Write an operating system "One" by yourself, make a bootable U disk, and start the real machine

There are many articles on the Internet that introduce and write a simple operating system, most of which are to create a floppy disk image file and then boot from the virtual floppy drive. I want to be able to put the system directly into the USB flash drive and boot directly from the USB flash drive. After some attempts, it worked.

1. A centos linux physical machine

2, as86, ld86 tools

Download address ftp://rpmfind.net/linux/centos/6.8/os/x86_64/Packages/dev86-0.16.17-15.1.el6.x86_64.rpm

install rpm -ivh dev86-0.16.17-15.1.el6.x86_64.rpm

3. Create a new assembly file boot.s

1.     BOOTSEG = 0x07c0
   
2.     entry     start
   
3. start:
   
4.     jmpi    go, BOOTSEG
   
5. go:    
6.     mov ax , cs    
   
7.     movdx,ax     
   
8.     moves,ax     
   
9.     mov[msg+17],ah     
   
10.     movcx, #20     
    
11.     movdx, #0x1004     
    
12.     mov     bx, #0x000c
    
13.     movbp, #msg     
    
14.     movax, #0x1301     
    
15.     int     0x10
    
16. loop0:    
17.     jmp     loop0
    
18. msg:   
    
19.     .ascii    "Loading system..."
    
20.     .byte     0x0d, 0x0a, 0x00
    
21.     .org      510
    
22.     .word     0xaa55

4. Create a new Makefile

boot.bin: boot.o
        ld86 -0 -d -s -o boot.bin boot.o

boot.o: boot.s
        as86 -0 -o boot.o boot.s

5. Execute make to get boot.bin

6. Insert the u disk into the machine

7. Switch to root user

8. The fdisk command checks the device name of the U disk. What I found here is /dev/sdb

9. Write boot.bin to the U disk

dd if=boot.bin of=boot.bin bs=512 count=1

10. Restart the system and set the U disk as the boot device

11. Great success

You can see that the system starts up, and the red Loding system is displayed on the screen...

Attached:

If you are making a software image file Makefile can be written like this

boot.img: boot.img_
        dd if=/dev/zero of=boot.img seek=1 bs=512 count=2879

boot.img_: boot.bin
        dd if=boot.bin of=boot.img_ bs=512 count=1

boot.bin: boot.o
        ld86 -0 -d -s -o boot.bin boot.o

boot.o: boot.s
        as86 -0 -o boot.o boot.s