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.

Brief History

	The ABC in 1941-2. ASMs are partially visible behind leg at lower right.

In the late 1930s, John Vincent Atanasoff, an associate professor in mathematics and physics at Iowa State University, was working on problems requiring the solution of large systems of linear equations. As with other researchers, both earlier and contemporary, whose interests had bumped up against the practical limitations of manual calculation and the then-available aids to calculation, his thoughts turned to automated methods. After considering some possibilities, such as ganging together mechanical adding machines, Atanasoff conceived of a machine utilising electronics technology functioning in a binary mode.

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.

Contents

• Proof-of-Concept Machine (with simulation)
• Architecture of the ABC
• The Add-Subtract Mechanism of the ABC
• An ABC Operator's Manual
  • 1. Principles of the Solution Process
  • 2. Stages of Operation
  • 3. Equipment and Controls
  • 4. Flowchart of Operation
• An Online Simulation of the ABC
  • Simulation OttoScript Program

References and Links

The following book contains a great deal of historical and technical information about the ABC:

• "The First Electronic Computer", by Alice R. Burks and Arthur W. Burks, University of Michigan Press, 1988

• "Computing Machine for the Solution of Large Systems of Linear Algebraic Equations", by John V. Atanasoff, 1940
  (Published in the "Origins of Digital Computers", Randell, 1973)

• John V. Atanasoff Archive
• ABC Reconstruction Project of the Scalable Computing Laboratory, Ames Lab, Iowa, USA