The Digi-Comp II is a classic mechanical computer originally invented by John "Jack" Godfrey in 1965. Instead of electricity, it uses gravity and steel marbles (or balls) rolling down an inclined ramp to perform basic binary arithmetic and logic operations like counting, addition, subtraction, multiplication, and division.

How It Works

The device serves as a physical, educational model of an Arithmetic Logic Unit (ALU). As marbles roll down the board, they interact with mechanical gates and flip-flops. 

• State Changes: Each marble represents an electronic pulse. The balls trigger switches and flip-flops to change state (e.g., redirecting the ball's path left or right), representing binary values of 1 or 0.

• Registers: The machine includes memory and accumulator registers to hold data and build up to complex functions. For example, multiplication is accomplished via looped mechanical addition.

Our Digi-Comp II was donated by:  William Delnicki - June 23, 2026