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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 has stored in its memory.  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 there can only be a 1 or a 0 in any data.  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 for a one.  Ternary systems are far more complicated, and still in development.  Most computers use binary.

==History==

==History==

==Hardware Classifications==

==Hardware Classifications==

===Mainframe===

===Mainframe===

[[File:NASAComputerRoom-1962.gif|250px|thumbnail|NASA's Mainfram computer (1962)]]

[[File:NASAComputerRoom-1962.gif|250px|thumbnail|NASA's Mainframe computer (1962)]]

Mainframes were the first kind of commercially used digital computers, and always used to be the fastest option.  They had the ability to process much more information at a faster rate than any other kind.<ref name="WorldBook01"/> However, with the rapid advancement of technology in recent years, these have fallen behind somewhat.  They consume an enormous amount of space, and use much more electricity than modern computers.  In many cases, they have since been replaced with the client-server architecture.<ref>"mainframe." Encyclopaedia Britannica. Britannica Academic. Encyclopædia Britannica Inc., 2016. Web. 31 May. 2016. <http://0-academic.eb.com.www.consuls.org/EBchecked/topic/358715/mainframe>.</ref> However, mainframes (mainly the IBM System Z) are still used by a number of companies.  Although an older technology, they are still powerful, durable, and reliable systems.  Some have been in fault-tolerant operation for at least forty years.<ref name="interview with DavidB4">Personal interview of an anonymous individual with [[User:DavidB4]]</ref><br />

Mainframes were the first kind of commercially used digital computers, and always used to be the fastest option.  They had the ability to process much more information at a faster rate than any other kind.<ref name="WorldBook01"/> However, with the rapid advancement of technology in recent years, these have fallen behind somewhat.  They consume an enormous amount of space, and use much more electricity than modern computers.  In many cases, they have since been replaced with the client-server architecture.<ref>"mainframe." Encyclopaedia Britannica. Britannica Academic. Encyclopædia Britannica Inc., 2016. Web. 31 May. 2016. <http://0-academic.eb.com.www.consuls.org/EBchecked/topic/358715/mainframe>.</ref> However, mainframes (mainly the IBM System Z) are still used by a number of companies.  Although an older technology, they are still powerful, durable, and reliable systems.  Some have been in fault-tolerant operation for at least forty years.<ref name="interview with DavidB4">Personal interview of an anonymous individual with [[User:DavidB4]]</ref><br />

Manufacturers of mainframes included Burroughs, CDC, Univac, and IBM.  IBM mainframes were the most commonly used mainframes in the world, and are still being manufactured today.<br />

Manufacturers of mainframes included Burroughs, CDC, Univac, and IBM.  IBM mainframes were the most commonly used mainframes in the world, and are still being manufactured today.<br />

Most mainframes, including the IBM System Z, use the [[Cobol|COBOL]] language (short for COmmon Business-Oriented Language).  This is a very easy to understand programming language.  For example, a line of this code is, <code>MULTIPLY HOURLY-RATE BY TOTAL-HOURS GIVING TOTAL-PAY</code>.<ref>https://answers.yahoo.com/question/index?qid=20110121224151AAaIkmF</ref>  Although not used exclusively by mainframes, this is one of the main ways it is used.  In 2009, 70-75% of the world's business transactions and 90% of global financial transactions were processed by COBOL.<ref>https://cis.hfcc.edu/faq/cobol</ref>  In 2016, it was estimated that at least 60% of business systems still used it, much of which was running on mainframes.<ref name="interview with DavidB4"/> Although now an outdated technology, mainframes are still a vital part of many systems.<ref>https://www.theguardian.com/technology/2009/apr/09/cobol-internet-programming</ref><ref>http://www.mainframes.com/COBOL.html</ref><ref>http://www.eweek.com/servers/ibm-mainframe-keeps-major-chinese-bank-up-and-running</ref>

Most mainframes, including the IBM System Z, use the [[Cobol|COBOL]] language (short for COmmon Business-Oriented Language).  This is a very easy to understand [[programming language]].  For example, a line of this code is, <code>MULTIPLY HOURLY-RATE BY TOTAL-HOURS GIVING TOTAL-PAY</code>.<ref>https://answers.yahoo.com/question/index?qid=20110121224151AAaIkmF</ref>  Although not used exclusively by mainframes, this is one of the main ways it is used.  In 2009, 70-75% of the world's business transactions and 90% of global financial transactions were processed by COBOL programs.<ref>https://cis.hfcc.edu/faq/cobol</ref>  In 2016, it was estimated that at least 60% of business systems still used it, much of which was running on mainframes.<ref name="interview with DavidB4"/> Although now an outdated technology, mainframes are still a vital part of many systems.<ref>https://www.theguardian.com/technology/2009/apr/09/cobol-internet-programming</ref><ref>http://www.mainframes.com/COBOL.html</ref><ref>http://www.eweek.com/servers/ibm-mainframe-keeps-major-chinese-bank-up-and-running</ref>

===Supercomputer===

===Supercomputer===

==Thin vs. fat clients==

==Thin vs. fat clients==

"Fat clients" are client devices which can process data themselves, without requiring a remote server or mainframe.  Personal computers, for example, are fat clients, since they process data on their own.  "Thin clients" are user terminals which do little or no data processing themselves.  These are much less common than they have been in the recent past.  In older systems, client terminals were little more than links to a mainframe.  The user would enter a command and set of data in the terminal, and it would be passed on the mainframe.  The mainframe would then store, retrieve, or process the data as needed, and return anything needed to the terminal.<br />

"Fat clients" are client devices which can process data themselves, without requiring a remote server or mainframe.  Personal computers, for example, are fat clients, since they process data on their own.  "Thin clients" are user terminals which do little or no data processing themselves.  These are much less common than they have been in the recent past.  In older systems, client [[terminals]] were little more than links to a mainframe.  The user would enter a command and set of data in the terminal, and it would be passed on the mainframe.  The mainframe would then store, retrieve, or process the data as needed, and return anything needed to the terminal.<br />

The newer client-server architecture has largely done away with this thin clients, but some networks still use this sort of system.  Sometimes, there is no operating system or local storage at all on a client "computer." Everything done is downloaded from and uploaded to a central server.  Most people now use "fat clients," which only occasionally need to communicate with a server.  <br />

The newer client-server architecture has largely done away with this thin clients, but some networks still use this sort of system.  Sometimes, there is no operating system or local storage at all on a client "computer." Everything done is downloaded from and uploaded to a central server.  Most people now use "fat clients," which only occasionally need to communicate with a server.  <br />

Cloud computing has to some degree started bringing back thin clients, however.  Since "Software as a Service" and other cloud-based solutions are becoming more popular, thick clients (personal computers) and to some degree being made into thinner clients again.

Cloud computing has to some degree started bringing back thin clients, however.  Since "Software as a Service" and other cloud-based solutions are becoming more popular, thick clients (personal computers) and to some degree being made into thinner clients again.

==Architecture==

==Architecture==

All digital computer systems, regardless of classification or usage, consist of the following components:

All digital computer systems, regardless of classification or usage, consist of the following components:

* <b>Processing.</b> Provided by one or more [[Central processing unit|CPU]]s, sometimes with ancillary processors, such as [[floating-point]] processors (now usually included as part of the CPU), and array processors (in mainframes and [[supercomputer]]s).

* '''Processing.''' Provided by one or more [[Central processing unit|CPU]]s, sometimes with ancillary processors, such as [[floating-point]] processors (now usually included as part of the CPU), and array processors (in mainframes and [[supercomputer]]s).

* <b>Memory.</b> High-speed local storage, such as [[Random-access memory]]

* '''Memory.''' High-speed local storage, such as [[Random-access memory]]

* <b>Software.</b> Each unique computer hardware environment needs [[software]] that works with the model of processor used in that computer.

* '''Software.''' Each unique computer hardware environment needs [[software]] that works with the model of processor used in that computer.

* <b>Input/Output.</b> Computers are only useful if they can generate output.  Output can vary from control lines for engine components to characters on a video screen.  Input also varies in form, but most computers need input to process, which then drives the output.

* '''Input/Output.''' Computers are only useful if they can generate output.  Output can vary from control lines for engine components to characters on a video screen.  Input also varies in form, but most computers need input to process, which then drives the output.

Most modern computer systems also have peripheral devices:

Most modern computer systems also have peripheral devices:

* <b>Storage.</b> Large amounts of lower-speed, less-expensive hardware where data can be stored for later retrieval.  Storage can be local or it can be remotely accessed via a network.  The most typical form of local storage are hard disks, SSDs, thumb drives, and DVDROMs.  Older mass storage devices include punch cards, paper tapes, magnetic tapes, and CDROMs.

* '''Storage.''' Large amounts of lower-speed, less-expensive hardware where data can be stored for later retrieval.  Storage can be local or it can be remotely accessed via a network.  The most typical form of local storage are hard disks, SSDs, thumb drives, and DVDROMs.  Older mass storage devices include punch cards, paper tapes, magnetic tapes, and CDROMs.

* <b>Other I/O devices.</b> Any number of optional peripheral devices are available for computers, including [[Computer mouse|mice]], scanners, card readers, [[network]] interfaces, [[terminals]], and [[printers]].

* '''Other I/O devices.''' Any number of optional peripheral devices are available for computers, including [[Computer mouse|mice]], scanners, card readers, [[network]] interfaces, [[terminals]], and [[Printer (computing)|printers]].

==Binary and ternary==

==Binary and ternary==

*[[Apple Computer|Apple]] [[iOS]] for [[iPhone]]-[[iPod]]-[[iPad]]

*[[Apple Computer|Apple]] [[iOS]] for [[iPhone]]-[[iPod]]-[[iPad]]

*[[Acorn computers]]

*[[Acorn computers]]

*[[ZX Spectrum]]

*[[ZX Spectrum]]