The Atanasoff-Berry digital computer

May 12, 2023
by Mark Ollig

A young individual’s extraordinary life journey began in 1913 when he was shown a mathematical tool called a slide rule.

John Vincent Atanasoff was born in Hamilton, NY, Oct. 4, 1903.

He was still nine years old in 1913 when his father, Ivan, an electrical engineer, purchased a brand new Dietzgen slide rule.

For young people, think of a slide rule as a mechanical analog computing device.

John was fascinated with the slide rule and became proficient in its use.

His curiosity about mathematics led him to take apart an early 1900s Monroe calculating machine to learn how it provided the correct answers.

Iva, a mathematician, and John’s mother, helped him understand arithmetic textbooks covering the base-10 (decimal) and other numbering systems, including the base-2 (binary) system.

Early in high school, John decided mathematical physics would become his life’s work.

“The Theory of Functions of a Real Variable and the Theory of Fourier’s Series” by mathematician Ernest William Hobson was a book employing base-2 numbers John had read with great interest.

In 1925, John Atanasoff received a Bachelor of Science in electrical engineering from the University of Florida.

During the same year, while attending Iowa State College (Iowa State University), he earned a master’s degree in mathematics.

In 1930, Atanasoff completed his Ph.D. in theoretical physics at the University of Wisconsin; he then returned to Iowa State College, where he taught mathematics and physics.

By 1936, Atanasoff was an associate professor of math and physics at Iowa State College and studied electronics.

Recognizing the potential of binary numbers to represent all combinations using “one” and “zero,” he designed an electronic digital computing machine with logic gates using Boolean expressions to solve mathematical problems faster and more accurately than the existing mechanical analog devices.

In 1937, Atanasoff and an Iowa State college student named Clifford Berry began constructing an electronic digital computer in the basement of the Iowa State Physics building.

The computer used thyratron and thermionic vacuum tubes, resistors, condensers (capacitors) for data storage, electronic circuits to perform arithmetical operations, electromechanical relay switches, and an estimated mile of copper wiring.

The human operator’s computer control console included a variety of switches, buttons, meters, and lights.

The computer utilized a mechanical cam-driven rotational feed-in binary-card device that employed paper punch cards for in and output data.

The three-by-seven-inch paper punch card featured holes that represented binary “ones” arranged in rows and columns, while the non-holed empty spaces, pre-stamped as “-” represented binary “zeros.”

Numerical input data from a human operator used a mechanical keypunch apparatus to cut holes into the paper punch cards at specific locations. They were then fed into the computer for processing.

On the paper punch card, an arc hole symbolized a binary “one,” formed by an electrical discharge from the computer’s output via thyratron gas-filled tubes. Conversely, the lack of electrical discharge represented a zero, indicated on the card by the default “-” stamp.

In 1939, a functional electronic digital computer prototype using binary digital calculations named the Atanasoff-Berry Computer (ABC) was built. It operated on 120VAC 60Hz power.

The ABC used arithmetic logic circuits, a binary arithmetic system, serial calculations, and parallel processing as fundamental components of its design.

The computer would “read” or detect the presence or absence of a binary value of one or zero on punch cards by passing a low electrical current through the holes on the cards, completing a circuit without any damage.

The Atanasoff-Berry Computer used 280 dual-triode vacuum tubes to perform digital computations.

Some of the computer’s parts were telephone switching relays.

The computer’s memory contained 1,600 regenerative charged capacitors on 32 spheroidal bands inside rotating drum cylinders.

Insulated capacitors are positioned radially within a hollow cylinder drum made of Bakelite (a synthetic plastic).

The capacitors’ inner connector terminals are joined to a shared wiring lead, while the outer terminals are connected to contacts that pass through the cylinder wall.

The computer’s regenerative capacitor memory stores a maximum of 3,000 bits. Each capacitor represents a binary bit value of zero or one, as its electrical charge determines the bit value.

The capacitors require periodic refreshing; however, their data can stay intact for up to five minutes before the charge dissipates.

The ABC, weighing approximately 700 pounds and occupying a space similar to an office desk, could execute 30 calculations per second and solve 29 linear equations simultaneously.

From 1939 to 1940, Iowa State College Research provided $1,500 (equivalent to $32,000 today) to support the construction of the computer.

On Jan. 15, 1941, the Des Moines Tribune newspaper reported, “An electrical computing machine said here to operate more like the human brain than any other such machine known to exist is being built by Dr. John V. Atanasoff, Iowa State college physics professor.”

By 1942, the Atanasoff-Berry Computer, the first electronic linear algebraic digital computer, was completed.

The same year, Atanasoff left to serve in WWII, and Clifford Berry transitioned to a career in the private sector.

Next week’s column covers the legal battle at the Federal District Courthouse in Minneapolis between the Atanasoff-Berry Computer and a computer initially named “Project X.”

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