This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
For nearly three decades after it ran its first calculation in 1945, ENIAC held an uncontested place in the history books as the first computer. Built by J. Presper Eckert and John Mauchly at the University of Pennsylvania under an Army contract for artillery firing tables, unveiled to the public in February 1946, it filled a room with eighteen thousand vacuum tubes and could add five thousand numbers a second, a staggering figure for its time. Sperry Rand, the company that eventually owned the ENIAC patent, spent years collecting licensing royalties from the computer industry on the strength of that 1964 patent grant.
The challenge came from an unlikely place: a small, forgotten machine built at Iowa State College between 1939 and 1942 by physics professor John Atanasoff and his graduate student Clifford Berry. The Atanasoff-Berry Computer, or ABC, was the first machine to compute electronically, using vacuum tubes and binary numbers rather than mechanical gears or relays, the same basic electronic approach ENIAC would later use. But it was narrow in purpose, built only to solve systems of linear equations, and its punch card based memory system was never fully perfected. When Atanasoff left for wartime work, the project was abandoned, and the machine itself was eventually dismantled for parts. It was never patented.
The connection between the two machines was not circumstantial. In June 1941, John Mauchly visited Atanasoff's laboratory at Iowa State and spent several days examining the ABC in operation, before he and Eckert began designing ENIAC. When Honeywell sued Sperry Rand in the early 1970s to break its licensing grip on the computer industry, that visit became the center of a trial that ran from June 1971 through 1973, with seventy seven witnesses testifying in person and eighty more by deposition, compiled into a decision over two hundred and forty pages long. On October 19, 1973, Judge Earl R. Larson ruled that Eckert and Mauchly had derived the electronic digital computer's essential ideas from Atanasoff's earlier work, and he declared the ENIAC patent invalid, placing the invention of the electronic digital computer in the public domain rather than crediting either machine outright.
The ruling did not simply hand ENIAC's crown to the ABC. Atanasoff's machine, whatever its priority in electronic computation, was never general purpose and never ran reliably enough to be called a computer in the fuller sense that ENIAC embodied; a separate machine, Konrad Zuse's Z3, completed in Berlin in May 1941, has its own claim as the first programmable, fully automatic computer of any kind, built from telephone relays rather than vacuum tubes. What the 1973 decision actually settled was narrower and, in a way, more interesting than a simple changing of the guard: it established, as a matter of law rather than legend, that the computer's origin is not a single moment or a single genius, but a set of overlapping, competing claims, each real, each incomplete on its own, which is exactly how this atlas records it.