Bushnell and Dabney began to design custom hardware to run the game's functions, and in January 1971 they had a dot moving on a screen. Bushnell drafted an letter dated January 26 to order six Data Nova computers. He did not send the letter, however; near the end of January, he tried to run their program on a local Nova, and found that they had miscalculated the requirements. Even with several of the functions removed from the program, now named "Cosmic Combat", the computer still could not run multiple instances at once. Although upset, Bushnell soon realized that it would be possible to entirely replace the Nova with custom hardware, and that the cost to build the whole game's computing systems would be much lower. As a result, they would not need to have multiple instances of the game running on the same machine in order to be profitable. On the other hand, the custom hardware was not as powerful as the more expensive Nova computer, which meant that the pair needed to make gameplay modifications. "Spacewar!" was a two-player game featuring dogfights around the gravitational field of a central star; neither of these features could be run on the dedicated circuits the pair were making, so the game was cut down to a single-player game wherein the player would fight against two computer-controlled spaceships in open space.