Retrocomputing with Turbo Pascal, Part 2: Developing Text Mode Screen I/O Routines

This is the second part of an article regarding retro-computing using Turbo Pascal. For the first part, please see this post.

Also: note that the source code these example programs can be downloaded from downloaded from the public Github repository here

With the advent of modern high resolution graphical mode screens and GUI-based operating systems such as Microsoft Windows, it is easy to forget that personal computers primarily ran in something called text mode in the early days.

To understand text mode, simply imagine a computer screen that consists only of letters and numbers, and a few specialized line-drawing shapes primarily for drawing boxes on the screen. Text mode can be contrasted with Graphics mode, in which the screen consists of millions of individually colored pixels.

Remember when computer screens looked like this:

Image retrieved from:

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< coming soon >

{ let's us get at video memory easily }
var video : array[0..4000] of char absolute $B800:0000;
var attr  : array[0..4000] of byte absolute $B800:0000;