The First Computers Were Built in the 1940s

The first electronic computers were built during World War II, between 1943 and 1946. ENIAC (Electronic Numerical Integrator and Computer), completed in 1946 at the University of Pennsylvania, is widely recognized as the first general-purpose electronic computer. It weighed 30 tons, occupied 1,800 square feet of floor space, and used 18,000 vacuum tubes to process information. ENIAC could perform 5,000 additions per second—a speed that seemed miraculous at the time but is now slower than a pocket calculator.

Before ENIAC, machines existed that could perform calculations, but they were either mechanical (like the Analytical Engine designed by Charles Babbage in 1837) or electromechanical (like the Mark I, completed in 1944). These earlier machines were not truly electronic and could not be reprogrammed for different tasks without physical rewiring. ENIAC changed that by using electricity to process information and allowing operators to reprogram it by rearranging cables and switches.

Key Takeaways

  • ENIAC, built in 1946, was the first general-purpose electronic computer and used vacuum tubes instead of mechanical parts.
  • Earlier calculating machines existed, but they were mechanical or electromechanical and could not be easily reprogrammed.
  • Computers shrank dramatically from room-sized machines in the 1950s to desktop computers in the 1980s to smartphones today.
  • The transistor, invented in 1947, replaced vacuum tubes and made computers smaller, faster, and more reliable.
  • Personal computers became common in homes and offices during the 1980s and 1990s, changing how people work and communicate.

Vacuum Tubes and the First Generation of Computers (1946–1956)

The first generation of computers all relied on vacuum tubes to process information. A vacuum tube is a glass bulb with no air inside that glows when electricity passes through it. Thousands of these tubes worked together to represent data as on-off electrical signals. The problem was that vacuum tubes generated enormous amounts of heat, burned out frequently, and consumed huge amounts of electricity.

Computers from this era filled entire rooms and required dedicated cooling systems. UNIVAC I, delivered to the U.S. Census Bureau in 1951, was one of the first computers sold commercially. It cost $159,000 (roughly $1.8 million in today's money) and weighed 13 tons. Only a handful of organizations—government agencies, universities, and large corporations—could afford to own and operate these machines.

The Transistor Revolution (1956–1964)

The invention of the transistor in 1947 by Bell Labs scientists transformed computing. A transistor is a tiny electronic switch made from semiconductor material (usually silicon) that can turn on and off millions of times per second. Unlike vacuum tubes, transistors generated far less heat, lasted much longer, and consumed far less power. Second-generation computers, built between 1956 and 1964, replaced vacuum tubes with transistors.

Transistor-based computers were smaller, faster, and more reliable than their vacuum-tube predecessors. The IBM 1401, released in 1959, became one of the most widely used computers of its time. It was still room-sized and cost tens of thousands of dollars, but it was affordable enough for medium-sized businesses to purchase. Programming was still done by punching holes in paper cards or magnetic tape, and results were printed on paper.

Integrated Circuits and Miniaturization (1964–1971)

The next breakthrough came with the integrated circuit (IC), developed independently by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor in 1958. An integrated circuit combines many transistors and other electronic components onto a single chip of silicon. Third-generation computers, built from 1964 onward, used integrated circuits and became even smaller and more powerful.

The IBM System/360, introduced in 1964, was a family of computers that could run the same software regardless of size or power. This standardization made it easier for businesses to upgrade without rewriting all their programs. Computers were still large machines kept in air-conditioned rooms, but they were becoming more practical for organizations beyond the largest corporations and government agencies.

Personal Computers Arrive (1971–1985)

The microprocessor—a complete computer processor on a single chip—made personal computers possible. Intel released the 4004 microprocessor in 1971, followed by more powerful chips throughout the 1970s. The Apple II, released in 1977, was the first mass-produced personal computer with a keyboard, monitor, and color graphics. The IBM PC, released in 1981, became the standard for business computers and home use.

These early personal computers had limited memory (often just 64 kilobytes), slow processors, and small screens, but they were affordable enough for individuals and small businesses to own. The Apple II cost around $1,300 in 1977 (roughly $6,500 today), while the IBM PC cost about $3,000 in 1981 (roughly $9,000 today). Software like VisiCalc (a spreadsheet) and WordStar (a word processor) made these machines useful for real work, not just hobbyists.

Desktop Computing and the Internet Era (1985–2000)

The 1980s and 1990s saw personal computers become standard equipment in offices and homes. The IBM PC and its clones (computers built by other manufacturers using the same design) dominated the business market, while Apple computers remained popular in education and creative fields. Microsoft's Windows operating system, released in 1985 and improved throughout the 1990s, made computers easier to use by replacing text commands with a graphical interface of windows and icons.

The World Wide Web, invented by Tim Berners-Lee in 1989 and released to the public in 1991, transformed how computers were used. The internet connected computers together, allowing people to share information, send email, and access websites. By the late 1990s, owning a computer with internet access became common in developed countries. Computers that once filled entire rooms now fit on a desk, and the price had dropped from hundreds of thousands of dollars to under $1,000.

Modern Computing: Laptops, Tablets, and Smartphones (2000–Present)

The 21st century brought computers into even smaller and more portable forms. Laptops became powerful enough to replace desktop computers for most tasks. Smartphones, beginning with the iPhone in 2007, put a computer in everyone's pocket. Tablets like the iPad (2010) offered a middle ground between phones and laptops. Cloud computing—storing data and running programs on distant servers rather than on your own machine—changed how people think about what a computer is.

Today's computers are vastly more powerful than ENIAC. A smartphone has more processing power than all the computers that existed in 1980 combined. Computers are now embedded in cars, appliances, watches, and countless other devices. The basic principles remain the same—electricity represents data as on-off signals, and circuits process those signals—but the scale and speed have changed beyond recognition.

Frequently Asked Questions

Who invented the computer?

No single person invented the computer. Charles Babbage designed the Analytical Engine in 1837, which had the basic ideas of a programmable computer, but it was never built. ENIAC, completed in 1946 by a team at the University of Pennsylvania led by John Mauchly and J. Presper Eckert, was the first electronic computer actually constructed and operated.

What was the first personal computer?

The Apple II, released in 1977, was the first mass-produced personal computer sold to the general public. The Altair 8800 (1975) came earlier but was sold as a kit for hobbyists. The IBM PC (1981) became the standard for business and home computing and led to the computers most people use today.

How much did early computers cost?

ENIAC cost about $500,000 to build in 1946 (roughly $8 million today). The Apple II cost $1,300 in 1977 (roughly $6,500 today). The IBM PC cost $3,000 in 1981 (roughly $9,000 today). Modern computers cost between $300 and $2,000, making them affordable for most people.

Why were early computers so large?

Early computers were large because they used vacuum tubes, which are bulky glass components. Each tube performed the function of a single transistor, so thousands of tubes were needed. Computers also needed large power supplies and cooling systems. As transistors and integrated circuits replaced vacuum tubes, computers shrank dramatically while becoming more powerful.

When did computers become common in homes?

Personal computers began appearing in homes in the late 1970s and early 1980s, but they remained expensive and mostly for enthusiasts. By the 1990s, as prices fell and the internet became popular, home computers became common in developed countries. Today, most households have at least one computer, whether a desktop, laptop, tablet, or smartphone.