An operating system from Microsoft that runs on early x86 era PCs. There were multiple flavors of DOS, but MS-DOS was the big one.
Compile with wcl386.exe to use the protected mode wrapper and skip all the DOS memory model junk.
If you can't mount a floppy image, try setting Option: mount images read-only
In Z:TEXTUTIL there are COM files you can run to change the text size.
This is the C/C++ compiler I've been using the most lately. It installs pretty cleanly into a virtual directory using DosBox-X.
https://open-watcom.github.io/
An SDK for DOS programs that lets you skip low level programming.