computer is a device that can be instructed to carry out arbitrary sequences of arithmetic or logical operations automatically. The ability of computers to follow generalized sets of operations, called programs , enables them to perform an extremely wide range of tasks.

Such computers are used as control systems for a very wide variety of industrial and consumer devices . This includes single special purpose devices like microwave ovensand remote controls , factory Devices Such As industrial robots and computer assisted design , goal aussi in general purpose devices like personal computers and mobile devices Such As smartphones . The Internet is running on computers and it connects millions of other computers.

Since ancient times, simple manual devices like the abacus aided people in doing calculations. 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 speed, power, and versatility of computers has always been dramatic.

Conventionally, a modern computer Consists of au moins un processing element , Typically a central processing unit (CPU), and Some form of memory . 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 . Peripheraldevices include input devices (keyboards, mice, joystick, etc.), output devices (monitor screens, printers, etc.), and input / output devices that perform both functions (eg, the 2000s-era touchscreen ). Peripheral devices allow retrieved from an external source and they enable the result of operations to be saved and retrieved.


According to the Oxford English Dictionary , the first known use of the word “computer” was in 1613 in a book called The Yong Mans Gleanings by English writer Richard Braithwait: “I haue [sic] read the truest computer of Times, and the best Arithmetician that [sic] breathed, and he reduceth thy dayes into a short number. ” This use of the term refers to a person who has made calculations or computations. The word continues with the same meaning until the middle of the 20th century. From the end of the nineteenth century, it was a machine that carries out computations. [1]

The Online Etymology Dictionary gives the first impression of “computer” in the “1640s,” meaning “one who calculates,” this is an “… agent from compute (v.).” The Online Etymology Dictionary states that the use of the term “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 “. [2]


Devices have been used for many years, mostly using one-to-one correspondence with fingers . The earliest counting device was probably a form of tally stick . Later record keeping aids Throughout The Fertile Crescent included calculi (clay spheres, cones, etc.) qui Represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. [3] [4] The use of counting rods is one example.

The abacus was first used for arithmetic tasks. The Roman abacus was developed from devices 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.

The Antikythera mechanism is believed to be the mechanical analog “computer”, according to Derek J. of Solla Price . [5] 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 circa 100 BC. Devices of a level of complexity comparable to that of the Antikythera mechanism would not reappear until a thousand years later.

Many mechanical aids to calculation and measurement have been constructed for astronomical and navigation use. The planisphere Was a star chart invented by Abu Rayhan al-Bīrūnī in the early 11th century. [6] The astrolabe was invented in the Hellenistic world in 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 several different kinds of problems in spherical astronomy . An astrolabe incorporating a mechanical calendar computer [7] [8]and gear -wheels was invented by Abi Bakr of Isfahan , Persia in 1235. [9] Abū Rayhān al-Bīrūnī invented the first mechanical geared lunisolar calendar astrolabe, [10] an early fixed- wired knowledge processing machine [11] with a gear train and gear-wheels, [12] circa 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, 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 (automata) 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.[13]

The tide-predicting machine invented by 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 Lord Kelvin had already discussed the possible construction of such calculators, but he had been stymied by the limited output torque of the ball-and-disk integrators.[14] 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 computing device

Charles Babbage, an English mechanical engineer and polymath, originated the concept of a programmable computer. Considered the “father of the computer”,[15] 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.[16][17]

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 difficulties not only of politics and financing, but also to 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 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. [18] The first modern analog computer was a tide-predicting machine , invented by Sir William Thomson in 1872. The differential analyzer , a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in 1876 by James Thomson, the brother of the most famous Lord Kelvin. [14]

The art of mechanical analog computing reached its zenith with the differential analyzer , built by HL Hazen and Vannevar Bush at MIT starting in 1927. This built on the mechanical integrators of James Thomson and the torque amplifiers invented by HW Nieman. A dozen of these devices were made before their obsolescence became obvious. The analog computing machines, but analog computers remained in use during the 1950s in some specialized applications such as education ( control systems ) and aircraft ( slide rule ).

Digital computers


By 1938, the United States Navy had developed an electromechanical analog computer small enough to use a submarine aboard . 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 mechanical 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, was one of the earliest examples of an electromechanical relay computer. [19]

In 1941, Zuse followed up with the Z3 , the world’s first working electromechanical programmable , fully automatic digital computer. [20] [21] The Z3 was built with 2000 relays , implementing a 22 bit word length that operates at a frequency of about 5-10 Hz . [22] The code was supplied on a punched film while data could be stored in 64 words of memory or supplied by the keyboard. It was quite similar to modern machinery 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 that Zuse’ s machines were easier to build and more reliable. [23] The Z3 was Turing complete . [24] [25]

Vacuum tubes and digital electronic circuits

Purely electronic circuit elements and their analog and electromechanical equivalents, at the same time. The engineer Tommy Flowers , working at the Post Office Research Station in London in the 1930s, Began to explore the feasible 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 . [18] In the US, John Vincent Atanasoff andClifford E. Berry of Iowa State University developed and tested the Atanasoff-Berry Computer (ABC) in 1942, [26] the first “automatic electronic digital computer”. [27] This design was also all-electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory. [28]

During World War II, the British at Bletchley Park achieved a number of successes at breaking encrypted German military communications. The German Enigma encryption machine was first attacked with the help of electro-mechanical bombs . To the most sophisticated German Lorenz SZ 40/42 machine, used for high-level Army Communications, Max Newman and his colleagues commissioned Flowers to build the Colossus . [28] He spent eleven months from early February 1943 designing and building the first Colossus. [29]After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944 [30] and attacked its first message on 5 February. [28]

Colossus was the world’s first electronic digital programmable computer. [18] 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 faster and easier to operate than Mark I, greatly speeding the decoding process. [31] [32]

The US-built ENIAC [33] (Electronic Numerical Integrator and Computer) was the first electronic programmable computer built in the US. 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 ict patch cables and switches, a far cry from the Stored program electronic machinery That cam later. Once a program was written, it had to be mechanically set in the machine with manual resetting of plugs and switches.

It combines the high speed of electronics with the ability to be programmed for many complex problems. It could add or subtract 5000 times to a second, to 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 contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors. [34]

Modern computers

Concept of modern computer

The principle of the modern computer was proposed by Alan Turing in his seminal paper 1936, [35] On Computable Numbers . Turing proposed a simple device that he called “Universal Computing machine” and that is known as a universal Turing machine . It 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. [36]Turing machines are to this day a central object of study in the theory of computation . Except for the limitations imposed by their finite memory stores, they are said to be Turing-complete , which is to say, they have an algorithmexecution capability equivalent to a universal Turing machine.

Stored programs

Early computing machines had fixed programs. Changing its function requires the re-wiring and re-structuring of the machine. [28] With the proposal of the stored-program computer this changed. A stored-program computer includes an instruction set and can store a set of instructions (a program ) that details the computation . The theoretical basis for the stored-program computer Was ugly by Alan Turing In His 1936 paper. In 1945 Turing joined the National Physical Laboratoryand 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. [18]

The Manchester Small-Scale Experimental Machine, nicknamed Baby, was the world’s first stored-program computer. It was built at the Victoria University of Manchester by Frederic C. Williams, Tom Kilburn and Geoff Tootill, and ran its first program on 21 June 1948.[37] It was designed as a testbed for the Williams tube, the first random-access digital storage device.[38]Although the computer was considered “small and primitive” by the standards of its time, it was the first working machine to contain all of the elements essential to a modern electronic computer.[39] As soon as the SSEM had demonstrated the feasibility of its design, a project was initiated at the university to develop it into a more usable computer, the Manchester Mark 1.

The Mark 1 in turn became the prototype for the Ferranti Mark 1 , the world’s first commercially available general-purpose computer. [40] 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 . [41] In October 1947, the directors of the British catering company J. Lyons & Company decided to take an active role in promoting the commercial development of computers. The LEO I became operational in April 1951 [42]and ran the world’s first regular routine office computer job .


The bipolar transistor was invented in 1947. 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. Silicon junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life. Transistorized computers could contain a relatively compact space.

At the University of Manchester , Tom Kilburn , a team under the leadership of the United States, developed a machine using newly developed transistors instead of valves. [43] Their first transistorised computer and the first in the world, Was operational by 1953 , and a second release Was completed there in April 1955. HOWEVER, DID the machines make use of valves to generate icts 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, [44]The Atomic Energy Research Establishment at Harwell . [44] [45]

Integrated circuits

The next great advance in computing power with the advent of the integrated circuit . The idea of ​​the integrated circuit was first conceived by a radar scientist working for the Royal Radar Establishment of the Ministry of Defense , Geoffrey WA Dummer . Dummer presented the first public of an integrated circuit at the Symposium on Progress in Electronics Quality Electronics in Washington, DC on May 7, 1952. [46]

The first practical ICs were invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor . [47] Kilby Recorded His initial ideas concernant the integrated system in July 1958 successfully integrated Demonstrating the first working example is 12 September 1958. [48] In His obvious implementation of 6 February 1959 Kilby Described His new device as “a body of semiconductor material … all the components of the electronic circuit are completely integrated “. [49] [50] Also operates with Kilby’s own idea of ​​an integrated circuit. [51]His chip solved many practical problems that Kilby’s had not. Produced at Fairchild Semiconductor, it was made of silicon , while Kilby’s chip was made of germanium .

This new development is an explosion in the commercial and personal use of computers and the invention of the microprocessor . While the subject of the first microprocessor is closely related, it is widely believed that the first single-chip microprocessor was Intel 4004 , [52] Realized and designed by Ted Hoff , Federico Faggin , and Stanley Mazor at Intel . [53]

Mobile computers become dominant

With the continued miniaturization of computing resources, and advances in portable battery life, portable computers grew in popularity in the 2000s. [54] The same developments in the development of computers and other computing devices. These so-called smartphones and tablets run on a variety of operating systems and have a leading 237 million devices in 2Q 2013. [55]


Computers are typically classified based on their uses:

Based on uses

  • Analog computer
  • Digital computer
  • Hybrid computer

Based on sizes

  • smartphone
  • Microcomputer
  • Personal computer
  • Laptop
  • minicomputer
  • Mainframe computer
  • Supercomputer


The term hardware covers all of those parts of a computer that are tangible physical objects. Circuits, computer chips, graphic cards, sound cards, memory, motherboard, displays, power supplies, cables, keyboards, printers and “mice”.


History of Computing Hardware

Main article: History of Computing Hardware
First generation (mechanical / electromechanical) Calculators Pascal’s calculator , Arithmometer , Difference engine , Quevedo’s analytical machines
Programmable devices Jacquard loom , Analytical engine , IBM ASCC / Harvard Mark I , Harvard Mark II , IBM SSEC , Z1, Z2 , Z3
Second generation (vacuum tubes) Calculators Atanasoff-Berry Computer , IBM 604 , UNIVAC 60 , UNIVAC 120
Programmable devices Colossus , ENIAC , Manchester Small-scale Experimental Machine , EDSAC , Manchester Mark 1, Ferranti Pegasus , Ferranti Mercury , CSIRAC , EDVAC , UNIVAC I , IBM 701 , IBM 702 , IBM 650 , Z22
Third generation (discrete transistors and SSI, MSI, LSIintegrated circuits ) mainframes IBM 7090 , IBM 7080 , IBM System / 360 , BUNCH
minicomputer HP 2116A , IBM System / 32 , IBM System / 36 , LINC , PDP-8 , PDP-11
Desktop Computer Programma 101 , HP 9100
Fourth generation (VLSI integrated circuits) minicomputer VAX , IBM System i
4-bit microcomputer Intel 4004 , Intel 4040
8-bit microcomputer Intel 8008 , Intel 8080 , Motorola 6800 , Motorola 6809 , MOS Technology 6502 , Zilog Z80
16-bit microcomputer Intel 8088 , Zilog Z8000 , WDC 65816/65802
32-bit microcomputer Intel 80386 , Pentium , Motorola 68000 , ARM
64-bit microcomputer [56] Alpha , MIPS , PA-RISC , PowerPC , SPARC , x86-64 , ARMv8-A
Embedded computer Intel 8048 , Intel 8051
Personal computer Desktop computer , Home computer , Laptop computer, Personal digital assistant (PDA), Portable computer , Tablet PC , Wearable computer
Theoretical / experimental Quantum computer , Chemical computer , DNA computing , Optical computer , Spintronics based computer

Other hardware topics

Peripheral device ( input / output ) Input Mouse , keyboard , joystick , image scanner , webcam , graphics tablet , microphone
Output Monitor , printer , loudspeaker
Both Floppy disk drive, hard disk drive , optical disk drive, teleprinter
Computer nozzles Short range RS-232 , SCSI , PCI , USB
Long range ( computer networking ) Ethernet , ATM , FDDI

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 nozzles , often made of groups of wires . Inside each of these parts, they are thousands to trillions of small electrical circuits which can be turned off by an electronic switch . Each circuit represents a bit (binary digit) of information when the circuit is on it represents a “1”, and when off it represents a “0” (in positive logic representation). The circuits are arranged inlogic gates so that one or more of the circuits.

Input devices

When a data is sent to the computer with the help of the input devices, the data is processed and sent to the 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
  • Scanner image
  • joystick
  • Microphone
  • Mouse
  • Overlay keyboard
  • Real-time clock
  • trackball
  • Touchscreen

Output devices

The means through which the computer provides output as known. 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. [57] Control systems in advanced computers may change the order of 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 statement is to be read from. [58]

The control system is a function of the following: it 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 statement from the cell by the program counter.
  2. Decode the numerical code for the instruction in 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 statement requires from cells in memory (or perhaps from an input device). The location of this data is typically stored within the 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 of 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 is being (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program would be next to 100 places further down the program. Instructions that are known to be “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 is in the process of being controlled by a microprocessor, and indeed, in some more complex CPU designs, there is another yet smaller microsequencer , which runs to 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 have been composed of many separate components but have been built on a single integrated circuit called a microprocessor .

Arithmetic logic unit (ALU)

Main article: Arithmetic logic unit

The ALU is capable of performing two classes of operations: arithmetic and logic. [59] 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 only operate one 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 into more complex operations. Therefore, any computer can be used to perform any arithmetic operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether or not it is greater than the other (“is 64 greater than 65?”). Logic operations involve Boolean logic : AND , OR , XOR , and NOT . These can be useful for complicatedconditional statements and processing boolean logic .

Superscalar computers may contain multiple ALUs, permitting them to process multiple instructions simultaneously. [60] Graphics processors and computers with SIMD and MIMD features often contain ALUs that can perform arithmetic on vectors and matrices .


A computer’s memory can be viewed as a list of cells in 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 in the cell number 1357” or “to the number that is in cell 1357 to the number that is in cell 2468 and the answer to cell 1595.” The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed in 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 the world.

In almost all modern computers, each memory 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); from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes can be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two complementary notation. Other arrangements are possible, but are usually not included outside of specialized applications or historical contexts. 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 Expired registers That can be read and written to much more than the memory area Rapidly hand. There are two types of CPUs in the world. Registers are used for the most frequently needed data to be avoided. As data is constantly being worked on, it is greatly increasing the computer’s speed.

Computer hand comes in two main types:

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

RAM can be read and written to anytime the CPU commands it, but it 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 is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called BIOS that orchestrates the computer’s operating system from the hard disk drive to RAM when the computer is turned on or reset. In embedded computers , which can be used frequently, all of the software can be stored in ROM. Software stored in ROM is often called firmwarebecause 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 usually much more important than ROM and RAM however, so it is not necessary to use it. [61]

RAM cache memories , which are slower than registers but faster than main memory. These computers are usually designed to be used in the field of data processing, often without the need for programming.

Input / output (I / O)

I / O is the means by which a computer exchanges information with the outside world. [62] Devices that provide input or output to the computer are called peripherals . [63] We have 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 . 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. ATgraphics 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.


Main article: Computer multitasking

While a computer can be viewed as one of several types of memory, it is necessary to provide the same. This is achieved by multitasking ie having the computer switch rapidly between running each program in turn. [64] One means by which this is done with a special signal called an interrupt, which can periodically cause the computer to stop executing where it was and do something else instead. By remembering where it was executing prior to the interruption, the computer can return to that task later. If several programs are running “at the same time”. then the interrupt generator may be causing several hundred interrupts per second, causing a program switch each time. Since it is possible to do so, it is possible that it is possible to do so, but it is always possible to do so. This method of multitasking is sometimes termed “time-sharing” since each program is allocated to “slice” of time in turn. [65]

Before the era of inexpensive computers, the main use for multitasking was to allow many people to share the same computer. Seemingly, multitasking would be more likely to be successful, but it would be more likely that they would be able to work on their tasks. If a program is waiting for the user to click on the mouse or a key on the keyboard, then it will not take a “time slice” until the event it is waiting for has occurred. This program can be run simultaneously without an acceptable speed loss.


Some computers are designed to distribute their work across multiple CPUs in a multiprocessing configuration, a technique that has been used only in large and powerful machines such as supercomputers , mainframe computers and servers . Multiprocessor and multi-core (multiple CPUs on a single integrated circuit) are more widely available, and are being used as a result.

Supercomputers in particular often have highly unique architectures that differ greatly from the basic stored-program architecture and from general purpose computers. [66] High-speed interconnects, and specialized computing hardware. Such designs are likely to be used only for the purpose of successful implementation. Supercomputers usually use in large-scale simulation, graphics rendering , and cryptography applications, as well as other so-called ” embarrassingly parallel ” tasks.


Main article: Computer 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 a computer system, or information system, which is in contrast to the physical hardware of which the system is built. Computer software includes computer programs , libraries and related non-executable data , such as online documentation or digital media . Computer hardware and software can not be realistically used on its own. When software is stored in hardware that can not be modified, such as with BIOS ROM in anIBM PC compatible computer, it is sometimes called “firmware”.

Operating systems

Operating system / System Software Unix and BSD UNIX System V , IBM AIX , HP-UX , Solaris ( SunOS ), IRIX , List of BSD operating systems
GNU / Linux List of Linux distributions , Comparison of Linux distributions
Microsoft Windows Windows 95 , Windows 98 , Windows NT , Windows 2000 , Windows ME , Windows XP , Windows Vista , Windows 7 , Windows 8 , Windows 8.1 , Windows 10
Macintosh operating systems Mac OS , MacOS (previously OS X and Mac OS X)
Embedded and real-time List of embedded operating systems
Experimental Amoeba , Oberon / Bluebottle , Plan 9 from Bell Labs
Library Multimedia DirectX , OpenGL , OpenAL , Vulkan (API)
Programming library C standard library , Standard Template Library
Data Protocol TCP / IP , Kermit , FTP , HTTP , SMTP
File format HTML , XML , JPEG , MPEG , PNG
User interface Graphical user interface (WIMP ) Microsoft Windows , GNOME , KDE , Photon QNX , CDE , GEM , Aqua
Text-based user interface Command-line interface , Text user interface
Application Software Office continued Word processing , Desktop publishing , Presentation program , Database management system , Scheduling & Time management, Spreadsheet , Accounting software
Internet Access Browser , Email client , Web server , Mail transfer agent , Instant messaging
Design and manufacturing Computer-aided design , Computer-aided manufacturing , Plant Management, Robotic Manufacturing, Supply Chain Management
Graphics Raster graphics editor , Vector graphics editor , 3D modeling , Animation editor , 3D computer graphics , Video editing , Image processing
audio Digital audio editor , Audio playback , Mixing , Audio synthesis , Computer music
Software engineering Compiler , Assembler , Interpreter , Debugger , Text editor , Integrated development environment , Software performance analysis , Revision control , Software configuration management
Educational Edutainment , Educational game , Serious game , Flight simulator
Games Strategy , Arcade , Puzzle , Simulation , First-person shooter , Platform , Massively multiplayer , Interactive fiction
Misc Artificial Intelligence , Antivirus software , Malware Scanner , Install / Package Management Systems , File Manager


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

Programming languages
Lists of programming languages Timeline of programming languages , List of programming languages by category , Generational list of programming languages , List of programming languages , Non-English-based programming languages
Commonly used assembly languages ARM , MIPS , x86
Commonly used high-level programming languages Ada , BASIC , C , C ++ , C # , COBOL , Fortran , PL / 1 , REXX , Java , Lisp , Pascal , Object Pascal
Commonly used scripting languages Bourne script , JavaScript , Python , Ruby , PHP , Perl

Application Software


The defining feature of modern computers which distinguishes them from other machines is that they can be programmed . That is to Say That Some kind of instructions (the program ) Can Be Given To the computer, and it will process em. Modern computers based on the 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 trillions 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 programs to write to, 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 to one another, move to another, and so on. These instructions are read from the computer’s memory and are Generally the 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 from there. These are called “jump” instructions (or branches ). Furthermore, jump instructions may be made to happen conditionallySo that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Many computers Directly supporting subroutines by providing good has kind of jump That “remembers” the rent from it jumped Reviews and another instruction to return to The Following instruction That jump instruction.

Program performance might be likened to reading a book. While they are in the process of becoming more familiar with each other, they may at times be more likely to be interested. Similarly, a computer may sometimes be used in some areas of the world. This is called the flow of control within the program and it is what allows the computer to perform tasks.

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 be a lot of time, with a certain certainty of making a mistake. On the other hand, a computer can be programmed with just a few simple instructions. The following example is written in the MIPS assembly language :

 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 # could sum in output register

Once again, the computer will perform the repetitive task. 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 being white Each statement Given a single number (its operation code or opcodefor 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 a different type of instruction; the more complex computers have several hundred to choose from, 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 fact that all programs can be represented as lists of numbers and can be manipulated in the same way as numeric data. The fundamental concept of storing programs in the computer of the memory of the data of the Neumann, or stored program [citation needed ], architecture. In some cases, a computer might be able to operate in a computer that works on its own. This is called theHarvard architectureafter theHarvard Mark Icomputer. Modern von Neumann computers display some features of the Harvard architecture in their designs, such as inCPU caches.

While it is feasible to write computer programs as long lists of numbers ( Machine language ) and while technical This Was used with Many early computers, [67] 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 . A computer program is usually done by a computer program called an assembler.

Programming language

Main article: Programming language

Different languages ​​for different types of programs. Unlike natural languages , programming languages ​​are designed to be ambiguous and concise. They are strictly speaking languages ​​and are often difficult to read aloud. They are Generally Either translated into machine code by a compiler or an assembly before being white run, gold Directly translated at run time by an interpreter . Sometimes programs are executed by a hybrid method of the two techniques.

Low-level languages
Main article: Low-level programming language

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 smartphone or a hand-held videogame ) can not understand the machine language of an x86 CPU that might be in a PC . [68]

High-level languages ​​/ third generation
Main article: High-level programming language

The language is also difficult to understand and is also difficult to understand. Therefore, Most practical programs are written in more abstract high-level programming languages That are reliable to express the needs of the programmore conveniently (and thereby help Reduce programming error). High level languages ​​are usually “compiled” into a machine language, using another computer program called a compiler . [69]High level languages ​​are more related to the workings of the target group, and more related to the language and structure of the problem (s) to be solved by the final program. It is very much possible to use different types of computer programs. This video game isavailable for different computer architectures as well as for personal computers and various video game consoles .

Fourth-generation languages

Main article: Fourth-generation programming language

Fourth-generation languages ​​(4GL) are less procedural than 3G languages. The benefit of 4GL is that they provide ways to obtain information without requiring programming.

Program design

Program de design des programs d’application de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention de l’invention, la collection des input de l’invention de l’invention de l’invention. As problems become larger and more complex, features such as subprograms, modules, formal documentation, and new paradigms such as object-oriented programming are encountered. Large programs involving formal software methodologies. The task of developing large softwaresystems 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.


Errors in computer programs are called ” bugs “. They may be affected by the program, or only subtle effects. But in some cases, they can cause the program or the entire system to ” hang “, becoming unresponsive to such or such a mouse clicks or keystrokes, to completely fail, or to crash . Otherwise benign bugs can be harmed 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 they are given, they are almost always the result of programming error or oversight in the program design. [70] Admiral Grace Hopper , an American computer scientist and developer of the first compiler , is credited for having used the term “bugs” in computation after a dead moth was found in the Harvard Mark II computer in September 1947. [71]


Firmware is the technology which has the combination of both hardware and software such as BIOS chip inside a computer. This chip (hardware) is located on the motherboard and has the BIOS set up (software) stored in it.

Networking and the Internet

Computers have been used to coordinate information between multiple locations since the 1950s. The US 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 Saber . [72] In the 1970s, computer engineers at research institutions across 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 was called the ARPANET . [73] The technologies that made the Arpanet possible spread and evolved.

In time, the network spreads beyond academic and military institutions and has become known to the Internet. The emergence of networking involved in the redefinition of the nature and boundaries of the computer. Computer operating systems and applications have been 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 are available mainly 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 fast, fast networking technologies like Ethernet and ADSLsaw 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 become more mobile networking.

Unconventional computers

Main article: Human computer
See also: Harvard Computers

A computer does not need to be electronic , nor has a processor , nor RAM , nor even a hard disk . While popular use of the word “computer” is synonymous with a personal electronic computer, the modern [74] of a computer is literally: ” A device that computes , especially a programmable [usually] electronic machine that performs high-speed mathematical gold logical operations or that assembles, stores, correlates, or otherwise processes information. ” [75] Any device which processes information qualifies as a computer, especially if the processing is purposeful. quote needed ]

Unconventional computing

Further information: Unconventional computing

Historically, computers evolved from mechanical computers and eventually from vacuum tubes to transistors . However, conceptually 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 ); an often quoted example. citation needed ] More realistically, modern computers are made of transistors made of photolithographed semiconductors .


There is active research to make computers out of Many promising new kinds of technology, Such As optical computers , DNA computers , neural computers , and quantum computers . Most computers are universal, and are capable of calculating any 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; 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 , the quantum computer holds the most promise for revolutionizing computing. [76] Logic gates are a common abstraction qui can apply to MOST of the above digital or analog paradigms. The Ability to store and execute lists of instructions called Expired programs Makes computers extremely versatile, distinguishing em 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 as any other computer can perform. Therefore, any type of computer (netbook , supercomputer , cellular automaton , etc.) is able to perform the same computational tasks, given sufficient time and storage capacity.

Artificial intelligence

A computer will solve problems, without looking at 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 on two major categories: rule based systems and pattern recognition systems. Rules based on the rules of the world and the use of them by the experts Pattern based systems use data on a general problem conclusions. Examples of pattern based systems include voice recognition, font recognition, translation and the emerging field of on-line marketing.

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