This is my poor-man's RGBi to VGA converter that can be built with just a Teensy 4.0 and a bunch of resistors. Works quite well with low resolution modes and works also but with a little less quality ...

This is a very simple engine to create MS-DOS games for slow PCs. To run fast on the first PC's (8088/86 and 286), it uses CGA/Tandy/EGA/VGA hardware capabilities, and gets rid of some slow techniques ...

There was MDA, familiar through the original text-based DOS prompt, CGA, then EGA, and the non-IBM Hercules along the way. Finally in 1987 IBM produced the VGA, or Video Graphics Array standard ...

Most computer monitors today are digital but may also have an optional input that accepts analog signals from a VGA graphics card ... the earlier MDA, CGA and EGA monitors used with PCs.