In about 1980 or so i got a TI 99/4A (I was about 12) and figured out how to do high-res graphics within the limitations of what was essentially a text-only machine. By redefining the 8x8 character blocks you could manipulate individual pixels. The main limitation was that when you redefined one character, every one of that number on the screen would change, and I think there were 256 available...still though, i managed to create programs that could graph a line and draw circles, and something that was similar to Missile Command. it was also interesting in that if, for example, you filled the whole screen with a single character and then redefined it in a loop or something, the whole screen would instantly update creating mesmerizing effects. You had to be creative in those days.