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A '''computer''' is a [[machine]] that is designed to perform a wide variety of information-processing tasks, depending on the program it is running.  It processes (computes) everything as mathematical problems, although many non-mathematical functions can be ultimately performed. Digital computers manipulate all data in the form of numbers, and encode all numbers in either [[binary|binary code]], which is base 2, or in the case of quantum computers, ternary code which is base 3. Binary means that each value can only be a 1 or a 0.  This makes it possible to process data electronically, since one voltage can be used to represent a zero and another voltage for a one.  Ternary systems are far more complicated, and still in development.  Most computers use binary.

A '''computer''' is a [[machine]] that is designed to perform a wide variety of information-processing tasks, depending on the program it is running.  It processes (computes) everything as mathematical problems, although many non-mathematical functions can be ultimately performed. Digital computers manipulate all data in the form of numbers, and encode all numbers in either [[binary|binary code]], which is base 2, or in the case of quantum computers, ternary code which is base 3. Binary means that each value can only be a 1 or a 0.  This makes it possible to process data electronically, since one voltage can be used to represent a zero and another voltage to represent a one.  Ternary systems are far more complicated, and still in development.  Most computers use binary.

==History==

==History==

Prior to the advent of computing machines, the definition for ''computer'' was a human being who performed complex mathematical calculations. This was accomplished with the aid of a manual counting device, such as an [[abacus]] or a [[slide rule]], and was mainly performed by traders and early bankers to keep a reliable record of funds.

Prior to the advent of computing machines, the definition for ''computer'' was a human being who performed complex mathematical calculations. This was accomplished with the aid of a manual counting device, such as an [[abacus]] or a [[slide rule]], and was mainly performed by traders and early bankers to keep a reliable record of funds.

Charles Babbage, a [[British]] scientist who lived in the 19th century, has been credited as the designer of the first digital computer, the Difference Engine, a machine set to do calculations reliably up to six decimal places.  It was entirely mechanical. However, the Engine was never constructed, being deemed as "had derived no emolument whatsoever from the government" by a member of parliament. He also designed an even more sophisticated "Analytical Engine", that would actually have been a programmable computer in the modern sense; it, too was mechanical.  Though it was never built, [[Ada Lovelace|Augusta Ada]] wrote some programs for it (to compute Bernoulli polynomials), making her the world's first computer programmer.  A small version of the Difference Engine, was built after his death by his son.<ref>http://ei.cs.vt.edu/~history/Babbage.html</ref>

Charles Babbage, a [[British]] scientist who lived in the 19th century, has been credited as the designer of the first digital computer, the Difference Engine, a machine set to do calculations reliably up to six decimal places.  It was entirely mechanical. However, the Engine was never constructed, being deemed "had derived no emolument whatsoever from the government" by a member of parliament. He also designed an even more sophisticated "Analytical Engine", that would actually have been a programmable computer in the modern sense; it, too, was mechanical.  Though it was never built, [[Ada Lovelace|Augusta Ada]] wrote some programs for it (to compute Bernoulli polynomials), making her the world's first computer programmer.  A small version of the Difference Engine was built after his death by his son.<ref>http://ei.cs.vt.edu/~history/Babbage.html</ref>

Babbage later designed a simpler and even more clever "Difference Engine Number 2", which was also not completed in his lifetime.  But in 1991, the bicentennial of Babbage's birth, this computer was built in the British Science Museum, from Babbage's original plans.  It operates flawlessly, though a few billion times slower than modern electronic computers.  It is operated by turning a crank.

Babbage later designed a simpler and even more clever "Difference Engine Number 2", which was also not completed in his lifetime.  But in 1991, the bicentennial of Babbage's birth, this computer was built in the British Science Museum from Babbage's original plans.  It operates flawlessly, though a few billion times slower than modern electronic computers.  It is operated by turning a crank.

[[File:SSEM Replica.jpg|thumb|left|The Manchester Small-Scale Experimental Machine is considered  the world's first stored-program computer, 1948.]]

[[File:SSEM Replica.jpg|thumb|left|The Manchester Small-Scale Experimental Machine is considered  the world's first stored-program computer, 1948.]]

The first computer comparable to the modern day computer, an electronic calculation machine, was the [[ENIAC]]. Built as an artillery support machine, it was unveiled in early 1946.<ref>http://ftp.arl.army.mil/~mike/comphist/</ref>

The first computer comparable to the modern day computer, an electronic calculation machine, was the [[ENIAC]]. Built as an artillery support machine, it was unveiled in early 1946.<ref>http://ftp.arl.army.mil/~mike/comphist/</ref>

===Minicomputer===

===Minicomputer===

Minicomputers were smaller, cheaper cousins of the mainframe computer.  They were also slower than mainframes.  Over time, minicomputers became available in many configurations and sizes, up to the threshold of mainframes.  In the 1970s, a typical minicomputer cost between $100,000 and $200,000 and could support up to 63 timeshared users.  Larger minicomputers had large power requirements and often required special rooms with adequate air conditioning to remove the large amounts of heat that they generated.  The first commercially successful minicomputer was the pdp/8 released by Digital Equipment Corporation in 1958.  Unlike mainframes, the entire computer could fit on top of a desk.  Minicomputers fell out of favor when powerful microcomputers became wildly available.

Minicomputers were smaller, cheaper cousins of the mainframe computer.  They were also slower than mainframes.  Over time, minicomputers became available in many configurations and sizes, up to the threshold of mainframes.  In the 1970s, a typical minicomputer cost between $100,000 and $200,000 and could support up to 63 timeshared users.  Larger minicomputers had large power requirements and often required special rooms with adequate air conditioning to remove the large amounts of heat that they generated.  The first commercially successful minicomputer was the pdp/8, released by Digital Equipment Corporation in 1958.  Unlike mainframes, the entire computer could fit on top of a desk.  Minicomputers fell out of favor when powerful microcomputers became wildly available.

===Microcomputers===

===Microcomputers===

[[File:CERN Server room 03.jpg|250px|thumbnail|A Client-Server Architecture Server Room]]

[[File:CERN Server room 03.jpg|250px|thumbnail|A Client-Server Architecture Server Room]]

Client-server is a means of connecting computers together (called a "[[Network topology|topology]]"). It is a powerful approach that separates the "back end" computation onto a computer referred to as the server, and one or more client computers which present an interface for the user. In other words, a server provides services or data, while the client is the computer that requests those services from the server.  In many cases, server computers host websites, send and receive [[e-mail]] messages, store information, and handle all other basic services offered on the Internet.  Individuals connect to the internet using their computers which serve as the clients that use the services of those servers.  Some servers perform less publicly accessible functions such as crawling websites and running any number of advanced calculations.  Servers are also used by some companies to store records which are usually only available on their intranet (local network).  For example, hospitals will often keep patient records on a secure server.  Some computers can serve as both a server to other clients while at the same time being a client of another server.<ref>"client-server architecture." Encyclopaedia Britannica. Britannica Academic. Encyclopædia Britannica Inc., 2016. Web. 31 May. 2016. <http://0-academic.eb.com.www.consuls.org/EBchecked/topic/1366374/client-server-architecture>.</ref><br />

Client-server is a means of connecting computers together (called a "[[Network topology|topology]]"). It is a powerful approach that separates the "back end" computation onto a computer referred to as the server, and one or more client computers which present an interface for the user. In other words, a server provides services or data, while the client is the computer that requests those services from the server.  In many cases, server computers host websites, send and receive [[e-mail]] messages, store information, and handle all other basic services offered on the Internet.  Individuals connect to the internet using their computers which serve as the clients that use the services of those servers.  Some servers perform less publicly accessible functions such as crawling websites and running any number of advanced calculations.  Servers are also used by some companies to store records which are usually only available on their intranet (local network).  For example, hospitals will often keep patient records on a secure server.  Some computers can serve as both a server to other clients while at the same time being a client of another server.<ref>"client-server architecture." Encyclopaedia Britannica. Britannica Academic. Encyclopædia Britannica Inc., 2016. Web. 31 May. 2016. <http://0-academic.eb.com.www.consuls.org/EBchecked/topic/1366374/client-server-architecture>.</ref><br />

Servers can also be clustered so that although they appear to be one server, a sometimes large quantity of servers are actually running.  When multiple server computers are used, the storage, processing, and client capabilities of the whole increase dramatically.  This fact has led the creation of many "server farms," which house little other than but thousands of servers.

Servers can also be clustered so that although they appear to be one server, a sometimes large quantity of servers are actually running.  When multiple server computers are used, the storage, processing, and client capabilities of the whole increase dramatically.  This fact has led the creation of many "server farms," which house little other than thousands of servers.

===Dedicated===

===Dedicated===