How old is the word computer

A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These programs enable computers to perform a wide range of tasks. A computer system is a nominally complete computer that includes the hardware, operating system (main software), and peripheral equipment needed and used for full operation. This term may also refer to a group of computers that are linked and function together, such as a computer network or computer cluster.

A broad range of industrial and consumer products use computers as control systems. Simple special-purpose devices like microwave ovens and remote controls are included, as are factory devices like industrial robots and computer-aided design, as well as general-purpose devices like personal computers and mobile devices like smartphones. Computers power the Internet, which links billions of other computers and users.

Early computers were meant to be used only for calculations. Simple manual instruments like the abacus have aided people in doing calculations since ancient times. Early in the Industrial Revolution, some mechanical devices were built to automate long, tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century. The first digital electronic calculating machines were developed during World War II. The first semiconductor transistors in the late 1940s were followed by the silicon-based MOSFET (MOS transistor) and monolithic integrated circuit chip technologies in the late 1950s, leading to the microprocessor and the microcomputer revolution in the 1970s. 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.

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

Etymology

According to the Oxford English Dictionary, the first known use of computer was in a 1613 book called The Yong Mans Gleanings by the English writer Richard Brathwait: «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.» This usage of the term referred to a human computer, a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century. During the latter part of this period women were often hired as computers because they could be paid less than their male counterparts.^[1] By 1943, most human computers were women.^[2]

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.)». The Online Etymology Dictionary states that the use of the term to mean «‘calculating machine’ (of any type) is from 1897.» 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«.^[3]

History

Pre-20th century

Devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was most likely a form of tally stick. Later record keeping aids throughout the Fertile Crescent included calculi (clay spheres, cones, etc.) which represented counts of items, likely livestock or grains, sealed in hollow unbaked clay containers.^[a][4] The use of counting rods is one example.

The abacus was initially used for arithmetic tasks. The Roman abacus was developed from devices used in Babylonia as early as 2400 BC. Since then, many other forms of reckoning boards or tables have been invented. 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.^[5]

The Antikythera mechanism is believed to be the earliest known mechanical analog computer, according to Derek J. de Solla Price.^[6] It was designed to calculate astronomical positions. It was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to approximately c. 100 BC. Devices of comparable complexity to the Antikythera mechanism would not reappear until the fourteenth century.^[7]

Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. The planisphere was a star chart invented by Abū Rayhān al-Bīrūnī in the early 11th century.^[8] The astrolabe was invented in the Hellenistic world in either the 1st or 2nd centuries BC and is often attributed to Hipparchus. 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. An astrolabe incorporating a mechanical calendar computer^[9][10] and gear-wheels was invented by Abi Bakr of Isfahan, Persia in 1235.^[11] Abū Rayhān al-Bīrūnī invented the first mechanical geared lunisolar calendar astrolabe,^[12] an early fixed-wired knowledge processing machine^[13] with a gear train and gear-wheels,^[14] c. 1000 AD.

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.

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

The slide rule was invented around 1620–1630 by the English clergyman William Oughtred, shortly after the publication of the concept of the logarithm. It is a hand-operated analog computer for doing multiplication and division. 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. 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.

In the 1770s, Pierre Jaquet-Droz, a Swiss watchmaker, built a mechanical doll (automaton) that could write holding a quill pen. By switching the number and order of its internal wheels different letters, and hence different messages, could be produced. In effect, it could be mechanically «programmed» to read instructions. Along with two other complex machines, the doll is at the Musée d’Art et d’Histoire of Neuchâtel, Switzerland, and still operates.^[15]

In 1831–1835, mathematician and engineer Giovanni Plana devised a Perpetual Calendar machine, which, through 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. The tide-predicting machine invented by the Scottish scientist Sir William Thomson in 1872 was of great utility to navigation in shallow waters. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location.

The differential analyser, a mechanical analog computer designed to solve differential equations by integration, used wheel-and-disc mechanisms to perform the integration. In 1876, Sir William Thomson 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.^[16] In a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. The torque amplifier was the advance that allowed these machines to work. Starting in the 1920s, Vannevar Bush and others developed mechanical differential analyzers.

First computer

Charles Babbage, an English mechanical engineer and polymath, originated the concept of a programmable computer. Considered the «father of the computer»,^[17] he conceptualized and invented the first mechanical computer in the early 19th century. 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. 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. For output, the machine would have a printer, a curve plotter and a bell. The machine would also be able to punch numbers onto cards to be read in later. 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.^[18][19]

The machine was about a century ahead of its time. All the parts for his machine had to be made by hand – this was a major problem for a device with thousands of parts. Eventually, the project was dissolved with the decision of the British Government to cease funding. 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. Nevertheless, his son, Henry Babbage, completed a simplified version of the analytical engine’s computing unit (the mill) in 1888. He gave a successful demonstration of its use in computing tables in 1906.

Analog computers

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.^[20] The first modern analog computer was a tide-predicting machine, invented by Sir William Thomson (later to become Lord Kelvin) in 1872. 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 elder brother of the more famous Sir William Thomson.^[16]

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. This built on the mechanical integrators of James Thomson and the torque amplifiers invented by H. W. Nieman. A dozen of these devices were built before their obsolescence became obvious. 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).

Digital computers

Electromechanical

By 1938, the United States Navy had developed an electromechanical analog computer small enough to use aboard a submarine. This was the Torpedo Data Computer, which used trigonometry to solve the problem of firing a torpedo at a moving target. During World War II similar devices were developed in other countries as well.

Early digital computers were electromechanical; electric switches drove mechanical relays to perform the calculation. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes. The Z2, created by German engineer Konrad Zuse in 1939 in Berlin, was one of the earliest examples of an electromechanical relay computer.^[21]

In 1941, Zuse followed his earlier machine up with the Z3, the world’s first working electromechanical programmable, fully automatic digital computer.^[24][25] The Z3 was built with 2000 relays, implementing a 22 bit word length that operated at a clock frequency of about 5–10 Hz.^[26] Program code was supplied on punched film while data could be stored in 64 words of memory or supplied from the keyboard. It was quite similar to modern machines in some respects, pioneering numerous advances such as floating-point numbers. 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.^[27] The Z3 was not itself a universal computer but could be extended to be Turing complete.^[28][29]

Zuse’s next computer, the Z4, became the world’s first commercial computer; after initial delay due to the Second World War, it was completed in 1950 and delivered to the ETH Zurich.^[30] The computer was manufactured by Zuse’s own company, Zuse KG [de], which was founded in 1941 as the first company with the sole purpose of developing computers in Berlin.^[30]

Vacuum tubes and digital electronic circuits

Purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. 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. 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.^[20] In the US, John Vincent Atanasoff and Clifford E. Berry of Iowa State University developed and tested the Atanasoff–Berry Computer (ABC) in 1942,^[31] the first «automatic electronic digital computer».^[32] This design was also all-electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory.^[33]

During World War II, the British code-breakers at Bletchley Park achieved a number of successes at breaking encrypted German military communications. The German encryption machine, Enigma, was first attacked with the help of the electro-mechanical bombes which were often run by women.^[34][35] 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.^[33] He spent eleven months from early February 1943 designing and building the first Colossus.^[36] After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944^[37] and attacked its first message on 5 February.^[33]

Colossus was the world’s first electronic digital programmable computer.^[20] It used a large number of valves (vacuum tubes). 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. Nine Mk II Colossi were built (The Mk I was converted to a Mk II making ten machines in total). Colossus Mark I contained 1,500 thermionic valves (tubes), but Mark II with 2,400 valves, was both five times faster and simpler to operate than Mark I, greatly speeding the decoding process.^[38][39]

The ENIAC^[40] (Electronic Numerical Integrator and Computer) was the first electronic programmable computer built in the U.S. Although the ENIAC was similar to the Colossus, it was much faster, more flexible, and it was Turing-complete. 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. Once a program was written, it had to be mechanically set into the machine with manual resetting of plugs and switches. The programmers of the ENIAC were six women, often known collectively as the «ENIAC girls».^[41][42]

It combined the high speed of electronics with the ability to be programmed for many complex problems. It could add or subtract 5000 times a second, a thousand times faster than any other machine. It also had modules to multiply, divide, and square root. High speed memory was limited to 20 words (about 80 bytes). Built under the direction of John Mauchly and J. Presper Eckert at the University of Pennsylvania, ENIAC’s development and construction lasted from 1943 to full operation at the end of 1945. 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.^[43]

Modern computers

Concept of modern computer

The principle of the modern computer was proposed by Alan Turing in his seminal 1936 paper,^[44] On Computable Numbers. Turing proposed a simple device that he called «Universal Computing machine» and that is now known as a universal Turing machine. 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. The fundamental concept of Turing’s design is the stored program, where all the instructions for computing are stored in memory. Von Neumann acknowledged that the central concept of the modern computer was due to this paper.^[45] Turing machines are to this day a central object of study in theory of computation. 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.

Stored programs

Early computing machines had fixed programs. Changing its function required the re-wiring and re-structuring of the machine.^[33] With the proposal of the stored-program computer this changed. 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. The theoretical basis for the stored-program computer was laid out by Alan Turing in his 1936 paper. In 1945, Turing joined the National Physical Laboratory and began work on developing an electronic stored-program digital computer. His 1945 report «Proposed Electronic Calculator» was the first specification for such a device. John von Neumann at the University of Pennsylvania also circulated his First Draft of a Report on the EDVAC in 1945.^[20]

The Manchester Baby was the world’s first stored-program computer. It was built at the University of Manchester in England by Frederic C. Williams, Tom Kilburn and Geoff Tootill, and ran its first program on 21 June 1948.^[46] It was designed as a testbed for the Williams tube, the first random-access digital storage device.^[47] Although the computer was described as «small and primitive» by a 1998 retrospective, it was the first working machine to contain all of the elements essential to a modern electronic computer.^[48] As soon as the Baby had demonstrated the feasibility of its design, a project began at the university to develop it into a practically useful computer, the Manchester Mark 1.

The Mark 1 in turn quickly became the prototype for the Ferranti Mark 1, the world’s first commercially available general-purpose computer.^[49] Built by Ferranti, it was delivered to the University of Manchester in February 1951. At least seven of these later machines were delivered between 1953 and 1957, one of them to Shell labs in Amsterdam.^[50] In October 1947 the directors of British catering company J. Lyons & Company decided to take an active role in promoting the commercial development of computers. Lyons’s LEO I computer, modelled closely on the Cambridge EDSAC of 1949, became operational in April 1951^[51] and ran the world’s first routine office computer job.

Grace Hopper was the first to develop a compiler for a programming language.^[2]

Transistors

The concept of a field-effect transistor was proposed by Julius Edgar Lilienfeld in 1925. 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.^[52][53] From 1955 onwards, transistors replaced vacuum tubes in computer designs, giving rise to the «second generation» of computers. Compared to vacuum tubes, transistors have many advantages: they are smaller, and require less power than vacuum tubes, so give off less heat. Junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life. Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. 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.^[54]

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.^[55] Their first transistorised computer and the first in the world, was operational by 1953, and a second version was completed there in April 1955. 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. That distinction goes to the Harwell CADET of 1955,^[56] built by the electronics division of the Atomic Energy Research Establishment at Harwell.^[56][57]

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.^[58] It was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of uses.^[54] With its high scalability,^[59] and much lower power consumption and higher density than bipolar junction transistors,^[60] the MOSFET made it possible to build high-density integrated circuits.^[61][62] 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. The MOSFET led to the microcomputer revolution,^[63] and became the driving force behind the computer revolution.^[64][65] The MOSFET is the most widely used transistor in computers,^[66][67] and is the fundamental building block of digital electronics.^[68]

Integrated circuits

The next great advance in computing power came with the advent of the integrated circuit (IC).
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. Dummer. 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.^[69]

The first working ICs were invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor.^[70] Kilby recorded his initial ideas concerning the integrated circuit in July 1958, successfully demonstrating the first working integrated example on 12 September 1958.^[71] 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».^[72][73] However, Kilby’s invention was a hybrid integrated circuit (hybrid IC), rather than a monolithic integrated circuit (IC) chip.^[74] Kilby’s IC had external wire connections, which made it difficult to mass-produce.^[75]

Noyce also came up with his own idea of an integrated circuit half a year later than Kilby.^[76] Noyce’s invention was the first true monolithic IC chip.^[77][75] His chip solved many practical problems that Kilby’s had not. Produced at Fairchild Semiconductor, it was made of silicon, whereas Kilby’s chip was made of germanium. Noyce’s monolithic IC was fabricated using the planar process, developed by his colleague Jean Hoerni in early 1959. In turn, the planar process was based on Mohamed M. Atalla’s work on semiconductor surface passivation by silicon dioxide in the late 1950s.^[78][79][80]

Modern monolithic ICs are predominantly MOS (metal–oxide–semiconductor) integrated circuits, built from MOSFETs (MOS transistors).^[81] The earliest experimental MOS IC to be fabricated was a 16-transistor chip built by Fred Heiman and Steven Hofstein at RCA in 1962.^[82] General Microelectronics later introduced the first commercial MOS IC in 1964,^[83] developed by Robert Norman.^[82] 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.^[84] The MOSFET has since become the most critical device component in modern ICs.^[81]

The development of the MOS integrated circuit led to the invention of the microprocessor,^[85][86] and heralded an explosion in the commercial and personal use of computers. 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,^[87] designed and realized by Federico Faggin with his silicon-gate MOS IC technology,^[85] along with Ted Hoff, Masatoshi Shima and Stanley Mazor at Intel.^[b][89] In the early 1970s, MOS IC technology enabled the integration of more than 10,000 transistors on a single chip.^[62]

System on a Chip (SoCs) are complete computers on a microchip (or chip) the size of a coin.^[90] They may or may not have integrated RAM and flash memory. 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. 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.

Mobile computers

The first mobile computers were heavy and ran from mains power. The 50 lb (23 kg) IBM 5100 was an early example. Later portables such as the Osborne 1 and Compaq Portable were considerably lighter but still needed to be plugged in. 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.^[91] The same developments allowed manufacturers to integrate computing resources into cellular mobile phones by the early 2000s.

These smartphones and tablets run on a variety of operating systems and recently became the dominant computing device on the market.^[92] These are powered by System on a Chip (SoCs), which are complete computers on a microchip the size of a coin.^[90]

Types

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

By architecture

• Analog computer
• Digital computer
• Hybrid computer
• Harvard architecture
• Von Neumann architecture
• Complex instruction set computer
• Reduced instruction set computer

By size, form-factor and purpose

• Supercomputer
• Mainframe computer
• Minicomputer (term no longer used),^[93] Midrange computer
• Server
  • Rackmount server
  • Blade server
  • Tower server
• Personal computer
  • Workstation
  • Microcomputer (term no longer used)^[94]
    • Home computer (term fallen into disuse)^[95]
  • Desktop computer
    • Tower desktop
    • Slimline desktop
      • Multimedia computer (non-linear editing system computers, video editing PCs and the like, this term is no longer used)^[96]
      • Gaming computer
    • All-in-one PC
    • Nettop (Small form factor PCs, Mini PCs)
    • Home theater PC
    • Keyboard computer
    • Portable computer
    • Thin client
    • Internet appliance
  • Laptop
    • Desktop replacement computer
    • Gaming laptop
    • Rugged laptop
    • 2-in-1 PC
    • Ultrabook
    • Chromebook
    • Subnotebook
    • Netbook
• Mobile computers:
  • Tablet computer
  • Smartphone
  • Ultra-mobile PC
  • Pocket PC
  • Palmtop PC
  • Handheld PC
• Wearable computer
  • Smartwatch
  • Smartglasses
• Single-board computer
• Plug computer
• Stick PC
• Programmable logic controller
• Computer-on-module
• System on module
• System in a package
• System-on-chip (Also known as an Application Processor or AP if it lacks circuitry such as radio circuitry)
• Microcontroller

Hardware

The term hardware covers all of those parts of a computer that are tangible physical objects. Circuits, computer chips, graphic cards, sound cards, memory (RAM), motherboard, displays, power supplies, cables, keyboards, printers and «mice» input devices are all hardware.

History of computing hardware

Other hardware topics

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). These parts are interconnected by buses, often made of groups of wires. Inside each of these parts are thousands to trillions of small electrical circuits which can be turned off or on by means of an electronic switch. Each circuit represents a bit (binary digit) of information so that when the circuit is on it represents a «1», and when off it represents a «0» (in positive logic representation). The circuits are arranged in logic gates so that one or more of the circuits may control the state of one or more of the other circuits.

Input devices

When unprocessed data is sent to the computer with the help of input devices, the data is processed and sent to output devices. The input devices may be hand-operated or automated. The act of processing is mainly regulated by the CPU. Some examples of input devices are:

• Computer keyboard
• Digital camera
• Digital video
• Graphics tablet
• Image scanner
• Joystick
• Microphone
• Mouse
• Overlay keyboard
• Real-time clock
• Trackball
• Touchscreen
• Light pen

Output devices

The means through which computer gives output are known as output devices. Some examples of output devices are:

• Computer monitor
• Printer
• PC speaker
• Projector
• Sound card
• Video card

Control unit

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.^[d] Control systems in advanced computers may change the order of execution of some instructions to improve performance.

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.^[e]

The control system’s function is as follows— 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:

1. Read the code for the next instruction from the cell indicated by the program counter.
2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
3. Increment the program counter so it points to the next instruction.
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.
5. Provide the necessary data to an ALU or register.
6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.
8. Jump back to step (1).

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. 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).

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.

Central processing unit (CPU)

The control unit, ALU, and registers are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components. Since the 1970s, CPUs have typically been constructed on a single MOS integrated circuit chip called a microprocessor.

Arithmetic logic unit (ALU)

The ALU is capable of performing two classes of operations: arithmetic and logic.^[97] 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. Some can operate only on whole numbers (integers) while others use floating point to represent real numbers, albeit with limited precision. 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. 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. 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?»). Logic operations involve Boolean logic: AND, OR, XOR, and NOT. These can be useful for creating complicated conditional statements and processing Boolean logic.

Superscalar computers may contain multiple ALUs, allowing them to process several instructions simultaneously.^[98] Graphics processors and computers with SIMD and MIMD features often contain ALUs that can perform arithmetic on vectors and matrices.

Memory

A computer’s memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered «address» and can store a single number. 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.» The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. 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.

In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers (2⁸ = 256); either from 0 to 255 or −128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two’s complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.

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. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. 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 main memory comes in two principal varieties:

• random-access memory or RAM
• read-only memory or ROM

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. ROM is typically used to store the computer’s initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. 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. In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.^[f]

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

Input/output (I/O)

I/O is the means by which a computer exchanges information with the outside world.^[100] Devices that provide input or output to the computer are called peripherals.^[101] On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.
I/O devices are often complex computers in their own right, with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics.^{[citation needed]} Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O. A 2016-era flat screen display contains its own computer circuitry.

Multitasking

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. This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn.^[102] 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. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running «at the same time». then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. 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. This method of multitasking is sometimes termed «time-sharing» since each program is allocated a «slice» of time in turn.^[103]

Before the era of inexpensive computers, the principal use for multitasking was to allow many people to share the same computer. 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. 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. This frees up time for other programs to execute so that many programs may be run simultaneously without unacceptable speed loss.

Multiprocessing

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

Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general-purpose computers.^[g] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful for only specialized tasks due to the large scale of program organization required to use most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called «embarrassingly parallel» tasks.

Software

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

Languages

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

Programs

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that some type of instructions (the program) can be given to the computer, and it will process them. Modern computers based on the von Neumann architecture often have machine code in the form of an imperative programming language. 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. A typical modern computer can execute billions of instructions per second (gigaflops) and rarely makes a mistake over many years of operation. 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.

Stored program architecture

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

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. These instructions are read from the computer’s memory and are generally carried out (executed) in the order they were given. 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. These are called «jump» instructions (or branches). 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. 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.

Program execution might be likened to reading a book. 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. 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. This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention.

Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. 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. On the other hand, a computer may be programmed to do this with just a few simple instructions. The following example is written in the MIPS assembly language:

  begin:
  addi $8, $0, 0           # initialize sum to 0
  addi $9, $0, 1           # set first number to add = 1
  loop:
  slti $10, $9, 1000       # check if the number is less than 1000
  beq $10, $0, finish      # if odd number is greater than n then exit
  add $8, $8, $9           # update sum
  addi $9, $9, 1           # get next number
  j loop                   # repeat the summing process
  finish:
  add $2, $8, $0           # put sum in output register

Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in a fraction of a second.

Machine code

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). The command to add two numbers together would have one opcode; the command to multiply them would have a different opcode, and so on. 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. Since the computer’s memory is able to store numbers, it can also store the instruction codes. 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. 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.^[105][106] 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. This is called the Harvard architecture after the Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches.

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,^[h] it is extremely tedious and potentially error-prone to do so in practice, especially for complicated programs. 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. These mnemonics are collectively known as a computer’s assembly language. 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.

Programming language

Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. 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. Sometimes programs are executed by a hybrid method of the two techniques.

Low-level languages

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). 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.^[i] 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.

High-level languages

Although considerably easier than in machine language, writing long programs in assembly language is often difficult and is also error prone. 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). 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.^[j] 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. 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. 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.

Program design

Program design of small programs is relatively simple and involves the analysis of the problem, collection of inputs, using the programming constructs within languages, devising or using established procedures and algorithms, providing data for output devices and solutions to the problem as applicable.^[107] As problems become larger and more complex, features such as subprograms, modules, formal documentation, and new paradigms such as object-oriented programming are encountered.^[108] Large programs involving thousands of line of code and more require formal software methodologies.^[109] The task of developing large software systems presents a significant intellectual challenge.^[110] Producing software with an acceptably high reliability within a predictable schedule and budget has historically been difficult;^[111] the academic and professional discipline of software engineering concentrates specifically on this challenge.^[112]

Bugs

Errors in computer programs are called «bugs». They may be benign and not affect the usefulness of the program, or have only subtle effects. However, 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.^[113] 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. Bugs are usually not the fault of the computer. 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.^[k] 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.^[114]

Networking and the Internet

Computers have been used to coordinate information between multiple locations since the 1950s. 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.^[115] In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. The effort was funded by ARPA (now DARPA), and the computer network that resulted was called the ARPANET.^[116] The technologies that made the Arpanet possible spread and evolved.

In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 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. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. «Wireless» networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.

Unconventional computers

A computer does not need to be electronic, nor even have a processor, nor RAM, nor even a hard disk. While popular usage of the word «computer» is synonymous with a personal electronic computer,^[l] a typical modern definition of a computer is: «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.»^[117] According to this definition, any device that processes information qualifies as a computer.

Future

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

There are many types of computer architectures:

• Quantum computer vs. Chemical computer
• Scalar processor vs. Vector processor
• Non-Uniform Memory Access (NUMA) computers
• Register machine vs. Stack machine
• Harvard architecture vs. von Neumann architecture
• Cellular architecture

Of all these abstract machines, a quantum computer holds the most promise for revolutionizing computing.^[118] Logic gates are a common abstraction which can apply to most of the above digital or analog paradigms. The ability to store and execute lists of instructions called programs makes computers extremely versatile, distinguishing them from calculators. 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. Therefore, any type of computer (netbook, supercomputer, cellular automaton, etc.) is able to perform the same computational tasks, given enough time and storage capacity.

Artificial intelligence

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 programs that learn and adapt are part of the emerging field of artificial intelligence and machine learning. Artificial intelligence based products generally fall into two major categories: rule-based systems and pattern recognition systems. Rule-based systems attempt to represent the rules used by human experts and tend to be expensive to develop. Pattern-based systems use data about a problem to generate conclusions. Examples of pattern-based systems include voice recognition, font recognition, translation and the emerging field of on-line marketing.

Professions and organizations

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

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.

See also

Notes

References

Sources

External links

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem. An important class of computer operations on some computing platforms is the accepting of input from human operators and the output of results formatted for human consumption. The interface between the computer and the human operator is known as the user interface.

Conventionally a computer consists of some form of memory for data storage, at least one element that carries out arithmetic and logic operations, and a sequencing and control element that can change the order of operations based on the information that is stored. Peripheral devices allow information to be entered from an external source, and allow the results of operations to be sent out.

A computer’s processing unit executes series of instructions that make it read, manipulate and then store data. Conditional instructions change the sequence of instructions as a function of the current state of the machine or its environment.

The first electronic digital computers were developed in the mid-20th century (1940–1945). Originally, they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs).^[1] In this era mechanical analog computers were used for military applications.

Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space.^[2] Simple computers are small enough to fit into mobile devices, and mobile computers can be powered by small batteries. Personal computers in their various forms are icons of the Information Age and are what most people think of as «computers». However, the embedded computers found in many devices from mp3 players to fighter aircraft and from toys to industrial robots are the most numerous.

History of computing

The first use of the word «computer» was recorded in 1613, referring to a person who carried out calculations, or computations, and the word continued with the same meaning until the middle of the 20th century. From the end of the 19th century onwards, the word began to take on its more familiar meaning, describing a machine that carries out computations.^[3]

Limited-function early computers

The history of the modern computer begins with two separate technologies—automated calculation and programmability—but no single device can be identified as the earliest computer, partly because of the inconsistent application of that term. A few devices are worth mentioning though, like some mechanical aids to computing, which were very successful and survived for centuries until the advent of the electronic calculator, like the Sumerian abacus, designed around 2500 BC^[4] which descendant won a speed competition against a modern desk calculating machine in Japan in 1946,^[5] the slide rules, invented in the 1620s, which were carried on five Apollo space missions, including to the moon^[6] and arguably the astrolabe and the Antikythera mechanism, an ancient astronomical computer built by the Greeks around 80 BC.^[7] The Greek mathematician Hero of Alexandria (c. 10–70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when.^[8] This is the essence of programmability.

Around the end of the tenth century, the French monk Gerbert d’Aurillac brought back from Spain the drawings of a machine invented by the Moors that answered Yes or No to the questions it was asked (binary arithmetic).^[9] Again in the thirteenth century, the monks Albertus Magnus and Roger Bacon built talking androids without any further development (Albertus Magnus complained that he had wasted forty years of his life when Thomas Aquinas, terrified by his machine, destroyed it).^[10]

In 1642, the Renaissance saw the invention of the mechanical calculator,^[11] a device that could perform all four arithmetic operations without relying on human intelligence.^[12] The mechanical calculator was at the root of the development of computers in two separate ways; initially, it is in trying to develop more powerful and more flexible calculators^[13] that the computer was first theorized by Charles Babbage^[14][15] and then developed,^[16] leading to the development of mainframe computers in the 1960s, but also the microprocessor, which started the personal computer revolution, and which is now at the heart of all computer systems regardless of size or purpose,^[17] was invented serendipitously by Intel^[18] during the development of an electronic calculator, a direct descendant to the mechanical calculator.^[19]

First general-purpose computers

In 1801, Joseph Marie Jacquard made an improvement to the textile loom by introducing a series of punched paper cards as a template which allowed his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.

It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer, his analytical engine.^[22] Limited finances and Babbage’s inability to resist tinkering with the design meant that the device was never completed ; nevertheless his son, Henry Babbage, completed a simplified version of the analytical engine’s computing unit (the mill) in 1888. He gave a successful demonstration of its use in computing tables in 1906. This machine was given to the Science museum in South Kensington in 1910.

In the late 1880s, Herman Hollerith invented the recording of data on a machine readable medium. Prior uses of machine readable media, above, had been for control, not data. «After some initial trials with paper tape, he settled on punched cards …»^[23] To process these punched cards he invented the tabulator, and the keypunch machines. These three inventions were the foundation of the modern information processing industry. Large-scale automated data processing of punched cards was performed for the 1890 United States Census by Hollerith’s company, which later became the core of IBM. By the end of the 19th century a number of ideas and technologies, that would later prove useful in the realization of practical computers, had begun to appear: Boolean algebra, the vacuum tube (thermionic valve), punched cards and tape, and the teleprinter.

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.

Alan Turing is widely regarded to be the father of modern computer science. In 1936 Turing provided an influential formalisation of the concept of the algorithm and computation with the Turing machine, providing a blueprint for the electronic digital computer.^[24] Of his role in the creation of the modern computer, Time magazine in naming Turing one of the 100 most influential people of the 20th century, states: «The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine».^[24]

The Atanasoff–Berry Computer (ABC) was the world’s first electronic digital computer, albeit not programmable. ^[25] Atanasoff is considered to be one of the fathers of the computer.^[26] Conceived in 1937 by Iowa State College physics professor John Atanasoff, and built with the assistance of graduate student Clifford Berry,^[27] the machine was not programmable, being designed only to solve systems of linear equations. The computer did employ parallel computation. A 1973 court ruling in a patent dispute found that the patent for the 1946 ENIAC computer derived from the Atanasoff–Berry Computer.

The first program-controlled computer was invented by Konrad Zuse, who built the Z3, an electromechanical computing machine, in 1941.^[28] The first programmable electronic computer was the Colossus, built in 1943 by Tommy Flowers.

George Stibitz is internationally recognized as a father of the modern digital computer. While working at Bell Labs in November 1937, Stibitz invented and built a relay-based calculator he dubbed the «Model K» (for «kitchen table», on which he had assembled it), which was the first to use binary circuits to perform an arithmetic operation. Later models added greater sophistication including complex arithmetic and programmability.^[29]

A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as «the first digital electronic computer» is difficult.^{Shannon 1940} Notable achievements include.

• Konrad Zuse’s electromechanical «Z machines». The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world’s first operational computer.^[30]
• The non-programmable Atanasoff–Berry Computer (commenced in 1937, completed in 1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory. The use of regenerative memory allowed it to be much more compact than its peers (being approximately the size of a large desk or workbench), since intermediate results could be stored and then fed back into the same set of computation elements.
• The secret British Colossus computers (1943),^[31] which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.
• The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.^[32]
• The U.S. Army’s Ballistic Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse’s Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.

Stored-program architecture

Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the «stored program architecture» or von Neumann architecture. This design was first formally described by John von Neumann in the paper First Draft of a Report on the EDVAC, distributed in 1945. A number of projects to develop computers based on the stored-program architecture commenced around this time, the first of these being completed in Great Britain. The first working prototype to be demonstrated was the Manchester Small-Scale Experimental Machine (SSEM or «Baby») in 1948. The Electronic Delay Storage Automatic Calculator (EDSAC), completed a year after the SSEM at Cambridge University, was the first practical, non-experimental implementation of the stored program design and was put to use immediately for research work at the university. Shortly thereafter, the machine originally described by von Neumann’s paper—EDVAC—was completed but did not see full-time use for an additional two years.

Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word «computer» is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture.

Beginning in the 1950s, Soviet scientists Sergei Sobolev and Nikolay Brusentsov conducted research on ternary computers, devices that operated on a base three numbering system of −1, 0, and 1 rather than the conventional binary numbering system upon which most computers are based. They designed the Setun, a functional ternary computer, at Moscow State University. The device was put into limited production in the Soviet Union, but supplanted by the more common binary architecture.

Semiconductors and microprocessors

Computers using vacuum tubes as their electronic elements were in use throughout the 1950s, but by the 1960s had been largely replaced by transistor-based machines, which were smaller, faster, cheaper to produce, required less power, and were more reliable. The first transistorised computer was demonstrated at the University of Manchester in 1953.^[33] In the 1970s, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the late 1970s, many products such as video recorders contained dedicated computers called microcontrollers, and they started to appear as a replacement to mechanical controls in domestic appliances such as washing machines. The 1980s witnessed home computers and the now ubiquitous personal computer. With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household^{[citation needed]}.

Modern smartphones are fully programmable computers in their own right, and as of 2009 may well be the most common form of such computers in existence^{[citation needed]}.

Programs

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that some type of instructions (the program) can be given to the computer, and it will carry process them. While some computers may have strange concepts «instructions» and «output» (see quantum computing), modern computers based on the von Neumann architecture often have machine code in the form of an imperative programming language.

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

Stored program architecture

This section applies to most common RAM machine-based computers.

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. These instructions are read from the computer’s memory and are generally carried out (executed) in the order they were given. 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. These are called «jump» instructions (or branches). 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. 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.

Program execution might be likened to reading a book. 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. 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. This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention.

Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. 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. On the other hand, a computer may be programmed to do this with just a few simple instructions. For example:

      mov #0, sum     ; set sum to 0
      mov #1, num     ; set num to 1
loop: add num, sum    ; add num to sum
      add #1, num     ; add 1 to num
      cmp num, #1000  ; compare num to 1000
      ble loop        ; if num <= 1000, go back to 'loop'
      halt            ; end of program. stop running

Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in about a millionth of a second.^[34]

Bugs

Errors in computer programs are called «bugs». Bugs may be benign and not affect the usefulness of the program, or have only subtle effects. But in some cases they may cause the program — or the entire system — to «hang»—become unresponsive to input such as mouse clicks or keystrokes, or to completely fail or «crash». 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. Bugs are usually not the fault of the computer. 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.^[35]

Rear Admiral Grace Hopper is credited for having first used the term ‘bugs’ in computing after a dead moth was found shorting a relay of the Harvard Mark II computer in September 1947.^[36]

Machine code

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). The command to add two numbers together would have one opcode, the command to multiply them would have a different opcode and so on. 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. Since the computer’s memory is able to store numbers, it can also store the instruction codes. 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. 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. 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. This is called the Harvard architecture after the Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches.

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,^[37] it is extremely tedious and potentially error-prone to do so in practice, especially for complicated programs. 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. These mnemonics are collectively known as a computer’s assembly language. 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. Machine languages and the assembly languages that represent them (collectively termed low-level programming languages) tend to be unique to a particular type of computer. For instance, an ARM architecture computer (such as may be found in a PDA or a hand-held videogame) cannot understand the machine language of an Intel Pentium or the AMD Athlon 64 computer that might be in a PC.^[38]

Higher-level languages and program design

Though considerably easier than in machine language, writing long programs in assembly language is often difficult and is also error prone. 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). 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.^[39] 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. 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. 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.

The task of developing large software systems presents a significant intellectual challenge. Producing software with an acceptably high reliability within a predictable schedule and budget has historically been difficult; the academic and professional discipline of software engineering concentrates specifically on this challenge.

Function

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). These parts are interconnected by busses, often made of groups of wires.

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

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

Control unit

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 a series of control signals which activate other parts of the computer.^[40] Control systems in advanced computers may change the order of some instructions so as to improve performance.

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.^[41]

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:

1. Read the code for the next instruction from the cell indicated by the program counter.
2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
3. Increment the program counter so it points to the next instruction.
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.
5. Provide the necessary data to an ALU or register.
6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.
8. Jump back to step (1).

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. 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).

It is noticeable that 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 that runs a microcode program that causes all of these events to happen.

Arithmetic/logic unit (ALU)

The ALU is capable of performing two classes of operations: arithmetic and logic.^[42]

The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc.) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. 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. 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. 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?»).

Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.

Superscalar computers may contain multiple ALUs so that they can process several instructions at the same time.^[43] Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.

Memory

A computer’s memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered «address» and can store a single number. 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». The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. 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.

In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers (2^8 = 256); either from 0 to 255 or −128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two’s complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.

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. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. 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 main memory comes in two principal varieties: random-access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer’s initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. 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. In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.^[44]

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

Input/output (I/O)

I/O is the means by which a computer exchanges information with the outside world.^[45] Devices that provide input or output to the computer are called peripherals.^[46] On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.

Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics^{[citation needed]}. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.

Multitasking

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. This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn.^[47]

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. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running «at the same time», then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. 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. This method of multitasking is sometimes termed «time-sharing» since each program is allocated a «slice» of time in turn.^[48]

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

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. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. 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. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.

Multiprocessing

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. 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.

Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.^[49] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. 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. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called «embarrassingly parallel» tasks.

Networking and the Internet

Computers have been used to coordinate information between multiple locations since the 1950s. 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 like Sabre.^[50]

In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. This effort was funded by ARPA (now DARPA), and the computer network that it produced was called the ARPANET.^[51] The technologies that made the Arpanet possible spread and evolved.

In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 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. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. «Wireless» networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.

Misconceptions

A computer does not need to be electronic, nor even have a processor, nor RAM, nor even a hard disk. While popular usage of the word «computer» is synonymous with a personal computer, the 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.»^[52] Any device which processes information qualifies as a computer, especially if the processing is purposeful.

Required technology

Computational systems as flexible as a personal computer can be built out of almost anything. For example, a computer can be made out of billiard balls (billiard ball computer); this is an unintuitive and pedagogical example that a computer can be made out of almost anything. More realistically, modern computers are made out of transistors made of photolithographed semiconductors.

Historically, computers evolved from mechanical computers and eventually from vacuum tubes to transistors.

There is active research to make computers out of many promising new types of technology, such as optical computing, DNA computers, neural computers, and quantum computers. Some of these can easily tackle problems that modern computers cannot (such as how quantum computers can break some modern encryption algorithms by quantum factoring).

Computer architecture paradigms

There are many types of computer architectures:

• Quantum computer vs Chemical computer
• Scalar processor vs Vector processor
• Non-Uniform Memory Access (NUMA) computers
• Register machine vs Stack machine
• Harvard architecture vs von Neumann architecture
• Cellular architecture

The quantum computer architecture holds the most promise to revolutionize computing.^[53]

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

The ability to store and execute lists of instructions called programs makes computers extremely versatile, distinguishing them from calculators. 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. Therefore any type of computer (netbook, supercomputer, cellular automaton, etc.) is able to perform the same computational tasks, given enough time and storage capacity.

Limited-function computers

Conversely, a computer which is limited in function (one that is not «Turing-complete») cannot simulate arbitrary things. For example, simple four-function calculators cannot simulate a real computer without human intervention. As a more complicated example, without the ability to program a gaming console, it can never accomplish what a programmable calculator from the 1990s could (given enough time); the system as a whole is not Turing-complete, even though it contains a Turing-complete component (the microprocessor). Living organisms (the body, not the brain) are also limited-function computers designed to make copies of themselves; they cannot be reprogrammed without genetic engineering.

Virtual computers

A «computer» is commonly considered to be a physical device. However, one can create a computer program which describes how to run a different computer, i.e. «simulating a computer in a computer». Not only is this a constructive proof of the Church-Turing thesis, but is also extremely common in all modern computers. For example, some programming languages use something called an interpreter, which is a simulated computer built using software that runs on a real, physical computer; this allows programmers to write code (computer input) in a different language than the one understood by the base computer (the alternative is to use a compiler). Additionally, virtual machines are simulated computers which virtually replicate a physical computer in software, and are very commonly used by IT. Virtual machines are also a common technique used to create emulators, such game console emulators.

Further topics

• Glossary of computers

Artificial intelligence

A computer will solve problems in exactly the way they are programmed to, without regard to efficiency nor alternative solutions nor possible shortcuts nor possible errors in the code. Computer programs which learn and adapt are part of the emerging field of artificial intelligence and machine learning.

Hardware

The term hardware covers all of those parts of a computer that are tangible objects. Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware.

Software

Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. When software is stored in hardware that cannot easily be modified (such as BIOS ROM in an IBM PC compatible), it is sometimes called «firmware» to indicate that it falls into an uncertain area somewhere between hardware and software.

Programming languages

Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. 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. Sometimes programs are executed by a hybrid method of the two techniques. There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications.

Professions and organizations

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

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.

See also

Notes

References

External links

• A Brief History of Computing — slideshow by Life magazine

The computer is one of the greatest inventions of its time. Billions of people use computers in their daily lives around the world. For decades, the computer has evolved from a very expensive and slow device to today’s extremely smart machines with incredible computing power.

The word computer came to us from the distant eighteenth century. It is first found in the Oxford dictionary. Initially, the concept of computer was interpreted as a calculator. It was different from today’s in that it could be applied to absolutely any computing device, and not necessarily electronic.

The first computers or calculators were mechanical devices and were able to perform simple mathematical operations such as addition and subtraction. In 1653, the first computer appeared capable of solving more complex problems, or rather, divide and multiply.

For some time, the technological improvement of computers has stopped, and the emphasis was on the perfection of mechanisms and size reduction. Computers also performed four basic arithmetic operations, but became lighter and more compact.

In 1822, a machine capable of solving simple equations was first invented. This was the greatest breakthrough in the field of computer technology. After approval of the project by the government, funds were allocated, and the invention was able to further develop. Soon the machine received a steam engine and became fully automatic. After a decade of continuous research, the first analytical engine appeared-a multi-purpose computer that can operate with many numbers, work with memory and be programmed using punch cards.

Since then, the evolution of the computer has gone at an accelerated pace. To mechanical devices, added electrical relays. They were joined by vacuum tubes. Power and Speed of computers grew from year to year. And in 1946, the first computer appeared. Its weight, size and power consumption, for our understanding, were simply shocking. Enough mention of the weight of 30 tons to represent the scale of the machine, but at the time it was a huge achievement.

With the advent of semiconductor devices, gradually displacing vacuum tubes, the reliability of computers increased, and the size became smaller. The computer has RAM to store information. Machines have learned to write data to magnetic disks. The leader in the production of computers at that time was IBM.

And at one point, scientists were able to integrate into a single chip several semiconductor devices. This moment was a new impetus in the development of computer technology. The computer has a disk drive, a hard drive, a mouse and a graphical interface. Its size was reduced so much that the car could be put on the table. It was the birth of a personal computer, the prototype that we know today.

Since then, mankind has been able to mass use the computer for home use. The first personal computer is the IBM 5150. Computer made on the basis of Intel 8088 processor. The computer cost $ 1,565, was easy to use and took up relatively little space. IBM 5150 was equipped with an Intel 8088 processor with a clock frequency of 4.77 megahertz and pre-installed RAM size of 16 or 64 kilobytes. In just one month, IBM was able to sell 241,683 IBM PC computers. In agreement with the leaders of Microsoft, IBM paid the creators of the program a certain amount for each copy of the operating system installed on the IBM PC. Thanks to the popularity of the IBM PC personal computer, Microsoft executives Bill Gates and Paul Allen soon became billionaires, and Microsoft took a leading position in the software market.

After the creation of the first commercial version of the personal computer, the main emphasis in the development of computer technology, was made to improve the quality and performance of machines.

Gradually, progress has brought the computer to what we see today. Machines became increasingly stronger and more compact. There were laptops, netbooks, tablet PCs, etc.

Today, computers are something extremely powerful and more affordable than ever. They have penetrated almost every aspect of our lives. They are used as a powerful tool for communication and trade. The future of computers is huge.

So we are on the threshold of a new computer age, when artificial intelligence may be invented. And only time will tell whether computers will become our best friends or our worst enemies, as shown in some movies.

That’s interesting. What will the development of computer technology lead to in the near future? What will our children use?

— Howard Aiken, father of the Mark I IBM computer^[1]

Definitions[]

Computer Fraud and Abuse Act[]

Computer is

Computing[]

A computer is a machine which manipulates data according to a list of instructions.

General[]

U.S. copyright law[]

A computer is

Overview[]

Computers take numerous physical forms. The first devices that resemble modern computers date to the mid-20th century (around 1940-1941), although the computer concept and various machines similar to computers existed prior. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers.

Modern computers are based on comparatively tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space. Personal computers in various forms are icons of the Information Age and are what most people think of as a «computer.» However, the most common form of computer in use today is by far the embedded computer. Embedded computers are small, simple devices that are often used to control other devices — for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and even children’s toys.

The ability to store and execute lists of instructions (called programs) makes computers extremely versatile and distinguishes them from calculators.

History of computing[]

It is difficult to identify any one device as the earliest computer, partly because the term «computer» has been subject to varying interpretations over time.

Originally, the term «computer» referred to a person who performed numerical calculations (a human computer), often with the aid of a mechanical calculating device. Examples of early mechanical computing devices included the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC). The end of the Middle Ages saw a re-invigoration of European mathematics and engineering, and Wilhelm Schickard’s 1623 device was the first of a number of mechanical calculators constructed by European engineers.

However, none of those devices fit the modern definition of a computer because they could not be programmed. In 1801, Joseph Marie Jacquard made an improvement to the textile loom that used a series of punched cards as a template to allow his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.

In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer that he called The «Analytical Engine.» Due to limited finance, and an inability to resist tinkering with the design, Babbage never actually built his Analytical Engine.

Large-scale automated data processing of punched cards was performed for the U.S. Census in 1890 by tabulating machines designed by Herman Hollerith and manufactured by the Computing Tabulating Recording Corporation, which later became International Business Machines, Inc. (IBM). By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card, Boolean algebra, the vacuum tube (thermionic valve) and the teleprinter.

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.

A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as «the first digital electronic computer» is difficult. Notable achievements include:

• EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.

• Konrad Zuse’s electromechanical «Z machines.» The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. The Z3 was the world’s first operational computer.

• The non-programmable Atanasoff-Berry Computer (1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory.

• The secret British Colossus computer (1944), which had limited programmability but demonstrated that a device using thousands of vacuum tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.

• The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.

• The U.S. Army’s Ballistics Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse’s Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.

Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the stored program architecture or «von Neumann architecture.» A number of projects to develop computers based on the stored program architecture commenced around this time, the first of these being completed in Great Britain. The first to be demonstrated working was the Manchester Small-Scale Experimental Machine (SSEM) or «Baby». However, the EDSAC, completed a year after SSEM, was perhaps the first practical implementation of the stored program design. Shortly thereafter, the machine originally described by von Neumann’s paper — EDVAC — was completed but did not see full-time use for an additional two years.

Nearly all modern computers implement some form of the stored program architecture, making it the single trait by which the word «computer» is now defined. By this standard, many earlier devices would no longer be called computers by today’s definition, but are usually referred to as such in their historical context. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture. The design made the universal computer a practical reality.

Vacuum tube-based computers were in use throughout the 1950s, but were largely replaced in the 1960s by transistor-based devices, which were smaller, faster, cheaper, used less power and were more reliable. These factors allowed computers to be produced on an unprecedented commercial scale. By the 1970s, the adoption of integrated circuit technology and the subsequent creation of microprocessors such as the Intel 4004 caused another leap in size, speed, cost and reliability. By the 1980s, computers had become sufficiently small and cheap to replace simple mechanical controls in domestic appliances such as washing machines. Around the same time, computers became widely accessible for personal use by individuals in the form of home computers and the now ubiquitous personal computer. In conjunction with the widespread growth of the Internet since the 1990s, personal computers are becoming as common as the television and the telephone and almost all modern electronic devices contain a computer of some kind.

Computer capabilities[]

Computer capabilities fall into seven main categories:

1. Data collection. When attached to various sensing devices, computers can detect and measure such external physical phenomena as temperature, time,
pressure, flow rate, consumption rate, or any number of other variables. Also,
computers can keep a record of transactions. For example, a computerized cash register can collect and store information about a sale that includes bookkeeping entries, taxes, commissions and inventory, and can even reorder stock. Some computer-based door locks require individuals to carry magnetic identity cards. Such locks not only control access but also create a record of whose card was granted access, when, and for how long.

Computers can also process visual and audio input, thus greatly increasing their applicability to data collection. Computers also can recognize human speech, read directly a variety of typewritten forms and handprinted texts, and detect patterns in video images.

2. Information storage. Computers can store large amounts of information for long periods of time in an electronic-readable form that is easily and quickly recoverable. Depending on the particular application, the methods of storage vary widely. Memory technology allows trillions of bits of [information]] to be stored conveniently and cheaply.

3. Information organization. Computers can be used to organize and rearrange information so that it is more suitable for particular applications. Computers can simplify and restructure vast amounts of raw data to assist people in drawing significant meanings or conclusions.

4. Calculations. Computers perform arithmetic calculations millions of times faster than human beings. They are used to make numerous simple calculations, such as those required in processing the payroll for a sizable organization; to make sophisticated statistical calculations on large amounts of data, such as those for social science research; or to perform highly complex scientific calculations, such as those needed for weather research or for modeling fusion energy systems.

5. Communication. Through connections over a telecommunication system, computers can transmit data around the world either to human users or to other computers, permitting the sharing of work and data among groups of linked computers (computer networks).

6. Information presentation. Computers can output information in a variety of forms. Through graphical display and voice response, they can make data readily understandable and useful to non-experts. It is possible to have data and computer schematics displayed on screens in a multicolored, three-dimensional format for design and analytical purposes. Also,
data such as numbers and statistics can be organized by the computer in an
easy-to-understand tabular presentation.

7. Control. Computers can be used to control a machine tool or a production line without human intervention. Many consumer devices, including microwave ovens, automated home thermostats, automobile engines, television sets, and telephones, incorporate computer controls.

Several of these capabilities can be combined, for example in computer-aided design of aircraft structures (or computer logic elements, for that matter) and computer-based modeling of the saltwater penetration in San Francisco Bay (a function of tidal action and ground water runoff). Both computer-aided design and computer modeling have found wide application and are illustrative of what is sometimes referred to as the “intelligence amplifying” capability of computers.

Stored program architecture[]

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that a list of instructions (the program) can be given to the computer and it will store them and carry them out at some time in the future.

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. These instructions are read from the computer’s memory and are generally carried out (executed) in the order they were given. 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. These are called «jump» instructions (or branches). 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. Many computers directly support subroutines by providing a type of jump that «remembers» the location it jumped from and another instruction to return to that point.

Structure of a computer[]

A general purpose computer has four main sections: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.

References[]

See also[]

Do we really need to tell you about the impact the computer has had on modern society?

No other invention changed our world like the computer. Today, we’re going to tell you where the computer came from and explain where it could be going in the future.

Early Foundations for the Computer

The computer is a relatively new invention. Even the most basic computers didn’t appear until the 20th century.

However, the idea for a computer has its roots way back in ancient times. For thousands of years, humans have sought to use mechanical processes to quantify, understand, and compute the world around themselves.

In one timeline of computer history, the writer starts way back in 50,000 BCE, for example, which is when “the first evidence of counting” appeared.

Other notable ancient-era improvements that led to the modern computer included the following timeline events:

• 3400 BCE: Egyptians develop a number 10-based counting system, which made it easier to count large numbers.
• 2600 BCE: Ancient Chinese introduce the abacus.
• 1350 BCE: The Ancient Chinese introduce the first decimal.
• 300 BCE: The Romans introduce the Salamis Tablet, the Roman Calculi, and hand-abacus, all of which functioned in a similar way to the modern abacus.
• 260 BCE: The Mayans develop a base-20 system of mathematics, which notably introduces the concept of zero.
• 1500 AD: Leonardo da Vinci invents the mechanical calculator.
• 1605: Francis Bacon creates a cipher that uses A’s and B’s to encode messages, calling it the Baconian Cipher.
• 1613: The word “computer” is used for the very first time, when it was used to describe a person who was really good at performing mathematical calculations or “computations”. That definition would remain unchanged until the end of the 1800s.
• 1614: John Napier introduces the idea of logarithms.
• 1617: John Napier introduces a rudimentary computer-like device called Napier’s Bones where were made from bone, horns, and ivory. This device let the user calculate multiplications by adding numbers. You could also divide numbers by subtracting.
• 1623: The first known mechanical calculating machine is invented by Germany’s Wilhelm Schickard. Schickard’s work was largely influenced by Napier’s Bones, which we just mentioned.

1600s and the Invention of the Slide Rule

Throughout the 1600s, slide rules began to be used for the first time. Slide rules were mechanical analog computers used for multiplication and division. You could also use the slide rule for roots, logarithmic functions, and trigonometry. Unlike modern calculators, you could not use the slide rule for addition or subtraction.

Slide rules were heavily influenced by the work of John Napier, who we mentioned above. However, credit for the invention of the first slide rule goes to the Reverend William Oughtred. Oughtred (and several others during this time period) would develop multiple types of slide rules throughout the 17th century.

The slide rule remained enormously popular until the invention of the pocket calculator. Right up until the 1970s, when scientific calculators were introduced, slide rules were a booming business across America.

1800 and Punch Card Systems

Throughout the 1800s, three major inventors theorized that you could combine punch cards with mechanical processes to create a computer.

These early inventors included French inventor Joseph Marie Jacquard. In 1801, Jacquard invented a loom that used punched wooded cards to automatically weave fabric designs. Over a century later, the world’s first computers would use similar punch cards.

In 1822, Charles Babbage conceived of a steam driven calculator that could compute tables of numbers. Babbage was on the right track. However, despite receiving financing from the British government, Babbage’s computer was never built.

Then, in 1890, inventor Herman Hollerith created a punch card system to process information from the 1880 census. That system processed data in just three years, which saved the government a reported $5 million. You might recognize Hollerith’s name: he later went on to establish the company that eventually became IBM.

1936 and Alan Turing’s Computer

Most people credit Alan Turing with the development of the first computer. In 1936, Alan Turing presented the notion of a “universal machine” called the Turing machine. A few years later, Turing would put that concept into reality. As we all saw in The Imitation Game, Turing’s computer would eventually be used to famously crack the Enigma encryption system during World War II.

The Turing Machine manipulates symbol on a strip of tape according to a table of rules. One of the most useful parts of a Turing machine is that it can be as useful as you want: you can give the machine any computer algorithm and it will simulate that algorithm’s logic.

Alan Turing called his machine an “a-machine”, or automatic machine.

Today, the Turing Machine is viewed as the original multi-purpose computer. Turing is also viewed as the creator of artificial intelligence.

One of the major differences between a Turing Machine and modern computers is that Turing machines do not use random access memory (RAM).

J.V. Atanasoff Creates the First Computer with Memory

While Turing gets most of the credit for creating the first thing that looked like a modern computer, J.V. Atanasoff is credited with building the first computer able to store information on its main memory.

Atanasoff was a professor of physics and mathematics at Iowa State University. In 1937, he attempted to build the world’s first computer without any gears, cams, belts, or shafts.

A few years later, in 1941, Atanasoff was more successful, designing a computer that was capable of simultaneously solving 29 equations. For the first time in history, a computer was able to store information on its main memory.

The Grandfather of Digital Computers, the ENIAC

Between 1943 and 1944, two American professors, John Mauchly and J. Presper Eckert, built the Electronic Numerical Integrator and Calculator (ENIAC).

This pair is credited with inventing the “grandfather of digital computers”. That computer was enormous. It consisted of 18,000 vacuum tubes and filled a 20 foot x 40 foot room.

After receiving funding from the Census Bureau to build a follow-up machine, the pair of professors would leave the University of Pennsylvania. That follow-up machine was called the UNIVAC and would go on to become the first commercial computer for business and government applications.

Computers Become Smaller in 1947

Part of the reason why early computers were so big was the need for vacuums. As mentioned above, the world’s first digital computer consisted of 18,000 vacuum tubes.

The pair who invented that first computer must have felt pretty silly when, in 1947, three researchers from Bell Laboratories invented the transistor. This allowed them to make an electric switch with solid materials and no need for a vacuum. Computers were still enormously large by today’s standards, but this paved the way for smaller and smaller sizes.

The First Computer Language, COBOL, is Created in the Late 1950s

Grace Hopper is credited with inventing the first computer programming language, called COBOL. COBOL stood for Common Business Oriented Language.

Prior to creating COBOL, Grace Hopper had invented a predecessor to that language called FLOW-MATIC. COBOL First appeared in 1959. By 1999, one firm estimated that there were a total of 200 billion lines of COBOL in existence running 80% of all business programs.

1958 and the Invention of the Computer Chip

The world’s first computer chip was invented in 1958, when Jack Kilby and Robert Noyce unveiled something they called the “integrated circuit”. We now know that device as a computer chip. In the year 2000, 40 years after his invention, Kilby received the Nobel Prize in Physics for his work.

1964: The World’s First GUI Makes Computers Accessible to the Public

In 1964, researcher Douglas Engelbart showed off a prototype of the modern computer. This computer is credited as the first one with a “modern” graphical user interface (GUI) as well as mouse support. For the first time, researchers believed computers could be made more accessible to the general public.

Of course, computers were still a long ways away from releasing to the public. But for the first time, people realized that computers could be more than just a scientific and mathematical tool: they could be used by average people.

1969 to 1973: Paving the Way for Modern Computers

Between 1969 and 1973, a number of critical inventions hit the market that would pave the way for the modern computer systems we know today.

In 1969, for example, a team of developers at Bell Labs created an operating system called UNIX. UNIX aimed to “unify” different computer hardware platforms and was usable across multiple devices. It became the operating system of choice for larger companies with mainframes. Due to its slow performance, UNIX never gained major support among PC users at home.

Then, in 1970, Intel (which had just recently launched as a company) unveiled the Intel 1103, which was the first Dynamic Access Memory (DRAM) chip.

One year later, IBM researchers unveiled the portable storage device known as the floppy disk, which allowed data to be shared between computers.

In 1973, Robert Metcalfe, who was a senior researcher at Xerox, enhanced computer-to-computer communication by developing the Ethernet cable. This allowed computers to be connected to one another and to other hardware.

1974: Personal Computers Hit the Market for the Very First Time

Before 1974, computers were those cool devices that you may have read about in newspapers – but could never actually own in your own home.

That all changed in 1974, when a number of personal computers hit the market. Between 1974 and 1977, four major computer systems hit the market and changed the computer hardware industry forever. Those computer systems included:

• Scelbi & Mark-8 Altair
• IBM 5100
• RadioShack TRS-80 (also known as the Trash 80)
• Commodore PET

Follow-ups to these models were also released. 1975 saw the release of the Altair 8080. In one advertisement in Popular Electronics, the Altair 8080 was described as being the “world’s first minicomputer kit to rival commercial models.”

The TRS-80, on the other hand, sold like crazy at RadioShack locations across the country. This computer allowed average people with limited knowledge of coding to write programs and make a computer do what they wanted.

As you’ll learn below, the release of these computer models inspired Paul Allen, Bill Gates, Steve Jobs, and Steve Wozniak to do some pretty special things in the world of computing over the coming decades.

Microsoft is Founded in 1975

After the release of the Altair 8080, two computer geeks named Paul Allen and Bill Gates offered to develop software for the ALTAIR. The two considered themselves to be experts at the new BASIC coding language.

After being successful coders, the two childhood buddies founded their own software company, Microsoft, on April 4, 1975.

Apple is Founded in 1976

Around the same time Microsoft was kicking into action, Apple was a glimmer in the eyes of Steve Jobs and Steve Wozniak. The company was founded in 1976 and, on April 1, 1976, the pair introduced the Apple I, which was the first computer that used a single-circuit board.

By 1977, Jobs and Wozniak had incorporated Apple and released the Apple II. They showed off the Apple II at the first West Coast Computer Faire. Notable improvements with the Apple II included color graphics and an audio cassette drive for easy storage.

The World’s First Computer Applications

In the late 1970s, all of these new programming platforms led to a surge in amateur (and professional) developers creating their own applications.

In 1978, the accounting world was changed forever with the invention of VisiCalc, which was the world’s first computerized spreadsheet program.

Then, in 1979, writing on computers became a lot easier thanks to the world’s first word processing software, WordStar, which was created by MicroPro International.

IBM’s First Personal Computer

IBM’s first personal computer is also notable because it popularized the term “personal computer”. That’s why IBM gets credit for creating the term “PC”.

1983: Apple Releases Its Own PC, Lisa

Today, we associate the term “PC” with Windows computers. However, soon after IBM released its first PC in 1983, Apple released a PC of its own called Lisa.

Lisa was notable for being the first computer with a GUI – including relatively modern features like a drop down menu and icons.

Despite Apple’s best intentions, the Lisa was a flop. Nevertheless, Apple would learn from its lessons with Lisa and eventually release the Mac.

That same year, Apple also released the world’s first laptop, called the Gavilan SC. The Gavilan SC was described as a portable computer and featured the same flip-style form we see in today’s modern laptops.

1985: Microsoft Announces Windows

Microsoft saw what Apple did with its GUI, so it decided to do something better: Microsoft announced Windows.

The first version of Windows, Windows 1.0, was released on November 20, 1985. Contrary to Microsoft’s expectations, Windows 1.0 was not well-received or popular.

Nevertheless, the name “Windows” was an important development. Microsoft had originally planned to call its operating system the extremely uncatchy and unmarketable “Interface Manager”. And obviously, judging by the success of later versions of Windows, Microsoft was unfazed by the failure of Windows 1.0

1985 to 1996: The Foundations of the Internet

Between 1985 and 1996, the internet went from a niche computing service to a global system filled with massive potential.

It started in 1985 when the world’s first dot-com domain name was registered. That first domain name probably wasn’t as exciting as you think: it was Symbolics.com, which was registered by The Symbolic Computer Company from Massachusetts.

In 1990, a CERN researcher named Tim Berners-Lee created HTML, which eventually led to the creation of the World Wide Web.

By 1996, Sergey Brin and Larry Page had developed Google.

1994: The Year PC Gaming Exploded

Computer games were common throughout the 1970s and 1980s in arcades and gaming systems. Starting around 1994, however, the PC began to be viewed as legitimate gaming machine.

PC developers created games like Command & Conquer, for example, along with Descent and Little Big Adventure. In the coming years, we’d see games like Doom, Quake, Age of Empires, Half Life, and many more.

Apple Unveils Mac OS X in 2001

People seem to forget that Apple and Microsoft were once embroiled in a huge legal battle. In 1997, Apple alleged that Microsoft had copied the “look and feel” of its operating system by developing Windows.

Later that year, Microsoft invested $150 million in Apple, which was a struggling company at the time. This ended Apple’s court case against Microsoft.

Then, in 2001, Apple introduced its own operating system, Mac OS X. Later that same year, Microsoft rolled out its own groundbreaking operating system, Windows XP.

Today, tablet computers and mobile devices are changing the future of computing technology. We’ve come a long ways in 70 years – how much further can computers go in another 70 years?