Philadelphia schoolchildren are drilled on the names of its accomplished citizens. William Penn. Benjamin Franklin. Betsy Ross. But during all the baby-boomer years I attended schools in the City of Brotherly Love, none of my teachers mentioned J. Presper Eckert Jr. It was not until the mid-1970s, when I was in my 20s, that I learned that Gatsbian moniker—I’d write it every month on a rent check for a one-bedroom apartment in the Germantown section of the city. It was only when I became a technology writer some years later that I realized that my landlord had invented the computer.

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In the early 1940s John Presper “Pres” Eckert Jr. was a grad student at the Moore School of Engineering (affiliated with the University of Pennsylvania). A professor, John W. Mauchly, had circulated some memos about how a powerful new kind of electronic calculator could produce benefits to the war effort in areas like setting munitions trajectories. When the Army’s Ordnance Ballistic Research Laboratory approved the project, Eckert became the driving force behind what experts now consider to be the world’s first digital, general-purpose computer. As summarized by Herman Goldstine, a pioneering contemporary, “Eckert’s contribution...exceeded all others. As chief engineer he was the mainspring of the entire mechanism.”

The idea of huge computing machines was in the air at that time. In late 1939, Harvard professor Howard Aiken was building the Mark 1, a giant calculator. At Bletchley Park in England, cryptographers would oversee the construction of a special-purpose code-breaking machine called Colossus. In 1941 Mauchly himself had discussed the field with an Iowa State professor named John V. Atanasoff, who had plans to build his own huge calculating machine (but never completed the task). What distinguished Eniac from the others was that a working machine performing thousands of calculations a second could be easily reprogrammed for different tasks. It was a breathtaking enterprise. The original cost estimate of $150,000 would rise to $400,000. Weighing in at 30 tons, the U-shaped construct filled a 1,500-square-foot room. Its 40 cabinets, each of them nine feet high, were packed with 18,000 vacuum tubes, 10,000 capacitors, 6,000 switches and 1,500 relays. Looking at the consoles, observers could see a tangle of patch cords that reminded them of a telephone exchange.

But by the time Eniac was completed, the war was over. The machine did not boot up until November 1945, when 300 neon lights attached to accumulators lit up a basement room at the Moore School. Two 20-horsepower blowers exhaled cool air so that Eniac wouldn’t melt down.

On February 14, 1946, the government released Eniac from its shroud of secrecy. “A new machine that is expected to revolutionize the mathematics of engineering and change many of our industrial design methods was announced today by the War Department,” began an Army press release. It described a “mathematical robot” working at “phenomenal” speed that “frees scientific thought from the drudgery of lengthy calculating work.”

Subsequent years were not kind to the inventors. Mauchly and Eckert began the first commercial computer corporation, building an Eniac successor. But their firm struggled and the pair sold the company to Sperry Rand. Worse, a rival operation, Honeywell, cited John Atanasoff’s work in an attempt to invalidate the Eniac patent. Though the Iowan’s never-completed computer was not a general-purpose machine and lacked many of Eniac’s groundbreaking attributes (like a “clock” that governed the timing of computational events), Honeywell launched a court battle that led a judge to declare Atanasoff the true inventor of the computer. That blow forever haunted Mauchly and Eckert.

Meanwhile, Eniac itself was broken up, with sections on display at Penn and the Smithsonian. It finally got its rightful recognition in 1996, fifty years to the day after the government revealed its existence. The city of Philadelphia, finally alerted to the fact that it could claim to be not just the cradle of the Constitution but of computation as well, hosted festivities (including the first exhibition match between an Eniac descendant, IBM’s Deep Blue computer, and the world chess champion Garry Kasparov). Enough of Eniac had survived at Penn to perform some work: Vice President Al Gore threw a switch and the remaining pieces clattered out the answer to an addition problem.

Now such calculations occur billions of times a second in devices that fit in our pockets. Eckert used to joke about that phenomenon, “How would you like to have most of your life’s work end up on a square centimeter of silicon?” But the question could easily have been put another way: How would you like to have invented the machine that changed the course of civilization?

I didn’t get to ask that question of the man whose name I used to write on rent checks. Pres Eckert died of leukemia less than a year before Eniac’s 50th anniversary event. I met his widow there, however. Judy Eckert told me that the family still owned the apartment building in Germantown.

An editor for Wired, Steven Levy defined what became known as the “hacker ethic” in his seminal 1984 book Hackers: Heroes of the Computer Revolution.