Chapter 10 | Introduction to Windows Operating System | IX Class

Chapter 10 | Introduction to Windows Operating System | IX Class Computer Science Notes

Windows Desktop

Windows “Desktop” is like a working surface of a desk. Desktop is where your applications, folders and shortcuts are located. Desktop contains the following items.

1. Icons

2. Taskbar

3. Start Button

The function of these desktop items is given below:

1. Icon

An icon is a small colourful graphical picture that represents an object like a file, folder, program or any hardware components of the computer. Every icon has a lable, which identifies it. The labels can be changed.
Windows operating system uses different icons to represent files, folders and applications. Icons found on the desktop are normally left aligned. Icons of the Desktop. The icons provided by windows are:

1. My Documents

2. My Computer

3. My Network Places

4. Recycle Bin

5. Internet Explorer

2. Task Bar

The task bar is at the bottom of the desktop but you can move it to the top or either side of the screen by clicking and dragging it to the new location. Buttons representing programs currently running on your computer appears on the task bar. At the very left of the task bar is the start button. At the right side is an area called the system tray? Here you will find graphical representation of various background operations. It also shows the system clock.

3. Start Button

Start button is found at the lower left corner of the screen. Click once on the start button to open a menu of choices. Through this button we can open the programs, installed on your computer and access all the utilities available in the windows environment.

We can shutdown, restart and/or standby the computer by using the start button.

Start menu displays a menu of choices:

1. Programs

2. Favorites

3. Documents

4. Settings

5. Find

6. Help

7. Run

8. Shutdown

Short Notes

Recycle Bin

Recycle bin makes it easy to delete and undelete files and folders. When a file or folder is deleted from any location, Windows stores it in the recycle bin. If a file is deleted accidentally, you can move it back from the recycle bin. We can also empty recycle bin to save disk space.

Steps to move back the file or folder from the recycle bin.

1. Open Recycle bin by double clicking on its icon.

2. Select the file or folder you want to move back.

3. Click the right mouse.

4. A menu will appear, choose restore from it.

5. Windows will move the file or folder back to the location from where it was deleted.

My Computer

My computer lets you browse the contents of your computer. The common tasks that we can perform through my computer are:

1. Access information stored as different storage devices connected with the computer, such as hard disk, floppy disk or CD ROM.

2. Create, move, copy, delete or rename files, folders and programs from one disk to another disk.

3. Execute or run programs from the disks.

4. Configure devices of the computer.

5. Add or remove a printer.

My Documents

It is a desktop folder that provides a convenient place to store documents, graphics or other files that you want to access quickly. On the desktop it is represented by a folder with a sheet of paper in it. When you save a file in a program such as word pad or paint, the file is by default saved in my documents unless you choose a different location.

The following steps may be followed to open a document from its window.

1. Move the mouse pointer to My Documents icon.

2. Double click on it to open its windows.

3. Double click on any of its item to open it.

Windows

It is a rectangular area of Screen that displays different information. In windows every folder or application has a window. Following are the properties of a window:

1. Every window has a title bar which displays the name of the window.

2. A window can be resized, minimized and maximized by pressing the buttons at the top right corner, of the title bar.

3. A window can be closed by pressing the x button at the right of the title bar.

4. A window can be moved at any location of the screen.

Items of Start Menu

Start menu displays a menu of choices:

1. Programs

2. Favorites

3. Documents

4. Settings

5. Find

6. Help

7. Run

8. Shutdown

Programs

Place the mouse pointer to the programs entry and a sub menu will open, showing all programs or applications currently installed. To open a program, which has been installed on your computer, click on it and the program will open.

Favorites

Favorites menu present a list of the Internet addresses that you have added to your Internet Explorer Favorite List.

Documents

The Documents menu lists the files you have recently worked on. You can open the most recently used document directly from here. To open a document from this list, simply click on it and the document will open.

Settings

This menu provides the facility to change or configure the hardware or software settings of the computer. This menu leads to several choices.
The individual icons in the Control Panel refer to a variety of tools to control the way of your computer, its components presents information, as well as the tools to control the behavior and appearance of the Windows interface.

The Find/Search

This option of the start menu helps in locating files or folders stored on the hard disk or network. This command is very helpful in case we forget the exact location of a file or folder that we want to access. The search option present different ways for finding a file or folder. These options include search based on name, type, size, and date and storage location of the file or folder. It opens a dialog box, where the user can type a name of the file or folder to search for.

The procedure of using this command is given below:

1. Click on Find option of the start menu, the Find dialog box will appear.

2. Enter the name of the file or folder in the Named text box.

3. From the Look in drop down list box choose the location where you imagine that your desired file or folder may be present.

4. Click on the Find now button to start search.

5. If find dialog box successfully searches the location of the desired file or folder, it will display it in the window below this dialog box.

Help

To access the Help system of windows, you can select Help from the start menu. Help option helps us how to use the commands and menus and in case of problems how to trouble shoot the windows operating system.

Run

This command is used to execute a command or program directly instead of using the icon or program menu. Press the “Browse” button to locate the program you want to open through Run command.

Shut Down

Shutdown is a process in which computer closes all programs currently running and disconnects the devices connected with it and turns it self off.

Following step are followed to shutdown the computer.

1. Click on the start button to open the Start Menu.

2. Click on the Shut Down.

3. Shut down dialog box will appear.

4. Choose the shut down option from the list nd click the “OK” button.

Item of the Control Panel

Control Panel contains a number of icons used to perform different settings of the computer. The frequently used icons are:

Accessibility Options

The accessibility options make it easier for people with disabilities to operate a computer without installing special software. Accessibility options such as Sticky Keys, Show Sounds and Mouse Keys are designed to help users with specific disabilities take full advantage of the computer.

Add New Hardware

It is used to install a new hardware to the computer. Every new hardware comes with a device driver program that connects it to the computer. For example we can connect a digital camera and installs its driver with this icon.

Add/Remove Programs

This option helps us in installing new software or removes software that we no longer want to keep in the computer. It lists all the applications or programs currently installed on the computer. Programs should be un-installed or removed through this icon instead of deleting them one by one.

Date/Time

This option allows us to change or set the Date and Time of the computer system. The date and time are displayed on the system tray on Task bar. We can also bring the date and time settings dialog box by double clicking time from the system tray.

Display

It is used to change the display setting of the monitor. It has a number of tabs that changes or sets the display properties of the monitor screen. We can also bring the display properties dialog box right from the desktop by clicking the right mouse button on any blank space and selecting properties from the menu.

Fonts

This option can be used to add new fonts in the systems font’s folder can also copy or remove fonts from this icon.

Internet Options

It changes settings from the web browser software. Web Browser software is used in the Internet to open web pages.

Modems

Modem is a hardware device that enables the computers to make a dialup networking. We can connect to the Internet by modems. By using this option we can add modern driver and change its dialing settings.

Mouse

By using this option we change the mouse pointer styles and button setting of the mouse.

Printers

This option allows us to add or remove a driver of the printer that is connected to the computer or on a network. Settings of the printer can also change through this option.

System

This option provided us system information about all the devices connected to the computer.

Users

This option is helpful in managing different users of the same computer.

Computer Virus

In the pas few years, a new processing crimes has gained the attention of compute users all over the world. Some people have found a way to create programs that silently replicate themselves on storage media without the computer users realizing it. These programmers are referred to as computer viruses. A computer virus is a program that literally infects other programs and databases upon contact. When the program is loaded into the computer, the virus attaches itself to other programs that are residing in the system. When some one inserts an infected disk into a computer, the files in computer’s memory become infected. The reverse is also true, that is a disk used in an infected computer becomes infected. Computer can be infected when a hacker creates a virus and sends it over the phone lines to a network. Since network is connected to thousands of computer, the infection is carried to all the connected computers. Running a program or accessing the network or infected disk activities the virus without the user’s knowledge.
There are many types of viruses. Some act quickly by erasing user programs and files on disk. Other grow like a cancer, destroying small parts of a file each day. Some acts like a time bomb. They lay dormant for days or months and all of a sudden becomes active, attacking on any software on the system at a particular time. When the virus at a computer, it performs the activities assigned to it for which it was created.

Virus Activities

Some of the activities that a virus has been programmed to do are:

1. Copy themselves to other programs.

2. Display information on the screen.

3. Destroy data files

4. Erase an entire hard disk

5. Lie dormant for a specified time or until a given condition is met.

Like the viruses that cause cold and diseases in humans, computer viruses do not occur naturally. A virus program may be harmless, simply producing an obscene or silly unexpectedly on the computer screen. But it may also be a very destructive and harmful. It may wipe out huge amount of data or corrupt files on the user’s hard disk. Whatever is the motive behind it anger, revenge or intellectual challenge, it is clear that people creating virus do not have respect for other people’s hard work.

Anti-Virus

Computer users need to protect their computers from viruses until they are eradicated from the source and until they no longer exist. Fortunately there are solutions to safe guard your system against viruses. The first thing that you need to know is the ways in which your system may be infected. The most common ways that may infect your system are:

1. A floppy or a removable hard disk from another user may be a carrier of virus.

2. Virus may be transmitted to other computers via Network. That is your system may be infected when you link your system with another user, an online service, or the Internet.

3. Program purchased from unauthorized dealers may be the potential carrier of viruses.

A number of programs have been designed to protect software from viruses. These are called anti-virus programs. However no anti-virus programs guarantees protection against all viruses. If you suspect that a program is a carrier of virus, you can analyze the program using anti-virus program to see if it contains any know viruses. Most anti-virus programs can be used to eliminate to a virus found in a disk. Many computer users have installed these anti-virus programs on their computers. A good anti-virus program checks for infected files automatically every time you insert any kind of disk or use your modem to retrieve a file, several anti-virus programs are available and some are even free. Some common anti-virus programs are:

1. McAfee Virus Scan

2. Norton Antivirus

3. Virex

Chapter 08 | Boolean Algebra | IX Class Computer Science Notes

Chapter 08 | Boolean Algebra | IX Class Computer Science Notes

Boolean Algebra

The Boolean algebra was developed by the English mathematician George Boole; it deals with statements in mathematical logic, and puts them in the form of algebraic equations. The Boolean algebra was further developed by the modern American mathematician Claude Shannon, in order to apply it to computers. The basic techniques described by Shannon were adopted almost universally for the design and analysis of switching circuits. Because of the analogous relationship between the actions of relays, and of modern electronic circuits, the same techniques which were developed for the design of relay circuits are still being used in the design of modern high speed computers. Thus the Boolean algebra founds its applications in modern computers after almost one hundred years of its discovery.
Boolean algebra provides an economical and straightforward approach to the design of relay and other types of switching circuits. Just as an ordinary algebraic expression may be simplified by means of the basic theorems, the expression describing a given switching circuit network may also be reduced or simplified using Boolean algebra.
Boolean algebra is used in designing of logic circuits inside the computer. These circuits perform different types of logical operations. Thus, Boolean algebra is also known as logical algebra or switching algebra. The mathematical expressions of the Boolean algebra are called Boolean expressions. Boolean algebra describes the Boolean expressions used in the logic circuits. The Boolean expressions are simplified by means of basic theorems. The expressions that describe the logic circuits are also simplified by using Boolean theorems.
Boolean algebra is now being used extensively in designing the circuitry used in computers. In short, knowledge of Boolean-algebra is must in the computing field.

DEFINITIONS

Constants

Boolean algebra uses binary values 0 and 1 as Boolean constants.

Variable

The variables used in the Boolean algebra are represented by letters such as A, B, C, x, y, z etc, with each variable having one of two and only two distinct possible values 0 and 1.

Truth Table

It is defined as systematic listing of the values for the dependent variable in terms of all the possible values of independent variable. It can also be defined as a table representing the condition of input and output circuit involving two or more variables. In a binary system, there is 2(n) number of combinations, where n is he number of variables being used for e.g. each combination of the value of x and y, there is value of z specified by the definition. These definitions may listed in compact form using “Truth Tables”. Therefore a truth table is able of all possible combinations of the variables.

AND Operation

In Boolean algebra AND operator is represented by a dot or by the absence of any symbol between the two variables and is used for logical multiplication. For example A.B = X or AB = X.
Thus X is 1 if both A and B are equal to 1 otherwise X will be 0 if either or both A and B are 0 i.e.

1.1 = 1

1.0 = 0

0.1 = 0

0.0 = 0

OR Operation

OR operation is represented by a plus sign between two variables. In Boolean algebra OR is used for logical addition. For example A+B = X.
The resulting variable X assumes the value 0 only when both A nd B are 0, otherwise X will be 1 if either or both of A and B are 1 i.e.

1+1 = 1

1+0 = 1

0+1 = 1

0+0 = 0

Laws of Boolean Algebra

As in other areas of mathematics, there are certain well-defined rules and laws that must be followed in order to properly apply Boolean algebra. There are three basic laws of Boolean algebra; these are the same as ordinary algebra.

1. Commutative Law

2. Associative Law

3. Distributive Law

1. Commutative Law

It is defined as the law of addition for two variables and it is written as:

A + B = B + A

This law states that the order in which the variables are added makes no difference. Remember that in Boolean algebra addition and OR operation are same. It is also defined as the law of multiplication for two variables and it is written as:

A.B = B.A

2. Associative Law

The associative law of addition is written as follows for three variables:
A + (B + C) = (A + B) + C

This law states that when Oring more than two variables, the result is the same regardless of the grouping of the variables.
The associative law of multiplication is written as follows for three variables.
A(BC) = (AB)C

This law states that it makes no difference in what order the variables are grouped when ANDing more than two variables.

3. Distributive Laws

The distributive law is written for three variables is as follows:
A(B+C) = AB + AC

This law states that ORing two or more variables and then ANDin the result with a single variable is equivalent to ANDing the single variable with each of the two or more variables and then ORing the products. The distributive law also expresses the process of factoring in which the common variable A is factored out of the product terms. For example:
AB + AC = A (B + C).

Chapter 09 | Computer Software | IX Class Computer Science Notes

Chapter 09 | Computer Software | IX Class Computer Science Notes

Machine Language

Machine language is the only language that a compute understands directly without any translation, it is the binary language. It is the language of 0′s and 1′s . It consists of strings of binary numbers.
The binary codes are very difficult to memorize for human beings that is why a machine language is cumbersome for a user.

Difference Between a High-Level Language and Low-Level Language

High-Level Languages

High-Level language are more suitable for human use than machine languages and enable the programmer to write instructions easily using English words and familiar mathematical symbols. These symbolic languages are called High-Level languages. These high-level languages consist of simple English sentences, which are very easy to understand and memorize for human being.

Low-Level Languages

Both the machine and assembly languages are called Low-Level Languages. An assembly language is one step higher than the machine language in human readability. A machine language consists of totally of numbers and is almost impossible for humans to read. In an assembly language, some of these numbers are replaced by human readable symbols called language for humans and almost of the same efficiency as machine language for computer operations. An assembly language is a combination of mnemonic operation codes and symbolic codes for address.
Assembly language is very difficult but it requires good skills for programming. A program written in an assembly language is translated into a machine language before computer can understand and execute it. A computer program, which translates an assembly language program into its equivalent machine language, is called assembler.
A program can be written in much shorter time and much precisely when a high level language is used. A program written in a high level language can be executed in any computer system, which has a compiler for that programming language.

Operating System

Operating system provides link between the user and the computer. It enables the user to have complete control over the computer system by commands through the keyboard or any other input device. The supervisor part of an operating system resides all the times in the memory (RAM) of the computer after the computer is turned on. An operating system performs the following tasks:
1. Controls basic Input and Output devices.

2. Allocates system resources.

3. Manages storage space

4. Supports application software

5. Maintains security

6. Detects equipment failure

This enables the user to achieve high efficiencies of which the processing systems are capable. Operating systems can be classified as:

1. Single User Operating System

2. Multi-User Operating System

1. Single User Operating System

Single user operating systems are used on individual systems or Personal Computers. These operating systems reside on disks and re called Disk Operating Systems (DOS). Some of the most widely used single user operating systems are:

1. MS-DOS

2. PCDOS

3. OS/2

4. Windows 95

2. Multi-User Operating System

Multi-User Operating Systems are used for data processing on lrge computer systems. They enhance the potential of computer systems with multiprogramming, multiprocessing and timesharing facilities making them suitable for large organizations. Some of the multi-user operating systems are:

1. UNIX / XENIX

2. MACOSX

3. Windows NT

4. Windows 2000 Server

DOS

DOS stands for “Disk Operating System”. It is a program, which acts as an interface between the user and the computer hardware. DOS allows manipulation of files and programs by interpreting and processing the commands typed by the user.

The DOS software is automatically copied from a floppy disk or the hard drive into the computer’s memory whenever the computer is turned on or booted(made a computer ready to be used by putting in its instructions). DOS is not an application package that you start and then exit when done. This is an operating system runs from the moment you turn the computer on until you turn the machine off. The major tasks the DOS must carry out are:

1. To control input and output devices.

2. To enable user to load and execute program.

3. To maintain an orderly system of data in the disk.

Types of DOS Commands

There are two types of DOS Commands:

1. Internal Commands

2. External Commands

1. Internal Commands

Internal commands are a part of the DOS program COMMAND.COM and are loaded into memory when you boot your computer. These commands are needed to be used most often, although they are not seen when we display the disk directory of filenames on our screen. Some internal DOS commands are:

CLS
This command is used to clear the screen of a monitor.

Syntax: CLS

DIR
This command is used to display a list of current directly files and subdirectories.
Syntax: DIR[drive:][path][filename][/p][1w]

CHDIR (CD)

This command is used to display the current directory or changes in the current (default) directory.

Syntax: CD[drive:][path]

DEL
This command is used to deletes one or more specified files from the disk.
Syntax: DEL[drive][path]file name[/p]

e.g. DEL Aslam.Doc

External Commands

External Commands are programs, which exist on the DOS disk or the hard disk. They are run when you type their name on the command line. For example, typing FORMAT at the DOS prompt results in a program called FORMAT.COM being executed.

External Commands are not frequently used and DOS saves valuable memory space by loading them only when required. Some the external commands are:

CHKDSK
This command is used to checks the validity of a disk and reports the total space, used and free space on the selected disk.
Syntax: CHKDSK [drive][path][/f][/v]

SYS
This command is used to create a bootable drive and installs the main DOS files.

Syntax: SYS[drive:][path]drive2:

e.g. SYS A:

TREE
This command is used to display directory structure.

Syntax: TREE[drive:][path][/f][/a]

XCOPY
This commands is used to copy files (except hidden and system files) and directories, including sub directories.

Syntax: XCOPY source

[destination][/a|/m][/d:date][/p][/s][/e][/v][/w]
e.g. XCOPY *.*A:

DELTREE
This command is used to delete all files and sub directories in a directory.
Syntax: DELTREE[/Y][pathname]

Booting the System

The term boot or bootstrap, when used with computers, means start or startup. When we boot our computers, we are turning it on and loading the Disk Operating System (DOS) into our computer’s memory. The sequence of events that occur between the time you turn on your computer and the time it is ready for you to issue commands is referred to as the boot process. At the completion of the boot up process the system gives a DOS Prompt as soon as it is ready for operations.