Someone Built a Working Four-Bit Computer Out of Cardboard and Marbles

Computers aren’t magic. Underneath your fingertips right now are wires and logic gates. Switches. A 1 becomes a 0; two 1s become a 1; a 1 and a 0 become a 0; a 1 and a 0 become a 1; two 0s become a 1. Simply, different sorts of gates take on/off signals or pairs of on/off signals and emit more on/off signals in response. The most basic idea of logical computation and binary arithmetic goes back to Leibniz in 1705.

You don’t need electricity to implement binary operations, though it certainly helps. All you really need is a way to ensure that somehow the binary inputs to the gates below (the As and Bs) result in the correct binary output (the X). When you have that, you have the materials for a computer and can theoretically do anything.

For those that remain doubtful, Github user lapinozz is here to the rescue with a 4-bit computer constructed out of cardboard and marbles. It’s pretty amazing:

half-adders and full-adders lapinozz writes