sector of the disk (the MBR) into memory and then executes the boot loader in it. The boot loader will find the partition where the operating system is located based on the partition table information in the MBR, and read the operating system kernel into the memory for execution. Therefore, it can be said that MBR is the first step in computer startup and plays a key role.
2. The structure of MBR
   The structure of MBR is very simple. It occupies a total of 512 bytes of space and can be divided into three parts:
3. Boot code area: occupies the first 446 words of MBR section, which stores the code for the boot loader. This code is responsible for loading the operating system kernel and booting the system.
4. Partition table: occupies the next 64 bytes of the MBR and is used to record disk partition information, including the starting position and size of each partition.
5. End flag: occupies the last two bytes of the MBR and is used to identify the end of the MBR.
6. Principle Analysis of Linux MBR
   For Linux systems, the structure of MBR is not much different from other systems. The boot loader of Linux is usually GRUB (GRand Unified Bootloader), which is written into the MBR and loads the Linux kernel based on the partition table information. GRUB also supports booting of multiple operating systems, and users can select different operating systems for booting at startup.

A simple code example is given below to illustrate how to write a simple MBR boot loader. The following code is written in assembly language, assuming we want to write a simple bootloader that prints a message and stays there forever.

section .text
global _start

_start:
    mov ah, 0x0E  ; 设置打印字符串的功能号
    mov al, 'H'   ; 打印字符'H'
    int 0x10      ; 调用BIOS的视频服务
    mov al, 'e'   ; 打印字符'e'
    int 0x10
    mov al, 'l'   ; 打印字符'l'
    int 0x10
    mov al, 'l'   ; 打印字符'l'
    int 0x10
    mov al, 'o'   ; 打印字符'o'
    int 0x10

    jmp $         ; 无限循环停留在这里

times 510 - ($ - _start) db 0  ; 填充剩余空间为0，使代码长度达到512字节
dw 0xAA55                      ; MBR结尾标志

Through the above code example, we can see how a simple MBR boot loader works. It uses the video service provided by the BIOS to print characters and adds the MBR end flag at the end. When the computer starts, this code will be executed to implement a simple boot function.

To sum up, Linux MBR, as a key part of computer startup, plays an important role in the operating system startup process. By having an in-depth understanding of the structure and principles of MBR, we can better understand the process of computer startup and debug and repair it if necessary. I hope this article can help readers better understand the function and principle of Linux MBR.

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