A computer is a machine
that manipulates data
according to a list of
The first devices that
resemble modern computers date to the mid-20th century (1940–1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers (PC). Modern computers are
based on tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space. Today, simple computers may be made small enough to fit into a wristwatch and be
powered from a watch battery. Personal computers, in various forms,
are icons of the Information Age and are what most people think of as "a computer"; however, the most common form of computer in use today is the embedded computer. Embedded computers are
small, simple devices that are used to control other devices — for
example, they may be found in machines ranging from fighter aircraft
to industrial robots, digital cameras, and children's toys.
The ability to store and execute lists of instructions called programs
makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement
of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a
supercomputer are all able to perform the same computational tasks given enough time and storage capacity.
; 1 History of computing
; 2 Stored program architecture
o 2.1 Programs
o 2.2 Example
; 3 How computers work
o 3.1 Control unit
o 3.2 Arithmetic/logic unit (ALU)
o 3.3 Memory
o 3.4 Input/output (I/O)
o 3.5 Multitasking
o 3.6 Multiprocessing
o 3.7 Networking and the Internet
; 4 Further topics
o 4.1 Hardware
o 4.2 Software
o 4.3 Programming languages
o 4.4 Professions and organizations
History of computing
Main article: History of computer hardware
The Jacquard loom was one of the
first programmable devices.
It is difficult to identify any one device as the earliest computer, partly because the term "computer" has been subject to varying
interpretations over time. Originally, the term "computer" referred to a person who performed numerical
calculations (a human computer), often with the aid of a mechanical
The history of the modern computer begins with two separate technologies - that of automated calculation and that of programmability.
Examples of early mechanical calculating devices included the
, the slide rule and arguably the astrolabe and the Antikythera abacus
mechanism (which dates from about 150-100 BC). Hero of Alexandria
(c. 10–70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when. This is the essence of programmability.
The "castle clock", an astronomical clock invented by Al-Jazari in
1206, is considered to be the earliest programmable analog computer.
It displayed the zodiac, the solar and lunar orbits, a crescent
moon-shaped pointer travelling across a gateway causing automatic
doors to open every hour, and five robotic musicians who play music
when struck by levers operated by a camshaft attached to a water
wheel. The length of day and night could be re-programmed every
day in order to account for the changing lengths of day and night throughout the year.
The end of the Middle Ages saw a re-invigoration of European
mathematics and engineering, and Wilhelm Schickard's 1623 device
was the first of a number of mechanical calculators constructed by European engineers. However, none of those devices fit the modern definition of a computer because they could not be programmed. In 1801, Joseph Marie Jacquard made an improvement to the textile