Build your own bootloader...!

MUHAMMAD ILYAS

BS(Computer Scince)

How To Make Your Own Bootloader:

First you make sure that what is boot. boot means when you ON your computer/laptop,it first boot,then black window come.I give you very easy easy step to how to write your own bootlaoder.This is simple and easy steps:


Bootloader is a small program that is executed under boot up in 16-bit Real Mode. It is very small, in fact, it is only 512 bytes and it resides on the very first sector of a boot device. The bootloader is used to load more complex programs like an OS Kernel. The 512 byte bootloader code is stored with the Master Boot Record (MBR) and is loaded by the Basic Input/Output System (BIOS) via Interrupt (INT) 0x19 at0x0000:0x7c00h. This is a standard sequence in booting for almost all x86 PCs, except that in some PCs it can be loaded to 0x7c00:0x0000h.

Secondly you need some tools,which are following:

http://notepad-plus-plus.org/

http://www.nasm.us/

http://www.vmware.com/products/workstation/

https://www.virtualbox.org/

Let’s build our own bootloader with assembly programming language. Open Notepad++ and created a new file, set the language to Assembly, and replace the content with the code below. Don’t be afraid, I will explain line-by-line below.

bits 16 ; 16-bit Real Mode
org 0x7c00 ; BIOS boot origin 

jmp main ;Jump to start main() entry-point 

;;;;;;;;;;;;;;
; Variables 
;;;;;;;;;;;;;;

Message db "Muhammad Ilyas", 0x0 
MessageB db "Ilyas own bootloader program written in x86 assembly language.", 0x0
AnyKey db "Press any key to reboot...", 0x0 

;Print characters to the screen 
Println:
    lodsb ;Load string 
    or al, al
    jz complete
    mov ah, 0x0e  
    int 0x10 ;BIOS Interrupt 0x10 - Used to print characters on the screen via Video Memory 
    jmp Println ;Loop    
complete:
    call PrintNwL

;Prints empty new lines like '\n' in C/C++  
PrintNwL: 
    mov al, 0 ; null terminator '\0'
    stosb       ; Store string 

    ;Adds a newline break '\n'
    mov ah, 0x0E
    mov al, 0x0D
    int 0x10
    mov al, 0x0A 
    int 0x10
 ret

;Reboot the Machine 
Reboot: 
    mov si, AnyKey
    call Println
    call GetPressedKey 

    ;Sends us to the end of the memory
    ;causing reboot 
    db 0x0ea 
    dw 0x0000 
    dw 0xffff 

;Gets the pressed key 
GetPressedKey:
    mov ah, 0
    int 0x16  ;BIOS Keyboard Service 
    ret 

;Bootloader entry-code 
main:
   cli ;Clear interrupts 
   ;Setup stack segments 
   mov ax,cs              
   mov ds,ax   
   mov es,ax               
   mov ss,ax                
   sti ;Enable interrupts 

   ;Print the first characters  
   mov si, Message 
   call Println 

   mov si, MessageB
   call Println 

   call PrintNwL
   call PrintNwL

   call Reboot 

   times 510 - ($-$$) db 0 ;Fill the rest of the bootloader with zeros 
   dw 0xAA55 ;Boot signature

Green colour show the comment what going on int htis assemly language code.

huh its hard to remember that, so i explain this:

dont worry...!

DB measn Declare Byte

AX (Accumulator)

data segment (DS)

stack segment (SS)

To build this using NASM, open the Windows Command Prompt (CMD) and move to the directory where you’ve stored the NASM files, make sure boot.asm is stored in the exact same location and execute the following command:

nasm -f bin boot.asm -o boot.img

This will produce boot.img, now open VMware Workstation, and select one of your virtual machines, and click the Floppy icon and select Use Floppy Image file, and browse and select the boot image file produced by NASM. Next power the virtual machine.

If everything worked, congratulations! If something did not work, it is probably because there is a difference between your machine and mine. Or you might have had some issues with the assembly code, but this is easy to fix.

Currently,we working own colour of that bootstrap.

If u find any problem then mail me:

muhammad_ilyas192@hotmail.com