A computer is a machine that can be programmed to carry out sequences of arithmetic and logical operations automatically. Modern computers are electronic and digital. They represent information as binary numbers and process it with circuits made from billions of transistors. By changing its program, the same machine can handle very different tasks, from scientific simulation and accounting to communication, entertainment and artificial intelligence. Computers range from tiny embedded controllers in appliances to personal computers, smartphones and room-sized supercomputers. The academic field that studies computation and its applications is computer science.
Early calculating devices
People used tools to help with calculation long before electronic machines existed. The earliest known computing devices date back to ancient civilizations, such as the abacus and the Antikythera mechanism. The abacus helped with counting and arithmetic. The Antikythera mechanism, a geared device from ancient Greece, modelled astronomical cycles. In the 17th century Blaise Pascal built a mechanical adding machine. Gottfried Wilhelm Leibniz designed a calculator that could also multiply, and he described the binary number system that modern machines now use.
In the 19th century the English mathematician Charles Babbage designed first the Difference Engine and then the far more ambitious Analytical Engine. Like modern computers, the Analytical Engine was to encompass various integrated components, including a readable/writable memory (which Babbage called the store) for holding data and programs and a control unit (which he called the mill). The design took punched cards from the Jacquard loom as its input method. Babbage never finished the machine, but Ada Lovelace published notes on it that included a method for calculating Bernoulli numbers. Many people regard this as the first published computer program. In 1854 George Boole published an algebra of logic, now called Boolean algebra, which later became the mathematical basis of digital circuit design.
Theoretical foundations
In 1936 Alan Turing described an abstract device, now called the Turing machine. It reads and writes symbols on a tape according to a fixed set of rules. Turing showed that one "universal" machine could simulate any other such machine, which set out the idea of a general-purpose, programmable computer. He also showed that some problems cannot be solved by any algorithm. Around the same time, Claude Shannon showed that Boolean algebra could describe relay and switching circuits, which connected abstract logic to practical electrical engineering.
The first electronic computers
World War II sped up computer development. German engineer Konrad Zuse completes the Z3, a computer that was used for aerodynamic calculations. In Britain, the Colossus machines helped break German teleprinter codes. In the United States, John Mauchly and J. Presper Eckert built ENIAC at the University of Pennsylvania. Originally announced on February 14, 1946, the Electronic Numerical Integrator and Computer (ENIAC), was the first general-purpose electronic computer. ENIAC used 17,480 vacuum tubes. Programming it meant rewiring the machine by hand.
John von Neumann took part in the ENIAC project. He designed an alternative computer architecture in which programs could be stored in memory along with data. This stored-program design, known as the von Neumann architecture, was first put into practice in machines such as the Manchester Baby (1948) and EDSAC (1949). It is still the basic design of most computers today. UNIVAC I becomes the first commercial computer in 1951.
Transistors, integrated circuits and microprocessors
The invention of the transistor in 1947 revolutionized computing technology, paving the way for smaller, more efficient computers. The transistor was developed at Bell Labs by John Bardeen, Walter Brattain and William Shockley. It is a semiconductor switch that controls the flow of electrons, and it replaced fragile, power-hungry vacuum tubes. Jack Kilby and Robert Noyce independently invent the integrated circuit, a compact electronic circuit that combines multiple transistors on a single chip, in 1958–1959. The integrated circuit made machines smaller, cheaper and more reliable. In 1971 Intel's 4004 put a whole central processing unit on one chip, the first commercial microprocessor.
For decades, the number of transistors on a chip roughly doubled about every two years. This trend is known as Moore's law, and it drove steady growth in performance. As components shrink toward atomic scales, quantum effects and heat dissipation have made further scaling harder.
Architecture and components
A typical computer has these main parts:
- Central processing unit (CPU): fetches instructions from memory, decodes them and executes them using an arithmetic logic unit and control circuitry. Modern CPUs contain several cores that work in parallel.
- Memory: fast, volatile main memory (RAM) holds the programs and data currently in use. A hierarchy of caches sits between memory and the processor.
- Storage: non-volatile devices such as hard disks and solid-state drives keep data when the power is off.
- Input/output devices: keyboards, displays, network interfaces and sensors connect the machine to users and to other systems.
- Specialized accelerators: graphics processing units (GPUs) and similar chips perform massively parallel calculations. They are now central to machine learning.
Software
Hardware does useful work only when it runs software. An operating system manages hardware resources, memory and files, and it gives applications a common platform to run on. Programmers write instructions in programming languages such as C, Java or Python. Compilers or interpreters then translate these instructions into machine code. Open-source software such as the Linux kernel now runs on everything from phones to supercomputers.
Types of computers
Mainframes served large organizations from the 1950s onward. Minicomputers in the 1960s and 1970s made computing affordable for laboratories and universities. Personal computers spread in the late 1970s and 1980s, with machines such as the Apple II and IBM PC. Smartphones and tablets later became the main computing devices for many people. Embedded computers, often invisible to users, control cars, appliances and industrial equipment.
Supercomputers handle the most demanding scientific workloads. According to the June 2026 TOP500 list, the world's most powerful supercomputer is LineShine, installed at the National Supercomputing Centre in Shenzhen, China, with 2.198 Exaflop/s on the HPL benchmark. El Capitan ranked second with 1.809 exaflops.
Networks and new paradigms
Linking computers together produced the Internet and the World Wide Web. Through cloud computing, users can rent processing power and storage from remote data centres. Since the 2010s, very large computing clusters have been used to train large language models and other AI systems. Researchers are also building quantum computers, which use quantum bits to tackle certain problems that classical machines handle poorly. Optical and neuromorphic computing are being studied as other alternatives to conventional digital electronics.
Social impact
Computers have changed science, industry, finance, education and communication. They have automated many routine tasks and created new industries. They have also raised problems around privacy, cybersecurity, unequal access to technology and the energy use of data centres.
References
- History of Computers Timelinepreceden.com
- C4: The History of Computers - freecsc.comfreecsc.com
- History of Computersstudy.com
- ENIACengineering.upenn.edu
- A History of Computingcs.bsu.edu
- Evolution and History of Computer: From ENIAC to AIsuperprof.co.in
- The World’s Most Powerful Supercomputers in 2026: LineShine Takes the Leadstackscale.com
- China beats US in TOP500 ranking with world’s fastest supercomputertechwireasia.com