Pseudographic Resolution
By taking advantage of half blocks characters 220 (DCh) ▄ (bottom half) or 223 (DFh) ▀ (upper half) in the code page 437 (adapter's native) character set, one can effectively double the vertical resolution (from 80×25 to 80×50 in the default text mode).
Enhanced Graphics Adapter (EGA) and better adapters natively support text modes beyond 80×25 character cells: 80×43 (EGA), 80×50 (Video Graphics Array, VGA), 132×50 and 132×60 (VESA compatible Super VGA), etc., increasing the simulated graphic resolution available, doubled again through the half block characters.
Also, by tweaking the display's hardware, higher resolutions can be achieved. For example, a tweak mode can be set even in the original IBM Color Graphics Adapter (CGA) to give an extra, non-standard 160×100 pixels, 16-color graphic mode.
Custom graphics and effects can also be achieved by customizing the character set (with the EGA and better adapters) on a per-pixel basis. Halving the available colors from 16 to 8, up to two customized character sets can be used simultaneously on screen with most Super VGA graphic cards, blurring the border between pure text modes and true graphic modes.
Read more about this topic: Text Mode Demos
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