computer.reading

8/8/2019 Computer.reading

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ComputerA computer is a programmable machine that receives input, stores and manipulates data, and provides

output in a useful format.

While a computer can, in theory, be made out of almost anything (see misconceptions section), and

mechanical examples of computers have existed through much of recorded human history, the first

electronic computers were developed in the mid-20th century (19401945). Originally, they were the

size of a large room, consuming as much power as several hundred modern personal computers (PCs).

Modern computers based on integrated circuits are millions to billions of times more capable than the

early machines, and occupy a fraction of the space.Simple computers are small enough to fit into mobile

devices, and can be powered by a small battery. Personal computers in their various forms are icons of

the Information Age and are what most people think of as "computers". However, the embedded

computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robotsare the most numerous.

Contents

1.Misconceptions

A computer does not need to be electric, nor even have a processor, nor RAM, nor even hard

disk. The minimal definition of a computer is anything that transforms information in a

purposeful way.

o 1.1 Required technology Computational systems as flexible as a personal computer can be built out of almost

anything. For example, a computer can be made out of billiard balls (billiard ballcomputer); this is an unintuitive and pedagogical example that a computer can be made

out of almost anything. More realistically, modern computers are made out of transistorsmade of photolithographed semiconductors.

Historically, computers evolved from mechanical computers and eventually from vacuumtube transistors.

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

factoring).

o 1.2 Computer architecture paradigms ~ modelSome different paradigms of how to build a computer from the ground-up:

RAM machines


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These are the types of computers with a CPU, computer memory, etc.,which understand basic instructions in a machine language. The concept evolved from

the Turing machine. Brains

Brains are massively parallel processors made of neurons, wired in intricate

patterns, that communicate via electricity and neurotransmitter chemicals. Programming languages

Such as the lambda calculus, or modern programming languages,

are virtual computers built on top of other computers. Cellular automata

For example, the game of Life can create "gliders" and "loops"and other constructs that transmit information; this paradigm can be applied to DNA

computing, chemical computing, etc. Groups and committees

The linking of multiple computers (brains) is itself a computerLogic gates are a common abstraction which can apply to most of the above digital or

analog paradigms.The ability to store and execute lists of instructions called programs makes computers

extremely versatile, distinguishing them from calculators. The ChurchTuring thesis is amathematical statement of this versatility: any computer with a certain Turing-complete

is, in principle, capable of performing the same tasks that any other computer canperform. Therefore any type of computer (netbook, supercomputer, cellular automaton,

etc.) is able to perform the same computational tasks, given enough time and storagecapacity

o 1.3 Limited-function computersConversely, a computer which is limited in function (one that is not "Turing-complete")

cannot simulate arbitrary things. For example, simple four-function calculators cannot

simulate a real computer without human intervention. As a more complicated example,

without the ability to program a gaming console, it can never accomplish what a

programmable calculator from the 1990s could (given enough time); the system as a

whole is not Turing-complete, even though it contains a Turing-complete component

(the microprocessor). Living organisms (the body, not the brain) are also limited-

function computers designed to make copies of themselves; they cannot be

reprogrammed without genetic engineering.

o 1.4 Virtual computersA "computer" is commonly considered to be a physical device. However, one can create

a computer program which describes how to run a different computer, i.e. "simulating a

computer in a computer". Not only is this a constructive proof of the Church-Turing

thesis, but is also extremely common in all modern computers. For example, some

programming languages use something called an interpreter, which is a simulated


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computer built on top of the basic computer; this allows programmers to write code

(computer input) in a different language than the one understood by the base computer

(the alternative is to use a compiler). Additionally, virtual machines are simulated

computers which virtually replicate a physical computer in software, and are very

commonly used by IT. Virtual machines are also a common technique used to create

emulators, such game console emulators.

2 History of computing

The first use of the word "computer" was recorded in 1613, referring to a person who carried

out calculations, or computations, and the word continued to be used in that sense until the

middle of the 20th century. From the end of the 19th century onwards though, the word began

to take on its more familiar meaning, describing a machine that carries out computations

o 2.1 Limited-function ancient computers The history of the modern computer begins with two separate technologiesautomated

calculation and programmabilitybut no single device can be identified as the earliestcomputer, partly because of the inconsistent application of that term. Examples of earlymechanical calculating devices include the abacus, the slide rule and arguably the

astrolabe and the Antikythera mechanism, an ancient astronomical computer built by theGreeks around 80 BC.

[4]The Greek mathematician Hero of Alexandria (c. 1070 AD)

built a mechanical theater which performed a play lasting 10 minutes and was operatedby a complex system of ropes and drums that might be considered to be a means of

deciding which parts of the mechanism performed which actions and when.[5]This is theessence of programmability.

The "castle clock", an astronomical clock invented by Al-Jazari in 1206, is considered tobe the earliest programmable analog computer.

[6][verification needed]It displayed the zodiac,

the solar and lunar orbits, a crescent moon-shaped pointer travelling across a gatewaycausing automatic doors to open every hour,

[7][8]and five robotic musicians who played

music when struck by levers operated by a camshaft attached to a water wheel. Thelength of day and night could be re-programmed to compensate for the changing lengths

of day and night throughout the year.[6]

The Renaissance saw a re-invigoration of European mathematics and engineering.

Wilhelm Schickard's 1623 device was the first of a number of mechanical calculatorsconstructed by European engineers, but none fit the modern definition of a computer,

because they could not be programmed.

o 2.2 First general-purpose computersIn 1801, Joseph Marie Jacquard made an improvement to the textile loom by introducing a series

of punched paper cards as a template which allowed his loom to weave intricate patternsautomatically. 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.


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It was the fusion of automatic calculation with programmability that produced the firstrecognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a

fully programmable mechanical computer, his analytical engine. Limited finances and Babbage'sinability to resist tinkering with the design meant that the device was never completed.

In the late 1880s,H

ermanH

ollerith invented the recording of data on a machine readablemedium. Prior uses of machine readable media, above, had been for control, not data. "Aftersome initial trials with paper tape, he settled on punched cards ..." To process these punched

cards he invented the tabulator, and the keypunch machines. These three inventions were thefoundation of the modern information processing industry. Large-scale automated data

processing of punched cards was performed for the 1890 United States Census by Hollerith'scompany, which later became the core of 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 toappear: the punched card, Boolean algebra, the vacuum tube (thermionic valve) and the

teleprinter.

During the first half of the 20th century, many scientific computing needs were met byincreasingly 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 generallylacked the versatility and accuracy of modern digital computers.

Alan Turing is widely regarded to be the father of modern computer science. In 1936 Turingprovided an influential formalisation of the concept of the algorithm and computation with the

Turing machine, providing a blueprint for the electronic digital computer.[11]

Of his role in thecreation of the modern computer, Time magazine in naming Turing one of the 100 most

influential people of the 20th century, states: "The fact remains that everyone who taps at akeyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of

aT

uring machine".

[11]

The Zuse Z3, 1941, considered the world's first working programmable, fully automaticcomputing machine.


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The ENIAC, which became operational in 1946, is considered to be the first general-purpose

electronic computer.

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

architecture.

Die of an Intel 80486DX2 microprocessor (actual size: 126.75 mm) in its packaging.

The inventor of the program-controlled computer was Konrad Zuse, who built the first workingcomputer in 1941 and later in 1955 the first computer based on magnetic storage.[12]

George Stibitz is internationally recognized as a father of the modern digital computer. While

working at Bell Labs in November 1937, Stibitz invented and built a relay-based calculator hedubbed the "Model K" (for "kitchen table", on which he had assembled it), which was the first to


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use binary circuits to perform an arithmetic operation. Later models added greater sophisticationincluding complex arithmetic and programmability.

[13]

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 byC

laude Shannon in 1937) and more flexibleprogrammability were vitally important steps, but defining one point along this road as "the firstdigital electronic computer" is difficult.

Shannon 1940Notable achievements include.

y Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the first workingmachine featuring binary arithmetic, including floating point arithmetic and a measure ofprogrammability. In 1998 the Z3 was proved to be Turing complete, therefore being the

world's first operational computer.[14]

y The non-programmable AtanasoffBerryComputer (1941) which used vacuum tube

based computation, binary numbers, and regenerative capacitor memory. The use ofregenerative memory allowed it to be much more compact than its peers (being

approximately the size of a large desk or workbench), since intermediate results could bestored and then fed back into the same set of computation elements.

y The secret British Colossus computers (1943),[15] which had limited programmability butdemonstrated that a device using thousands of tubes could be reasonably reliable and

electronically reprogrammable. It was used for breaking German wartime codes.y The Harvard Mark I (1944), a large-scale electromechanical computer with limited

programmability.y The U.S. Army's Ballistic Research Laboratory ENIAC (1946), which used decimal

arithmetic and is sometimes called the first general purpose electronic computer (sinceKonrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however,

ENIAC had an inflexible architecture which essentially required rewiring to change itsprogramming.

o 2.3 Stored-program architecture Several developers of ENIAC, recognizing its flaws, came up with a far more flexible

and elegant design, which came to be known as the "stored program architecture" or vonNeumann architecture. This design was first formally described by John von Neumann in

the paperFirst Draft of a Report on the EDVAC, distributed in 1945. A number ofprojects to develop computers based on the stored-program architecture commenced

around this time, the first of these being completed in Great Britain. The first workingprototype to be demonstrated was the Manchester Small-Scale Experimental Machine

(SSEM or "Baby") in 1948. The Electronic Delay Storage Automatic Calculator(EDSAC), completed a year after the SSEM at Cambridge University, was the first

practical, non-experimental implementation of the stored program design and was put touse immediately for research work at the university. Shortly thereafter, the machine

originally described by von Neumann's paperEDVACwas completed but did not seefull-time use for an additional two years.


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Nearly all modern computers implement some form of the stored-program architecture,making it the single trait by which the word "computer" is now defined. While the

technologies used in computers have changed dramatically since the first electronic,general-purpose computers of the 1940s, most still use the von Neumann architecture.

Beginning in the 1950s, Soviet scientists Sergei Sobolev and Nikolay Brusentsovconducted research on ternary computers, devices that operated on a base threenumbering system of 1, 0, and 1 rather than the conventional binary numbering systemupon which most computers are based. They designed the Setun, a functional ternary

computer, at Moscow State University. The device was put into limited production in theSoviet Union, but supplanted by the more common binary architecture.

o 2.4 Semiconductors and microprocessors Computers using vacuum tubes as their electronic elements were in use throughout the

1950s, but by the 1960s had been largely replaced by transistor-based machines, which

were smaller, faster, cheaper to produce, required less power, and were more reliable.The first transistorised computer was demonstrated at the University of Manchester in

1953.[16] In the 1970s, integrated circuit technology and the subsequent creation ofmicroprocessors, such as the Intel 4004, further decreased size and cost and further

increased speed and reliability of computers. By the late 1970s, many products such asvideo recorders contained dedicated computers called microcontrollers, and they started

to appear as a replacement to mechanical controls in domestic appliances such aswashing machines. The 1980s witnessed home computers and the now ubiquitous

personal computer. With the evolution of the Internet, personal computers are becomingas common as the television and the telephone in the household

].

Modern smartphones are fully programmable computers in their own right, and as of2009 may well be the most common form of such computers in existence.

3 Programso 3.1 Stored program architectureo 3.2 Bugso 3.3 Machine codeo 3.4 Higher-level languages and program design

4 Functiono 4.1 Control unito 4.2 Arithmetic/logic unit (ALU)o 4.3 Memoryo 4.4 Input/output (I/O)o 4.5 Multitaskingo 4.6 Multiprocessingo 4.7 Networking and the Internet

5 Further topicso 5.1 Artificial intelligence


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o 5.2 Hardwareo 5.3 Softwareo 5.4 Programming languageso 5.5 Professions and organizations

6 See also

7 Notes 8 References 9 External links

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