137022446 Computer Course

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1 COMPUTER COURSE

k.suresh

Introducing Computer Systems
What is Computer? Computer is an advanced electronic device that takes raw data as input from the user and processes these data under the control of set of instructions (called program) and gives the result (output) and saves output for the future use. It can process both numerical and non-numerical (arithmetic and logical) calculations. (O ) ! Computer is an electronic device that can perform activities that involve "athematical# logical and graphical manipulations. $enerally# the term is used to describe a collection of devices that function together as a system. ! computer has four functions% Input a. accepts data b. processes data c. produces output d. stores results Input (Data) Input is the raw information entered into a computer from the input devices. It is the collection of letters# numbers# images etc. Process &rocess is the operation of data as per given instruction. It is totally internal process of the computer system. Output Output is the processed data given by computer after data processing. Output is also called as esult. 'e can save these results in the storage devices for the future use. Processing Output Storage

!"#antages o$ computers
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1 COMPUTER COURSE

k.suresh

0. %igh spee" Computers have the ability to perform routine tasks at a greater speed than human beings. 1hey can perform millions of calculations in seconds. 2. !ccurac& Computers are used to perform tasks in a way that ensures accuracy. 3. Storage Computers can store large amount of information. !ny item of data or any instruction stored in the memory can be retrieved by the computer at lightning speeds. 4. !utomation Computers can be instructed to perform comple5 tasks automatically (which Increases the productivity). 6. Di'igence Computers can perform the same task repeatedly + with the same without getting tired. 7. (ersati'it& Computers are fle5ible to perform both simple and comple5 tasks. 8. Cost e$$ecti#eness Computers reduce the amount of paper work and human effort# thereby reducing costs.



OR)!*I+!TIO* O, COMPUTER (OR) ,U*CTIO*!- U*ITS O, ! COMPUTER (OR) .-OC/ DI!)R!M O, ! COMPUTER

! computer system has the following main components% ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 2

1 COMPUTER COURSE 0) Input unit 2) Central &rocessing 9nit (C&9). 3) Output unit.

k.suresh

Input unit%
Input unit accepts coded information from human operators through electromechanical devices such as the 0e&1oar". 1he information received is either stored in the memory for later reference or immediately used by the !rithmetic and ,ogic circuitry to perform the desired operation. :inally the result is sent back to the outside through the output unit. *5amples% keyboard# ;oy stick# track ball# mouse (pointing devices)# scanner etc.

Central &rocessing 9nit%
Central &rocessing 9nit (C&9) is the main component or <brain= of a computer. It performs all the processing of input data. Its e5amine and e5ecute the instructions stored in the main memory of a computer. In microcomputers# C&9 is built on a single chip or Integrated Circuit (IC) and is called a microprocessor. ! C&9 consists of the following distinct parts% • !rithmetic -ogic Unit (!-U) • Contro' Unit (CU) • Registers • .uses • C'oc0

2 Memor& unit
!rithmetic -ogic Unit (!-U) 1he arithmetic and logic unit of C&9 is responsible for all arithmetic operations like addition# subtraction# multiplication and division as well as logical operations# such as less than# e>ual to and greater than. !ll calculations and comparisons are performed in arithmetic logic unit.

Contro' Unit ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 3

1 COMPUTER COURSE

k.suresh

1he control unit is responsible for controlling the transfer of data and instructions among other units of a computer. It is considered as the <central nervous system= of a computer as it manages and coordinates all the units of computer. It also performs the physical data transfer between memory and hardware devices. . Registers (ata is temporarily stored in small# local memory locations of ?# 07# 32 or 74 bits called registers. (epending on the type of processor# the overall number of registers can vary from about ten to many hundreds. 1he main registers are% 1he accumu'ators register (ACC)# which stores the results of arithmetic and logical operations. 1he status register (PSW# Processor Status Word)# which holds system status indicators (carry digits# overflow# etc.)@ 1he instructions register (RI)# which contains the current instruction being processed@ 1he or"ina' counter (OC or PC for Program Counter)# which contains the address of the ne5t instruction to process@ 1he 1u$$er register# which temporarily stores data from the memory. .uses (ata is stored as a unit of eight bits (bit stands for binary digit# i.e. A or 0) in a register. *ach bit is transferred from one register to another by means of a separate wire. 1his group of eight wires that is used as a common way to transfer data between registers is known as a 1us. It is actually a connection between two components to transmit signal between them. ! bus can be of three maBor types. 1hese types are as follows% 02 Data 1us-- It is used to move data. 2. Contro' 1us-- It is used to move address or memory location. 3. !""ress 1us-- It is used to send control signals between various components of a computer. C'oc0 ! clock is another important component of C&9. It measures and allocates a fi5ed time slot for processing each and every micro computer. 1he clock speed of C&9 varies from one model to another in the range 4.88 ".C (in ?A?? processor) to 277 ".C (in &entium II). 1he speed of C&9 is also specified in terms of "illions of Instructions &er Second ("I&S) or "illion of :loating &oint Operations &er Second (":,O&S). ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 4

1 COMPUTER COURSE

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Memor& Unit
"emory unit is that component of a computer system which is used to store data# instructions and information before and after the processing by !,9. It is actually a work area within a computer where C&9 stores data and instructions. It is also known as a main memory or primary or internal memory.

Output unit%
Output unit accept binary data from the computer and decodes it into original form and supplies this result to the outside world. *.g. monitor# &rinter# /ideo terminals (provides both input + output functions)# graphic displays etc )E*ER!TIO* O, COMPUTERS (%istor& o$ computers) 1he first electronic computer was designed and built at the 9niversity of &ennsylvania based on vacuum tube technology. /acuum tubes were used to perform logic operations and to store data. $enerations of computers has been divided into five according to the development of technologies used to fabricate the processors# memories and IDO units. I )eneration 1345 6 55 II )eneration 1355 6 75 III )eneration 1375 6 85 I( )eneration 1385 6 93 ( )eneration 1393 to present



,irst )eneration (1345 6 55)
0. In this generation </acuum tubes= were used for basic arithmetic operations. 2. 1ook few milliseconds for processing -ulky data. 3. 1his computer cost is very high and speed is low and consumes more power with limited performance. 4. In this time assembly language is used to prepare programs. 1hese were translated into machine level language for e5ecution. 6. &unched cards and paper tape were invented to store programs and data and to get results. 7. "agnetic tape D magnetic drum were used as secondary memory storage devices. 8. It was mainly used for scientific computations. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 6

1 COMPUTER COURSE ?. 0st generation computers are called% (*)I!C - *lectronic )umerical Integrator and Calculator

k.suresh

*(S!C E *lectronic (elay Storage !utomatic Calculator *(/!CE*lectronic (iscrete /ariable !utomatic computer 9)I/!C E 9niversal !utomatic Computer I-" 8A0)

Secon" )eneration (1355 6 75)
0. In this generation <1ransistors= were used in place of vacuum tubes. (Invented at !1+1 -ell lab in 0F48). 2. 1he siCe of computers is small and less power consumption and better performance# ,ower cost. 3. In this generation# .igh level languages such as :O 1 !)# CO-O, etc were used for prepare programs# the high-level program translate into corresponding assembly language program which was then translated into machine language using with Compilers. 4. 1he "agnetic ferrite core memories were used as main memory which is a <randomaccess non-volatile memory=. 6. "agnetic tapes and magnetic disks were used as secondary memory# and also &unched cards continued during this period. 7. .ardware for floating point arithmetic operations was developed and Inde5 registers were introduced which increased fle5ibility of programming. 8. Separate input-output processors were developed that could operate in parallel with C&9. ?. It was used in business# industry and commercial organiCations for preparation of payroll# inventory control# marketing# production planning# research# scientific + engineering analysis and design etc. F. In 2nd generation computers are called% ("anufacturers E I-" 8A3A# (igital (ata CorporationGs &(& 0D6D?# .oneywell 4AA).

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1 COMPUTER COURSE

k.suresh

Thir" )eneration (1375 6 85)
0. In this generation <IC= (Integrated circuits) was used for basic operations. 2. Small Scale Integration and "edium Scale Integration technology were also implemented in C&9# IDO processors etc. 3. 1he siCe of computer is Smaller + better performance and lesser cost and :aster processors. 4. In the generation magnetic core memories were replaced by semiconductor memories ( !" + O") 6. 1he .igh level languages were standardiCed by !)SI eg. !)SI :O 1 !)# !)SI CO-O,. 7. Introducing "icroprogramming# parallel processing# pipelining# multiprocessor system# multiprogramming# multi-user system (time shared system) etc. 8. 1he Operating system software was introduced (efficient sharing of a computer system by several user programs). ?. Cache and virtual memories were introduced (Cache memory makes the main memory appear faster than it really is. /irtual memory makes it appear larger) F. It was used in (atabase management# multi-user application# online systems like closed loop process control# airline reservation# interactive >uery systems# automatic industrial control etc. 0A. In 3rd generation computers are called% (System 37A "ainframe from I-"# &(&-? "ini Computer Corporation). from (igital *>uipment

,ourth )eneration (1385 6 93)
0. /,SI (/ery ,arge Scale Integrated Circuits) was used for basic operations. 2. /,SI design with 1ens of thousands of transistors can be placed in a single chip. 3. It consumes less power with high performance# lower cost and very compact and much increase in the speed of operation. 4. In this time Semiconductor memory chips were used as the main memory. 6. C 1 screen# laser + ink Bet printers# scanners are also developed. 7. 1he Secondary storage memories# i.e. hard disks# :loppy disks + magnetic tapes were used for backup memory. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 8

1 COMPUTER COURSE

k.suresh

8. 1he &arallelism# pipelining cache memory and virtual memory were applied in a better way. ?. In this generation ,!) and '!)S were developed used for desktop work stations interconnected. F. C language# 9ni5 OS# and $raphical 9ser Interface was introduced. 0A. In 4th generation computers are called% (IntelGs ?A??#?A2?7#?A3?7#?A4?7 ..# "otorolaGs 7?AAA# 7?A3A# 7?A4A# !pple II# C !H ID2DID"& etc).

,i$th )eneration (1393 to at present)
0. Introduced 9,SI (9ltra ,arge Scale Integration) technology is developed for operations. :or e5ample IntelGs &entium 4 microprocessor contains 66 million transistors millions of components on a single IC chip. 2. In this generation also developed Superscalar processors# /ector processors# SI"( processors# 32 bit micro controllers and embedded processors# (igital Signal &rocessors ((S&) etc. 3. 1he ObBect oriented language like ;!/! for developed internet programming and new operating systems 'indows F6DF?DI&DJ# ,I)9I# etc were developed. 4. 1he Computers based on artificial intelligence and &ortable note book computers introduced in this time. 6. Computers are used base on e5tensive parallel processing# multiple pipelines# multiple processors# massive parallel machines and e5tensively distributed system connected by communication networks etc. 7. In this time also Introduced 'orld 'ide 'eb and other e5isting applications like e-mail# e-Commerce# /irtual librariesDClassrooms# multimedia applications etc. 8. "emory chips up to 0 $-# hard disk drives up to 0?A $- and optical disks up to 28 $are available (still the capacity is increasing). Storage technology and advanced large main memory and disk storage available. ?. 1he Kuantum mechanism and nanotechnology will radically change the phase and variation of computers. F. In this generation computers are called% (I-" notebooks# &entium &Cs-&entium 0D2D3D4D (ual coreDKuad core# S9) work stations# Origin 2AAA# &! !" 0AAAA# I-" S&D2). ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" ?

1 COMPUTER COURSE  COMPUTERS ,OR I*DI(IDU!- USERS (or) T:PES O, COMPUTERS (or)

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C-!SSI,IC!TIO*S O, COMPUTERS (or) COMPUTERS ,OR OR)!*I+!TIO*S% "ost computers arc meant to be used by only one person at a time. Such computers are often shared by several people (such as those in your schoolGs computer lab)# but only one user can work with the machine at any given moment. 1he primary types of computers in this category are% 12 Main$rame Computers ;2 Minicomputers <2 Supercomputers

"ainframe Computers%
"ainframe computers are used in large organiCations such as insurance companies and banks# where many people fre>uently need to use the same data. In a traditional mainframe environment# each user accesses the mainframeGs resources through a device called a termina'. 1here are two kinds of terminals# ! "um1 termina' does not process or store data@ it is simply an inputDoutput (IDO) device that functions as a window into a computer located somewhere else. !n inte''igent termina' can perform some processing operations# but it usually does not have any storage. In some mainframe environments# however# workers can use a standard personal computer to access the mainframe. E=amp'es of mainframe computers are% 9nivac 00?A# and (*C. I-" 3AAA series# -urroughs -8FAA#

"inicomputers%
It was first released in the 0F7As. "inicomputers are small siCe compared to other computers of the day. 1he capabilities of a minicomputer are somewhere between those of mainframes and personal computers. :or this reason# minicomputers are often called <mi"range computers>. "inicomputers can handle much more input and output than personal computers. !lthough some mini computers are designed for a single user# the most powerful minicomputers can serve the input and output needs of hundreds of users at a time. 9sers can access a central minicomputer through a terminal or a standard &C. E=amp'es of mini computers are (igital *>uipments &(& 00D46 and /!I 00. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" F

1 COMPUTER COURSE

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Super computers
Supercomputers are the most powerful computers made# and physically they are some of the largest. 1hese systems can process huge amounts of data# and the fastest. Super computers can perform more than one trillion calculations per second. Some supercomputers can contains thousands of processors. Supercomputers are ideal for handling large and highly comple5 problems that re>uire e5treme calculating power. :or e5ample# supercomputers have long been used in the mapping of the human genome# forecasting weather# and modeling comple5 processes like nuclear fission. *5amples of super computers are C !H esearch %- C !H-0 + C !H-2# :uBitsu (/&2AAA)# .itachi (S?2A)# )*C (SI2A)# &! !" 0AAAA by C-(!C# !nupam by -! C# &!C* Series by ( (O.

"icro Computers%
1hey are designed to be used by only one person at a time. ! microcomputer uses a microprocessor as its central &rocessing 9nit (C&9). "icrocomputers are tiny computers that can be different in siCe from a single chip to the siCe of a desktop model. ItGs having Small to medium data storage capacities 6AA"- E 2$-.1he common e5amples of microcomputers are chips used in washing machines# 1/s# Cars and )ote bookD&ersonal computers. *5amples of super computers are% I-" &C# &SD2 and !pple "acintosh 1his can be divided based on siCes as fallows% a2 (esktop computers. 12 'orkstations. c2 )otebook computers. "2 1ablet computers. e2 .andheld computers. $2 Smart phones. Des0top computers 1he desktop computer is a &ersonal Compute. 1hat is designed to sit on (or under) a desk or table. 1hese are the systems you sec all around you# in schools# homes# and offices. (esktop computers are more powerful and are used for an amaCing array of tasks or Bobs with greater easy and efficiency. -ut they can be also used to communicate# produce music# edit photographs and videos# play sophisticated games. -ut it was much more used by everyone from preschoolers (,.L.$) to nuclear physicists@ desktop computers are indispensable for learning# work# and play. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 0A

1 COMPUTER COURSE Wor0stations

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! workstation is a specialiCed@ single-user computer that typically has more power and features than a standard desktop &C. 1hese machines are popular among scientists# engineers# and animators who need a system with greater-than-average speed and the power to perform sophisticated tasks. 'orkstations often have large# high-resolution monitors and accelerated graphics handling capabilities# making them suitable for advanced architectural or engineering design# modeling# animation# and video editing. *ote1oo0 Computers )otebooks computers are appro5imate the shape of notebook and easily fit inside a briefcase. -ecause people fre>uently set these computers on their lap# they are also called laptop computers. )otebook computers can operate on alternating current or special batteries. 1hese computers is generally weigh less than eight pounds# and some of weigh less than three pounds based on a thin monitor and a keyboard and easy storage. )otebooks are fully functional microcomputers@ the people who use them need the power of a full-siCe desktop computer. Ta1'et PCs 1he tablet &C is the newest development in portable# full-featured computers). 1ablet &Cs offer all the functionality of a notebook &C# but they are lighter and can accept input from a special pen called a st&'us or a "igita' pen. 1hat is used to tap or write directly on the screen. "any tablet &Cs also have a built-in microphone and special software that accepts input from the userMs voice. ! few models even have a fold-out keyboard# so they can be transformed into a standard notebook &C. 1ablet &Cs run specialiCed versions of standard programs and can be connected to a network. Some models also can be connected to a keyboard and a full siCe monitor. %an"he'" PCs .andheld personal computers are computing devices small enough to fit in your hand. ! popular type of handheld computer is the persona' "igita' assistant (&(!). ! &(! is no larger than a small appointment book and is normally used for special applications# such as taking notes# displaying telephone numbers and addresses# and keeping track of dates or agendas. "any &(!Gs can be connected to larger computers to e5change data. "ost &(!s come with a pen that lets the user write on the screen. Some handheld computers feature tiny built-in keyboards or microphones that allow voice input. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 00

1 COMPUTER COURSE Smart Phones

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Some cellular phones double as miniature &Cs. -ecause these phones offer advanced features not typically found in cellular phones# they are sometimes called smart phones. 1hese features can include 'eb and c-mail access# special software such as personal organiCers# or special hardware such as digital cameras or music players. Some models even break in half to reveal a miniature keyboard.



'.!1 ! * 1.* I)I1I!, &! 1S O: ! CO"&91* SHS1*"N
Computers come in many varieties# from the tiny computers built into household appliances# to the astounding supercomputers that have helped scientists map the human genome. -ut no matter how big it is or how it is used# every computer is part of a system. ! complete computer system consists of four parts% 12 %ar"?are ;2 So$t?are <2 Data 42 User

.ardware%
1he mechanical devices that make up the computer are called hardware. .ardware is any part of the computer you can touch. ! computerGs hardware consists of interconnected electronic devices that you can use to control the computerGs operation# input# and output. (1he generic term device refers to any piece of hardware.) .ardware refers to any physical component of computer. :or e5ample# C&9# monitor (/(9)# keyboard# hard disk# floppy disk# printer etc. are physical components and# thus# are all hardware.

Software%
Software is a <set of instructions that makes the computer perform tasks and software tells the computer what to do=. (1he term program refers to any piece of software.) Some programs e5ist primarily for the computerMs use to help it perform tasks and manage its own resources. Other types of programs e5ist for the user# enabling him or her to perform tasks such as creating documents. 1housands of different software programs arc available for use on personal computers. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 02

1 COMPUTER COURSE

k.suresh

:or e5ample% (OS ((isk Operating System)# -!SIC# CO-O,# d-ase# !ccounting Software etc.

(ata%
(ata consist of individual facts# figures or pieces of information that by themselves may not make much sense to a person. ! computerGs primary Bob is to process these tiny pieces of data in various ways# converting them into useful information.

9sers%
&eople are the computer operators# also known as users. It can be argued that some computer systems are complete without a personGs involvement@ however# no computer is totally autonomous. *ven if a computer can do its Bob without a person sitting in front of it# people still design# build# program# and repair computer systems. 1his lack of autonomy is especially true of personal computer systems# which arc the focus of this book and are designed specifically for use by people.



'.!1 ! * 1.* <I)&91 (*/IC*S=N
0. Leyboard% 2. "ouse% 3. Scanner% 4. 1rack ball% 6. 1rack pad or touchpad% 7. 1ouch Screen% 8. ,ight pen% ?. ;oystick% F. Optical "ark eader (O" )% 0A.-ar Code eader% 00.Optical Character eader (OC )% 02."agnetic Ink Character ecognition ("IC )%

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1 COMPUTER COURSE /E:.O!RD

k.suresh

/E: .O!RD 1. Leyboard is the main input device of a computer (similar to a typewriter). ;. It contains three types of keys a'phanumeric 0e&s2 Mo"i$ier 0e&s2 *umeric 0e&s2 Specia' 0e&s2 ,unction 0e&s. <. 1he function of each and every key can be well understood only after working on a &C. 'hen any key is pressed# an electronic signal is produced. 1his signal is detected by a keyboard encoder that sends a binary code corresponding to the key pressed to the C&9. 42 1here are many types of keyboards but 0A0 keys keyboard is the most popular one.

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1 COMPUTER COURSE The !'phanumeric /e&s

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1he alphanumeric keys are looks like a typewriterMs keys. 1hose are arranged the same way on almost every keyboard. Sometimes this common arrangement is called the K'* 1H layout. -ecause the first si5 keys on the top row of letters are K# '# *# # 1# and H. !long with the keys that produce letters and numbers. 1he alphanumeric key group includes four keys having specific functions. 1he 1!-# C!&S ,OCL# -!CLS&!C*# and *)1* keys are described !lphanumeric keys. 1hat are used to type all alphabets# numbers and special symbols like O# P# Q# ! etc. The Mo"i$ier /e&s 1he S.I:1# !,1 (!lternate)# and C1 , (Control) keys are called modifier keys. because they modify the input of other keys. In other words# if you hold down a modifier key while pressing another key# then you are changing the second keyMs input in some way. :or e5ample# if you press the ; key# you input a small letter. -ut if you hold down the S.I:1 key while pressing the ; key# you input a capital. "odifier keys arc e5tremely useful because they give all other keys multiple capabilities. The *umeric 0e&s 1he numeric keypad is usually located on the right side of the keyboard. 1he numeric keypad looks like a calculatorMs keypad# with its 0A digits (A to F) mathematical operators (R# -# S# and D). 1he numeric keypad also features a )9" ,OCL key# which forces the numeric keys to input numbers. 'hen )9" ,OCL is deactivated# the numeric keypadMs keys perform cursor movement control and other functions. The ,unction /e&s 1he :unction keys such as T:lU# T:2U# T:3UJJ. Tf02U.are used to give special commands depending upon the software used. 1hey are usually arranged in a row along the top of the keyboard. 1hey allow you to input commands without typing long strings of characters or navigating menus or dialog bo5es. *ach function keyMs purpose depends on the program you are using. :or e5ample# in most programs# :l is the help key. 'hen you press it# a special window appears to display information about the program you are using. "ost I-"-compatible keyboards have 02 function keys. "any programs use function keys along with modifier keys to give the function keys more capabilities. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 06

1 COMPUTER COURSE

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S(&OI)1I)$ (*/IC*S) "O9S*%
! mouse is an input device that you can move around on a flat surface (usually on a desk or keyboard tray) and controls the pointer. 1he pointer (also called the mouse pointer) is an onscreen obBect# usually an arrow# that is used to select te5t@ access menus@ and interact with programs# files# or data that appear on the screen. :igure 2!.00 shows an e5ample of a pointer in a program window. 1he mouse can mainly divided into two types% 12 The mechanica' mouse ;2 The optica' mouse. 1he "*C.!)IC!, "O9S* is the most common type of pointing device. ! mechanical mouse contains a small rubber ball that can see through a hole in the bottom of the mouseMs case. 1he ball rolls inside the case when you move the mouse around on a flat surface. So Inside the mouse# the ro''ers and sensors send signals to the computer# telling it the "istance@ "irection@ an" spee" of the ballMs motions. 1he computer uses this data to position the mouse pointer on the screen.

1he O&1IC!, "O9S* is a non-mechanical mouse. 1his type of mouse emits a 1eam o$ 'ight from its underside. It uses the lightMs reflection to Budge the "istance@ "irection@ an" spee" o$ its tra#e'.

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1 COMPUTER COURSE Uses o$ Mouse

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Hou use a mouse to move the pointer to a location on the screen# a process called pointing. *verything you do with a mouse is accomplished by combining pointing with four techni>ues% a. Clicking b. (ouble-clicking c. (ragging d. ight-clicking

C'ic0ing is used for click an item with the mouse and move the pointer to the item on the screen. 'hen the pointer touches the obBect# >uickly press and release the primary mouse button once. Clicking or single clicking is the most important mouse action. 1o select any obBect on the screen# such as a menu# command# or button# you click it. Dou1'eAc'ic0ing means pointing to the item with the mouse pointer and then pressing and releasing the mouse button twice in rapid succession. (ouble-clicking is primarily used with desktop obBects such as icons. :or e5ample# you can double-click a programMs icon to launch the program. Dragging an item means positioning the mouse pointer over the item# pressing the left mouse button# and holding it down as you move the mouse. !s you move the pointer# the item is <dragged= along with it across the screen. Hou can then drop the item in a new position on the screen. 1his techni>ue is also called "ragAan"A"rop e"iting# or Bust "rags an" "rop. RightAc'ic0ing means pointing to an item on the screen# then pressing and releasing the right mouse button. ight-clicking usually opens a shortcut menu that contains commands and options that pertain to the item to which you are pointing.

SC!))* %
! scanner is widely used in (esktop &ublishing ((1&) applications. It is used for digitiCing images such as photographs# forms# documents etc. 1here are many types of scanners which can also read te5t by converting them to digital code. 1he scanners are very useful for converting the typed pages into word processing files. $raphic scanners convert a printed image into video image without converting it to digital code.V ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 08

1 COMPUTER COURSE

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1 !CL -!,,%
! trackball is a pointing device. 1hat works like an upside-down mouse. Hou put your second finger or thumb on an e5posed ball# then place your other fingers on the buttons. Hou roll the ball with your second finger or thumb for move the pointer around the screen. -ut you do not move the whole device. a trackball re>uires less space than a mouse. 1rackballs come in different models. Some trackballs are large and heavy with a ball about the same siCe as a cue ball. "ost trackballs having two buttons# although three-button models are also available. 1rackball units also are available in right- and left-handed models.

1 !CL&!( O 1O9C.&!(%
1he trac0 pa" also called a touchpa". It is a pointing device that many people find less tiring to use than a mouse or trackball. 1he movement of a finger across a small touch-sensitive surface is translated into pointer movement on the computer screen. 1he touch pad surface may be only 0.6 or 2 inches s>uare. 1he track padGs siCe also makes it suitable for a notebook computer. Some notebook models feature a built-in track pad rather than a mouse or trackball. 1rack pads include two or three buttons# which perform the same functions as mouse buttons. Some track pads arc also <strike sensitive#W meaning you can tap the pad with your fingertip instead of using its buttons.

1O9C. SC **)%
It allows the user to operateDselections by simply touching the display screen. Some special /(9 devices have touch screens. 1hese screens are sensitive to human fingers and act as tactile input devices. 9sing touch screen# the user can point to a selection on the screen instead of pressing keys. 1ouch screen helps users to get information >uickly. It is mainly used in hote's or airports to convey information to visitors. Common e5amples of touch screen include information kiosks# and bank !1"s.

,I$.1 &*)%
,ight pen similar to a pen and it is a pointing device. 1his is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photoce'l and an optica' s&stem placed in a sma'' tu1e. 'hen its tip is moved over monitor and pen button is pressed# its photocell-sensing element detects the screen location and sends corresponding signal to C&9. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 0?

1 COMPUTER COURSE

k.suresh

;OHS1ICL%
;oystick is also a pointing device used to move cursor position on a monitor screen. It is a stick having a spherica' 1a'' at its both lower and upper ends. 1he lower spherical ball moves in a soc0et. It can be moved in all the four directions. 1he function of a Boystick is similar to that of a mouse. It is mainly used in Computer-!ided (esigning (C!() and playing computer games.

O&1IC!, "! L *!(* (O" )%
Optical "ark eader (O" ) is a special type of optical scanner used to recogniCe the type of mar0 ma"e 1& pen or penci' . It is especially used for checking answer sheets of e5amination having multiple-choice >uestions. 1he answer sheet contains special marks such as sBuares or 1u11'es. 1he student fills in these s>uares with soft pencil or ink to indicate the correct choice. 1he O" detects these marks and sends corresponding signals to the processor. If a mark is present# the amount of reflected light is reduced. O" detects the presence of mark for each and every answer. 1hese are widely used for almost all competitive e5aminations having obBective type >uestions.

-! CO(* *!(* %
-ar code reader is an optical scanner used for reading bar coded data (data in the form of light and dark lines). 1he bar coded data consists of a number of bars of varying thickness and spacing between them. 1he bar code reader reads the bar coded data and converts it into electrical pulses which are then processed by computer. -ar coded data is generally used in labeling goods# numbering the books# or encoding I( or !Dc numbers.

O&1IC!, C.! !C1*

*!(* (OC )%

Optical Character eader (OCR) is an optical scanner which is capable of identifying !'phanumeric characters typed or printed on paper using an OC font. 1he te5t which is to be scanned by a low fre>uency light source. 1he dark areas on the te5t collect the light while light areas reflect it. 1he photocells of OC device receive this reflected light and provide binary data corresponding to dark and light areas. OC devices are used for large volume applications like reading of passenger tickets# computer printed bills of credit card companies and XI& codes in postal services. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 0F

1 COMPUTER COURSE

k.suresh *CO$)I1IO) ("IC )%

"!$)*1IC I)L C.! !C1*
<"agnetic Ink Character

ecognition= (MICR) is used to recogniCe the magnetically "IC device reads the patterns of these

charged characters mainly found on bank che>ues. 1he magnetically charged characters are written by special ink called <magnetic in0=. characters and compares them with special patterns stored in memory.

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2A

1 COMPUTER COURSE

k.suresh



'.!1 ! * 1.* O91&91 (*/IC*S%
("onitors# printers

and plotters)

"O)I1O S%
1he monitor is the most commonly used output device on most personal computer systems. 'hen you are typing a letter# copying files# or surfing the Internet that are looking at your monitor. 1hey want to see whether the image is crisp and clear and how well graphics are displayed on the monitor. 1wo important hardware devices determine the >uality of the image you see on any monitor% (0) 1he monitor (2) 1he video controller. Color monitors can display between 07 colors and 07 million colors. 1oday# most new monitors display in color. "any color monitors can be set to work in monochrome or grayscale mode. 1he monitors can be divided into to types based on color% Monochrome monitors It can display only one color that is black. (Such as green# amber# or white) against a contrasting background. 1hese monitors are used for only displays <te=t>. 'here the user does not need to see color graphics. )ra&sca'e monitors It can display various intensities of gray from a very little gray to black against a white or off-white background. !nd these are essentially a type of monochrome monitor. $rayscale flat panel displays are used in low-end portable systems. 1here are two types of monitors are used with &Cs. ! catho"e ra& tu1e (CRT) ! $'atApane' "isp'a& 1)2 ! catho"e ra& tu1e (CRT) 0. 1he cathode ray tube (C 1) monitor comes with most desktop computers. 2. It looks a television screen. 1his type of monitor uses a large vacuum tube for display2 3. 1he C 1 monitor works from back o f a monitorMs housing is an e'ectron gun. 4. 1he gun shoots a beam of electrons through a magnetic coil called a &o0e. 1his aims the beam at the front of the monitor. 6. 1he back of the monitorGs screen is coated with phosphors# chemicals that glow when they are struck by the electron beam. 7. 1he screenGs phosphor coating is organiCed into a gri" o $ "ots. 8. 1he smallest number of phosphor dots that the gun can focus on is called a pi=e'2 ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 20

1 COMPUTER COURSE

k.suresh

?. 1he &i5el is a contraction of the term picture element. *ach pi5el has a uni>ue address# which the computer uses to locate the pi5el and control its appearance. Some electron guns can focus on pi5els as small as a single phosphor dot. F. 1he electron gun does not Bust focus on a spot and shoot electrons at it. 0A. It systematically aims at every pi5el on the screen# starting at the top left corner and scanning to the right edge. 1hen it drops down a tiny distance and scans another line. 00. ! C 1 monitor contains a shadow mask# it is a fine mesh made of metal# fitted to the shape and siCe of the screen. 02. 1he holes in the shadow maskGs mesh are used to align the electron beams# to ensure that they strike precisely the correct phosphor dot. In most shadow masks# these holes are arranged in triangles. C 1 monitors have long been the standard for use with desktop computers because they provide a bright# dear picture at a relatively low cost.

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22

1 COMPUTER COURSE ;)2 ! $'atApane' "isp'a&

k.suresh

1he :lat-panel monitors have been used primarily on portable computers. a new generation of large# high-resolution# flat-panel displays is gaining popularity among users of desktop systems. 1hese new monitors provide the same viewable area as C 1 monitors# but they take up less desk space and run cooler than traditional C 1 monitors. 1here are several types of flat-panel monitors% I)2 -iBui" cr&sta' "isp'a& (-CD) 1he ,C( monitor creates images with a special kind of li>uid crystal. 1hat is normally transparent but becomes opa>ue when charged with electricity. ,C( monitors is that their images can be difficult to see in bright light. :or this reason# laptop computer users often look for shady places to sit when working outdoors or near windows. ! bigger disadvantage of ,C( monitor is their limited viewing angle. 1hat is the angle from which the displayMs image can be viewed clearly. Hou can sec the image clearly even when standing at an angle to the screen with most C 1 monitors. In ,C( monitors the viewing angle shrinks and as you increase your angle to the screen# the image becomes fuCCy >uickly. II)2 The passi#e matri= -CD The passi#e matri= -CD works based on transistors for each row and each column of pi5els. ! grid that defines the location of each pi5el. 1he color displayed by a pi5el is determined by the electricity coming from the transistors at the end of the row and the top of the column. !nother disadvantage is that they donGt <refresh= the pi5els very >uickly. If you move the pointer too >uickly# it seems to disappear an effect known as submarining. !nimated graphics can appear blurry on a passive matri5 monitor. Other T&pes o$ Monitors (epending upon the resolution# monitors can be classified as follows% a2 C)!% (Color Graphics Adapter): It is a circuit board introduced by I-" and the first graphics standard for the I-" &C. 'ith a C$! monitor# it is harder to read than with a monochrome monitor# because the C$! (32A I 2AA) has much fewer pi5els than the monochrome monitor (74A I 36A). It supports 4 colors.

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1 COMPUTER COURSE 12 E)!% (Enhanced Graphics Adapter)%

k.suresh

*$! is a video display standard that has a resolution of 74A by 36A pi5els and supports 07 colors. *$! supports previous display modes and re>uires a new monitor. c2 ()!% (Video Graphics Array) t This is a video display standard that provides medium to high resolution. In a te5t mode# the resolution of this board is 82A by 4AA pi5els. It supports 07 colors with a higher resolution of 74A by 4?A pi5els and 267 colors with 32A I 2AA pi5els. "2 Super ()!% 1his is a very high resolution standard that displays up to 76#637 colors. Super ()! can support 07.? million colors at ?AA by 7AA pi5els and 267 colors at 0A24 by 87? pi5els. ! high-priced super /$! allows 02?A by 0A24 pi5els. ,arger monitors (08W or 20W and larger) with a high resolution of 07AA by 02?A pi5els are available. VESA (Video Electronics Standards Association) has set a standard for super /$!.

PRI*TERS
! printer is an output device that produces a hard copy of data. 1he resolution of printer output is e5pressed as (&I. &rinters can produce te5t and images on paper. &aper can be either separate sheets such as !4 !6 !3 etc. or they may be able to print on continuous (fanfold) paper that feed through the machine.

Dais&AWhee'@ Chain Printer@

Drum printer

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1 COMPUTER COURSE

k.suresh

1) Impact Printers
In this hammers or pins strike against a ribbon and paper to print the te5t. 1his mechanism is known as electro-mechanical mechanism. 1hey are of two types. (i) (ii) (iii) (i#) (#) (vi) Character Printer% It prints only one character at a time. It has relatively slower speed. *.g. Of them are (ot matri5 printers. Dot Matri= Printer% (ot-matri5 printers print about 4CA<CC characters per secon" (cps) and can print some graphics# although the reproduction Bua'it& is poor. Co'our ri11ons are available for limited use of colour. (ot-matri5 printers are nois&@ ine=pensi#e# and they can print through multipart forms# creating several copies of a page at the same time# -ine Printer It is a high-speed printer capable of printing an entire line at one time. ! fast line printer can print as many as <@CCC lines per minute. 1he disadvantages of line printers are that they cannot print graphics# the print >uality is low# and they are very noisy. Dais&AWhee' Printer aisy!Wheel is a printer mechanism that uses any kind of hub (wheel) having a set of spokes at the margin of the hub. 1he wheel can be removed to use a different character set. 1he end of each spoke is a raised image of a type character. 'hen the wheel is turned and the re>uired character is aligned to the print hammer# the character is then struck into a ribbon and onto a paper with the hammer. (aisy-wheel printers cannot print graphics@ an" in general they are noisy and slow@ printing from 1C to a1out 85 characters per second. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 26 Character Printer Dot matri= printer -ine Printer Dais&AWhee' Printer Drum printer Chain Printer

1 COMPUTER COURSE

k.suresh

Drum printer In which each complete set of characters for each print position on a line is on a continuously rotating drum behind an inked ribbon. In front of the ribbon identical characterGs are printed continues with a ribbon at all re>uired position on a line. Chain Printer It is the character printer. 1he print element in a chain printer is a meta''ic 1an" or chain containing the embossed characters that rotates horiDonta''& in front of paper. ! complete chain consists of the five sections@ each section consists of 4? characters. !s the print chain rotates# properly timed print hammers strike the paper along with linked ribbon# against the proper character on the chain as it passes. Chain printers are one of the fastest impact printers that can produce up to 4AA to 26AA characters per second. Chain &rinter also called band printers# contain characters on a rotation band. Speeds of up to 3AAA lines a minute may be possible with these machines.

;) *onAImpact Printers%
1here printers use non-Impact technology such as ink-Bet or laser technology. 1here printers provide better >uality of OD& at higher speed. )on-impact printers# used almost everywhere now# are faster and >uieter than impact printers because they have fewer moving parts. )on-impact printers form characters and images without direct physical contact between the printing mechanism and the paper. 1hese printers are of two types% 0. In0AEet Printer ;2 -aser Printer

In0AEet Printer
Ink-Bet printers also print images ?ith 'itt'e "ots. In0AFet printers spra& sma''@ e'ectrica''& charge" "rop'ets o$ in0 from four noCCles through holes in a matri5 at high speed onto paper. Ink-Bet printers can print in co'our and are >uieter and much less e5pensive than a colour laser printer. .owever# they are slower and print in a somewhat lower reso'ution (<CCA 8;C "pi) than laser printers. Some new# e5pensive ink-Bet printers print up 1;CC or 14CC "pi. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 27

1 COMPUTER COURSE

k.suresh

1he another type of ink-Bet technology is the 1u11'eAFet printer# which use miniature heating elements to force specially formulated inks through print heads with 1;9 tin& noDD'es. 1he mu'tip'e noDD'es print $ine images at high spee"s . 1his technology is commonly used in portable printers.

-aser Printer
,aser &rinter is a type of printer that utiliCes a laser beam to produce an image on a drum. 1he light of the laser alters the electrical charge on the drum wherever it hits. 1he drum is then rolled through a reservoir of toner# which is picked up by the charged portions of the drum. :inally# the toner is transferred to the paper through a combination of heat and pressure. 1his is also the way copy machines work. -ecause an entire page is transmitted to a drum before the toner is applied# laser printers are sometimes called page printers. 1here are two other types of page printers that fall under the category of laser printers even though they do not use lasers at all. One uses an array of ,*(s to e5pose the drum and 1he other uses ,C(s. Once the drum is charged# however# they both operate like a real laser printer. One of the chief characteristics of laser printers is their resolution E how many dots per inch (dpi) they lay down. 1he available resolutions range from 3AA dpi at the low end to 0#2AA dpi at the high end.

P-OTTERS
! plotter is a computer printing device for printing #ector graphics. In previous days# plotters were widely used in computer-aided design applications. 1hough they have generally been replaced with wide-format conventional printers. It is now common place to refer to such wide-format printers as Wplotters#W &lotter is a device that "ra?s pictures on paper based on commands from a computer. &lotters different $rom printers in that they draw lines using a pen2 !s a result# they can produce continuous lines# whereas printers can only simulate lines by printing a closely spaced series of dots. "ulti colour plotters use different-collared pens to draw different colours. In general# plotters are considerably more e5pensive than printers. 1hey are used in engineering applications where precision is mandatory.

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1 COMPUTER COURSE

k.suresh

& OC*SSI)$ (!1!
 .O' *& *S*)1 (!1! CO"&91* SN 1he data can be represented in computers in different ways. 1hey are% 1) )umber system( -inary number# and (ecimal number ) ;) -its and bytes. <) 1e5t codes (*-C(IC# !SCII#*!SCII# and 9)ICO(*) 12 *um1er s&stem "ost modern computer systems do not represent numeric values using the decimal system. Instead# they typically use a binary or twoGs complement numbering system. 1o understand the limitations of computer arithmetic# you must understand how computers represent numbers. 1hese are two types of number system used to represent data% a2 .inar& *um1er S&stem 12 Decima' num1er s&stem a2 .inar& *um1er S&stem (igital computers internally use the binary number system (base 2) to represent data and perform arithmetic calculations. 1he binary number system is very efficient for computers# but not for humans. epresenting even relatively small numbers with the binary system re>uires working with long strings of 1 and C2 "ost modern computer systems (including the I-" &C) operate using binary logic. 1hese two values# co-incidentally# correspond to the two digits used by the binary numbering system. 1herefore# it is very easy to convert a binary number to decimal. :or each <0= in the binary string# add in 2n. 'here <n= is the Cero-based position of the binary digit.

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1 COMPUTER COURSE

k.suresh

;2 .ITS !*D .:TES ! bit is the smallest possible unit of data a computer can recogniCe or use. ! binary digit is a single numeral in a binary number. *ach 0 and A in the number below is a binary digit% E 0 A A 0 A 0 A 0. 1he term <binary digit or binary integer= is commonly called a <.it.= ! group of eight bits is called a <.&te>. .alf of a byte is called a <ni11'e=. 'ith one byte# the computer can represent one of 267 different symbol s or characters because the eight 0s and A s is can be combined in 267 different ways. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 2F

1 COMPUTER COURSE <2 TEGT CODES

k.suresh

*arly programmers realiCed that they needed a standard te5t code that was agreeable to all of them. In such a system# numbers would represent the letters of the alphabet# punctuation marks# and other symbols. 1his standard code system would enable any programmer or program to use the same combinations of numbers to represent the same individual pieces of data. 1he $our most popu'ar te5t code systems invented are the following% I) E.CDIC% *-C(IC (pronounced *--si- dic) stands for *5tended -inary Coded (ecimal interchange Code. *-C(IC b an eight-bi t code that defines 267 symbols. It is still used in I-" mainframe and midrange systems# but it is rarely encountered in personal computers. II) !SCII !SCII (pronounced !S-key) stands for the !merican Standard Code for Information Interchange. 1oday# the !SCII character set is by far the most commonly used in computers of all types. !SCII is an eight-bi t code that specifics characters for values from A to 028 . III) EGTE*DED !SCII *5tended !SCII is an eight-bi t code that specifies the characters for values from 02 ? to 266. 1he first 4A symbols represent pronunciation and special punctuation. 1he remaining symbols are graphic symbols. I() U*ICODE2 1he 9nicode 'orldwide Character Standard provides up to four bytesY32 bitsYto represent each letter@ number# or symbol. 9nicode codes can be created to represent more than 4 billion different characters or symbols with four bytes. 1his total is enough for every uni>ue character and symbol in the world# including the vast Chinese# Lorean# and ;apanese character sets and t hose found in known classical and historical te5ts. In addition to world letters# special mathematical and scientific symbols are represented in 9nicode. One maBor advantage that 9nicode has over other te5t code systems is its compatibility with !SCII codes. he first 267 codes in 9nicode are identical to the 267 codes used by the !SCII and *5tended !SCII systems.

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3A

1 COMPUTER COURSE  .O' & OC*SS 1.* (!1! I) CO"&91* N

k.suresh

Processing is the thin0ing that the computer does - the calculations# comparisons# and decisions. Computers process very large amounts of data because they can communicate the data much more >uickly than a person. "ost data processing is mundane# and would be prone to human error if not processed by computer. 1he processing can be done in computer at t?o places. 1hey are • • CPU MEMOR:

12 CPU ( Centra' Processing Unit ) 1he CPU# or Centra' Processing Unit# is the part of the computer where work gets done. In most computers# there is one processing chip. C&9 performance is often measured in mi''ions o$ instructions per secon" ("I&S). )ewer C&9s can be measured in 1i''ions o$ instructions per secon" (-I&S). C&9 has two parts called CO)1 O, 9)I1 and !,9. Contro' Unit 1he control unit is responsible for controlling the transfer of data and instructions among other units of a computer. It is considered as the <central nervous system= of a computer as it manages and coordinates all the units of computer. It also performs the physical data transfer between memory and hardware devices. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 30

1 COMPUTER COURSE !rithmetic 'ogic unit (!-U)

k.suresh

!,9 stands for !rithmeticD,ogic 9nit. 1his is the part that e5ecutes the computerMs commands. ! command must be either a basic arithmetic operation or one of the 'ogica' comparisons. Operations Per$orme" 1& the !rithmetic -ogic Unit (!rithmetic Operations) R S P !dd Subtract "ultiply (ivide ise by a power 1he !-U includes a group of registers with high-speed memory locations built directly into the C&9 that are used to hold the data currently being processed. Hou can think of the register as a scratchpad. 1he !,9 w ill use the register to hold the data currently being used for a calculation. :or the data processing and e5ecution C&9 can take four steps% 12 ,etching% -efore the C&9 can e5ecute an instruction# the control unit must retrieve (or fetch) a command or data from the computerGs memory. ;. Deco"ing -efore a command can be e5ecuted# the control unit must break down (or decode) the command into instruct ions that correspond to those in the C&9Gs instruction set. <2 E=ecuting 'hen the command is e5ecuted# the C&9 carries out the instructions in order by converting them into microcode. 42 Storing2% 1he C&9 may be re>uired to store the results of an instruction in memory (but this condition is not always re>uired). (-ogica' Operations) Z# [ e>ual to# not e>ual to U# \U greater than# not greater than T# \ T (,ess than# not less than

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1 COMPUTER COURSE

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2. "emory%
1he C&9 contains the basic instructions needed to operate the computer@ but it cannot store entire programs or large set s of data permanently. 1he C&9 needs to have millions (or even trillions) of bytes of space where it can >uickly read or write programs and data while they are being used. 1his area is called memory# and it consists of chips either on the motherboard or on a small circuit board attached to the motherboard. 1here are three types of built-in memory% permanent@ nonApermanent an" $'ash memor&2 I) Permanent or *onA#o'ati'e Memor& Some memory chips contain or stores the data even when the computer is turned off. 1his type of permanent memory is called non#o'ati'e2 1he data in t these chip is only read and used but it can not changed the data. so the memory is called read only memory (RO M )2 1he O" contains a set of start-up instructions called the <-asic input output system= (.IOS) for a computer. .IOS contains another set of routines@ this routine is called the <power on self test= (POST)2 1he omGs can be divided into PROM@ EPROM an" EEPROM. II) *onApermanent or (o'ati'e Memor& /olatile memory re>uires power to store data. 1he volatile memory in a computer is called <random access memory= (R!M). !"Ms Bob is to hold programs and data while they are in use. !"Ms lose the programs and data when the computer is switch-off. R!M consists of Single in-line memory modules (SIMMs) and dual in-line memory module (DIMM) chips are found in <desktop computers=. Small outline (I"" (SOADIMM) chips are found in <laptop computers=. III) ,'ash Memor& :lash memory is a special type of nonvolatile memory. It is often used in portable digital devices for storage. (igital cameras# portable "&3 players# 9S- < key chainW storage devices# and game consoles all use flash memory. 1he flash memory works by having actual switches store the binary values that make up the data. 1hus# on a camera with a flash card# the picture is stored on the card by turning millions of tiny switches on and off. -arring catastrophic damage to the card# the picture is stored indefinitely. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 33 chips on a small circuit board.

1 COMPUTER COURSE  '.!1 IS .USN '.!1 ! * 1.* (I::* *)1 1H&*S O: -9SGSN

k.suresh

The .us
<! bus is a path between the components of a computer= 1here are two main b uses in a computer% <Interna' or s&stem 1us>2 HE=terna' or e=pansion 1us=. a2 1he s&stem 1us displayed on the motherboard and connects the C&9 to other devices that reside on the motherboard. Cables from disk drives and other internal devices are plugged into the bus. 12 !n e=terna' 1us connects e5ternal devices# such as the keyboard# mouse# modem# and printer and so on# to the C&9. c2 1he s&stem 1us has two parts HThe "ata 1us> HThe a""ress 1us>

The Data .us
1he "ata 1us is an electrical path that connects the C&9# memory and the other hardware devices on the motherboard. 1he bus is a group of parallel wires. 1he number of wires in the bus affects the speed at which data can travel between hardware components. -ecause each wire can transfer one bit of data at a time. !n eight ?ire bus can move 9 1its at a time. ! 17 1it bus can transfer ; .&tes at a time ! <;A1it bus can transfer 4 .&tes at a time. 1he new model computers have a 74-bit data bus called the ,ront Si"e .us that transfers 9 .&tes at a time. 1he busMs spee" is measured in megahertC (M%D)2 1he maBority of todayGs &Cs have a bus speed of either 1CC M%D or 1<< M%D# but higher speeds of bus is 9CC M%D2 ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 34

1 COMPUTER COURSE

k.suresh

The !""ress .us
1he address bus is a set o$ ?ires similar to the data bus. 1he address bus connects only the C&9 and !" and carries only memory addresses. emember each byte in !" is associated with a num1er@ which is its memory address.

Categories of busGs%
12 IS! 1us The In"ustr& Stan"ar" !rchitecture (IS!) bus. It is a 17 A1it data bus. It became the de facto industry standard on its release in the mid-0F?As and is still used in many computers to attach slower devices (such as modems and input devices) to the C&9. ;2 The -oca' 1us 1he -oca' 1us was developed to attach faster devices to the C&9. ! local bus is an internal system bus that runs between components on the motherboard. "ost system buses uses some type of local bus technology today and are coupled with one or more kinds of e5pansion bus. <2 PCI 1us 1he Periphera' Component Interconnect (&C I) bus. It is a type of local bus designed by Intel to make it easier to integrate new data types# such as audio# video# and graphics. 42 !)P 1us 1he !cce'erate" )raphics Port (!$&) bus. It is incorporates a special architecture that allows the video card to access the systemGs !" directly. It is increasing the speed of graphics performance. 1he !)P standard has led to the development of many types of accelerated video ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 36

1 COMPUTER COURSE

k.suresh

cards that support 3-( and full- "otherboard motion video. 'hile !$& improves graphics performance# it cannot be used with all &Cs. 52 US. 1us 1he Uni#ersa' Seria' .us (9S-) is a relatively new bus found on all modern machines. 9nlike the &CI and !$&# 9S- is a hot swappable bus. 1his means that a user can connect then disconnect a 9S- device without affecting the machine. 9S- supports up to 028 devices connected in either a "ais& chain or hu1 layout. 72 IEEE 1<34 I*** 03F4 (,ire W ire) ports were once found only on "acintosh computers# but they are now increasingly common in I-"-compatible &Cs. :ire'ire is used to connect video devices such as cameras and video cameras. "any digital 1/ connections also use :ire'ire. 82 PC Car" 1us 1he PC Car" bus is used e5clusively on laptop computers. ,ike 9S-# &C Card is hot swappable. ! &C Card is about the siCe of a stack of four credit cards. Common uses for &C Card include 'i:i cards# network cards# and e5ternal modems.

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MEMORY
'.!1 IS "*"O H (O ) S1O !$* (*/IC*N (Or) '.!1 ! * 1.* (I::* *)1 1H&*S O: S1O !$* (*/IC*SN (Or) *I&,!I) !-O91 (I::* *)1 1H&*S O: "*"O HSN S&rimary memory devices%
De$inition 0. "emory or storage capacity is one of the important components of a computer.

!ny storage unit of a computer system is classified on the basis of the following criteria% !ccess time% 1his is the time re>uired to locate and retrieve stored data from the storage unit in response to program instructions. 2. Storage capacit&% It is the amount of data that can be stored in the storage unit. 3. Cost per 1it o$ storage. 1he computer stores a character in the storage cells with binary (A#0) mechanism. 1hus the basic unit of memory is a bit (binary digit A# 0). 1o store a character in a computer re>uires ? bits or 0 byte. 1his is called the word length of the storage unit. 1he different units of measurement are ? -its Z 0 -yte 20A (or) 0A24 -ytes Z 0 Lilo -yte (L-) 20A L- (or) 0A24 L- Z 0 "ega -yte ("-) 20A "- (or) 0A24 "- Z 0 $ega -yte ($-) 20A $( or)

0A24 $- Z 0 1erra -yte (1-) 12Primar& memor& (main memor&) ;2 Secon"ar& memor&

1here are mainly two types of memories%

12 Primar& memor& (main memor&) a. &rimary memory is the one of the main memory of the computer. b. &rimary memory is accessible directly by the central processing unit.

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c. In &rimary memory the contents or data is lost as soon as if the computer is switched off. Hou can store and retrieve data much faster with primary memory. d. -ut the &rimary memory is more e5pensive and siCe is less. e. It can stores the necessary programs of the system software for e5ecute user programs. 1he main memory or primary memory can be divided into two types% a. R!M ( andom !ccess "emory) b. ROM ( ead Only "emory).

Ran"om !ccess Memor& (R!M)
a) R!M stands for Ran"om !ccess Memor&2 1) It is possible to select randomly and use any location of the memory directly store and retrieve data. c) It is also called read or write memory. ") 1he data or instructions can be stored in the !" is temporarily. e) In !" data is disappears as soon as the power to the computer is switched off. $) So now we can say that !" is #o'ati'e memory. g) 1his can be divided into 2 types% S1!1IC !" and (H)!"IC !". h) In the static ram the data or instruction can stores only as long as the power supply is O). i) -ut in the dynamic ram the information or data can be stored very short time and it refreshed periodically.

Rea" On'& Memor& (ROM)
a) ROM stands for Rea" on'& Memor&2 1) 1his can store the programs and data is permanently. c) 1he O" stores some standard processing programs supplied by the manufacturers to operate the personal computer. ") 1he O" can only be rea" by the C&9 but it cannot be changed or write any data. e) It does not loose their content# data or instructions if the power supply is failure or supply off. $) O" also called as nonA#o'ati'e memory. g) 1his can be divided into 3 types% PROM@ EPROM@ EEPROM an" ,-!S% ROM

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1 COMPUTER COURSE PROM%

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PROM (&rogrammable ead Only "emory) memories were developed at the end of the 8As by a company called HTexas Instruments”2 1hese memories are chips comprising thousands of fuses or diodes that can be I1urntI using a device called a < O" programmerW# applying high voltage (02/) to the memory bo5es to be marked. 1he fuses thus burnt correspond to A and the others to 0. EPROM EPROM (*rasable &rogrammable ead Only "emory) memories are & O"s that can be deleted. 1hese chips have a glass panel that lets ultra-violet rays through. 'hen the chip is subBected to ultra-violet rays with a certain wavelength# the fuses are reconstituted# meaning that all the memory bits return to 0. 1his is why this type of & O" is called erasa"le. EEPROM% EEPROM (*lectrically *rasable ead Only "emory) memories are also erasable & O"s# but unlike *& O"Gs# they can be erased by a simple electric current# meaning that they can be erased even when they are in position in the computer. ,'ash ROM ,'ash ROM is also called flash BIO or flash memory. It is a type of constantly powered nonvolatile memory that can be erased and re-programmed in blocks. It is a variation of **& O"# which is erased and rewritten at the byte level. :lash memory is often used to hold the control code such as the -IOS in a personal computer. 'hen -IOS needs to be changed or rewritten# the flash memory can be written in block (rather than byte) siCes# thus making it easier to update.

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JSECO*D!R: STOR!)E MEMOR: DE(ICES 1he secondary storage devices where used to overcome the problems with primary memory. 1he Secondary "emory is also known as !u5iliary "emory or -ackup "emory. 1hese are divided into two typesG magnetic memor& and optica' memories. 1here are so many types of secondary memory devices% 12 ,'opp& Dis0s ;2 %ar" Dis0 (-oca' Dis0) <2 CDAR@ CDARW@ D(DAR@ D(DARW 42 Pen Dri#e 52 +ip Dri#e 72 Memor& Car"s 82 E=terna' %ar" Dis0 M!)*ETIC MEMOR: DE(ICES 12 ,'opp& "is0 a) It is also referred as <(iskette=# and is made of fle5ible </inyl material=. b) It has a small hole on one side called < ight protect notch=# which protects accidental writingDdeleting the information from the disk. c) 1here is a hole in the centre through which the <spindle= of drive unit rotates the disk. d) 1he disks are available in two siCes of 6.26 and 3.6 inches and these could be either lowdensity or high-density floppies. e) Storage capacities of floppies are measured in kilobytes (L-) and megabytes ("-). f) 1he details about the storage capacities of the floppies are presented below%

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1 COMPUTER COURSE (a) (a) (a) (a) (a) (a) 60D4-inch floppy disk ;2 %ar" "is0

k.suresh

a) 1he hard disk can hold more information than the floppy disk and the retrieval of information from hard disk is faster when compared to floppies or tapes. b) ! hard disk is fi5ed inside the C&9 and its capacity ranges from 2A "- onwards. c) 1he hard disk is made up of a collection of discs (one below the other) known as <platters= on which the data is recorded. d) 1hese platters are coated with <magnetic material=. It is less sensitive to e5ternal environmental disorders and hence the storage in hard disk is safe. e) 1he hard disk rotates while recording data. 1his rotation speed is measured in the unit of revolutions per minute (rpm). 1he normal speed of hard disks is 37AA revolutions per second. f) 1he readDwrite head of the hard disks moves across its surface. g) ! small hard disk might be as much as 26 times larger than a floppy disk. h) Storage Capacity of hard disks varies from 2A "- to several $ega bytes like ?A$-# 07A$-.

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JOPTIC!- MEMORIE DE(ICES <2 CDAR@ CDARW@ D(DAR@ D(DARW (i) CDAR (Compact disc ecordable)% (ata can be written onto it Bust once. 1he stored data can be read. (ata once written onto it cannot be erased. Its main advantage is that it is portable and can hold a large amount of data. (ii) CDARW (Compact disc ewritable)% It is also called erasable C(. (ata once written onto it can be erased to write or record new information many times. 1he storage capacity of most C(- O"s is appro5imately 76A "or 8AA "-. C(- O"% C(- O" stands for Compact (iskE ead Only "emory iii) D(D ((igital /ersatile (isc)% (/( stands for (igital /ersatile (isc. It is similar to a C(- O"# e5cept that it can store larger amounts of data. 1he storage capacity of a (/( is at least 4.8"-. (/(s that can store up to 08$-s are also available. -ecause of their capacity# (/(s are generally used to store a very large multimedia presentations and movies that combine high >uality sound and graphics.

42 pen "ri#e(,'ash Dri#e) It is a small# portable device that can be used to store# access and transfer data. (ue to its small siCe# it is commonly called &en drive. It is also called 9S- drive. 'e can read# write# copy# delete# and move data from computer to pen drive or pen drive to computer. It comes in various storage capacities of 2$-# 4$-# ?$- etc.

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1his device is plugged into the 9S- port of the computer and the computer automatically detects this device. 52 +ip "ri#e ! Cip drive is a device for reading and writing data from removable storage (evices called Xip discs. Internal models typically take up a 2.6W drive bay (like a floppy disk drive). *5ternal models are about the siCe of a thick paperback book. ! Cip disk is about the siCe of 3 3.6W floppy disks stuck back to back# but has significantly larger capacity. Xip disks are now# like floppy disks# obsolete. 1hey are physically larger# more e5pensive# slower# store less data and are less reliable then 9S- memory sticks. 72 Memor& car"s ! memor& car" or $'ash car" is an electronic flash memory data storage device used for storing digital information. 1hey are commonly used in many electronic devices# including digital cameras# mobile phones# laptop computers# "&3 players and video game consoles. 1hey are small# re-recordable# and able to retain data without power. 82 E=terna' %ar" "is0 ! hard drive that is outside of the computer case in its own enclosure. "ost e5ternal hard drives support the I(* interface and are slightly bigger than a hard drive itself. 'hen purchasing an e5ternal hard drive you can buy a full e5ternal hard drive system that consists of both the hard drive and the enclosure# or you can purchase Bust the enclosure to hold your own hard drive.

SSolid-State Storage (evices%
Solid state storage devices are uni>ue# among todayGs storage devices because they do not use disks or tapes and have no moving parts. Solid-state storage is either magnetic or optical. Instead# it relies on integrated circuits to hold data. Some solid-state storage devices are nonvolatile% means they can retain their data even when the systemGs power is turned off. Others are volatile% means they re>uire a constant supply of electricity or they will lose their data. 1he deviceGs volatility depends on the type of memory circuits it uses. 1hey are divided into fallowing types% ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 43

1 COMPUTER COURSE 12 ,'ash Memor& ;2 Smart Car"s <2 So'i" State Dis0s

k.suresh

12 ,'ash Memor& :lash memory is a special type of memory chip that combines the features of ! " and O". user or program access data randomly in flash memory and over write any or all of its contents at any time. :lash memory is nonvolatile memory# so data is retained even when power is off. :lash is commonly used in digital cameras and multimedia playersG i.e. " &3 players. 1hese devices usually connect to a computerGs 9S- or :ire'ire port and can store 267 "- or more of data. ;2 Smart Car"s Smart cord is a device with e5traordinary potential and looks like an ordinary credit card. Smart cards contain a small chip that stores data. 1he user can read data from the card# add new data# or revise e5isting data from smart card using a special device called a smart car" rea"er. Some smart cards# called <intelligent smart card=# also contain their own tiny microprocessor@ and they function like a computer. <2 So'i" State Dis0s ! solid-state disk (SS() is not a disk at all. 1his device uses very last memory chips# such as synchronous dynamic !" (S( !" ) to store data. S( !" is much faster than standard !". ,arge-scale SS( systems can store a terabyte or more of data. !n SS( may be a free-standing unit that connects to a server computer or a card that plugs into one of the serverM s e5pansion slots.

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Software + languages
S'hat is software + types of softwareGsN
SO:1'! *% Software is a program or set of instructions that causes the .ardware to
function in a desired way. 1here are two types of software - s&stem so$t?are an" app'icationK uti'it& so$t?are2

!pp'ication so$t?are !pplication software allows end users to accomplish one or more specific (non-computer related) tasks. 1ypical applications include industrial automation# business software# educational software# medical software# databases# and computer games. -usinesses are probably the biggest users of application software# but almost every field of human activity now uses some form of application software. It is used to automate all sorts of functions. S&stem So$t?are or uti'it& so$t?are System Software enables an application software to interact with the computer hardware. System software is the ]backgroundG software that helps the computer to manage its internal resources. 1he most important system software is the operating system. 1he system software performs important tasks such as running the program# storing data# processing data etc. 'indows I& is an e5ample of system software.

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'hat is language and what are the different types of languagesN

COMPUTER -!*)U!)ES ,anguage is the source of communication among human beings. (ifferent countriesDregions have different languages. Similarly# in order to communicate with the computer user also needs to have a language that should be understood by the computer. :or this purpose# different languages are developed for performing different types of work on the computer. -asically# languages are divided into two categories according to their interpretation.

12 -o? -e#e' -anguages
,ow level computer languages are machine codes or close to it. Computer cannot understand instructions given in high level languages or in *nglish. It can only understand and e5ecute instructions given in the form of machine language i.e. language of A and 0. 1here are two types of low level languages% Machine -anguage2 ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 47

1 COMPUTER COURSE !ssem1'& -anguage

k.suresh

a) Machine -anguage It is the lowest and most elementary level of &rogramming language and was the first type of programming language to be developed. "achine ,anguage is basically the only language which computer can understand. In fact# a manufacturer designs a computer to obey Bust one ,anguage# its machine code# which is represented inside the computer by a String of binary digits (bits) A and 0. 1he symbol A stands for the absence of *lectric pulse and 0 for the presence of an electric pulse. Since a computer is Capable of recogniCing electric signals# therefore# it understands machine ,anguage. !"#antages o$ Machine -anguage i) It makes fast and efficient use of the computer. ii) It re>uires no translator to translate the code i.e. directly understood by the computer Disa"#antages o$ Machine -anguage i) !ll operation codes have to be remembered ii) !ll memory addresses have to be remembered. iii) It is hard to amend or find errors in a program written In the machine language iv) 1hese languages are machine dependent i.e. a particular 1) !ssem1'& -anguage It was developed to overcome some of the many inconveniences of machine language. 1his is another low level but a very important language in which operation codes and operands are given in the form of alphanumeric symbols instead of AGs and lGs. 1hese alphanumeric symbols will be known as mnemonic codes and can have ma5imum up to 6 letter combination e.g. !(( for addition# S9- for subtraction# S1! 1#,!-*, etc. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 48

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-ecause of this feature it is also known as ]Symbolic &rogramming ,anguageG. 1his language is also very difficult and needs a lot of practice to master it because very small

;2 %igh -e#e' -anguages
.igh level computer languages give formats close to *nglish language and the purpose of developing h igh level languages is to enable people to write programs easily and in their own native language environment (*nglish). .igh-level languages are basically symbolic languages that use *nglish words andDor mathematical symbols rather than mnemonic codes. *ach instruction in the high level language is translated into many machine language instructions thus showing one-to-many translation

T&pes o$ %igh -e#e' -anguages -!SIC (-eginners !ll &urpose Symbolic Instruction Code). :O 1 !) (,ormu'a Trans'ation)2 &,DI (Programming -anguage@ (ersion 1)2 !,$O, (!lgorithmic ,anguage). !&, (! Programming -anguage)2

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NETWORKS
0K) what is networkN 2K) what are the uses of networksN 3K) what are the different types of networksN 4K) what is topologyN 6K) what are the different types of topologiesN

What is net?or0?
! network is a set of technologies including hardware# software# and media that can be used to connect computers together# enabling them to communicate# e5change information# and share information. )etworks allow many users to access shared data and programs almost instantly. 'hen data and programs are stored on a network and are shared# individual users can substantially reduce the need for programs on their own computers.

What are the uses o$ net?or0s?
12 Simu'taneous !ccess 1here are moments in any business when several workers may need to u se the same data at the same time. 'ithout a network that allows workers to share files# workers must keep separate copies of data stored on different disks by each worker who accesses the data. 'hen the data is modified on one computer# data on the other computers be comes outdated. It becomes difficult to determine which copy of the data is the most current. ;2 Share" Periphera' De#ices ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 4F

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1he ability to share peripheral devices (especially e5pensive ones such as high volume laser printers# which can cost thousands of dollars) is one of the best reasons for small businesses to set up a network. !lthough printers are more affordable than they were a few years ago# it is still too e5pensive to provide every worker with a personal printer. !side from the cost of buying multiple printers# maintenance contracts and supplies increase the total cost of ownership. 'hen several people can share a printer on a network# printing becomes less e5pensive and easier to manage. <2 Persona' Communications One of the most far-reaching applications of personal data communications is electronic mail (e-mail)# a system for e5changing written messages (and# increasingly# voice and video messages) through a network. a) (i"eo con$erencing% /ideo conferencing enables real-time communication over a distance by allowing people at two or more sites to communicate with each other by seeing a video picture of the people at the other sites. *ach site has one or more cameras# microphones# loudspeakers# and monitors# as well as a CO(*C (compressorDde-compressor)# which processes the audio and video. 1) !u"ioAcon$erencing% !udio-conferencing provides an audio link similar to that of a conventional telephone# e5cept that it offers much higher->uality audio and enables more than two sites to be linked together% 9sing hands-free audio units with sensitive microphones and sophisticated echo-cancellation software. !udio-conferencing enables communication between groups of participants. c) DataAcon$erencing% (ata conferencing enables participants at two or more sites to have a shared workspace on their computer desktops. 1his might be a shared <white board=. where they can draw# write# or import and manipulate images collaboratively in real time. Or it might be Wapplication sharing#W where a piece of software can be run and controlled by both users. 42 Easier Data .ac0up In business# data is e5tremely valuable# so it is important that employees back up their data. One way to assure that data is backed up is to keep it on a shared storage device that employees can access through a network. Often the network manager makes regular backups of the data on the shared storage device. "anagers also can use special software to back up files stored on employeesM hard drives from a central location. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 6A

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'hat are the different types of networksN
1here are three main types of networks% 12 -oca' area net?or0s (-!*s) ;2 Wi"e area net?or0s (W!*s)2 <2 Metropo'itan area net?or0s (M!*s) -oca' area net?or0s (-!*s) ! local area network (-!*) is a data communication system consisting of several devices such as computers and printers. 1his type of network contains computers that are physically connected using cables# infrared links# or wireless media. ! ,!) can consist of Bust two or three &Cs connected together to share resources. ! local area network (,!)) is a computer network covering a small physical area# like a home# office# or small group of buildings# such as a school# or an airport.

Wi"e area net?or0s (W!*s) 'ide area network ('!)) is two or more ,!)s connected together# generally across a wide geographical area. 'ide !rea )etwork ('!)) is a computer network that covers a broad ( C.S.) (*$ ** + &.$ CO,,*$* 60 -.I"!/! !"

1 COMPUTER COURSE area In personal (&!)s)# (,!)s)# networks

k.suresh
contrast with area networks local area networks campus area (C!)s)# or metropolitan area

networks ("!)s) which are usually limited to a room# building# campus or specific metropolitan area (e.g.# a city) respectively. 1he largest and most well-known e5ample of a '!) is the Internet.

Metropo'itan area net?or0s (M!*s) 1he metropolitan area network ("!)) is a large scale network that connects multiple corporate ,!)s together. "!)s usually are not owned by a single organiCation@ their communication devices and e>uipment are usually maintained by a group or single network provider that sells its networking services to corporate customers. "!)s often take the role of a high speed network that allows for the sharing of regional resources. "!)s also can provide a shared connection to other networks using a '!) link.

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What is topo'og&?
1O&O,O$H is the physical layout of the workstations# severs# gateways# hubs and cabling# configuration of network# including the types of cable and connectivity devices used. T&pes o$ topo'ogies 1here are 7 types of topologies and are as follows. 12 .us Topo'og&@ ;2 Ring Topo'og&@ <2 Star Topo'og&@ 42 Mesh Topo'og&@ 52 Tree Topo'og&2 .us Topo'og& 0. !ll the nodes (file server# workstations# and peripherals) on a bus topology are connected by one single cable. 2. ! bus topology consists of a main run of cable with a terminator at each end. !ll nodes (file server# workstations# and peripherals) are connected to the linear cable. 3. &opular on ,!)s because they are ine5pensive and easy to install.

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Ring Topo'og& 0. In a ring network# every device has e5actly two neighbors for communication purposes. 2. !ll messages travel through a ring in the same direction. 3. ! failure in any cable or device breaks the loop and can take down the entire network. 4. 1o implement a ring network we use the 1oken ing technology 6. ! token# or small data packet# is continuously passed around the network. 'hen a device needs to transmit# it reserves the token for the ne5t trip around# and then attaches its data packet to it.

Star Topo'og& 0. In a star network# each node (file server# workstations# and peripherals) is connected to a central device called a hu12 2. 1he hub takes a signal that comes from any node and passes it along to all the other nodes in the network. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 64

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3. (ata on a star network passes through the hub# switch# or concentrator before continuing to its destination. 4. 1he hub# switch# or concentrator manages and controls all functions of the network. 6. 1he star topology reduces the chance of network failure by connecting all of the systems to a central node.

Mesh Topo'og& 0. In this topology# each node is connected to every other node in the network. 2. Implementing the mesh topology is e5pensive and difficult. 3. In this type of network# each node may send message to destination through multiple paths. 4. 'hile the data is traveling on the "esh )etwork it is automatically configured to reach the destination by taking the shortest route which means the least number of hops.

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0. ! tree topology (hierarchical topology) can be viewed as a collection of star networks arranged in a hierarchy. 2. 1his tree has individual peripheral nodes which are re>uired to transmit to and receive from one other only and are not re>uired to act as repeaters or regenerators. 3. 1he tree topology arranges links and nodes into distinct hierarchies in order to allow greater control and easier troubleshooting. 4. 1his is particularly helpful for colleges# universities and schools so that each of the connect to the big network in some way.

(!1! CO""9)IC!1IO)S
Data communication (ata communications are the e5change of data between two devices via some form of transmission medium such as a wire cable. :or data communications to occur# the communicating devices must be part of a communication system made up of a combination of hardware (physical e>uipment) and software (programs). 1he effectiveness of a data communications system depends on four fundamental characteristics% delivery# accuracy# timeliness# and Bitter. 12 De'i#er&. 1he system must deliver data to the correct destination. (ata must be received by the intended device or user and only by that device or user. ;2 !ccurac&. 1he system must deliver the data accurately. (ata that have been altered in transmission and left uncorrected are unusable. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 67

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<2 Time'iness2 1he system must deliver data in a timely manner. (ata delivered late are useless. In the case of video and audio# timely delivery means delivering data as they are produced# in the same order that they are produced# and without significant delay. 1his kind of delivery is called real-time transmission. 42 Eitter. ;itter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. :or e5ample# let us assume that video packets are sent every 3( ms. If some of the packets arrive with 3(-ms delay and others with 4(-ms delay# an uneven >uality in the video is the result JW%!T !RE T%! P%:SIC!- COMMU*IC!TIO* MEDI!?

T?iste"Apair ca1'e
! cable made by intertwining two separate insulated wires together. 1here are two t?iste" pair types. Shielded and 9nshielded. Shielded 1wisted &air (S1&) has a fine wire mesh surrounding the wires to protect the transmission@ 9nshielded 1wisted &air (91&) does not. Shielded cable is used in older telephone networks# network# and data communications to reduce outside interference..

Coa=ia'
! cable

ca1'e
that is used in

video# communications# and audio. 1his cable has high bandwidths and greater transmission capacity. "ost users relate to a coa=ia' or coa= ca1'e as a cable used to connect their 1/s to a cable 1/ service. .owever# these cables are also used in networks and what allow a broadband cable Internet connection using a cable modem. In the picture to the right# is an e5ample of a coa5ial cable. !s can be seen in this picture# the cable is a thick cable with a metal male connector end that is screwed onto a female connector.

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,i1erAoptic ca1'e
,i1erAoptic ca1'es are hollow cables that send data by pulses of light. :iber optics allows for a much faster data transmission because of the capability of transmitting data at the speed of light. "ost home computer users will never get the opportunity to work with fiber-optic cables because almost all home networks use other cables or wireless connections to connect their computers together. :iber-optic cables are most often used in corporate networks or worldwide networks such as Internet backbones because of the capabilities of the cable.

SOperating SystemS
De$inition
!n Operating system is a program that controls the e5ecution of application programs and acts as an interface between the user of a computer and the computer hardware.

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%istor& o$ Operating S&stem

,unctions o$ Operating S&stem
1oday most operating systems perform the following important functions% 0. Processor management% It manages the assignment of processor to different tasks being &erformed by the computer system. 2. Memor& management It manages the allocation of main memory and other storage areas to the system programsG as well as user programsG and data. 3. Input K Output management% It manages the co-ordination and assignment of different Input and Output devices while one or more programs are e5ecuted .4. ,i'e management% It allows all files to be easily changed and modified through the use of te5t editors or some other file manipulation routines. 6. Esta1'ishment an" en$orcement o$ a priorit& s&stem % It determines and maintains the order in which Bobs are to be e5ecuted in the computer system. 7. Interpretation of commands and instructions. ( C.S.) (*$ ** + &.$ CO,,*$* -.I"!/! !" 6F

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8. :acilitates easy communication between the computer system and the computer operator.

T&pes o$ operating s&stem
12 .atch Operating S&stem ;2 Rea'ATime Operating S&stem (RTOS) <2 Sing'e User@ Sing'e Tas0 42 Sing'e User@ Mu'titas0ing 52 Mu'tiAuser 72 Distri1ute" Operating S&stem 12 .atch Operating S&stem In a batch processing operating system interaction between the user and processor is limited or there is no interaction at all during the e5ecution of work. (ata and programs that need to be processed are bundled and collected as a ]batchG and e5ecuted together. -atch processing operating systems are ideal in situations where% a) 1here are large amounts of data to be processed. b) Similar data needs to be processed. c) Similar processing is involved when e5ecuting the data. 1he system is capable of identifying times when the processor is idle at which time ]batchesG maybe processed. &rocessing is all performed automatically without any user intervention.

;2 Rea'ATime Operating S&stem (RTOS) eal-time operating systems are used to control machinery# scientific instruments and industrial systems such as embedded systems (programmable thermostats# household appliance controllers)# industrial robots# spacecraft# industrial control (manufacturing# production# power generation# fabrication# and refining)# and scientific research e>uipment. !n 1OS typically has very little user-interface capability# and no end-user utilities# since the system will be a Wsealed bo5W when delivered for use. ! very important part of an

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1 COMPUTER COURSE

k.suresh

1OS is managing the resources of the computer so that a particular operation e5ecutes in precisely the same amount of time# every time it occurs. !n early e5ample of a large-scale rea'Atime operating system was 1ransaction &rocessing :acility. Current users include Sabre (reservations)# !madeus (reservations)# /IS! Inc (authoriCations)# .oliday Inn (central reservations)# C-O* (order routing)# Singapore !irlines# L,"# Kantas# !mtrak# "arriott International # 'orldspan and the )H&( (F00 system). <2 Sing'e User@ Sing'e Tas0 1his operating system is designed to manage the computer# so that one user can effectively do one computer at a time. 1he &alm OS for &alm handheld computers is a good e5ample of a modern single-user# single-task operating system. 42 Sing'e User@ Mu'titas0ing 1his is the type of operating system most people use on their desktop and laptop computers today. "icrosoftMs 'indows and !ppleMs "ac OS platforms are both e5amples of operating systems. In that a single user has multiple or several programs in operation at the same time. :or e5ample# itMs entirely possible for a 'indows user to be writing a note in a word processor while downloading a file from the Internet while printing the te5t of an e-mail message.

52 Mu'tiAuser Mu'tiAuser is a term that defines an operating system or application software that allows concurrent or continues access by multiple users of a computer. ! multi-user operating system allows many different users to take advantage of the computerMs resources simultaneously. 9ni5# /"S and mainframe operating systems# such as #VS# are e5amples of multi-user operating systems. 1ime-sharing systems are multi-user systems. "ost batch processing systems for mainframe computers may also be considered Wmulti-userW# to avoid leaving the C&9 idle ( C.S.) (*$ ** + &.$ CO,,*$* 70 -.I"!/! !"

1 COMPUTER COURSE

k.suresh

while it waits for IDO operations to complete. .owever# the term WmultitaskingW is more common in this conte5t.

72 Distri1ute" Operating S&stem In a distributed system# software and data maybe distributed around the system# programs and files maybe stored on different storage devices which are located in different geographical locations and maybe accessed from different computer terminals. 'hile we are mostly accustomed to seeing multi-tasking and multi-user operating systems# the other operating systems are usually used in companies and firms to power special systems.

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