tugas b.inggris 2

8/6/2019 Tugas B.Inggris 2

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What's a computer?

Short Answer: A computer is a collection of electrical and mechanical devicesthat can accept inputvia input devices and can provide outputvia output devices.

Long Answer: A computer is a collection of electrical and mechanical devicesthat can accept human or electro-mechanical inputvia input devices and canprovide visual, auditory and kinetic outputvia output devices.

Human inputis generally provided by moving and clicking buttons on amouse, from pressing keys on a keyboard, writing on an electronic tablet,touching the screen or with spoken commands. Electro-mechanical inputcan come from a variety of data storage devices or from another, attachedcomputer.

Visual output is typically displayed on a monitor while audible outputisplayed through speakers, while an example of kinetic output might be

back pressure from a joystick. The mouse, keyboard, monitor and speakers are all connected to IO

(Input/Output) ports on the computer.

Wikipedia.

A computer is as stupid as a stone and has no more value than a stone withoutan operating system and programs.

A computer is amachine that manipulates data according to a set ofinstructions.

Although mechanical examples of computers have existed through much of recordedhuman history, the first electronic computers were developed in the mid-20th century

(19401945). These were the size of a large room, consuming as much power as several

hundred modern personal computers (PCs).[1] Modern computers based on integratedcircuitsare millions to billions of times more capable than the early machines, and

occupy a fraction of the space.[2] Simple computers are small enough to fit into a

wristwatch, and can be powered by awatch battery.Personal computers in their variousforms are icons of the Information Age and are what most people think of as

"computers". Theembedded computers found in many devices from MP3 players to

fighter aircraft and from toysto industrial robots are however the most numerous.

The ability to store and execute lists of instructions calledprogramsmakes computersextremely versatile, distinguishing them from calculators. TheChurchTuring 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 ranging from a mobile phone to a supercomputerareall able to perform the same computational tasks, given enough time and storage

capacity.
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Main article: History of computing hardware

The Jacquard loom, on display at the Museum of Science and Industry in Manchester,

England, was one of the first programmable devices.

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 senseuntil 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.[3]

The history of the modern computer begins with two separate technologiesautomatedcalculation and programmabilitybut no single device can be identified as the earliest

computer, partly because of the inconsistent application of that term. Examples of early

mechanical calculating devices include the abacus, theslide rule and arguably theastrolabeand the Antikythera mechanism(which dates from about 150100 BC). Hero of

Alexandria(c. 1070 AD) built a mechanical theater which performed a play lasting

10 minutes and was operated by a complex system of ropes and drums that might be

considered to be a means of deciding which parts of the mechanism performed whichactions and when.[4] This is the essence of programmability.

The "castle clock", an astronomical clockinvented byAl-Jazari in 1206, is considered to

be the earliestprogrammableanalog computer.[5] It displayed the zodiac, the solarand

lunar orbits, acrescent moon-shapedpointertravelling across a gateway causingautomatic doors to open every hour,[6][7] and fiverobotic musicians who played music

when struck by levers operated by acamshaft attached to awater wheel. The length ofday and night could be re-programmed to compensate for the changing lengths of day andnight throughout the year.[5]

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

Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators

constructed by European engineers, but none fit the modern definition of a computer,because they could not be programmed.
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In 1801, Joseph Marie Jacquard made an improvement to the textile loom by introducing

a series ofpunched paper cardsas a template which allowed his loom to weave intricate

patterns automatically. The resulting Jacquard loom was an important step in thedevelopment of computers because the use of punched cards to define woven patterns can

be viewed as an early, albeit limited, form of programmability.

It was the fusion of automatic calculation with programmability that produced the first

recognizable computers. In 1837, Charles Babbage was the first to conceptualize anddesign a fully programmable mechanical computer, his analytical engine.[8] Limited

finances and Babbage's inability to resist tinkering with the design meant that the device

was never completed.

In the late 1880s, Herman Hollerith invented the recording of data on a machine readablemedium. Prior uses of machine readable media, above, had been for control, not data.

"After some initial trials with paper tape, he settled on punched cards ..."[9] To process

these punched cards he invented the tabulator, and thekeypunchmachines. These three

inventions were the foundation of the modern information processing industry. Large-scale automated data processing of punched cards was performed for the1890 United

States Censusby Hollerith's company, which later became the core ofIBM. By the end ofthe 19th century a number of technologies that would later prove useful in the realization

of practical computers had begun to appear: thepunched card,Boolean algebra, the

vacuum tube (thermionic valve) and theteleprinter.

During the first half of the 20th century, many scientific computing needs were met byincreasingly sophisticated analog computers, which used a direct mechanical orelectrical

model of the problem as a basis forcomputation. However, these were not programmable

and generally lacked the versatility and accuracy of modern digital computers.

Alan Turing is widely regarded to be the father of moderncomputer science. In 1936Turing provided an influential formalisation of the concept of thealgorithmand

computation with the Turing machine. Of his role in the modern computer,Time

Magazine in naming Turing one of the 100 most influential people of the 20th century,states: "The fact remains that everyone who taps at a keyboard, opening a spreadsheet or

a word-processing program, is working on an incarnation of a Turing machine."[10]

The inventor of the program-controlled computer wasKonrad Zuse, who built the first

working computer in 1941 and later in 1955 the first computer based on magneticstorage.[11]

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

While working at Bell Labs in November 1937, Stibitz invented and built a relay-based

calculator he dubbed the "Model K" (for "kitchen table", on which he had assembled it),which was the first to usebinary circuits to perform an arithmetic operation. Later models

added greater sophistication including complex arithmetic and programmability.[12]

Defining characteristics of some early digital computers of the 1940s (In thehistory of
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computing hardware)

NameFirst

operational

Numeral

system

Computing

mechanismProgramming

Turing

complete

ZuseZ3(Germany)

May 1941BinaryElectro-

mechanical

Program-controlled by

punched film stock(but

no conditional branch)

Yes (1998)

Atanasoff

Berry

Computer(US)

1942Binary ElectronicNot programmable

single purposeNo

Colossus Mark

1(UK)

February

1944Binary Electronic

Program-controlled bypatch cables and

switches

No

Harvard Mark

I IBM ASCC(US)

May 1944DecimalElectro-

mechanical

Program-controlled by24-channelpunched

paper tape (but no

conditional branch)

No

Colossus Mark

2(UK)June 1944Binary Electronic


switches

No

ENIAC(US) July 1946Decimal ElectronicProgram-controlled bypatch cables and

switches

Yes

Manchester

Small-Scale

Experimental

Machine(UK)

June 1948Binary ElectronicStored-program inWilliams cathode ray

tube memory

Yes

Modified

ENIAC(US)

September

1948Decimal Electronic


switches plus a

primitive read-only

stored programmingmechanism using the

Function Tables as

program ROM

Yes

EDSAC(UK) May 1949Binary Electronic

Stored-program in

mercury delay line

memory

Yes

Manchester

Mark 1(UK)

October


Stored-program inWilliams cathode ray

tube memory and

magnetic drum memory

Yes

CSIRAC(Australia)

November


Stored-program in

mercury delay line

memory

Yes
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edia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machinehttp://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machinehttp://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machinehttp://en.wikipedia.org/wiki/Binary_numeral_systemhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Stored-programhttp://en.wikipedia.org/wiki/Williams_tubehttp://en.wikipedia.org/wiki/Williams_tubehttp://en.wikipedia.org/wiki/ENIAChttp://en.wikipedia.org/wiki/ENIAChttp://en.wikipedia.org/wiki/Decimalhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Read-only_memoryhttp://en.wikipedia.org/wiki/EDSAChttp://en.wikipedia.org/wiki/Binary_numeral_systemhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Stored-programhttp://en.wikipedia.org/wiki/Delay_line_memoryhttp://en.wikipedia.org/wiki/Delay_line_memoryhttp://en.wikipedia.org/wiki/Manchester_Mark_1http://en.wikipedia.org/wiki/Manchester_Mark_1http://en.wikipedia.org/wiki/Binary_numeral_systemhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Stored-programhttp://en.wikipedia.org/wiki/Williams_tubehttp://en.wikipedia.org/wiki/Williams_tubehttp://en.wikipedia.org/wiki/Drum_memoryhttp://en.wikipedia.org/wiki/CSIRAChttp://en.wikipedia.org/wiki/Binary_numeral_systemhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Stored-programhttp://en.wikipedia.org/wiki/Delay_line_memoryhttp://en.wikipedia.org/wiki/Delay_line_memory


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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:

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

architecture.

Die of an Intel 80486DX2microprocessor(actual size: 126.75 mm) in its packaging.

Konrad Zuse's electromechanical "Z machines". TheZ3 (1941) was the first

working machine featuringbinary arithmetic, including floating point arithmeticand a measure of programmability. In 1998 the Z3 was proved to be Turing

complete, therefore being the world's first operational computer.[13]

The non-programmable AtanasoffBerry Computer(1941) which used vacuum

tube based computation, binary numbers, and regenerative capacitor memory. Theuse of regenerative memory allowed it to be much more compact then its peers

(being approximately the size of a large desk or workbench), since intermediateresults could be stored and then fed back into the same set of computation

elements.

The secret British Colossus computers (1943),[14]which had limited

programmability but demonstrated that a device using thousands of tubes could be
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reasonably reliable and electronically reprogrammable. It was used forbreaking

German wartime codes.

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

The U.S. Army's Ballistic Research LaboratoryENIAC (1946), which used

decimal arithmetic and is sometimes called the first general purpose electroniccomputer (since Konrad Zuse's Z3 of 1941 usedelectromagnets 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 flexibleand elegant design, which came to be known as the "stored program architecture" orvon

Neumann 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 inGreat Britain. The first to be

demonstrated working was the Manchester Small-Scale Experimental Machine (SSEM or"Baby"), while theEDSAC, completed a year after SSEM, was the first practicalimplementation of the stored program design. Shortly thereafter, the machine originally

described by von Neumann's paperEDVACwas completed but did not see full-time

use for an additional two years.

Nearly all modern computers implement some form of the stored-program architecture,

making it the single trait by which the word "computer" is now defined. While the

technologies used in computers have changed dramatically since the first electronic,

general-purpose computers of the 1940s, most still use the von Neumann architecture.

Computers using vacuum tubes as their electronic elements were in use throughout the1950s, 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 Manchesterin1953.[15] In the 1970s, integrated circuit technology and the subsequent creation of

microprocessors, such as the Intel 4004, further decreased size and cost and further

increased speed and reliability of computers. By the late 1970s, many products such asvideo recorderscontained dedicated computers calledmicrocontrollers, and they started

to appear as a replacement to mechanical controls in domestic appliances such as

washing machines. The 1980s witnessed home computers and the now ubiquitouspersonal computer. With the evolution of theInternet, personal computers are becoming

as common as the televisionand the telephone in the household.

Modern smartphones are fully-programmable computers in their own right, and as of

2009 may well be the most common form of such computers in existence.

Stored program architecture

Main articles: Computer program and Computer programming
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The defining feature of modern computers which distinguishes them from all other

machines is that they can beprogrammed. That is to say that a list ofinstructions (the

program) can be given to the computer and it will store them and carry them out at sometime in the future.

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

instructions are read from the computer'smemory 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 (orbranches). 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 byproviding a type of jump that "remembers" the location it jumped from and another

instruction to return to the instruction following that jump instruction.

Program execution might be likened to reading a book. While a person will normally read

each word and line in sequence, they may at times jump back to an earlier place in thetext 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 andit is what allows the computer to perform tasks repeatedly without human intervention.

Comparatively, a person using apocket calculatorcan 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

timewith a near certainty of making a mistake. On the other hand, a computer may beprogrammed to do this with just a few simple instructions. For example:

mov #0,sum ; set sum to 0

mov #1,num ; set num to 1

loop: add num,sum ; add num to sum

add #1,num ; add 1 to num

cmp num,#1000 ; compare num to 1000

ble loop ; if num


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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 theHarvard Mark I computer. Modern von Neumanncomputers display some traits of the Harvard architecture in their designs, such as in CPU

caches.

While it is possible to write computer programs as long lists of numbers (machine

language) and this technique was used with many early computers,[19] it is extremelytedious 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

remembera mnemonic such as ADD, SUB, MULT or JUMP. These mnemonics arecollectively 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. Machinelanguages and the assembly languages that represent them (collectively termed low-levelprogramming languages) tend to be unique to a particular type of computer. For instance,

anARM architecturecomputer (such as may be found in a PDAor ahand-held

videogame) cannot understand the machine language of an Intel Pentiumor the AMDAthlon 64 computer that might be in a PC.[20]

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 languagesthat are able to express theneeds of theprogrammermore conveniently (and thereby help reduce programmer error).

High level languages are usually "compiled" into machine language (or sometimes intoassembly language and then into machine language) using another computer programcalled a compiler.[21]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 ispart of the means by which software like video games may be made available for

different computer architectures such as personal computers and various video game

consoles.

The task of developing large software systems presents a significant intellectualchallenge. Producing software with an acceptably high reliability within a predictable

schedule and budget has historically been difficult; the academic and professional

discipline ofsoftware engineering concentrates specifically on this challenge.

Example
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A traffic light showing red

Suppose a computer is being employed to drive atraffic light at an intersection between

two streets. The computer has the following three basic instructions.

1. ON(Streetname, Color) Turns the light on Streetname with a specified Color on.2. OFF(Streetname, Color) Turns the light on Streetname with a specified Color off.

3. WAIT(Seconds) Waits a specifed number of seconds.

4. START Starts the program5. REPEAT Tells the computer to repeat a specified part of the program in a loop.

Comments are marked with a // on the left margin. Comments in a computer program do

not affect the operation of the program. They are not evaluated by the computer. Assume

the streetnames are Broadway and Main.

START

//Let Broadway traffic go

OFF(Broadway, Red)

ON(Broadway, Green)

WAIT(60 seconds)

//Stop Broadway traffic

OFF(Broadway, Green)

ON(Broadway, Yellow)

WAIT(3 seconds)

OFF(Broadway, Yellow)

ON(Broadway, Red)

//Let Main traffic go

OFF(Main, Red)

ON(Main, Green)

WAIT(60 seconds)

//Stop Main traffic

OFF(Main, Green)

ON(Main, Yellow)

WAIT(3 seconds)

OFF(Main, Yellow)ON(Main, Red)

//Tell computer to continuously repeat the program.

REPEAT ALL

With this set of instructions, the computer would cycle the light continually through red,green, yellow and back to red again on both streets.
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However, suppose there is a simple on/offswitch connected to the computer that is

intended to be used to make the light flash red while some maintenance operation is

being performed. The program might then instruct the computer to:

START

IF Switch == OFF then: //Normal traffic signal operation

{//Let Broadway traffic go

OFF(Broadway, Red)

ON(Broadway, Green)

WAIT(60 seconds)

//Stop Broadway traffic

OFF(Broadway, Green)

ON(Broadway, Yellow)

WAIT(3 seconds)

OFF(Broadway, Yellow)

ON(Broadway, Red)

//Let Main traffic go

OFF(Main, Red)

ON(Main, Green)WAIT(60 seconds)

//Stop Main traffic

OFF(Main, Green)

ON(Main, Yellow)

WAIT(3 seconds)

OFF(Main, Yellow)

ON(Main, Red)

//Tell the computer to repeat this section continuously.

REPEAT THIS SECTION

}

IF Switch == ON THEN: //Maintenance Mode

{

//Turn the red lights on and wait 1 second.

ON(Broadway, Red)

ON(Main, Red)

WAIT(1 second)

//Turn the red lights off and wait 1 second.

OFF(Broadway, Red)

OFF(Main, Red)

WAIT(1 second)

//Tell the comptuer to repeat the statements in this section.

REPEAT THIS SECTION

}

In this manner, the traffic signal will run a flash-red program when the switch is on, and

will run the normal program when the switch is off. Both of these program examplesshow the basic layout of a computer program in a simple, familiar context of a traffic

signal. Any experienced programmer can spot many software bugs in the program, for

instance, not making sure that the green light is off when the switch is set to flash red.

However, to remove all possible bugs would make this program much longer and morecomplicated, and would be confusing to nontechnical readers: the aim of this example is

a simple demonstration of how computer instructions are laid out.
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Function

Main articles: Central processing unit and Microprocessor

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 bybusses, often made of groups ofwires.

Inside each of these parts are thousands to trillions of smallelectrical circuits which can

be turned off or on by means of an electronic switch. Each circuit represents abit (binarydigit) of information so that when the circuit is on it represents a "1", and when off it

represents a "0" (in positive logic representation). The circuits are arranged in logic gates

so that one or more of the circuits may control the state of one or more of the other

circuits.

The control unit, ALU, registers, and basic I/O (and often other hardware closely linked

with these) are collectively known as acentral processing unit(CPU). Early CPUs werecomposed of many separate components but since the mid-1970s CPUs have typicallybeen constructed on a single integrated circuit called amicroprocessor.

Control unit

Main articles: CPU design and Control unit

Diagram showing how a particularMIPS architectureinstruction would be decoded by

the control system.

The control unit (often called a control system or central controller) manages thecomputer's various components; it reads and interprets (decodes) the program

instructions, transforming them into a series of control signals which activate other parts

of the computer.[22] Control systems in advanced computers may change the order ofsome instructions so as to improve performance.

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

from.[23]

The control system's function is as followsnote that this is a simplified description, andsome of these steps may be performed concurrently or in a different order depending on

the type of CPU:
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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 signalsfor 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 perhapsfrom 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 wouldcause the next instruction to be read from a place 100 locations further down theprogram. 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 ofcontrol flow).

It is noticeable that the sequence of operations that the control unit goes through to

process an instruction is in itself like a short computer programand indeed, in some

more complex CPU designs, there is another yet smaller computer called a

microsequencerthat runs a microcode program that causes all of these events to happen.

Arithmetic/logic unit (ALU)

Main article: Arithmetic logic unit

The ALU is capable of performing two classes of operations: arithmetic and logic.[24]

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) whilstothers use floating pointto representreal numbersalbeit 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 canperform. Therefore, any computer can be programmed to perform any arithmetic

operationalthough it will take more time to do so if its ALU does not directly support

the operation. An ALU may also compare numbers and returnboolean truth values(true

or false) depending on whether one is equal to, greater than or less than the other ("is 64greater than 65?").
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Logic operations involve Boolean logic: AND,OR, XORandNOT. These can be useful

both for creating complicatedconditional statementsand processingboolean logic.

Superscalarcomputers may contain multiple ALUs so that they can process severalinstructions at the same time.[25]Graphics processors and computers withSIMD and

MIMD features often provide ALUs that can perform arithmetic onvectorsandmatrices.

Memory

Main article: Computer data storage

Magnetic core memory was the computer memory of choice throughout the 1960s, until

it was 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 thenumber that is in cell 1357 to the number that is in cell 2468 and put the answer into cell

1595". The information stored in memory may represent practically anything. Letters,

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

the CPU does not differentiate between different types of information, it is the software'sresponsibility to give significance to what the memory sees as nothing but a series of

numbers.

In almost all modern computers, each memory cell is set up to storebinary numbers ingroups of eight bits (called abyte). Each byte is able to represent 256 different numbers

(2^8 = 256); either from 0 to 255 or -128 to +127. To store larger numbers, several

consecutive bytes may be used (typically, two, four or eight). When negative numbers are

required, they are usually stored intwo's complement notation. Other arrangements arepossible, but are usually not seen outside of specialized applications or historical

contexts. A computer can store any kind of information in memory if it can be

represented numerically. Modern computers have billions or even trillions of bytes ofmemory.

The CPU contains a special set of memory cells calledregistersthat 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 themost frequently needed data items to avoid having to access main memory every time

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

the computer's speed.

Computer main memory comes in two principal varieties:random-access memory orRAM 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 theCPU can only read from it. ROM is typically used to store the computer's initial start-up

instructions. In general, the contents of RAM are erased when the power to the computeris turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a

specialized program called the BIOS that orchestrates loading the computer's operating

system from the hard disk drive into RAM whenever the computer is turned on or reset.In embedded computers, which frequently do not have disk drives, all of the required

software may be stored in ROM. Software stored in ROM is often called firmware,

because it is notionally more like hardware than software.Flash memory blurs thedistinction between ROM and RAM, as it retains its data when turned off but is also

rewritable. It is typically much slower than conventional ROM and RAM however, so its

use is restricted to applications where high speed is unnecessary.

[26]

In more sophisticated computers there may be one or more RAMcache memorieswhichare slower than registers but faster than main memory. Generally computers with this sort

of cache are designed to move frequently needed data into the cache automatically, often

without the need for any intervention on the programmer's part.

Input/output (I/O)

Main article: Input/output

Hard disk drivesare common I/O devices used with computers.

I/O is the means by which a computer exchanges information with the outside world.[27]

Devices that provide input or output to the computer are calledperipherals.[28]On atypicalpersonal computer, peripherals include input devices like the keyboard and

mouse, and output devices such as the display andprinter. Hard disk drives,floppy diskdrives and optical disc drives serve as both input and output devices. Computernetworking is another form of I/O.

Often, I/O devices are complex computers in their own right with their own CPU and

memory. A graphics processing unitmight contain fifty or more tiny computers that

perform the calculations necessary to display 3D graphics[citation needed]. Modern desktopcomputers contain many smaller computers that assist the main CPU in performing I/O.
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Multitasking

Main article: Computer multitasking

While a computer may be viewed as running one gigantic program stored in its main

memory, in some systems it is necessary to give the appearance of running severalprograms simultaneously. This is achieved by multitasking i.e. having the computerswitch rapidly between running each program in turn.[29]

One means by which this is done is with a special signal called an interrupt which can

periodically cause the computer to stop executing instructions where it was and do

something else instead. By remembering where it was executing prior to the interrupt, thecomputer can return to that task later. If several programs are running "at the same time",

then the interrupt generator might be causing several hundred interrupts per second,

causing a program switch each time. Since modern computers typically executeinstructions several orders of magnitude faster than human perception, it may appear that

many programs are running at the same time even though only one is ever executing inany given instant. This method of multitasking is sometimes termed "time-sharing" sinceeach program is allocated a "slice" of time in turn. [30]

Before the era of cheap computers, the principle use for multitasking was to allow many

people to share the same computer.

Seemingly, multitasking would cause a computer that is switching between several

programs to run more slowly in direct proportion to the number of programs it isrunning. However, most programs spend much of their time waiting for slow input/output

devices to complete their tasks. If a program is waiting for the user to click on the mouse

or press a key on the keyboard, then it will not take a "time slice" until the event it iswaiting for has occurred. This frees up time for other programs to execute so that many

programs may be run at the same time without unacceptable speed loss.

Multiprocessing

Main article: Multiprocessing

Cray designed many supercomputers that used multiprocessing heavily.

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

multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers

are now widely available, and are being increasingly used in lower-end markets as aresult.

Supercomputers in particular often have highly unique architectures that differsignificantly from the basic stored-program architecture and from general purpose

computers.[31] They often feature thousands of CPUs, customized high-speedinterconnects, and specialized computing hardware. Such designs tend to be useful only

for specialized tasks due to the large scale of program organization required to

successfully utilize most of the available resources at once. Supercomputers usually seeusage in large-scalesimulation,graphics rendering, and cryptographyapplications, as

well as with other so-called "embarrassingly parallel" tasks.

Networking and the Internet

Main articles: Computer networking and Internet

Visualization of a portion of the routes on the Internet.

Computers have been used to coordinate information between multiple locations since

the 1950s. The U.S. military's SAGE system was the first large-scale example of such asystem, which led to a number of special-purpose commercial systems likeSabre.[32]

In the 1970s, computer engineers at research institutions throughout the United States

began to link their computers together using telecommunications technology. This effort

was funded by ARPA (now DARPA), and the computer networkthat it produced was

called the ARPANET.[33]The technologies that made the Arpanet possible spread andevolved.

In time, the network spread beyond academic and military institutions and became known

as the Internet. The emergence of networking involved a redefinition of the nature andboundaries of the computer. Computer operating systems and applications were modified

to include the ability to define and access the resources of other computers on the

network, such as peripheral devices, stored information, and the like, as extensions of the
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resources of an individual computer. Initially these facilities were available primarily to

people working in high-tech environments, but in the 1990s the spread of applications

like e-mail and the World Wide Web, combined with the development of cheap, fastnetworking technologies like Ethernet and ADSL saw computer networking become

almost ubiquitous. In fact, the number of computers that are networked is growing

phenomenally. A very large proportion ofpersonal computersregularly connect to theInternetto communicate and receive information. "Wireless" networking, often utilizing

mobile phone networks, has meant networking is becoming increasingly ubiquitous even

in mobile computing environments.

Further topics

Hardware

Main article: Personal computer hardware

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

Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware.

History of computing hardware

First Generation

(Mechanical/Electromechanical)

CalculatorsAntikythera mechanism,Difference engine,Norden

bombsight

Programmable DevicesJacquard loom,Analyticalengine, Harvard Mark I,Z3

Second Generation (Vacuum

Tubes)

Calculators AtanasoffBerry 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,

Z22Third Generation (Discrete

transistors and SSI, MSI, LSI

Integrated circuits)

MainframesIBM 7090, IBM 7080,IBMSystem/360, BUNCH

MinicomputerPDP-8, PDP-11, IBM

System/32, IBM System/36

Fourth Generation (VLSI integrated

circuits)

Minicomputer VAX, IBM System i

4-bit microcomputer Intel 4004, Intel 4040

8-bit microcomputer Intel 8008, Intel 8080,
http://en.wikipedia.org/wiki/E-mailhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_linehttp://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Personal_computer_hardwarehttp://en.wikipedia.org/wiki/History_of_computing_hardwarehttp://en.wikipedia.org/wiki/Antikythera_mechanismhttp://en.wikipedia.org/wiki/Difference_enginehttp://en.wikipedia.org/wiki/Norden_bombsighthttp://en.wikipedia.org/wiki/Norden_bombsighthttp://en.wikipedia.org/wiki/Norden_bombsighthttp://en.wikipedia.org/wiki/Jacquard_loomhttp://en.wikipedia.org/wiki/Analytical_enginehttp://en.wikipedia.org/wiki/Analytical_enginehttp://en.wikipedia.org/wiki/Analytical_enginehttp://en.wikipedia.org/wiki/Harvard_Mark_Ihttp://en.wikipedia.org/wiki/Z3_(computer)http://en.wikipedia.org/wiki/Z3_(computer)http://en.wikipedia.org/wiki/Atanasoff%E2%80%93Berry_Computerhttp://en.wikipedia.org/wiki/IBM_604http://en.wikipedia.org/wiki/Remington_Rand_409http://en.wikipedia.org/wiki/Remington_Rand_409http://en.wikipedia.org/wiki/List_of_vacuum_tube_computershttp://en.wikipedia.org/wiki/Colossus_computerhttp://en.wikipedia.org/wiki/ENIAChttp://en.wikipedia.org/wiki/ENIAChttp://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machinehttp://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machinehttp://en.wikipedia.org/wiki/Electronic_Delay_Storage_Automatic_Calculatorhttp://en.wikipedia.org/wiki/Manchester_Mark_1http://en.wikipedia.org/wiki/Manchester_Mark_1http://en.wikipedia.org/wiki/Manchester_Mark_1http://en.wikipedia.org/wiki/Ferranti_Pegasushttp://en.wikipedia.org/wiki/Ferranti_Mercuryhttp://en.wikipedia.org/wiki/Ferranti_Mercuryhttp://en.wikipedia.org/wiki/CSIRAChttp://en.wikipedia.org/wiki/CSIRAChttp://en.wikipedia.org/wiki/EDVAChttp://en.wikipedia.org/wiki/UNIVAC_Ihttp://en.wikipedia.org/wiki/UNIVAC_Ihttp://en.wikipedia.org/wiki/IBM_701http://en.wikipedia.org/wiki/IBM_701http://en.wikipedia.org/wiki/IBM_702http://en.wikipedia.org/wiki/IBM_650http://en.wikipedia.org/wiki/Z22http://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Mainframe_computerhttp://en.wikipedia.org/wiki/IBM_7090http://en.wikipedia.org/wiki/IBM_7080http://en.wikipedia.org/wiki/IBM_System/360http://en.wikipedia.org/wiki/IBM_System/360http://en.wikipedia.org/wiki/IBM_System/360http://en.wikipedia.org/wiki/BUNCHhttp://en.wikipedia.org/wiki/Minicomputerhttp://en.wikipedia.org/wiki/PDP-8http://en.wikipedia.org/wiki/PDP-11http://en.wikipedia.org/wiki/IBM_System/32http://en.wikipedia.org/wiki/IBM_System/32http://en.wikipedia.org/wiki/IBM_System/36http://en.wikipedia.org/wiki/VAXhttp://en.wikipedia.org/wiki/IBM_System_ihttp://en.wikipedia.org/wiki/4-bithttp://en.wikipedia.org/wiki/Intel_4004http://en.wikipedia.org/wiki/Intel_4040http://en.wikipedia.org/wiki/8-bithttp://en.wikipedia.org/wiki/Intel_8008http://en.wikipedia.org/wiki/Intel_8080http://en.wikipedia.org/wiki/E-mailhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_linehttp://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Personal_computer_hardwarehttp://en.wikipedia.org/wiki/History_of_computing_hardwarehttp://en.wikipedia.org/wiki/Antikythera_mechanismhttp://en.wikipedia.org/wiki/Difference_enginehttp://en.wikipedia.org/wiki/Norden_bombsighthttp://en.wikipedia.org/wiki/Norden_bombsighthttp://en.wikipedia.org/wiki/Jacquard_loomhttp://en.wikipedia.org/wiki/Analytical_enginehttp://en.wikipedia.org/wiki/Analytical_enginehttp://en.wikipedia.org/wiki/Harvard_Mark_Ihttp://en.wikipedia.org/wiki/Z3_(computer)http://en.wikipedia.org/wiki/Atanasoff%E2%80%93Berry_Computerhttp://en.wikipedia.org/wiki/IBM_604http://en.wikipedia.org/wiki/Remington_Rand_409http://en.wikipedia.org/wiki/Remington_Rand_409http://en.wikipedia.org/wiki/List_of_vacuum_tube_computershttp://en.wikipedia.org/wiki/Colossus_computerhttp://en.wikipedia.org/wiki/ENIAChttp://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machinehttp://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machinehttp://en.wikipedia.org/wiki/Electronic_Delay_Storage_Automatic_Calculatorhttp://en.wikipedia.org/wiki/Manchester_Mark_1http://en.wikipedia.org/wiki/Manchester_Mark_1http://en.wikipedia.org/wiki/Ferranti_Pegasushttp://en.wikipedia.org/wiki/Ferranti_Mercuryhttp://en.wikipedia.org/wiki/Ferranti_Mercuryhttp://en.wikipedia.org/wiki/CSIRAChttp://en.wikipedia.org/wiki/EDVAChttp://en.wikipedia.org/wiki/UNIVAC_Ihttp://en.wikipedia.org/wiki/IBM_701http://en.wikipedia.org/wiki/IBM_701http://en.wikipedia.org/wiki/IBM_702http://en.wikipedia.org/wiki/IBM_650http://en.wikipedia.org/wiki/Z22http://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Mainframe_computerhttp://en.wikipedia.org/wiki/IBM_7090http://en.wikipedia.org/wiki/IBM_7080http://en.wikipedia.org/wiki/IBM_System/360http://en.wikipedia.org/wiki/IBM_System/360http://en.wikipedia.org/wiki/BUNCHhttp://en.wikipedia.org/wiki/Minicomputerhttp://en.wikipedia.org/wiki/PDP-8http://en.wikipedia.org/wiki/PDP-11http://en.wikipedia.org/wiki/IBM_System/32http://en.wikipedia.org/wiki/IBM_System/32http://en.wikipedia.org/wiki/IBM_System/36http://en.wikipedia.org/wiki/VAXhttp://en.wikipedia.org/wiki/IBM_System_ihttp://en.wikipedia.org/wiki/4-bithttp://en.wikipedia.org/wiki/Intel_4004http://en.wikipedia.org/wiki/Intel_4040http://en.wikipedia.org/wiki/8-bithttp://en.wikipedia.org/wiki/Intel_8008http://en.wikipedia.org/wiki/Intel_8080


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Motorola 6800, Motorola

6809, MOS Technology

6502, Zilog Z80

16-bit microcomputerIntel 8088, Zilog Z8000,

WDC 65816/65802

32-bit microcomputerIntel 80386, Pentium,Motorola 68000, ARM

architecture

64-bit microcomputer[34]Alpha,MIPS,PA-RISC,

PowerPC,SPARC,x86-64

Embedded computer Intel 8048, Intel 8051

Personal computer

Desktop computer,Home

computer,Laptopcomputer,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)

InputMouse,Keyboard, Joystick, Image scanner,

Webcam,Graphics tablet,Microphone

Output Monitor, Printer, LoudspeakerBoth

Floppy disk drive,Hard disk drive, Optical

disc drive, Teleprinter

Computer busses

Short range RS-232,SCSI, PCI,USB

Long range (Computernetworking)

Ethernet,ATM, FDDI

Software

Main article: Computer software

Software refers to parts of the computer which do not have a material form, such asprograms, data, protocols, etc. When software is stored in hardware that cannot easily be

modified (such as BIOSROM in an IBM PC compatible), it is sometimes called"firmware" to indicate that it falls into an uncertain area somewhere between hardware

and software.
http://en.wikipedia.org/wiki/Motorola_6800http://en.wikipedia.org/wiki/Motorola_6809http://en.wikipedia.org/wiki/Motorola_6809http://en.wikipedia.org/wiki/MOS_Technology_6502http://en.wikipedia.org/wiki/MOS_Technology_6502http://en.wikipedia.org/wiki/Zilog_Z80http://en.wikipedia.org/wiki/16-bithttp://en.wikipedia.org/wiki/Intel_8088http://en.wikipedia.org/wiki/Zilog_Z8000http://en.wikipedia.org/wiki/WDC_65816/65802http://en.wikipedia.org/wiki/32-bithttp://en.wikipedia.org/wiki/Intel_80386http://en.wikipedia.org/wiki/Pentiumhttp://en.wikipedia.org/wiki/Motorola_68000http://en.wikipedia.org/wiki/ARM_architecturehttp://en.wikipedia.org/wiki/ARM_architecturehttp://en.wikipedia.org/wiki/64-bithttp://en.wikipedia.org/wiki/Computer#cite_note-33http://en.wikipedia.org/wiki/DEC_Alphahttp://en.wikipedia.org/wiki/MIPS_architecturehttp://en.wikipedia.org/wiki/MIPS_architecturehttp://en.wikipedia.org/wiki/PA-RISChttp://en.wikipedia.org/wiki/PA-RISChttp://en.wikipedia.org/wiki/PowerPChttp://en.wikipedia.org/wiki/SPARChttp://en.wikipedia.org/wiki/SPARChttp://en.wikipedia.org/wiki/X86-64http://en.wikipedia.org/wiki/X86-64http://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Intel_8048http://en.wikipedia.org/wiki/Intel_8051http://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Desktop_computerhttp://en.wikipedia.org/wiki/Home_computerhttp://en.wikipedia.org/wiki/Home_computerhttp://en.wikipedia.org/wiki/Home_computerhttp://en.wikipedia.org/wiki/Laptophttp://en.wikipedia.org/wiki/Laptophttp://en.wikipedia.org/wiki/Laptophttp://en.wikipedia.org/wiki/Personal_digital_assistanthttp://en.wikipedia.org/wiki/Personal_digital_assistanthttp://en.wikipedia.org/wiki/Personal_digital_assistanthttp://en.wikipedia.org/wiki/Portable_computerhttp://en.wikipedia.org/wiki/Portable_computerhttp://en.wikipedia.org/wiki/Tablet_PChttp://en.wikipedia.org/wiki/Tablet_PChttp://en.wikipedia.org/wiki/Wearable_computerhttp://en.wikipedia.org/wiki/Quantum_computerhttp://en.wikipedia.org/wiki/Chemical_computerhttp://en.wikipedia.org/wiki/DNA_computinghttp://en.wikipedia.org/wiki/Photonic_computinghttp://en.wikipedia.org/wiki/Spintronicshttp://en.wikipedia.org/wiki/Spintronicshttp://en.wikipedia.org/wiki/Peripheralhttp://en.wikipedia.org/wiki/Input/outputhttp://en.wikipedia.org/wiki/Mouse_(computing)http://en.wikipedia.org/wiki/Keyboard_(computing)http://en.wikipedia.org/wiki/Keyboard_(computing)http://en.wikipedia.org/wiki/Joystickhttp://en.wikipedia.org/wiki/Image_scannerhttp://en.wikipedia.org/wiki/Webcamhttp://en.wikipedia.org/wiki/Graphics_tablethttp://en.wikipedia.org/wiki/Graphics_tablethttp:

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