Between 1943 and 1951, a small group of engineers, mathematicians, and physicists at the University of Pennsylvania built two machines that launched the computer age. The first, ENIAC (Electronic Numerical Integrator and Computer), proved that electronic computation was possible. The second, EDVAC (Electronic Discrete Variable Automatic Computer), introduced the stored-program concept that made computers truly versatile. Together, they transformed the computer from a theoretical idea into a working technology that would reshape civilization.
The story of these machines involves wartime urgency, mathematical brilliance, engineering improvisation, and a bitter credit dispute that has never been fully resolved. It is one of the great origin stories of the modern world.
The Problem: Ballistic Tables
The immediate impetus for ENIAC was military. During World War II, the United States Army needed firing tables for its artillery. Each type of gun firing each type of shell at each combination of angle, wind speed, temperature, and altitude required a separate calculation of the projectile’s trajectory. These calculations were performed by teams of human “computers” (the original meaning of the word), mostly women with mathematics degrees, using mechanical desk calculators.
The work was slow. A single trajectory calculation took about twenty hours by hand. Each firing table required hundreds of trajectories. The Army’s Ballistic Research Laboratory at Aberdeen Proving Ground was falling months behind in producing the tables that gunners needed in the field.
In 1943, John Mauchly, a physics professor at the University of Pennsylvania’s Moore School of Electrical Engineering, proposed building an electronic calculator that could compute trajectories thousands of times faster than human computers. The Army, desperate for speed, approved the project. J. Presper Eckert, a brilliant young engineer at the Moore School, was appointed chief engineer. The machine they built was ENIAC.
ENIAC: The Electronic Giant
ENIAC was completed in late 1945, too late to contribute to the war effort but early enough to demonstrate the potential of electronic computation. It was enormous: 30 tons of equipment filling an entire room, containing approximately 18,000 vacuum tubes, 70,000 resistors, 10,000 capacitors, and 6,000 switches. It consumed 150 kilowatts of power. According to legend (probably apocryphal), turning on ENIAC dimmed the lights across Philadelphia.
The machine could perform about 5,000 additions per second, a speed that was almost incomprehensible at the time. A trajectory calculation that took a human computer twenty hours could be completed by ENIAC in thirty seconds. The machine proved, beyond any doubt, that electronic computation worked and that it was fast enough to be useful.
But ENIAC had a fundamental limitation. It was programmed by physically reconfiguring its circuits. To change from one calculation to another, operators had to reconnect cables, set switches, and rearrange plug boards. This process could take days. The machine’s extraordinary speed in executing calculations was offset by the extraordinary slowness of setting it up for each new problem.
The Women Who Programmed ENIAC
The first programmers of ENIAC were six women: Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas, and Ruth Lichterman. They had been working as human computers at the Ballistic Research Laboratory. When ENIAC was completed, they were assigned to program it, a task for which no manual, training program, or precedent existed.
They learned the machine by studying its logical diagrams and figuring out how to configure its circuits to perform the required calculations. Their work was intellectually demanding and essential to the machine’s operation, but for decades it received almost no recognition. The famous photograph of ENIAC that appeared in newspapers in 1946 showed the women at work, but captions identified them only as “models” or “operators.” Their contributions to the birth of computing were not properly acknowledged until the 1990s.
Von Neumann Enters the Picture
In the summer of 1944, while ENIAC was still under construction, the mathematician John von Neumann learned about the project and visited the Moore School. Von Neumann was already one of the most famous mathematicians in the world, known for his work on quantum mechanics, game theory, and the Manhattan Project. He immediately grasped both the potential and the limitations of ENIAC.
Von Neumann joined the team working on EDVAC, the successor machine. His contribution was the crucial idea that would define all subsequent computers: the stored-program concept. Instead of encoding the program in the physical wiring of the machine, the program would be stored in the computer’s memory as a sequence of coded instructions, alongside the data. This meant that changing the program required only loading new instructions into memory, not rewiring the hardware.
In June 1945, von Neumann wrote a document titled First Draft of a Report on the EDVAC, describing the architecture of the new machine. The report was distributed to researchers across the United States and Britain. It became the foundational text of computer science, the blueprint for every computer built since.
The Credit Controversy
The EDVAC report listed only von Neumann as its author. This created a lasting controversy. Eckert and Mauchly argued that many of the ideas in the report, including the stored-program concept itself, had been developed collaboratively by the entire team. They felt that von Neumann had taken credit for ideas that were not solely his.
The dispute had practical consequences. The wide distribution of the report, with von Neumann’s name alone, made the ideas public and undermined Eckert and Mauchly’s ability to patent the stored-program concept. They later sued (the case was settled in the 1970s), and the question of who truly originated the stored-program idea remains debated among historians of computing.
What is not debated is the importance of the idea itself. Whether it originated with von Neumann, Eckert, Mauchly, or (as some historians argue) the entire ENIAC/EDVAC team collectively, the stored-program concept was the single most important innovation in the history of computing.
EDVAC: The Stored-Program Machine
EDVAC was designed to be everything ENIAC was not: programmable without rewiring, capable of storing its instructions in memory, and built with a more efficient electronic design. Where ENIAC used decimal arithmetic (base 10), EDVAC used binary (base 2), which simplified the electronic circuits enormously. Where ENIAC required thousands of vacuum tubes for each decimal digit, EDVAC needed far fewer components for each binary digit (bit).
EDVAC used mercury delay lines for its memory, a technology in which pulses of sound circulated through tubes of mercury, storing data as patterns of acoustic vibrations. This was slow and unreliable by modern standards, but it worked, and it provided enough storage to hold both programs and data.
The machine was not completed until 1951, delayed by personnel conflicts (Eckert and Mauchly left the Moore School in 1946 to found their own company) and engineering challenges. By the time EDVAC became operational, other stored-program computers had already been built, including the Manchester Baby (1948) and EDSAC (1949) in Britain. But EDVAC’s influence, through von Neumann’s widely distributed report, had shaped the design of all of them.
The Machines That Followed
The transition from ENIAC to EDVAC established the template for the computer age. Within a decade, stored-program computers were being built at universities and corporations around the world. The architecture that von Neumann described in 1945 proved so versatile that it survived every subsequent technological revolution: from vacuum tubes to transistors (1950s), from transistors to integrated circuits (1960s), from integrated circuits to microprocessors (1970s), and from microprocessors to the multi-core chips of today.
The programming languages, operating systems, and applications that run on modern computers are all built on the assumption that the machine follows the von Neumann architecture: a single memory storing both programs and data, a processor that fetches and executes instructions sequentially, and input/output devices that connect the machine to the outside world.
Holding the Blueprint
Kronecker Wallis’s edition of the EDVAC Report presents von Neumann’s foundational document as a physical object: printed on blue Fabriano paper in monospace type, it preserves the austere technical clarity of the original. Holding the report is holding the architectural drawing of the digital world.
The intellectual tradition that made EDVAC possible extends beyond engineering. Turing’s Treatise on the Enigma documents the cryptanalytic work at Bletchley Park that produced some of the earliest electronic computing devices and that shaped Turing’s own thinking about universal machines. And the mathematical foundations on which all computation rests trace back to Euclid’s Elements, where the idea of an algorithm (a step-by-step procedure guaranteed to produce a result) first appears in the form of the Euclidean algorithm for finding the greatest common divisor of two numbers.
From Thirty Tons to Your Pocket
ENIAC weighed 30 tons and filled a room. The smartphone in your pocket is millions of times more powerful and weighs a few hundred grams. But both machines share the same fundamental architecture: a processor that executes instructions stored in memory. The journey from ENIAC to the modern world is a story of relentless miniaturization and acceleration, but the underlying idea has not changed.
The transition from ENIAC to EDVAC, from a machine programmed by wiring to a machine programmed by software, is the moment when the computer became what it is today: a universal tool, capable of any task that can be expressed as a sequence of instructions. That transition happened in a few rooms at the University of Pennsylvania in the mid-1940s, driven by a handful of people who understood that the future of computing lay not in faster hardware but in a better architecture. They were right. Every computer on Earth is their descendant.
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