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Programming and Basics

9th Class Computer Notes

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


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.


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.


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

<= less than or equal to

Example

A > 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


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.


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.

Computer Components

9th Class Computer Notes

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


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.


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


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.


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)


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.


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.


Storage Devices

9th Class Computer Notes

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.

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Data Representation - Computer Studies

9th Class Computer Notes



Data Representation - Computer Studies



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 


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: 
1. Integer Data 
2. Real Data 


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 


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. 


Character Data

Character data falls into two groups. 
1. String Data 
2. Graphical Data 


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. 
1. Alphabetic Data 
2. 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. 
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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.


Boolean Algebra

9th Class Computer Notes

Boolean Algebra


The Boolean algebra was developed by the English mathematician George Boole; it deals with statements in mathematical logic, and puts them in the form of algebraic equations. The Boolean algebra was further developed by the modern American mathematician Claude Shannon, in order to apply it to computers. The basic techniques described by Shannon were adopted almost universally for the design and analysis of switching circuits. Because of the analogous relationship between the actions of relays, and of modern electronic circuits, the same techniques which were developed for the design of relay circuits are still being used in the design of modern high speed computers. Thus the Boolean algebra founds its applications in modern computers after almost one hundred years of its discovery.

Boolean algebra provides an economical and straightforward approach to the design of relay and other types of switching circuits. Just as an ordinary algebraic expression may be simplified by means of the basic theorems, the expression describing a given switching circuit network may also be reduced or simplified using Boolean algebra.

Boolean algebra is used in designing of logic circuits inside the computer. These circuits perform different types of logical operations. Thus, Boolean algebra is also known as logical algebra or switching algebra. The mathematical expressions of the Boolean algebra are called Boolean expressions. Boolean algebra describes the Boolean expressions used in the logic circuits. The Boolean expressions are simplified by means of basic theorems. The expressions that describe the logic circuits are also simplified by using Boolean theorems.

Boolean algebra is now being used extensively in designing the circuitry used in computers. In short, knowledge of Boolean-algebra is must in the computing field.


Definitions
Constants

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


Variable

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


Truth Table

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


AND Operation

In Boolean algebra AND operator is represented by a dot or by the absence of any symbol between the two variables and is used for logical multiplication. For example A.B = X or AB = X.

Thus X is 1 if both A and B are equal to 1 otherwise X will be 0 if either or both A and B are 0 i.e.

1.1 = 1

1.0 = 0

0.1 = 0

0.0 = 0


OR Operation

OR operation is represented by a plus sign between two variables. In Boolean algebra OR is used for logical addition. For example A+B = X.

The resulting variable X assumes the value 0 only when both A nd B are 0, otherwise X will be 1 if either or both of A and B are 1 i.e.

1+1 = 1

1+0 = 1

0+1 = 1

0+0 = 0

Laws of Boolean Algebra

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

1. Commutative Law

2. Associative Law

3. Distributive Law


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


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.


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)

Computer Software

9th Class Computer Notes

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


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


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


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


Introduction to Windows Operating System

9th Class Computer Notes

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: 


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 


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. 


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 
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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. 
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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


Glossary of Computer Studies Class IX

9th Class Computer Notes



Glossary of Computer Studies Class IX


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)

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