The Digi-Comp II was a toy computer manufactured by E.S.R., Inc. that used marbles rolling down a ramp to perform basic calculations. 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 went. The plastic cams played the part of flip-flops

Flip-flop (electronics)

In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic...

 in an electronic computer - as a marble passed one of the cams, it would flip the cam around - in one position, the cam would allow the marble to pass in one direction, in the other position, it would cause the marble to drop through a hole and roll to the bottom of the ramp.

The Digi-Comp II followed on from the Digi-Comp I

Digi-Comp I

The Digi-Comp I is a functioning, mechanical digital computer sold in kit form. It was originally manufactured from polystyrene parts by E.S.R., Inc...

, which used an assortment of plastic slides, tubes, and bent metal wires to perform simple calculations.

External links

• The Old Computer Museum - Collection of old analog, digital and mechanical computers.
• Extra-large recreation, video showing the multiplication of 13 x 3 on a scaled-up re-creation.