one to stay productive. Robinett was finishing his work on Slot Racers when he was given an opportunity to visit the Stanford Artificial Intelligence Laboratory by Julius Smith, one of several friends he was sharing a house with. There, he was introduced to the 1977 version of the computer text game Colossal Cave Adventure, created by Will Crowther and modified by Don Woods. After playing the game for several hours, he was inspired to create a graphical version. Robinett began designing his graphics-based game on a Hewlett-Packard 1611A microprocessor computer around May to June 1978. He was soon aware that memory use was critical because Atari 2600 cartridge ROMs have only 4096 bytes (4 KB), and the system has 128 bytes of RAM for program variables. In contrast, Colossal Cave Adventure uses hundreds of kilobytes of memory on a large computer. The final game uses nearly all of the available memory (including 5% of the cartridge storage for Robinett's Easter egg), with 15 unused bytes from the ROM capacity. Robinett credits Ken Thompson, his professor at University of California, Berkeley, with teaching him the skills needed to use the limited memory efficiently. Thompson had required his students to learn the C programming language that he had invented at AT&T, and Robinett carried C techniques into assembly language. Robinett first identified ways to translate the elements of Colossal Cave Adventure into simple, easily recognizable graphics that the player interacts with directly, replacing text-based commands with joystick controls. Due to the system's low resolution pixels, Robinett noted the dragons look more like ducks. Robinett developed workarounds for various technical limitations of the Atari 2600, which has only one playfield and five memory-mapped registers available to represent moving objects. Only two of these registers are capable of representing more complex sprites, so he used those for objects and creatures within the game. He used the register originally designated for the ball in games such as Pong to represent the player's avatar. Finally, he used the registers assigned for missiles, such as the bullets in Combat, for additional walls in the playing field to be able to represent different rooms within the game with the same playfield. Another hardware limitation forces the left and right sides of nearly every screen to be mirrored, which fostered the creation of the game's confusing mazes. The exceptions include two screens in the Black Castle catacombs and two