 1937
 George Stibitz (c.1910) of Bell Labs, New York City, constructs a
demonstration 1bit binary adder using relays.
 1937
 Alan M. Turing (19121954), 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.
 1938
 Claude E. Shannon (c.1918) publishes a paper on the implementation of
symbolic logic using relays.
 1938
 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 16bit adder. This
is the first machine to calculate using vacuum tubes.
 c.1940
 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 specialpurpose
calculator for their needs, actually builds them the "Z3", which
is the first operational programcontrolled calculator, and has 64 22bit
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 35 seconds.
