Hello World in x86 Assembly (16-bit OS/2)

A minimal Hello World implementation in x86 16-bit assembly for OS/2 1.x systems, using OpenWatcom tools.

Installation

OS/2

1. Install OpenWatcom C/C++ for OS/2
2. Add OpenWatcom's bin directory to your PATH
3. Ensure INCLUDE and LIB environment variables point to OS/2 API directories

Building and Running

:: Assemble with Watcom Assembler
wasm -ms hello.asm

:: Link with OpenWatcom Linker
wlink system os2 file hello.obj

:: Run the program
hello.exe

Code Explanation

The implementation uses OS/2 1.x API through INT 21h calls:

• Uses the SMALL memory model (64KB code, 64KB data)
• DosWrite (function 0x0040) writes to console
• DosExit (function 0x004C) terminates the program

Key differences from MASM:

• Uses OpenWatcom syntax for directives
• Main procedure must be public
• Different segment naming conventions
• System-specific linker directives

Building Details

OpenWatcom requires specific options:

• -ms assembler flag specifies SMALL memory model
• system os2 linker directive creates proper OS/2 executable
• Default OS/2 libraries are automatically linked

Note: This code targets OS/2 1.x 16-bit environment. For newer versions of OS/2, consider using the 32-bit implementation instead.