Class IX Computer notes Chapter 11 - Glossary

Algorithm
A series of instructions or procedural steps for the solution of a specific problem.
Algorithm Code
A system of coding data by the use of combination of letters to represent item of information.
Alphanumeric Code
Pertaining to character set or field of data in which the coded characters may represent numerals or letters of the alphabets.
Analog Computers
Analog computers are machines designed to perform arithmetical functions upon numbers where the numbers are represented by some physical quantity.
Antivirus Utility
A program that scans disks and memory for virus, detects and remove them.
Application Program
A program forming part of a user’s job and written by the user. As distinct from program forming part of the general purpose software used to manage the operation of the total computer system.
ASCII Code
Acronym for American Standard Code for Information Interchange.
Assembler
A computer program that converts the assembly language program into machine on a language.
Assembly Language
Any symbolic language used for programming which must go through an assembler in order to be converted into the machine code required for operation on a computer.
BASIC
An acronym for Beginner’s All-purpose Symbolic Instruction Code. It is a high level programming language. Because of its simplicity and comparative power, the language is much used on personal computers.
BIT
An acronym for Binary digit, one of the two digits (0 and 1) used in binary notation.
BUG
Any mistake or malfunction of a computer program or system.
BYTE
A set of bits considered as a unit, normally consist of 8 bits and corresponds to a single character of information.
Character
One of a set of symbols in a data processing system used to denote, for example the numerals 0-9, the letters of the alphabet, punctuation marks, etc.
COBOL
COBOL is an acronym for Common Business Oriented Language. It is an internationally accepted programming language developed for general commercial use.
Code
The representation of data or instruction in symbolic form.
Coding
The written instruction for a computer coding is the part of activity of programming.
Compilation
The process of using a compiler to create an object program from a source language.
Compile
To create an object program by means of a compiler.
Compiler
A complex program which converts computer instructions written in a source language into machine code.
Computer
Any machine which can accept data in a prescribed form process the data and supply the results of the processing in a specific format as information or as signals to control automatically some further machine or process.
Computer Program
A program written in a computer language. Computer Simulation, Representing a system or a process by a computer model constructed from a computer program.
Computer Word
A fixed sequence of bits, bytes, or characters treated as a unit and capable of being stored in one storage location.
Constants
In a program constants are items of data which remain unchanged for each run.
Cursor
A special character, usually a flashing square block or underline, which indicates the position on a screen at which the next information character will displayed.
Data
A general expression used to describe any group of operands or factors consisting of numbers, alphabetic characters or symbols which denote any conditions, value or state.
Data processing
The operations performed on data, usually by automatic electronic equipment, in order to derive information or to achieve order among files.
Debugging
Debugging is the technique of detecting, diagnosing and correcting errors or bugs which may occur in programs or system.
Decision Symbol
A flow charting symbol used to indicate a choice or branching in the information processing path. A diamond shape figure is used to represent this symbol.
Difference
The result obtained in the arithmetic operation of subtraction.
Digit
A component of an item of data.
Digital Computer
A digital computer is a machine capable of performing operations on data represented in digital or number form, Disk: A revolving plate upon which data and programs are stored.
DOS
An acronym for Disk Operating System.
Document
Any form or voucher containing detail of some factors.
Documentation
It is the process of collecting, organizing and storing all the information related to a specific program like flowchart, algorithm, coding sheets, manuals etc, on papers.
EBCDIC
EBCDIC a data communication code in which 8 information bits are used to form 256 unique character codes. The term is an abbreviation of Extended Binary Coded Decimal Interchange Code.
EOF BASIC
EOF BASIC reserved word which is an abbreviation of End Of File.
Equivalence
A logical relationship in which two statement are said to be equivalent.
Error
Any condition in which the unexpected results of an compiled object code is obtained.
Expression
The symbolic representation of a mathematical or logical statement.
Field
A sub division of a record containing a unit of information.
File
An organized collection of records.
Floating Point Number
A form of number representation in which quantities are represented by a number called the mantissa multiplied by a power of the number base called exponent.
Flow Chart
The diagrammatic representation of a sequence of events, usually drawn with conventional symbol representing different types of events and their interconnection.
Format
The predetermined arrangement of data.
Function
That part of a computer instruction which specifies the operation to be performed.
Giga
A prefix denoting one thousand million.
Graphics
The use of images generated by software for output to a graphic display.
Hard Disk
A magnetic disk which is rigid.
High Level Language
A computer language which is nearest to human language. A language in which each instruction or statement corresponds to several machine code instructions.
Hybrid Computer
Any mixed computer system in which analog and digital computing devices are combined.
Hz
Abbreviation of Hertz.
Information
These are the result which is derived from the processing of data.
Input
The process of transferring data, or program instructions, into memory from sone peripheral unit.
Instruction
That part of a computer program which tells the computer what function to perform at that stage.
Interprpeter
Software that translates each statement of source program into a sequence of machine instructions and executes these machine instructions one by one before translating the next source language statement.
Jump
Synonymous with branch.
Keyboard
An input device to feed alphabetic and numeric data.
Kilobyte
1024 bytes.
Label
It is a DOS command which is used to assign a lable to the disk.
Load
This is BASIC command which is used to load a BASIC program from a secondary storage device to computer’s memory.
Locate
This is BASIC command which is used to show the location of cursor on the screen.
Loop
A series of instructions which are performed repeatedly until some specified condition is satisfied.
Machine Language
The coding system adopted in the design of a computer to represent the instruction of the computer.
Magnetic Disk
A storage device consisting of a number of flat circular plates each coated on both surface with some magnetable material.
Main Storage
The store from which instructions are executed.
Megabyte
A million bytes.
Memory
This term is usually reserved for describing the internal store of a computer.
Microcomputer
A computer based on microprocessor.
Modem
A device which transmits over distances without error.
Nested Loop
Programs fling technique in which a loop of instructions contains another loop, which may in turn contain another, and so on.
Numeral
One of a set of digits that may be used in a particular system of number system.
Numerical Data
Any field of characters which contains numeric digits only.
Object Program
A program in which language produced by translating the program written in source language through the use of a compiler.
Operating System
A set of programs which manages resources of computer include hardware, programs, data and operators.
Output
Result produced by a computer.
Output Device
The device which produces the results from the computer in human readable form.
Printer
An output device which produce results in printed form.
Procedure
The sequence of steps required in order to solve a problem.
Program
A set of instructions composed for solving a given problem by computer.
Programming Language
A language used for writing computer programs.
Prompt
Any message given to an operator by an operating system.
RAM
Abbreviation of Random Access Memory. Memory into which data can be written and from which data can be read.
Reserved Word
In a programming language, a data name not available to the user because it has some specific significance to the computer.
Resolution
The number of individually addressable and variable picture elements available in a graphic display.
ROM
Acronym for Read only Memory. Memory containing information which is permanent and which cannot be written to, but can be read by program functions.
RUN
The performance of one program or routine.
Soft Copy
Output from a computer process which is displayed on a visual display unit.
Software
The term is applied to all those programs which in some way can assist all users of a particular type of computer to make the best use of their machine.
Source Program
A program written in a source language.
Statement
A source language instruction.
Structured Programming
A methodology for programming which involves systematic described in increasing detail until the final stage of coding is required.
Subroutine
Part of a program which performs a logical section of the overall function of the program and which is available whenever the particular set of instructions is required.
Subscripted Variable
Whose numeric value can change? It is denoted by an array name followed by a subscript; e.g. A(5) or AB$(22).

Class IX Computer notes Chapter 10 - Introduction to Windows Operating System

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 behaviour 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 obcene 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 rae available and some are even free. Some common anti-virus programs are:
1. McAfee Virus Scan
2. Norton Antivirus
3. Virex

Class IX Computer notes Chapter 9 - Computer Software

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.

Class IX Computer notes Chapter 8 - Boolean Algebra

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)

Class IX Computer notes Chapter 7 - Data Representation

Data
The word data is derived from Latin language. It is plural of Datum (But Data is usually used as a singular term.) Datum (singular) – Data (plural). Data is any collection of facts of figures. The data is the raw material to be processed by a computer.
Example
Names of students, marks obtained in the examination, designation of employees, addresses, quantity, rate, sales figures or anything that is input to the computer is data. Even pictures, photographs, drawings, charts and maps can be treated as data. Computer processes the data and produces the output or result.
Types of Data
Mainly Data is divided into two types:
1. Numeric Data
2. Character Data
1. Numeric Data
The data which is represented in the form of numbers is known as Numeric Data. This includes 0-9 digits, a decimal point (.), +, /, – sign and the letters “E” or “D”. The numeric data is further divided into two groups:
i. Integer Data
ii. Real Data
i. Integer Data
Integer Data is in the form of whole numbers. It does not contain a decimal point, however it may be a positive or a negative number.
Example
Population of Pakistan, numbers of passengers traveling in an airplane, number of students in a class, number of computer in a lab etc.
2543, 7, -60, 5555, 0, + 72 etc
ii. Real Data
Real data is in the form of fractional numbers. It contains a decimal point. It can also be positive or negative number.
Real Data is further divided into two types.
a. Fixed Point Data
b. Floating Point Data
(a) Fixed Point Data
Fixed point data may include digits (0–9), a decimal point, + / – sign.
Example
Percentage of marks, weight, quantity temperature etc.
-23.0007, 0.0002, + 9243.9, 17013 etc
(b) Floating Point Data
Floating point data may include digits (0-9), decimal point, + / – sign and letters “D”, “d”, “E”, or “e”. The data, which is in the exponential form, can be represented in the floating point notation.
Example
Speed of light, mass of atomic particles, distance between stars and etc.
1.602 x 10(-19) (Charge of electron in coulomb) – Here -19 = power
The value can be feed into the computer as 1.602 E-19.
2. Character Data
Character data falls into two groups.
i. String Data
ii. Graphical Data
i. String Data
String data consists of the sequence of characters. Characters may be English alphabets, numbers or space. The space, which separates two words, is also a character. The string data is further divided into two types.
a. Alphabetic Data
b. Alphanumeric Data
(a) Alphabetic Data
The data, which is composed of English alphabets, is called alphabetic data. Names of people, names of places, and names of items are considered alphabetic data.
For example : Ahmed, Hyderabad, Chair etc
(b) Alphanumeric Data
The data that consists of alphabets as well as numerals and some special characters is called alphanumeric data. Address, employee’s code, etc are alphanumeric data.
For example: 10/B, Block No 2, E103 etc.
Graphical Data
It is possible that pictures, charts and maps can be treated as data. The scanner is normally used to enter this type of data. The common use of this data is found in the National Identity Card. The photographs and thumb impression are scanned and stored into the computer to identify a person.
Number System
The number system is the system of counting and calculation. Number system is based on some characters called digits. Each number is made up of these characters. The number of digits a sysem uses is called its base or radix. For example the number system we use in our daily life is called Decimal System. Its base is 10 (As the name ‘Deci’ implies which mean that it uses 10 digits (i.e. 0-9)
Codes
When numbers, letters or words are represented by a special group of symbols, we say they are being encoded and the group of system is called “Code”.
Types of Codes
The codes include Binary code, Binary-coded-decimal code (BCD), and alpha numeric codes. Alphanumeric codes include ASCII and EBCDIC.
ASCII Code
ASCII stands for American Standard Code for Information Interchange. It is a 7-bit code used to handle alphanumeric data. This code allows manufacturers to standardize input/output devices such as keyboard, printers, visual display units etc. An extension of ASCII code uses 8-bits called as ASCII-8 code with an extra 8th-bit as a parity bit to make the total number of 1’s either odd or even.
EBCDIC Code
EBCDIC (Extended Binary Coded Decimal Interchange Code) is an extended form of BCD (Binary Coded Decimal), which can represent only 16 characters because it is a 4-bit code. EBCDIC is an 8-bit code, so it can represent 256 different characters. It was developed by IBM and is used in most IBM models and many other computers.

Class IX Computer notes Chapter 6 - Storage Devices

Primary Storage Devices
The names of some computer’s primary storage devices are as follows:
1. Random Access Memory (RAM)
· DRAM
· SRAM
2. Read Only Memory (ROM)
· EPROM
· PROM
3. Memory
4. Cache Memory
Secondary Storage Devices
1. Hard Disk
2. Floppy Disk
3. CD-ROM (Compact Disc Read only Memory)
RAM
RAM is that part of main memory in which data and instructions are held temporarily. RAM provides a working area to the user to enter and process data. In RAM each data element has its own address (location). Any data element can be read easily and quickly by using that address. It is also called as Read-And-Write Memory (RAM) since the computer can store or write data at any selected location (address) and can retrieve or read data when needed. It is a temporary memory of a computer used to store data and an instruction when the computer is on; everything that is stored in RAM is lost when the computer is turned off. For this reason it is also called volatile memory. Large RAM sizes provide larger data that computer can hold and process. Additional RAM chips can be installed in a computer simply by plugging them on motherboard. This increases the storage capacity of RAM of computer.
RAM is a semiconductor memory with no moving part. Data can be accessed from RAM at very high speed very close to the speed of light. A memory chip less than one-fourth size of a postage stamp can store more than 500,000 bytes equivalent to the printed matter on a popular daily newspaper.
ROM
ROM stands for Read Only Memory. The instructions written in ROM can only be read but cannot be changed or deleted. The ROM is, there fore, also called non-volatile memory. It is not possible to write new information or instructions into the ROM. This is the reason why it is called Read Only Memory.
ROM stores data and instructions permanently. When the power is turned off, the instructions stored in ROM are not lost. The instructions are written into the ROM chips at the time of its manufacturing. When the computer is switched on, the instructions in the ROM are automatically loaded into the memory of the computer. These instructions prepare the computer system for use and display the initial operating system screen.
A variation of ROM is programmable read only memory (PROM). PROM is a ROM into which you can load read only programs and data. Some microcomputer software packages, such as electronic spreadsheets are available as PROM units as well as on interchangeable disks. ROM and PROM are used in variety of capabilities within a computer system.
Difference Between RAM and ROM
Everything that is stored in RAM is lost when the computer is turned off. For this reason it is also called volatile memory.
In contrast the Read Only Memory (ROM) is non-volatile memory. Instructions can only be read from ROM. Instructions once written on ROM chip cannot be changed. It is a permanent memory of a computer, i.e. the contents of this type of memory are not lost when the computer is turned off. As soon as the computer is turned on, a program that resides on ROM automatically makes the computer ready for use. ROM is a semiconductor memory generally programmed by the manufacturer.
Difference Between SIMMs and DIMMs
The capacity of RAM in a computer affects computer’s power. More RAM can make computer run faster. The computer does not necessarily have to load a complete program into its main memory to run it. However greater is the part of a program it can fit into memory, the faster the program will run.
Many RAM chips are installed on a small circuit board. These RAM chips are wired together to form a single module of large memory called Single In-Line Memory Modules (SIMMs). SIMM has contact terminals on it one side. It can easily be plugged into the motherboard. SIMMs had different capacities such as 1 Mbyte, 4Mbytes, and 16Mbytes with varying speed.
SIMMs were popular by PC users in 1980s but has now been replaced by DIMMs. Like SIMMs, Dual In-Line Memory Modules (DIMMs) have been developed installing many RAM chips. DIMMs provide larger capcity as compared to SIMMs. DIMMs have wider data bus and thus have higher rate of data transfer. DIMMs are available in several configurations having different capacities and speeds. You can expand RAM capacity of your computer by simply plugging in more DIMMs.
Short Notes
Floppy Diskette
It is a small removable, portable storage device that is made of polyester film coated with a metal oxide compound. It looks like a 45 rpm phonograph record except that it is enclosed in a jacket square in shape. It is readable by a computer with a floppy disk drive. The physical size of disks has shrunk from the early 8 inch to 5.25 inch square and about 1 millimeter thick (mini-floppy) to 3.5 inch square and about 2 millimeters thick (microfloppy) while the data capacity has risen.
Hard Disk
A hard drive is a a magnetic disk on which you can store computer data. The term hard is used to distinguish it from a soft, or floppy disk. Hard disk holds more data and is faster than floppy disks. In general, hard disks are less portable than floppies, although it is possible to buy removable hard disks. Today’s computers typically come with a hrd disk that contains several billion bytes (giga bytes) of storage.
CD-ROM
CD-ROM (Compact Disc, Read Only Memory) is an adaption of the CD that is designed to store computer data in the form of text and graphics, as well as hi-fi stereo sound. It is a non-volatile optical data storage medium that is physically the same as an audio CD and is capable of storing large amounts of data up to 1 GB, althrough the most common size is 650 MB about 12 million bytes per pound weight. All CD-ROMs confirm to a standard size and format, so you can load any type of CD-ROM into any CD-ROM player. In addition CD-ROM players are also capable of playing audio CDs. A standard CD is 120mm (4.75 inches) in diameter and 1.2 mm (0.05 inches) thick.
Magnetic Tape
A magnetic tape is also a storage device from which you can access data serially like an audio cassette from which you can hear the songs in the order in which they are stored. Serial access is slower than the direct access provided by media such as diskettes. When you want to access some particular data from the tape, the device has to scan through all the data you do not need but that data is stored before the required one. The access speed can be quite slow when the tape is long and what you want is not near the start. So the best use of the magnetic tape is for the data that you do not use very often.
Magnetic Disk
A magnetic disk is a metal or plastic disk coated with magnetic material. Data is recorded into the magnetic material in machine code. Disks have became popular due to their random access. These disk spin in the disk drives Read/Write heads moving on the disk along its radius can read data at any location under the heads.
Different types of disk drives and magnetic disks are in use. The most popular types of magnetic disks are interchangeable disks called the floppy disks and fixed disks called the hard disks.
Generally PCs are configured with at least one hard disk drive and on floppy disk drive. Hard Disk provided a very big storage capacity and are very fast but these are not inter changeable. Floppy disks are smaller than the hard disk, because they always consists only one platter. Floppies are available in size of 3.5″ and 5.25″ inches. Both of them are available in double density and high-density storage capacities. The storage capacities of these diskettes used for IBM compatible computer.
Floppy Disk, although slower than a hard disk, are inexpensive and can easily moved from computer to computer. They are comparatively fragile and must be handled with care.
Difference in the Capacity Between Hard Disk and Floppy Disk
A hard disk contains several disk platters stacked on a single rotating spindle. Data are stored on all recording surfaces. For a disk with four platters, there are eight recording surfaces on which data can be stored. A floppy disk has only one platter on which data is written, that is why the storage capacity of a hard disk is more as compared to the floppy disk. Hard disks or fixed disks are also called Winchester disk are permanently installed or fixed with in the system unit.

Class IX Computer notes Chapter 5 - Computer Components

Central Processing Unit – CPU
The central processing unit (CPU), also called the microprocessor, the processor or central processor is the brains of the computer. The CPU is housed on a tiny silicon chip. This chip contains millions of switches and pathways that help your computer make important decisions. The switches control the flow of the electricity as it travels across the miles of pathways. The CPU knows which switches to turn on and which to turn off because it receives its instructions from computer programs. Programs are a set of special instructions written by programmers that control the activities of the computer. Programs are also known as software.
The CPU has two primary sections:
· Control Unit
· Arithmetic/Logic Unit
Arithmetic/Logic Unit
Because all computer data is stored as numbers, a lot of the processing that takes place involves comparing numbers or carrying out mathematical operations. In addition to establishing ordered sequences and changing those sequences the computer can perform only two types of operations: arithmetic operations and logical operations. Arithmetic operations include addition, subtraction, multiplication and divisions. Logical operations include comparisons, such as determining whether one number is equal to, greater than or less than another number. Also, every logical operation has an opposite. For example, in addition to “equal to” there is “not equal to.”
Many instructions carried out by the control unit involve simply moving data from one place to another – from memory to storage, from memory to the printer and so forth. However, when the control unit encounters an instruction that involves arithmetic or logic, it passes that instruction to the second component of the CPU, the arithmetic or logic unit, or ALU. The ALU includes a group of registers – high-speed memory locations built directly into the CPU that are used to hold the data currently being processed. For example, the control unit might load two numbers from memory into the registers in the ALU. Then, it might tell the ALU to divide the two numbers (an arithmetic operation) or to see whether the numbers are equal (a logical operation).
Secondary Storage
Secondary storage or secondary memory also referred as backing storage is used to supplement the capacity of main storage; the memory stores a bulk of information. It is also called auxiliary storage or mass storage. The information stored in this memory is used by the CPU by first bringing it to main memory.
Examples of Secondary Storage Devices
Some Examples of secondary storage devices are as follows:
1. Magnetic Disks
2. Magnetic Tape
3. Mass Cartridge Systems
Types of Secondary Storage/Backing Storage Access Methods
There are two types of secondary storage/backing storage access methods:
Sequential Access Storage
Access through sequential access storage is non-addressable that is why an operator cannot refer directly to the contents of a particular storage location such as used with magnetic tape. This involves examining sequentially all beginning of the tape and continuing to search through all record until the desired information area is found.
Direct Access Storage
Direct Access Storage is addressable that is a given item can be selected from anywhere in storage by simply specifying the address where it is located direct access devices such as magnetic disks provide immediate access to individual records and do not require reading from the beginning of a file to find a particular record.
Computer Bus
In computer the term bus refers that paths between the components, actually bus, is a group of a wire. The bus is the common path way through which the processors send/receive data and commands to/from primary and secondary storage and all can transport 8 bits at a time whereas a bus with 16 lines can transport 16 bits at a time.
Types of Computer Bus
There are two main buses in a computer:
1. Data Bus
2. Address Bus
1. Data Bus
The data bus is an electrical path that connects the central processing unit (CPU) memory, and the other hardware devices on the motherboard. Actually, the bus is a group of parallel wires. The number of wires in the bus affects, the speed at which data can travel between components, just as the number of lanes on a highway effects how long it takes people to get to their destinations. Because each wire can transfer one bit at a time, an eight-wire bus can move eight bits at a time. A 16-bit bus can transfer two bytes and a 32-bit bus can transfer four bytes at a time.
2. Address Bus
The second bus that is found in every micro computer is the address bus. The address bus is a set of wires similar to the data bus, but is connects only the CPU and memory and all it carries are memory addresses. The reason that the address bus is important is that the number of lines in it determines the maximum number of memory address. For example, one byte of data is enough to represent 2 = 256 different values, if the address bus could carry only eight bits at a time, the CPU could address only 256 bytes of memory. Most of the early PCs had 20-bit addres bus, so the CPU could address only 2(20) bytes or 1 MB of data.
Computer Ports
A system board with its processor and memory unit can work only when linked to input/output storage and communication devices to receive data and communicate results of processing. Peripheral devices such as a keyboard, mouse, monitor and a printer come with a cable and a multiple connector. To link a device to the PC, you plug its connector into a receptacle called a port in much the same way you plug a lamp cord into electrical outlet. A port is one of the entry lines coming into the computer. A port provides a direct link to the microcomputer’s common electrical bus.
Types of Computer Ports
There are two types of ports used in computer:
1. Serial Ports
2. Parallel Ports
1. Serial Ports
A serial port provides a connection for transmitting data one bit at a time. A serial port connects your computer to a device such as modem, which requires two-way data transmission, or to a device such as a mouse, which requires only one-way data transmission. IBM-compatible computers use either 9-pin or 25-pin connectors for their serial ports COM1, COM2 etc.
2. Parallel Ports
A parallel port provides a connection for transmitting data eight bits at a time over a cable with eight separate dta lines. Parallel transmission is fast because eight bits travel simultaneously. Parallel transmission is typically used to send data to the printer. The cable that connects two parallel ports contains 25 wires, eight wires carry data and the remaining wires carry control signals that help to maintain orderly transmission and reception. IBM-compatible computes generally allow you to use up to three ports which are designated as LPT1, LPT2 etc.
Memory Unit
Memory unit is the place where the computer program and data are stored during processing. It is the area, through which all the data which is input into or output of the CPU must pass. It is monitored by OU which keeps track of every thing in the storage. It is a random access device, which consists of thousands upon thousands of storage locations, each of which can be directly reached by the CU. Each storage location is distinguished by the address.
Types of Memory Unit
It is divided into two parts:
1. Read Only Memory (ROM)
2. Random Access Memory (RAM)
1. Read Only Memory (ROM)
This part of memory contains permanently stored information. When the power is switched off. ROM does not wash away. This information is available to a computer to read and process but not to be changed is kept on ROM. This information is stored on small pieces of memory chips, before the computer is assembled.
2. Random Access Memory (RAM)
This part of memory consists of blank chips and hence the computer can use it to store and retrieve (write and read) information during its processing. The information stored in RAM is volatile, that is, when the computer is shut down the stored information is lost.

Class IX Computer notes Chapter 4 - Programming and Basics

LOOP
While writing a program it is necessary to repeat a part of a program for a number of times. The best solution for this is to use a loop it is a method which executes a part of the program repeatedly as specified by the programmer.
TYPES OF LOOPS
a) Pre-Test Loop
b) Post-Test Loop
a) PRE – TEST LOOP
As its name indicates, checks the looping condition at the start of the loop if the condition is true the loop execution starts otherwise stops. This loop is used in a situation when part of program is to be repeated for a fixed number of time.
e.g., FOR …… NEXT.
b) POST – TEST LOOP
This loop checks the looping condition at the end of loop and decides whether or not to continue the execution. This loop is used when a part of the program needs to be repeated until a specified condition is met.
e.g., WHILE …… WEND.
FLOW CHART
Flow chart is a symbolic representation of flow of programme. It can graphically represent data processing procedure Flow chart serves two purposes, i.e., the planning of the program structure as an aid in writing the computer program. Secondly the documentation of the program logic and work flow for the purpose of the communication with other person and to recall a program at a later time. If the program needs to be changed. The second purpose is very important because it is very difficult to check the logic of the program.
SYMBOLS OF FLOW CHART
TERMINAL
The terminal symbol is used to indicate the beginning, ending of the program logic flow. It is the first and last symbol of the flow chart.
INPUT / OUTPUT BOX
The input/output box is used to denote any function of an input and output in the program. If there is a program instruction to input or output the data from any I/O device that step will be indicated on this symbol.
PROCESS BOX
A processing symbol is used in a flow chart to represent arithmetical and data movement instructions.
FLOW LINES
Flow lines are used to indicate the flow of operations. The exact sequence in which the instructions are to be executed. The flow of flow chart is normally from top to bottom and left to right.
DECISION BOX
The decision box is used in a flow chart to indicate a point at which a decision has to be made and to branch to one or more alternative points that is possible during execution. The appropriate path followed, depends on the result of the decision.
CONNECTOR
A flow chart becomes complex, when the number and direction of flow lines is confusing or it spread over more than one page. It is useful to utilize the connector symbol as a substitute for flow lines.
SYSTEM FLOW CHART
System Flow Chart is used to describe complete data processing cycle including the hardware devices and media used. A System Flow Chart shows flow of data in a system where and in what form it is received by the system, how it is input to the computer and what storage media are used to hold it. The symbol used in system flow chart indicates the peripherals to be used in data processing procedure, where output will be produced. System flow chart do not explain the logic of the programs.
ERRORS
Errors are the mistakes made by the programmer during program writing. A program relays run perfectly for the first time and each program needs to be tested to ensure that it is correct and contains no errors. There are three types of errors generally encountered.
a) Syntax Error
b) Logical Error
c) Run Time Error
a. SYNTAX ERROR
The syntax of a programming language is the set of rules to be followed when writing a program in that language. These rules are similar to the grammar rules of Urdu or English language. When a program violates these rules, computer generates a syntax error. Syntax must be correct before program execution.
b. LOGICAL ERROR
These errors are the most difficult ones to find, if a programmer enters a sign of multiply instead of addition at the time of making the program, the answer will not be correct because interpreter will not be able the detect these types of errors. A logical error will not stop the execution of the program but the result will not be accurate.
c. RUN TIME ERROR
These types of errors stop the execution of the program. It may be due to entering the invalid data at the time of executing a program. For example, if a program is expecting the user to enter the numeric data and the user enters a string data, computer will display an error message.
BITS & BYTES
The smallest piece of data that can be recognized and used by a computer, is the bit, a binary digit. A bit is a single binary value, either a 1 or 0. A group of eight bits is called a byte. The byte is the basic unit for measure of the size of the memory, with today’s computer memory sizes. It is more common to hear the term kilobyte (KB) or megabyte (MB).
COMPUTER WORD
A computer word is the number of adjacent bits that can be stored and manipulated as a unit. Just an English vocabulary words are of varying lengths so are computer words. Many microcomputers have the ability to manipulate a 32 bit word, while some models have words length of 8 and 16 bits.
LIBRARY FUNCTIONS
GW-BASIC provides many built in functions which are called binary functions. Each function is composed of a format or a short program, that requires at least one parameter to be passed. A parameter is a value which is in that formula or program and this formula or program returns a result. This result can be stored in any appropriate variable or directly displayed on monitor. A library function which has “$” sign is called string library function while others are called numeric library function. A string function returns string value while a numeric function returns numeric value. Following are some library functions.
ABS, MID$, LEN, LEFT$, ASC, CHR$, TAB
EXPRESSIONS
An expression is a combination of constants and variables linked by arithmetic operators like (+, -, *, /, \). Expressions are used to perform different operations. The expressions are evaluated from left to right but some operators have priority over the others. Parenthesis are evaluated first then multiplication and division have the same priority from left to right. Similarly the addition and subtraction are evaluated with equal priorities. If all the operators are used in an expression have the same priority then the expression be executed from left to right.
The expressions can be of three types.
· Arithmetic expressions
· Logical expressions
· Relational expressions.
ARITHMETICAL EXPRESSIONS
In an arithmetic expression the following operators are used in conjunction with the operands.
SymbolMeaning
+ Addition
– Subtraction
· Multiplication
/ Division
^ Exponentiation
( Left parenthesis
) Right parenthesis
RELATIONAL EXPRESSION
A Relational expression is composed of operands linked by the relational operators. The relational operators used in the relational expression are given.
SymbolMeaning
= equal to
> greater than
< less than
<> not equal to
>= greater than or equal to
B
B <> C
LOGICAL EXPRESSIONS
When a selections is based upon one or more condition being true. It is possible to combine the condition together using logical operators and the resulting condition would either be true or false the most commonly used logical operators are AND, OR and NOT.
COMPUTER LANGUAGE
Language is a system for representation and communication of information or data. Like human beings, a language or signal is required to communicate between two persons. Similarly, we cannot obtain any result by computer without langtage. Computer does not understand directly what we are communicating with computer as English or Arabic, it understands only machine language (binary codes 0-1). Computer translates English language into machine codes through interpreter then process instructions and give us the results.
The computer languages can be divided into two main levels.
· Machine language (0-1)
· Symbolic language (A-Z)
Symbolic languages are further divide into two main levels
· High-level language
· Low-level language
MACHINE LANGUAGE
Although computers can be programmed to understand many different computer language. There is only one language understood by the computer without using a translation program. This language is called the machine language or the machine codes. Machine codes are the fundamental language of the computer and is normally written as strings of binary 0-1.
ADVANTAGES AND LIMITATIONS OF MACHINE LANGUAGE
Programs written in machine language can be executed very fast by the computer. This is mainly because machine instructions are directly understood by the CPU and no translation of program is required.
However, writing a program in machine language has several disadvantage.
MACHINE DEPENDENT
Because the internal design of every type of computer is different from every other type of computer and needs different electrical signals to operate. The machine language also is different from computer to computer.
DIFFICULT TO PROGRAM
Although easily used by the computer, machine language is difficult to program. It is necessary for the programmer either to memorize the dozens of code number for the commands in the machine’s instruction set or to constantly refer to a reference card.
DIFFICULT TO MODIFY
It is difficult to correct or modify machine language programs. Checking machine instructions to locate errors is difficult as writing them initially.
In short, writing a program in machine language is so difficult and time consuming.
SYMBOLIC LANGUAGES
In symbolic languages, alphabets are used (a-z). symbolic languages are further divide into two main levels.
· High level languages
· Low level languages
LOW LEVEL LANGUAGE
A language which is one step higher than machine language in human readability is called Assembly Language or a low-level language. In an assembly language binary numbers are replaced by human readable symbols called mnemonics. Thus a low-level language is better in understanding than a machine language for humans and almost has the same efficiency as machine language for computer operation. An assembly language is a combination of mnemonic, operation codes and symbolic codes for addresses. Each computer uses and has a mnemonic code for each instruction, which may vary from computer to computer. Some of the commonly used codes are given in the following table.
COMMAND NAMEMNEMONIC
Add – ADD
Subtract – SUB
Multiply – MUL
Compare Registry – CR
Compare – COMP
Branch Condition -BC
Code Register -LR
Move Characters -MVE
Store Characters -STC
Store Accumulator – STA
An assembly language is very efficient but it is difficult to work with and it requires good skills for programming. A program written in an assembly language is translated into a machine language before execution. A computer program which translates any assembly language into its equivalent machine code is known as an assembler.
HIGH – LEVEL LANGUAGE
A language is one step higher than low-level languages in human readability is called high-level language. High – level languages are easy to understand. They are also called English oriented languages in which instruction are given using words. Such as add, subtract, input, print, etc. high level language are very easy for programming, programmer prefer them for software designing that’s why these languages are also called user’s friendly languages. Every high level language must be converted into machine language before execution, therefore every high level language has its own separate translating program called compiler or interpreter. That’s why some time these languages are called compiler langauges. COBOL, BASIC, PASCAL, RPG, FORTRAN are some high level languages.
INTERPRETER
An interpreter is a set of programs which translates the high-level language into machine acceptable form. The interpreters are slow in speed as compared to compilers. The interpreter takes a single line of the source code, translates that line into object code and carries it out immediately. The process is repeated line by line until the whole program has been translated and run. If the program loops back to earlier statements, they will be translated afresh each time round. This means that both the source program and the interpreter must remain in the main memory together which may limit the space available for data. Perhaps the biggest drawback of an interpreter is the time it takes to translate and run a program including all the repetition which can be involved.
PROGRAM DEVELOPMENT PROCESS
In order to develop a computer program, a programmer has to go through the following stages:
1. DEFINING AND ANALYSING THE PROBLEM
In this step a programmer studies the problem and decides how the problem will be best solved. Studying a problem is necessary because it helps a programmer to decide about:
· The facts and figures to be collected.
· The way in which the program will be designed.
· The language in which the program will be most suitable.
· What is the desired output and in which form it is needed, etc.
2. DESIGNING THE ALGORITHM
An algorithm is a set of instructions or sequence of steps that must be carried out before a programmer starts preparing his program. The programmer designs an algorithm to help visualize possible alternatives in a program.
3. FLOWCHARTING
A flow chart is a graphical representation of a program which helps a programmer to decide on various data processing procedures with the help of labeled geometrical diagrams. A flow chart is mainly used to describe the complete data processing system including the hardware devices and media used. It is very necessary for a programmer to know about the available devices before developing a program.
4. CODING OR WRITING THE PROGRAM
The next job after analysing the problem is to write the program in a high-level language, usually called coding. This is achieved by translating the flow chart in an appropriate high-level language, of course according to the syntax rules of the language.
5. TEST EXECUTION
The process of execution of any program to find out for errors or bugs (mistakes) is called test execution. This is very important because it helps a programmer to check the logic of the program and to ensure that the program is error-free and workable.
6. DEBUGGING
It is a term which is used extensively in programming. Debugging is the process of detecting, locating and correcting the bugs by running the programs again and again.
7. FINAL DOCUMENTATION
It is written information about any computer software. Final document guides the user about how to use the program in the most efficient way.
MODES OF OPERATION
There are two modes of operation for BASIC. The mode that you are in determines what BASIC will do with the instruction you give it. When you start BASIC you receive the OK prompt. You then have two modes available to you immediately.
DIRECT MODE
In the direct mode BASIC acts like a calculator. No line numbers are required. Direct mode is not of course the main purpose of BASIC, but it is useful at times particularly when you are debugging program or short problems in which you want to perform quick calculation e.g., PRINT 3+4.
INDIRECT MODE
In this mode you first put a line number on each statement. Once you have a program you can run it and get your results. The indirect mode saves your instructions in the computer along with their line number, you can execute the program as many times as you wish simply by typing RUN.
STEPS OF PROGRAMMING
There are five steps in preparing a computer programme which are also called ABCDE of Programming.
ANALYSIS
In this step the system analyst tries to become familiar with the problem. He has to study the problem and prepare some notes upon that problem. He also notes that what is given, what is required and what will computer can do.
BLOCKING
In this step the programmer converts the analyst report to a series of steps through which the computer will give the required result. The steps are commonly known as Algorithm. There are different ways to write those detailed sequential steps. The most common method used is flow charting. A flow chart is symbolic representation of flow of a programme.
CODING
In this step the programmer writes the programme in any computer language. This step is known as coding. After this programme is fed into the computer and is compiled with the help of a given compiler.
DEBUGGING
Debugging is a step in which a programmer corrects a syntax error which may come after the compilation.
TESTING
Testing is a step where the programmer is finally testing the programme for execution (there may be any logical mistake which compiler cannot trace).
EXECUTION
In this step we send the programme for execution where company’s data will be fed and process.
VARIABLES AND CONSTANTS
VARIABLES
Variables are names used to represent values used in BASIC programme. The values of a variable may be assigned by the programmer or it may be assigned as the result of calculation in the programme. Before a variable is assigned a value is assumed to be zero (or null for string variable).
VARIABLES NAMES & DECLARATION CHARACTERS
Variable names may be of any length up 40 characters are significant. Variable name can contain letters, numbers and decimal point. However, the first character must be a letter. A variable should not be a reserve word.
Variable may represent either a numeric value or a string.
NUMERIC VARIABLE
Numeric variable names may be declared as integer, single precision, double precision values. The type of declaration characters for these variable names are as follows.
STRING VARIABLE
In programming we often use to handle alphanumeric or string variables. String variables consist of names, addresses or in general any string or series of letters, number or special characters.
Without the use of string variable whenever any differentiation needs to be made e.g., from employee to employee or from application no. to application no., a number has to be assign to each employee or each application.
A string variable name starts with an alphabet and terminate with a dollar sign ($). In a string the value must be in quotation marks. No arithmetic operations except addition and in addition the values do not add they are just written together. The maximum number of character allowed in a string varies from system to system but a typical value is 256.
CONSTANTS
Constants are those that do not change while executing the programme. BASIC deals with two types of constant.
1. Numeric constant
2. String constant
1. NUMERIC CONSTANT
All numbers belong to this category because their values remain constant during execution.
They may take any of the following forms:
1. Commas are not allowed in a numeric constant.
2. The use of the positive sign is optional but negative sign should be used if the number is negative.
2. STRING CONSTANT
A string constant is any set of valid basic characters enclosed in quotation marks. The quotation marks do not form part of string. Strings are used to represent non-numeric information such:
1. Name of persons and places
2. Addresses
3. Days, Months, Years.
INTRODUCTION TO BASIC
BASIC is a high level language used for purpose of writing a program on a computer. It stands for Beginners All-purpose Symbolic Instruction Code. BASIC is an easy to use “friendly” language where instruction resembles elementary, algebraic formulas and certain English keywords such Let, Read, Print, Goto etc.
HISTORY OF BASIC
The language was developed at Dartmouth College in 1967, under the direction of John Kemeny and Thomas Kurtz. It was quickly discovered and adopted. All the major computer manufacturers offered their own version of BASIC for their particular computers.
In 1978, the American National Standard Institute standardized an essential subset of BASIC in order to promote uniformity from one version of BASIC into another.
In recent years some new version of BASIC have been developed which included a variety of features that are not included in more traditional versions.
STRUCTURE OF BASIC PROGRAM
Each instruction in a BASIC program is written as a separate statement. Thus a program will be composed of a sequence of statements.
The following rules apply to all BASIC statements:
1. Every statement must appear on a separate line number.
2. Each statement number must be followed by a BASIC keyword which indicates the type of instruction.
3. On one single line number we cannot write two statements, if we need we must use “colon”.
4. We can write 255 characters on one line.

Class IX Computer notes Chapter 3 - Input and Output Devices

PRINTER
A computer peripheral that puts text or a computer generated image on paper or on another medium, such as a transparency. Printer can be categorized in several ways the most common distinction is IMPACT and NON-IMPACT.
IMPACT PRINTING
Is the method used by the conventional type writers. In some type of impact printing a metal “hammer” embossed with a character strikes a print ribbon, which presses the characters image into paper. In other types the hammer strikes the paper and presses it into the ribbon characters created through impact printing can be formed by either a solid font or dot matrix printing mechanism.
NON – IMPACT PRINTING
Does not depend on the impact of metal on paper. In fact no physical contact at all occurs between the printing mechanism and the paper. The most popular non-impact methods today utilize thermal transfer, ink-jet.
TYPES OF PRINTERS
1. DOT MATRIX PRINTER
Any printer that produces character made up of dots using a wire pin printed head. The quality of output from a dot matrix printer depends largely on the number of dots in the matrix, which might be low enough to show individual dots or might be high enough to approach the look of fully formed characters. Dot matrix printers are often categorized by the number of pins in the printer head typically, 9 or 24.
2. LINE PRINTERS
Any printer that prints one line at one time, as opposed to one character at a time or one page at a time. Line printer typically produce the 11 by 17 inch “computer” printout. They are high speed devices and are often used with mainframes, minicomputers, or networked machines rather than with single user system. Types of line printers include chain printers and band printer.
3. LASER PRINTERS
An electrophotographic printer that is based on the technology used by photocopiers. A focussed laser beam and a rotating mirror are used to draw an image of the desired page on a photosensitive drum. This image is converted on the drum into an electrostatic charge, which attracts and holds toner. A piece of electrostatically charged paper is rolled against the drum, which pulls the toner away from the drum and onto the paper. Heat is then applied to fuse the toner to the paper. Finally, the electrified charge is removed from the drum and the excess toner is collected. By omitting the final step and repeating only the toner application and paper handling steps, the printer can make multiple copies.
4. DAISY WHEEL PRINTER
Daisy wheel printer are some times called letter quality printer because they are often used to produce attractive correspondence. The D.W.P is a flat circular device made of metal with character embossed on it. As this wheel spins at a very high speed the hammer hits the specific character against the ribbon which presses against the paper.
5. THERMAL TRANSFER PRINTER
It is a kind of non-impact printer. In electrothermal printing, characters are burned on to a special paper by heated rods on a print heat. They transfer ink from a wax-based ribbon onto plain paper. These printer can support high quality graphic.
6. INK – JET PRINTER
It is a kind of non-impact spray small dots of electrically charged ink onto a paper to form images. Ink jet printer are flexible enough to be used as plotters.
SECONDARY STORAGE DEVICES
Secondary storage devices are also called backup storage because it is used to store data. Volume of data on permanent basis which can be partially transferred to the primary storage, when required for data processing. Afterwards these devices are comparatively cheap and provide greater space to store the data /instructions are stored on secondary storage devices in the same binary codes as in primary storage.
NEEDS OF SECONDARY STORAGE DEVICE
The storage capacity of the primary storage of today’s computer is not sufficient. To store a large volume of data as a result additional memory called secondary storage is needed with most of the computer system.
These devices also provides the fast communication than I/O devices. The internal memory of a computer is a volatile memory. Therefore, we cannot save the data permanently. In that case we require secondary storage device which provide the facility to store the data for future use.
RANDOM ACCESS DEVICES
Random Access Devices are those devices on which we can directly access the data. These devices are comparatively provide the fast communication.
For example, hard disk, floppy disk, optical disk.
FLOPPY DISK
A floppy disk, also called simply a diskette or disk, is a small flexible Mylar disk coated with iron oxide on which data are stored. The floppy disk has been around since early 1970s, today it is available in three 3½ inch, 5¼ inch and 8 inch sizes. The 5¼ and 8 inch diskettes are covered by stiff protective jacket with different holes. The central big hole called hub ring which is used to hold by disk drive during rotation. The elongated read write window is used to read and write data through read/write head. The small hole next to the hub ring is called index hole which is used to locating data through computer. The cut out on the side of the floppy disk is called write protect notch. If we cover this opening with a piece of paper then we can’t write data on to disk.
In small diskette a hard plastic cover and protective metal is used to protect disk. Before using a disk we have to format a disk in which disk is divided into tracks and sectors for storing the data. Diskettes may be double sided and single sided while the storage capacity become less or more.
Floppy diskettes are more convenient to use with microcomputers. A floppy disk which is a random access device can access data fast than magnetic tape.
SEQUENTIAL ACCESS DEVICES
Sequential Access Devices are those in which we can access the data one by one in a sequence. These devices provide slow communication as compared to Random Access Device.
MAGNETIC TAPE
Magnetic tape is a sequential access device about one half or one fourth inch in size and made of Mylar (a plastic material) coated with a thin layer of iron oxide. Data can be read and write through a device which is called tape drive. The read/write head of tape drive which is an electromagnetic component read, write and erase data from magnetic tape. Magnetic tape is divided into nine separate strips or tracks in which eight tracks are used to store data and ninth track is used for error checking bit.
Magnetic tape can store large quantities of data therefore they are erasable, usable and durable secondary storage device. But it can use with large computers.
INPUT DEVICES
Input devices are used to provide data or information to the computer. The computer follows the instructions given to it by and input device. A variety of input devices are used with the computer depending on the type and purpose of input information. For example, a keyboard is commonly used to transfer data or information from human readable form to machine readable form. Other examples of input devices are: mouse, joystick, trackball, light pens, digitizers, scanners, optical character reader (OCR), touch window, etc.
MOUSE
The mouse is an input device that usually contains one or two buttons. As a user moves the mouse on a flat surface, the mouse controls the cursor movement on the screen. When the user presses one of the buttons, the mouse either marks a place on the screen or makes selection from data or menu on the screen. A mouse has a sphere on its underside. This rotates as the mouse is moved along a flat surface.
The mouse translate the direction and speed of rotation into a digital signals that identifies the position or control, the cursor on the computer.
A mouse can be used for many application, ranging from games to drawing and designing products with computer graphics. It provides an alternative for people who are uncomfortable with a keyboard but it also can be used in combination with a keyboard to input data.
TRACKBALL
A Trackball is a pointing device almost like a mouse turned upside down. The user controls the cursor on the screen by rolling a plastic ball with a fingertip or wrist. To execute commands with a Trackball, one or more buttons are pressed, much in the same way as is done with a mouse. The cursor can be moved around on the screen by rolling the ball with a thumb or finger.
Trackball is popular among users of laptop computers when space is limited and may be mounted on either side of the keyboard. For handicapped people who may have difficulty pressing keys on a standard keyboard or using a mouse, the trackball may be the answer since it edoes not require to moves the entire arm to use it.
SCANNER
Scanner is an input device. It is also called Optical Reader or Digital Scanner. It scans or reads text and picture printed on a paper and enters them directly into the computer memory.
The advantage of a scanner is that the user needs not type the input data in. This is a lust and accurate method for entering data into the computer. The scanner takes electronic images, of text or pictures from the paper it breaks each image into light and dark dots and stores them into the computer memory in machine codes. Scanned text can be edited by OCR software. Optical Character Recognition (OCR) software translates the scanned document into text that can be edited.
The image scanner is useful because it translates printed images into an electronic format than can be stored in computer’s memory. The stored image can be transferred into a paint program or directly into a word processor. You can use software to organize and manipulate the electronic image.
KEYBOARD
A keyboard is the most commonly used input device which helps us in simply keying in required information in a computer. This information is subsequently stored in the computer’s memory. A keyboard can be used effectively to communicate with the computer but considered to be relatively slow as compared to other input devices. The keyboard is divided into following divisions:
ALPHABETIC KEYPAD
These keys are similar to a standard typewriter and is used to type general information.
NUMBERIC KEYPAD
These keys are used to input numeric data only. These are very useful in case of large numeric data input because all numeric keys can be accessed by one hand only. These keys can also be used as an alternative to the screen navigation and editing keys.
FUNCTION KEYS
These are keys marked as F1 – F12, located normally at the top of the keyboard. These are special keys provided to a programmer which allow him to attach special functions to each key. Each of these function keys are also given some special function in different packages.
SCREEN NAVIGATION AND EDITING KEYS
These keys are provided to move around in the screen. May programs use these keys to let the user move around the screen display. In some keyboards these keys are also provided inside the numeric keypad as alternate keys.
The description of commands assigned to function keys under the BASIC mode.
F1 – LIST Function – Used to display the lines of your program on the screen.
F2 – RUN Function – Used to execute a program from its beginning.
F3 – LOAD Function – Used to read a program from a storage device and store it in main memory.
F4 – SAVE Function – Used to store a program on a storage device from Memory.
F5 – COUNT Function – Used to restart a program after it has temporarily interrupted by a stop or CTRL + BREAK.
F6 – LPT1 Function – Used to transfer data from the video screen to the line printer.
F7- TRON Function – Refers to “trace on”. This function causes the line number of program line to be displayed as these lines are executed.
F8 – TROFF Function – Refers to “trace off”. This function cancels TRON function.
F9 – KEY Function – Use to change the function of the other function keys.
F10 – SCREEN Function – Used to return program to the character mode from the graphic mode and a;so to turn off the colour.
OUTPUT DEVICES
An output device is used to display the data or information that we receive from the computer. An output device can be used to display or print the intermediate or final results performed by computer. A variety of output devices are used with computer. The use of these devices depends on the type and purpose of output. Some examples of output devices are: Monitors, Printer, Plotters, Visual display unit (VDU), liquid crystal display (LCD), etc.
MONITOR
To display result or output from computer, a T.V like device is used which is called monitor. The monitors are also referred as C.R.T (Cathode Ray Tube), V.D.U (Visual Display Unit). The monitor assist during input from the keyboard, this display is called a soft copy. The monitor can be of various kinds, depending on the type of application. Monitors are categorized into two groups:
1. Monochrome monitors
2. Colour monitors
1. MONOCHROME MONITORS
Monochrome monitors are used specially for text editing purpose. These monitors can display only one colour. Normally amber, green or paper white.
2. COLOUR MONITORS
Colour monitors serves a wide range of selection according to the application. Such as red, green, blue, Enhance Graphic Array (EGA), Colour Graphic Array (CGA), Video Graphics Array (VGA), Super Video Graphics Array (SVGA).
There are two types of colour monitors:
i. CRT Monitor
ii. LCD Monitor
i. CRT MONITOR
The CRT monitors are a lot like television set, using the same CRT or Cathorde Ray Tube technology. The CRT monitor has two major parts; the screen and the cathode ray tube (CRT). The screen is the front of the monitor and CRT is fitted inside the monitor.
ii. LCD OR FLAT PANEL MONITOR
Another monitor type is LCD or Liquid Crystal Display. LCD monitors are a lot like CRT monitors without the bulkiness but they do not have CRT. LCD monitors use a flat lightweight surface filled with millions of tiny glass bubbles, each having a phosphoric covering. These phosphoric coverings glow to create an image. LCD screens provide clarity and flicker-free viewing.
PLOTTER
Plotter is a special output device, which is used to produce high quality, perfectly proportional hard copy output. Plotters are designed to produce large drawings or images such as construction plans for buildings or blue prints for mechanical devices. Plotters have been used in automotive and aircraft design, topological surveys, architectural layouts and other similar complex drafting jobs.
A plotter is composed of a pen, a move-able carriage, a drum and a holder for chart paper. Both the pen and the paper can move up and down and back and forth. This permits very detailed drawings. Some plotter having coloured pens can make coloured drawings also.
There are two types of plotters, which are as follows:
1. Drum Plotter
2. Flatbed Plotter
1. DRUM PLOTTER
On the drum plotter, the pens, and the drum move concurrently in different axes to produce the image. Drum plotters are used to produce continuous output, such as plotting earthquake activity, or for long graphic output, such as structural view of a skyscraper.
2. FLATBED PLOTTER
On some flatbed plotters, the pen moves in both axes while the paper remains stationary. However, on most desktop plotters, both paper and pen move concurrently in much the same way as on drum plotters.
HARD DISK
Hard disk is a thin circular metal plate coated both side with a magnetic material. A hard disk pack consist of a number of disk mounted on central shaft which rotate at a speed of 2400 rpm or more. In a hard disk information is stored on both the surfaces of each disk plate except the upper and the lower surfaces of the bottom plate which are not used. Information is recorded on the track of the disk surfaces in the form of invisible tiny magnetic spot. The presence of a magnetic spot represent 1 bit and its absence represents 0 bit.
Hard disk are potentially very high capacity storage devices typically in the range of 20 megabyte to 1 gigabyte. Data are recorded on the tracks of a spinning disk surface and read from the surface by one or more read/write heads. There are two basic types of disk system.
1. Moving head
2. Fixed head
1. MOVING HEAD
The moving head consist of one read/write head for each disk surface mounted on an axis and which can be moved in and out. In this system each read/write head moves horizontally across the surface of the disk. So that it is able to access each track individually. Information stored on the tracks which constitute a cylindrical shape through the disk pack are therefore accessed simultaneously.
2. FIXED HEAD
In the fixed head system the axis are non-movable. A large number of read/write heads are distributed over the disk surfaces. One head for each track as a result no head movement is required and therefore information is accessed more quickly.
VOICE RECOGNITION
A voice recognition system compares a person’s live speech to their stored voice pattern. Larger organizations sometimes use voice verification systems as time attendance devices. Many companies also use this technology for access to sensitive files and networks. Some financial services use voice verification systems to secure telephone banking transactions. These systems use speaker dependent voice recognition software. This type of software requires the computer to make a profile of your voice, that is, you train the computer to recognize your inflection patterns.
SHORT NOTES
DISK DRIVE
Disk drive is a peripheral device that reads or write the disks (hard disks, floppy disks, etc) that store information. Disk drives are called “Storage Device” because they store information or portabel or permanent disks. The drive contains a motor to rotate the disk at a constant rate and one or more read/write heads, which are positioned over the desired track.
CD-WRITER
A CD writer is a device connected to your computer which can write on CD-WR and CD-R discs. CD-WR discs may be written, erased and rewritten, while CD-R discs may be written only once. CD writer performances is measured in X unit, where IX =150 kilobytes/sec. This allows user to master a CD-ROM or audio CD for publishing CD-R devices can also read CD-ROMs and play audio CDs. The CD writer is also called a CD-R drive (short for Compact Disc – Recordable Drive)