The Atanasoff-Berry Computer (ABC)

John Atanasoff was born in 1903 in New York State. He first became interested in mathematics when, while he was still a boy, his father purchased a Dietzgen slide rule, similar to the one shown above. He became fascinated with the device, and began to analyze the mathematics behind it. He soon taught himself algebra with the help of his mother.3

Being completed by 1942, the Atanasoff-Berry Computer (ABC) was the first electronic computer. It was designed and built by John Vincent Atanasoff and his assistant, Clifford E. Berry. At the time, Atanasoff was teaching Physics, and Berry was a graduate student in Electrical Engineering. They worked on the computer from 1939 until 1942 when it was abandoned due to WWII. Although it still needed some work, it was completely functional.1 While it was smaller than other computers of the time period, it was also the first to use capacitors for storage, as in current RAM, and was capable of performing 30 simultaneous operations.2 Unfortunately, after being abandoned, it was neglected and eventually disassembled for parts. However, in 1994, a team from Iowa State University began to rebuild the computer, finishing it in 19972.

The ABC was a specific use computer, designed to solve systems of linear algebraic equations, and was capable of solving systems with up to 29 unknowns. Such math problems were very challenging and time consuming, and often encountered by scientists and engineers. At the time of construction, the 1930s and 1940s, the only device available to help with calculations were  desk calculators capable of simple operations, such as add, subtract, multiply, and divide.1 

The ideas behind the ABC were later used in the construction of the ENIAC, the world’s first general purpose computer.1 The methods and technology developed for the ABC made a huge impact on its successors and helped pave the way for electronic computing.

  1. 1.Last known picture of the original ABC

  2. 2.John Atanasoff in 1938

  3. 3.Clifford Berry, a electrical engineering graduate student who helped Atanasoff in constructing the ABC


The Atanasoff-Berry Computer (ABC)

After graduating from high school, he attended the University of Florida, where he received a degree for electrical engineering. He continued to get a MS in mathematics at Iowa State University, and a PhD in physics from the University of Wisconsin.1 During his work in getting a PhD, Atanasoff, like many others, was forced to complete long, complex systems of linear algebraic equations by hand. This was a long and arduous procedure, taking several hours to complete one system. Atanasoff states that

“Since an expert [human] computer takes about eight hours to solve a full set of eight equations in eight unknowns, k is about 1/64. To solve twenty equations in twenty unknowns should thus require 125 hours . . . The solution of general systems of linear equations with a number of unknowns greater than ten is not often attempted.”2

After receiving his PhD, he began to experiment with other, better  methods including the use of mechanical and electromechanical techniques. Then in 1937, he came up with a design of a fully electronic computer.1

John Atanasoff’s Purpose

  1. John Atanasoff and his mother Iva, 1906

  1. A Dietzgen slide rule

  1. 1.Design Sketch of the ABC

  2. 2.ABC Electrostatic store-drum, used for memory. Also known as the keyboard and counter drum. One of the original two

    This is the only surviving part of the original ABC

  1. 3.The ABC’s arithmetic unit


The breakthrough that Atanasoff made was the following ideas, which he jotted down on a napkin in a tavern.2

  1. Electricity and electronics, not mechanical methods

  2. Binary numbers internally

  3. Separate memory made with capacitors, refreshed to maintain 0 or I state

  4. Direct 0-1 logic operations, not enumeration

From these ideas, and from the help of Berry, he was able to successfully build the ABC.

Furthermore, the ENIAC successor, along with modern computers, are based on these ideas. Atanasoff even had direct contact with Mauchly, one of the chief builders of the ENIAC computer, as seen in Atanasoff’s letter to him, written in 1941.


For memory, the ABC used electrostatic store-drums made up of 1600 capacitors each.1 These capacitors are used to store a small charge representing the 1, or “on”, state. The “off”, or 0, state was represented by no charge. Therefore, binary numbers could be stored onto the drums. This is the first use of the idea now known as DRAM, a modern day technology used in today’s computers.

From 1994 to 1997, a team of scientists, engineers, and students at Iowa State University built a replica of the ABC. The only modifications they performed on it was that they changed the original width so that it would fit through the standard door frame.2 The computer, as seen in the original design sketch to the upper right, is mounted on a cart, allowing it to be moved from place to place. In addition, the replica only weighed 700 pounds, not much compared to other computers constructed during the time period.2 This portability was far ahead of its time.

A demonstration of the replica in action is shown above.