It was written on the Electronic Delay Storage Automatic Calculator (EDSAC). EDSAC was one of the first stored-program computers, with memory that could be read from or written to, and had three small cathode ray tube screens to display the state of the memory; Douglas re-purposed one screen to demonstrate portraying other information to the user, such as the state of a noughts and crosses game. After the game served its purpose, it was discarded on the original hardware but later successfully reconstructed.