•This article is about the machine. For the magazine, see Computer (magazine).
The NASA Columbia Supercomputer
A computer in a wristwatch
is a machine
which manipulates data
according to a list of instructions
Computers take numerous physical forms. The first devices that resemble modern computers date to the mid-20th century
), although the computer concept and various machines similar to computers existed prior. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers.
Modern computers are based on comparatively 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 wrist watch
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 by far the embedded computer
. Embedded computers are small, simple devices that are often used to control other devices — for example, they may be found in machines ranging from fighter aircraft
to industrial robots
, digital cameras
, and even 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.
History of computingMain article: History of computing
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 calculating device
. Examples of early mechanical computing devices included the abacus
, the slide rule
and arguably the astrolabe
and the Antikythera mechanism
(which dates from about 150-100 BC). 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 loom
that used a series of punched paper cards
as a template to allow his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.
In 1837, Charles Babbage
was the first to conceptualize and design a fully programmable mechanical computer that he called "The Analytical Engine
Due to limited finance, and an inability to resist tinkering with the design, Babbage never actually built his Analytical Engine.
Large-scale automated data processing of punched cards was performed for the U.S. Census in 1890
by tabulating machines
designed by Herman Hollerith
and manufactured by the Computing Tabulating Recording Corporation
, which later became IBM
. By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card
, Boolean algebra
, the vacuum tube
(thermionic valve) and the teleprinter
During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers
, which used a direct mechanical or electrical
model of the problem as a basis for computation
. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.
A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon
in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as "the first digital electronic computer" is difficult (Shannon 1940)
. Notable achievements include: