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A '''computer''' is a programmable [[machine]] that receives input, stores and [[manipulates]] [[data]], and provides output in a useful [[format]].

A '''computer''' is a programmable [[machine]] that receives input, stores and [[manipulates]] [[data]], and provides output in a useful [[format]].

Although [[mechanical]] examples of computers have existed through much of recorded [[human]] [[history]], the first electronic computers were developed in the mid-[http://www.wikipedia.org/wiki/1940's 20th century] (1940–1945). These were the size of a large room, consuming as much [[power]] as several hundred modern [http://en.wikipedia.org/wiki/Personal_computer personal computers (PCs)]. Modern computers based on [http://en.wikipedia.org/wiki/Integrated_circuit integrated circuits] are millions to billions of times more capable than the early [[machines]], and occupy a [[fraction]] of the [[space]]. Simple computers are small enough to fit into small pocket devices, and can be powered by a small battery. Personal computers in their various forms are [[icons]] of the [http://en.wikipedia.org/wiki/Information_Age Information Age] and are what most people [[think]] of as "computers". However, the embedded computers found in many devices from [http://en.wikipedia.org/wiki/Digital_audio_player MP3 players] to fighter aircraft and from toys to [http://en.wikipedia.org/wiki/Industrial_robot industrial robots] are the most numerous.

Although [[mechanical]] examples of computers have existed through much of recorded [[human]] [[history]], the first electronic computers were developed in the mid-[https://www.wikipedia.org/wiki/1940's 20th century] (1940–1945). These were the size of a large room, consuming as much [[power]] as several hundred modern [https://en.wikipedia.org/wiki/Personal_computer personal computers (PCs)]. Modern computers based on [https://en.wikipedia.org/wiki/Integrated_circuit integrated circuits] are millions to billions of times more capable than the early [[machines]], and occupy a [[fraction]] of the [[space]]. Simple computers are small enough to fit into small pocket devices, and can be powered by a small battery. Personal computers in their various forms are [[icons]] of the [https://en.wikipedia.org/wiki/Information_Age Information Age] and are what most people [[think]] of as "computers". However, the embedded computers found in many devices from [https://en.wikipedia.org/wiki/Digital_audio_player MP3 players] to fighter aircraft and from toys to [https://en.wikipedia.org/wiki/Industrial_robot industrial robots] are the most numerous.

The [[ability]] to store and [[execute]] lists of instructions called [http://en.wikipedia.org/wiki/Computer_program programs] makes computers extremely [[versatile]], distinguishing them from [http://en.wikipedia.org/wiki/Calculator calculators]. The [http://en.wikipedia.org/wiki/Church%E2%80%93Turing_thesis 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 ranging from a netbook to a supercomputer are all able to [[perform]] the same [[computational]] tasks, given enough [[time]] and storage [[capacity]].

The [[ability]] to store and [[execute]] lists of instructions called [https://en.wikipedia.org/wiki/Computer_program programs] makes computers extremely [[versatile]], distinguishing them from [https://en.wikipedia.org/wiki/Calculator calculators]. The [https://en.wikipedia.org/wiki/Church%E2%80%93Turing_thesis 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 ranging from a netbook to a supercomputer are all able to [[perform]] the same [[computational]] tasks, given enough [[time]] and storage [[capacity]].

==Function==

==Function==

A general [[purpose]] computer has four main components: the [http://en.wikipedia.org/wiki/Arithmetic_logic_unit arithmetic logic unit] (ALU), the [http://en.wikipedia.org/wiki/Control_unit control unit], the [http://en.wikipedia.org/wiki/Computer_data_storage memory], and the input and output devices (collectively termed I/O). These parts are [[interconnected]] by [http://en.wikipedia.org/wiki/Bus_(computing) busses], often made of [[groups]] of wires.

A general [[purpose]] computer has four main components: the [https://en.wikipedia.org/wiki/Arithmetic_logic_unit arithmetic logic unit] (ALU), the [https://en.wikipedia.org/wiki/Control_unit control unit], the [https://en.wikipedia.org/wiki/Computer_data_storage memory], and the input and output devices (collectively termed I/O). These parts are [[interconnected]] by [https://en.wikipedia.org/wiki/Bus_(computing) busses], often made of [[groups]] of wires.

Inside each of these [[parts]] are thousands to trillions of small electrical [[circuits]] which can be turned off or on by means of an electronic switch. Each [[circuit]] [[represents]] a [http://en.wikipedia.org/wiki/Bit bit] (binary digit) of [[information]] so that when the [[circuit]] is on it represents a "1", and when off it represents a "0" (in positive [[logic]] [[representation]]). The circuits are arranged in [http://en.wikipedia.org/wiki/Logic_gate logic gates] so that one or more of the circuits may [[control]] the [[state]] of one or more of the other circuits.

Inside each of these [[parts]] are thousands to trillions of small electrical [[circuits]] which can be turned off or on by means of an electronic switch. Each [[circuit]] [[represents]] a [https://en.wikipedia.org/wiki/Bit bit] (binary digit) of [[information]] so that when the [[circuit]] is on it represents a "1", and when off it represents a "0" (in positive [[logic]] [[representation]]). The circuits are arranged in [https://en.wikipedia.org/wiki/Logic_gate logic gates] so that one or more of the circuits may [[control]] the [[state]] of one or more of the other circuits.

The [[control]] [[unit]], ALU, registers, and basic I/O (and often other hardware closely linked with these) are [[collectively]] known as a [http://en.wikipedia.org/wiki/Central_processing_unit central processing unit] (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single [http://en.wikipedia.org/wiki/Integrated_circuit integrated circuit] called a [http://en.wikipedia.org/wiki/Microprocessor microprocessor].

The [[control]] [[unit]], ALU, registers, and basic I/O (and often other hardware closely linked with these) are [[collectively]] known as a [https://en.wikipedia.org/wiki/Central_processing_unit central processing unit] (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single [https://en.wikipedia.org/wiki/Integrated_circuit integrated circuit] called a [https://en.wikipedia.org/wiki/Microprocessor microprocessor].

==Networking and the Internet==

==Networking and the Internet==

Computers have been used to [[coordinate]] [[information]] between multiple locations since the [http://www.wikipedia.org/wiki/1950's 1950s]. The U.S. military's [http://en.wikipedia.org/wiki/Semi_Automatic_Ground_Environment SAGE] system was the first large-scale example of such a [[system]], which led to a number of special-purpose commercial systems like [http://en.wikipedia.org/wiki/Sabre_(computer_system) Sabre].

Computers have been used to [[coordinate]] [[information]] between multiple locations since the [https://www.wikipedia.org/wiki/1950's 1950s]. The U.S. military's [https://en.wikipedia.org/wiki/Semi_Automatic_Ground_Environment SAGE] system was the first large-scale example of such a [[system]], which led to a number of special-purpose commercial systems like [https://en.wikipedia.org/wiki/Sabre_(computer_system) Sabre].

In the 1970s, computer engineers at [[research]] [[institutions]] throughout the United States began to link their computers together using telecommunications [[technology]]. This [[effort]] was funded by ARPA (now [http://en.wikipedia.org/wiki/DARPA DARPA]), and the [http://en.wikipedia.org/wiki/Computer_network computer network] that it produced was called the [http://en.wikipedia.org/wiki/ARPANET ARPANET]. The technologies that made the Arpanet possible spread and evolved.

In the 1970s, computer engineers at [[research]] [[institutions]] throughout the United States began to link their computers together using telecommunications [[technology]]. This [[effort]] was funded by ARPA (now [https://en.wikipedia.org/wiki/DARPA DARPA]), and the [https://en.wikipedia.org/wiki/Computer_network computer network] that it produced was called the [https://en.wikipedia.org/wiki/ARPANET ARPANET]. The technologies that made the Arpanet possible spread and evolved.

In [[time]], the network spread beyond [[academic]] and military [[institutions]] and became known as the [[Internet]]. The emergence of networking involved a redefinition of the [[nature]] and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and [[access]] the [[resources]] of other computers on the network, such as peripheral devices, stored [[information]], and the like, as extensions of the [[resources]] of an [[individual]] computer. Initially these facilities were available primarily to people [[working]] in high-tech [[environments]], but in the [http://www.wikipedia.org/wiki/1990's 1990s] the spread of [[applications]] like e-mail and the [http://en.wikipedia.org/wiki/World_Wide_Web World Wide Web], combined with the development of cheap, fast networking technologies like [http://en.wikipedia.org/wiki/Ethernet Ethernet] and [http://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line ADSL] saw computer networking become almost ubiquitous. In [[fact]], the number of computers that are networked is growing phenomenally. A very large [[proportion]] of personal computers regularly [[connect]] to the [[Internet]] to [[communicate]] and receive [[information]]. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing [[environments]].

In [[time]], the network spread beyond [[academic]] and military [[institutions]] and became known as the [[Internet]]. The emergence of networking involved a redefinition of the [[nature]] and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and [[access]] the [[resources]] of other computers on the network, such as peripheral devices, stored [[information]], and the like, as extensions of the [[resources]] of an [[individual]] computer. Initially these facilities were available primarily to people [[working]] in high-tech [[environments]], but in the [https://www.wikipedia.org/wiki/1990's 1990s] the spread of [[applications]] like e-mail and the [https://en.wikipedia.org/wiki/World_Wide_Web World Wide Web], combined with the development of cheap, fast networking technologies like [https://en.wikipedia.org/wiki/Ethernet Ethernet] and [https://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line ADSL] saw computer networking become almost ubiquitous. In [[fact]], the number of computers that are networked is growing phenomenally. A very large [[proportion]] of personal computers regularly [[connect]] to the [[Internet]] to [[communicate]] and receive [[information]]. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing [[environments]].

[[Category: Computer Science]]

[[Category: Computer Science]]