The DOS SDK

There's a rather more sophisticated DOS SDK available: doslib from the guy who maintains dosbox-x.

https://github.com/joncampbell123/doslib

Most of the stuff that's emulated in DosBox-X has a corresponding SDK in doslib. It's a treasure-trove of information

You can get a free C and C++ compiler for DOS at:

https://www.digitalmars.com/download/freecompiler.html

320x240 mode was the coolest thing back in the days - https://github.com/Scalibq/DOS_SDK/blob/main/C/VGA.c#L38

not really sure what this is about - i was programming in assembler and c on ibm xt and at in the early to mid 1980s, with no problems.