The first electronic computer was the ENIAC, built in 1946
The ENIAC (Electronic Numerical Integrator and Computer) is widely recognized as the first general-purpose electronic computer. It was completed in November 1946 at the University of Pennsylvania and weighed 30 tons. ENIAC used vacuum tubes instead of mechanical parts to perform calculations, which made it far faster than any machine before it — it could do 5,000 additions per second.
However, "first computer" depends on what you count as a computer. If you mean a machine that could be programmed to solve different problems, ENIAC holds that title. If you mean any calculating machine, the history stretches back much further. The distinction matters because earlier machines were powerful but built for one specific task, while ENIAC could be rewired to do different jobs.
Key Takeaways
- ENIAC, completed in 1946, was the first general-purpose electronic computer and could perform 5,000 calculations per second using vacuum tubes.
- Earlier mechanical calculating machines like the Analytical Engine (designed in 1837) could perform calculations but were not programmable for multiple tasks.
- The Colossus computer, built in 1943 for code-breaking during World War II, was electronic but designed for a single purpose rather than general use.
- The shift from mechanical to electronic computing happened in the 1940s, driven by the need for faster calculations during wartime.
Mechanical calculating machines came centuries before electronics
Long before electricity, inventors built machines to do math. The Pascaline, created by Blaise Pascal in 1642, could add and subtract using gears and wheels. It was a real machine that worked, but it could only do arithmetic — you could not reprogram it to do something else.
In the 1830s, Charles Babbage designed the Analytical Engine, which is often called the first computer because it could be programmed using punched cards (the same idea used in ENIAC decades later). The Analytical Engine was never fully built during Babbage's lifetime, but the design showed that a machine could be made to follow different instructions. Ada Lovelace wrote notes about how to program it, making her one of the first people to write computer instructions.
These machines were brilliant designs, but they were mechanical — they used gears, levers, and human power to turn. They were slow and could not scale up to handle the complex calculations that scientists and engineers needed by the 20th century.
Colossus was electronic but built for one job only
During World War II, the British built Colossus in 1943 to break German military codes. It was electronic — it used vacuum tubes like ENIAC would — and it was faster than any mechanical machine. But Colossus was purpose-built. You could not reprogram it to do something completely different; it was designed to attack one specific type of cipher.
Colossus was kept secret after the war and was largely unknown to the public and to American computer scientists at the time. ENIAC, by contrast, was built in the open and became the model that other researchers copied and improved. That is partly why ENIAC gets the credit as the first general-purpose electronic computer.
ENIAC was massive, expensive, and required constant maintenance
ENIAC occupied 1,800 square feet — roughly the size of a small house — and consumed 150 kilowatts of electricity. It generated so much heat that it needed its own cooling system. The machine had 18,000 vacuum tubes, and tubes burned out regularly, so technicians had to replace them constantly to keep the computer running.
Operating ENIAC cost thousands of dollars per day in today's money. It was not a machine you could buy; it was a research tool that only universities and government agencies could afford. Despite these limitations, ENIAC proved that electronic computing was possible and far superior to mechanical methods. Once the principle was established, engineers worked to make computers smaller, cheaper, and more reliable.
The vacuum tube era led to smaller, faster machines
After ENIAC, computers got better quickly. The UNIVAC (Universal Automatic Computer), completed in 1951, was the first computer sold commercially. It was still enormous by modern standards, but it was smaller and more reliable than ENIAC. UNIVAC used the same vacuum tube technology but with better engineering.
Vacuum tubes remained the standard until the late 1950s, when the transistor was invented. Transistors were smaller, used less power, and generated less heat. Computers built with transistors could be smaller and faster. This shift from tubes to transistors marked the beginning of the second generation of computers and set the stage for everything that followed.
The timeline from mechanical to electronic computing
| Year | Machine | Type | What it could do |
|---|---|---|---|
| 1642 | Pascaline | Mechanical | Add and subtract only |
| 1837 | Analytical Engine (designed) | Mechanical | Programmable for different math tasks |
| 1943 | Colossus | Electronic | Code-breaking only; not reprogrammable |
| 1946 | ENIAC | Electronic | General-purpose; could be reprogrammed for any task |
| 1951 | UNIVAC | Electronic | General-purpose; first commercial computer |
Why ENIAC gets the credit despite earlier designs
ENIAC is called the first computer because it combined three things: it was electronic (fast), it was general-purpose (programmable for different tasks), and it actually existed and worked. The Analytical Engine had the right idea but was never built. Colossus was electronic but locked into one job. ENIAC did all three.
The other reason ENIAC became the reference point is that it was public. Scientists and engineers could study it, learn from it, and build on it. The knowledge spread, and within a few years, other institutions were building their own computers based on ENIAC's design. That ripple effect made ENIAC the ancestor of modern computing.
Frequently Asked Questions
Did anyone build a computer before ENIAC?
Yes, but with caveats. Colossus was electronic and ran in 1943, three years before ENIAC. However, Colossus was built for code-breaking only and could not be reprogrammed for other tasks. The Analytical Engine, designed in 1837, was programmable but was mechanical and never fully built. ENIAC was the first machine that was both electronic and general-purpose.
Why do people say ENIAC was the first if Colossus came earlier?
Colossus was kept secret by the British government until decades after the war. American computer scientists did not know about it when they were building ENIAC and the machines that followed. ENIAC became the public reference point and the model that shaped the industry. Additionally, ENIAC's general-purpose design made it more influential than Colossus's single-task approach.
How long did it take to build ENIAC?
ENIAC took about three years to build, from 1943 to 1946. The team, led by John Mauchly and J. Presper Eckert, faced constant engineering challenges because vacuum tube technology was new and unreliable. Despite the difficulties, they proved the concept worked and opened the door to the computer age.
Could ENIAC do anything a modern computer can do?
In theory, yes — ENIAC was Turing-complete, meaning it could solve any problem that any computer can solve, given enough time and memory. In practice, no — ENIAC was slow, had tiny memory, and could not connect to other machines or display graphics. But the principle was the same: it followed instructions to process information and produce results.