Digi-Comp II

The Digi-Comp II was a toy computer invented by John "Jack" Thomas Godfrey (1924–2009)[1][2] in 1965[1] and manufactured by E.S.R., Inc. in the late 1960s, that used 1⁄2 inch (12.5 mm) marbles rolling down a ramp to perform basic calculations.

product line that used an assortment of plastic slides, tubes, and bent metal wires to solve simple logic problems.

A natural abstraction is a directed acyclic graph (DAG) in which each internal vertex has an out-degree of 2, representing a toggle cam that routes balls to one of two other vertices.

He also showed that the variant of the problem in which the number of balls is encoded in binary, allowing the machine to run for an exponentially longer time, is still in the P class of complexity.

The Stata Center at the Massachusetts Institute of Technology displays one copy of the giant version for hands-on operation by visitors.