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2025 01 18

Assembler

Getting Started with Assembler

To write, compile, and run assembler programs, you’ll need:

Microsoft Macro Assembler (MASM): Download from the official MASM page.
Linker: Often included with MASM as LINK.EXE.
Text Editor: Use editors like Notepad++ or Visual Studio Code.
Command-Line Interface: Assemble, link, and run programs from the terminal.

Installing MASM

Follow these steps:

Download MASM from Microsoft or use an alternative like TASM or NASM.
Install MASM and add its directory to the PATH environment variable.

Code: Hello World in Assembly


; HelloWorld.asm
; A simple program to print "Hello, World!" to the console
.MODEL SMALL ; Define memory model
.STACK 100h ; Define stack size
.DATA ; Section for variables and strings
message DB 'Hello, World!$' ; Message to display, terminated with $
.CODE ; Section for code
main PROC
       MOV AX, @DATA ; Load data segment address into AX
       MOV DS, AX ; Move AX into DS to set data segment
       LEA DX, message; Load effective address of message into DX
       MOV AH, 9 ; Function to display string (INT 21h)
       INT 21h ; Call DOS interrupt
       MOV AH, 4Ch ; Terminate program function (INT 21h)
       INT 21h ; Call DOS interrupt to exit
main ENDP
END main ; End of program

Steps to Compile and Execute

Write the Code: Save the code above in a file named HelloWorld.asm.
Assemble the Code:
ml HelloWorld.asm
Link the Object File:
link HelloWorld.obj
Run the Program: Execute the program with:
HelloWorld.exe

Explanation of the Code

Memory Model: .MODEL SMALL uses one segment for code and one for data.

Data Section: .DATA defines the message. The $ signals the end of the string.

Code Section:

MOV AX, @DATA / MOV DS, AX: Sets up the data segment.
LEA DX, message: Loads the message's address into the DX register.
MOV AH, 9 / INT 21h: Calls DOS interrupt 21h to display the string.
MOV AH, 4Ch / INT 21h: Terminates the program using DOS interrupt 21h.

Additional Notes

Emulation: Use a DOS emulator like DOSBox on modern systems.
Resources: Check out the MASM documentation and books like Assembly Language for x86 Processors by Kip Irvine.