Further information: Honeywell v. Sperry Rand Atanasoff first met John Mauchly at the December meeting of the American Association for the Advancement of Science in Philadelphia, where Mauchly was demonstrating his "harmonic analyzer", an analog calculator for analysis of weather data. Atanasoff told Mauchly about his new digital device and invited him to see it. Mauchly visited Atanasoff multiple times in Washington during and discussed computing theories, but did not mention that he was working on a computer project himself until early

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The ABC innovations included electronic computation, binary arithmetic, parallel processing , regenerative capacitor memory , and a separation of memory and computing functions. A grant application to build a proof of concept prototype was submitted in March to the Agronomy department which was also interested in speeding up computation for economic and research analysis.

The initial funds were released in September, and the tube prototype was first demonstrated in October A December demonstration prompted a grant for construction of the full-scale machine.

A January 15, story in the Des Moines Register announced the ABC as "an electrical computing machine" with more than vacuum tubes that would "compute complicated algebraic equations" but gave no precise technical description of the computer.

It contained approximately 1-mile 1. Nor did it implement the stored program architecture that made practical fully general-purpose, reprogrammable computers. Add-subtract module reconstructed from Atanasoff—Berry Computer The machine was, however, the first to implement three critical ideas that are still part of every modern computer: Using binary digits to represent all numbers and data Performing all calculations using electronics rather than wheels, ratchets, or mechanical switches Organizing a system in which computation and memory are separated.

The memory of the Atanasoff—Berry Computer was a system called regenerative capacitor memory, which consisted of a pair of drums, each containing capacitors that rotated on a common shaft once per second. Data was represented as bit binary fixed-point numbers. The electronics of the memory and arithmetic units could store and operate on 60 such numbers at a time bits. The arithmetic logic functions were fully electronic, implemented with vacuum tubes.

The family of logic gates ranged from inverters to two and three input gates. The input and output levels and operating voltages were compatible between the different gates. Each gate consisted of one inverting vacuum tube amplifier, preceded by a resistor divider input network that defined the logical function. The control logic functions, which only needed to operate once per drum rotation and therefore did not require electronic speed, were electromechanical, implemented with relays.

Although the Atanasoff—Berry Computer was an important step up from earlier calculating machines, it was not able to run entirely automatically through an entire problem.

An operator was needed to operate the control switches to set up its functions, much like the electro-mechanical calculators and unit record equipment of the time.

Selection of the operation to be performed, reading, writing, converting to or from binary to decimal, or reducing a set of equations was made by front panel switches and in some cases jumpers. There were two forms of input and output: primary user input and output and an intermediate results output and input.

The intermediate results storage allowed operation on problems too large to be handled entirely within the electronic memory.

The largest problem that could be solved without the use of the intermediate output and input was two simultaneous equations , a trivial problem.

Intermediate results were binary, written onto paper sheets by electrostatically modifying the resistance at locations to represent 30 of the bit numbers one equation.

Each sheet could be written or read in one second. In retrospect a solution could have been to add a parity bit to each number as written. This problem was not solved by the time Atanasoff left the university for war-related work. Primary user input was decimal, via standard IBM column punched cards and output was decimal, via a front panel display. Function[ edit ] The ABC was designed for a specific purpose, the solution of systems of simultaneous linear equations.

It could handle systems with up to twenty-nine equations, a difficult problem for the time. Problems of this scale were becoming common in physics, the department in which John Atanasoff worked. The machine could be fed two linear equations with up to twenty-nine variables and a constant term and eliminate one of the variables. This process would be repeated manually for each of the equations, which would result in a system of equations with one fewer variable.

Then the whole process would be repeated to eliminate another variable. George W. He submitted many of these problems to Atanasoff. The ABC was quite modest technology, and it was not fully implemented. At the very least we can infer that Mauchly saw the potential significance of the ABC and that this may have led him to propose a similar, electronic solution.

District Judge Earl R. Judge Larson explicitly stated, Eckert and Mauchly did not themselves first invent the automatic electronic digital computer, but instead derived that subject matter from one Dr. John Vincent Atanasoff. Herman Goldstine , one of the original developers of ENIAC wrote: Atanasoff contemplated storing the coefficients of an equation in capacitors located on the periphery of a cylinder. This machine was, it should be emphasized, probably the first use of vacuum tubes to do digital computation and was a special-purpose machine.

This machine never saw the light of day as a serious tool for computation since it was somewhat premature in its engineering conception and limited in its logical one. Nonetheless it must be viewed as a great pioneering effort. Perhaps its chief importance was to influence the thinking of another physicist who was much interested in the computational process, John W.

The discussion greatly influenced Mauchly and through him the entire history of electronic computers.

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## Atanasoff : forgotten father of the computer

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