This was a technique
used in creating graphics on the Commodore 64
. Each character is created by an 8x8 pixel bitmap
and to poke
a series of machine language data into the area of memory which represented text characters with a new bitmap. The new bitmap would be displayed when the character was typed.
This created faster screen flipping and costed less memory when creating games since it was easier to replace a screen of characters that it was to replace one of an entire bitmap. Combined with sprites, this also made backgrounds independent from the action but allowed for sprite collisions with text.