Digi-Comp I

Manufactured By: E.S.R., Inc.

Release Date: 1963

The Digi-Comp I was an amazing mechanical computer. At the core of the Digi-Comp I were three horizontal sliders or “flip-flops” that could be in one of two positions “0” or “1”. There are 6 control rods on both the front and back of the unit made from stiff piano wire. They are labeled from 1 to 6 left to right when facing the front. The rods on the front are called "logic rods" and on the back "clock rods". Each logic rod is "associated" with the clock rod that is directly behind it. Clock rods in the odd positions (1,3,5) can perform a reset operation moving a flip flop from the 1 to the 0 position. Even numbered clock rods can perform set operations moving a flip flop from the 0 to the 1 position.

You program the Digi-Comp I by pushing short "logic" tubes onto tabs in the front of the unit, and longer tubes onto "clock" tabs on the back. The pictures here show an original Digi-Comp I "programmed" to count from zero to seven.

The clocking mechanism for the original Digi-Comp I is ingenious. When you cycle the clock by pushing the lever on the right in towards the machine and then pulling it out, any logic rod that is not blocked by a logic tube will cause it's corresponding clock rod to swing to the right for odd numbers rods (reset) or to the left for even numbered rods (set). The swinging action will cause flip flops to move provided that a clock tube has been positioned beside the clock rod. For any logic rod that is blocked by a logic tube, the corresponding clock rod will be inactive for that cycle.

As the flip flops shift back and forth for each clock cycle, and the pattern of logic tubes changes, different clock rods become active for the next cycle. Each cycle is thus one step of the "program" being executed. Pretty cool.

To fully appreciate the mechanical genius of a Digi-Comp I you really need to see one in action.