The first computer depends on how you define "computer"

There is no single answer because the word "computer" meant different things at different times. If you mean a machine that could be programmed to solve many kinds of problems, the ENIAC (Electronic Numerical Integrator and Computer) built in 1946 at the University of Pennsylvania is usually called the first general-purpose electronic computer. It weighed 30 tons, filled a room, and used 18,000 vacuum tubes instead of transistors or chips.

If you mean a smaller, practical machine that businesses and people could actually own, that was the IBM System/360, released in 1964. It was the first computer family where different models could run the same software, which made it possible for companies to upgrade without rewriting everything.

If you mean a computer you could hold in your hands, the Apple II, released in 1977, was the first personal computer sold in large numbers to regular people. Before that, computers were room-sized machines in universities and corporations.

Key Takeaways

  • ENIAC, built in 1946, was the first general-purpose electronic computer, but it was the size of a room and used vacuum tubes.
  • The IBM System/360 in 1964 introduced the idea of a computer family where different models could run the same programs.
  • The Apple II in 1977 was the first personal computer that regular people could buy and use at home.
  • Each of these machines was "first" in a different way because "computer" has meant different things across different eras.

ENIAC and the vacuum tube era (1946)

ENIAC was built to calculate artillery firing tables for the U.S. Army during World War II, though the war ended before it was finished. It contained 18,000 vacuum tubes, which are glass bulbs that act like electronic switches. The machine was 8 feet tall, 100 feet long, and weighed as much as 30 elephants. It consumed 150 kilowatts of electricity and generated so much heat that the room had to be air-conditioned.

Programming ENIAC meant physically rewiring cables and flipping switches by hand. A single program could take days to set up. Despite these limitations, ENIAC could perform 5,000 additions per second, which was revolutionary for the time. It proved that electronic computation was possible and faster than any mechanical calculator.

Other early computers followed the same vacuum tube design: the Manchester Mark 1 in 1948, the UNIVAC in 1951, and the IBM 701 in 1952. All of them were enormous, expensive, and required teams of engineers to operate and maintain.

The transistor and the IBM System/360 (1950s–1960s)

In 1947, Bell Labs invented the transistor, a much smaller electronic switch that could do the same job as a vacuum tube but used far less power and generated far less heat. Computers built with transistors were smaller and more reliable. The IBM 1401, released in 1959, was the first mass-produced computer and became the standard in business offices.

The real turning point came in 1964 with the IBM System/360. IBM released it as a family of computers in different sizes, from small to large, all running the same software. Before this, each computer model required its own programs and training. The System/360 meant a company could start with a small model and upgrade to a larger one without throwing away its software investment. This made computers practical for businesses of all sizes.

The System/360 was so successful that it defined what a computer should be for the next 20 years. Competitors built "IBM-compatible" machines, and the idea of standardized computer families became the norm.

The integrated circuit and the minicomputer (1960s–1970s)

In the early 1960s, engineers learned how to put many transistors on a single piece of silicon, creating an integrated circuit or chip. This made computers smaller and cheaper. A new category called minicomputers emerged — machines smaller than room-sized mainframes but more powerful than calculators. The DEC PDP-8, released in 1965, was the first successful minicomputer and cost around $20,000, which was expensive but within reach of universities and medium-sized companies.

Minicomputers were important because they showed that computers did not have to be enormous to be useful. They could sit on a desk or in a closet. They also introduced the idea that a single department or research group could own its own computer instead of sharing time on a mainframe with hundreds of other users.

The personal computer revolution (1970s–1980s)

In 1975, the Altair 8800 was released as a kit for hobbyists. It had no keyboard or screen — you toggled switches on the front panel to enter data and read the results as blinking lights. It was the first computer you could buy for under $400, but it required serious technical knowledge to use.

The Apple II, released in 1977, changed everything. It came with a keyboard, a screen, and a cassette drive for storing programs. It was designed for people who were not engineers. The Apple II became the first personal computer to sell in the millions. It proved that computers could be consumer products, not just industrial tools.

The IBM Personal Computer, released in 1981, brought IBM's reputation and manufacturing scale to the personal computer market. It ran an operating system called MS-DOS, made by a young company called Microsoft. IBM's PC became the standard that other manufacturers copied, and "IBM-compatible" computers flooded the market in the 1980s and 1990s.

What counted as a computer before electronics

Before ENIAC, the word "computer" meant a person — usually a woman — who did calculations by hand or with a mechanical calculator. During World War II, the U.S. military employed hundreds of human computers to calculate ballistics tables. Machines that could do arithmetic automatically, like the Analytical Engine designed by Charles Babbage in the 1830s, were called "calculating machines" rather than computers.

Babbage's Analytical Engine was never built during his lifetime, but it had all the features of a modern computer: a memory, a processor, and the ability to be programmed with punched cards. If it had been built and worked, it would have been the first programmable computer by more than a century. Some historians count it as the first computer in theory, even though no working version existed until the 1990s.

Frequently Asked Questions

Was the Analytical Engine the first computer?

Charles Babbage designed the Analytical Engine in the 1830s with all the features of a modern computer, but it was never built during his lifetime. A working replica was constructed in the 1990s. Most historians credit ENIAC in 1946 as the first actual working general-purpose electronic computer, though Babbage's design was theoretically first.

Why was ENIAC so big and hot?

ENIAC used 18,000 vacuum tubes as electronic switches. Vacuum tubes are glass bulbs that work like light bulbs — they generate heat and take up space. A single tube is about the size of a thumb. Transistors, invented in 1947, could do the same job in a fraction of the space and with much less heat, which is why computers shrank rapidly after that.

Could you actually use a computer in the 1950s and 1960s?

Only if you worked for a large organization like a bank, university, or government agency. These computers cost hundreds of thousands of dollars and required teams of specialists to operate. Most people never saw a computer until the 1970s or 1980s. Personal computers did not exist until the Apple II in 1977.

What is the difference between a mainframe and a personal computer?

A mainframe is a large, expensive computer designed to serve many users at once through terminals. A personal computer is designed for one person to use directly. Mainframes still exist and are used by banks and large corporations, but personal computers have become far more powerful and are now the standard way most people interact with computers.