Assemble an MS-DOS .COM binary with DEBUG.EXE

The 8-Bit Guy has a video where he demonstrates the assembler built right into the monitor ROM on a C64.

This fascinated me and made me wonder… If I was stuck on an old MS-DOS machine and wanted to assemble a binary… Could I do it? Byte by byte? With what tool? Those of us stuck with “IBM compatible” PCs didn’t have no fancy monitor ROMs.

Turns out MS-DOS’ DEBUG.EXE is and was entirely up for the job.

C:\>debug
-a 100
0DAB:0100 mov dx,10c
0DAB:0103 mov ah,9
0DAB:0105 int 21
0DAB:0107 mov ax,4c00
0DAB:010A int 21
0DAB:010C db 'Hello, world!$'
0DAB:011A
-n hello.com
-r cx
CX 0000  :1a
-w
Writing 001A bytes
-q

C:\>hello.com
Hello, world!
C:\>