In 1945, 20-year-old mathematician Betty Jean Jennings moved to Philly and started work on a secret military project: the first modern electronic computer. Now, in a fascinating posthumous memoir, the tech pioneer tells her own story.
We were known as “the two Bettys.” One of us had dark brown hair; one of us had auburn hair that, in childhood, had been carrot-red. One of us had grown up on the Main Line railroad of Philadelphia, the daughter of a highly respected astronomy teacher at a prestigious boys’ school. And one of us had grown up on a Missouri farm, the daughter of a hardscrabble farmer who had also once taught in a one-room schoolhouse. What brought us together initially was an advertisement for recently graduated female math majors. But what brought us to this moment was a remarkable fate. It seemed to open doors at every turn and usher us through them until there was just the two of us, Betty Snyder and Betty Jennings, alone in a room with the largest and most impressive electronic machine ever created.
We were the best of friends, and we were on the verge of making history. It was late—quite late, in fact—on a frigid February night in 1946. Betty and I (I went by my first name then, although now I use my middle name, Jean) were holed up on the first floor of the Moore School of Electrical Engineering on the campus of the University of Pennsylvania, in Philadelphia. Betty was twenty-eight, and I had just turned twenty-one a few weeks earlier.
It happened to be the night of Valentine’s Day, but we were unconcerned about that. Besides, we had no boyfriends at the moment. We were serious young ladies with important things on our minds. For that reason, we did not resent having to spend the evening cooped up in the Moore School working. We never gave a thought that evening to valentines or romantic dinners. What we were thinking of was an all-important demonstration we were to run the next day for the world.
We were all by ourselves, except that we weren’t. There was something else inhabiting that space. Like the proverbial elephant in the room, it was hard to miss. In fact, it took up most of the room, surrounding us on all sides. Standing nearly nine feet tall, it towered over us, its forty panels—each measuring two feet wide and a foot deep—looked like some strange sci-fi floor-to-ceiling cabinetry. And stretching, all told, eighty feet in length, it not only took up three entire walls, but there were also rolling islands of function tables on wheels in the center of the room that could be turned this way and that. The fourth wall was covered with its power supplies, which were also housed in big, black panels.
Counting all of its panels and parts, it weighed thirty tons, or the equivalent of about forty-five of the horses I had ridden and driven as a teenager on the farm in Missouri. As Betty and I worked on it that night, its vacuum tubes flickered like distant lightning. A storm was rolling in, one might say—if one were given to poetical fancy—and in its wake, twentieth-century technology would never look the same again.
The machine was the reason we were there that night—now past eleven p.m., long after the city’s couples had gone home from their Valentine’s Day dinners out—and the reason we had been in that room for countless hours over the previous two weeks. But this was the final night; tomorrow all of our hard work would be put to the test—and before some of the greatest minds in the United States.
What was this behemoth that surrounded us as we plugged cables into its circuitry, with more than two thousand neon bulbs flashing as we ran the test problem again and again, searching for the final piece of a puzzle? It was the world’s first electronic computer—or, to use its official name, the Electronic Numeric Integrator and Computer. But that’s a mouthful, even to designate something as complex and revolutionary as this was, and no one actually called it by that name, not even the mathematicians. Instead, the world would soon come to know it as the ENIAC.
There had been other computers of a sort, but they weren’t nearly as impressive or as capable as the ENIAC. Today, of course, a silicon chip smaller than the tip of a pencil can hold the same capacity as the ENIAC, which occupied a large room. But at that time, the ENIAC left all the other prototype “computers” in its dust with its power of computation and speed. As mathematicians, we were awestruck to work with such power in harness. It felt how I imagine it might have felt to Thomas Watson when he heard Alexander Graham Bell say over the first telephone, “Come here, Watson—I want you.” It was a thrilling experience to work with the ENIAC.
But just now, it was more like a curse, because the great machine was giving us trouble.
Our task, which we had been given a little over two weeks before, was to program the ENIAC to calculate the trajectory of a shell fired from an artillery gun.
We had one major problem with our program, which we were trying to fix that evening of February 14, 1946: While we had made the ENIAC trace the actual flight path just fine, at the point in the simulation where the shell should have hit the ground and stopped, it kept going, as if it were tunneling under the earth at the same velocity that it had traveled through the air. We couldn’t stop the shell on impact. Unless we solved that problem, we knew the demonstration would be a dud, and the ENIAC’s inventors and engineers would be embarrassed.
Now it was the last night before the ENIAC would be unveiled to the scientific community, and while we knew we were close to solving the problem, we couldn’t find the magic fix for which we were searching. We worked and worked, checking and adjusting the myriad settings for the computer, but we couldn’t find the answer.
Finally, with the clock nearing midnight, we shut off the lights, locked up, and left the building, terribly discouraged. Betty lived in the suburbs, and the last train for her home departed at midnight. I left her on Walnut Street, a block from the train station, and walked home, she going one way and I the other. I don’t know what her thoughts were as she rode the Main Line out to Narberth, but mine were gloomy.
In the morning, which was bitterly cold, Betty and I returned to the Moore School with the problem still before us. But not for long: Betty walked up to the computer, flipped one switch, and the program ran perfectly. We were suddenly in business; the shell now stopped on impact. And a good thing, too—the demonstration was only a few hours away.
How had Betty done it? How had she known which switch was set wrong, out of the thousands that were on the ENIAC? What I called her “nighttime logic” had been at work. Betty often solved logical problems by sleeping on them. While she slept, her subconscious untangled the knot that her conscious mind had been unable to. She was the best I ever saw at this.
We were now ready for the eminent mathematicians and other distinguished guests who would soon descend on the room. It was nearly time for the ENIAC to make history.
Jean, a recent mathematics graduate from Missouri, had moved to Philadelphia to take a job at Penn calculating artillery trajectories for the U.S. Army’s Aberdeen Proving Ground, a weapons-testing facility. She recalls what it was like settling into 1940s campus life:
Aberdeen had advertised for women with math majors in the Philadelphia area, but as time went on the Proving Ground began an advertising campaign that reached across the country and to me in Missouri. When I arrived, there were four other women who had gotten there a month or two earlier. Two were from Kansas, one from Ohio, and one from Wisconsin. We became friends and spent Sundays, our day off, running around seeing the sights of the city.
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