The ENIAC “Computers” Part 1

12 Jun

If Augusta Ada Lovelace’s notes are recognised as one of the first descriptions of a computer and software our next set of historical stories involves 6 ladies who did most of the programming of ENIAC by manipulating its switches and cables. These ladies job titles became known as ‘computers‘. The ENIAC (Electronic Numerical Integrator And Computer) was the first large-scale, reprogrammable, electronic, digital computer. Its first programs were related to the design of the hydrogen bomb. It is during World War II where we will meet our next historical pioneers, the original programmers of the ENIAC , Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman.

The original programmers of the ENIAC

Programmers operate the ENIAC’s main control panel at the Moore School of Electrical Engineering. “U.S. Army Photo” from the archives of the ARL Technical Library.
Left: Betty Jean Jennings; right: Fran Bilas.

The Electronic Numerical Integrator and Computer [ENIAC], was the first large-scale, electronic, digital computer capable of being reprogrammed to solve a full range of computing problems, although earlier computers had been built with some of these properties. ENIAC was designed and built to calculate artillery firing tables for the U.S. Army’s Ballistics Research Laboratory.

The contract was signed on June 5, 1943 and Project PX was constructed by the University of Pennsylvania’s Moore School of Electrical Engineering from July, 1943. It was unveiled on February 14, 1946 at Penn, having cost almost $500,000. ENIAC was shut down on November 9, 1946 for a refurbishment and a memory upgrade, and was transferred to Aberdeen Proving Ground, Maryland in 1947. There, on July 29 of that year, it was turned on and would be in continuous operation until 11:45 p.m. on October 2, 1955.

ENIAC was a “one-off” design and was never repeated. The design freeze in 1943 meant that the computer had a number of technical problems which were not solved, notably the inability to store a program. But the ideas generated from the work and the impact it had on people were profoundly influential in the development of later computers, initially EDVAC, EDSAC and SEAC.

Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman, were the six women who did most of the programming of ENIAC by manipulating its switches and cables.

Kathleen “Kay” McNulty Mauchly Antonelli
Born Kathleen Rita McNulty in the Creeslough Gaeltacht (Irish-speaking region) of County Donegal, Ireland in 1921 during the Irish War of Independence. On the night of her birth, her father, James, who was an Irish Republican Army training officer, was arrested and imprisoned in

Kay McNulty

Kathleen's Graduation picture from Wikipedia

Derry Gaol for 2 years. On his release, the family emigrated to the United States in October 1924 and settled in Pennsylvania where James McNulty established a successful stone masonry business. At the time, Kathleen was unable to speak any English, only Gaelic; she would remember prayers in Gaelic for the rest of her life.

After attending parochial grade school in Chestnut Hill and Hallahan Catholic Girls High School in Philadelphia, she graduated with a degree in mathematics from Chestnut Hill College for Women in June 1942 (the attack on Pearl Harbour had shaken her senior year). Out of a class of 92 women, Kathleen was one of 3 math majors to graduate that year, and all of them had taken every mathematics course offered: two semesters of algebra, the history of math, integral calculus, spherical trigonometry, differential calculus, projective geometry, partial differential equations, and statistics. (In high school she had taken a year of algebra, a year of plane geometry, a second year of algebra, and a year of trigonometry and solid geometry.)

During her third year of college, Kathleen began to look for work. She knew that she wanted to work in mathematics but she didn’t want to be a schoolteacher. She learned that insurance companies’ actuarial positions required a master’s degree and were seldom filled by women anyway. Feeling that business training would make her more employable, she took as many business courses as her college schedule would permit: accounting, money and banking, business law, economics, and statistics.

A week or two after graduating, she happened to see a U.S. Civil Service ad in The Philadelphia Inquirer. Under the headline “Wanted: Women With Degrees in Mathematics,” it read,

The need for women engineers and scientists is growing both in industry and government… Women are being offered scientific and engineering jobs where formerly men were preferred. Now is the time to consider your job in science and engineering…

The slogan could be found elsewhere as ‘WOMEN WANTED!’.
The Army was looking for women with mathematics degrees–right there in Philadelphia. She immediately called her two co-math majors,
Frances Bilas and Josephine Benson. The latter couldn’t meet up with them, so Kathleen and Fran met in Philadelphia one morning in June 1946 for an interview in a building on South Broad Street (likely the Union League Building), where they were informed of positions available through Aberdeen Proving Grounds at the University of Pennsylvania. Shortly thereafter, the two both received letters telling them to report for a week at the Moore School of Electrical Engineering, University of Pennsylvania, 33rd and Walnut Streets, beginning a day in early July 1942. At a starting annual salary of $1,620, pay for the position for computing ballistics trajectories used for artillery firing tables (mostly using mechanical desk calculators and extremely large sheets of columned paper) was low (S.P. 4, a “sub-professional” pay grade), but both Kathleen and Fran were satisfied to have attained employment that utilized their educations, during wartime, having had no prior employment experience, and that served the war effort. Her official civil service title, as printed on her employment documentation, was “computer.” With about 10 other “girls” (as the female ‘computers’ were called) and 4 men, a group recently brought to the Moore School from Aberdeen Proving Grounds in Maryland. Kay and Fran would conduct their work in a large, empty classroom on the first floor of the Moore School; the same room would later be the one where the ENIAC was built and operated until December 1946.

Despite all their coursework, their mathematics training had not prepared Kay (as she came to be called early on at the Moore School) and Fran for their work calculating trajectories for firing tables: they were both unfamiliar with numerical integration methods used to compute the trajectories, and the textbook lent to them to study from (Numerical Mathematical Analysis, 1st Edition by James B. Scarborough, Oxford University Press, 1930) provided little enlightenment.

The two newcomers ultimately learned how to perform the steps of their calculations, accurate to ten decimal places, through practice and the advisement of a well-liked supervisor, Lila Todd. A total of about 75 young female ‘computers’ were employed at the Moore School in this period, many of them taking courses from Adele Goldstine (who wrote the complete technical description for the first digital computer), Mary Mauchly, and Mildred Kramer. The work was tedious, and many of them dropped out due to workload, but Kay became prominent among the computing women.

Kay, Alyse and Sis

Kay, Alyse and Sis, picture from Wikipedia

Kay McNulty, Alyse Snyder, and Sis Stump operate the differential analyzer in the basement of the Moore School of Electrical Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, circa 1942-1945.

After 2 or 3 months, Kay and Fran were moved to work on the differential analyzer (picture above) in the basement of the Moore School, the largest and most sophisticated analog mechanical calculator of the time, of which there were only 3 in the United States and 5 or 6 in the world (all of the others were in Great Britain). Using the analyzer (invented by Vannevar Bush of MIT a decade prior and made more precise with improvements by the Moore School staff), a single trajectory computation, about 40 hours of work on a mechanical desk calculator, could be performed in about 50 minutes.

Vannevar Bush

Vannevar Bush, picture from Wikipedia

The computer could complete the same ballistics calculations described above in about 10 seconds, but it would often take one or two days to set the computer up for a new set of problems, via plugs and switches. It was the women’s responsibility to determine the sequence of steps required to complete the calculations for each problem and set up the ENIAC. Early on, they consulted with ENIAC engineers such as Arthur Burks to determine how the ENIAC could be programmed.

The ENIAC was developed for the purpose of performing these same calculations between 1943-1946. In June 1945, Kay was selected to be one of its first programmers, along with several other women from the computer corps: Betty Snyder, Marlyn Wescoff, and Ruth Lichterman, and a fifth computer nicknamed “Greenie.” When Greenie declined to go to Aberdeen for training because she had a nice apartment in West Philadelphia and a 1st alternate refused to cut short a vacation in Missouri, Betty Jean Jennings, the 2nd alternate, got the job, and between June and August of 1945 they received training at Aberdeen Proving Grounds in the IBM punch card equipment that was to be used as the I/O for the ENIAC. Later, Kay’s college schoolmate and fellow computer Fran Bilas would join the team of ENIAC programmers at the Moore School, though she did not attend the initial training at Aberdeen.

Because the ENIAC was a classified project, the programmers were not at first allowed into the room to see the machine, but they were given access to blueprints from which to work out programs in an adjacent room.

Programming the ENIAC involved discretizing the differential equations involved in a trajectory problem to the precision allowed by the ENIAC and calculating the route to the appropriate bank of electronics in parallel progression, with each instruction having to reach the correct location in time to within 1/5,000th of a second. Having devised a program on paper, the women were allowed into the ENIAC room to physically program the machine.

Much of the programming time of the ENIAC consisted of setting up and running test programs that assured its operators of the whole system’s integrity, every vacuum tube, every electrical connection needed to be verified before running a problem.

Kay transferred to Aberdeen Proving Ground’s Ballistics Research Laboratory along with the ENIAC when it was moved there in mid-1947; she was joined by Ruth Lichterman and Fran Bilas, but the other three women began families or started other jobs, preferring to stay in Philadelphia rather than relocate to remote Aberdeen and live an Army base life.

ENIAC co-inventor John Mauchly, who had since departed his post as a professor at the Moore School to found his own computer company along with Presper Eckert, made frequent trips to Washington, D.C. during this period, and stopped in to check up on the ENIAC in Aberdeen. Mauchly had already hired Betty Jean Jennings (who had married and now went by Jean Bartik) and Betty Snyder (now called Betty Holberton) and had hoped to attract Kay to his fledgling company as well. But Mauchly’s wife had died in a September 1946 drowning accident, and as a recent widower with two children, Mauchly instead proposed to Kay, who was almost 14 years his junior.

Resigning her post at Aberdeen, and without the blessing of her Irish Catholic parents, she married him in 1948. They lived initially in his row house on St. Mark’s Street near the University of Pennsylvania, and later in a large farmhouse called Little Linden in Ambler, Pennsylvania. Together they had five children.

She later worked on the software design for later computers including the BINAC and UNIVAC I computers whose hardware was designed by her husband.

John Mauchly died in 1980 following several bouts of illness and recoveries, and she married photographer Severo Antonelli in 1985. After a long struggle with Parkinson’s disease, her second husband died in 1996; Kay had suffered a heart attack while caring for him, but made a full recovery.

Following Mauchly’s death, Kay carried on the legacy of the ENIAC pioneers by authoring articles, giving talks (frequently along with Jean Bartik, with whom she remained lifelong friends), and making herself available for interviews with reporters and researchers. She was inducted into the Women in Technology International Hall of Fame in 1997 along with the other original ENIAC programmers, and she accepted the induction of John Mauchly into the National Inventors Hall of Fame in Akron, Ohio in 2002.

Kay was diagnosed with inoperable cancer in early 2006, and died in April at the age of 85.


The next blog post will look at the work of Jean Bartik, Betty Holberton, Marlyn Meltzer, Frances Spence and Ruth Teitelbaum on the ENIAC computer,

 Legal bit
All rights reserved. No part of this publication may be reproduced, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the authors.  Although great care has been taken to ensure the accuracy and completeness of the information contained in this work neither the author, contributors, employees or advisers are able to accept any legal liability for any consequential loss or damage, however caused, arising as a result of any actions taken on the basis of the information contained in this work. All third-party brands and trademarks belong to their respective owners.  Copyright : Maggie Baldry

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Posted by on June 12, 2011 in Soft Footsteps


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