- 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.