Introduction to ComputerSystems, Interacting with Computers,Computer Organization

8/8/2019 Introduction to ComputerSystems, Interacting with Computers,Computer Organization

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Unit-1: Introduction to Computer

Systems, Interacting with Computers,

Computer Organization

Mahesh Lohith K.S, Senior Lecturer,AIeMS

1 Introduction

1.1 Computer Defined

A computer is an electronic programmable device that receives input, storesand manipulates data/information, and provides output in the desired useful. Acomputer does computation and the computaion inclueds the logical operations,which calculators cannot perform. A typical computer performs four major tasksand are given by

1. Data Input

2. Processing and manipulation data according to the instructions given

3. Information Output in the desired format

4. Storing the Input Data, Instructionas and Output Information in theMemory

1.2 Early History

In the year 1837 Charles Babbage designed a device which could performthe automatic calucalation and was programmable. Thus began an eraof computers with the design of a Mechanical computer which is fullyprogrammable.

In the decade of 1880 Herman Hollerith invented a storage device whichcould record data on a machine readable medium which latter settled as

Punched Cards.

Allen Turing in the year 1936 provided the blue print for electronic digitalcomuputer. The machines were called Turing Machines. Thus he becamethe Father of Modern Computers.

The first working computer was built in the year 1941 by Konard Zuseand was called Program-Controlled Computer

In the year 1945 John Von Neumann brought in the concept Stored-Program Concept.

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In the year 1948 Electronic Delay Storage Automatic Calculator (EDSAC)

was designed. Soviet scientists designed a functional ternary computer called Setun based

on numbering systems with three elements 1,0 and 1 instead of binary.

A first transistorized computer was demonstrated in Manchestor univer-sity in the year 1953

Konard Zuse built a new computer with magnetic storage in the year 1955.

A New generation of computers was started with the design of Micropro-cessors with the help of Integrated Circuit Technology.

2 Basic Parts and Structure of a Computer (VonNeumann Architecture

The Basic parts of a modern digital computer is as shown in the figure.1. Itconsists of a Monitor, CPU, Memoruy, Key Board, Mouse, Speakers, CD Drive,DVD Drive,Floppy disk drive and printer The structure of the computer is as

Figure 1: Basic Parts of a Computer

shown inthe figure.2. A computer has four main units which are described asbelow

Input Unit: This unit contains input devices like Keyboard, Mouse and Mag-netic Tapes etc using which data and instructions can be input to thecomputer for processing. User can control the system by issuing suitablecommands through the input devices. The input unit converts the datainto suitable format which is understood by the computer.

Central Processing Unit: The Central Processing unit consists of two moreunits

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Control Unit(CU): As the name itself indicates it controal all processes

by passing control signals. It maintains the co-ordination betweendifferent units, by issuing commands, so that the information pro-cessing life cycle is carried out.It issues commands to Input devicesto input the data. It issues commands to ALU to perform operations.It identifies the actions to be taken. It passes instructions to Memoryto store the data. It issues signals for the output devices to performthe desired information output operations.

Arithmetic and Logic Unit(ALU): The ALU does actual operationsand is controled by control unit. It does basic Arithmetic operations(addition, subtractions, multiplication and division)and Logical op-erations.

Memory Unit: This unit contains Primary Memory and Secondary Memory.It

stores the input data and instructions. It also stores the intermediate re-sults generated during the processing of instructions. It consists of Ran-dom Access Memory(RAM), Read Only Memory (ROM)and Hard disksdrives (HDD) etc.

Output Unit: This unit displays the output information in the desired for-mat.This unit may various types of output devices from monitors to print-ers where output information can be obtained in human understandableformat. The working go the output unit depends on the signals issuedby the control unit which inturn depends on the instructions given by theuser.

3 Categorizing Computers

computers can be categorized based on the technique the data is handled anusage (Individuals and Organzation). The following are the classifications ofcomputers.

Classification of computers based on Data handling technique: The fol-lowing is the classification of computers based on the data handling.

1. The Digital computers process the data in digital form which isnothing but binary format containing 0s and 1s. The data andinstructions are interms of bits and bytes. Bit is a memory unit andgroup of consecutive 8 bits is a Byte.

2. The Analog Computer process data in analog form. The analogdata keeps changing with respect to time. The processing of inputsignal is continuous and so the output. The analog computer pro-cesses data like the continuous voltage, frequency etc.

3. The Hybrid Computer which can handle data in both analog anddigital forms.

Classification of computers based on individual usage: The comuputersfor individual usage are called as Personal Computers.It is a small low costcomputer with a microprocessor. Thus it is also called as Microcomputer.The classification of computers based on individual usage is as below

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Figure 2: Basic Parts of a Computer

1. Desktop Computer is an independent computer which can be placedon desk or table.

2. Workstations is a Desktop compouter with powerful Micropro-cessor containing high resolution monitors and accelerated graphiccards.

3. Notebooks or Laptops are the most liked types of Personal comput-ers since they are compact, easily portable and can be used keepingon the lap of the person.

4. Tablet PC is small computer in the form of slate containing a pencalled stylus. It has all features of a note book. The user can write onthe screen and the handwritten data is converted into the standard

text using appropriate software.

5. Handheld PCs can be operated keeping on the palm. Hence theycan also be called Palmtops. These devices are so small like mo-bile phones so that they can be placed in pockets.Personal DigitalAssistant (PDA) is an example for Handheld PC.

6. Smart Phones are the hand held electronic devices which performthe function of both mobile phone and PDA.

Classification of computers based on organizational usage: In an orga-nization there may be many users who operate computers at differenttimes.computers are used by the users in batches and groups.

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1. Minicomputers are the computers whose performance lies between

that of mainframe computers and micro computers. They are themulti-user computers which support many users simultaneously.

2. Computer Network Server is a powerful highspeed large storagecomputer which is connected to many computers, printers and scan-ners etc in the network. All the data in the network can be stored inthe server and can be shared among the different users.

3. Mainframe Computers are used in industries and other organi-zations for commercial application. They perform very large scalecomputations and processes data in large volumes for large no. ofusers. IBM main frame computers are the examples.

4. Super Computers are the very fast computers which perform fewtera operations in one second. They are used for scientific and engi-

neering applications where huge amount of data has to be processedwith a very high accuracy in a lesser time.

4 Information Processing Life Cycle

The computer using its various parts converts data into information by perform-ing various operations on data as instructed by the user. This process involvesmany steps and is referred to as Information processing life cycle. The stepsinvolved are

Data reception

Data processing based on the instructions Output informationor data disply

Storing the data in memory

The Information processing life cycle is pictorially as shown in the figure.3.

Figure 3: Information processing life cycle

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Input: In this stage of the information processing life cycle the computer re-

ceives data from the various sources like keyboard, mouse and magnetictapes.

Process: In this stage of the information processing life cycle the receiveddata from various sources is processed and manipulated according to thegiven instructions given by the user and is finally converted into usefulinformation.

Output: In this stage of the information processing life cycle the output ofthe processed data which is information is sent to the respective outputdevices where it is displayed. It may be even stored in the memory for thefurther use.

Storage: In this stage of the information processing life cycle the information

or the output is stored in the memory from where it can be repeatedlyaccessed for further computations. The storage devices involved are maybe Hard Disk Drive(HDD),Compact Disk(CD) or floppy.

5 Essential Computer Hardware

A computer is made of many physical components called Hardware. The hard-ware consists of physical electronic and electromechanical components. Thesecomponents are classifed into input, output, system and storage devices.

input devices The input devices are essential computers hardwares used toinput the data for processing. Keyboard and Mouse ar the essential com-

ponents of the input unit of a computer.

Output Devices The result is displyed in human readable form on the outputdevices. the essential output hardware devices of a computer are Monitor,Printer and speakers which output information in the form of text, videoand audio.

System Unit Devices The system unit controls all necessary other hardwaresand performs all operations as instructed by the user. It is the core of thecomputer which performs all arithmetic and logical operations operations.The essential system unit devices are the Microprocessors, Memory andData Buses, Video Graphic cards, Sound Cards, Power Supply RAM etc.,

Storage Devices The storage devices store the data, instructions and the out-put information generated during the information processing life cycle ina computer. The essential storage devices of a computer are Randomaccess Memory, Read Only Memory(CD-ROM,DVD-ROM), Hard DiskDrives(HDD). Random access memory is a volatile memory which storesthe data or information and as well as intermediate results till the powergoes off. Once the power is off the data are lost. Data can only be readfrom ROM. Hard Disk Drives are the powerful essential memory devicesin a computer which is based on stored program concept. They are madeof many cylinders which contain tracks where the data are stored.

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6 Essential Computer Software

The software is a package of instructions given to a computer to perform certainset of tasks in which the necessary input data is processed resulting in the outputin a desired format. the computer software is classified into two types

System Software: Working with the computer is possible if the data andinstructions are given to the computer in the machine readable format.But,for the user, it is very difficult to code the instructions in machinelanguage. Thus some kind of instructions are preloaded into the com-puter which interact with the user and the machine working like an inter-face. Such softwares are called system softwares. The Operating System,Assemblers and Compilers are the essential computer system softwares.

Application Software: The other softwares which are oriented towards differ-

ent applications like desktop publishing, Plotting, Graphing,Image Manip-ulation and Data handling are called application softwares. Nudi, GIMP,InkScape, Microsoft Word are the examples for application softwares. Ap-plication softwares are chosed by the preference and priority of hte user.

Thus hardware is the brain and software is the intellegence of a computer.

7 Input Devices

7.1 Key Board

A Key board is an essential input device for a computer using which the data and

instructions can be entered into the computer. It allows us to issue commandsso that computer can be controlled.It contains key switches which represent aparticular character. The no. of keys varies around 101. The character keyswitches layout in a keyboard is very much similar to that of a typewriter.In addtion there are many other switches which are meant for different taskslike altering the switch performing scrolls and data editiing etc., A typical key-board layout is as shown in the figure.4. and consists of the following groups ofkeys(Keypads).

Figure 4: Keyboard Layout

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Alphanumeric and Character

Numeric

Modifier

Cursor movement

Function

Special Purpose

When a key switch is pressed the Keybord Controller identifies the key strokeand electronic signals are generated corresponding to the key pressed forming acode called scan code. This code is stored in keyboard memory called KeyboardBuffer. The signals are sent to operating system (OD) informing that key is

available in the keyboard buffer. The scan code sent to CPU for processing fromthe OS. During the processng the key stroke is converted in to image and willbe displayed on the screen.

7.2 Mouse

Mouse is an hand held input device. It is used to control the movement ofpointer on the screen. It allows us to select and confirm a command on a GUI.A typical mouse has two buttons one on left and the other on to the right asshown in the figure.5. Based on the operations the buttons are classified asPrimary and secondary buttons. These buttons can be configured to performthe desired input action. The middle scrolling wheel is used for scrolling pages.

The actions performed by a mouse are as listed below

Figure 5: Typical Mouse

Pointing Moving and placing the cursor over a particular region on the screen.

Clicking and Double Clicking The action of pressing an releasing the mousebutton will perform the selection of a particular command and the initia-tion of a some action associated with it. Double clicking is the action ofpressing and releasing the mouse button twice.

Dragging It is the process of pressing the mouse button on the desired objectand controlling the dragging on the mouse pad.

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Scrolling It is the process of turing the scroll wheel on the mouse to scroll

through the documents. the Up and Down scrolling the document canperformed by rotating the wheel in forward and backword directions.

8 Inputting data in other ways

8.1 Pen based systems

The pen based input systems are Stylus and Digital pens(see fig.6.). Stylus isa pointing device that perfoms the action of selection and confirmation of com-mand on a touch screen based computers. Normally stylus is very compatiblewith the hand held devices. Since it is very sleek and can be fit into the deviceeasily. Digtal pens can be used like stylus on a digital writing pad. The datacan be written over the pad and a software converts the handwritten matter into digital electronic data which is displayed on the screen.

Figure 6: Digital Pen

8.2 Data scanning devices

8.2.1 Digital image scanners and Barcode scanners

Digital Image scanner is an input device which can do electronic capture ofdata(fig.7.).It is a peripheral input device used to assist in the entry of datainto a computer system.

Figure 7: Scanners

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In desktop publishing, a scanner may be used to digitize artwork or pho-

tographs so that they can be merged with text. Scanners are used to scan aprinted page or an illustration. These data are then converted into bit patternsfor processing storage or output. When an image is scanned, it is convertedinto light and dark picture elements or pixels. The scanned images are usedfor word processing and printing multiple copies. Scanners are also useful toscan fingerprints. The scanned fingerprints can be compared with another fin-gerprint to find probable match in investigative services. Photoelectric scannersare commonly used in supermarkets to read barcodes.

Scanners are available in different sizes. A handheld scanner is used to scana few lines of text or a small photograph. A page scanner is used to scan adrawing or page.The scanner is connected to the computer using a cable andcontrolled by software.

8.3 Game controllers

Game controller are the input and controlling devices used in computer gaming.Since the keyboards are not compatible as for as the compact layout of the keysare concerned. Hence specialized easy to use controllers are designed for gamingcalled Game conrollers. The two most important game controllers are Joystickand Game pad.

Joystick It is a commonly used game controller device to play games. Thejoystic is equipped with a lever which the user can use to move and controlthe pointer. The movement of the pointer continues in a direction with

which joystick is moved. The pointer returns to equilibrium once thejoystric returns to vertical equilibrium position. There are many buttonsassociated with a joystick which are associated with particular options ingaming. Clicking the buttons the respective action is performed. This canbe very useful in simulations like flight controller, racing etc.,

Game pad It is a game controller which can be held in both the hands tocontrol the game actions. A game pad consists of action and directionsbuttons. The whole gaming actions can be controlled by pressing theaction buttons only by using left and right thunbs. The game pad isalso called as Joy pad. The direction buttons can be used to contol thedirection in gaming. They are the primary input devices for all modernVideo Game Controllers.

8.4 Voice recognition devices

The process of converting voice in to text is called Voice or Speech recognition.The audio input devices that are used in voice recognition are the Microphones.To achieve the process of voice recognition the necessary hardware is a Soundcard. the sound card is a hardware which converts the electrical analog outputof the microphone into the digital format which can be stored in computermemory. The sound card also does the work of converting the digital formatin to electrical analog which can be fed to speeker to listen to music. Thus theessential Voice recognition devices are Microphone and Sound Card.

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8.4.1 Microphones

A microphone is a transducer which converts sound energy in to equivalentelectrical analog using the process of transduction. The microphones are ofdifferent types. Capacitive microphones, inductive microphones, Piezo electricmicrophones etc., The electrcial arrangement in the microphones is so done thatthe sound incident on the microphone generate electrical signal analogus to theincident sound energy.

8.4.2 Voice recognition

The process of voice recognition occures in the following steps

User speaks into microph+one which is connected into computers.

Micropnine converts the input sound energy into output electrial anlogsignal and sends the same into the Sound card.

The input electrical analog signal is converted into digital signal by theSound card. The process is called Coding.

The speech recognition software in the computer converts the digital sig-nals into the text format.

The text generated is displayed on the computer screen.

8.4.3 Sound Systems

The cobination of necessary devices that produce and process sound is called

Sound System.The audio devices microphones, speakers, Tape players, AudioCD players, DVD Drives are the different parts of a Sound System. The voiceis converted into electrical signal using micrphones which is fed to sound cardto for processing. The sound card drives the speaker to reconver the electricalsignals in to sound. Speaker is again a transducer which converts the electricalenergy into sound energy. It uses a magnet and a coil for transduction. Usingthe sound systems the following purposes are served

Multimedia product creation

To view the video

Listening to music

Tele-conferencing

Video-conferencing

8.5 Visual Input Devices

The devices which convert the visualization into the computer input or doesvideo capture are called video inpout devices. The moving picture with soundis called video. Video capturing is the process of capturing and storing the videointo the computer. The types of video capture devices are

VCRs

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Video Recorder

Web Camera

The process of video capture requires a necessary hardware called Video Cardor Video Capture Card. To capture Video the video input device is connectedto computer. The video input devices sends the video+audio signals and areconverted into digital signal which can be understood by the computer. Thisprocess is called digitization. Video input devices are very useful in video con-ferencing in which the live video of the person calling will be displayed on thescreen.

9 Output Devices

9.1 Monitors

Monitor is a standard output device. The information and other data stored ina coputer can be displayed on the monitor screen and is called soft copy. Thedisplay is of the information takes place in a very short interval of time. TheMonitor can also used like a television to display the video. Based on the typeof display monitors are classified into three types

Monochrome monitors display the information in only one color.

Grayscale monitors display the information in gray scale.

Color monistors display the output information in color. The range ofcolors are classified as True color, 16bit and 32bit.

Monitors can also be classified on the mechanism of operation.

CRT Monitors: The Cathode Ray Tube monitors work on the principle ofdefelction of electron beam in the electric and magnetic fields. The motionof an electron in an electron beam is alled a cathode ray. A CRT generatesa electron beam using an electron gun which is deflected by two sets ofdeflection plates situated in mutually perpendicular directions(X an Y).The electron beam, after deflecton, hits the phosphor coated on the backof the screen producing a glow. Phosphor is a material which exhibitsphosphorascence which is delayed fluorescence. The screen is devided intolarge number of small elements called pixels. The elctron beam sweepsacross horizontally to construct images and this is controlled by applying

proper AC signals to X and Y plates.

Flat Panel Monitors: The screen of such monitors is very flat and the mon-itor consumes very less power. They are made of LCD(Liquid crystaldisplay). The liquid crystals polarize the light which passes throgh themand allow the light to pass through in one direction. They are normallytransparent and become opaque when charged.

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9.2 Video Card

It is the physical hardware part fixed to the mother board which acts like anintermediate device betweeen CPU and monitorl. The data of the image to bedisplayed is sent to video card and it convert the data into electrical signals.The video cards of two types

VGA: Video Graphic Analyser which processes data of the image in 256colors.

SVGA: It is Super VGA which can process the data of hte image in morethan 256 colors and at higher resolution.

9.3 Printers

A printer is an output device used to print text or graphics on paper or onany other hardcopy medium which includes even microfilm. A permanent copyfrom the computer is produced using the printer. Printers are of two basic typesimpact and non-impact.

9.3.1 Impact and Non-Impact printers

The classification of printers is based on the physical contact of the print headwith the paper to produce a text or an image. In an impact printer the printhead will be in physical contact with the paper. In a nonimpact printer, on theother hand the print head will have no physical contact with the paper. TheDot matrix printer is an Impact printer.The Laser printer and Inkjet printer areNon-Impact printer.

9.3.2 Basic operations of a Prnter

The basic operations of a printer are as mentioned below.

Moving the paper to a given line.

Moving the print head along the line.

Generating the character or image.

Producing the character or image on the paper.

9.3.3 Dot-Matrix Printer

The dot-matrix printer forms characters as arrays of dots. Dot matrix print-ers are compact, reliable and relatively fast. The print head is the importanthardware which produces the character using pins arranged in a matrix form.Normally a print head has 9 pins or 24 pins arranged in a matrix form. Com-binations of pins strike an ink bed ribbon during the printing process. Theprint head moves in a line and the pattern of dots required for each characteris printed on the paper. After printing a line, the paper rolls to print the nextline. The print quality is average and corbon copies can be obtained easily.The cose is less and easy to maintain. The disadvantage is related to the tapemaintenance.

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9.3.4 Laser Printer

Laser printers are fastest type of non impact electrostatic printers. They pro-duce high quality prints at high speeds. It operates like a copier machine. Inthese printers, the controlled beam of intense laser forms images on an electri-cally charged rotating drum. The drum is rotated near the fine black powdercalled the toner. These charged images which sticks to the paper due to pres-sure and heat. The toner consists of oppositely charged ink particles which stickto the drum in the places where the laser has charged.The light beam strikesa multi-sided rotating mirror. As the mirror rotates, the side currently in thepath of the light beam sweeps the beam across the surface of the drum. As thebeam sweeps across the drum, the light is modulated and a single line is drawnafter a line has been drawn, the next side of the mirror is in place and a newline is drawn below the previous line. The quality of the printout is measured

by the number of dots per inch (dpi). The speed is measured in number ofpages printed per minute (PPM) which varies between 5 and 25. The printingis faster and easy to handle and maintain. The disadvantages are the price ishigh and higher print cost.

9.3.5 Ink-Jet Printers

The Ink-Jet printer sprays tiny drops of ink to form character and graphic imageson paper. The text and graphics printed in an inkjet printer are technicallysimilar to that of a dot matrix printer. These type of printers can also be usedcolor printing. The black inkjet printer uses black cartridge filled with black inkwhereas the color printer uses four color cartridges namely cyan (blue), magenta(red), yellow and black. These four colors are used in combination to generate

any color in the visible spectrum. The printer sends electrical pulses to thinresistors at the base of firing chambers behind the nozzle. A thin layer of ink isheated by the resistor which in turn forms a vapour bubble and the expansionforces ink through the nozzle and onto the paper at a rate of about 6000 dotsper second. The quality of the printout is equivalent to that of laser printouts.The speed of printing is slower than that of laser printers. The advantages ofthis type printer are the cost is low; quality of printing is equivalent to thatof laser printing, color printouts are cheaper easy to handle and maintain.Thedisadvantages are the ink cartridges may get spoiled if unused for a long time.Some inkjet printers are very expensive.

9.4 Plotters

A plotter is an output device used to print engineering drawing or graphicson large size sheets. These are also used to draw the patterns from whichmicroprocessors, memory chips, and other integrated circuits are manufactured.Plotters are used when highest quality and greatest accuracy are required. Thereare two basic types of plotters

Flat bed plotters: A pen plotter has a surface where the paper or drawingsheet is properly fixed. It has a pen holder in a movable arm. Under thecontrol of the computer the arm with the pen moves across the paper todraw the picture. A few pens are also placed in a row and the arm willpick the required color pen as per the instruction of the computer.

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Drum type plotters: A drum type plotter uses a drum where the paper will

be rolled. It has a print head/pen that moves like the print head in aprinter. Drum type plotters are capable of producing longer, continousdrawings. Drum type plotters that can produce color plots are available.Laser plotter and inkjet plotter are commonly used drum type plotters.

The disadvantages are these are expensive than printers. The cost of printing ishigh. Cost of maintenance is high. High skill of operation is required. Processtime of printing is longer.

9.4.1 Data Projectors

As the name itself indicates thery are the devices used to project the data/informationon a larger screen or on the wall so that may viewers can get the information

simultaneously. They are used to project the data both in text, graphical andvideo forms on a larger screen. Data projectors are easily portable and projectdata with high resolution and 16 million colors. The data projector is connectedto the computer in which the data projected to be stored then the projetor out-put the same on to the external surface.The Data projectors are classified intotwo types

LCD Projectors: Liquid Crystal Display technology is used to project thedata on to the wall using its own light source. The room should be dark-ened.

DLP Projectors: Digital Light Processing technology is used to project thedata on to the wall using many mirrors to reflect light. The room neednot be dakened.

10 Number Systems

In practice it is very important to have a count of objects or any other entities.Grouping of entities makes the counting very easy. Since past many sytems areused to group the entities and count. They are called as Number systems. If thecount is represented in groups of ten then the number system is referred to asBase 10 and is also called as Decimal System. Similarly we have Binary(Base 2),Octal(Base 8) and Hexadecimal(Base 16) numbers sytems which are very usefulin representing the nos. The four Numbers are very useful in representing datain computers with Binary system being the most important.

Decimal: In this system the digits are 0,1,2,3,4,5,6,7,8,9 used to represent num-bers.

Binary: In this systems the digits used are 0 and 1. Thus it can be used torepresent data in computers.A bit can hold either 0 or 1.

Octal: In this system the digits used are 0,1,2,3,4,5,6,7.

Hexadecimal: In this system the digits used are 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F.

Since Octal and Hexadecimal nubers can be easily converted into binary andvice-versa they are also used to process the data in computers.

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11 Text Codes

11.1 ASCII

The ASCII stands for American Standard Code for Information Interchange. It is a 7bit code used to represent the symbols. Thus it can represent128 characters with decimal numbers ranging from 0 to 127 in hexadecimalrepresentation. The compatibility between different types of data processingmethods in equipmments is achieved through ASCII. This is the most commonlyused character set in computers. In ASCII,for example,the letters a,b and c arerepresented by decimal numbers 61,62 and 63. It means a is represented by Hexnumber 61 and is represented in computer as 1010 0001 and so the noumbers band c as 62 - 1010 0010 and 1010 0011. Presently the ASCII character set usedis Extended ASCII. It uses 8bits thus can represent another 128 characters.

12 BCD numbers

BCD stands for Binary Coded Decimal. It is a kind of representation of decimalsin terms of binary codes. for example if 123 is the number in decimal thenthis can be represented in binary as 0001 0010 0011 where each part of binaryrepresents each digit in decimal. This is used in the data manipulation incomputers. BCDs are also used in EBCDIC text code representations.

13 Buses

A bus is a collection of wires which carry data in computers from one deviceto another. The speed of the CPU depends on the number of wires in the bus.The speed depends on the size of the data bus with all other factors remeiningthe same. The Buses are classified into the following types

Data Bus The bus which allows the transfer of data between two hardwaredevices is called a Data Bus

Address Bus The bus which connects CPU with memory. The memory sizedepends on the size of the address bus. Currently 64 bit address buscomputers can access the memory of the size 264.

External Bus It is also called as expansion bus. These are the bunch of wirewhich connect the CPU with other devices like monitor, printer, keyboard,

mouse etc.,

14 Mother Board

A mother board is the central printed circuit board (PCB) in may modern com-puters. It is designed to hold many hardware components and facilitates theslots for connecting other peripheral devices.The important components of theCPU housed on the mother board are microprocessor, controllers and chipset.The block diagram of the typical modern computer mother board is as in thebelow figure.8. Mother board also consists of audio video controllers, disk con-

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trollers, graphics cards, usb controllers and the network cards. The different

ports,sockets and slots in the mother board are Ram slots, microprocessor sock-ets, usb sockets, connector slots, audio video sockets, keyboard socket, mousesocket, monitor bus socket, heat sinks, IC sockets etc.,

15 Chipsets

Chipsets are referred to the set of speciallized chips (ICs) on the computermother board. The chipset is so specially designed to work with a specificfamily of microprocessors for example intel and amd.This is because it controlsthe communication between the processer and external devices and also it playsa major role in systems performance. The chipset on the mother board refersto a specific pair called northbridge and southbridge. The Northbridge links

CPU to very high speed peripherials like memory and graphic controllers whereas the south bridge links to lower speed pheripheral busses like ethernet, usband audio devices. A typical chipset block diagram is as shown in the figure.9.

16 Micro Processors

Micro Processor is the heart of acomputer it incorporates almost all functionsof the cpu. The speed and the quantum of the dataprocessing in the computerdepends on the speed and the register sizes of the microprocessor respectively.There are different series of microprocessors like Intel 4004 ,Intel 8085, Intelceleron, Intel Pentium, Intel dual core, Amd athlon etc., The Microprocessorscontaing millions of transistor circuits using with it performs computing op-

erations. Currently the size of the transistor on the chip is 30nm.Now Themicroprossoers are so designed so that they can handle data in 64 bit pattern.During the execution of a program the instructions are converted in to ma-chine codes and then it is processed by the microprocessor. The microprocessorconsists of Many registers, RAM , control and other units.

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Figure 8: Mother Board Block Diagram

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Figure 9: Chipset Block Diagram

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Introduction to ComputerSystems, Interacting with Computers,Computer Organization

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