Notably, Spacewar! is not a vector game, rather, it's X/Y point plotting. Meaning, each point is plotted individually on a high-res 1024 x 1024 screen and has to be refreshed regularly by the program in order to stay visible. (This is also the major bottleneck of the game, in terms of timing, and only became viable thanks to Dan Edwards' just-in-time compiler for the spaceship outlines.)

In other words, the burden of maintaining the display is entirely on the program and the instructions for this have to be recomputed for each frame (as memory for storing any screen related information was horribly expensive and thus unfeasible.) Which makes this even more remarkable.