The first general-purpose computer was the ENIAC, completed in 1946 by a team at the University of Pennsylvania

ENIAC stands for Electronic Numerical Integrator and Computer. It was built during World War II by engineers John Mauchly and J. Presper Eckert, along with a larger team at the Moore School of Electrical Engineering. The machine was finished in February 1946 and first put to work calculating artillery firing tables for the U.S. Army Ballistic Research Laboratory.

ENIAC was enormous—it weighed 30 tons, occupied 1,800 square feet of floor space, and used 18,000 vacuum tubes instead of transistors or chips. It consumed 150 kilowatts of electricity and generated so much heat that the room had to be air-conditioned. Despite its size and power hunger, ENIAC could perform about 5,000 additions per second, which was revolutionary for the time.

Before ENIAC, machines that could do arithmetic existed, but they were either mechanical (like adding machines) or special-purpose devices built for one narrow task. ENIAC was the first machine that could be reprogrammed to solve different problems without being physically rewired—that flexibility is what made it a true general-purpose computer.

Key Takeaways

  • ENIAC, built by John Mauchly and J. Presper Eckert at the University of Pennsylvania, was completed in 1946 and is recognized as the first general-purpose electronic computer.
  • The machine used 18,000 vacuum tubes, weighed 30 tons, and could perform 5,000 additions per second—fast for its era but requiring enormous amounts of electricity and cooling.
  • Earlier calculating machines existed, but ENIAC was the first that could be reprogrammed to solve different problems without physical rewiring.
  • ENIAC was initially built to calculate artillery firing tables for the U.S. Army during World War II.

Earlier machines that came close but were not general-purpose computers

Several inventors built calculating machines before ENIAC, and some of them were remarkably sophisticated. In the 1820s, Charles Babbage designed the Analytical Engine, a mechanical computer that could be programmed using punch cards—a concept that would not be fully realized for over a century. Babbage never built a working version, but his design contained the core ideas of modern computing.

In the 1930s and 1940s, other researchers were working on electromechanical and electronic calculating machines. Konrad Zuse in Germany built the Z3 in 1941, which some historians consider the first programmable digital computer, though it was less flexible than ENIAC and used a different architecture. In Britain, the Colossus computers were built during World War II to break German military codes, but they were single-purpose machines designed only for that task.

The key difference is that ENIAC could be reprogrammed by changing how its vacuum tubes were connected and configured, making it truly general-purpose. Earlier machines were either limited to one task or required so much physical rewiring that they were impractical for switching between problems.

How ENIAC was programmed and used

Programming ENIAC was nothing like programming a modern computer. There were no keyboards, screens, or programming languages. Instead, operators physically plugged cables into panels and flipped thousands of switches to set up the machine for each new calculation. A single program could take days or weeks to set up, and the machine itself had to be reconfigured between jobs.

The first major task ENIAC performed after its completion was calculating the feasibility of the hydrogen bomb for the U.S. government. It ran continuously for weeks on that single problem. Later, it was used for weather prediction, artillery calculations, and scientific research. Because ENIAC was so large and expensive to operate, it was kept at the University of Pennsylvania and used by researchers from many institutions who would submit their problems to be run.

Despite the difficulty of programming it, ENIAC demonstrated that electronic computing was practical and far faster than mechanical or electromechanical alternatives. This success sparked investment in computer research around the world and led to the development of smaller, more practical machines in the 1950s.

The transition from ENIAC to practical computers

ENIAC proved the concept, but it was too large and power-hungry to be practical for most institutions. The next major step came with the invention of the transistor in 1947 at Bell Labs, which could do the same job as a vacuum tube but was much smaller, more reliable, and used far less power. Computers built in the 1950s using transistors were smaller and more dependable than ENIAC.

The UNIVAC I, delivered in 1951, was one of the first commercial computers. It was still large by modern standards but much more practical than ENIAC. It became famous for correctly predicting the outcome of the 1952 U.S. presidential election based on early voting returns—a demonstration that caught public attention and showed that computers could handle real-world problems.

By the late 1950s and 1960s, computers were becoming smaller and more affordable, though still expensive enough that only large organizations could own them. The real revolution came in the 1970s with the microprocessor and personal computers, but that story begins with ENIAC's success in proving that electronic, programmable computing was possible.

Why ENIAC matters even though it is obsolete

ENIAC is historically important because it was the first machine to combine three essential features: it was electronic (using vacuum tubes instead of mechanical parts), it was programmable (you could change what it did without rebuilding it), and it was general-purpose (it could solve many different kinds of problems). No earlier machine had all three.

The principles that made ENIAC work—using electronic switches to represent numbers, performing calculations by manipulating those switches at high speed, and storing instructions that could be changed—are the same principles that underlie every computer today. A modern laptop is vastly smaller, faster, and more efficient, but it works on the same fundamental ideas that Mauchly and Eckert demonstrated in 1946.

Frequently Asked Questions

Was ENIAC really the first computer ever made?

ENIAC was the first general-purpose electronic computer. Simpler calculating machines existed before it, and some special-purpose electronic machines were built around the same time, but ENIAC was the first that could be reprogrammed to solve different kinds of problems without being physically rebuilt.

How much did ENIAC cost to build?

ENIAC cost approximately $400,000 to build during World War II, which would be roughly $6 million in today's dollars when adjusted for inflation. The cost was covered by the U.S. Army, which funded the project because of its military applications.

Could ENIAC do everything 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, it was limited by its tiny memory (about 5 kilobytes) and slow speed. A calculation that takes a modern computer milliseconds might take ENIAC hours or days.

Why did ENIAC use vacuum tubes instead of something smaller?

Vacuum tubes were the only electronic switches available in the 1940s that could operate fast enough for computing. Transistors, which are much smaller, were not invented until 1947 and were not reliable enough for computers until the 1950s. ENIAC's designers used the best technology that existed at the time.

Is ENIAC still in existence?

ENIAC was dismantled in 1955 after it was no longer needed. However, parts of it are preserved in museums, including the Smithsonian Institution and the University of Pennsylvania. You can see photographs and technical documentation of the machine in many computing history resources.