The opriginal Adventure (Crowther and Woods) consisted only of text, which the VCS wasn’t terribly adept at displaying, and its parser accepted typed commands from a keyboard, which the VCS didn’t possess; the latter’s input mechanism was limited to a joystick with a single fire button. The program code and data for Adventure took more than 100 K of storage space on the big DEC PDP-10 computer on which it ran. The Atari VCS, on the other hand, used cartridge-housed ROM chips capable of storing a program of a maximum of 4 K of code and data, and boasted just 128 bytes — yes, bytes — of memory for the volatile storage of in-game state. In contrast to a machine like the PDP-10 — or for that matter to just about any other extant machine — the VCS was shockingly primitive to program. There not being space enough to store the state of the screen in those 128 bytes, the programmer had to manually control the electron beam which swept left to right and top to bottom sixty times per second behind the television screen, telling it where it should spray its blotches of primary colors. Every other function of a game’s code had to be subsidiary to this one, to be carried out during those instants when the beam was making its way back to the left side of the screen to start a new line, or — the most precious period of all — as it moved from the end of one round of painting at the bottom right of the screen back to the top left to start another.
