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Six women translated mathematical procedures into the cables, switches and settings that made ENIAC calculate. Working before programming languages or instruction codes existed, Kathleen Antonelli, Jean Bartik, Betty Holberton, Marlyn Meltzer, Frances Spence and Ruth Teitelbaum helped turn the wartime computer into a working machine.
Why the Army needed ENIAC
During World War II, the U.S. Army needed ballistic trajectories calculated for different combinations of weather, guns and projectiles. A human computer using mechanical desk calculators could spend 30–40 hours on one trajectory, according to Kathy Kleiman as quoted by IEEE Spectrum in 2022. The Army sought a faster way to perform the calculations, and ENIAC was completed in 1945 as an electronic, programmable general-purpose computer.
John Mauchly and J. Presper Eckert designed ENIAC’s hardware. Herman Goldstine selected six women from the Army’s human-computing workforce to work out how to program it. They had been calculating trajectories by hand and with desk calculators; now they had to make the new machine carry out those procedures.
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Who were the six ENIAC programmers?
| Programmer | Name also used |
|---|---|
| Kathleen Antonelli | Kay McNulty |
| Jean Bartik | Betty Jennings |
| Betty Holberton | Betty Snyder |
| Marlyn Meltzer | Marlyn Wescoff |
| Frances Spence | Fran Bilas |
| Ruth Teitelbaum | Ruth Lichterman |
Their prior work as human computers gave them practical knowledge of the mathematics ENIAC was meant to perform. But programming the machine required a different kind of expertise: they had to understand its circuitry and configure the hardware to execute a calculation.
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How did they program ENIAC without a programming language?
ENIAC had no modern instruction codes or programming language. The programmers created a calculation by physically configuring cables, switches and function tables. They studied wiring and block diagrams, blueprints and circuitry to figure out how the machine’s components could represent the mathematical steps.
From a mathematical procedure to machine settings
A ballistic calculation had to be broken into arithmetic operations and arranged so ENIAC could carry them out. The women used the machine’s physical controls to set up those operations, including repeated sequences and conditional logic. In effect, they programmed by changing the machine’s connections and settings rather than typing instructions into software.
Programming meant learning the hardware
The work demanded both mathematical reasoning and a detailed understanding of ENIAC’s design. The programmers initially lacked security access to enter the room where the computer stood, so they learned from technical documentation and diagrams. Their work was not simply operating a finished machine: they had to determine how its hardware could perform the desired calculation.
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Their programming culminated in a ballistic-trajectory calculation demonstrated when ENIAC was unveiled on 6 February 1946. That public demonstration showed the machine performing a useful calculation for the kind of wartime problem that had motivated its development.
ENIAC’s story therefore includes more than the design and construction of its hardware. The six programmers converted mathematical procedures into a working arrangement of circuits and controls, making the computer perform its intended task.
Why were the programmers left out of computer history?
For decades, photographs of the women with ENIAC circulated without their names. Some historians even described them as models rather than programmers. Kathy Kleiman began investigating who the women were, found the programmers, recorded oral histories with four of the six and established the ENIAC Programmers Project. As she put it, “I tracked them down, and they weren’t models; they were programmers.”
The project helped bring their work to a wider audience through the documentary The Computers: The Remarkable Story of the ENIAC Programmers. Kleiman’s book, Proving Ground: The Untold Story of the Six Women Who Programmed the World’s First Modern Computer, was published by Grand Central Publishing on 26 July 2022. The publisher describes the book as restoring the women to their place in computing history.
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Where to learn more about the ENIAC programmers
Proving Ground tells the story of the six programmers and their work. The publisher’s listing includes ebook, audiobook and trade-paperback formats; the listed ebook edition is 432 pages and has ISBN 9781538718278. The audiobook is narrated by Erin Bennett and has ISBN 9781549185458. Format and availability may vary by retailer.
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