Computer

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For other uses, see Computer (disambiguation). Computer_sentence_0

Computer_table_infobox_0

A computer is a machine that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming. Computer_sentence_1

Modern computers have the ability to follow generalized sets of operations, called programs. Computer_sentence_2

These programs enable computers to perform an extremely wide range of tasks. Computer_sentence_3

A "complete" computer including the hardware, the operating system (main software), and peripheral equipment required and used for "full" operation can be referred to as a computer system. Computer_sentence_4

This term may as well be used for a group of computers that are connected and work together, in particular a computer network or computer cluster. Computer_sentence_5

Computers are used as control systems for a wide variety of industrial and consumer devices. Computer_sentence_6

This includes simple special purpose devices like microwave ovens and remote controls, factory devices such as industrial robots and computer-aided design, and also general purpose devices like personal computers and mobile devices such as smartphones. Computer_sentence_7

The Internet is run on computers and it connects hundreds of millions of other computers and their users. Computer_sentence_8

Early computers were only conceived as calculating devices. Computer_sentence_9

Since ancient times, simple manual devices like the abacus aided people in doing calculations. Computer_sentence_10

Early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. Computer_sentence_11

More sophisticated electrical machines did specialized analog calculations in the early 20th century. Computer_sentence_12

The first digital electronic calculating machines were developed during World War II. Computer_sentence_13

The first semiconductor transistors in the late 1940s were followed by the silicon-based MOSFET (MOS transistor) and monolithic integrated circuit (IC) chip technologies in the late 1950s, leading to the microprocessor and the microcomputer revolution in the 1970s. Computer_sentence_14

The speed, power and versatility of computers have been increasing dramatically ever since then, with transistor counts increasing at a rapid pace (as predicted by Moore's law), leading to the Digital Revolution during the late 20th to early 21st centuries. Computer_sentence_15

Conventionally, a modern computer consists of at least one processing element, typically a central processing unit (CPU) in the form of a microprocessor, along with some type of computer memory, typically semiconductor memory chips. Computer_sentence_16

The processing element carries out arithmetic and logical operations, and a sequencing and control unit can change the order of operations in response to stored information. Computer_sentence_17

Peripheral devices include input devices (keyboards, mice, joystick, etc.), output devices (monitor screens, printers, etc.), and input/output devices that perform both functions (e.g., the 2000s-era touchscreen). Computer_sentence_18

Peripheral devices allow information to be retrieved from an external source and they enable the result of operations to be saved and retrieved. Computer_sentence_19

Etymology Computer_section_0

According to the Oxford English Dictionary, the first known use of the word "computer" was in 1613 in a book called The Yong Mans Gleanings by English writer Richard Braithwait: "I haue [sic] read the truest computer of Times, and the best Arithmetician that euer [sic] breathed, and he reduceth thy dayes into a short number." Computer_sentence_20

This usage of the term referred to a human computer, a person who carried out calculations or computations. Computer_sentence_21

The word continued with the same meaning until the middle of the 20th century. Computer_sentence_22

During the latter part of this period women were often hired as computers because they could be paid less than their male counterparts. Computer_sentence_23

By 1943, most human computers were women. Computer_sentence_24

The Online Etymology Dictionary gives the first attested use of "computer" in the 1640s, meaning "one who calculates"; this is an "agent noun from compute (v.)". Computer_sentence_25

The Online Etymology Dictionary states that the use of the term to mean "'calculating machine' (of any type) is from 1897." Computer_sentence_26

The Online Etymology Dictionary indicates that the "modern use" of the term, to mean "programmable digital electronic computer" dates from "1945 under this name; [in a] theoretical [sense] from 1937, as Turing machine". Computer_sentence_27

History Computer_section_1

Main article: History of computing hardware Computer_sentence_28

Pre-20th century Computer_section_2

Devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. Computer_sentence_29

The earliest counting device was probably a form of tally stick. Computer_sentence_30

Later record keeping aids throughout the Fertile Crescent included calculi (clay spheres, cones, etc.) which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. Computer_sentence_31

The use of counting rods is one example. Computer_sentence_32

The abacus was initially used for arithmetic tasks. Computer_sentence_33

The Roman abacus was developed from devices used in Babylonia as early as 2400 BC. Computer_sentence_34

Since then, many other forms of reckoning boards or tables have been invented. Computer_sentence_35

In a medieval European counting house, a checkered cloth would be placed on a table, and markers moved around on it according to certain rules, as an aid to calculating sums of money. Computer_sentence_36

The Antikythera mechanism is believed to be the earliest mechanical analog computer, according to Derek J. de Solla Price. Computer_sentence_37

It was designed to calculate astronomical positions. Computer_sentence_38

It was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to c. 100 BC. Computer_sentence_39

Devices of a level of complexity comparable to that of the Antikythera mechanism would not reappear until a thousand years later. Computer_sentence_40

Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. Computer_sentence_41

The planisphere was a star chart invented by Abū Rayhān al-Bīrūnī in the early 11th century. Computer_sentence_42

The astrolabe was invented in the Hellenistic world in either the 1st or 2nd centuries BC and is often attributed to Hipparchus. Computer_sentence_43

A combination of the planisphere and dioptra, the astrolabe was effectively an analog computer capable of working out several different kinds of problems in spherical astronomy. Computer_sentence_44

An astrolabe incorporating a mechanical calendar computer and gear-wheels was invented by Abi Bakr of Isfahan, Persia in 1235. Computer_sentence_45

Abū Rayhān al-Bīrūnī invented the first mechanical geared lunisolar calendar astrolabe, an early fixed-wired knowledge processing machine with a gear train and gear-wheels, c. 1000 AD. Computer_sentence_46

The sector, a calculating instrument used for solving problems in proportion, trigonometry, multiplication and division, and for various functions, such as squares and cube roots, was developed in the late 16th century and found application in gunnery, surveying and navigation. Computer_sentence_47

The planimeter was a manual instrument to calculate the area of a closed figure by tracing over it with a mechanical linkage. Computer_sentence_48

The slide rule was invented around 1620–1630, shortly after the publication of the concept of the logarithm. Computer_sentence_49

It is a hand-operated analog computer for doing multiplication and division. Computer_sentence_50

As slide rule development progressed, added scales provided reciprocals, squares and square roots, cubes and cube roots, as well as transcendental functions such as logarithms and exponentials, circular and hyperbolic trigonometry and other functions. Computer_sentence_51

Slide rules with special scales are still used for quick performance of routine calculations, such as the E6B circular slide rule used for time and distance calculations on light aircraft. Computer_sentence_52

In the 1770s, Pierre Jaquet-Droz, a Swiss watchmaker, built a mechanical doll (automaton) that could write holding a quill pen. Computer_sentence_53

By switching the number and order of its internal wheels different letters, and hence different messages, could be produced. Computer_sentence_54

In effect, it could be mechanically "programmed" to read instructions. Computer_sentence_55

Along with two other complex machines, the doll is at the Musée d'Art et d'Histoire of Neuchâtel, Switzerland, and still operates. Computer_sentence_56

In 1831–1835, mathematician and engineer Giovanni Plana devised a Perpetual Calendar machine, which, though a system of pulleys and cylinders and over, could predict the perpetual calendar for every year from AD 0 (that is, 1 BC) to AD 4000, keeping track of leap years and varying day length. Computer_sentence_57

The tide-predicting machine invented by Sir William Thomson in 1872 was of great utility to navigation in shallow waters. Computer_sentence_58

It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location. Computer_sentence_59

The differential analyser, a mechanical analog computer designed to solve differential equations by integration, used wheel-and-disc mechanisms to perform the integration. Computer_sentence_60

In 1876, Lord Kelvin had already discussed the possible construction of such calculators, but he had been stymied by the limited output torque of the ball-and-disk integrators. Computer_sentence_61

In a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. Computer_sentence_62

The torque amplifier was the advance that allowed these machines to work. Computer_sentence_63

Starting in the 1920s, Vannevar Bush and others developed mechanical differential analyzers. Computer_sentence_64

First computing device Computer_section_3

Charles Babbage, an English mechanical engineer and polymath, originated the concept of a programmable computer. Computer_sentence_65

Considered the "father of the computer", he conceptualized and invented the first mechanical computer in the early 19th century. Computer_sentence_66

After working on his revolutionary difference engine, designed to aid in navigational calculations, in 1833 he realized that a much more general design, an Analytical Engine, was possible. Computer_sentence_67

The input of programs and data was to be provided to the machine via punched cards, a method being used at the time to direct mechanical looms such as the Jacquard loom. Computer_sentence_68

For output, the machine would have a printer, a curve plotter and a bell. Computer_sentence_69

The machine would also be able to punch numbers onto cards to be read in later. Computer_sentence_70

The Engine incorporated an arithmetic logic unit, control flow in the form of conditional branching and loops, and integrated memory, making it the first design for a general-purpose computer that could be described in modern terms as Turing-complete. Computer_sentence_71

The machine was about a century ahead of its time. Computer_sentence_72

All the parts for his machine had to be made by hand – this was a major problem for a device with thousands of parts. Computer_sentence_73

Eventually, the project was dissolved with the decision of the British Government to cease funding. Computer_sentence_74

Babbage's failure to complete the analytical engine can be chiefly attributed to political and financial difficulties as well as his desire to develop an increasingly sophisticated computer and to move ahead faster than anyone else could follow. Computer_sentence_75

Nevertheless, his son, Henry Babbage, completed a simplified version of the analytical engine's computing unit (the mill) in 1888. Computer_sentence_76

He gave a successful demonstration of its use in computing tables in 1906. Computer_sentence_77

Analog computers Computer_section_4

Main article: Analog computer Computer_sentence_78

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. Computer_sentence_79

However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers. Computer_sentence_80

The first modern analog computer was a tide-predicting machine, invented by Sir William Thomson in 1872. Computer_sentence_81

The differential analyser, a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in 1876 by James Thomson, the brother of the more famous Lord Kelvin. Computer_sentence_82

The art of mechanical analog computing reached its zenith with the differential analyzer, built by H. L. Hazen and Vannevar Bush at MIT starting in 1927. Computer_sentence_83

This built on the mechanical integrators of James Thomson and the torque amplifiers invented by H. W. Nieman. Computer_sentence_84

A dozen of these devices were built before their obsolescence became obvious. Computer_sentence_85

By the 1950s, the success of digital electronic computers had spelled the end for most analog computing machines, but analog computers remained in use during the 1950s in some specialized applications such as education (slide rule) and aircraft (control systems). Computer_sentence_86

Digital computers Computer_section_5

Electromechanical Computer_section_6

By 1938, the United States Navy had developed an electromechanical analog computer small enough to use aboard a submarine. Computer_sentence_87

This was the Torpedo Data Computer, which used trigonometry to solve the problem of firing a torpedo at a moving target. Computer_sentence_88

During World War II similar devices were developed in other countries as well. Computer_sentence_89

Early digital computers were electromechanical; electric switches drove mechanical relays to perform the calculation. Computer_sentence_90

These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes. Computer_sentence_91

The Z2, created by German engineer Konrad Zuse in 1939, was one of the earliest examples of an electromechanical relay computer. Computer_sentence_92

In 1941, Zuse followed his earlier machine up with the Z3, the world's first working electromechanical programmable, fully automatic digital computer. Computer_sentence_93

The Z3 was built with 2000 relays, implementing a 22 bit word length that operated at a clock frequency of about 5–10 Hz. Computer_sentence_94

Program code was supplied on punched film while data could be stored in 64 words of memory or supplied from the keyboard. Computer_sentence_95

It was quite similar to modern machines in some respects, pioneering numerous advances such as floating point numbers. Computer_sentence_96

Rather than the harder-to-implement decimal system (used in Charles Babbage's earlier design), using a binary system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time. Computer_sentence_97

The Z3 was not itself a universal computer but could be extended to be Turing complete. Computer_sentence_98

Vacuum tubes and digital electronic circuits Computer_section_7

Purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. Computer_sentence_99

The engineer Tommy Flowers, working at the Post Office Research Station in London in the 1930s, began to explore the possible use of electronics for the telephone exchange. Computer_sentence_100

Experimental equipment that he built in 1934 went into operation five years later, converting a portion of the telephone exchange network into an electronic data processing system, using thousands of vacuum tubes. Computer_sentence_101

In the US, John Vincent Atanasoff and Clifford E. Berry of Iowa State University developed and tested the Atanasoff–Berry Computer (ABC) in 1942, the first "automatic electronic digital computer". Computer_sentence_102

This design was also all-electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory. Computer_sentence_103

During World War II, the British at Bletchley Park achieved a number of successes at breaking encrypted German military communications. Computer_sentence_104

The German encryption machine, Enigma, was first attacked with the help of the electro-mechanical bombes which were often run by women. Computer_sentence_105

To crack the more sophisticated German Lorenz SZ 40/42 machine, used for high-level Army communications, Max Newman and his colleagues commissioned Flowers to build the Colossus. Computer_sentence_106

He spent eleven months from early February 1943 designing and building the first Colossus. Computer_sentence_107

After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944 and attacked its first message on 5 February. Computer_sentence_108

Colossus was the world's first electronic digital programmable computer. Computer_sentence_109

It used a large number of valves (vacuum tubes). Computer_sentence_110

It had paper-tape input and was capable of being configured to perform a variety of boolean logical operations on its data, but it was not Turing-complete. Computer_sentence_111

Nine Mk II Colossi were built (The Mk I was converted to a Mk II making ten machines in total). Computer_sentence_112

Colossus Mark I contained 1,500 thermionic valves (tubes), but Mark II with 2,400 valves, was both 5 times faster and simpler to operate than Mark I, greatly speeding the decoding process. Computer_sentence_113

The ENIAC (Electronic Numerical Integrator and Computer) was the first electronic programmable computer built in the U.S. Computer_sentence_114

Although the ENIAC was similar to the Colossus, it was much faster, more flexible, and it was Turing-complete. Computer_sentence_115

Like the Colossus, a "program" on the ENIAC was defined by the states of its patch cables and switches, a far cry from the stored program electronic machines that came later. Computer_sentence_116

Once a program was written, it had to be mechanically set into the machine with manual resetting of plugs and switches. Computer_sentence_117

The programmers of the ENIAC were six women, often known collectively as the "ENIAC girls". Computer_sentence_118

It combined the high speed of electronics with the ability to be programmed for many complex problems. Computer_sentence_119

It could add or subtract 5000 times a second, a thousand times faster than any other machine. Computer_sentence_120

It also had modules to multiply, divide, and square root. Computer_sentence_121

High speed memory was limited to 20 words (about 80 bytes). Computer_sentence_122

Built under the direction of John Mauchly and J. Computer_sentence_123 Presper Eckert at the University of Pennsylvania, ENIAC's development and construction lasted from 1943 to full operation at the end of 1945. Computer_sentence_124

The machine was huge, weighing 30 tons, using 200 kilowatts of electric power and contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors. Computer_sentence_125

Modern computers Computer_section_8

Concept of modern computer Computer_section_9

The principle of the modern computer was proposed by Alan Turing in his seminal 1936 paper, On Computable Numbers. Computer_sentence_126

Turing proposed a simple device that he called "Universal Computing machine" and that is now known as a universal Turing machine. Computer_sentence_127

He proved that such a machine is capable of computing anything that is computable by executing instructions (program) stored on tape, allowing the machine to be programmable. Computer_sentence_128

The fundamental concept of Turing's design is the stored program, where all the instructions for computing are stored in memory. Computer_sentence_129

Von Neumann acknowledged that the central concept of the modern computer was due to this paper. Computer_sentence_130

Turing machines are to this day a central object of study in theory of computation. Computer_sentence_131

Except for the limitations imposed by their finite memory stores, modern computers are said to be Turing-complete, which is to say, they have algorithm execution capability equivalent to a universal Turing machine. Computer_sentence_132

Stored programs Computer_section_10

Main article: Stored-program computer Computer_sentence_133

Early computing machines had fixed programs. Computer_sentence_134

Changing its function required the re-wiring and re-structuring of the machine. Computer_sentence_135

With the proposal of the stored-program computer this changed. Computer_sentence_136

A stored-program computer includes by design an instruction set and can store in memory a set of instructions (a program) that details the computation. Computer_sentence_137

The theoretical basis for the stored-program computer was laid by Alan Turing in his 1936 paper. Computer_sentence_138

In 1945, Turing joined the National Physical Laboratory and began work on developing an electronic stored-program digital computer. Computer_sentence_139

His 1945 report "Proposed Electronic Calculator" was the first specification for such a device. Computer_sentence_140

John von Neumann at the University of Pennsylvania also circulated his First Draft of a Report on the EDVAC in 1945. Computer_sentence_141

The Manchester Baby was the world's first stored-program computer. Computer_sentence_142

It was built at the Victoria University of Manchester by Frederic C. Williams, Tom Kilburn and Geoff Tootill, and ran its first program on 21 June 1948. Computer_sentence_143

It was designed as a testbed for the Williams tube, the first random-access digital storage device. Computer_sentence_144

Although the computer was considered "small and primitive" by the standards of its time, it was the first working machine to contain all of the elements essential to a modern electronic computer. Computer_sentence_145

As soon as the Baby had demonstrated the feasibility of its design, a project was initiated at the university to develop it into a more usable computer, the Manchester Mark 1. Computer_sentence_146

Grace Hopper was the first person to develop a compiler for programming language. Computer_sentence_147

The Mark 1 in turn quickly became the prototype for the Ferranti Mark 1, the world's first commercially available general-purpose computer. Computer_sentence_148

Built by Ferranti, it was delivered to the University of Manchester in February 1951. Computer_sentence_149

At least seven of these later machines were delivered between 1953 and 1957, one of them to Shell labs in Amsterdam. Computer_sentence_150

In October 1947, the directors of British catering company J. Computer_sentence_151 Lyons & Company decided to take an active role in promoting the commercial development of computers. Computer_sentence_152

The LEO I computer became operational in April 1951 and ran the world's first regular routine office computer job. Computer_sentence_153

Transistors Computer_section_11

Main articles: Transistor and History of the transistor Computer_sentence_154

Further information: Transistor computer and MOSFET Computer_sentence_155

The concept of a field-effect transistor was proposed by Julius Edgar Lilienfeld in 1925. Computer_sentence_156

John Bardeen and Walter Brattain, while working under William Shockley at Bell Labs, built the first working transistor, the point-contact transistor, in 1947, which was followed by Shockley's bipolar junction transistor in 1948. Computer_sentence_157

From 1955 onwards, transistors replaced vacuum tubes in computer designs, giving rise to the "second generation" of computers. Computer_sentence_158

Compared to vacuum tubes, transistors have many advantages: they are smaller, and require less power than vacuum tubes, so give off less heat. Computer_sentence_159

Junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life. Computer_sentence_160

Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. Computer_sentence_161

However, early junction transistors were relatively bulky devices that were difficult to manufacture on a mass-production basis, which limited them to a number of specialised applications. Computer_sentence_162

At the University of Manchester, a team under the leadership of Tom Kilburn designed and built a machine using the newly developed transistors instead of valves. Computer_sentence_163

Their first transistorised computer and the first in the world, was operational by 1953, and a second version was completed there in April 1955. Computer_sentence_164

However, the machine did make use of valves to generate its 125 kHz clock waveforms and in the circuitry to read and write on its magnetic drum memory, so it was not the first completely transistorized computer. Computer_sentence_165

That distinction goes to the Harwell CADET of 1955, built by the electronics division of the Atomic Energy Research Establishment at Harwell. Computer_sentence_166

The metal–oxide–silicon field-effect transistor (MOSFET), also known as the MOS transistor, was invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959. Computer_sentence_167

It was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of uses. Computer_sentence_168

With its high scalability, and much lower power consumption and higher density than bipolar junction transistors, the MOSFET made it possible to build high-density integrated circuits. Computer_sentence_169

In addition to data processing, it also enabled the practical use of MOS transistors as memory cell storage elements, leading to the development of MOS semiconductor memory, which replaced earlier magnetic-core memory in computers. Computer_sentence_170

The MOSFET led to the microcomputer revolution, and became the driving force behind the computer revolution. Computer_sentence_171

The MOSFET is the most widely used transistor in computers, and is the fundamental building block of digital electronics. Computer_sentence_172

Integrated circuits Computer_section_12

Main articles: Integrated circuit and Invention of the integrated circuit Computer_sentence_173

Further information: Planar process and Microprocessor Computer_sentence_174

The next great advance in computing power came with the advent of the integrated circuit (IC). Computer_sentence_175

The idea of the integrated circuit was first conceived by a radar scientist working for the Royal Radar Establishment of the Ministry of Defence, Geoffrey W.A. Computer_sentence_176 Dummer. Computer_sentence_177

Dummer presented the first public description of an integrated circuit at the Symposium on Progress in Quality Electronic Components in Washington, D.C. on 7 May 1952. Computer_sentence_178

The first working ICs were invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor. Computer_sentence_179

Kilby recorded his initial ideas concerning the integrated circuit in July 1958, successfully demonstrating the first working integrated example on 12 September 1958. Computer_sentence_180

In his patent application of 6 February 1959, Kilby described his new device as "a body of semiconductor material ... wherein all the components of the electronic circuit are completely integrated". Computer_sentence_181

However, Kilby's invention was a hybrid integrated circuit (hybrid IC), rather than a monolithic integrated circuit (IC) chip. Computer_sentence_182

Kilby's IC had external wire connections, which made it difficult to mass-produce. Computer_sentence_183

Noyce also came up with his own idea of an integrated circuit half a year later than Kilby. Computer_sentence_184

Noyce's invention was the first true monolithic IC chip. Computer_sentence_185

His chip solved many practical problems that Kilby's had not. Computer_sentence_186

Produced at Fairchild Semiconductor, it was made of silicon, whereas Kilby's chip was made of germanium. Computer_sentence_187

Noyce's monolithic IC was fabricated using the planar process, developed by his colleague Jean Hoerni in early 1959. Computer_sentence_188

In turn, the planar process was based on the silicon surface passivation and thermal oxidation processes developed by Mohamed Atalla at Bell Labs in the late 1950s. Computer_sentence_189

Modern monolithic ICs are predominantly MOS (metal-oxide-semiconductor) integrated circuits, built from MOSFETs (MOS transistors). Computer_sentence_190

After the first MOSFET was invented by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959, Atalla first proposed the concept of the MOS integrated circuit in 1960, followed by Kahng in 1961, both noting that the MOS transistor's ease of fabrication made it useful for integrated circuits. Computer_sentence_191

The earliest experimental MOS IC to be fabricated was a 16-transistor chip built by Fred Heiman and Steven Hofstein at RCA in 1962. Computer_sentence_192

General Microelectronics later introduced the first commercial MOS IC in 1964, developed by Robert Norman. Computer_sentence_193

Following the development of the self-aligned gate (silicon-gate) MOS transistor by Robert Kerwin, Donald Klein and John Sarace at Bell Labs in 1967, the first silicon-gate MOS IC with self-aligned gates was developed by Federico Faggin at Fairchild Semiconductor in 1968. Computer_sentence_194

The MOSFET has since become the most critical device component in modern ICs. Computer_sentence_195

The development of the MOS integrated circuit led to the invention of the microprocessor, and heralded an explosion in the commercial and personal use of computers. Computer_sentence_196

While the subject of exactly which device was the first microprocessor is contentious, partly due to lack of agreement on the exact definition of the term "microprocessor", it is largely undisputed that the first single-chip microprocessor was the Intel 4004, designed and realized by Federico Faggin with his silicon-gate MOS IC technology, along with Ted Hoff, Masatoshi Shima and Stanley Mazor at Intel. Computer_sentence_197

In the early 1970s, MOS IC technology enabled the integration of more than 10,000 transistors on a single chip. Computer_sentence_198

System on a Chip (SoCs) are complete computers on a microchip (or chip) the size of a coin. Computer_sentence_199

They may or may not have integrated RAM and flash memory. Computer_sentence_200

If not integrated, The RAM is usually placed directly above (known as Package on package) or below (on the opposite side of the circuit board) the SoC, and the flash memory is usually placed right next to the SoC, this all done to improve data transfer speeds, as the data signals don't have to travel long distances. Computer_sentence_201

Since ENIAC in 1945, computers have advanced enormously, with modern SoCs (Such as the Snapdragon 865) being the size of a coin while also being hundreds of thousands of times more powerful than ENIAC, integrating billions of transistors, and consuming only a few watts of power. Computer_sentence_202

Mobile computers Computer_section_13

The first mobile computers were heavy and ran from mains power. Computer_sentence_203

The 50lb IBM 5100 was an early example. Computer_sentence_204

Later portables such as the Osborne 1 and Compaq Portable were considerably lighter but still needed to be plugged in. Computer_sentence_205

The first laptops, such as the Grid Compass, removed this requirement by incorporating batteries – and with the continued miniaturization of computing resources and advancements in portable battery life, portable computers grew in popularity in the 2000s. Computer_sentence_206

The same developments allowed manufacturers to integrate computing resources into cellular mobile phones by the early 2000s. Computer_sentence_207

These smartphones and tablets run on a variety of operating systems and recently became the dominant computing device on the market. Computer_sentence_208

These are powered by System on a Chip (SoCs), which are complete computers on a microchip the size of a coin. Computer_sentence_209

Types Computer_section_14

See also: Classes of computers Computer_sentence_210

Computers can be classified in a number of different ways, including: Computer_sentence_211

By architecture Computer_section_15

Computer_unordered_list_0

By size, form-factor and purpose Computer_section_16

Computer_unordered_list_1

Hardware Computer_section_17

Main articles: Computer hardware, Personal computer hardware, Central processing unit, and Microprocessor Computer_sentence_212

The term hardware covers all of those parts of a computer that are tangible physical objects. Computer_sentence_213

Circuits, computer chips, graphic cards, sound cards, memory (RAM), motherboard, displays, power supplies, cables, keyboards, printers and "mice" input devices are all hardware. Computer_sentence_214

History of computing hardware Computer_section_18

Main article: History of computing hardware Computer_sentence_215

Computer_table_general_1

First generation (mechanical/electromechanical)Computer_cell_1_0_0 CalculatorsComputer_cell_1_0_1 Pascal's calculator, Arithmometer, Difference engine, Quevedo's analytical machinesComputer_cell_1_0_2
Programmable devicesComputer_cell_1_1_0 Jacquard loom, Analytical engine, IBM ASCC/Harvard Mark I, Harvard Mark II, IBM SSEC, Z1, Z2, Z3Computer_cell_1_1_1
Second generation (vacuum tubes)Computer_cell_1_2_0 CalculatorsComputer_cell_1_2_1 Atanasoff–Berry Computer, IBM 604, UNIVAC 60, UNIVAC 120Computer_cell_1_2_2
Programmable devicesComputer_cell_1_3_0 Colossus, ENIAC, Manchester Baby, EDSAC, Manchester Mark 1, Ferranti Pegasus, Ferranti Mercury, CSIRAC, EDVAC, UNIVAC I, IBM 701, IBM 702, IBM 650, Z22Computer_cell_1_3_1
Third generation (discrete transistors and SSI, MSI, LSI integrated circuits)Computer_cell_1_4_0 MainframesComputer_cell_1_4_1 IBM 7090, IBM 7080, IBM System/360, BUNCHComputer_cell_1_4_2
MinicomputerComputer_cell_1_5_0 HP 2116A, IBM System/32, IBM System/36, LINC, PDP-8, PDP-11Computer_cell_1_5_1
Desktop ComputerComputer_cell_1_6_0 HP 9100Computer_cell_1_6_1
Fourth generation (VLSI integrated circuits)Computer_cell_1_7_0 MinicomputerComputer_cell_1_7_1 VAX, IBM System iComputer_cell_1_7_2
4-bit microcomputerComputer_cell_1_8_0 Intel 4004, Intel 4040Computer_cell_1_8_1
8-bit microcomputerComputer_cell_1_9_0 Intel 8008, Intel 8080, Motorola 6800, Motorola 6809, MOS Technology 6502, Zilog Z80Computer_cell_1_9_1
16-bit microcomputerComputer_cell_1_10_0 Intel 8088, Zilog Z8000, WDC 65816/65802Computer_cell_1_10_1
32-bit microcomputerComputer_cell_1_11_0 Intel 80386, Pentium, Motorola 68000, ARMComputer_cell_1_11_1
64-bit microcomputerComputer_cell_1_12_0 Alpha, MIPS, PA-RISC, PowerPC, SPARC, x86-64, ARMv8-AComputer_cell_1_12_1
Embedded computerComputer_cell_1_13_0 Intel 8048, Intel 8051Computer_cell_1_13_1
Personal computerComputer_cell_1_14_0 Desktop computer, Home computer, Laptop computer, Personal digital assistant (PDA), Portable computer, Tablet PC, Wearable computerComputer_cell_1_14_1
Theoretical/experimentalComputer_cell_1_15_0 Quantum computer, Chemical computer, DNA computing, Optical computer, Spintronics-based computer, Wetware/Organic computerComputer_cell_1_15_1 Computer_cell_1_15_2

Other hardware topics Computer_section_19

Computer_table_general_2

Peripheral device (input/output)Computer_cell_2_0_0 InputComputer_cell_2_0_1 Mouse, keyboard, joystick, image scanner, webcam, graphics tablet, microphoneComputer_cell_2_0_2
OutputComputer_cell_2_1_0 Monitor, printer, loudspeakerComputer_cell_2_1_1
BothComputer_cell_2_2_0 Floppy disk drive, hard disk drive, optical disc drive, teleprinterComputer_cell_2_2_1
Computer busesComputer_cell_2_3_0 Short rangeComputer_cell_2_3_1 RS-232, SCSI, PCI, USBComputer_cell_2_3_2
Long range (computer networking)Computer_cell_2_4_0 Ethernet, ATM, FDDIComputer_cell_2_4_1

A general purpose computer has four main components: the arithmetic logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). Computer_sentence_216

These parts are interconnected by buses, often made of groups of wires. Computer_sentence_217

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. Computer_sentence_218

Each circuit represents a 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). Computer_sentence_219

The circuits are arranged in logic gates so that one or more of the circuits may control the state of one or more of the other circuits. Computer_sentence_220

Input devices Computer_section_20

When unprocessed data is sent to the computer with the help of input devices, the data is processed and sent to output devices. Computer_sentence_221

The input devices may be hand-operated or automated. Computer_sentence_222

The act of processing is mainly regulated by the CPU. Computer_sentence_223

Some examples of input devices are: Computer_sentence_224

Computer_unordered_list_2

Output devices Computer_section_21

The means through which computer gives output are known as output devices. Computer_sentence_225

Some examples of output devices are: Computer_sentence_226

Computer_unordered_list_3

Control unit Computer_section_22

Main articles: CPU design and Control unit Computer_sentence_227

The control unit (often called a control system or central controller) manages the computer's various components; it reads and interprets (decodes) the program instructions, transforming them into control signals that activate other parts of the computer. Computer_sentence_228

Control systems in advanced computers may change the order of execution of some instructions to improve performance. Computer_sentence_229

A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from. Computer_sentence_230

The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU: Computer_sentence_231

Computer_ordered_list_4

  1. Read the code for the next instruction from the cell indicated by the program counter.Computer_item_4_76
  2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.Computer_item_4_77
  3. Increment the program counter so it points to the next instruction.Computer_item_4_78
  4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.Computer_item_4_79
  5. Provide the necessary data to an ALU or register.Computer_item_4_80
  6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.Computer_item_4_81
  7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.Computer_item_4_82
  8. Jump back to step (1).Computer_item_4_83

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Computer_sentence_232

Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Computer_sentence_233

Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow). Computer_sentence_234

The sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program, and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer, which runs a microcode program that causes all of these events to happen. Computer_sentence_235

Central processing unit (CPU) Computer_section_23

Main articles: Central processing unit and Microprocessor Computer_sentence_236

The control unit, ALU, and registers are collectively known as a central processing unit (CPU). Computer_sentence_237

Early CPUs were composed of many separate components. Computer_sentence_238

Since the 1970s, CPUs have typically been constructed on a single MOS integrated circuit chip called a microprocessor. Computer_sentence_239

Arithmetic logic unit (ALU) Computer_section_24

Main article: Arithmetic logic unit Computer_sentence_240

The ALU is capable of performing two classes of operations: arithmetic and logic. Computer_sentence_241

The set of arithmetic operations that a particular ALU supports may be limited to addition and subtraction, or might include multiplication, division, trigonometry functions such as sine, cosine, etc., and square roots. Computer_sentence_242

Some can only operate on whole numbers (integers) while others use floating point to represent real numbers, albeit with limited precision. Computer_sentence_243

However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Computer_sentence_244

Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. Computer_sentence_245

An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?"). Computer_sentence_246

Logic operations involve Boolean logic: AND, OR, XOR, and NOT. Computer_sentence_247

These can be useful for creating complicated conditional statements and processing boolean logic. Computer_sentence_248

Superscalar computers may contain multiple ALUs, allowing them to process several instructions simultaneously. Computer_sentence_249

Graphics processors and computers with SIMD and MIMD features often contain ALUs that can perform arithmetic on vectors and matrices. Computer_sentence_250

Memory Computer_section_25

Main articles: Computer memory and Computer data storage Computer_sentence_251

A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Computer_sentence_252

Each cell has a numbered "address" and can store a single number. Computer_sentence_253

The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595." Computer_sentence_254

The information stored in memory may represent practically anything. Computer_sentence_255

Letters, numbers, even computer instructions can be placed into memory with equal ease. Computer_sentence_256

Since the CPU does not differentiate between different types of information, it is the software's responsibility to give significance to what the memory sees as nothing but a series of numbers. Computer_sentence_257

In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Computer_sentence_258

Each byte is able to represent 256 different numbers (2 = 256); either from 0 to 255 or −128 to +127. Computer_sentence_259

To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). Computer_sentence_260

When negative numbers are required, they are usually stored in two's complement notation. Computer_sentence_261

Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. Computer_sentence_262

A computer can store any kind of information in memory if it can be represented numerically. Computer_sentence_263

Modern computers have billions or even trillions of bytes of memory. Computer_sentence_264

The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. Computer_sentence_265

There are typically between two and one hundred registers depending on the type of CPU. Computer_sentence_266

Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. Computer_sentence_267

As data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed. Computer_sentence_268

Computer main memory comes in two principal varieties: Computer_sentence_269

Computer_unordered_list_5

RAM can be read and written to anytime the CPU commands it, but ROM is preloaded with data and software that never changes, therefore the CPU can only read from it. Computer_sentence_270

ROM is typically used to store the computer's initial start-up instructions. Computer_sentence_271

In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. Computer_sentence_272

In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. Computer_sentence_273

In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Computer_sentence_274

Software stored in ROM is often called firmware, because it is notionally more like hardware than software. Computer_sentence_275

Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. Computer_sentence_276

It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary. Computer_sentence_277

In more sophisticated computers there may be one or more RAM cache memories, which are slower than registers but faster than main memory. Computer_sentence_278

Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part. Computer_sentence_279

Input/output (I/O) Computer_section_26

Main article: Input/output Computer_sentence_280

I/O is the means by which a computer exchanges information with the outside world. Computer_sentence_281

Devices that provide input or output to the computer are called peripherals. Computer_sentence_282

On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Computer_sentence_283

Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer_sentence_284

Computer networking is another form of I/O. Computer_sentence_285

I/O devices are often complex computers in their own right, with their own CPU and memory. Computer_sentence_286

A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics. Computer_sentence_287

Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O. Computer_sentence_288

A 2016-era flat screen display contains its own computer circuitry. Computer_sentence_289

Multitasking Computer_section_27

Main article: Computer multitasking Computer_sentence_290

While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. Computer_sentence_291

This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn. Computer_sentence_292

One means by which this is done is with a special signal called an interrupt, which can periodically cause the computer to stop executing instructions where it was and do something else instead. Computer_sentence_293

By remembering where it was executing prior to the interrupt, the computer can return to that task later. Computer_sentence_294

If several programs are running "at the same time". Computer_sentence_295

then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Computer_sentence_296

Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. Computer_sentence_297

This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn. Computer_sentence_298

Before the era of inexpensive computers, the principal use for multitasking was to allow many people to share the same computer. Computer_sentence_299

Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly, in direct proportion to the number of programs it is running, but most programs spend much of their time waiting for slow input/output devices to complete their tasks. Computer_sentence_300

If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. Computer_sentence_301

This frees up time for other programs to execute so that many programs may be run simultaneously without unacceptable speed loss. Computer_sentence_302

Multiprocessing Computer_section_28

Main article: Multiprocessing Computer_sentence_303

Some computers are designed to distribute their work across several CPUs in a multiprocessing configuration, a technique once employed only in large and powerful machines such as supercomputers, mainframe computers and servers. Computer_sentence_304

Multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers are now widely available, and are being increasingly used in lower-end markets as a result. Computer_sentence_305

Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers. Computer_sentence_306

They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Computer_sentence_307

Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Computer_sentence_308

Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks. Computer_sentence_309

Software Computer_section_29

Main article: Computer software Computer_sentence_310

Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. Software is that part of a computer system that consists of encoded information or computer instructions, in contrast to the physical hardware from which the system is built. Computer_sentence_311

Computer software includes computer programs, libraries and related non-executable data, such as online documentation or digital media. Computer_sentence_312

It is often divided into system software and application software Computer hardware and software require each other and neither can be realistically used on its own. Computer_sentence_313

When software is stored in hardware that cannot easily be modified, such as with BIOS ROM in an IBM PC compatible computer, it is sometimes called "firmware". Computer_sentence_314

Computer_table_general_3

Operating system /System SoftwareComputer_cell_3_0_0 Unix and BSDComputer_cell_3_0_1 UNIX System V, IBM AIX, HP-UX, Solaris (SunOS), IRIX, List of BSD operating systemsComputer_cell_3_0_2
GNU/LinuxComputer_cell_3_1_0 List of Linux distributions, Comparison of Linux distributionsComputer_cell_3_1_1
Microsoft WindowsComputer_cell_3_2_0 Windows 95, Windows 98, Windows NT, Windows 2000, Windows ME, Windows XP, Windows Vista, Windows 7, Windows 8, Windows 8.1, Windows 10Computer_cell_3_2_1
DOSComputer_cell_3_3_0 86-DOS (QDOS), IBM PC DOS, MS-DOS, DR-DOS, FreeDOSComputer_cell_3_3_1
Macintosh operating systemsComputer_cell_3_4_0 Classic Mac OS, macOS (previously OS X and Mac OS X)Computer_cell_3_4_1
Embedded and real-timeComputer_cell_3_5_0 List of embedded operating systemsComputer_cell_3_5_1
ExperimentalComputer_cell_3_6_0 Amoeba, Oberon/Bluebottle, Plan 9 from Bell LabsComputer_cell_3_6_1
LibraryComputer_cell_3_7_0 MultimediaComputer_cell_3_7_1 DirectX, OpenGL, OpenAL, Vulkan (API)Computer_cell_3_7_2
Programming libraryComputer_cell_3_8_0 C standard library, Standard Template LibraryComputer_cell_3_8_1
DataComputer_cell_3_9_0 ProtocolComputer_cell_3_9_1 TCP/IP, Kermit, , HTTP, SMTPComputer_cell_3_9_2
Computer_cell_3_10_0 HTML, XML, JPEG, MPEG, PNGComputer_cell_3_10_1
User interfaceComputer_cell_3_11_0 Graphical user interface (WIMP)Computer_cell_3_11_1 Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM, AquaComputer_cell_3_11_2
Text-based user interfaceComputer_cell_3_12_0 Command-line interface, Text user interfaceComputer_cell_3_12_1
Application SoftwareComputer_cell_3_13_0 Office suiteComputer_cell_3_13_1 Word processing, Desktop publishing, Presentation program, Database management system, Scheduling & Time management, Spreadsheet, Accounting softwareComputer_cell_3_13_2
Internet AccessComputer_cell_3_14_0 Browser, Email client, Web server, Mail transfer agent, Instant messagingComputer_cell_3_14_1
Design and manufacturingComputer_cell_3_15_0 Computer-aided design, Computer-aided manufacturing, Plant management, Robotic manufacturing, Supply chain managementComputer_cell_3_15_1
GraphicsComputer_cell_3_16_0 Raster graphics editor, Vector graphics editor, 3D modeler, Animation editor, 3D computer graphics, Video editing, Image processingComputer_cell_3_16_1
AudioComputer_cell_3_17_0 Digital audio editor, Audio playback, Mixing, Audio synthesis, Computer musicComputer_cell_3_17_1
Software engineeringComputer_cell_3_18_0 Compiler, Assembler, Interpreter, Debugger, Text editor, Integrated development environment, Software performance analysis, Revision control, Software configuration managementComputer_cell_3_18_1
EducationalComputer_cell_3_19_0 Edutainment, Educational game, Serious game, Flight simulatorComputer_cell_3_19_1
GamesComputer_cell_3_20_0 Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform, Massively multiplayer, Interactive fictionComputer_cell_3_20_1
MiscComputer_cell_3_21_0 Artificial intelligence, Antivirus software, Malware scanner, Installer/Package management systems,Computer_cell_3_21_1

Languages Computer_section_30

There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications. Computer_sentence_315

Computer_table_general_4

Programming languagesComputer_table_caption_4
Lists of programming languagesComputer_cell_4_0_0 Timeline of programming languages, List of programming languages by category, Generational list of programming languages, List of programming languages, Non-English-based programming languagesComputer_cell_4_0_1
Commonly used assembly languagesComputer_cell_4_1_0 ARM, MIPS, x86Computer_cell_4_1_1
Commonly used high-level programming languagesComputer_cell_4_2_0 Ada, BASIC, C, C++, C#, COBOL, Fortran, PL/I, REXX, Java, Lisp, Pascal, Object PascalComputer_cell_4_2_1
Commonly used scripting languagesComputer_cell_4_3_0 Bourne script, JavaScript, Python, Ruby, PHP, PerlComputer_cell_4_3_1

Programs Computer_section_31

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. Computer_sentence_316

That is to say that some type of instructions (the program) can be given to the computer, and it will process them. Computer_sentence_317

Modern computers based on the von Neumann architecture often have machine code in the form of an imperative programming language. Computer_sentence_318

In practical terms, a computer program may be just a few instructions or extend to many millions of instructions, as do the programs for word processors and web browsers for example. Computer_sentence_319

A typical modern computer can execute billions of instructions per second (gigaflops) and rarely makes a mistake over many years of operation. Computer_sentence_320

Large computer programs consisting of several million instructions may take teams of programmers years to write, and due to the complexity of the task almost certainly contain errors. Computer_sentence_321

Stored program architecture Computer_section_32

Main articles: Computer program and Computer programming Computer_sentence_322

This section applies to most common RAM machine–based computers. Computer_sentence_323

In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc. Computer_sentence_324

These instructions are read from the computer's memory and are generally carried out (executed) in the order they were given. Computer_sentence_325

However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. Computer_sentence_326

These are called "jump" instructions (or branches). Computer_sentence_327

Furthermore, jump instructions may be made to happen conditionally so that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Computer_sentence_328

Many computers directly support subroutines by providing a type of jump that "remembers" the location it jumped from and another instruction to return to the instruction following that jump instruction. Computer_sentence_329

Program execution might be likened to reading a book. Computer_sentence_330

While a person will normally read each word and line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of interest. Computer_sentence_331

Similarly, a computer may sometimes go back and repeat the instructions in some section of the program over and over again until some internal condition is met. Computer_sentence_332

This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention. Computer_sentence_333

Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. Computer_sentence_334

But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time, with a near certainty of making a mistake. Computer_sentence_335

On the other hand, a computer may be programmed to do this with just a few simple instructions. Computer_sentence_336

The following example is written in the MIPS assembly language: Computer_sentence_337

Once told to run this program, the computer will perform the repetitive addition task without further human intervention. Computer_sentence_338

It will almost never make a mistake and a modern PC can complete the task in a fraction of a second. Computer_sentence_339

Machine code Computer_section_33

In most computers, individual instructions are stored as machine code with each instruction being given a unique number (its operation code or opcode for short). Computer_sentence_340

The command to add two numbers together would have one opcode; the command to multiply them would have a different opcode, and so on. Computer_sentence_341

The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from, each with a unique numerical code. Computer_sentence_342

Since the computer's memory is able to store numbers, it can also store the instruction codes. Computer_sentence_343

This leads to the important fact that entire programs (which are just lists of these instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer in the same way as numeric data. Computer_sentence_344

The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program, architecture. Computer_sentence_345

In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. Computer_sentence_346

This is called the Harvard architecture after the Harvard Mark I computer. Computer_sentence_347

Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches. Computer_sentence_348

While it is possible to write computer programs as long lists of numbers (machine language) and while this technique was used with many early computers, it is extremely tedious and potentially error-prone to do so in practice, especially for complicated programs. Computer_sentence_349

Instead, each basic instruction can be given a short name that is indicative of its function and easy to remember – a mnemonic such as ADD, SUB, MULT or JUMP. Computer_sentence_350

These mnemonics are collectively known as a computer's assembly language. Computer_sentence_351

Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler. Computer_sentence_352

Programming language Computer_section_34

Main article: Programming language Computer_sentence_353

Programming languages provide various ways of specifying programs for computers to run. Computer_sentence_354

Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. Computer_sentence_355

They are purely written languages and are often difficult to read aloud. Computer_sentence_356

They are generally either translated into machine code by a compiler or an assembler before being run, or translated directly at run time by an interpreter. Computer_sentence_357

Sometimes programs are executed by a hybrid method of the two techniques. Computer_sentence_358

Low-level languages Computer_section_35

Main article: Low-level programming language Computer_sentence_359

Machine languages and the assembly languages that represent them (collectively termed low-level programming languages) are generally unique to the particular architecture of a computer's central processing unit (CPU). Computer_sentence_360

For instance, an ARM architecture CPU (such as may be found in a smartphone or a hand-held videogame) cannot understand the machine language of an x86 CPU that might be in a PC. Computer_sentence_361

Historically a significant number of other cpu architectures were created and saw extensive use, notably including the MOS Technology 6502 and 6510 in addition to the Zilog Z80. Computer_sentence_362

High-level languages Computer_section_36

Main article: High-level programming language Computer_sentence_363

Although considerably easier than in machine language, writing long programs in assembly language is often difficult and is also error prone. Computer_sentence_364

Therefore, most practical programs are written in more abstract high-level programming languages that are able to express the needs of the programmer more conveniently (and thereby help reduce programmer error). Computer_sentence_365

High level languages are usually "compiled" into machine language (or sometimes into assembly language and then into machine language) using another computer program called a compiler. Computer_sentence_366

High level languages are less related to the workings of the target computer than assembly language, and more related to the language and structure of the problem(s) to be solved by the final program. Computer_sentence_367

It is therefore often possible to use different compilers to translate the same high level language program into the machine language of many different types of computer. Computer_sentence_368

This is part of the means by which software like video games may be made available for different computer architectures such as personal computers and various video game consoles. Computer_sentence_369

Program design Computer_section_37

Bugs Computer_section_38

Main article: Software bug Computer_sentence_370

Errors in computer programs are called "bugs". Computer_sentence_371

They may be benign and not affect the usefulness of the program, or have only subtle effects. Computer_sentence_372

But in some cases, they may cause the program or the entire system to "hang", becoming unresponsive to input such as mouse clicks or keystrokes, to completely fail, or to crash. Computer_sentence_373

Otherwise benign bugs may sometimes be harnessed for malicious intent by an unscrupulous user writing an exploit, code designed to take advantage of a bug and disrupt a computer's proper execution. Computer_sentence_374

Bugs are usually not the fault of the computer. Computer_sentence_375

Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design. Computer_sentence_376

Admiral Grace Hopper, an American computer scientist and developer of the first compiler, is credited for having first used the term "bugs" in computing after a dead moth was found shorting a relay in the Harvard Mark II computer in September 1947. Computer_sentence_377

Networking and the Internet Computer_section_39

Main articles: Computer networking and Internet Computer_sentence_378

Computers have been used to coordinate information between multiple locations since the 1950s. Computer_sentence_379

The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems such as Sabre. Computer_sentence_380

In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. Computer_sentence_381

The effort was funded by ARPA (now DARPA), and the computer network that resulted was called the ARPANET. Computer_sentence_382

The technologies that made the Arpanet possible spread and evolved. Computer_sentence_383

In time, the network spread beyond academic and military institutions and became known as the Internet. Computer_sentence_384

The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer_sentence_385

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. Computer_sentence_386

Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. Computer_sentence_387

In fact, the number of computers that are networked is growing phenomenally. Computer_sentence_388

A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. Computer_sentence_389

"Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments. Computer_sentence_390

Unconventional computers Computer_section_40

Main article: Human computer Computer_sentence_391

See also: Harvard Computers Computer_sentence_392

A computer does not need to be electronic, nor even have a processor, nor RAM, nor even a hard disk. Computer_sentence_393

While popular usage of the word "computer" is synonymous with a personal electronic computer, the modern definition of a computer is literally: "A device that computes, especially a programmable [usually] electronic machine that performs high-speed mathematical or logical operations or that assembles, stores, correlates, or otherwise processes information." Computer_sentence_394

Any device which processes information qualifies as a computer, especially if the processing is purposeful. Computer_sentence_395

Future Computer_section_41

There is active research to make computers out of many promising new types of technology, such as optical computers, DNA computers, neural computers, and quantum computers. Computer_sentence_396

Most computers are universal, and are able to calculate any computable function, and are limited only by their memory capacity and operating speed. Computer_sentence_397

However different designs of computers can give very different performance for particular problems; for example quantum computers can potentially break some modern encryption algorithms (by quantum factoring) very quickly. Computer_sentence_398

Computer architecture paradigms Computer_section_42

There are many types of computer architectures: Computer_sentence_399

Computer_unordered_list_6

Of all these abstract machines, a quantum computer holds the most promise for revolutionizing computing. Computer_sentence_400

Logic gates are a common abstraction which can apply to most of the above digital or analog paradigms. Computer_sentence_401

The ability to store and execute lists of instructions called programs makes computers extremely versatile, distinguishing them from calculators. Computer_sentence_402

The Church–Turing thesis is a mathematical statement of this versatility: any computer with a minimum capability (being Turing-complete) is, in principle, capable of performing the same tasks that any other computer can perform. Computer_sentence_403

Therefore, any type of computer (netbook, supercomputer, cellular automaton, etc.) is able to perform the same computational tasks, given enough time and storage capacity. Computer_sentence_404

Artificial intelligence Computer_section_43

A computer will solve problems in exactly the way it is programmed to, without regard to efficiency, alternative solutions, possible shortcuts, or possible errors in the code. Computer_sentence_405

Computer programs that learn and adapt are part of the emerging field of artificial intelligence and machine learning. Computer_sentence_406

Artificial intelligence based products generally fall into two major categories: rule based systems and pattern recognition systems. Computer_sentence_407

Rule based systems attempt to represent the rules used by human experts and tend to be expensive to develop. Computer_sentence_408

Pattern based systems use data about a problem to generate conclusions. Computer_sentence_409

Examples of pattern based systems include voice recognition, font recognition, translation and the emerging field of on-line marketing. Computer_sentence_410

Professions and organizations Computer_section_44

As the use of computers has spread throughout society, there are an increasing number of careers involving computers. Computer_sentence_411

Computer_table_general_5

Computer-related professionsComputer_table_caption_5
Hardware-relatedComputer_cell_5_0_0 Electrical engineering, Electronic engineering, Computer engineering, Telecommunications engineering, Optical engineering, NanoengineeringComputer_cell_5_0_1
Software-relatedComputer_cell_5_1_0 Computer science, Computer engineering, Desktop publishing, Human–computer interaction, Information technology, Information systems, Computational science, Software engineering, Video game industry, Web designComputer_cell_5_1_1

The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature. Computer_sentence_412

Computer_table_general_6

OrganizationsComputer_table_caption_6
Standards groupsComputer_cell_6_0_0 ANSI, IEC, IEEE, IETF, ISO, W3CComputer_cell_6_0_1
Professional societiesComputer_cell_6_1_0 ACM, AIS, IET, IFIP, BCSComputer_cell_6_1_1
Free/open source software groupsComputer_cell_6_2_0 Free Software Foundation, Mozilla Foundation, Apache Software FoundationComputer_cell_6_2_1

See also Computer_section_45

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Computer.