The Digi-Comp I was a functioning, mechanical digital computer sold in kit form. It was originally manufactured from polystyrene parts by E.S.R., Inc. starting in 1963 and sold as an educational toy for US$4.99 (equivalent to US$48 in 2022).^[1]

The Digi-Comp I has been referred to as the first home computer.^[2]

A successor, the Digi-Comp II, was not programmable, but in effect a visible calculator. A two-level Masonite platform with guides served as the medium for a supply of marbles that rolled down an inclined plane, moving plastic cams as they fell.^[3]

Operation

The Digi-Comp I contained three mechanical flip-flops, providing an ability to connect them together in a programmable way using thin vertical wires that were either pushed, or blocked from moving, by a number of cylindrical pegs. The whole arrangement was "clocked" by moving a lever back and forth. Different configurations of these cylinders caused the Digi-Comp to compute different Boolean logic operations. With a three binary digit (3-bit) readout of the state of the flip-flops, it could be programmed to demonstrate binary logic, to perform various operations such as addition and subtraction, and to play some simple logic games such as Nim.^[4]

Although promotional materials described it as an "actual working digital computer," the device is more accurately described as a finite-state machine, one of the underpinning concepts used to build computers.

Reproductions

Starting in 2005, Minds-On Toys has made available the Digi-Comp I version 2.0 as a relatively inexpensive binder's board version of the original Digi-Comp, albeit with a much enhanced instruction manual.^[5]