Prior Context
Mechanical devices for calculation have a long history, from the abacus and seventeenth-century adding machines built by Blaise Pascal and Gottfried Leibniz to nineteenth-century efforts by the British mathematician Charles Babbage to design a fully programmable mechanical computer, the Analytical Engine, which was intended to use punched cards for input and a mechanical memory but was never completed in his lifetime due to its enormous mechanical complexity and cost. By the early twentieth century, mechanical and electromechanical calculating machines, including adding machines, cash registers, and Herman Hollerith's punched-card tabulating equipment, developed for processing the 1890 United States census, were widely used in business and government for repetitive arithmetic and record-keeping.
Scientists and engineers also built specialized mechanical and electromechanical computers, such as differential analyzers built at institutions including MIT in the 1930s, to solve specific mathematical problems, including ballistics and artillery calculations. These machines demonstrated that automated calculation was commercially and scientifically valuable, but their mechanical parts, gears, shafts, and later electromechanical relays, limited how fast and how flexibly they could operate.
Historical Development
During the 1930s and early 1940s, several independent efforts moved calculation from purely mechanical systems toward electromechanical and then fully electronic ones. In Germany, engineer Konrad Zuse, working largely alone and later with limited government support, built a series of machines culminating in the Z3, completed in 1941, a programmable, electromechanical, binary computer controlled by punched celluloid film, making it among the earliest working programmable computers in the world, though its existence remained largely unknown outside Germany for years and the machine itself was destroyed in an Allied bombing raid in 1943. In the United States, Howard Aiken, a Harvard physicist, designed the Harvard Mark I in collaboration with IBM, which built it; completed in 1944, it was a room-sized electromechanical calculator that used mechanical relays and rotating shafts, and it was used for wartime ballistics and scientific calculations.
The decisive shift to fully electronic computing came with the ENIAC, the Electronic Numerical Integrator and Computer, completed in late 1945 and publicly unveiled in February 1946, built by John Mauchly and J. Presper Eckert at the University of Pennsylvania's Moore School of Electrical Engineering for the U.S. Army's Ballistic Research Laboratory. ENIAC used roughly 18,000 vacuum tubes rather than mechanical relays to perform calculations entirely electronically, making it dramatically faster, by orders of magnitude, than any electromechanical machine, though it had to be physically rewired using patch cables and switches to change its program. Mathematician John von Neumann, a consultant to the team building ENIAC's successor, EDVAC, helped describe in a widely circulated 1945 report the stored-program concept, in which a computer's instructions are held in the same electronic memory as its data and can be changed by loading new instructions rather than by rewiring the machine, an architecture that became standard for virtually every computer built since. By 1951, the UNIVAC I, built by Eckert and Mauchly's own company, became the first computer sold commercially in the United States, marking computing's transition from one-off wartime research projects into general government and business use.
Key Participants and Institutions
No single individual invented the electronic computer; it emerged from parallel and overlapping efforts in several countries, often without the different teams knowing of one another's work. Konrad Zuse built early programmable computers in Germany largely in isolation from Allied developments, financing some of his early work himself before receiving limited support from the German government. In Britain, codebreakers at Bletchley Park, including the mathematician Alan Turing, whose prewar theoretical papers had defined the logical limits of what any computing machine could calculate, worked on specialized electromechanical and later electronic machines; engineer Tommy Flowers led the design of Colossus, an electronic machine using vacuum tubes that helped break high-level German military codes from 1944 onward, work that remained classified by the British government for decades after the war and so was long excluded from popular accounts of computing's history.
In the United States, Howard Aiken designed the electromechanical Harvard Mark I in partnership with IBM's engineering staff, while John Mauchly, a physicist, and J. Presper Eckert, an electrical engineer, built the fully electronic ENIAC and later founded their own company to build the commercial UNIVAC. John von Neumann contributed the architectural concepts, described in his 1945 report on EDVAC, that shaped nearly all computers built after the mid-1940s. Each of these efforts addressed different problems, operated under different levels of secrecy, and built on different technical traditions.
How It Works
Mechanical and electromechanical calculators performed arithmetic using physical movement: gears turning to carry digits, levers shifting to register a value, or electrically controlled relay switches opening and closing to route a calculation through the machine's wiring. These moving parts imposed firm physical limits on speed, since nothing could happen faster than a gear could turn or a relay's metal contacts could physically snap shut, typically a matter of thousandths of a second at best, and the repeated physical motion caused mechanical wear, dust accumulation, and occasional failure.
Electronic computers replaced these moving parts with vacuum tubes, which used a heated filament to release a stream of electrons that could be switched between electrical states thousands of times faster than any mechanical or electromechanical part could move, with no mechanical motion involved at all. Early electronic computers like ENIAC performed calculations in decimal using large banks of tubes wired into counting circuits, while the stored-program architecture that followed represented both instructions and data as binary numbers, sequences of electronically stored zeros and ones, held in electronic memory, allowing a computer's task to be changed simply by loading a new set of instructions rather than by physically rewiring or resetting mechanical components.
Dates and Milestones
- 1642Blaise Pascal builds an early mechanical calculating machine.
- 1837Charles Babbage designs the Analytical Engine, a programmable mechanical computer that was never completed in his lifetime.
- 1941Konrad Zuse completes the Z3, an early programmable electromechanical computer, in Germany.
- 1944The Harvard Mark I, a large electromechanical calculator, is completed in the United States.
- 1945–1946ENIAC, the first large-scale electronic computer, is completed and publicly unveiled.
- 1951UNIVAC I becomes the first computer sold commercially in the United States.
Impacts
The shift from mechanical to electronic computation, compressed into roughly two decades, enabled calculations that would have been impractical by hand or with mechanical machines, including the ballistics firing tables, cryptographic codebreaking, and early nuclear weapons design calculations that drove much of the wartime research funding behind these machines. Codebreaking machines at Bletchley Park, including Colossus, are credited by historians with helping the Allies read encrypted German communications more quickly, contributing to the war effort in ways that remained secret for decades, while ENIAC and its successors went on to support weather prediction, nuclear research, and other scientific and military computation throughout the early Cold War.
The advent of the stored-program architecture and the arrival of commercially sold computers like UNIVAC in the early 1950s turned computing from a handful of one-off research machines built for specific government projects into the foundation of an entire industry, one in which companies such as IBM, Remington Rand, and later many others would compete for business and government customers. This period's two central innovations, electronic switching in place of mechanical motion, and stored-program design in place of physical rewiring, established the basic architecture that essentially all subsequent computers would continue to use.
Limitations
Early electronic computers were enormous, expensive, and difficult to maintain. ENIAC filled a room roughly the size of a small gymnasium, consumed on the order of 150 kilowatts of electricity, generated enough heat to require dedicated cooling, and relied on thousands of vacuum tubes that failed regularly and had to be located and replaced by hand, requiring teams of technicians working around the clock.
These machines also had very limited memory by later standards and, in ENIAC's case, had to be physically reconfigured through rewiring and switch-setting to run a different program, a slow and labor-intensive process that the later stored-program design was specifically meant to eliminate. Because of their size, cost, and specialized operation, computers of this era were accessible only to governments, the military, and a small number of universities and large corporations, not yet to ordinary businesses or individuals.
Common Misconceptions
ENIAC is frequently described as the first computer, but this depends heavily on how the term is defined; Zuse's Z3 was an earlier programmable computer, and the British Colossus machines performed specialized electronic computation during the war before ENIAC was completed, though Colossus remained classified until long after ENIAC's public unveiling made the American machine, for decades, the best-known candidate for the title.
It is also a misconception that ENIAC used the stored-program design associated with modern computers; its program was set by physically rewiring patch panels and setting switches, and the stored-program concept was introduced afterward, in its successor EDVAC and in related machines influenced by von Neumann's 1945 report. Women's crucial role in programming and operating early computers such as ENIAC, long underappreciated in popular histories, is now recognized as essential to these machines actually functioning once built.
