One of the earliest computer games was a 1952 tic-tac-toe simulation
Long before arcade games or home consoles existed, British computer scientist Alexander S. Douglas developed OXO in 1952 as part of his PhD thesis on human-computer interaction at the University of Cambridge. Running on the room-sized EDSAC computer, OXO allowed a human player to play tic-tac-toe against an artificial opponent, outputting graphics on a 35-by-16 dot cathode-ray tube screen.
An Academic Experiment in Interaction
In 1952, Alexander S. Douglas, a doctoral candidate at the University of Cambridge, set out to explore how human beings could interact directly with digital computers. At the time, computing machines were predominantly treated as automated calculators, designed to crunch large mathematical tables or process scientific equations in batches. Direct, turn-by-turn communication between a person and a machine in real time was largely untried territory.
To investigate this relationship, Douglas created a program called OXO, an electronic version of the traditional game of tic-tac-toe, also known as noughts and crosses. Developed as a practical demonstration for his PhD dissertation on human-computer interaction, OXO allowed a human user to play a full game against an artificial opponent programmed into the computer's memory. Rather than simply printing results onto paper tape after a batch run, the machine responded interactively to the player's choices.
Douglas was not setting out to launch an entertainment industry. The game was constructed purely as an experimental tool to observe and evaluate how users perceived and responded to machine decisions. Despite its humble academic origins, OXO stands today as one of the most critical milestones in the history of software and digital graphics.
The EDSAC Architecture
OXO was programmed for the Electronic Delay Storage Automatic Calculator, commonly known as EDSAC. Built at the University of Cambridge's Mathematical Laboratory under the direction of Maurice Wilkes, EDSAC began operations in 1949 and was one of the world's earliest stored-program electronic computers. It occupied an entire room, utilizing thousands of vacuum tubes and mercury delay lines to store and process instructions in binary form.
One of EDSAC's distinctive features was a small cathode-ray tube (CRT) monitor. This display was not originally installed to serve as an entertainment screen; its primary engineering purpose was to allow laboratory technicians to visually inspect the contents of the computer's memory registers and verify that data was circulating correctly through the delay lines. Douglas realized that this diagnostic display could be repurposed to show visual information directly to a human user.
Programming EDSAC required entering instructions on punched paper tape. Memory was extremely limited by modern standards, consisting of just over a thousand short words of storage. Douglas had to construct the entire game logic, board state evaluation, and visual rendering routines within these strict hardware constraints, making efficient code design essential to the program's success.
Mechanics of Gameplay and Display
To make player input intuitive, Douglas connected a standard rotary telephone dial directly to EDSAC. The tic-tac-toe board was conceived as a numbered three-by-three grid, with squares mapped to digits one through nine. When a player dialed a number, the electrical pulses were decoded by the computer, which immediately marked the corresponding square on the internal board representation.
The computer's visual output appeared on the cathode-ray tube as a 35-by-16 dot matrix. Using this low-resolution dot grid, the software dynamically drew the lines of the board and rendered the letters 'O' and 'X' in their respective positions. After the player registered a move via the rotary dial, EDSAC calculated its counter-move, updated its internal memory, and refreshed the dot pattern on the screen to show the new state of the match.
EDSAC's artificial intelligence was programmed with a deterministic strategy to play a perfect game. It evaluated the board state according to optimal tic-tac-toe algorithms, ensuring that it never made an error. A human player could achieve at best a draw through flawless play; any tactical mistake by the human resulted in a swift victory for the machine.
Early Contemporaries and the Video Game Definition
Historians frequently debate which creation deserves the title of the world's first video game, because several early computing demonstrations emerged around the same period. In 1950, a custom-built machine called Bertie the Brain played tic-tac-toe using illuminated light bulbs, and in 1951, the Ferranti Nimrod computer played the mathematical game of Nim using an array of lamps. In 1952, Christopher Strachey wrote a draughts program for the Ferranti Mark 1 computer.
Where OXO stands apart from machines like Bertie the Brain and Nimrod is its use of a general-purpose, stored-program computer and an electronic cathode-ray tube display to render a dynamic graphical image. Unlike dedicated game machines built with hardwired circuitry and light-bulb panels, OXO ran as software loaded into a general-purpose system's memory.
Some strict historical definitions reserve the term 'video game' for systems that output a raster-scan video signal to a television monitor or feature simulated real-time motion, which OXO lacked due to its static, turn-based display. Nevertheless, OXO is widely recognized by historians as the earliest known digital game to produce interactive graphics on an electronic CRT screen.
Preservation, Obsolescence, and Historical Impact
Because EDSAC was an expensive, specialized research tool restricted to academic and scientific work at Cambridge, OXO was never released to the public or distributed outside the laboratory. Only people with authorized physical access to the Cambridge Mathematical Laboratory were ever able to sit at the console and play the game against the machine.
EDSAC remained in active academic service until it was formally shut down and dismantled in the late 1950s to make way for EDSAC 2. Because the original physical machine no longer exists, OXO cannot be run on its original hardware. However, the original programming logic and system specifications survived in laboratory documentation.
In later decades, computer historians and software preservationists reconstructed EDSAC's instruction set in software. Modern EDSAC simulators accurately recreate the timing, logic, and CRT output of Douglas's 1952 code, allowing modern audiences to experience the exact visual interface and gameplay that marked the dawn of human-computer gaming.
Key takeaways
•Alexander S. Douglas developed OXO in 1952 at the University of Cambridge as a practical demonstration of human-computer interaction for his PhD thesis.
•The game ran on the room-sized EDSAC computer and used a repurposed diagnostic cathode-ray tube screen to render a 35-by-16 dot matrix display.
•Players interacted with the program using a rotary telephone dial to select board positions, facing an artificial opponent programmed to play optimal tic-tac-toe.
•OXO is widely regarded as one of the earliest computer games and the first to display dynamic graphics on an electronic CRT monitor.