A Chronology of Digital Computing Machines (to 1952)

A Chronology...The Jargon FileComputer Dictionary
George Stibitz (c.1910-) of Bell Labs, New York City, constructs a demonstration 1-bit binary adder using relays.
Alan M. Turing (1912-1954), of Cambridge University, England, publishes a paper on "computable numbers", which solves a mathematical problem by considering as a mathematical device the theoretical simplified computer that came to be called a Turing machine.
Claude E. Shannon (c.1918-) publishes a paper on the implementation of symbolic logic using relays.
Konrad Zuse (1910-) of Berlin completes a prototype mechanical programmable calculator, later called the "Z1". Its memory used sliding metal parts and stored about 1000 bits. The arithmetic unit was unreliable.
Oct 1939
Stibitz and Samuel Williams complete the "Model I", a calculator using relay logic. It is controlled through modified teletypes and these can be connected through phone lines. Later machines in the series also have some programmability.
c.Oct 1939
John V. Atanasoff (1903-) and Clifford Berry, of Iowa State College, Ames, Iowa, complete a prototype 16-bit adder. This is the first machine to calculate using vacuum tubes.
Zuse completes the "Z2", keeping the mechanical memory but using relay logic. He can't interest anyone in funding him.
Dec 1941
Zuse, having promised to a research institute a special-purpose calculator for their needs, actually builds them the "Z3", which is the first operational program-controlled calculator, and has 64 22-bit words of memory. However, its programmability doesn't include a conditional- jump instruction; Zuse never had that idea. The program is on punched tape. The machine includes 2600 relays, and a multiplication takes 3-5 seconds.
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