Electro-mechanical Computers, contAt the same time as Zuse's, at least three separate efforts to use electronic circuitry to address the problem of computation were made by John Atanasoff at Iova State College, the Brittish Intelligence, and IBM.
The Atanasoff-Berry Computer, designed to solve a complex system of linear equations, was about fully operational by 1941. In the late 1930s IBM, working with punch-card tabulating equipment, begun work with Wallace Eckert of Columbia University to explore how their equipment could be used in various scientific applications. By 1941 IBM in collaboration with Eckert was designing an electronic multiplier which would greatly speed up the kinds of computations being employed by Eckert.
In contrary to these small-scale efforts British Intelligence's Colossus, a computer built at Bletchy Park by Alan Turing and his team in late 1943, was a large-scale electronic machine developed to decode secret messages, produced by the famous German code machine Enigma. To achieve this Colossus performed only logical as opposed to arithmetical operations.
None of these three specialized computers were designed to carry out general purpose computation. In early 1943 Howard Aiken and his team at Harward University, sponsored by IBM, completed their ASCC Mark I (Automatic Sequence-Controlled Calculator Mark I), an electro-mechanical programmable computer, most similar to Z3. Mark I was about. 17 m long, 3 m high and weighted almost 5 tons. It hold 23 digit numbers, with addition taking 0.3 seconds and multiplication 3 seconds.
Electronic ComputersThe first general purpose all-electronic computer, ENIAC (Electronic Numerator, Integrator, Analyzer, and Computer), invention of John W. Mauchly and J. Presper Eckert, was designed in 1943-1946 at the Moore School of Electrical Engineering of the University of Pennsylvania. Like Colossus, ENIAC was built with resources for research and development resulting from the war effort. ENIAC contained close to 18,000 vacuum tubes, occupied a room at 30 by 50 feet and weighted 30 tons. It performed additions and multiplications at the speed of 5000 respectively 360 in a second. ENIAC had to be manually wired to operate a particular program. Conditional branching was not part of ENIAC's original design and its only memory was 20 10-digit accumulators.
In January 1948 Wallace Eckert of IBM completed SSEC (Selective Sequence Electronic Calculator), a computer with 8 20-digit registers and 150 20-digit words of relay memory, and a program that was partly stored but also controlled by a plugboard. IBM considers it the first computer.