The NASM Tutorial Page

Welcome to the NASM Tutorial.

Introduction

Here I will include source and such to help learn assembly using NASM syntax. I am currently learning myself, and was frustrated at not seeing much out there on NASM. This is a problem since in some ways NASM syntax is different from some other assemblers (e.g. MASM, TASM). So here goes!

But before we begin...

I am going to assume that you have some assembly programming knowledge, be it from experience or a textbook. There are several fine assembly sources referenced at my homepage here.

DOS .COM Programs

These are in my opinion the simplest programs to understand, so I thought it would be a good starting point. According to the NASM documentation (Section 7.2), to write a .COM program, you would create a source file looking like: 

  org 100h
  section .text
  ; put your code here...
start:
...
...
  section .data
  ; put your data items here
...
...
...
  section .bss
  ; put your uninitialized data here
...
...
...
where you would replace the ellipses(...) with instructions, data, and uninitialized data, respectively. Also note that there should not be an END directive. The code simply ends when it sees: 
mov ah, 4ch
int 21h
(the "exit to DOS" function).

To assemble such a program, use the command: 

nasm myprog.asm -fbin -o myprog.com

You may look at some source that I have written, but assemble and run it at your own risk!

What also helps is to download and use the freely available NASM-IDE. It provides an "ASM Assistant" that sets up the framework described above automatically.

Sidebar: What is a .COM program?