"Write Your Own Operating System" Boot Sector U Disk Implementation

Recently, I started to read "Write Your Own Operating System", Chapter 1 "The Operating System Completed in Ten Minutes", and found that it was implemented with a floppy disk~

It's really hard to find a floppy disk now, so I thought of using a U disk to achieve it.

 

Searching for information on the Internet, I found that there are already masters who have realized it. For details, please see:

Read and write U disk (FAT32) boot sector

 

This article discusses how to write MBR on a USB flash drive formatted with FAT32:

org 07c00h jmp short LABEL_START nop OEM db 'Dirichet' ;//8Bytes Bytes_per_sector dw 512 Sectors_per_cluster db 8 Reserved_sectors dw 584 Number_of_FATs db 2 Root_entries dw 0 Sectors_small dw 0 Media_descriptor db 0f8h Sectors_per_FAT_small dw 0 Sectors_per_track dw 63 Heads dw 255 Hidden_sectors dd 63 Sectors dd 3902913 Sectors_per_FAT dd 3804 Extended_flags dw 0 Version dw 0 Root_dir_1st_cluster dd 2 FSInfo_sector dw 1 Backup_boot_sector dw 6 times 12 db 0 BIOS_drive db 80h db 0 Ext_boot_signature db 29h Volume_serial_number dd 15329558 Volume_label db 'Dirichlet09' ;//11个字节 File_system db 'FAT32 ' ;//8个字节 LABEL_START: mov ax,cs mov ds,ax mov es,ax call DispStr jmp $ DispStr: mov ax,BootMessage mov bp,ax mov cx,15 mov ax,01301h mov bx,000ch mov dl,0 int 10h BootMessage: db 'hello, kitty!', 13, 10, '$' times 510-($-$$) db 0 dw 0xaa55 本代码出处：http://blog.csdn.net/zhanglei8893/archive/2010/09/28/5912903.aspx  

 

So after compiling the above code, how to write the compiled boot.bin into the MBR of the U disk?

I thought of the int 13 interrupt of the BIOS. Use this interrupt to realize the function of reading and writing disk sectors (ah=2 read sectors, ah=3 write sectors).

 

So, I booted with a U disk, entered pure DOS, and used Debug to execute the following code:

-n boot.bin //取文件“boot.bin” -l 300 //将“boot.bin“读到内存0300H处 -a 100 //开始汇编 xxxx:xxxx mov ah,03 //指定INT 13的3号功能，即写磁盘扇区 xxxx:xxxx mov al,01 //扇区数为1 xxxx:xxxx mov dh,00 //磁头号 xxxx:xxxx mov ch,00 //0磁道 xxxx:xxxx mov cl,01 //1扇区 xxxx:xxxx mov bx,0300 //指定boot.bin导入到内存中的起始区域 xxxx:xxxx mov dl,80 //驱动器号，C盘80h,D盘81h xxxx:xxxx int 13 xxxx:xxxx int 3 //返回Debug xxxx:xxxx 回车 g=100

After the execution of the above code is completed, restart the computer and start the U disk. You can see the effect :)