A 1973 court ruling stripped ENIAC of its title as the first electronic computer
For decades, textbooks celebrated the massive 1945 ENIAC as the world's first electronic computer. That changed in 1973, when a federal judge invalidated the ENIAC patent following a bitter corporate lawsuit. The court found that ENIAC co-inventor John Mauchly had derived key concepts—including binary arithmetic and regenerative capacitor memory—from a visit with physicist John Atanasoff, who had built a desktop-sized computing prototype at Iowa State College years earlier.
The Basement Prototype in Ames
In the late 1930s, John Vincent Atanasoff, a professor of physics and mathematics at Iowa State College (now Iowa State University), was hitting a computational wall. He was attempting to solve complex systems of simultaneous linear equations to model physical phenomena, but the mechanical calculators of the era—such as the Monroe calculator and the bush differential analyzer—were agonizingly slow, prone to mechanical wear, and limited in precision.
Frustrated by these limitations, Atanasoff took a long, solitary drive during the winter of 1937–1938 into Illinois, where he stopped at a roadside tavern. Over a drink, the basic architectural principles for a new kind of computing machine crystallized in his mind. He envisioned an electronic device that would use base-two (binary) arithmetic rather than human base-ten, employ vacuum tubes as electronic switches, and maintain a separate memory system that periodically refreshed itself.
Returning to Iowa State, Atanasoff secured a modest grant to hire Clifford Berry, an exceptionally talented graduate student in electrical engineering. Between 1939 and 1942, working in the basement of the college's physics building, the pair assembled a desk-sized device known as the Atanasoff-Berry Computer, or ABC. While modest in appearance compared to later military-funded projects, it embodied several fundamental concepts that would define digital computing.
The ABC was built to perform one specialized task: solving systems of simultaneous linear algebraic equations with up to 29 variables. While not a general-purpose, programmable machine, its internal mechanisms represented a radical departure from prevailing calculating technology. At a time when most computing projects relied on rotating mechanical gears, decimal wheels, or electromechanical relays, Atanasoff and Berry committed to pure electronic digital computation.
The machine utilized more than 300 vacuum tubes to execute arithmetic operations. Rather than attempting to mimic decimal notation, the arithmetic units operated entirely in binary, drastically simplifying the logic circuits required for addition and subtraction. It featured parallel processing capability, with multiple add-subtract mechanisms working simultaneously on data streams.
Memory was another breakthrough. The ABC stored binary numbers on two rotating drums lined with hundreds of small capacitors. Because capacitors naturally lose their electrical charge over time, the drums rotated once per second, passing contacts that read the charges, amplified them, and wrote them back onto the capacitors before the data degraded. This regenerative capacitor memory was the direct precursor to dynamic random-access memory (DRAM), which forms the main working memory of modern computers.
The 1941 Meeting and Forgotten Work
In December 1940, Atanasoff attended a meeting of the American Association for the Advancement of Science in Philadelphia, where he met John W. Mauchly, a physics professor from Ursinus College who was interested in weather prediction and computational methods. Intrigued by Atanasoff's claims of an electronic digital calculator, Mauchly accepted an invitation to visit Iowa.
In June 1941, Mauchly traveled to Ames, Iowa, staying as a houseguest with Atanasoff for several days. During this visit, Atanasoff and Berry demonstrated the partially completed ABC in the physics building basement. Mauchly inspected the machine, observed its components, and read Atanasoff's comprehensive 35-page manuscript detailing its theory and design principles. The two men discussed computing architecture at length before Mauchly departed.
Soon after, the United States entered World War II, bringing work on the ABC to a sudden halt. Both Atanasoff and Berry left Iowa State to participate in defense-related research. Atanasoff urged Iowa State College to file a patent application on the computer's inventions, but university officials never completed the filing. Abandoned in the basement, the original ABC was eventually dismantled, leaving behind only a few preserved parts, such as one of its capacitor memory drums.
ENIAC and the Corporate Royalties Battle
During the war, John Mauchly joined the Moore School of Electrical Engineering at the University of Pennsylvania, where he partnered with brilliant engineer J. Presper Eckert. Under contract with the U.S. Army to calculate artillery firing tables, they designed and constructed ENIAC (the Electronic Numerical Integrator and Computer). Unveiled in 1946, ENIAC was a colossal machine filling a large room, containing nearly 18,000 vacuum tubes and weighing roughly 30 tons.
Unlike the ABC, ENIAC was programmable and capable of executing a wide variety of general calculations, though it relied on decimal arithmetic and stored programs through reconfigurable cables and switches. In the postwar era, ENIAC captured the public imagination as the dawn of the electronic computer era. Eckert and Mauchly went on to file a broad patent application covering the automatic electronic digital computer, a patent eventually granted in 1964 and acquired by the Sperry Rand Corporation.
Armed with the ENIAC patent, Sperry Rand attempted to collect royalties from other emerging computer manufacturers across the industry. Most companies resisted paying these sweeping licensing fees. In 1967, Honeywell Inc. challenged Sperry Rand, initiating a high-stakes corporate antitrust and patent infringement lawsuit in federal court that would re-examine the origins of electronic computing.
The Decision in Honeywell v. Sperry Rand
The trial of Honeywell Inc. v. Sperry Rand Corp. became one of the longest and most exhaustive patent litigations in American history. Over 135 days of testimony, lawyers introduced thousands of exhibits, including Atanasoff's 1940 manuscript, correspondence between Atanasoff and Mauchly, and extensive technical comparisons of both machines. Atanasoff himself testified for several days, explaining the ABC's internal workings and his interactions with Mauchly.
On October 19, 1973, Federal District Judge Earl R. Larson issued a massive, landmark ruling. Larson invalidated the ENIAC patent on several grounds, including prior public use and failure to meet statutory requirements. Critically, Larson addressed the question of inventorship, explicitly finding that Eckert and Mauchly did not independently invent the electronic digital computer.
Larson ruled that the subject matter of the ENIAC patent was substantially derived from Atanasoff's work. The court documented that Mauchly had acquired foundational concepts—such as the separation of memory and arithmetic circuits, vacuum tube logic, and binary digital computation—during his 1941 visit to Ames. Despite the legal magnitude of the decision, it received scant national press coverage at the time, as the ruling occurred on the very weekend of the Watergate 'Saturday Night Massacre.'
Historical Nuance and Technological Legacy
The 1973 court decision did not render ENIAC an insignificant copy. ENIAC and the ABC represented fundamentally different engineering philosophies and served different purposes. The ABC was a special-purpose machine that lacked a stored program and was never fully operational as an integrated whole, largely due to reliability issues with its spark-based paper-card input/output mechanism. In contrast, ENIAC was fully realized, remarkably fast for its time, and capable of general computation.
Eckert and Mauchly contributed immense original engineering to the field, pioneering solutions to system-wide vacuum tube reliability and complex pulse-circuit timing that made large-scale digital computing viable. However, the legal judgment firmly corrected the historical record regarding conceptual precedence, demonstrating that many of electronic computing's foundational ideas had been formulated and physically tested years earlier in Iowa.
In the decades following the trial, the computing community reassessed Atanasoff and Berry's work. In the 1990s, a team of engineers and researchers at Iowa State constructed a working, full-scale replica of the ABC, proving that the original design was fundamentally sound. While ENIAC remains the first operational general-purpose electronic computer, the ABC is now recognized as the machine that first established electronic digital computing principles.
Key takeaways
•A 1973 federal court ruling in Honeywell v. Sperry Rand invalidated the ENIAC patent, finding that co-inventor John Mauchly derived fundamental computing concepts from John Atanasoff.
•Built between 1939 and 1942, the Atanasoff-Berry Computer introduced key architectures still in use today, including binary digital logic, electronic vacuum-tube switching, and regenerative capacitor memory.
•While the ABC was the first electronic digital computer, it was a special-purpose solver for linear equations; ENIAC retained its distinction as the first operational, general-purpose electronic computer.
•Because Iowa State College failed to patent Atanasoff and Berry's work, their early breakthroughs remained obscure until the high-stakes corporate patent dispute brought them to light.