These pages present a technical description of the architecture and operation of the Atanasoff-Berry Computer, leading up to a graphical-interface simulation of the ABC which can be run in one's browser.
Atanasoff hired a graduate student, Clifford Berry, and they constructed a small proof-of-concept machine in 1939. They then proceeded to construct the Atanasoff-Berry Computer (ABC) in 1940-41. The machine was completed and functional except for a small, but problematic, error rate during the reading and writing of base-2 cards. Atanasoff and Berry left Iowa State University for other tasks as World War II progressed, the problem was not resolved, and the machine saw little practical use.
Using electronics in the binary mode was quite a departure from the practice of the time, which tended to stay in the continuous (analog) mode. While some use of electronics had been made previously for calculating in the analog mode (electronic implementations of harmonic analyers), and simple digital electronic counters were existent (based on the Eccles-Jordan trigger circuit - now known as the flip-flop), the ABC was the first application of electronics to calculation using discrete, or digital, principles. In this regard the Add-Subtract Mechanism (ASM) of the ABC is perhaps it's most historically significant aspect.
The functional design of the ABC was prescient of modern processor design, with separated memory, arithmetic, and control sections. Missing was the stored-program concept, which would arise a few years later (1944-48).
Another pioneering development of the ABC was the use of capacitors with periodic refreshing of their charge for memory. This is the same principle employed in modern dynamic RAM memory chips.
The following book contains a great deal of historical and technical information about the ABC: