Redefining ‘A’ in VGA Mode 03h

This story was originally published on HackerNoon at: https://hackernoon.com/redefining-a-in-vga-mode-03h.
Change the appearance of an ASCII character - in this case 'A' - by redefining its pixel data.
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In the 8086-era DOS environment, text display typically relied on the BIOS and the graphics adapter’s built-in character generator. The fonts were firmly tied to specific text modes implemented by adapters such as CGA, EGA, or VGA. One of the most common modes was text mode 03h, which presented an 80×25 text grid. This time, we’ll change the appearance of an ASCII character - in this case 'A' - by redefining its pixel data.