Desktop Laptop Basic Knowledge I

8/10/2019 Desktop Laptop Basic Knowledge I

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Part I:

Basic Concepts in

Desktop and Portable

Computing


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2Part I: Basic Concepts in Desktop and PortableComputing

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At the end of this chapter you will be able to:

Define a computer

Identify characteristics of a computer

Identify application areas of a computer

Define communication

Identify means of early communication

Explain how telegraph and radio communication works

Explain how computer stored data internally

Explain how data movement is performed inside a computer

Differentiate between serial and parallel communication

Identify basic elements of a computer

Discuss the basic operation of a computer from inputting data to producing output

Identify components and peripherals of computer

Introduction to Computers

De'inition o' Computer

The computer is an electronic machine made with electronic devices. It accepts the rawdata through input device processes it based on the set of instructions given calledprograms! and produces the information as output on the output device. The importantfeature of computers is its storage capability which can store the information and can beretrieved as and when re"uired.

C(aracteristics o' Computer

#omputers are popular because of following characteristics:

$peed: #omputer can perform a task much faster than done manually.

Accuracy: #omputer gives accurate results compared to task done manually.

$torage: #omputer stores the information in its main memory and the same can

be retrieved based on the re"uirement.

%ultitasking: #omputer performs multiple tasks simultaneously. &or example' one

can use the computer to take a printout of an inventory report and at the sametime can use it to draft letters.

#ommunication: #omputer can be used to exchange information between two or

more computers. Internet is the best example of this.


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Part I: Basic Concepts in Desktop and PortableComputing

3

Application Areas o' Computers

The influences of computers are widespread and are used in various application areasmentioned below.

(usiness Area

(usiness people use computers to track accounts' cash transactions inventorymanagement' to store client information' order history' maintaining sale transactionrecords and prepare the reports.

)ow a days' several organi*ation uses computer for doing transaction online. They havetheir own web sites where one can purchase an item and make payment online.

Entertainment Area

+# can be used to play audio' video and can be connected to T,' -#D +roector to havereal time home theater experience.

%ost movie goers like science fiction or action movies' especially the ones that haveda**ling special/effects. 0ell' those graphics were mostly made by computers.

#omputer gamming is another area where +# can be used as a gamming device owing toits multimedia capabilities. The computer gaming industry is currently a hugeprofit/making industry.

Education Area

#omputer being known for its speed and accuracy it plays a maor roll in education area.

Its storage feature enables to maintain digital library which can be retried based onre"uirement.

%edicinal Area

#omputeri*ation of 1ospitals helps to keep record of patients admitted' keep track ofe"uipment and their status.

In addition' medical practitioners use telemedicine to diagnose patients. In telemedicine' adoctor or a specialist provide diagnosis to a patient through video conferencing systemattached to computer and connected to Internet link. This is especially useful in the casewhere a patient is in remote place or it is not practically possible to move a patient.

&inance AreaThe advantages due to computeri*ation of banks are multidimensional / to the customer'and the banks.

#ustomers can logon to bank2s website through Internet and transact with their account inany part of the world.

Immediate responses to customer "ueries without the need to look at ledger/keeper asterminals are provided to all bank employees.

$peedy information transfer enabling fast decisions' because of interconnectedcomputeri*ed branches and controlling offices.

Accurate calculation of cumbersome and time/consuming obs such as calculating balancesand interest accrued for customers on due dates.


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$ignature retrieval facility assisted bank employees to verify transactions by sitting at theirown terminal.

Apart from the above #omputers are used extensively in 34D' Telecommunications'Transportation' %anufacturing etc.

Basics o' Computer Communication

De'ining Communication

The term 5communication6 is defined as the act of transmitting' receiving ideas orexchanging information. A key element in designing of a computer is establishing amethod of communication' both internally and externally. 7nderstanding the process ofcomputer communication is fundamental to understanding how computers work.

Earl) Communication

The main form of communication between humans is through words. The human beingscan express their thoughts both verbally and written. And this form of communicationamongst humans is not a recent one. 1umans used to communicate in this way sinceancient times.

1owever' in early times' people used to send messages through messengers. A messengercan be a fellow human being or a bird' such as pigeon' which is responsible to deliver themessage at the specified address or to the specified person. 1owever' the disadvantage ofthis mechanism is that the time elapsed between when the message is send and when themessage is received is often "uite long. In addition' there is a chance of the message orsometimes even the messenger getting lost during the message delivery process.

To overcome these problems' people devised certain techni"ues to send messages. 8ne ofthe most widely used techni"ues is to use items like lanterns' flags and mirrors to send hemessages. 1owever' this can be used only within the visibility range.

Another popular method to send messages is by using drum sounds. The pattern in whichthe drum sound is produced helps other people to understand the message beingcommunicated. 1owever' this is also not a perfect method. This is because a sound overlong distance often gets less clear which may result in not getting the message clearly.

Telegrap( and Radio Communication

As time and technology progressed' people constructed various devices that help them tocommunicate over long distance in a short time. 1owever' there is some commonality

amongst all these devices.All these devices re"uire some type of mechanism to convert human language to a form ofinformation that can be packaged and sent to the remote location. This called coding themessage. 8n the receiving end' this coded message again needs to be converted back tolanguage that people can understand. This is called decoding the message. The two mostwidely used devices implementing this coding and decoding mechanism are telegraph andradio communication.

The most widely used coding mechanism is the %orse code. In %orse code' each singletransmitted value can have either of the states' dot or dash. 7sing the combination of dotsand dashes an operator can represent letters' and combining these letters can form words.

These combinations of dots and dashes are then send as pulses through a wire inse"uential order. 8perator at the receiving end then translates back the coded message

into its original written form' which is the human readable form.


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5

In %orse code any single transmitted value can have two states' on and off. This on/offstate is represented by the numbers 9 and . The number' 9' represents off state meaningno signal is send. 8n the other hand' the number' ' represents on state meaning thesignal is being sent.

T(e #anguage o' Computers

#omputer being electronic machine it knows only 58)6 or 58&&6 ;92 or ;2!. Any data thatis to be fed' processed or stored should be converted into combination of 9s and s. This iscalled binary notation and 9 or is called a (it.

(it is a basic memory unit.(yte is unit of data consists of < bits=ilo (yte =(! e"uals 9>? @ (ytes%ega (yte %(! e"uals 9>? =ilo (ytesiga (yte (! e"uals 9>? %ega (ytes

Data Trans'er inside a Computer

All the data movements within a computer occur through buses. A bus is a group ofelectrical conductors' mostly wires' running parallel to each other carrying a charge fromone point to another within the computer. A bus can be copper traces on a circuit board orwires in a cable.

7sually' a bus is found in multiples of eight ' B?' and so on!. In the earlycomputers' manufacturers used a set of eight wires for constructing buses. This allows thetransmission of eight bits' or one byte' of information at a time.

1owever with the advancement in computer technology' faster microprocessor comes intomarket. As a result faster means of data communication is re"uired. 1ence to provide fast

data transmission B/' C>/' or B?/bit buses are constructed.The bus width is one of the important characteristic to optimi*e the performance of thecomputer. The number of parallel wires in a bus is called the bus width. 0ider the bus'more bits can be transferred simultaneously resulting in faster data transmission.


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In the preceding figure' observe that only one bit travels at a time between the two points and F.

1owever' the disadvantage of serial communication is that it provides a slow mean of datacommunication. And with the advancement in computer development' faster means of

communication is re"uired. 1ence to fasten the communication more wires are used toconnect the components of the computer. In this way we can send multiple bitssimultaneously. This enables the data to travel faster. This type of communication is calledparallel communication.

The following diagram illustrates the parallel communication:

Fig 1.2 Parallel data Communication

In the preceding figure' observe that four bits travel at a time' through four wires'between the two points and F.

0e can draw analogy of the computer communication with cinema ticket booking. $upposea cinema hall has only a single ticket booking counter. The ticket clerk can handle only onecustomer at a time and since there is only one counter only a single customer can book aticket at any given time. This may result in long "ueue and more time for a customer toreach the booking counter and then getting the ticket. 1owever' if there are multiplewindows for booking tickets' result in multiple customers to book a ticket at any giventime. In addition' the "ueue will also get divided amongst the multiple counters resulting inshorter "ueue. This will result a customer to get the cinema ticket in much lesser time.

In the above analogy' if the cinema hall has a single ticket booking counter' then it is serialcommunication. And if the cinema hall has multiple ticket booking counters' then it is aparallel communication.

999 999

* &

9

9

9


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7

Basic Elements o' Computer

Hardware & Software#omputer consists of two basic building blocks called 1ardware and $oftware.

All the physical parts of the computer which can be felt are 1ardware components.Example: %otherboard' 1ard disk' $%+$' +rocessor' 3A% etc.

$oftware is set of programs containing set of instructions to perform the task. It can beclassified in to 8perating system and Application $oftware.

Operating SystemIt acts as an interface between #omputer and peripherals and optimi*es the utili*ation ofresources. It also acts as a mediator between 7ser and #omputer. It #onverts the Englishlike language to machine language 92s and 2s! and fed to computer for necessary

processing. The processed data which is in the form of machine language converts back toEnglish like language for 7ser understanding.

-iterally it is difficult to work with the +# effectively without 8perating $ystem. Example:0indows +' -inux etc.

Application Software$et of programs developed to perform a specific task.

Example: %icrosoft 0ord/ this is application software used to prepare letters with featureslike formatting the data' Dictionary etc.

Ho+ Computer ,orks

Introduction

A computer usually performs four maor operations or functions mentioned below

Input: Accepting data and instructions

+rocessing: +rocess the data based on instructions

8utput: +roduce the processed data to the output devices

$torage: $tores the dataInformation on the 1ard disk

The following block diagram illustrates the basic functionality of computer:

Fig 1.3 Basic Functionality of a Computer

I"P%T#ontrol 7nit

ST!RA-E

!%TP%T

Arithmetic and-ogical 7nit

Processing


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Input

This is the process of computer accepting the data or instructions through input devicenamely =eyboard for the necessary processing. In this process the raw data is converted

into machine language and fed to #+7 #entral +rocessing 7nit! for necessary processing.

Processing

This is the process of performing operations' such as arithmetic and logical operations'based on instructions. The #+7 takes data and instructions from input device andprocesses it. The processed data is then sent to the output or storage unit.

+rocessing unit consists of two parts mainly known as 5#ontrol 7nit6 and 5Art hermetic and-ogical 7nit6. The #ontrol unit controls the flow of data from various I8 devices andinternal components. The Arithmetic and -ogical 7nit performs the data processing. This isalso known as %icro +rocessor.

!utput

The processed data Information! from #+7 which is in the form of machine language willbe converted to user understandable language like English! and then fed to output devicelike monitor or +rinter.

Storage

The storage unit is used to store the data or Information permanently for future retrieval.It acts as an input' output device. It feeds the raw data stored within to the #+7 andstores processed data. 1ard disk is considered to be one of the main storage device.


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9

Components . Perip(erals o' Computer

Introduction to Computer Components . Perip(erals

A computer consists of several physical components and each physical component isdesignated to perform one of the operations discussed in the previous section. Thesephysical components of a computer are called computer hardware.

The computer hardware device can be attached internally or externally to the computer.Devices connected internal are called the +rimary components and connected external arecalled peripherals.

The following diagram shows some of the computer components.

Fig 1.4 Computer Organization


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Primar) Components o' Computer

(elow are some of the devices that are attached internally to the computer are called

+rimary components. %otherboard

o It is the %ain circuit board accommodates +rocessor slot' #hipset' &ront

side bus' #ontroller bus' 3A% $lots' Extension slots +#I!' #ontrollers 4#onnectors for internal components' +orts for =(D 4 %ouse' 7$( +orts'Display #onnector' Audio processing circuitry and connectors for $peakers4 %icrophone' +arallel port for printer connection' $erial port for datacommunication etc..

+rocessor

o It is the brain of the computer. Data +rocessing and Execution of the task

is performed in it.

#+7 1eat sink 4 &an

o 1eat sink and &an is placed on the top of the processor to maintain the

temperature at pre defined level. The $peed of fan can be controlled basedon the heat generated by the processor.

3A%

o 3A% 3andom Access %emory! is a $emiconductor %emory used as a

temporary storage supporting the processor. #+7 retrieves the raw datafrom 3A% and pushes the processed data to it.

&loppy Disk Drive

o 7sed to read' write &loppy disks

1ard disk

o It is a %agnetic memory device used for bulk permanent storage. The

data stored in this can be retrieved based on re"uirement.

8ptical Drive

o 8ptical drives are used to read 0rite Depends on Drive! data from the

optical media called #D38%' D,D 38%s. These 8ptical media can storehuge amount of data ranging from G99 %( to ?.H ( compared to &loppydisk capacity of .?? %(. $ome of the advantage are data portability anddata retention.

+rocessing Devices

%otherboard

$%+$

o $witch %ode +ower $upply $%+$! #onverts the A# input into D# out put.

The 8ut put ,oltages are constant irrespective of the input ,oltage. The D#8ut of the $%+$ will be fed to various components of #omputer

+ort

#onnector

Add on #ards / %odem' )etwork card' +#I Express #ard etc.

o Add on cards are used to expand the computer functionalities. These are

attached to the +#I slots available on the motherboard. These are used

based on re"uirement.


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%odem card: enables the computer to connect to the internet

)etwork card: enables the computer to connect to the -ocal

)etwork

+#I Express card: 7sed display high end CD graphics

In addition to above mentioned devices' there are two more devices that are thoughattached externally are called computer components. These are keyboard and mouse.

Computer Perip(erals

(elow are some of the devices that are attached externally to the computer' exceptkeyboard and mouse' are called computer peripherals. The various computer peripheraldevices are:

=eyboard 4 %ouse

o =eyboard is an Input device used to input the data to the computer.

o %ouse is a pointing device used to select a particular option shown on themonitor

+rinter

o +rinter is an output device used to take the print out of files. It could be a

document or a photograph. The "uality of the printout depends on type ofprinter we are using.

$canner

o $canner is used to digiti*e physical documents +hotographs.

8utput devices %onitor #3T-#D!

o %onitor is an output device displays images and texts generated by

computer.

+ower $upply

$canner

oystick

o It is a gamming devices used while playing animated games in computers

%icrophone

o %icrophone used to record the voice' Dictate to a computer #onverts to

text' chat!'

0ebcam

o 0ebcam used for lower level video conferencing through internet. In this

techni"ue the users can see live each other during the session.

Input De/ices

,(at are Input De/ices0

0hen you work with the computer you enter your data and instructions through somedevices to the computer. These devices are called input devices. The input devices are

necessary to convert data or instructions enter into the computer to a form which can be


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recogni*ed by the computer. A good input device should provide timely' accurate andmeaningful data to the main memory of the computer for processing.

$ome of the commonly used input devices are:

=eyboard

%ouse

$canner

oystick

%icrophone

Digital camera

e)board

=eyboard is the standard input device attached to all computers. The layout of keyboard isust like the traditional typewriter of the type J0E3TF. The computer keyboards consist ofrectangular or near/rectangular buttons' called KkeysK. The characters are engraved orprinted on the keys. A standard keyboard contains a total of 9 to 9? keys.

In most cases' each press of a key corresponds to a single written symbol. 1owever' toproduce some special characters' re"uires pressing and holding several keyssimultaneously or in se"uence.

In addition to standard keys' a keyboard contains some extra command keys and functionkeys. These keys do not produce any symbol' but instead affect the operation of thecomputer or the keyboard itself.

There are various variations of keyboard that are available in market such as multimediakeyboard' Internet keyboard' folding keyboard and wireless keyboard.

The following figure shows a standard and a multimedia keyboard:

Fig 1. !ey"oards

$ouse

%ouse is the pointing device used to move a graphical pointer on the screen. This graphicalpointer is also called cursor. 7sing mouse you can give commands' draw images and

perform other input tasks.


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+hysically' a mouse consists of a small case' held under one of the userLs hands' with oneor more buttons. 0hen you roll the mouse across a flat surface' the screen censors thedirection of mouse movement and the cursor on the screen follows the motion of themouse.

A mouse also has two or three buttons on its top surface. These buttons can be clicked ordouble/clicked to perform tasks' like to select an icon on the screen or to open the selecteddocument.

There are several variants of mouse available in market today. 8ne of the most popular isoptical mouse. An optical mouse doesn2t have a ball. It uses a laser to sense the motion ofthe mouse instead.

The following figure shows an image of an optical mouse:

Fig 1.# $n Optical %ouse

Scanner

The keyboard can input only text through keys provided in it. If we want to input a picturea keyboard cannot do that. To input a picture we need a scanner.

A scanner is an optical device that analy*es images' printed text' or handwriting andconverts it to a digital image.

The common scanner devices are: %agnetic Ink #haracter 3ecognition %I#3! reader

8ptical %ark 3eader 8%3! scanner

8ptical #haracter 3ecognition 8#3! scanner

(arcode reader

%I#3 3eader

%I#3 is widely used by banks to process large volumes of che"ues and drafts. The bottomline on all che"ues and drafts has special characters printed in special font called %I#3.#he"ues are put inside a %I#3 reader. As they enter the reading unit the che"ues passthrough the magnetic field which causes the read head to recogni*e the character of theche"ues.

The following is an image of a %I#3 reader:


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Fig 1.& $ %'C( (eader

8%3 $canner

8%3 techni"ue is used when students have appeared for obective type tests and they hadto mark their answer by darkening a s"uare or circular space by pencil. These answersheets are directly fed to a computer for grading where 8%3 is used.

The 8%3 scanner puts a shining beam of light on the document and detects the markedarea from unmarked ones. This is possible because a marked area reflects more light incomparison to an unmarked area.

The following is an image of a 8%3 scanner:

Fig 1.) $n O%( Scanner

8#3 $canner

8#3 is used for direct reading of any printed character. It translates images of handwritten

or typewritten text' usually captured by a scanner' into machine/editable text. 8#3 isgenerally used in the field of pattern recognition' artificial intelligence and machine vision.

$uppose you have a set of hand written documents. Fou put a document inside thescanner of the computer. The characters in the document are compared with a site ofpatterns stored inside the computer. 0hichever pattern is matched is then successfullyconverted tomachine/editable text. This is called a character read. +atterns that cannot be identifiedare reected.

8#3s are more expensive than %I#3' though they are better than %I#3.

The following is an image of an 8#3 scanner:


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Fig 1.* $n OC( Scanner

(arcode 3eader

(arcode reader is used to read the barcodes printed on practically every item purchasedfrom a department store. This helps in keep tracking of items in the store and also reducesthe instances of shoplifting.

A barcode is a machine/readable representation of information in a visual format on asurface. This represented using dark ink on white substrate to create high and lowreflectance which is converted to s and 9s. 8riginally barcodes stored data in the widthsand spacing of printed parallel lines' but today they also come in various other patterns

such as dots' concentric circles' and text codes hidden within images.A barcode reader consists of a light source' a lens and a photo conductor that translatesoptical impulses into electrical ones.

The following figure shows a barcode reader:

Fig 1.1+ $ Barcode Scanner

o)stick

A oystick is an input device that is used to control onscreen obects or cursor bymaneuvering a small lever called stick instead of using the cursor keys or mouse.. It iscommonly used for controlling player movements in video or computer games.


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%ost oysticks are configured for two/dimensional movement. %oving the stick left or rightsignals movement along the axis' and moving it forward up! or back down! signalsmovement along the F axis.

There are certain oysticks that control three/directional movement also. In oysticks that

are configured for three/dimensional movement' twisting the stick left counter/clockwise!or right clockwise! signals movement along the M axis.

The following is an image of a oystick:

Fig 1.11 $ ,oystic-

$icrop(one

A microphone is an input device used for recording audio in a computer. 1owever' to dothis you also need a sound card installed in your computer. A sound card converts ananalog sound signal to digital form and a digital sound signal to its analog form.

Fou can use speech recognition software with your microphone to dictate text' navigateprograms and select commands.

The following figure shows a microphone:

Fig 1.12 $ %icropone

Digital Camera

A digital camera is an input device used for capturing and storing still images. Fou canconnect a digital camera to a computer and transfer the images from the digital cameradirectly to the computer. The following figure shows a digital camera:


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Fig 1.13 $ /igital Camera


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!utput De/ices

Introduction to !utput De/ices

As similar to input devices re"uire for inputting data' the computer displays or print theoutput on devices called output devices. $ome of the commonly used output devices are:

,isual Display 7nits ,D7s!

+rinters

$peakers

2D%s

The most popular output device is the ,D7' which is the standard output device. It is alsocalled the monitor. It is a piece of electrical e"uipment which displays images and texts asgenerated by a computer without producing a permanent record.

A monitor is usually consists of either a cathode ray tube #3T! or some form of flat panelsuch as a T&T -#D display. The following is an image of a #3T monitor:

Fig 1.14 $ C(0 %onitor

The following is an image of a -#D monitor:

Fig 1.1 $ C/ %onitor


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19

The monitor comprises of a display device' circuitry to generate a viewable image or textfrom electronic signals sent by the computer' and an enclosure or case.

A ,D7 can be either monochrome or colored.

#haracteristics of %onitor

The two important features that characteri*e a ,D7 are resolution and aspect ratio. Theresolution refers to the number of distinct pixels in each dimension of a monitor that canbe displayed. A pixel short for +icture Element! is a single point in a graphic image. Itgenerally represents a single dot.

The aspect ratio is the ratio of the width of a graphic image to the height of the graphicimage.

In addition to the above mentioned characteristics' computer monitor exhibits certainother characteristics which are:

$onitor si3e

The monitor si*e' also called screen si*e' is specified in two ways.

o 0e nominal size

It is the si*e by which monitors are advertised and referred to. This si*e isthe diagonal measurement of the actual display screen itself. 1owever' thefront be*el The metal or plastic frame surrounding the display screen iscalled a be*el. 8n -#D displays' the be*el is typically very narrow.! of themonitor hides part of the display screen' making the usable si*e of themonitor less than stated.

o 0e iea"le 'mage Size 'S5

It is the portion of the monitor that is actually visible. Typically' ,I$ is an

inch or so less than nominal. &or example' a nominal G/inch monitor mayhave a H.9/inch and larger monitors are still "uite expensive' and are used primarily bygraphic artists and others who re"uire huge displays.

Re'res( rate

The refresh rate is the number of times an image is repainted or refreshed persecond. The refresh rate is expressed in hert* 1*!. This means that if a monitor2s

refresh rate is specified as GH 1*' the image is refreshed GH times in a second.

The refresh rate is dependent on the video card used. Fou can change the refreshrate in the display properties. 1owever' if you change the refresh rate that thedisplay or video card cannot support' the display goes blank or the image becomesdistorted. It is recommended to consult the display and video card manuals beforechanging the monitor refresh rate.


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%onitor Types

8n the basis of resolution and aspect ratio' we can classify monitors broadly in different

categories shown in the following table.

Monitor

Type

Full name Description Display

resolution

(pixels)

Aspect

ratio

%DA %onochromeDisplay Adapter

Introduced in O9PCH9 text! G>:CH

#A #olor raphics

Adapter

Introduced in O


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MonitorType

Full name Description Display resolution

(pixels)

Aspectratio

0A 0idescreenExtendedraphics Array

A version of the Aformat' which isbecoming popular insome recent notebookcomputers.

>9O>>k!

>OBk!

B:O orB:9

$A $uper A Introduced in OO9 byI(% as the mostcommon resolution onGK' ?C9k!

H:?

0AQ 0idescreenExtendedraphics Array+-7$

A version of the 0Aformat. This isbecoming popular inOK widescreen -#Dmonitors where it isthe native resolutionand also in somerecent notebookcomputers.

??9PO99>OBk!

B:9

7A 7ltra A A de facto Truecolorstandard.

B99P>99O>9k!

?:C

07A 0idescreen 7ltraExtendedraphics Array

A version of the 7Aformat. This displayaspect ratio wasbecoming popular inhigh end HK and GKwidescreen notebookcomputers.

O>9P>99>C9?k!

B:9

JA Juad Extendedraphics Array

>9?HB9PB99?9OBk!

B:9

J7A Juad 7ltraExtendedraphics Array

C>99P>?99GB>H9PC>99BC


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MonitorType

Full name Description Display resolution

(pixels)

Aspectratio

1$A 1exRadecatupleS$uper Extendedraphics Array

H>9P?9OB>9OG>k! H:?

01$A 0ide1exRadecatupleS$uper Extendedraphics Array

B?99P?9OB>B>?k!

>H:B

17A 1exRadecatupleS7ltra Extendedraphics Array

B?99P?9k!

?:C

017A 0ide

1exRadecatupleS7ltra Extendedraphics Array

GB


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Dot %atrix +rinter

A dot matrix printer or impact matrix printer refers to a type of computer printer with a

print head that contains a cluster of pins. The pins run back and forth on the page andprint by impact' striking an ink/soaked cloth ribbon against a paper similar to a typewriter.

0ith each pin strike' a dot is printed on a paper. #ollection of several such dots producesthe desired text or image on the paper.

A dot matrix printer can be classified as:

-ow resolution dot matrix printer: 7ses O pins

1igh resolution dot matrix printer: 7ses >? pins

A dot matrix printer can print at a speed of H99 cps.

Dot matrix printers can be used in low/cost' low/"uality applications like cash registers' orin demanding' very high volume applications like invoice printing.

The following is an image of a dot matrix printer:

Fig 1.1# $ /ot %atri6 Printer

Inket +rinter

An inket printer refers to a type of printer where the printer sprays tiny droplets of inkonto the media. These ink droplets are slightly electrically charged. The ink droplet2s

placement on the media is then determined by the charge of a cathode and electrodebetween which the ink moves towards the media.

Inket printers can produce both color and black/and/white printing. They offer printingspeed of >/? ppm and resolution of C99/B99 dpi.

Inket printers are inexpensive' have low operating cost and produce high/"ualityprintouts. (ecause of this inket printers are the most widely used consumer printers.


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The following is an image of an inket printer:

Fig 1.1& $n 'n-7et Printer

Dye/$ublimation +rinter

A dye/sublimation printer refers to a type of printer where the printer uses a printingprocess that utili*es heat to transfer dye to a medium such as a printer paper' plastic cardor poster paper. The process is to lay one color at a time using a ribbon that consists ofcolor panels.

Dye/sublimation printers are targeted primarily for printing high/"uality color applications'such as color photography and are less well/suited for text. Therefore' they are commonlyused as dedicated consumer photo printers.

The following is an image of a dye/sublimation printer:

Fig 1.1) $ /ye8Su"limation Printer

-aser +rinter

A laser printer refers to a type of printer where the printer uses a laser beam to produceimage or text on a paper. The main components of a laser printer are drum and toner. Thelight of the laser modify the electrical charge on the drum wherever it hits. The drum isthen rolled through toner' which is picked up by the charged portions of the drum. &inally'

with the help of heat and pressure particles on the toner are transferred to the paper. Thisis also the way copy machines work.


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25

A laser printer can print both in black/and/white and color. It can print with a speed of?/B ppm and the resolution of C99/>99 dpi and higher.

-aser printers are known for high "uality prints' good print speed' and a low (lack and0hite! cost/per/copy. 1owever' they are "uite expensive and hence are mostly used in

corporate world.The following is an image of a laser printer:

Fig 1.1* $ aser Printer

+lotter

A plotter is a speciali*ed graphical printer that is operated by moving a pen over thesurface of a paper. It uses mechanical' inket or thermal technology to create large formatimages. (ecause of this' plotters are used for printing technical drawing or #AD applicationimages. A niche use of plotters is in creating tangible images for visually handicappedpeople on special thermal cell paper.

The following is an image of a plotter:

Fig 1.2+ $ Plotter


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Speaker

$peakers are used to produce audio output. The speakers work in conunction with sound

card to produce the audio output. A sound card translates digital signals into analog signalthat drive the speakers. The computer speakers vary widely in terms of price and range.

$ome of the common features that are included in most of the speakers are:

A) -ED indicator

A C.Hmm


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27

E4ternal Inter'ace Components

An !/er/ie+ o' E4ternal Inter'ace Components

As discussed earlier' the processor controls the function of the entire computer. 1ence theprocessor needs some mechanism to exchange data with other components of thecomputer system. The processor uses dedicated bundle of wires to exchange data withother computer components. These dedicated bundles of wires are called buses. The busesare the processorLs external interfaces' which can be different even for otherwise similar#+7s.

There are several different types of buses on a computer system. (ut at the processorlevel the important buses are the processor bus and memory bus.

Processor Bus

The processor bus is the set of wires used to carry information to and from the processor.

The processor bus further constitutes of two parts:

+rocessor data bus: $pecifies that part of processor bus that carries the actual

data to and fro from the processor and the computer components.

+rocessor address bus: $pecifies that part of processor bus that carries the

information specifying where in memory the data is to be transferred to or from.

A processor bus is also called the front/side bus &$(!.

$emor) Bus

The memory bus is the set of wires used to carry information to and from the mainmemory of the computer. $imilar to processor bus' the memory bus is also classified into

two categories: %emory data bus: $pecifies that part of memory bus that carries the actual data

transferred to and fro from the computer main memory.

%emory address bus: $pecifies that part of memory bus that contains the

information about the memory locations from where the memory data is to be readfrom or written to.

Peeking Inside t(e $icroprocessor

In addition to the external interfaces' the microprocessor has several internal components.A-7 and #7 are the two most important internal components of a microprocessor. Inaddition to these two components' microprocessor has several other internal components.These are listed below:

Transistors

Integrated #ircuits

3egisters

The #lock

(I7

- #ache

-> #ache


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Integer Execution 7nit

&+7

(ranch +rediction 7nit

The following figure illustrates some of the components of a microprocessor:

Fig 1.22 %icroprocessor Components ayout


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29

Transistors

Transistors are the most basic components of microprocessors. These are small electroniccomponents which can have either onoff state. Although by looking at transistors' itseems simple in design' but its development re"uired several years of careful research.

+rior to the development of transistors' computers are constructed using slow andunproductive vacuum tubes and mechanical switches to process information. These earliercomputers are constructed using thousands of vacuum tubes and several mechanicalswitches which make their si*es huge. They are so huge that technicians actually wentinside the computer to KprogramK by turning on and off specific tubesU

%any materials' including most metals' allow electrical current to pass through them.These are called conductors. %aterials that do not allow electrical current to pass throughthem are called insulators. 1owever' in addition to conductors and insulators' there isanother category of materials which are called semiconductors.

The semiconductors are the materials whose conductivity lies between conductors andinsulators. The degree of conductivity of the semiconductors can be adusted by addingimpurities in the material during production. An example of a semiconductor is the pureform of the silicon. $ilicon is the most favoured material for constructing transistors.

Integrated Circuits

In the late OH9s' a maor development in transistor technology took place. A team ofengineers put two transistors on a thin slice of silicon' called silicon wafer' creating theworldLs first integrated circuit I#!.

An integrated circuit I#! is an electronic device consisting of a number of very small/si*edtransistors and other circuit elements' like capacitors and resistors. An I# functions in the

same way as manual assembly of circuits constructed using separate electroniccomponents.

1owever' the advantage of I# is that it is a fraction of the si*e of the earlier circuits anduses a fraction of the power. The development of I#s makes the way for the developmentof modern day compact computers.

A maor usage of I#s is in the designing of the microprocessor.

Registers

3egisters are local storage areas within the processor that are used to store data used bymicroprocessor for data manipulation. +hysically' registers are rows of very small switches'which can be set on or off.

The microprocessor uses registers to hold data while it works on a task. Any changes indata during an operation are also stored in a register. The data stored in registers are thensent to other components after the microprocessor completes the task that it wasperforming.

The number and width of register varies from one computer to another. The width ofregisters also has an impact on the computer performance. The wider the register' themore bits the microprocessor can handle at any given time' resulting in improvement ofcomputer performance. As register width moved from ? to < to B to C> to B? bits' theperformance of the computer also improved considerably.


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T(e Clock

Timing is essential in any computer operations. 0ithout any time management' confusionwould definitely arise. Timing allows the electronic components of the computer tocoordinate and execute all internal commands in proper order. This coordination based ontime is called synchroni*ation.

Timing is achieved by placing a special conductor in the #+7 and providing voltage pulse toit. This special conductor is called the clock. Each voltage pulse received by the clock iscalled a clock cycle. The clock generates a regular beat' similar to the ticking of your wallclock' and all the computer operations are times to this beat.

Fou can draw the analogy to several violinists playing their violins in synchroni*ation. Thismeans that all the violinists move their bows at the same time. (ecause of thissynchroni*ation' you get to hear the music instead of some umble of notes.

The speed of a clock is measured in terms of number of pulses generated by the clock in

one second. This is called the fre"uency of the clock. And the unit to measure the clockfre"uency is %1* megahert*!. %ost modern day microprocessor has the clock fre"uencyin 1* gigahert*!.

BI%

The bus interface unit (I7! is that component of the microprocessor that communicateswith the rest of the computer. Its name comes from the fact that it deals with theprocessor bus. The main function of (I7 is to generate all signals that go frommicroprocessor to other computer components and to respond to all signals that go to themicroprocessor.

#1 Cac(eThe - cache level cache! is a small' fast memory cache that is built/in to amicroprocessor. (ecause this cache is closest to the microprocessor it is also called primarycache.

These - cache memories help the computer to improve its speed to access thefre"uently/used data. The typical - cache ranges from < =( to B? =(' with larger memorycapacity on the newer processors. 8lder processors in fact have no primary cache at all.

The - caches are very fast because they are integrated into the processor because ofwhich these memories run at the same speed as that of the processor.

#5 Cac(e

In addition to - cache' most computers have additional cache memory called -> cache.The -> cache is called the secondary cache.

The -> cache level > cache! is the cache memory that is not built into the processor itselfbut is a separate chip. It stores some of the recently used data that doesnLt fit in thesmaller primary cache. 0henever we are referring to a cache memory' we are actuallyreferring to the -> cache.

Integer E4ecution %nit

%ost of the work done on a computer is done with integers and data that are representedby the integers. The integers include the characters as well. 1owever' the integers do notinclude any decimal point numbers.


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31

The integer execution unit IE7! is that component of the microprocessor which executesany arithmetic or logical operation performed on integer data. It is a part of the A-7.

Earlier microprocessors used to have only single IE7' and instructions are processedse"uentially. 1owever' the new microprocessors use to have several different IE7s'

allowing more than one instruction to be executed simultaneously. This feature of themicroprocessor is called superscalability and the microprocessor that shows superscalability are called superscalar microprocessors. The superscalability feature improvesthe performance of the microprocessor. %ore advanced processors may have somededicated execution units designed only for executing certain types of instructions.

6loating Point %nit

$imilar to IE7' the floating point unit &+7! is also a part of A-7. It is that component ofthe microprocessor which executes any arithmetic or logical operation performed onfloating point data. The floating point data includes the decimal point numbers.

Earlier microprocessors used to have only the integer unit' which also performs floatingpoint operations' which is very slow. 1ence to improve the performance' some

microprocessors had a second chip dedicated to performing floating point calculations. Thissecond chip is called a math coprocessor.

The math coprocessor work in combination with the regular microprocessor to improveperformance for mathematical applications' such as scientific applications' spreadsheetsetc. 1owever' the math coprocessors are not nearly as efficient as the &+7' which areintegrated into the microprocessor. All the modern day computers have the &+7 built/in themicroprocessor.

Branc( Prediction %nit

%ost modern day microprocessors have a special component called branch prediction unit(+7!. The (+7 is responsible to perform the branching instructions as specified in an

instruction.A branch instruction is a point in the instruction stream of a program where the nextinstruction is not necessarily the next se"uential one. There are two types of branchinstructions: unconditional branches and conditional branches. The unconditional branchespass the control of execution of instructions to any specified part in the instruction stream.This may or may not be the next se"uential set of instructions. It is usually performedusing 8T8' (3A)#1 or 7%+ instructions in a program.

In the conditional branches' the decision to execute or not to execute a set of instructiondepends on some condition that must be evaluated in order to make the correct decision.The set of instruction to be executed based on a condition is called a branch. Themicroprocessor makes a guess of the set of instructions to be executed. If themicroprocessor makes a correct guess' the execution continues without any delays.

1owever' if the guess is wrong' which is called a misprediction' the set of instructions thatwere guessed by the microprocessor for execution' have to be discarded and the executionstarts over from the mispredicted path. This results in increased execution time for themicroprocessor.

1ence to overcome this problem' (+7 is integrated into the modern day microprocessor.The (+7 consists of two components' the (ranch Target (uffer (T(! and the predictor.The (T( is the memory area where the microprocessor stores the target addresses of theprevious branches. 1owever' this buffer is limited in si*e' and hence can store only limitednumber of target addresses. Any previously stored addresses may be removed from thememory area if a new address needs to be stored instead.

The predictor is that part of the (+7 that makes the guess on the outcome of a branch.

The use of (+7 to perform all branch instructions makes the main processor available to

perform other tasks. The (+7 also saves the increased execution time for a microprocessor


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resulted because of misprediction. As a result' the use of (+7 overall improves theperformance of the microprocessor.

Ho+ $icroprocessor ,orksThe microprocessor performs all its task using the following four basic operations:

&etch: -oads the instruction to be executed into the microprocessor from computer

memory. (ut for modern microprocessors' the speed of microprocessor is muchfaster than the computer memory. This means that the instructions cannot beread fast enough to keep the microprocessor busy. 1ence to overcome thisproblem prefetching is done.

+refetching is the process of getting the next instruction to be executed from thememory well before it will need it. In this way' the processor will not need to waitfor the memory to answer its re"uest. In most modern microprocessors' there is aspecial component of microprocessor to do this task. It is called +refetch unit.

In addition to prefetching' there is another component in microprocessor thatimproves its performance. It is called Instruction #ache. It is a small memory areawhere the copies of instructions to be executed are stored and which can bedirectly accessed by the microprocessor.

Decode: Transfers the data into binary code that can be understood by the

microprocessor. There are special components in microprocessor to do this calledDecode unit.

Execute: +erforms the specified arithmetic and logical function on the data.

$tore: $tores the result of the execution in computer memory or registers.

The above operations that are performed by a microprocessor are collectively calledfetch/execute cycle or instruction cycle.


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33

The following illustrates the fetch/execute cycle of a microprocessor:

Fig 1.23 8 Fetc896ecute Cycle

-et2s understand how a microprocessor works with a simple example of adding twonumbers' H and ?' and obtaining the result. To illustrate this' we divide the operation intonumber of subtasks. These subtasks are listed below:

8n pressing H

8n pressing Q

8n pressing ?

8n pressing V


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On Pressing

8n pressing the number H' following steps are performed by the microprocessor:

. 0hen the user presses the number key' H in the above example' the keystrokecauses the microprocessorLs +refetch unit to ask for what instruction need toperform on the new data.

>. The data' in this case the number H' is sent through the address bus to thecomputer memory and is stored in the Instruction cache. The code assigned to thedata is sayH V x.

C. The +refetch unit then asks the Instruction #ache for a copy of the code KH V xKand sends it to the Decode unit for further processing.

?. The Decode unit then translates the instruction referred by the code 5H V x6 intobinary format. This binary data is then send to the #ontrol 7nit with furtherinstruction on what to do with the data.

H. The #ontrol 7nit on receiving the instruction store the number' H' in the computermemory' x.

On Pressing :

8n pressing the Q symbol' following steps are performed by the microprocessor:

. 0hen the user presses the ;Q2 symbol' microprocessor again asks its +refetch unitwhat to do with the new data.

>. The data' in this case the symbol' Q' is sent through the address bus to thecomputer memory and is stored in the Instruction cache.

C. The +refetch unit then retrieves the Q symbol from Instruction cache and sends it

to the Decode unit for further processing.

?. The Decode unit then translates the Q symbol into binary format. This binary datais then send to the #ontrol 7nit with further instruction on what to do with thedata.

H. The #ontrol 7nit on receiving the instruction alerts the A-7 that an ADD operationwill be performed.

On Pressing 4

8n pressing the number ?' following steps are performed by the microprocessor:

. )ext' when the user presses the number' key' ?' microprocessor again asks its

+refetch unit what to do with the new data.>. The data' in this case the number ?' is sent through the address bus to the

computer memory and is stored in the Instruction cache. The code assigned to thedata is say? V y.

C. The +refetch unit then asks the Instruction #ache for a copy of the code K? V yKand sends it to the Decode unit for further processing.

?. The Decode unit then translates the instruction referred by the code 5? V y6 intobinary format. This binary data is then send to the #ontrol 7nit with furtherinstruction on what to do with the data.

H. The #ontrol 7nit on receiving the instruction store the number' ?' in the computermemory' y.

B. The #ontrol 7nit then sends the value stored in memories' x and y' to the A-7.


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35

G. The #ontrol 7nit next sends the actual ADD command to the A-7.

Duo processor. Each new processor hasbrought improved performance and introduced new technology. (ut whatever be theprocessor' there are some basic factors that are primarily used to udge the performanceand capability of a #+7 design:

#lock speed: 1igher the clock speed' the faster will a processor executes an

instruction.

)umber of transistors: %ore the number of transistors' the faster will be the

processing power.

3egisters: -arger the si*e of the register' more instructions can be executed in a

single step.

External data bus: -arger the data bus si*e' more data can be transferred between

the processor and other components. As a result' the processor can executeinstructions on a large amount of data which in turn will reduce the number ofexecutions. This improves the processor performance.

Internal cache: %ore the cache memory capacity' faster will be the processor

speed. (ut cache are expensive memory' hence the best approach is to effectively

use the existing cache capacity to give better processor performance.


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37

e) Components o' a Hard DiskA hard disk consists of several key components which are listed below:

+latters and %edia

3ead0rite 1eads

1ead $liders' Arms and Actuator

$pindle %otor

#onnectors and umpers

-ogic (oard

Integrated #ache

The following figure shows some of the key components of a hard disk drive:

Fig 1.24


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Read8,rite Heads

The readwrite heads of the hard disk are the interface between the magnetic physicalmedia on which the data is stored and the electronic components that make up the rest of

the hard disk and the +#!. The readwrite heads are responsible for converting bits tomagnetic pulses and storing them on the platter when data is written on the hard disk. Thereadwrite head then again converts back the magnetic pulses stored on the hard disk intobits when data is read from the hard disk.

Actuator Assembl)

The readwrite heads of a hard disk are responsible for reading data and writing data onthe hard disk. To perform its task effectively' the readwrite head must be held in a fixedposition relative to the surface it is reading and should also be allowed to move from trackto track to allow access to the entire disk surface area. The surface on which thereadwrite heads are mounted is called the actuator assembly. The actuator assemblylooks similar to a comb with its teeth inserted between the platters.

An actuator assembly is further composed of three parts: head slider' head arm andactuator. The component of the actuator assembly on which heads are actually mounted iscalled the head slider. The sliders are suspended over the surface of the disk by the meansof the head arms. The head arms are all combined together into a single structure that ismoved around the surface of the disk by the actuator. The actuator is the device used toposition the head arms to different tracks on the surface of the platter.

Spindle $otor

The spindle motor' also called the spindle shaft' is responsible for moving the plattersaround that make the hard disk operational. The spindle motor provides stable' reliableand consistent turning power to the hard disk to function it properly.

Hard Disk Connectors and umpers

(efore we go into discussing connectors and umpers used in a hard disk' let2s first discusswhat umpers areW umpers are small devices that are used to directly control theoperation of hardware devices' without using any software. A umper has two maincomponents:

umper: umper itself is a small piece of plastic and metal that is used to connect

or remove the hardware device from the computer.

umper +ins: A set of pins' across two of which a umper is placed to make a

specific connection.

A hard disk uses several different connectors and umpers to connect it to the rest of the

system. The number and type of the connector depend on the number of factors like themanufacturer of the drive' data interface it uses to connect to the system' and any specialfeature that the drive may have. Instructions for setting common umpers are usuallyprinted right on the drive. In addition' full instructions for setting of all umpers will be inthe productLs manual or on the manufacturerLs web site.

The different type of connectors and umpers used in a hard disk are:

+ower #onnector

Data Interface #onnector

IDEATA #onfiguration umpers

$#$I #onfiguration umpers

-ED #onnector


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39

+ower #onnector

1ard disk drives use a standard' ?/pin male connector plug to connect to the powerconnectors coming from the power supply. This power connector for the hard disk provides

QH and Q> voltage to the hard disk.

Data Interface #onnector

%odern hard disk drives use one of two interfaces: Integrated Drive Electronics IDE! Xalsoknown as AT Attachment ATA!Y and its variants' or $mall #omputer $ystem Interface$#$I!. 1owever' it can be easily identified which interface is being used by simply lookingat the back of the hard disk. This is how you can identify the hard disk interface beingused:

IDEATA or its variant hard disks have a ?9/pin connector at its back.

$#$I hard disks have a H9/pin' B SCS' and oter types of ard dis-s ill "e discussed in te section ?


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Termination Activate: The devices on the ends of the $#$I bus must terminate the

bus to function it properly. If the hard disk is at the end of the bus' setting thisumper will cause it to terminate the bus for proper functioning. )ot all systemshave this umper.

Disable Auto $tart: This umper specifies the hard disk not to startup automaticallywhen the power is supplied. Instead' it instructs the hard disk to wait for a startcommand over the $#$I bus. This umper is also not present on all hard disks.

Delay Auto $tart: This umper instructs the hard disk to wait for sometime before

being started automatically' when the power is applied.

$tagger $pin: This umper is an enhanced version of the Delay Auto $tart umper.

0hen this umper is set' the hard disk wait for sometime' this is calculated bymultiplying a user/defined constant with the $#$I device ID. This umper setting isuseful in the case when a system have many hard disks and setting this umperensures no two drives on the same $#$I channel start up simultaneously.

)arrow0ide: $ome hard disks have a umper to control whether they will function

in narrow or wide mode.

Disable +arity: $ome hard disks have this umper to turn off parity checking on the

$#$I bus. This is especially for compatibility with host adapters that donLt supportthe feature of parity checking.

-ED #onnector

The hard disks use an -ED to indicate its activity. This -ED also enables a user todetermine whether a system is active or not. This hard disk -ED is mounted on thecomputer case itself. In earlier computers a for the hard disk -ED wire run to a two/pinconnector on the hard disk itself. Though this worked fine in case of single hard disk butbecomes problem in case of systems having multiple hard disks. To solve this problem' thecase -ED was made to connect to the hard disk controller. This hard disk controller is

responsible for controlling any hard disk activity.%odern computers have integrated IDEATA hard disk controllers built into the chipset onthe motherboard. (ecause of this the -ED is usually connected to special pins on themotherboard itself.

Hard Disk #ogic Board

All modern hard disks contain an intelligent circuit board built in the hard disk unit itself.1owever' in early hard disks all of the control logic for controlling the hard disk operationswas placed into the controller plugged into the +#. (ut with newer drives with advancefeatures and high performance' the placing of control logic on the controllers becomesimpractical. In addition' with the reduction in the si*e of electronic components' the harddisk manufacturers move most of the control functions to the drive itself.

The logic board is responsible to control hard disk functions' and as hard disks becomefaster and more sophisticated more functions are added to the logic board. This results inlogic board being designed with support to handle more complicated head technologies'faster interfaces' and higher bandwidth data streaming from the disk itself.

TodayLs hard disks contain logic boards that are in most ways more sophisticated than anentire early +#U In fact' most of the modern hard disk logic boards contain more memoryand faster internal processors than the +#s of even the mid/O


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41

from the disk' and also Kpre/fetchK information that is likely to be re"uested in the nearfuture.

The use of this cache greatly improves the hard disk performance by reducing the numberof accesses to the hard disk. %ost modern hard disks have internal cache memory of upto

< %( although some high/performance $#$I drives have about B %( of internal cache.Note= en someone spea-s generically a"out a dis- cace> e or se is usuallyreferring to te system cace and not to te ard dis- cace.

-eometr) o' Hard Disk Dri/e

!/er/ie+ o' Hard Disk Dri/e -eometr)

The geometry of a hard disk drive is the organi*ation of data on the platters. The geometry

of the hard disk drive specifies how and where the data is stored on the surface of eachplatter. The geometry of the hard disk drive is usually specified by the following numericalvalues:

1eads

#ylinders

$ectors per track

0rite precompensation

-anding *one

Heads

The head of a hard disk drive represents the total number of sides on all the platters thatstore data. &or example if a hard disk drive has < platters' the hard disk drive can havemaximum upto B heads.

$ome hard disk drive manufacturers use a technology called sector translation. As per thistechnology a hard disk drive can have more than two heads per platter. Therefore as persector translation' it is possible that a hard disk drive can have > heads on only oneplatter. 1owever' irrespective of technology used for manufacturing hard disk drive' themaximum number of heads a hard disk drive can contain is B.

C)linders

All the data on a hard disk drive is stored on concentric circles on the surface of each head.Each concentric circle is called track. All tracks are numbered' starting from *ero' startingat the outside of the platter and increasing as you go in.

A set of all tracks of same diameter present on a head is called a cylinder. It is the numberof cylinders that is used for measuring the drive geometry and not the number of tracks.

The number of cylinders in a drive and the number of tracks on a platter in a drive areexactly same. (oth these numbers are determined by the manufacturer at the time ofmanufacturing the drive. In most hard disks' the number of cylinders is set by a magneticpattern called a servo pattern.

The number of cylinders affects the storage capacity of the hard disk drive. The more thenumber of cylinders the more the data can be stored on the hard disk. 1owever' themaximum number of cylinders on a hard disk is restricted by the (I8$ limitations.

Sectors per Track


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%ost hard disks subdivide the tracks into small arcs called sectors. Each sector can holdH> bytes of data. 1owever' the number of sectors is not a measuring unit for drivegeometry it is the number of tracks present on a sector. (I8$ limitations set the numberof sectors per track at BC.


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43

The following figure shows the relationship between sectors and tracks:

Fig 1.2 Sectors and 0rac-s

,rite Precompensation

In the older hard disks' each sector contains the same number of tracks. 1owever' thesectors present on the outside of a platter are physically longer than those closer to thecenter. (ecause of this difference in si*es of the sector make it difficult for the hard disk towrite on sectors especially on the inner sectors. As a result' the older hard disks re"uiresome kind of adustment while writing to the inner sectors. This adustment is called writeprecompensation. The setting in the (I8$ specifies at what track number thecompensation was to begin. This value is called write precompensation value.

The write precompensation value is however not found on modern hard disks but seen onolder hard disks only.

#anding 9one

The earlier hard disks are highly prone to damage when the machine is switched off. Assoon as the computer is switched off' the platters of the hard disk stop spinning' and theairflow that keeps the heads flying stops. This head will then land on the disk drive.1owever there is a possibility that the head lands on a cylinder that already contains data.This may result in disk damage. To avoid this situation an unused cylinder number isspecified in the (I8$ settings where the heads will land when the machine is switched off.This value is called the landing *one.

1owever' like write precompensation' this is also not applicable for the modern hard disks.This is because the modern hard disks have a mechanism to automatically write the heads

on a special area on the hard disk when the computer is switched off.


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Hard Disk !perational !/er/ie+

All hard disks are constructed similarly with a central spindle supporting one or moreplatters. Each platter has two surfaces' called heads' and each head is coated with amagnetic medium. %ost hard disks consist of multiple platters mounted concentrically onthe spindle' like stack of coins one coin placed over another!. The central spindle rotatesat several thousand revolutions per minute' thereby rotating the platters in tandem with it.

A small gap separates each platter from its adacent platters. 0ithin this gap' thereadwrite head mounted on an actuator assembly is placed to fit between the platters.The readwrite heads KfloatK on the cushion of air formed because of the rapid rotation ofthe platter. 0hen a disk rotates' the heads fly above the disk surfaces at a distance of onlymillionths of an inch. The actuator assembly then move the heads in tandem radiallytoward or away from the centre of rotation.

The heads are responsible for writing data on the hard disk surfaces. The data are written

on the tracks. Each track contains several discrete positions' called magnetic domains.Each magnetic domain can store a single bit of information as a binary 9 or . 0henwriting the data' the head exerts a magnetic force on the domain to change the state of adomain to a 9 or ' as appropriate. 0hen reading' the head simply determines the existingstate of a domain.

(ecause the magnetic domains are so near to each other' it is important for a head tolocate the correct track and sector when reading data from the hard disk. Early hard diskdrives used a stepper/motor to move the heads to where the track is supposed to be'without reference to its actual location. 1owever' the stepper/motor hard disks were lastproduced in about OO9.

-ater hard disk drives used a voice/coil actuator mechanism in conunction with adedicated servo surface. The servo surface also called servo track! is a dedicated surface

on a hard disk that stores only the servo information. The servo information is a specialmagnetic pattern that allows the hard disk drive to identify each storage location on thedisk. Therefore' the servo information is helpful in identifying the correct track.

A voice/coil drive does not search for an absolute track position. Instead' the headactuator assembly searches for the approximate position where it expects the track to belocated. The servo head then adust the positioning by searching for the servo track thatcorresponds to the desired track. (y locating the correct servo track automatically enablesthe disk drive to locate the correct track.

1owever' the hard disk designers were against the wasting of an entire surface and headon servo data. To overcome this problem the hard disk designers decided to allowcombining the servo data with the user data on a normal track. This does away with theneed of a dedicated servo surface and as a result all disk surfaces can be used to storeuser data. This mixing of servo and user data is called embedded servo information.

8ne more important point that you should know about regarding the mechanism of writingdata on a hard disk is how the data is written on a hard disk when the data does not fit ona single track. In such cases the hard disk drive first writes the data on the current trackand then writes the remainder of the data se"uentially to the next available track in thesame cylinder. 8nly if the capacity of the current cylinder is exceeded does the drive movethe heads to the next available cylinder.


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Hard Disk Dri/e T)pes

Introduction to Hard Disk Dri/e T)pes

In the O9/pin data cable and the other a C?/pin control cable. 1owever' both the $T/H9B?> and the E$DI hard disks have become obsolete now.

A modern +# uses one or more of the following hard disks:

IDE ATA!

$#$I

$ATA

IDE ATA; Hard DiskIntegrated Drive Electronics IDE! hard disks' also called AT Attachment ATA! or +arallelATA +ATA!' have been around for many years. The IDE hard disks integrate the diskcontrolling function in the hard disk unit itself. This reduces the cost of disk manufacturingthan having the disk controlling function separately. In addition' a data cache is added inthe hard disk itself to improve the disk performance. (ecause of the reduced cost and theimproved performance' the IDE hard disks became the most widely used hard disks in themarket.

The popularity of IDE hard disks gives rise to various IDE standards which are maintainedby Technical #ommittee TC of the )ational #ommittee on Information Technology$tandards )#IT$!. These standards include:

ATA/: It is the original IDE specification. ATA defines a standard ?9/pin interface

that supports two hard disks on a single cable. 1owever' ATA/ was withdrawn as astandard in OOO.

ATA+I ATA +acket Interface!: It is the first ATA standard that supported only the

hard disks. 1owever' manufacturers soon reali*ed that with the cost andperformance advantages IDE interface can be used for other devices also like #D/38% and tape drives.

ATA/>: It is an updated specification of the original ATA standard. It has faster data

transfer rate' improved +lug/and/+lay support and adds -ogical (lock Addressing-(A! scheme. -(A is the method used for specifying the location of blocks of datastored on computer storage devices like hard disks. -(A uses an indexing schemewhere blocks are located by an index' with the first block being -(AV9' the second-(AV' and so on. 1owever' ATA/> was withdrawn as a standard in >99.

ATA/C: It is a minor improved version of the ATA/> standard. It has better power

management' enhanced reliability' and the inclusion of $elf %onitoring Analysisand 3eporting Technology $%A3T! technology. $%A3T allows the hard disk towarn the operating system of any coming problems.

ATAATA+I/?: It merges ATA/C and ATA+I standards into a single integrated

standard and formali*es 7ltra D%A CC as a part of that standard.

ATAATA+I/H: It is a minor improvement to ATAATA+I/? standards and formali*es

7ltra D%A BB as a part of that standard.

ATAATA+I/B: It is an enhancement to ATAATA+I/H standards and formali*es 7ltra

D%A 99 as a part of that standard. It supports ?


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ATAATA+I/G: It is the final ATAATA+I standard and has relatively minor

enhancements to the ATAATA+I/B standard. It has some new commands for useby digital video recorders and formali*es the 7ltra D%A CC as a part of thestandard.

The above standards are actually theoretical specifications. The hard disks are marketednot using the above specifications but using the following ad hoc standards:

Enhanced IDE EIDE!: It is a 0estern Digital IDE implementation that is an

enhancement to the original IDE hard disk drives. 0hen the EIDE was launched itwas based only on ATA/> and ATA+I standards. (ut later EIDE hard disk drivesincorporate some or all of the ATAATA+I/? and ATAATA+I/H standards. The EIDEhard disk enhancements include increased data throughput and greater storagecapacity upto . &astATA is based on ATA standards whereas &ast ATA/> is based on ATA/> standards.1owever' unlike EIDE &ast ATA do not support ATA+I standard.

7ltra ATA: It is an enhancement to EIDE and was proposed ointly by Juantum and

Intel. It incorporates ATAATA+I/? standard' ATAATA+I/H standard' ATAATA+I/Bstandard and ATAATA+I/G standard. Enhancements to 7ltra ATA include fasterdata transfer rate. 7ltra ATA supports data transfer rate twice that of the EIDE.

SCSI Hard Disk

$#$I often pronounced as 5scu**y6! stands for 5$mall #omputer $ystem Interface6. $#$Ihard disks are generally used in servers and high/end workstations because of thefollowing advantages:

Improved performance over IDE and $ATA in multitasking' multiuser

environments. The ability to daisy/chain many drives on one computer.

$#$I interfaces are available in various subtypes' which have different physical andelectrical interfaces and transfer rates. %odern $#$I hard disks are the largest' fastestdisks available' but IDE and $ATA hard disks are fast reaching $#$I in terms of capacityand speed.

%odern hard disks like $ATA are "uite inexpensive and give almost the same performanceas $#$I. In addition' $#$I hard disks are difficult to configure on a standard +#. (ecauseof the disadvantages' $#$I hard disk drives are rarely used in desktop computers.

1owever' sometimes spending a little amount of extra money on $#$I hard disk drive thanspending the same sum on a faster processor or a more enhanced video card to improvethe overall system performance is worth considering. This is especially true if you heavilyuse multitasking using operating systems like 0indows )T>999+ and -inux.

Serial ATA SATA; Hard Disk

$erial ATA $ATA! is the latest technology that is introduced to replace parallel IDEATA.$ATA has several advantages over +ATA' which are:

$uperior cabling and connectors

1igher bandwidth

reater reliability

(ut $ATA and +ATA are incompatible with each other. This means that a $ATA hard disk

drive cannot be connected using the data bus of a +ATA hard disk and vice/versa. Inaddition' $ATA hard disks are connected on a special $ATA interface on the motherboard.


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(ecause of the different designs of $ATA and +ATA' a $ATA hard disk drive cannot beconnected to a +ATA hard disk drive interface on the motherboard' and same holds true for+ATA hard disk drive also.

(ecause of its superior performance' $ATA hard disks are increasingly gaining popularity

and will eventually replace the +ATA hard disks completely.

An !/er/ie+ o' Computer $emor)

Introduction to Computer $emor)

The term computer memory refers to any form of electrical storage device inside acomputer. 1owever' most often the term refers to fast' temporary forms of storage. If theprocessor needs to retrieve each and every piece of data from the hard disk drive' thespeed of the processor will become considerable slow. (ut when the same piece of data is

stored in the computer memory' the processor can access it more "uickly. %ost forms ofmemory are intended to store data temporarily.

T)pes o' Computer $emor)

The computer memory is classified into following types:

3andom Access %emory 3A%!: It is the type of computer memory that holds data

and instructions before being used by the processor. It is called random accessbecause data and instructions can be stored randomly at any location of thememory and can also be retrieved randomly from any memory location.

$ince data and instructions can be both written to and read from 3A%' it is alsocalled readwrite memory.

1owever' the storage of data and instructions inside a 3A% is temporary. It canhold content as long as the power is on. 0hen the power is switched off' thecontent in 3A% is also lost. The memories' which loose their content on failure ofpower supply' are called volatile memories. $o 3A% is also a volatile memory.

3ead/8nly %emory 38%!: It is the type of computer memory that stores

manufacturer supplied programs re"uired to operate the personal computer. &orexample' the instructions re"uired to examine the various devices attached to thecomputer when the power is switched on.

The processor can only read from 38%' but cannot modify its content. (ecause ofthis it is called read/only memory. The memories' which do not loose their contenteven on the occasion of power failure' are called non/volatile memories. $o 38% isalso a non/volatile memory.

+rogrammable 3ead/8nly %emory +38%!: It is the type of computer memory that

allows you to store your own set of instructions in it' permanently. 8nce theinstructions are written in a +38%' it cannot be modified and will remain as is evenin the case of power failure. +38% is also a non/volatile memory.

Erasable +rogrammable 3ead/8nly %emory E+38%!: It is the type of computer

memory that is similar to +38% but with exception. The exception is that it alsoallows you to store new instructions by erasing the existing instruction contained init.

To erase existing content from an E+38%' you need to expose it to ultraviolet lightfor some time. After the existing content is removed' you can then again put newcontent in it using special programming facility.

0hen the E+38% is in use information can only be read. It is also a non/volatilememory.


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#ache: It is the type of computer memory that holds data and instruction that are

currently being executed or temporary data fre"uently used by processor. Thecache memory is a small chip attached between processor and 3A%. Its accesstime is approximately same as the processing speed of the processor.

(ecause of the faster access of cache than 3A%' you can store data andinstructions in cache for faster access or execution. 1owever' caches are kept smallin si*e because of their high cost. Therefore' you should consider carefully beforestoring any data or instruction in cache.

3egisters: It is a special type of computer memory that stores data and

information temporarily and pass them as directed by control units. The registerspass the data or information with a very high speed.

T)pes o' RA$

0hen we refer to a computer memory' it usually is the 3A%. The 3A% itself is categori*edinto different types. $ome of the most popular 3A%s are:

$tatic 3A% $3A%!: The $3A% typically consists of multiple transistors' usuallyranging from four to six transistors' but does not have any capacitor. (ecause ofthis reason' the $3A% does not need to be refreshed on a periodic basis. 5%emoryrefresh6 is the process of periodically reading information from a portion ofcomputer memory' and immediately rewriting the read information to the samearea with no modifications.

Dynamic 3A% D3A%!: The D3A% like $3A% too consists of transistors' but it has

only a pair of transistor unlike four to six transistors in $3A%. Another difference isthat' D3A% stores each bit of data in a separate capacitor within an integratedcircuit. )ow a capacitor leaks charge' because of which data is stored in a D3A%for only a tiny fraction of a second before getting lost. To overcome this problem'the D3A% needs to be refreshed periodically. (ecause of periodic refreshing it getits name as 5dynamic6 and hence called Dynamic 3A% D3A%!.

The D3A% is slower than $3A%' but the advantage is that it re"uires less powerand is also inexpensive.

&+% D3A%: The &ast +age %ode D3A% &+% D3A%! is slightly faster than

conventional D3A%. This is because of the fact that &+% D3A% works byeliminating the need for a row address if data is located in the row previouslyaccessed. %ore on memory access later in this chapter!. It is sometimes calledpage mode memory.

ED8 D3A%: Extended data/out D3A% ED8 D3A%! is much faster version of

D3A%. 7nlike conventional D3A% which can only access one block of data at atime' ED8 3A% usually start fetching the next block of memory as soon as it sendsthe previous block to the processor. It is about five percent faster than &+%.%aximum transfer rate to -> cache is approximately >B? %bps.

$D3A%: $ynchronous D3A% $D3A% or $D3 for short! is a synchronous form of

D3A%. The D3A%s that we discuss till now all are of asynchronous mode. Thismeans that these D3A%s react as "uickly as possible to changes in control inputs.1owever' $D3A% waits for a clock signal before responding to its control inputs. Itis synchroni*ed with the computerLs system bus' and thus with the processor.(ecause of synchroni*ation' a $D3A% have a more complex pattern of operationthan asynchronous D3A%s.

$D3A% is about five percent faster than ED8 3A% and its transfer rate to -> cacheis approximately H>< %bps.

DD3 $D3A%: Double data rate $D3A% DD3 $D3A% or DD3 for short! is ust like

$D3A% except that is has higher bandwidth' meaning greater speed. This is

achieved by transferring data on the up and down tick of a clock cycle. %aximumtransfer rate to -> cache is approximately '9B? %bps for DD3 $D3A% CC %1M!.


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3D3A%: 3ambus D3A% also called Direct 3ambus D3A% or D3D3A% or 3D3A%!

is a radical departure from the previous D3A% architecture. It was designed by3ambus and uses a special high/speed data bus called the 3ambus channel totransfer data between memory and processor. 3D3A% memory chips work inparallel to achieve a data rate of : DD3> is the recent version of DD3 $D3A%. It offers new features and

functions that enable higher clock and data rate operations. DD3> transfers B? bitsof data twice every clock cycle. 1owever' a drawback of

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