Atanasoff-Berry Computer

The Atanasoff–Berry Computer (ABC) was the first electronic digital computing device. Conceived in 1937, the machine was capable of solving up to 29 simultaneous linear equations and was successfully tested, though its input/output mechanism was still unreliable in 1942 when its inventors left Iowa State College for World War II assignments. The ABC pioneered important elements of modern computing, including binary arithmetic and electronic switching elements, but its special-purpose nature and lack of a changeable, stored program distinguish it from modern computers.
See more at Wikipedia.org...

<computer> (ABC) An early design for a binary calculator, one of the predecessors of the digital computer. The ABC was partially constructed between 1937 and 1942 by Dr. John Vincent Atanasoff and Clifford Berry at Iowa State College. As well as binary arithmetic, it incorporated regenerative memory, parallel processing, and separation of memory and computing functions.
The electronic parts were mounted on a rotating drum, making it hybrid electronic/electromechanical. It was designed to handle only a single type of mathematical problem and was not automated. The results of a single calculation cycle had to be retrieved by a human operator, and fed back into the machine with all new instructions, to perform complex operations. It lacked any serious form of logical control or conditional statements.
Atanasoff's patent application was denied because he never have a completed, working product. Ideas from the ABC were used in the design of ENIAC (1943-1946).
http://www.cs.iastate.edu/jva/jva-archive.shtml.
(2003-09-28)