OS Devloping Tutorial, Easy As Pie

Easy OS Developing Tutorial

I’ve found some articles on developing a REAL operating system, easier than most. I’ll give you a slight tutorial, but don’t think I know a lot about OS development, beacase I know next to zero. I just give you the steps that worked for me:

1. Download NASM. Extract in folder C:\OS and re-name all the NASM-????? funky crap to nasm.
2. Paste this code into Notepad:

[BITS 16] ; 16 bit code generation
[ORG 0x7C00] ; Origin location

; Main program
main: ; Label for the start of the main program

mov ax,0x0000; Setup the Data Segment register
; Location of data is DS:Offset
mov ds,ax; This can not be loaded directly it has to be in two steps.
; ‘mov ds, 0x0000’ will NOT work due to limitations on the CPU

mov si, HelloWorld; Load the string into position for the procedure.
call PutStr; Call/start the procedure

jmp $ ; Never ending loop

; Procedures
PutStr: ; Procedure label/start
; Set up the registers for the interrupt call
mov ah,0x0E; The function to display a chacter (teletype)
mov bh,0x00; Page number
mov bl,0x07; Normal text attribute

.nextchar; Internal label (needed to loop round for the next character)
lodsb ; I think of this as LOaD String Block
; (Not sure if thats the real meaning though)
; Loads [SI] into AL and increases SI by one
; Check for end of string ‘0’
or al,al; Sets the zero flag if al = 0
; (OR outputs 0’s where there is a zero bit in the register)
jz .return; If the zero flag has been set go to the end of the procedure.
; Zero flag gets set when an instruction returns 0 as the answer.
int 0x10; Run the BIOS video interrupt
jmp .nextchar; Loop back round tothe top
.return ; Label at the end to jump to when complete
ret ; Return to main program

; Data

HelloWorld db ‘Hello World’,13,10,0

; End Matter
times 510-($-$$) db 0; Fill the rest with zeros
dw 0xAA55 ; Boot loader signature

3. Save the file in C:\OS (so when you use DOS directory changing is easier) as mybootloader.txt
4. Go to Start, Run, Cmd, Ok.
5. cd C:\OS\nasm\nasm
6. nasm C:\OS\mybootloader.txt, this should produce a file called mybootloader in your C:\OS folder.
7. Insert a floppy into your drive and format it (My Computer, Right-Click, Format[/i).
7. Get rawwrite, and extract.
8. Open it up rawwritewin.exe, make sure you are on the [i]Write tab, and browse for an image file, make sure you select All Files under Files of Type: at the bottom of the dialog.
9. Find the mybootloader file, generated by NASM.
10. Select it and click Write.
11. Next to run your OS off the floppy you could leave it in and reboot your system, or as I did pop it in a less important computer’s drive and boot that one up. Just in case.
12. Presto! A hello world OS!
13. I accept no responsibilty for any errors that might result.

Thanks for reading,

gamehawk

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Note: This was copy and pasted from my original here. It’s what I think is an easier version of this hello world bootloader by Daniel Rowell Faulkner, who’s code this is. Thanks Daniel. I learned about the RawWrite tools from here.

Cheers,

gamehawk

Edit: Make sure that the file generated by NASM is exactly 512 bytes.

Edit 2:  This is code is called the bootloader of your OS.