Mechanical computer

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Hamann Manus R

A mechanical computer is built from mechanical components such as levers and gears, rather than electronic components. The most common examples are adding machines and mechanical counters, which use the turning of gears to increment output displays. More complex examples could carry out multiplication and division—Friden used a moving head which paused at each column—and even differential analysis. One model[ which? ] sold in the 1960s calculated square roots.


Mechanical computers can be either analog, using smooth mechanisms such as curved plates or slide rules for computations; or digital, which use gears.

Mechanical computers reached their zenith during World War II, when they formed the basis of complex bombsights including the Norden, as well as the similar devices for ship computations such as the US Torpedo Data Computer or British Admiralty Fire Control Table. Noteworthy are mechanical flight instruments for early spacecraft, which provided their computed output not in the form of digits, but through the displacements of indicator surfaces. From Yuri Gagarin's first manned spaceflight until 2002, every manned Soviet and Russian spacecraft Vostok, Voskhod and Soyuz was equipped with a Globus instrument showing the apparent movement of the Earth under the spacecraft through the displacement of a miniature terrestrial globe, plus latitude and longitude indicators.

Mechanical computers continued to be used into the 1960s, but were quickly replaced by electronic calculators, which—with cathode-ray tube output—emerged in the mid-1960s. The evolution culminated in the 1970s with the introduction of inexpensive handheld electronic calculators. The use of mechanical computers declined in the 1970s and was rare by the 1980s.

In 2016, NASA announced that its Automaton Rover for Extreme Environments program would use a mechanical computer to operate in the harsh environmental conditions found on Venus. [1]


Curta Calculator Curta - National Museum of Computing.jpg
Curta Calculator

Electro-mechanical computers

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Harwell Dekatron

Early electrically powered computers constructed from switches and relay logic rather than vacuum tubes (thermionic valves) or transistors (from which later electronic computers were constructed) are classified as electro-mechanical computers. These varied greatly in design and capabilities, with some later units capable of floating point arithmetic. Some relay-based computers remained in service after the development of vacuum-tube computers, where their slower speed was compensated for by good reliability. Some models were built as duplicate processors to detect errors, or could detect errors and retry the instruction. A few models were sold commercially with multiple units produced, but many designs were experimental one-off productions.

Automatic Relay Computer UK 1948 The Booths, experimental [14]
ARRA Netherlands 1952experimental
BARK Sweden 1952experimental
FACOM-100 Japan 1954 Fujitsu commercial [15]
FACOM-128 Japan1956commercial [16]
Harwell computer UK1951later known as WITCH
Harvard Mark I United States 1944(IBM Automatic Sequence Controlled Calculator)
Harvard Mark II USA1947
Imperial College Computing Engine (ICCE)UK1951Electro-mechanical [17] [18] [19] [20]
Office of Naval Research ONR Relay ComputerUSA19496-bit, drum storage, but electro-mechanical relay ALU based on Atlas, formerly Navy cryptology computer ABEL [21] [22] [23] [24]
OPREMA East Germany 1955Commercial use at Zeiss Optical in Jena [25]
RVM-1 Soviet Union 1957 Alexander Kronrod [26]
SAPO Czechoslovakia 1957
Simon USA1950Hobbyist logic demonstrator magazine article
Z2 Germany 1940 Konrad Zuse
Z3 Germany1941Zuse
Z4 Germany1945Zuse
Z5 Germany1953Zuse
Z11 Germany1955Zuse, commercial
Bell Labs Model IUSA1940 George Stibitz, "Complex Number Calculator",450 relays and cross bar switches, demonstrated remote access 1940, used until 1948 [27]
Bell Labs Model IIUSA1943"Relay Interpolator", used for wartime work, shut down 1962 [27]
Bell Labs Model IIIUSA1944"Ballistic Computer", used until 1949 [27]
Bell Labs Model IVUSA1945Navy "Mark 22 Error Detector", used until 1961 [27]
Bell Labs Model V USA1946, 1947Two units delivered, general purpose, built in trig functions, floating point [27]
Bell Labs Model VI USA1949General purpose, simplified Model V with several enhancements
Unnamed cryptanalysis multiplierUK1937Turing [28] [29]
Relay ComputerUSA2006Harry Porter's Relay Computer, demonstrator/hobby, but integrated circuit memory. [30]

See also

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The Digi-Comp II was a toy computer invented by John "Jack" Thomas Godfrey (1924–2009) in 1965 and manufactured by E.S.R., Inc. in the late 1960s that used 12 inch (12.5 mm) 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 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 platform measures 14 by 28.5 inches.

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