China DOS Union

The Chinese name of MSDOS.SYS is file management program. It is a core file in the DOS system, so it is also called the DOS kernel. In PC-DOS, this file is named IBMDOS.COM.
After the system initialization program in the IO.SYS module gains control, it loads and relocates the MSDOS.SYS module, and at the same time calls the kernel initialization program DOSINIT to complete initialization of the DOS kernel.
The MSDOS.SYS module carries out file management for the DOS operating system and provides many system function calls. It is also made up of two parts:
1. Kernel initialization program DOSINIT;
2. System function call program.
The kernel initialization program DOSINIT mainly does the following 4 things:
1. Set the relevant interrupt vectors for DOS;
2. Check the linked structure of the device headers in the IO.SYS module (equivalent to device control blocks), and complete their initialization;
3. Establish the corresponding Drive Parameter Blocks (DPB) for block devices;
4. According to the BUFFERS command in CONFIG.SYS, allocate and establish the system's disk buffer chain.
After DOSINIT completes the above 4 tasks, control returns to SYSINIT.
The system function call program mainly refers to the INT 21H (H is the hexadecimal marker) interrupt handler. Current microprocessors all support many types of interrupts. According to the cause of the interrupt, they can be divided into three major categories: external hardware interrupts, internal hardware interrupts, and software interrupts. Microprocessors of the Intel86 series can support 256 interrupts. The interrupt numbers are 00-FFH, that is, all 256 interrupts of the 3 types are identified by one unique interrupt number. INT 21H belongs to the software interrupt category. It is a program interrupt caused when the CPU executes an INT n instruction (n is the interrupt number).
MS-DOS has about more than 100 system functions, used to implement character device management, clock management, disk management, file and directory operations, record reading and writing, memory management, program execution, network sharing, and so on. Each function corresponds to a "function" number. As long as the function number is first placed into register AH (a general-purpose register of the CPU, used for storing data), and the corresponding input parameters are set as required, then by executing an INT 21H instruction, branching can be performed according to the provided function number, and a certain system function call can be completed by interrupt.

Looks like you have to learn some assembly before you'll understand it. Are there any Chinese tutorials on interrupts and assembly instructions?

I want to learn too. Are there any teaching materials on this? Recommend some.

Yeah! Are there any?

Isn't there an assembly language textbook?
I'm learning it now too, but I'm doing a terrible job of it

So impressive! Admire you! Admire you!