China DOS Union

From tutorial (1) we know that after the computer starts, the ROM-BIOS first checks for the location of the BOOT bootstrap program. The bootstrap program BOOT is written by the FORMAT command to relative sector 0 of a floppy disk or hard disk. It is a very small program. Its first task is to check whether drive A or C is a DOS system disk, then check whether the first two files in the root directory of drive A or C are IO.SYS and MSDOS.SYS. If so, it reads the IO.SYS file into memory, thus completing the task of booting DOS.
At this point, IO.SYS takes control of the system and formally enters the DOS startup process (in PC-DOS it is called IBMBIO.COM).
The I0.SYS module mainly completes basic input/output management work. It consists of two parts:
　　1. The system initialization program SYSINIT;
　　2. A set of device drivers.
　　The system initialization program SYSINIT mainly does the following 6 things:
　　1. Determine memory capacity;
　　2. Load and relocate the MSDOS.SYS module;
　　3. Call the MSDOS.SYS kernel initialization program DOSINIT to complete kernel initialization;
　　4. Interpret the CONFIG.SYS file and set the system operating environment;
　　5. Load installable device drivers;
　　6. Load the COMMAND.COM module.
　　From this it can be seen that after taking over control of the system from the bootstrap program BOOT, SYSINT plays the leading role in the entire DOS system startup process. It arranges all system initialization work, and only after reading COMMAND.COM from disk into main memory does it hand over control to the latter's initialization program CMDINIT. It is then overwritten and disappears, ultimately completing its DOS startup mission (the DOS prompt appears on the screen).
Device drivers are programs that let MS-DOS use some physical device or add some function to MS-DOS. When the system is first started, there are altogether the following 6 types of device drivers:
1. Standard input/output device driver: supports the keyboard and display, and the logical device name is CON.
2. Standard printer device driver: supports printers, and the logical device names are PRN, LPT1, LPT2, LPT3.
3. Auxiliary input/output device driver: supports the asynchronous serial communication interface, and the logical device names are AUX, COM1, COM2.
4. Clock device driver: supports time and date services, and the logical device name is CLOCK$.
5. “Null” device driver: supports simulated operations for application programs, and the logical device name is NUL.
6. Block device driver: supports floppy and hard disk operations, and has no logical device name.
In the DOS hierarchy, the IO.SYS module lies between the kernel module MSDOS.SYS and the ROM-BIOS. By calling the device drivers in IO.SYS, the DOS kernel interprets specific input/output requests and converts them into the relevant control commands for different hardware device controllers. These commands then tie in with the hardware driver programs built into the ROM-BIOS chip, thereby truly carrying out the requested input/output tasks.

Written very thoroughly, good!

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I bump this!!
Continue.

The line of thought is very clear, not bad.

Is it possible by editing io.sys so that when loading DOS, you can choose to boot from floppy or hard disk, or boot from CD-ROM, without paying attention to the boot order set in the BIOS
?

Study hard and make progress every day

Isn't msdos.sys a text file? Then how can there also be a "kernel initialization program DOSINIT"? Also, how is kernel initialization carried out?

Only the msdos.sys in win9x is a text file.

Written well. Learning. Where is (1)?

Very useful

The msdos.sys in DOS7.1 is also a text file

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