Eniac 1945

ENIAC, unveiled publicly in February 1946 after being completed in late 1945, is where this history's many separate threads finally converge into one machine that could be called, without much qualification, a general-purpose computer. Built at the University of Pennsylvania's Moore School of Electrical Engineering by John Mauchly and J. Presper Eckert, funded by the US Army to compute wartime artillery firing tables faster than human "computers" (at the time, that word still meant a person with a desk calculator), ENIAC combined vacuum-tube electronic speed, proven first by Atanasoff and Berry and scaled up dramatically by Colossus, with true general-purpose programmability that neither of those machines had. It used roughly 18,000 vacuum tubes, weighed about 30 tons, filled a room roughly 30 by 50 feet, and could perform around 5,000 additions per second — thousands of times faster than any mechanical or electromechanical calculator that came before it in this history. Unlike Colossus, which was purpose-built for one kind of cipher-pattern comparison, ENIAC could be reconfigured to solve an open-ended range of numerical problems, which is the real meaning of "general-purpose" here. The catch, and it was a significant one, is how that reprogramming actually worked: ENIAC had no stored-program capability in the sense Babbage's Analytical Engine or a modern computer has it. Changing what ENIAC computed meant physically rewiring it, moving hundreds of cables between plugboards and resetting thousands of switches by hand, a process that could take days for a complex new problem. This is also the point in the story where credit, after decades of being distorted, was finally set right for a group of people history had mostly erased from the record: the six original ENIAC programmers were women — Kathleen McNulty, Jean Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas, and Ruth Lichterman — who worked directly from the machine's logical wiring diagrams to physically configure ENIAC for each new calculation, effectively inventing much of the discipline of programming as a practical craft, with essentially no documentation or training to draw on, because none existed yet. For decades their contribution was uncredited or attributed to the machine's male engineers; their role has only been properly recognized by historians in recent decades. Legally, ENIAC's own patent did not survive history's scrutiny either: the 1973 Honeywell v. Sperry Rand ruling that this series covered earlier (item 8) invalidated it, finding that Mauchly's 1941 visit to see Atanasoff's machine had informed ENIAC's design more than its patent application acknowledged. ENIAC's own limitation, the rewiring problem, is exactly what John von Neumann's 1945 "First Draft of a Report on the EDVAC" proposed to solve: store the program itself as data in the same electronic memory as the numbers it operates on, so reprogramming becomes a matter of loading new instructions rather than rewiring hardware. That stored-program architecture, refined through EDVAC, EDSAC, and the machines that followed in the late 1940s, is the direct blueprint every computer since has used, including the one serving this page. From here, the thread this series has followed for roughly 220 years — from a loom in 1804 reading punched cards, through mechanical calculators, electrical relays, mechanical binary logic, and finally thousands of vacuum tubes wired by hand — hands off to a different kind of component. In December 1947, at Bell Labs, John Bardeen and Walter Brattain demonstrated the point-contact transistor, the device that would replace the vacuum tube entirely and make every computer built after it smaller, faster, and more reliable by orders of magnitude — which is where this site's own deep semiconductor history begins.

ENIAC's own vacuum tubes were already a dead end by the time anyone fully appreciated what its stored-program successors would become — within two years, Bardeen and Brattain's point-contact transistor would start the process of replacing those 18,000 glowing tubes with a device small enough, reliable enough, and cheap enough to eventually put a computer more capable than ENIAC into a pocket, which is the story this site exists to tell in detail from here forward.