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Diehl Combitron Desktop Electronic Calculator

Diehl Combitron S
(Note: Unit pictured is missing the clear plastic piece that provides an edge for tearing off printed paper tape)
Image Courtesy Martin Willemsen

The Combitron was the first all-electronic calculator from famous German mechanical and electromechanical calculator manufacturer Diehl Calclating Machine Company. Diehl was famous for beautifully-designed mechanical and electromechanical machines, built in the tradition of fine German craftsmanship.

The Combitron, introduced in late 1966, beneitted from Diehl's mechanical prowess as far as the mechanical aspects of the machine were concerned, but the electronics were another story.

The design of the electronic logic of the machine was contracted out to an independent engineer in the US, specifically Southern California. That contractor was Stanley Frankel, a brilliant electronic engineer who previously worked on the Top Secret Manhattan Project, the government project to develop the Atomic Bomb. Frankel was educated as a nuclear physicist, but during his time on the Manhattan Project, he became enthralled with calculating machines, especially machines that could compute electronically. He was responsible for acquring IBM's earliest programmable punched card calculating machines for the Manhattan Project and developing programs for these primitive machines to speed the extraordinarily complex calculations for modeling the critical atomic fission reactions during the first few moments of an atomic detonation. These calculations were used to prove that the bomb designs were going to work, and were of major consequence in assuring that the US developed a successful atomic weapon before the Nazis.

After his work on the Manhattan Project, and prior to the calculator design work Frankel did for Diehl, he had worked on the design of a number of small computer systems, and also had developed the design of a pair of first-generation transistorized electronic calculators, the Smith Corona/Marchant (SCM) Cogito 240 and Cogito 240SR.

The design for the Diehl Combitron grew from a prototype machine that Frankel had built in his home workshop. This prototype he called NIC-NAC. NIC-NAC was based on the fairly new concept of a microcoded architecture, utilizing magnetostrictive delay lines for storing both the microcode and the working registers. A pair of telephone dials were used to hand-load the microcode into the microcode delay line, and an oscilloscope was used to observe the input and results of calculations. Frankel shopped his design around, trying to find a calculator company he could sell the design to. Through his earlier relationship with SCM, Diehl found out about it, and a deal was made for Frankel to go to Germany and develop Diehl's first electronic calculator based on the NIC-NAC design, which became the Combitron.

The Combitron, and the later Combitron-S (which added more more program and memory storage, as well as the ability to interace to external devices such as a punched paper tape reader and punch), were learn-mode programmable, and had sophisticated decision-making and branching capabilities. The machines offered the usual four math functions, along with one-key automatic square root calculations. Both machines utilized a built-in digit wheel per column line-at-a-time printer for output. The microcode is loaded from a punched stainless steel tape at power-on time, meaning that it takes a short time to "boot up" when first powered on. These machines utilize fully-transistorized logic with amazingly few transistors due to their highly efficient design.

The machine pictured is a Combitron S model. The museum has recently acquired a Combitron S that is currently undergoing restoration and documentation for an upcoming exhibit. At this time, the museum is looking for a Combitron model to compliment the Combitron S. The machines are visually identical other than a small peripheral connector on the left side of the machine, toward the front, on the Combitron S.