Basic Concepts of Computer :: 1

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BASIC CONCEPTS OF COMPUTER

1.1 INTRODUCTION

A computer is a programmable machine designed to perform arithmeticand logical operations automatically and sequentially on the input givenby the user and gives the desired output after processing. Computercomponents are divided into two major categories namely hardware andsoftware. Hardware is the machine itself and its connected devices such asmonitor, keyboard, mouse etc. Software are the set of programs that makeuse of hardware for performing various functions.

1.2 OBJECTIVES

After going through this lesson you would be able to:

familiarise yourself with characteristics of computers identify thebasic components of a computer

explain the importance of various units of a computer

differentiate between system software and application software

explain the importance of operating system getacquainted with open source

appreciate the need of computer security

1.3 CHARACTERISTICS OF COMPUTERS

The characteristics of computers that have made them so powerful anduniversally useful are speed, accuracy, diligence, versatility and storagecapacity. Let us discuss them briefly.

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Speed

Computers work at an incredible speed. A powerful computer is capableof performing about 3-4 million simple instructions per second.

Accuracy

In addition to being fast, computers are also accurate. Errors that mayoccur can almost always be attributed to human error (inaccurate data,poorly designed system or faulty instructions/programs written by theprogrammer)

Diligence

Unlike human beings, computers are highly consistent. They do not sufferfrom human traits of boredom and tiredness resulting in lack ofconcentration. Computers, therefore, are better than human beings inperforming voluminous and repetitive jobs.

Versatility

Computers are versatile machines and are capable of performing any taskas long as it can be broken down into a series of logical steps. Thepresence of computers can be seen in almost every sphere – Railway/Airreservation, Banks, Hotels, Weather forecasting and many more.

Storage Capacity

Today’s computers can store large volumes of data. A piece ofinformation once recorded (or stored) in the computer, can never beforgotten and can be retrieved almost instantaneously.

1.4 COMPUTER ORGANIZATION

Fig.1.1: Computer System

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A computer system (fig.1.1) consists of mainly four basic units; namelyinput unit, storage unit, central processing unit and output unit. CentralProcessing unit further includes Arithmetic logic unit and control unit, asshown in Figure 1.2.

A computer performs five major operations or functions irrespective of itssize and make. These are

it accepts data or instructions as input, it storesdata and instruction

it processes data as per the instructions,

it controls all operations inside a computer, and it givesresults in the form of output.

1.4.1 Functional Units:

a. Input Unit: This unit is used for entering data and programs into thecomputer system by the user for processing.

– –

––

Dotted lines (– – – –)indicateflow of instruction solid lines

Fig. 1.2: Basic computer Organization (–––––) indicate flow ofdata

b. Storage Unit: The storage unit is used for storing data andinstructions before and after processing.

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c. Output Unit: The output unit is used for storing the result as outputproduced by the computer after processing.

d. Processing: The task of performing operations like arithmetic andlogical operations is called processing. The Central Processing Unit(CPU) takes data and instructions from the storage unit and makes allsorts of calculations based on the instructions given and the type ofdata provided. It is then sent back to the storage unit. CPU includesArithmetic logic unit (ALU) and control unit (CU)

Arithmetic Logic Unit: All calculations and comparisons, basedon the instructions provided, are carried out within the ALU. Itperforms arithmetic functions like addition, subtraction,multiplication, division and also logical operations like greaterthan, less than and equal to etc.

Control Unit: Controlling of all operations like input, processingand output are performed by control unit. It takes care of step bystep processing of all operations inside the computer.

1.4.2 Memory

Computer’s memory can be classified into two types; primary memoryand secondary memory

a. Primary Memory can be further classified as RAM and ROM.

RAM or Random Access Memory is the unit in a computersystem. It is the place in a computer where the operating system,application programs and the data in current use are kepttemporarily so that they can be accessed by the computer’sprocessor. It is said to be ‘volatile’ since its contents areaccessible only as long as the computer is on. The contents ofRAM are no more available once the computer is turned off.

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ROM or Read Only Memory is a special type of memory whichcan only be read and contents of which are not lost even when thecomputer is switched off. It typically contains manufacturer’sinstructions. Among other things, ROM also stores an initialprogram called the ‘bootstrap loader’ whose function is to startthe operation of computer system once the power is turned on.

b. Secondary Memory

RAM is volatile memory having a limited storage capacity.Secondary/auxiliary memory is storage other than the RAM. Theseinclude devices that are peripheral and are connected and controlledby the computer to enable permanent storage of programs and data.

Secondary storage devices are of two types; magnetic and optical.Magnetic devices include hard disks and optical storage devices areCDs, DVDs, Pen drive, Zip drive etc.

Hard Disk

Fig. 1.3: Hard Disk

Hard disks are made up of rigid material and are usually a stack ofmetal disks sealed in a box. The hard disk and the hard disk driveexist together as a unit and is a permanent part of the computer wheredata and programs are saved. These disks have storage capacitiesranging from 1GB to 80 GB and more. Hard disks are rewritable.

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Compact Disk

Compact Disk (CD) is portable disk having data storage capacitybetween 650-700 MB. It can hold large amount of information suchas music, full-motion videos, and text etc. CDs can be either readonly or read write type.

Digital Video Disk

Digital Video Disk (DVD) is similar to a CD but has larger storagecapacity and enormous clarity. Depending upon the disk type it canstore several Gigabytes of data. DVDs are primarily used to storemusic or movies and can be played back on your television or thecomputer too. These are not rewritable.

1.4.3 Input / Output Devices:

These devices are used to enter information and instructions into acomputer for storage or processing and to deliver the processed data to auser. Input/Output devices are required for users to communicate with thecomputer. In simple terms, input devices bring information INTO thecomputer and output devices bring information OUT of a computersystem. These input/output devices are also known as peripherals sincethey surround the CPU and memory of a computer system.

a) Input Devices

An input device is any device that provides input to a computer.There are many input devices, but the two most common ones are akeyboard and mouse. Every key you press on the keyboard and everymovement or click you make with the mouse sends a specific inputsignal to the computer.

Keyboard: The keyboard is very much like a standard typewriterkeyboard with a few additional keys. The basic QWERTY layout ofcharacters is maintained to make it easy to use the system. Theadditional keys are included to perform certain special functions.These are known as function keys that vary in number from keyboardto keyboard. (see fig. 1.4)

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AlphanumericKeypad/

Special-function KeysFunctionKeys

Cursor Movement

Keys

Numeric Keypad

Fig. 1.4: Keyboard

Mouse: A device that controls the movement of the cursor or pointeron a display screen. A mouse is a small object you can roll along ahard and flat surface (Fig. 1.5). Its name is derived from its shape,which looks a bit like a mouse. As you move the mouse, the pointeron the display screen moves in the same direction.

Fig. 1.5: Mouse

Trackball: A trackball is an input device used to enter motion datainto computers or other electronic devices. It serves the same purposeas a mouse, but is designed with a moveable ball on the top, whichcan be rolled in any direction.

Touchpad: A touch pad is a device for pointing (controlling inputpositioning) on a computer display screen. It is an alternative to the

mouse. Originally incorporated in laptop computers, touch pads arealso being made for use with desktop computers. A touch pad worksby sensing the user’s finger movement and downward pressure.

Touch Screen: It allows the user to operate/make selections bysimply touching the display screen. A display

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screen that is sensitive to the touch of a finger or stylus. Widely usedon ATM machines, retail point-of-sale terminals, car navigationsystems, medical monitors and industrial control panels.

Light Pen: Light pen is an input device that utilizes a light-sensitivedetector to select objects on a display screen. (Fig. 1.6)

Fig. 1.6 Light Pen

Magnetic ink character recognition (MICR): MICR can identifycharacter printed with a special ink that contains particles of magneticmaterial. This device particularly finds applications in bankingindustry.

Optical mark recognition (OMR): Optical mark recognition, alsocalled mark sense reader is a technology where an OMR devicesenses the presence or absence of a mark, such as pencil mark. OMRis widely used in tests such as aptitude test.

Bar code reader: Bar-code readers are photoelectric scanners thatread the bar codes or vertical zebra strips marks, printed on productcontainers. These devices are generally used in super markets,bookshops etc.

Scanner: Scanner is an input device that can read text or illustrationprinted on paper and translates the information into a form that thecomputer can use. A scanner works by digitizing an image. (Fig. 1.7)

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Fig. 1.7 Scanner

b. Output Devices:

Output device receives information from the CPU and presents it tothe user in the desired from. The processed data, stored in thememory of the computer is sent to the output unit, which thenconverts it into a form that can be understood by the user. The outputis usually produced in one of the two ways – on the display device, oron paper (hard copy).

Monitor: is often used synonymously with “computer screen” or“display.” Monitor is an output device that resembles the televisionscreen (fig. 1.8). It may use a Cathode Ray Tube (CRT) to displayinformation. The monitor is associated with a keyboard for manualinput of characters and displays the information as it is keyed in. Italso displays the program or application output. Like the television,monitors are also available in different sizes.

Fig. 1.8: Monitor

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Printer: Printers are used to produce paper (commonly known ashardcopy) output. Based on the technology used, they can beclassified as Impact or Non-impact printers.

Impact printers use the typewriting printing mechanism wherein ahammer strikes the paper through a ribbon in order to produce output.Dot-matrix and Character printers fall under this category.

Non-impact printers do not touch the paper while printing. They usechemical, heat or electrical signals to etch the symbols on paper.Inkjet, Deskjet, Laser, Thermal printers fall under this category ofprinters.

Plotter: Plotters are used to print graphical output on paper. Itinterprets computer commands and makes line drawings on paperusing multicoloured automated pens. It is capable of producinggraphs, drawings, charts, maps etc. (Fig. 1.9)

Fig. 1.9 Plotter

Facsimile (FAX): Facsimile machine, a device that can send orreceive pictures and text over a telephone line. Fax machines work bydigitizing an image.

Sound cards and Speaker(s): An expansion board that enables acomputer to manipulate and output sounds. Sound cards are necessaryfor nearly all CD-ROMs and have become commonplace on modernpersonal computers. Sound cards enable the computer to output soundthrough speakers connected to the board, to record sound input from amicrophone connected to the computer, and manipulate sound storedon a disk.

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1.5 COMPUTER SOFTWARE

Computer software is the set of programs that makes the hardwareperform a set of tasks in particular order. Hardware and software arecomplimentary to each other. Both have to work together to producemeaningful results. Computer software is classified into two broadcategories; system software and application software.

1.5.1 System Software:

System software consists of a group of programs that control theoperations of a computer equipment including functions like managingmemory, managing peripherals, loading, storing, and is an interfacebetween the application programs and the computer. MS DOS(Microsoft’s Disk Operating System), UNIX are examples of systemsoftware.

1.5.2 Application software:

Software that can perform a specific task for the user, such as wordprocessing, accounting, budgeting or payroll, fall under the category ofapplication software. Word processors, spreadsheets, databasemanagement systems are all examples of general purpose applicationsoftware.

Types of application software are:

Word processing software: The main purpose of this software is toproduce documents. MS-Word, Word Pad, Notepad and some othertext editors are some of the examples of word processing software.

Database software: Database is a collection of related data. Thepurpose of this software is to organize and manage data. Theadvantage of this software is that you can change the way data isstored and displayed. MS access, dBase, FoxPro, Paradox, and Oracleare some of the examples of database software.

Spread sheet software: The spread sheet software is used to maintainbudget, financial statements, grade sheets, and sales records. Thepurpose of this software is organizing numbers. It also allows theusers to perform

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simple or complex calculations on the numbers entered in rows andcolumns. MS-Excel is one of the example of spreadsheet software.

Presentation software: This software is used to display theinformation in the form of slide show. The three main functions ofpresentation software is editing that allows insertion and formattingof text, including graphics in the text and executing the slide shows.The best example for this type of application software is MicrosoftPowerPoint.

Multimedia software: Media players and real players are theexamples of multimedia software. This software will allow the user tocreate audio and videos. The different forms of multimedia softwareare audio converters, players, burners, video encoders and decoders.

1.6 COMPUTER LANGUAGE

Computer language or programming language is a coded syntax used bycomputer programmers to communicate with a computer. Computerlanguage establishes a flow of communication between softwareprograms. The language enables a computer user to dictate whatcommands the computer must perform to process data. These languagescan be classified into following categories (Fig. 1.10).

1. Machine language

2. Assembly language

3. High level language

Fig. 1.10: Computer Languages

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1.6.1 Machine Language

Machine language or machine code is the native language directlyunderstood by the computer’s central processing unit or CPU. This type ofcomputer language is not easy to understand, as it only uses a binarysystem, an element of notations containing only a series of numbersconsisting of one and zero, to produce commands.

1.6.2 Assembly Level Language

Assembly Level Language is a set of codes that can run directly on thecomputer’s processor. This type of language is most appropriate in writingoperating systems and maintaining desktop applications. With theassembly level language, it is easier for a programmer to definecommands. It is easier to understand and use as compared to machinelanguage.

1.6.3 High Level Language

High Level Languages are user-friendly languages which are similar toEnglish with vocabulary of words and symbols. These are easier to learnand require less time to write.

They are problem oriented rather than ‘machine’ based.

Program written in a high-level language can be translated into manymachine languages and therefore can run on any computer for which thereexists an appropriate translator.

1.6.4 Compiler & Interpreter

These are the programs that execute instructions written in a high-levellanguage. There are two ways to run programs written in a high-levellanguage. The most common is to compile the program; the other methodis to pass the program through an interpreter.

a. Compiler

A compiler is a special program that processes statements written in aparticular programming language called as source code and convertsthem into machine language or “machine code” that a computer’sprocessor uses.

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Compiler translates high level language programs directly intomachine language program. This process is called compilation. (Fig1.11)

Fig. 1.11: Compilation

b. Interpreter

An interpreter translates high-level instructions into an intermediateform, which it then executes. Compiled programs generally run fasterthan interpreted programs. The advantage of an interpreter, however,is that it does not need to go through the compilation stage duringwhich machine instructions are generated. This process can be time-consuming if the program is long. (Fig 1.12)

Fig. 1.12: Interpretation

1.6.5 Open source software:

Open source refers to a program or software in which the source code (theform of the program when a programmer writes a program in a particularprogramming language) is available to the general public for use and/ormodification from its original design free of charge.

Open source code is typically created as a collaborative effort in whichprogrammers improve upon the code and share the changes within thecommunity.

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The rationale for this movement is that a larger group of programmers notconcerned with proprietary ownership or financial gain will produce amore useful and bug-free product for everyone to use.

The basics behind the Open Source Initiative is that when programmerscan read, redistribute and modify the source code for a piece of software,the software evolves. Open source sprouted in the technologicalcommunity as a response to proprietary software owned by corporations.

Proprietary software is privately owned and controlled. In the computerindustry, proprietary is considered the opposite of open. A proprietarydesign or technique is one that is owned by a company. It also implies thatthe company has not divulged specifications that would allow othercompanies to duplicate the product.

1.7 OPERATING SYSTEM

An operating system is a software component of a computer system that isresponsible for the management of various activities of the computer andthe sharing of computer resources. It hosts several applications that run ona computer and handles the operations of computer hardware. Users andapplication programs access the services offered by the operating systems,by means of system calls and application programming interfaces. Usersinteract with a computer operating system through Command LineInterfaces (CLIs) or Graphical User Interfaces known as GUIs. In short, anoperating system enables user interaction with computer systems by actingas an interface between users or application programs and the computerhardware. Some of the common operating systems are LINUX,Windows,etc.

1.8 WINDOWS XP DESKTOP ELEMENTS

Start Menu

When clicked on the start button, start menu appears on the screen givingall the available options to start using the

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Windows (See Fig. 1.13). Desktop icons provide access to commonly usedprograms, folders and files.

Fig. 1.13

Overview of the options available in the start menu.

Task Description

All Programs Displays a list of installed program,which a user can start or use

My Documents Displays a list of documents used bythe current user

My Recent Documents Displays a list of recently useddocuments by the current user

My Picture Displays a list of pictures/photos usedby the current user

My Music Displays a list of music/songs used by

the current userControl Panel Displays a list of utilities to configure

the computer system and installsoftware and hardware

Printers and Faxes Displays a list of currently installedprinters and faxes in the currentcomputer system

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Help and Support Start the XP help and support programto find how to do a task in windows

Search Helps the user to find any file or folderfrom a list of document used by thecurrent user.

Run Starts an application program orexecutes a DOS command

Log Off Log off the currently logged in user ofthe system

Turn Off Computer Close currently opened program, logoff the current user and switch off thecomputer system.

Task Bar

When you start the computer system, then start button and task barappears on the bottom of the screen and by default remains visible whenWindows is running (See Fig. 1.14).

Whenever a program is run or a window is opened, an icon representingthe program appears on the taskbar. To switch between windows orprogram, click on the icon representing the window on the task bar. Whenthe program or window is closed, the icon disappears from the task bar.

Task bar System Tray

Fig. 1.14

The system tray is part of the task bar and displays the current time as wellas the status icons.

1.8.1 Start a Program

To start a program, do the following;

1. Click on the Start Button.

2. Click on the All Programs, you will see a list of all the programicons and program folders.

3. Point to the desired folder say Accessories and select the desiredprogram to run such as Paint.

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1.8.2 Quit a Program

To quit a program, select the close button (×) in the upper-right corner ofthe window OR

Click on File menu and select Close option.

1.8.3 Getting Help

Online help and support provided is of great help in using and learningwindows. One can get help on a specific topic or on current task which isbeing executed. To start help

click on the Start button

click on Help and support option

A list of help and support topics and online tutorial is displayed on thescreen (see Fig. 1.15). One can use the tabs in the screen to search for thedesired information in several ways.

Fig. 1.15

Click on a topic or task to know more about how to get the jobdone or type in a search word to locate the help on a specific topic.

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Click on the Index tab to locate specific topic listed alphabeticallyand the follow the instructions displayed on the screen.

Click on Favourites tab to add Help Topics, search results to yourFavourites list to make them easy to locate in the future

Click on History to pick from a list of Help and Support pages thatyou have read in the past.

Click on Support to get various kind of online support such asMicrosoft online support, News Group on Windows.

Click on Option to configure the help and support center as peryour requirement.

To close Help and Support windows, select the close button (×) in theupper-right corner of the window.

1.8.4 Searching Files and Folders

If you don’t know where a document or folder is located, you can use theSearch option to locate it in the local storage such as Hard Disk, CD or inthe network drive (if the system is part of a network). The IndexingService provided by the Search maintains an index of all the files on yourcomputer, making searches faster.

To search for a file or folder

1. Click Start, and click on Search.

2. Select All files and folders from the left hand side of the windows(see Fig. 1.16).

3. Type the name of the file or folder in part or full, or type a word orphrase that exists in the file to be searched.

4. If you do not know either piece of information select one or moreof the remaining options:

In Look in, click the drive, folder, or network you want tosearch.

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Fig. 1.16

Click on When was it modified? to look for files that werecreated or modified on or between specific dates.

To look for files of a specific size, click on What size is it?Select a size.

Click on More advanced options to specify additionalsearch criteria.

5. Once you finish specifying the search criteria, click on Search tolocate the file.

Similarly you can search for specific information on Internet, orpeople in your address book, search for a printer or a computer onyour network.

1.8.5 Changing System settings

By using Control Panel’s tools you can customize the way Windows lookand work! Also you can install new hardware, add and remove(install/uninstall) software programs, change the look and feel of yourdesktop and much more. It also includes a number of administrative toolsin Administrative

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Tools option for better administration of Windows in terms of UserManagement, Event viewer, Component Service etc. To start ControlPanel and use the available tool, do the following;

Click on Start

Click on Control Panel

Select the desired tool to use

For example to create a new or modify the settings for an existing userclick on ‘User Account’ icon in the control panel.

1.8.6 Using 'My Computer'for browsing your disk drives

Your disk drives hold all the information on your computer:

all the files, folders, programs as well as the documents.

My Computer displays the contents of floppy, hard disk, CD-ROM, andnetwork drives. One can also search for and open files and folders, and useoptions in Control Panel to modify computer’s settings.

To use My Computer, click on Start, and then click on MyComputer or double click the My computer icon on the desktop.My computer windows opens to show all the drives present onyour computer. (see Fig. 1.17).

Fig. 1.17

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Display the storage Contents

To see what’s on your hard disk, under Hard Disk Drives, double-click the drive you want to see such as C:, D: etc.

To find a file or folder on a CD-ROM, or other media, underDevices with Removable Storage, double-click on the respectivestorage media you want to see.

To find a file in a folder, under Files Stored on This Computer,double-click a folder.

1.9 FILE MANAGEMENT IN WINDOWS

File management in windows can be done through Windows Explorer orMy Computer. Windows Explorer displays the hierarchical list of files,folders, and storage drives (both fixed and removable) on your computer.It also lists any network drives that have been mapped to as a drive letterson your computer. Windows Explorer can be used to copy, move, rename,and search for files and folders. For example, to copy a file, you can opena folder that contains the desired file to be copied or moved, and then justdrag and drop the file to target folder or drive. (see fig. 1.18)

Fig. 1.18

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When files or folders are deleted from hard disk, Windows places them inthe Recycle Bin, from where they can be retrieved, until the Recycle Binis made empty. Files or folders deleted from a removable storage mediasuch as network drive are permanently deleted and are not sent to theRecycle Bin.

1.9.1 Using Windows Explorer

Windows offer another utility "Windows Explorer" which helps you inworking with files and folders on your computer.

To open Windows Explorer,

Click on Start,

Point to All Programs,

Point to Accessories, and then click on Windows Explorer (seeFig. 1.19)

Fig. 1.19

The left pane of the Explorer window shows a hierarchy of all the drives,folders and desktop items on your computer. A drive or folder thatcontains other folders has a plus sign to the left of the icon. Click the plussign to expand it and see the folders inside. (see Fig. 1.20)

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1.9.2 Opening drives and folders

Two drives nearly all computers have are a floppy drive (drive A:) and ahard drive (drive C:). If you have more than one drive, then they arenamed D:, E: and so on. If you have a CD drive or a DVD drive, it also isnamed with a letter. Opening a hard drive is easy. Just double click theicon representing the drive you want to open. Files and folders containedin the drive are now shown in the opened window. Now for opening afolder, double click its icon.

Fig. 1.20

1.9.3 Copying or Moving a file or Folder using MyDocument

Click on Start, and then click on My Documents.

Click the file or folder to be copied. More than one file or foldercan be copied at a time.

To select more than one consecutive files or folders, click the firstfile or folder, press and hold down SHIFT key, and then click thelast files or folders.

To select non-consecutive files or folders, press and hold downCTRL key, and then click each of the files or folders to be copied.

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Under Edit menu, select Copy.

Select the target drive or folder to which you want to copy the files

Under Edit menu, select Paste to copy the desired file or folder tothe target drive.

1.9.4 View file details

1. Click on Start, and then click on My Documents.

2. Double-click the folder that contains the files to be viewed.

3. On the View menu, click Details (see Fig. 1.21).

4. It will display all the details about the files such as Name, Type,size etc.

Fig. 1.21

1.9.5 Copying and moving files using Explorer

Click Start, point to All Programs, point to Accessories, and thenclick Windows Explorer.

Make sure the destination for the file or folder you want to move isvisible (see Fig. 1.22).

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Fig. 1.22

Drag the file or folder from the right pane and drop it on to thedestination folder in the left pane to move the file or folder there.

If you drag an item while pressing the right mouse button, you canmove, copy, or create a shortcut to the file in its new location.

To copy the item instead of moving it, press and hold down CTRLwhile dragging.

If you drag an item to another disk, it is copied, not moved. Tomove the item, press and hold down SHIFT while dragging.

Dragging a program to a new location creates a shortcut to thatprogram. To move a program, right-click and then drag theprogram to the new location.

1.9.6 Create a new folder

Folders help you to organize your files. You can create a folder either byusing My Computer window or through Windows Explorer. You cancreate a Folder in any existing disk drive or folder or on the windowsdesktop. The steps for creating a folder are:

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1. Click on Start, and then click on My Documents

2. Under File menu click New and select Folder. (see Fig. 1.23)

3. A new folder is displayed with the default name, New Folder.

4. Type a name for the new folder, and then press ENTER.

5. A new folder can also be created directly on the desktop by right-clicking a blank area on the desktop, pointing to New, and thenclicking Folder.

1.9.7 Rename a file or folder

1. Click on Start, and then click on My Documents

2. Click on the file or folder you want to rename.

3. Under File menu click on Rename (see Fig. 1.23).

4. Type the new name, and then press ENTER key.

5. Alternately file or folder can also be renamed by right-clicking itand then clicking on Rename.

1.9.8 Delete a file or folder

1. Click on Start, and then click on My Documents

2. Click on the file or folder you want to delete.

3. Under File menu click on Delete (see Fig. 1.23).

4. Files or folders can also be deleted by right-clicking the file orfolder and then clicking Delete.

5. Deleted files or folders are stored in the Recycle Bin, till they arepermanently removed from the Recycle Bin.

6. To retrieve a deleted file, double-click the Recycle Bin icon on thedesktop. Right-click on the file to be retrieved, and then clickRestore.

7. To permanently delete a file, press and hold down SHIFT key anddrag it to the Recycle Bin.

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Fig. 1.23

1.10 COMPUTER SECURITY

Security has always been an overriding concern of human kind. For manyorganization, information plays a very important role in running business.Therefore, it becomes necessary to safeguard information from reachingthe illegal hands. When data takes the shapes of digital form, a differentsecurity procedure is required. This branch of security is called computersecurity.

Information technology has also some loopholes associated with it, likethe possibility of stealing of vital information and intentionally implantingdestructive or malicious programs on the other's computer system. The

motive behind such activities is to show down the pace of an organizationand harm it economically. We shall discuss now about these maliciousprograms which are often called virus, worms, Trojan horse, logic bomb,spyware and so on.

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1.10.1 Virus

Virus is a program which has been written to interfere with the normalfunctioning of the computer. It does this by clogging the memory of thesystem by making copies of itself or it may destory critical informationused by other computer prgrams.

There are three main types of viruses: Boot sector viruses which infectthe boot sector in the hard disk and affect the partition table, File virusesattach with executable files. The commonly infected files are those withCOM or EXE extensions. The third, System viruses infect specific systemfiles such as command.com. Computer viruses can be grouped into TimeBomb, Trojan Horse, Worm etc. Time Bomb will start on a particular date,at a particular time. The computer will loose its ability to functionproperly.

The virus known as Trojan Horse will enter into a computer through an e-mail or free programs that have been down loaded from the internet andcasue plenty of damage. Viruses known as Worms are constructed toinfiltrate on the legitimate data processing programs and alter or destroythe data. Worm programs often use network connections to spread fromone computer system to another system, thus, worms attach system thatare linked through communication lines.

1.10.2 Protecting computer system using antivirus software

In case the virus is present, it becomes our duty to use some anti-virussoftware for preventing virus attacks in future. Anti-virus software fallsinto two categories: Scanners and Integrity checkers.

A scanner is a program that will detect the virus by checking the files onthe disk, the boot sector of the disk and programs in the memory bylooking for the signature of the virus. The signature is a piece of programcode that is unique to the virus. It is very necessary to update regularly thevirus scanner that you have bought. This is essential because new virusesare constantly appearing.

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Integrity checkers work using simple checksums or complicatedalgorithms or cryptographic checksums which check if a file has beenmodified. It may be boring for you to check for virus every time you runthe system. But you should not worry. Help is at hand with HomeGuarda unique device which once fitted to the computer automatically scans inthe background for viruses. If there are viruses found in the system,HomeGuard will clean it up automatically without even having to pressa key.

1.10.3 Precautions to be taken against viruses

Install a memory-resident program in RAM that will detect andwarn if a virus is present.

Do not allow hardware engineers or sales persons to put a writeenabled floppy into your computer uless they can guarantee that itis not infected.

Backup copies of all programs and data files should be kept.

Backup copies of programs should be held as read-only disks toprevent infection.

At least 2 copies of the backup must be kept.

Never boot your machine with a floppy from an unknown source.

Always write-protect your disk when you use it in anothermachine.

Operating systemAn operating system (OS) is system software that manages computer hardware and softwareresources and provides common services for computer programs.

Time-sharing operating systems schedule tasks for efficient use of the system and may alsoinclude accounting software for cost allocation of processor time, mass storage, printing, and otherresources.

For hardware functions such as input and output and memory allocation, the operating system acts

as an intermediary between programs and the computer hardware,[1][2] although the applicationcode is usually executed directly by the hardware and frequently makes system calls to an OSfunction or is interrupted by it. Operating systems are found on many devices that contain acomputer – from cellular phones and video game consoles to web servers and supercomputers.

Types of operating systems

Single- and multi-taskingA single-tasking system can only run one program at a time, while a multi-tasking operatingsystem allows more than one program to be running in concurrency. This is achieved by time-sharing, where the available processor time is divided between multiple processes. Theseprocesses are each interrupted repeatedly in time slices by a task-scheduling subsystem of theoperating system. Multitasking may be characterized in preemptive and co-operative types. Inpreemptive multitasking, the operating system slices the CPU time and dedicates a slot to each ofthe programs. Unix-like operating systems, such as Solaris and Linux—as well as non-Unix-like,such as AmigaOS—support preemptive multitasking. Cooperative multitasking is achieved byrelying on each process to provide time to the other processes in a defined manner. 16-bitversions of Microsoft Windows used cooperative multi-tasking. 32-bit versions of both WindowsNT and Win9x, used preemptive multi-tasking.

Single- and multi-userSingle-user operating systems have no facilities to distinguish users, but may allow multipleprograms to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging tomultiple users, and the system permits multiple users to interact with the system at the same time.Time-sharing operating systems schedule tasks for efficient use of the system and may also includeaccounting software for cost allocation of processor time, mass storage, printing, and otherresources to multiple users.

DistributedA distributed operating system manages a group of distinct computers and makes them appear to bea single computer. The development of networked computers that could be linked and communicatewith each other gave rise to distributed computing. Distributed computations are carried out on morethan one machine. When computers in a group work in cooperation, they form a distributed system.

TemplatedIn an OS, distributed and cloud computing context, templating refers to creating a single virtualmachine image as a guest operating system, then saving it as a tool for multiple running virtual

machines. The technique is used both in virtualization and cloud computing management, and iscommon in large server warehouses.

EmbeddedEmbedded operating systems are designed to be used in embedded computer systems. They aredesigned to operate on small machines like PDAs with less autonomy. They are able to operate witha limited number of resources. They are very compact and extremely efficient by design. WindowsCE and Minix 3 are some examples of embedded operating systems.

Real-timeA real-time operating system is an operating system that guarantees to process events or data by aspecific moment in time. A real-time operating system may be single- or multi-tasking, but whenmultitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavioris achieved. An event-driven system switches between tasks based on their priorities or externalevents while time-sharing operating systems switch tasks based on clock interrupts.

LibraryA library operating system is one in which the services that a typical operating system provides,such as networking, are provided in the form of libraries and composed with the application andconfiguration code to construct a unikernel: a specialized, single address space, machine image thatcan be deployed to cloud or embedded environments.

Operating System Utilities

We have seen that the fundamental purpose of the operating system is to manage the various systemresources. We have also examined the human computer interface which allows us to interact withthe operating system. There is, however, a significant body of software that, while not strictly partof the operating system itself, cannot be described as application software. This software is oftenbundled with the operating system software, and comes under the general heading of utilitysoftware.

Utility software can include file re-organisation utilities, backup programs, and a whole range ofcommunication services. Many of the utilities that are bundled with a particular operating system areinstalled by default, although a significant number are optional and must be explicitly selected forinstallation.

The number and type of utility program provided varies from one operating system to another, butcommon examples include facilities to partition and format hard drives and floppy disks, fileencryption and compression utilities, and task scheduling programs. These utilities are oftenimplemented as stand-alone programs and can be run by the user in much the same way as anapplication program. In many cases, there are a number of proprietary utility programs on themarket that carry out the same tasks, but with additional value added features.

Unix and Unix-like operating system

Unix was originally written in assembly language.[13] Ken Thompson wrote B, mainly based onBCPL, based on his experience in the MULTICS project. B was replaced by C, and Unix, rewrittenin C, developed into a large, complex family of inter-related operating systems which have beeninfluential in every modern operating system (see History).

The Unix-like family is a diverse group of operating systems, with several major subcategoriesincluding System V, BSD, and Linux. The name "UNIX" is a trademark of The Open Group whichlicenses it for use with any operating system that has been shown to conform to their definitions."UNIX-like" is commonly used to refer to the large set of operating systems which resemble theoriginal UNIX.

Unix-like systems run on a wide variety of computer architectures. They are used heavily forservers in business, as well as workstations in academic and engineering environments. FreeUNIX variants, such as Linux and BSD, are popular in these areas.

Unix interoperability was sought by establishing the POSIX standard. The POSIX standard can beapplied to any operating system, although it was originally created for various Unix variants.

macOS (formerly "Mac OS X" and later "OS X") is a line of open core graphical operating systemsdeveloped, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currentlyshipping Macintosh computers. macOS is the successor to the original classic Mac OS, which hadbeen Apple's primary operating system since 1984. Unlike its predecessor, macOS is a UNIXoperating system built on technology that had been developed at NeXT through the second half ofthe 1980s and up until Apple purchased the company in early 1997. The operating system was firstreleased in 1999 as Mac OS X Server 1.0, followed in March 2001 by a client version (Mac OS Xv10.0 "Cheetah"). Since then, six more distinct "client" and "server" editions of macOS have beenreleased, until the two were merged in OS X10.7 "Lion".

LinuxThe Linux kernel originated in 1991, as a project of Linus Torvalds, while a university student inFinland. He posted information about his project on a newsgroup for computer students andprogrammers, and received support and assistance from volunteers who succeeded in creating acomplete and functional kernel.

Linux is Unix-like, but was developed without any Unix code, unlike BSD and its variants. Becauseof its open license model, the Linux kernel code is available for study and modification, whichresulted in its use on a wide range of computing machinery from supercomputers to smartwatches.Although estimates suggest that Linux is used on only 1.82% of all "desktop" (or laptop) PCs, it has

been widely adopted for use in servers[16] and embedded systems[17] such as cell phones. Linuxhas superseded Unix on many platforms and is used on most supercomputers including the top 385.The Linux kernel is used in some popular distributions, such as Red Hat, Debian, Ubuntu,Linux Mint and Google's Android, Chrome OS, and Chromium OS.

Microsoft WindowsMicrosoft Windows is a family of proprietary operating systems designed by Microsoft Corporationand primarily targeted to Intel architecture based computers, with an estimated 88.9 percent totalusage share on Web connected computers.The latest version is Windows 10.

Microsoft Windows was first released in 1985, as an operating environment running on top of MS-DOS, which was the standard operating system shipped on most Intel architecture personalcomputers at the time. In 1995, Windows 95 was released which only used MS-DOS as a bootstrap.

For backwards compatibility, Win9x could run real-mode MS-DOSand 16-bit Windows 3.xdrivers.Windows ME, released in 2000, was the last version in the Win9x family. Later versions have allbeen based on the Windows NT kernel.Server editions of Windows are widely used. In recent years, Microsoft has expended significantcapital in an effort to promote the use of Windows as a server operating system. However,Windows' usage on servers is not as widespread as on personal computers as Windows competesagainst Linux and BSD for server market share. ReactOS is a Windows-alternative operatingsystem, which is being developed on the principles of Windows – without using any of Microsoft'scode.

USER INTERFACE

The user interface (UI), in the industrial design field of human– computer interaction , is thespace where interactions between humans and machines occur. The goal of this interaction is toallow effective operation and control of the machine from the human end, whilst the machinesimultaneously feeds back information that aids theoperators' decision-making process. Examples of this broad concept of user interfacesinclude the interactive aspects of computer operating systems , hand tools , heavy machinery operator controls, and process controls. The design considerations applicablewhen creating user interfaces are related to or involve such disciplines asergonomics and psychology .Generally, the goal of user interface design is to produce a user interface which makes it easy,efficient, and enjoyable (user-friendly) to operate a machine in the way which produces thedesired result. This generally means that the operator needs to provideminimal input to achieve the desired output, and also that the machine minimizesundesired outputs to the human.

Quality:

All great interfaces share eight qualities or characteristics:

1. Clarity :The interface avoids ambiguity by making everything clear through language,flow, hierarchy and metaphors for visual elements.

2. Concision: It’s easy to make the interface clear by over-clarifying and labeling everything, butthis

leads to interface bloat, where there is just too much stuff on the screen at the same time. Iftoo many things are on the screen, finding what you're looking for is difficult, and so theinterface becomes tedious to use. The real challenge in making a great interface is to make itconcise and clear at the same time.

3. Familarity: Even if someone uses an interface for the first time, certain elements can still befamiliar. Real-life metaphors can be used to communicate meaning.

4. Responsiveness: A good interface should not feel sluggish. This means that the interfaceshould provide good feedback to the user about what's happening and whether the user's inputis being successfully processed.

5. Consistency: Keeping your interface consistent across your application is important because itallows users to recognize usage patterns.

6. Aesthetics : While you don't need to make an interface attractive for it to do its job, makingsomething look good will make the time your users spend using your application moreenjoyable; and happier users can only be a good thing.

7. Efficiency :Time is money, and a great interface should make the user more productive throughshortcuts and good design.

TYPES OF INTERFACE

Attentive user interfaces manage the user attention deciding when to interrupt the user, the kindof warnings, and the level of detail of the messages presented to the user.Batch interfaces are non-interactive user interfaces, where the user specifies all the detailsof the batch job in advance to batch processing , and receives the output when all theprocessing is done. The computer does not prompt for further input after the processing hasstarted.

Command line interfaces (CLIs) prompt the user to provide input by typing a command string with the computer keyboard and respond by outputting text to the computer monitor. Usedby programmers and system administrators, in engineering and scientific environments, andby technically advanced personal computer users.Conversational interfaces enable users to command the computer with plain text English (e.g.,via text messages, or chatbots) or voice commands, instead of graphic elements. These interfacesoften emulate human-to-human conversations.Conversational interface agents attempt to personify the computer interface in the form of ananimated person, robot, or other character (such as Microsoft's Clippy the paperclip), andpresent interactions in a conversational form.Graphical user interfaces (GUI) accept input via devices such as a computer keyboard andmouse and provide articulated graphical output on the computer monitor . There are at least twodifferent principles widely used in GUI design: Object-oriented user interfaces (OOUIs) andapplication - oriented interfaces.[18]Hardware interfaces are the physical, spatial interfaces found on products in the real worldfrom toasters, to car dashboards, to airplane cockpits. They are generally a mixture of knobs,buttons, sliders, switches, and touchscreens.Motion tracking interfaces monitor the user's body motions and translate them intocommands,currently being developed by Apple.

Multi-screen interfaces, employ multiple displays to provide a more flexible interaction. This isoften employed in computer game interaction in both the commercial arcades and morerecently the handheld markets.Object-oriented user interfaces (OOUI) are based on object-oriented programming metaphors,allowing users to manipulate simulated objects and their properties.Reflexive user interfaces where the users control and redefine the entire system via the userinterface alone, for instance to change its command verbs . Typically, this is only possible withvery rich graphic user interfaces.

Search interface is how the search box of a site is displayed, as well as the visual representation of the search results.

Text-based user interfaces (TUIs) are user interfaces which interact via text. TUIsinclude command-line interfaces and text-based WIMP environments.Touch user interface are graphical user interfaces using a touchpad or touchscreen display as acombined input and output device. They supplement or replace other forms of outputwith haptic feedback methods. Used in computerized simulators , etc.

Voice user interfaces , which accept input and provide output by generating voice prompts. Theuser input is made by pressing keys or buttons, or responding verbally to the interface.

Web-based user interfaces or web user interfaces (WUI) that accept input and provide outputby generating web pages viewed by the user using a web browser program. Newer implementationsutilize PHP , Java , JavaScript , AJAX , Apache Flex , .NET Framework , or similar technologies toprovide real-time control in a separate program, eliminating the need to refresh a traditionalHTML-based web browser. Administrative web interfaces for web-servers, servers and networkedcomputers are often called control panels .