Monday, February 16, 2026

What Was It Like to Work on the ENIAC?

In the tech realm, everyone knows about the ENIAC. My mother's brothers were each more than acquainted with it. They worked with it.

Vacuum tube. I remember when
television sets had them.
The ENIAC (Electronic Numerical Integrator and Computer) was the world's first programmable, electronic, general-purpose digital computer. It was developed during World War II (1943–1945) at the University of Pennsylvania's Moore School of Electrical Engineering by John Mauchly, J. Presper Eckert, and their team, under U.S. Army contract for the Ballistics Research Laboratory.

The ENIAC was built to calculate artillery firing tables quickly—complex ballistic trajectories that took humans days but ENIAC handled in seconds (e.g., 5,000 additions per second, vastly faster than mechanical predecessors). 
Here are some key specs to wrap your head around:
  • Used approximately 17,468 vacuum tubes, 70,000 resistors, 10,000 capacitors.
  • Weighed 30 tons, occupied a 50x30-foot room (a little larger than my wife's 40x30-foot garage) and consumed 150 kW of power.
  • Programmed by rewiring plugboards and switches, not stored programs. It took days to change tasks.
  • Unveiled publicly in February 1946 (post-war), it influenced later computers like EDVAC and UNIVAC.
It would be fair to say that the ENIAC marked the dawn of modern electronic computing.  
According to The Evolution of Computers Wordpress site:
The first generation of computers occurred from 1946 to 1958, it was called The Vacuum Tube Years. The vacuum tube was an essential step in the progress of early computers. A vacuum tube was a sealed glass or metal-ceramic enclosure used in electronic circuit which controlled the flow of electrons inside. The air inside the sealed tubes was removed by a vacuum The purpose of the vacuum tubes in the first generation of computers was to be an amplifier and a switch at the same time. The vacuum tubes had no moving parts which enabled it to take weak signals and make them stronger. In other words, the vacuum tube could amplify weak signals. The second purpose for the vacuum tubes was for the easy management of stopping and starting the flow of electricity instantly. This was referred to as the switch. It was these two components, amplifier and switch, that made the ENIAC computer likely. 
Reading about the ENIAC brought to mind a comment my uncle Ferrell Sandy made around 15 years ago before he passed. When my mother and I would visit, we'd often go to an Italian restaurant at the bottom of the hill where he always ordered Chicken Marsala.* When I was growing up my dad would ask--at family reunions--what he was working on. He always replied, "I can't tell you." He was a physicist who worked in a consulting firm that had two clients, the CIA and the NSC. 
In 2010 or 11, fifty years had passed and things were very changed and he could share a few stories, including his experience working on the ENIAC. As noted above, the ENIAC had over 17,000 vacuum tubes. So when I asked about his experience, Uncle Ferrell said, "It would run for five minutes, and then stop, and you'd walk around and try to find which vacuum tube burned out." Once you found it, you could replace it and start it up again. A vacuum tube would burn out around every five minutes.
This was the beginning of the computer revolution.

Chicken Marsala is a classic Italian-American dish of thin, pan-fried chicken cutlets served in a rich sauce made with Marsala wine, mushrooms, and aromatics like garlic and shallots, often thickened and finished with butter or cream.

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