DOS Assembly Programs

These are a few programs I wrote in real mode x86 assembly for MS-DOS. They don't really serve any practical purpose, I just wanted to have a go at writing some programs in assembly so here they are.

I run DOS inside VirtualBox on Mac OS, so I have some shell scripts to build a disk image etc. They probably run under Linux (or Cygwin) too, but haven't tried them.

Instructions

Assuming you have mtools installed, just run ./build.sh. This will create a 1.44MB floppy image called Build/zutl.img. Now open that disk image in MS-DOS, and run ASMALL.BAT (assumes nasm is in your path). This will assemble all the programs.

Note that build wipes out your disk image, so if you edit the files on the DOS side, you will lose all your changes if you run this. You can use fromFloppy.sh to copy the changes from DOS back to Unix.

The Programs

• APMINFO - checks if APM BIOS is present, if so prints the APM version
• DUMPARGS - prints out its own command line and the environment vars
• INTDUMP - dumps the interrupt vector table in hex format
• PCTYPE - prints PC type stored in ROM BIOS. Meaningless value except on 1980s vintage IBM hardware.
• POWEROFF - uses APM to turn off the computer power
• RS232MON - shows RS-232 status flags in real-time. (I'm not sure whether values it displays are actually correct.)
• RUNSHELL - runs a subshell (i.e. child COMMAND.COM instance)
• VCLS - clears the screen
• VMODE - displays or changes video mode
• VPAGE - displays or changes video page
• VPAUSE - equivalent to the MS-DOS PAUSE command
• ZUTL - displays various system information