Hello World in x86 Assembly (16-bit DOS)

A minimal Hello World implementation in x86 16-bit assembly targeting DOS and compatible operating systems.

Installation

Install Open Watcom from http://www.openwatcom.org/

Building and Running

:: Assemble and link
wasm -ms hello.asm
wlink system dos file hello.obj

:: Run
hello.exe

Testing Environments

This program has been tested and works in:

• FreeDOS 1.3
• MS-DOS 6.22 or later
• DOSBox 0.74-3
• Windows DOS prompt (Windows 98/ME and earlier)
• QEMU with FreeDOS
• VirtualBox with FreeDOS

For FreeDOS, you can test using either:

1. A real computer with FreeDOS installed
2. QEMU with FreeDOS:

   qemu-system-i386 -hda freedos.img -drive file=hello.exe,format=raw

3. VirtualBox with FreeDOS:
   • Create new VM
   • Select "Other DOS" as OS type
   • Mount hello.exe via shared folder or disk image

Code Explanation

Uses DOS INT 21h services:

• Function 40h (Write to File Handle)
• Function 4Ch (Terminate Program)

All functions used are part of the original DOS API specification and are fully supported by FreeDOS, ensuring maximum compatibility across DOS implementations.