The first general-purpose computer was the ENIAC, completed in 1946

ENIAC (Electronic Numerical Integrator and Computer) was the first machine that could be reprogrammed to solve different problems. It was built at the University of Pennsylvania during World War II and finished in February 1946. ENIAC weighed 30 tons, occupied 1,800 square feet of floor space, and used 18,000 vacuum tubes instead of transistors or chips. It could perform about 5,000 additions per second—fast for the time, but slow compared to any calculator today.

Before ENIAC, machines existed that could do arithmetic or follow a fixed sequence of steps, but they could not be reprogrammed without physically rewiring them. ENIAC changed that. You could feed it new instructions on punch cards, and it would solve a completely different problem. That ability to be reprogrammed is what makes it the first true computer in the modern sense.

Key Takeaways

  • ENIAC, completed in 1946, was the first general-purpose computer because it could be reprogrammed to solve different types of problems.
  • Earlier machines like the Analytical Engine (designed in 1837) and mechanical calculators could perform calculations but could not be reprogrammed without physical rewiring.
  • ENIAC used vacuum tubes for processing and could perform 5,000 additions per second, which was revolutionary but is millions of times slower than modern computers.
  • The invention of the transistor in 1947 and the integrated circuit in 1958 made computers smaller, faster, and practical for everyday use.

Earlier machines that came close but were not computers

The Analytical Engine, designed by Charles Babbage in 1837, is often called the first computer because it was programmable—you could feed it punch cards with instructions. However, it was never fully built during Babbage's lifetime, and it was mechanical, not electronic. It could not be switched on and off to solve different problems the way ENIAC could.

In the 1930s and 1940s, several machines bridged the gap. The Z3, built by Konrad Zuse in Germany in 1941, was the first working programmable machine and used electromagnetic relays instead of mechanical parts. The Colossus, built in Britain during World War II to break German codes, was electronic and fast but was designed for one specific task and could not be easily reprogrammed. ENIAC was the first to combine all three: it was electronic, it was programmable, and it could solve many different types of problems.

Why vacuum tubes made ENIAC possible

ENIAC worked because of the vacuum tube, a glass bulb that could switch electricity on and off thousands of times per second. Mechanical relays (electromagnets that flipped switches) were too slow. Vacuum tubes had no moving parts, so they could flip much faster. Each tube represented a 1 or a 0 in binary code, and thousands of tubes working together could store numbers and perform calculations.

The downside was heat and power. ENIAC consumed 150 kilowatts of electricity and generated so much heat that it needed its own cooling system. The vacuum tubes also burned out frequently and had to be replaced. Despite these problems, ENIAC proved that electronic computing was possible and practical for serious scientific work.

How computers got smaller and faster after 1946

The transistor, invented at Bell Labs in 1947, was smaller than a vacuum tube, used less power, and lasted longer. By the 1950s, computers built with transistors were faster and more reliable than ENIAC. The integrated circuit, invented in 1958, put thousands of transistors on a single chip of silicon. This made computers even smaller and cheaper to manufacture.

By the 1970s, the microprocessor—a single chip that could do what ENIAC did with its 30 tons of equipment—made personal computers possible. The Apple II (1977) and the IBM PC (1981) brought computing into homes and offices. Today's smartphones contain more computing power than ENIAC and all the computers built in the 1950s combined.

What ENIAC was actually used for

ENIAC's first major task was calculating ballistic tables for artillery shells—work that had been done by hand or with mechanical calculators and took weeks. ENIAC could do the same work in hours. It was also used for weather prediction, nuclear weapons design, and early scientific research in physics and mathematics.

The machine was not secret, but it was not widely known either. Most people had never heard of it. Computers remained rare, expensive, and confined to universities, government agencies, and large corporations until the 1970s and 1980s. The idea that a computer would sit on a desk in every home or fit in a pocket would have seemed like science fiction to the engineers who built ENIAC.

Why the date 1946 matters

1946 is the year ENIAC was completed and tested, though work on it began in 1943. Some sources say 1945 because that is when the machine first ran a successful test. The exact date depends on whether you count the moment it was switched on or the moment it was declared fully operational. For practical purposes, 1946 is the standard date used in computing history.

What matters more than the exact date is what ENIAC represented: the moment when humans built a machine that could store information, follow instructions, and solve problems faster than any human or mechanical device before it. That capability—reprogrammable, electronic, general-purpose computing—is what defines a computer, and ENIAC was the first.

Frequently Asked Questions

Was the Analytical Engine the first computer?

The Analytical Engine, designed by Charles Babbage in 1837, was programmable and is considered a theoretical ancestor of the modern computer. However, it was never fully built, and it was mechanical, not electronic. ENIAC in 1946 was the first working, electronic, general-purpose computer.

How much did ENIAC cost?

ENIAC cost approximately $500,000 to build in 1946, which is roughly $8 million in today's money when adjusted for inflation. It was funded by the U.S. Army Ballistic Research Laboratory because the military needed faster calculations for weapons design.

Could ENIAC run multiple programs at the same time?

No. ENIAC could run only one program at a time. It had to be physically rewired or reprogrammed with new punch cards between jobs. Modern computers can run thousands of programs simultaneously through a technique called multitasking, which ENIAC could not do.

How long did it take to reprogram ENIAC?

Reprogramming ENIAC could take hours or even days, depending on how different the new task was from the previous one. Operators had to physically change cables and reset switches. Modern computers can switch between programs in milliseconds.

What happened to the original ENIAC?

ENIAC was shut down in 1955 after nine years of operation. Parts of it are now in the Smithsonian Institution and the University of Pennsylvania. The machine was too large and power-hungry to preserve in its entirety, but its design and principles live on in every computer built since.