The ENIAC was the first general-purpose electronic computer, completed in 1946
The ENIAC (Electronic Numerical Integrator and Computer) became operational in February 1946 at the University of Pennsylvania. It was the first machine that could solve a wide range of mathematical problems by changing its instructions, rather than being built for one specific task. ENIAC weighed 30 tons, occupied 1,800 square feet of floor space, and used 18,000 vacuum tubes to process information.
Before ENIAC, machines existed that could perform calculations, but they were either mechanical (like adding machines) or designed to solve only one type of problem. ENIAC's breakthrough was its ability to be reprogrammed for different tasks without rebuilding the hardware. This flexibility is what makes it the ancestor of modern computers.
Key Takeaways
- ENIAC, built at the University of Pennsylvania, began operating in February 1946 and is recognized as the first general-purpose electronic computer.
- Earlier calculating machines existed, but they could only perform one task or required mechanical operation, unlike ENIAC's programmable electronic design.
- ENIAC used vacuum tubes instead of mechanical parts, which allowed it to process information much faster than previous machines.
- The machine was enormous by today's standards—weighing 30 tons and using 18,000 vacuum tubes—yet performed calculations slower than a modern smartphone.
Why earlier machines don't count as computers
Machines that performed arithmetic existed long before 1946. The abacus, invented around 2700 BCE, let users calculate by moving beads on rods. In the 1600s, Blaise Pascal built a mechanical calculator that could add and subtract. In the 1800s, Charles Babbage designed the Analytical Engine, which had many features of a modern computer—it could be programmed with punch cards and perform different operations—but it was never fully built during his lifetime.
The key difference is that these machines either required a human operator to physically move parts (like the abacus), or they performed only arithmetic operations (like Pascal's calculator). ENIAC was the first machine that could store a program in its memory, follow that program automatically, and be reprogrammed for entirely different tasks without physical modification. That programmability is what makes it a true computer.
How ENIAC worked with vacuum tubes
ENIAC replaced mechanical gears and switches with vacuum tubes—glass bulbs that could turn electrical current on and off thousands of times per second. Each vacuum tube acted like a tiny switch, and by combining thousands of them, engineers could build circuits that performed logic and arithmetic. The tubes generated enormous heat, so ENIAC required a dedicated cooling system and consumed 150 kilowatts of electricity.
Programming ENIAC meant physically rewiring parts of the machine and setting thousands of switches by hand. A single program could take days to set up. The machine could perform about 5,000 additions per second, which was revolutionary at the time but is millions of times slower than a modern processor. Despite its size and power consumption, ENIAC could only store about 200 decimal digits in its memory—less information than a single sentence of text.
Computers that came after ENIAC
ENIAC proved that electronic computers were practical, and other machines followed quickly. The EDVAC (Electronic Discrete Variable Automatic Computer), also built at the University of Pennsylvania, was completed in 1949 and improved on ENIAC's design. The Manchester Mark 1, built in England, began operating in 1948. These machines were still room-sized and used vacuum tubes, but they were faster and more reliable than ENIAC.
The invention of the transistor in 1947 eventually made computers smaller and more efficient. Transistors replaced vacuum tubes starting in the 1950s, leading to computers that fit in a single cabinet rather than filling an entire room. By the 1960s, computers were becoming common in universities and large businesses, though still far too expensive for home use.
The difference between ENIAC and earlier calculating machines
| Machine | Year Built | How It Worked | Could Be Reprogrammed |
|---|---|---|---|
| Abacus | ~2700 BCE | Manual beads on rods | No—only for counting |
| Pascal's Calculator | 1642 | Mechanical gears | No—only addition and subtraction |
| Analytical Engine (design) | 1837 | Mechanical gears, punch cards | Yes—but never fully built |
| ENIAC | 1946 | Vacuum tubes, electronic circuits | Yes—and actually built and working |
Why historians credit ENIAC as the first computer
ENIAC gets the title of "first computer" because it combined three things that earlier machines lacked: it was electronic (using vacuum tubes instead of mechanical parts), it was programmable (instructions could be changed without rebuilding the hardware), and it was actually built and operational (unlike Babbage's Analytical Engine, which remained a design). Babbage's design was theoretically sound, but without a working machine, there was nothing to prove the concept worked in practice.
Some historians point to earlier machines like the Colossus, built in Britain during World War II to break German codes, as an electronic computer that predated ENIAC. Colossus was operational in 1943 and used vacuum tubes. However, Colossus was designed for a single task—breaking one type of code—and could not be easily reprogrammed for other work. ENIAC's general-purpose design is why it is more widely recognized as the first true computer.
Frequently Asked Questions
Was the computer invented in one place or by one person?
ENIAC was built by a team of engineers at the University of Pennsylvania, led by John Mauchly and J. Presper Eckert. However, the idea of an electronic computing machine developed across multiple countries. British engineers were working on similar ideas during World War II, and the concept of programmable machines goes back to Charles Babbage in the 1800s. No single person "invented" the computer.
Could ENIAC do anything a modern computer can do?
ENIAC could perform any calculation a modern computer can, but it would take much longer and could only work with numbers, not text or images. Modern computers are faster, smaller, and can store and process many types of information. ENIAC was limited to mathematical problems and could only hold tiny amounts of data in memory. The basic principle—following a stored program—is the same.
How long did it take to build ENIAC?
ENIAC took about three years to build, from 1943 to 1946. The project was funded by the U.S. Army during World War II because the military needed a machine to calculate artillery firing tables. After the war ended, the team finished the machine and demonstrated it to the public in 1946.
Why did ENIAC use so much electricity?
Vacuum tubes generate heat when they conduct electricity, and ENIAC used 18,000 of them. The machine consumed 150 kilowatts of power—roughly the amount needed to power 150 modern homes. This was one reason why early computers were expensive to operate and why the invention of the transistor, which used far less power, was so important to making computers practical.