The NASA Columbia Supercomputer.

A computer in a wristwatch.

A computer is a machine which manipulates data according to a list of instructions which makes it an ideal example of a data processing system. Computer is an IEEE Computer Society practitioner-oriented magazine issued to all members of the society. ... Image File history File links Download high-resolution version (2100x1524, 3508 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Supercomputer NASA Advanced Supercomputing facility Computer/Temp ... Image File history File links Download high-resolution version (2100x1524, 3508 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Supercomputer NASA Advanced Supercomputing facility Computer/Temp ... This article is about the American space agency. ... NASAs 10,240-processor Columbia supercomputer is built from 20 SGI Altix systems, each powered by 512 Itanium 2 processors. ... Download high resolution version (1024x1539, 87 KB)wristwatch computer from http://wearcam. ... Download high resolution version (1024x1539, 87 KB)wristwatch computer from http://wearcam. ... A watch is a timepiece or portable clock that displays the time and sometimes the day, date, month and year. ... This article is about devices that perform tasks. ... In Computer Science, data is often distinguished from code, though both are represented in modern computers as binary strings. ... In computer programming, the word code refers to instructions to a computer in a programming language. ... In data processing, a Data Processor or Data Processing System is a system which processes information after it has been encoded into data. ...

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.^[1] 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. ^[2] Today, simple computers may be made small enough to fit into a wrist watch and be powered from a watch battery. 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. (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901–2000 in the sense of the Gregorian calendar (1900–1999... Year 1940 (MCMXL) was a leap year starting on Monday (link will display the full 1940 calendar) of the Gregorian calendar. ... For other uses, see 1941 (disambiguation). ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... A watch is a timepiece or portable clock that displays the time and sometimes the day, date, month and year. ... Type CR2032 watch battery (lithium anode, 3 V, 20. ... A university computer lab containing many desktop PCs The transition of communication technology: Oral Culture, Manuscript Culture, Print Culture, and Information Age Information Age is a name given to a period after the industrial age and before the Knowledge Economy. ... An embedded system is a special-purpose computer system, which is completely encapsulated by the device it controls. ... An A-10 Thunderbolt II, F-86 Sabre, P-38 Lightning and P-51 Mustang fly in formation during an air show at Langley Air Force Base, Virginia. ... An industrial robot is officially defined by ISO[1] as an automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes. ... A SiPix digital camera next to a matchbox to show scale Nikon D200 SLR with Nikon film scanner, which converts film images to digital A Hasselblad 503CW with a digital camera back A digital camera is an electronic device used to capture and store photographs digitally, instead of using photographic... A teddy bear A toy is an object used in play. ...

The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators. The Church – Turing thesis is a mathematical statement of this versatility: Any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks given enough time and storage capacity. For other uses, see Calculator (disambiguation). ... In computability theory the Church–Turing thesis (also known as Churchs thesis, Churchs conjecture and Turings thesis) is a combined hypothesis about the nature of effectively calculable (computable) functions by recursion (Churchs Thesis), by mechanical device equivalent to a Turing machine (Turings Thesis) or by... Look up Personal digital assistant in Wiktionary, the free dictionary. ... A supercomputer is a computer that led the world (or was close to doing so) in terms of processing capacity, particularly speed of calculation, at the time of its introduction. ...

History of computing

Main article: History of computing

The Jacquard loom was one of the first programmable devices.

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. The history of computing is longer than the history of computing hardware and modern computing technology and includes the history of methods intended for pen and paper or for chalk and slate, with or without the aid of tables. ... Jacquard loom on display at the museum of science and industry. ... Jacquard loom on display at the museum of science and industry. ... Jacquard loom on display at Museum of Science and Industry in Manchester, England The Jacquard Loom is a mechanical loom, invented by Joseph Marie Jacquard in 1801, which utilized holes punched in pasteboard, each row of which corresponded to one row of the design. ...

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. Before mechanical and electronic computers, the term computer, in use from the mid 17th century, meant a human undertaking mathematical calculations. ... A basic arithmetic calculator. ... It has been suggested that Abax be merged into this article or section. ... A typical 10 inch student slide rule (Pickett N902-T simplex trig). ... A 16th century astrolabe. ... The Antikythera mechanism (main fragment). ... The Middle Ages formed the middle period in a traditional schematic division of European history into three ages: the classical civilization of Antiquity, the Middle Ages, and modern times, beginning with the Renaissance. ... Wilhelm Schickard Wilhelm Schickard (April 22, 1592 – October 23, 1635) was a German polymath who built the first computer in 1623. ...

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 paper 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. This does not adequately cite its references or sources. ... For other uses, see Loom (disambiguation). ... Punched cards (or Hollerith cards, or IBM cards), are pieces of stiff paper that contain digital information represented by the presence or absence of holes in predefined positions. ...

In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer that he called "The Analytical Engine".^[3] Due to limited finance, and an inability to resist tinkering with the design, Babbage never actually built his Analytical Engine. Babbage redirects here. ... The analytical engine, an important step in the history of computers, was the design of a mechanical general-purpose computer by the British professor of mathematics Charles Babbage. ...

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 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. The Eleventh United States Census was taken June 1, 1890. ... Tabulating machine constructed by Hollerith The tabulating machine was a machine designed to assist in tabulations. ... Herman Hollerith (February 29, 1860 – November 17, 1929) was an German-American statistician who developed a mechanical tabulator based on punched cards in order to rapidly tabulate statistics from millions of pieces of data. ... The Computing Tabulating Recording Corporation (CTR)[1] was incorporated on June 15, 1911 in Endicott, New York a few miles west of Binghamton. ... For other uses, see IBM (disambiguation) and Big Blue. ... Punched cards (or Hollerith cards, or IBM cards), are pieces of stiff paper that contain digital information represented by the presence or absence of holes in predefined positions. ... Boolean algebra is the finitary algebra of two values. ... Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ... Teletype machines in World War II A teleprinter (teletypewriter, teletype or TTY for TeleTYpe/TeleTYpewriter) is a now largely obsolete electro-mechanical typewriter which can be used to communicate typed messages from point to point through a simple electrical communications channel, often just a pair of wires. ...

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 page from the Bombardiers Information File (BIF) that describes the components and controls of the Norden bombsight. ... Electric redirects here. ... Look up computation in Wiktionary, the free dictionary. ...

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: The binary numeral system, or base-2 number system, is a numeral system that represents numeric values using two symbols, usually 0 and 1. ... This article is about the engineering discipline. ... A computer program is a collection of instructions that describe a task, or set of tasks, to be carried out by a computer. ... For the usage of this term in Turing reductions, see Turing complete set. ... Statue in Bad Hersfeld Konrad Zuse (June 22, 1910 Berlin - December 18, 1995 Hünfeld) was a German engineer and computer pioneer. ... Konrad Zuses Z3 was the first working programmable, fully automatic machine, whose attributes, with the addition of conditional branching, have often been the ones used as criteria in defining a computer. ... Film stock is the term for photographic film on which films are recorded. ... Konrad Zuses Z3 was the first working programmable, fully automatic machine, whose attributes, with the addition of conditional branching, have often been the ones used as criteria in defining a computer. ... Atanasoff–Berry Computer replica at 1st floor of Durham Center, Iowa State University The Atanasoff–Berry Computer (ABC) was the first electronic digital computing device. ... A Colossus Mark II computer. ... Portion of the Harvard-IBM Mark 1, left side. ... Konrad Zuses Z3 was the first working programmable, fully automatic machine, whose attributes, with the addition of conditional branching, have often been the ones used as criteria in defining a computer. ... ENIAC ENIAC, short for Electronic Numerical Integrator And Computer,[1] was the first large-scale, electronic, digital computer capable of being reprogrammed to solve a full range of computing problems,[2] although earlier computers had been built with some of these properties. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... Claude Shannon Claude Elwood Shannon (April 30, 1916 – February 24, 2001), an American electrical engineer and mathematician, has been called the father of information theory,[1] and was the founder of practical digital circuit design theory. ...

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. In 1998 the Z3 was proved to be Turing complete, therefore being 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 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. This design was first formally described by John von Neumann in the paper "First Draft of a Report on the EDVAC", published 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 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. Image File history File links EDSAC_(10). ... Image File history File links EDSAC_(10). ... EDSAC EDSAC (Electronic Delay Storage Automatic Calculator) was an early British computer (one of the first computers to be created). ... Design of the Von Neumann architecture For the robotic architecture also named after Von Neumann, see Von Neumann machine The von Neumann architecture is a computer design model that uses a single storage structure to hold both instructions and data. ... Statue in Bad Hersfeld Konrad Zuse (June 22, 1910 Berlin - December 18, 1995 Hünfeld) was a German engineer and computer pioneer. ... In engineering, electromechanics combines the sciences of electromagnetism of electrical engineering and mechanics. ... Konrad Zuses Z3 was the first working programmable, fully automatic machine, whose attributes, with the addition of conditional branching, have often been the ones used as criteria in defining a computer. ... The binary numeral system, or base-2 number system, is a numeral system that represents numeric values using two symbols, usually 0 and 1. ... For the usage of this term in Turing reductions, see Turing complete set. ... Look up computation in Wiktionary, the free dictionary. ... Regenerative capacitor memory is a type of computer memory that uses the electrical property of capacitance to store the data. ... A Colossus Mark II computer. ... Cryptanalysis (from the Greek kryptós, hidden, and analýein, to loosen or to untie) is the study of methods for obtaining the meaning of encrypted information, without access to the secret information which is normally required to do so. ... Portion of the Harvard-IBM Mark 1, left side. ... The US Army Ballistics Research Labatory is at Aberdeen Proving Ground, Aberdeen, Maryland. ... ENIAC ENIAC, short for Electronic Numerical Integrator And Computer,[1] was the first large-scale, electronic, digital computer capable of being reprogrammed to solve a full range of computing problems,[2] although earlier computers had been built with some of these properties. ... For other uses, see Decimal (disambiguation). ... This article is about the engineering discipline. ... Statue in Bad Hersfeld Konrad Zuse (June 22, 1910 Berlin - December 18, 1995 Hünfeld) was a German engineer and computer pioneer. ... Konrad Zuses Z3 was the first working programmable, fully automatic machine, whose attributes, with the addition of conditional branching, have often been the ones used as criteria in defining a computer. ... An electromagnet is a type of magnet in which the magnetic field is induced by a flow of electric current. ... This article is about the engineering discipline. ... Design of the Von Neumann architecture For the robotic architecture also named after Von Neumann, see Von Neumann machine The von Neumann architecture is a computer design model that uses a single storage structure to hold both instructions and data. ... For other persons named John Neumann, see John Neumann (disambiguation). ... The First Draft of a Report on the EDVAC (or First Draft) was an incomplete 101-page document written by John von Neumann and distributed on June 30, 1945 by Herman Goldstine, security officer on the classified ENIAC project. ... Replica of the SSEM The Manchester Small-Scale Experimental Machine (SSEM), nicknamed Baby, was the first stored-program computer to run a program, on June 21, 1948. ... EDSAC EDSAC (Electronic Delay Storage Automatic Calculator) was an early British computer (one of the first computers to be created). ... The EDVAC as installed in Building 328 at the Ballistics Research Laboratory. ...

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. Design of the Von Neumann architecture For the robotic architecture also named after Von Neumann, see Von Neumann machine The von Neumann architecture is a computer design model that uses a single storage structure to hold both instructions and data. ...

Microprocessors are miniaturized devices that often implement stored program CPUs.

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.
Image File history File links Download high resolution version (1341x1002, 803 KB) Summary Macro shot of an Intel 80486DX2 die in its packaging. ... Image File history File links Download high resolution version (1341x1002, 803 KB) Summary Macro shot of an Intel 80486DX2 die in its packaging. ... Microprocessors, including an Intel 80486DX2 and an Intel 80386 A microprocessor (abbreviated as µP or uP) is an electronic computer central processing unit (CPU) made from miniaturized transistors and other circuit elements on a single semiconductor integrated circuit (IC) (aka microchip or just chip). ... CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ... Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ... Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... The Intel 4004, a 4-bit central processing unit (CPU) released by Intel Corp. ... Front-loading washing machine. ... Children playing on a Amstrad CPC 464 in the 1980s. ... For other uses, see Telephone (disambiguation). ...

Stored program architecture

Main articles: Computer program and Computer programming

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. A computer program is a collection of instructions that describe a task, or set of tasks, to be carried out by a computer. ... “Programming” redirects here. ... “Programming” redirects here. ... In computer science, an instruction typically refers to a single operation of a processor within a computer architecture. ... A computer program is a collection of instructions that describe a task, or set of tasks, to be carried out by a computer. ...

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. This article does not cite any references or sources. ... In computer science, conditional statements are a vital part of a programming language. ... In computer science, a subroutine (function, method, procedure, or subprogram) is a portion of code within a larger program, which performs a specific task and can be relatively independent of the remaining code. ...

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. In computer science control flow (or alternatively, flow of control) refers to the order in which the individual statements, instructions or function calls of an imperative or functional program are executed or evaluated. ...

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: For other uses, see Calculator (disambiguation). ...

 sum ← 0 ; set sum to 0 num ← 1 ; set num to 1 loop: ; define the beginning of the loop sum ← (num + sum) ; add num to sum and store new result num ← (num + 1) ; add 1 to num if num ≤ 1000 loop ; continue to loop while num ≤ 1000, if not continue below 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.^[4]

However, computers cannot "think" for themselves in the sense that they only solve problems in exactly the way they are programmed to. An intelligent human faced with the above addition task might soon realize that instead of actually adding up all the numbers one can simply use the equation

and arrive at the correct answer (500,500) with little work.^[5] In other words, a computer programmed to add up the numbers one by one as in the example above would do exactly that without regard to efficiency or alternative solutions.

Programs

A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labelled "PROJ039" for identification purposes.

In practical terms, a computer program might include anywhere from a dozen instructions to many millions of instructions for something like a word processor or a web browser. A typical modern computer can execute billions of instructions every second and nearly never make a mistake over years of operation. Image File history File links Download high-resolution version (1687x809, 475 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Punch card ... Image File history File links Download high-resolution version (1687x809, 475 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Punch card ... A CTR census machine, utilizing a punched card system. ... Fortran (previously FORTRAN[1]) is a general-purpose[2], procedural,[3] imperative programming language that is especially suited to numeric computation and scientific computing. ... A computer program is a collection of instructions that describe a task, or set of tasks, to be carried out by a computer. ... A word processor (also more formally known as a document preparation system) is a computer application used for the production (including composition, editing, formatting, and possibly printing) of any sort of viewable or printed material. ... An example of a Web browser (Mozilla Firefox) A web browser is a software application that enables a user to display and interact with text, images, videos, music and other information typically located on a Web page at a website on the World Wide Web or a local area network. ...

Large computer programs may take teams of computer programmers years to write and the probability of the entire program having been written completely in the manner intended is unlikely. Errors in computer programs are called bugs. Sometimes bugs are benign and do not affect the usefulness of the program, in other cases they might cause the program to completely fail (crash), in yet other cases there may be subtle problems. Sometimes otherwise benign bugs may be used for malicious intent, creating a security exploit. 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.^[6] In computing, a programmer is someone who does computer programming and develops computer software. ... A software bug is an error, flaw, mistake, failure, or fault in a computer program that prevents it from behaving as intended (e. ... A crash in computing is a condition where a program (either an application or part of the operating system) stops performing its expected function and also stops responding to other parts of the system. ... An exploit is a piece of software, a chunk of data, or sequence of commands that take advantage of a bug, glitch or vulnerability in order to cause unintended or unanticipated behavior to occur on computer software, hardware, or something electronic (usually computerized). ...

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 instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer just as if they were 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. Machine code or machine language is a system of instructions and data directly understandable by a computers central processing unit. ... Microprocessors perform operations using binary bits (on/off/1or0). ... The term Harvard architecture originally referred to computer architectures that used physically separate storage and signal pathways for their instructions and data (in contrast to the von Neumann architecture). ... Portion of the Harvard-IBM Mark 1, left side. ... Diagram of a CPU memory cache A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. ...

While it is possible to write computer programs as long lists of numbers (machine language) and this technique was used with many early computers,^[7] it is extremely tedious 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.^[8] A system of codes directly understandable by a computers CPU is termed this CPUs native or machine language. ... For other uses, see Mnemonic (disambiguation). ... See the terminology section, below, regarding inconsistent use of the terms assembly and assembler. ... This article does not cite any references or sources. ... The ARM architecture (previously, the Advanced RISC Machine, and prior to that Acorn RISC Machine) is a 32-bit RISC processor architecture developed by ARM Limited that is widely used in a number of embedded designs. ... Look up Personal digital assistant in Wiktionary, the free dictionary. ... A handheld video game is a video game designed primarily for handheld game consoles such as Nintendos Game Boy line. ... This article does not cite any references or sources. ... The Athlon 64 is an eighth-generation, AMD64 architecture microprocessor produced by AMD, released on September 23, 2003. ... A personal computer (PC) is a computer whose price, size, and capabilities make it useful for individuals. ...

Though considerably easier than in machine language, writing long programs in assembly language is often difficult and error prone. Therefore, most complicated programs are written in more abstract high-level programming languages that are able to express the needs of the computer 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.^[9] Since high level languages are more abstract than assembly language, it is 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. A high-level programming language is a programming language that, in comparison to low-level programming languages, may be more abstract, easier to use, or more portable across platforms. ... In computing, a programmer is someone who does computer programming and develops computer software. ... A diagram of the operation of a typical multi-language, multi-target compiler. ... “Game console” redirects here. ...

The task of developing large software systems is an immense intellectual effort. It has proven, historically, to be very difficult to produce software with an acceptably high reliability, on a predictable schedule and budget. The academic and professional discipline of software engineering concentrates specifically on this problem. Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ... Software engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software. ...

Example

A traffic light showing red.

Suppose a computer is being employed to drive a traffic light. A simple stored program might say: Image File history File linksMetadata Download high-resolution version (2048x1536, 1138 KB)y bib y invntea the trafic File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Download high-resolution version (2048x1536, 1138 KB)y bib y invntea the trafic File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... “Traffic Signal” redirects here. ...

1. Turn off all of the lights
2. Turn on the red light
3. Wait for sixty seconds
4. Turn off the red light
5. Turn on the green light
6. Wait for sixty seconds
7. Turn off the green light
8. Turn on the yellow light
9. Wait for two seconds
10. Turn off the yellow light
11. Jump to instruction number (2)

With this set of instructions, the computer would cycle the light continually through red, green, yellow and back to red again until told to stop running the program.

However, suppose there is a simple on/off switch connected to the computer that is intended be used to make the light flash red while some maintenance operation is being performed. The program might then instruct the computer to: Electrical switches. ...

1. Turn off all of the lights
2. Turn on the red light
3. Wait for sixty seconds
4. Turn off the red light
5. Turn on the green light
6. Wait for sixty seconds
7. Turn off the green light
8. Turn on the yellow light
9. Wait for two seconds
10. Turn off the yellow light
11. If the maintenance switch is NOT turned on then jump to instruction number 2
12. Turn on the red light
13. Wait for one second
14. Turn off the red light
15. Wait for one second
16. Jump to instruction number 11

In this manner, the computer is either running the instructions from number (2) to (11) over and over or its running the instructions from (11) down to (16) over and over, depending on the position of the switch.^[10]

How computers work

Main articles: Central processing unit and Microprocessor

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. “CPU” redirects here. ... A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... ALU redirects here. ... A control unit is the part of a CPU or other device that directs its operation. ... This article does not cite any references or sources. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ... A wire is a single, usually cylindrical, elongated strand of drawn metal. ...

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. “CPU” redirects here. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ...

Control unit

Main articles: CPU design and Control unit

The control unit (often called a control system or central controller) directs the various components of a computer. It reads and interprets (decodes) instructions in the program one by one. The control system decodes each instruction and turns it into a series of control signals that operate the other parts of the computer.^[11] Control systems in advanced computers may change the order of some instructions so as to improve performance. CPU design is the hardware design of a central processing unit. ... A control unit is the part of a CPU or other device that directs its operation. ...

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.^[12] The program counter (also called the instruction pointer in some computers) is a register in a computer processor which indicates where the computer is in its instruction sequence. ... In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to frequently used values—typically, these values are involved in multiple expression evaluations occurring within a small region on the program. ...

Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.

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: Image File history File links Mips32_addi. ... Image File history File links Mips32_addi. ... A MIPS R4400 microprocessor made by Toshiba. ...

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). In computer science control flow (or alternatively, flow of control) refers to the order in which the individual statements, instructions or function calls of an imperative or functional program are executed or evaluated. ...

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. In the field of computer architecture and engineering, a sequencer or microsequencer, is a part of a control unit of a CPU. It generates the addresses used to step through the microprogram of a control store. ... A microprogram is a program consisting of microcode that controls the different parts of a computers central processing unit (CPU). ...

Arithmetic/logic unit (ALU)

Main article: Arithmetic logic unit

The ALU is capable of performing two classes of operations: arithmetic and logic. A typical schematic symbol for an ALU: A & B are operands; R is the output; F is the input from the Control Unit; D is an output status In computing, an arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logical operations. ...

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?"). Wikibooks has a book on the topic of Trigonometry All of the trigonometric functions of an angle θ can be constructed geometrically in terms of a unit circle centered at O. Trigonometry (from Greek trigōnon triangle + metron measure[1]), informally called trig, is a branch of mathematics that deals with... In mathematics, a square root of a number x is a number r such that , or in words, a number r whose square (the result of multiplying the number by itself) is x. ... The integers are commonly denoted by the above symbol. ... A floating-point number is a digital representation for a number in a certain subset of the rational numbers, and is often used to approximate an arbitrary real number on a computer. ... In mathematics, the real numbers may be described informally as numbers that can be given by an infinite decimal representation, such as 2. ... In logic and mathematics, a logical value, also called a truth value, is a value indicating to what extent a proposition is true. ...

Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic. Boolean logic is a complete system for logical operations. ... AND Logic Gate In logic and mathematics, logical conjunction (usual symbol and) is a two-place logical operation that results in a value of true if both of its operands are true, otherwise a value of false. ... OR logic gate. ... Exclusive disjunction, also known as exclusive or and symbolized by XOR or EOR, is a logical operation on two operands that results in a logical value of true if and only if one of the operands, but not both, has a value of true. ... Negation, in its most basic sense, changes the truth value of a statement to its opposite. ... In computer science, conditional statements are a vital part of a programming language. ... Boolean logic is a complete system for logical operations. ...

Superscalar computers contain multiple ALUs so that they can process several instructions at the same time. Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices. Simple superscalar pipeline. ... “GPU” redirects here. ... -1... Multiple Instruction Multiple Data (MIMD) is a type of parallel computing architecture where many functional units perform different operations on different data. ... A vector going from A to B. In physics and in vector calculus, a spatial vector, or simply vector, is a concept characterized by a magnitude and a direction. ... In mathematics, a matrix (plural matrices) is a rectangular table of elements (or entries), which may be numbers or, more generally, any abstract quantities that can be added and multiplied. ...

Memory

Main article: Computer storage

Magnetic core memory was popular main memory for computers through the 1960s until it was completely replaced by semiconductor 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 up to the software to give significance to what the memory sees as nothing but a series of numbers. This article does not cite any references or sources. ... Image File history File linksMetadata Download high-resolution version (1280x960, 259 KB) This is a 50x photograph of magnetic core random access memory from a 4 KiB memory plane. ... Image File history File linksMetadata Download high-resolution version (1280x960, 259 KB) This is a 50x photograph of magnetic core random access memory from a 4 KiB memory plane. ... A 16×16 cm area core memory plane of 128×128 bits, i. ...

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; 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 as long as it can be somehow represented in numerical form. Modern computers have billions or even trillions of bytes of memory. The binary or base-two numeral system is a system for representing numbers in which a radix of two is used; that is, each digit in a binary numeral may have either of two different values. ... This article is about the unit of information. ... In computer science a byte (pronounced bite) is a unit of measurement of information storage, most often consisting of eight bits. ... The twos complement of a binary number is the value obtained by subtracting the number from a large power of two (specifically, from 2N for an N-bit twos complement). ...

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. Since 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. In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to frequently used values—typically, these values are involved in multiple expression evaluations occurring within a small region on the program. ...

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 is erased when the power to the computer is turned off while 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 software required to perform the task may be stored in ROM. Software that is 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 by retaining data when turned off but being rewritable like RAM. However, flash memory is typically much slower than conventional ROM and RAM so its use is restricted to applications where high speeds are not required.^[13] “RAM” redirects here. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... For other uses, see Bios. ... // An operating system (OS) is the software that manages the sharing of the resources of a computer. ... An embedded system is a special-purpose computer system, which is completely encapsulated by the device it controls. ... A microcontroller, like this PIC18F8720 is controlled by firmware stored inside on FLASH memory In computing, firmware is a computer program that is embedded in a hardware device, for example a microcontroller. ... A USB flash drive. ...

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. Diagram of a CPU memory cache A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. ...

Input/output (I/O)

Main article: Input/output