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9th Class Computer Science Important Questions & Notes for Exam 2013

9th Class Computer Science Important Questions & Notes For Exam 2013

Introduction to Computers

 

 

 

Computer

A Computer is an automatic electronic, calculating device which can process a given input in a prescribed manner to produce a desired output, at a very high speed with remarkable accuracy. It can also perform all arithmetic and logical functions according to instructions given in a systematic order to solve any problem and produce processed information.

Advantages of Computers

Speed
Since Computer is an electronic machine and electrical pulses travel at the rate of passage of electric current. This speed enables the computer to perform millions of calculations per second.

Storage
A computer has too much storage capacity. Once recorded, a piece of information can never be forgotten.

High Accuracy
A computer can be considered as 100% accurate. Checking circuits are built directly into the computer, that computer errors that undetected are extremely rare.

Versatility
Computer can perform any task, provided it can be reduced to a series of logical steps.

Diligence
Computer never gets tired. It performs most boring, repetitive and monotnous task.

Automatic Operation
Once a program is fed into computer the individual instructions are processed on after the other. Thus computer works automatically without manual intervention.

Obedience
The ability to take in and store a sequence of instructions for the computer to obey. Such a sequence of instruction is called a PROGRAM and it must be written in the Computer Language.

Decision Making Capability
Computer can take simple decisions, such as less than, greater than or equal to. It also determines whether a statement is true or false.

Hardware

The physical components and other attached input and output devices of computers are called Hardware. All Hardware components may be connected mechanically, electrically or electronically with each other. Hardware includes input/output devices, CPU, backing storage devices and electronic circuit.

Software

Computer required a number of instructions to do any job. The set of these instructions forms programs. Numbers of programs are combined for some purposes are called software.
They are designed by manufactures and programmers.

Types of Software

1. System Software
2. Application Software

Ages of Computer

At the early age people used pebbles, stones, sticks, scratches, symbols and finger tips to count, which were later replaced by numbers.
The history of computing is divided into three ages during which man invented and improved different types of calculating machines. These ages are,
Dark age – 300 BC to 1890
Middle age – 1890 AD to 1944
Modern age – since 1944 AD

Dark Age (3000 BC to 1890 AD

ABACUS
About 3000 years BC, Chinese developed the first calculating machine named Abacus or Soroban.
Abacus consists of a rectangular wooden frame having rods which carry round beads. Counting is done by shifting the beads from one side to another.

OUGHTRED’S SLIDE RULES
In 1632 AD William Oughtred, an English mathematician developed a slide rule. This device consists of two movable rules placed side by side on which number were marked.

PASCAL’S CALCULATOR
Blasé Pascal (1623-1662), a French developed the first mechanical calculating machine in 1642. This machine consists of gears, wheels and dials. It was capable of adding and subtracting operations.

GOTTEFRIED WILHOLM LEIBNITZ
In 1671, a German, Gottfried Von Leibnitz (1646-1716) improved Pascal’s calculator to make it capable of performing all maths operations.

JACQUARD’S LOOM
In 1801, a French, Joseph Marie Jacquard developed the first punch card machine.

BABBAGE DIFFERENCE ENGINE
Charles Babbage (1792-1871) an English mathematician also called Father of modern computer. As he gave the true concept of computer at Cambridge University, he developed Babbage Difference Engine in 1823 and Babbage Analytical Engine in 1833.
Lady Ada Augusta an assistant of Babbage is called the first programmer.

Middle Age (1890 AD TO 1944 AD)

DOCTOR HERMAN HOLLERITH
In 1880s Herman Hollerith an American developed a machine which used punch card system. The machine could sense and punch holes, recognize the number and make required calculations. This machine was first used in 1890s by American Census Bureau.

HOWARD AIKEN- MARK-1 COMPUTER
In 1937, Professor Howard Aiken build the first electro-mechanical computer Mark-1, by trying to combine Babbage’s theory and Hollerith’s punching technologies. He completed his project in 1944 with the help of IBM Engineers.
Mark 1 could multiply two, twenty digit numbers in 5 seconds and made a lot of noise. It had a shape like a monster about 50 feet long, 8 feet high, having wiring of length equal to distance from Lahore to Gilgit or Karachi to Bahawalpur (800km) and had thousand ends of electro-magnetic relays.

ABC (ATANASOFF BERRY COMPUTER)
ABC a special purpose computer was developed in 1938 by Dr. John Vincent Atanasoff and Clifford Berry at Iowa State College, USA.

Modern Ages (Since 1944 AD)

JOHN VON NEUMAN
In 1945, Dr. John Von Neuman suggested the concept of Automatic Data Processing (ADP) according to the stored program and data. ENIAC

(FIRST ELECTRONIC COMPUTER)
Electronic Numerical Integrator And Calculator (ENIAC) was the first electronic computer made in 1946 by John Presper Eckert and John Williams Mauchly, at the University of Pennsylvania, USA. This was based on decimal number system and it has no memory.
It could perform 5000 additions or 350 multiplications in one second. It contained 18000 vacuum tubes, 70,000 resistors, 10,000 capacitors and 60,000 switches and occupied a two room car garage. It consumed 150 kW of power. It weighed 27 tons.

EDSAC (FIRST STORED PROGRAM COMPUTER)

Electronic Delay Storage Automatic Computer (EDSAC) was first computer based on stored program concept. It was completed by Mourice Wilkes at Cambridge University in 1949.

EDVAC
Electronic Discrete Variable Automatic Computer (EDVAC) was built by John Williams Mauchly, John Presper Eckert at Moore School, Pennsylvania in 1951.

UNIVAC (FIRST COMMERCIAL COMPUTER)
UNIVersal Automatic Computer (UNIVAC) was the first commercially used computer made by John Presper Eckert and John Williams Mauchly in June 14, 1951.

Classification of Computers According to Purpose

1. General Purpose Computers

General purpose computers are designed to solve a large variety of problems. The different programs can be used to solve many problems. Most digital computers are general purpose computers and used in business and commercial data processing.

2. Special Purpose Computers

A computer designed for machine control or process control would be different than a general purpose computer. The special purpose computers are designed to solve specific problems. The computer program for solving a specific problem is built right into the computer. Most analog computers are special purpose computers. These special purpose computers are widely used in industrial robotics.

Types of Computers

1. Analog Computers

Analog computers are used to process continuous data. Analog computers represent variables by physical quantities. Thus any computer which solve problem by translating physical conditions such as flow, temperature, pressure, angular position or voltage into related mechanical or electrical related circuits as an analog for the physical phenomenon being investigated in general it is a computer which uses an analog quantity and produces analog values as output. Thus an analog computer measures continuously. Analog computers are very much speedy. They produce their results very fast. But their results are approximately correct. All the analog computers are special purpose computers.

2. Digital Computers

Digital computer represents physical quantities with the help of digits or numbers. These numbers are used to perform Arithmetic calculations and also make logical decision to reach a conclusion, depending on, the data they receive from the user.

3. Hybrid Computers

Various specifically designed computers are with both digital and analog characteristics combining the advantages of analog and digital computers when working as a system. Hybrid computers are being used extensively in process control system where it is necessary to have a close representation with the physical world.
The hybrid system provides the good precision that can be attained with analog computers and the greater control that is possible with digital computers, plus the ability to accept the input data in either form.

Classification of Computers According to Size

1. Super Computers

Large scientific and research laboratories as well as the government organizations have extra ordinary demand for processing data which required tremendous processing speed, memory and other services which may not be provided with any other category to meet their needs. Therefore very large computers used are called Super Computers. These computers are extremely expensive and the speed is measured in billions of instructions per seconds.

2. Main Frame Computers

The most expensive, largest and the most quickest or speedy computer are called mainframe computers. These computers are used in large companies, factories, organizations etc. the mainframe computers are the most expensive computers, they cost more than 20 million rupees. In this computers 150 users are able to work on one C.P.U. The mainframes are able to process 1 to 8 bits at a time. They have several hundreds of megabytes of primary storage and operate at a speed measured in nano second.

3. Mini Computers

Mini computers are smaller than mainframes, both in size and other facilities such as speed, storage capacity and other services. They are versatile that they can be fitted where ever they are needed. Their speeds are rated between one and fifty million instructions per second (MIPS). They have primary storage in hundred to three hundred megabytes range with direct access storage device.

4. Micro Computers

These are the smallest range of computers. They were introduced in the early 70’s having less storing space and processing speed. Micro computers of todays are equivalent to the mini computers of yesterday in terms of performing and processing. They are also called “computer of a chip” because its entire circuitry is contained in one tiny chip. The micro computers have a wide range of applications including uses as portable computer that can be plugged into any wall.

5. Laptop Computers

The smallest computer in size has been developed. This type of small computers look like an office brief case and called “LAPTOP” computer. The laptops are also termed as “PORTABLE COMPUTERS.” Due to the small size and light weight, they become popular among the computer users. The businessmen found laptop very useful, during traveling and when they are far away frm their desktop computers. A typical laptop computer has all the facilities available in microcomputer. The smallest laptops are called “PALMTOP”.

Generations of Computer

First Generation of Computer (1946-1959)

Main Features
Major Innovation – Vacuum Tubes
Main Memory – Punched Cards
Input Output Devices – Punched cards and papers
Languages – Low level machine language
Operating System – No operating system, human operators to set
switches
Size – Main frame for example ENIAC, EDVAC, UNIVAC
The duration lasted from 1946-1959 was based on vacuum tubes. These vacuum tubes were about the size of 100 watt light bulb and used as the internal computer component. However because thousands of such bulbs were used, the computers were very large and generate a large amount of heat, causing many problems in temperature regulation and climate control.
In this generation input and out put device (punched card) that was used fro data storing purpose were very slow. The computers were operating manually and the language used was a low level machine language (symbolic language) with binary code that required a high programming skill. ENIAC, EDVAC, UNIVAC and Mark-1 were some of the major inventions of this generation.

Advantages of First Generation
1. Vacuum tubes were used as electronic component.
2. Electronic digital computers were developed for the first time.
3. These computers were the fastest calculating devices of their time.
4. Computations were performed in millisecond.

Disadvantages of First Generation
1. Too large in size.
2. They were unreliable.
3. Induce a large amount of heat due to the vacuum tubes.
5. Not portable.
6. Limited commercial use.

Second Generation of Computers (1959-1964)

Main Features
Major Innovation – Transistors as main component.
Main Memory – RAM and ROM.
External Storage – Magnetic tapes and Magnetic Disk.
Input Output Devices – Magnetic tapes and Magnetic Disk.
Languages – Assembly language, some high level languages for Example BASIC, COBOL, FORTRAN.
Operating System – Human handles punched card.
Size – Main frame for example IBM-1401, NCR-300, IBM-600 etc.
The period of this generation is from 1959 to 1964. During this period transistor were used for internal logic circuits of computers. These computers could execute 200000 instructions per second. The input/output devices became much faster by the use of magnetic table. During this period the low level programing language were used however the high level programming languages such as FORTRAN and COBOL were also used. The problem of heat maintenance was solved and size of computer reduced, while speed and reliability were increased. Many companies manufactured second generation computers and many of those for business applications. The most popular second generation computer was IBM-1401, introduced in 1960, while the following computers were used by many business organizations. IBM-1400 series, IBM-1600 series, UNIVAC-III, NCR-300 etc.

Advantages of Second Generation
1. Smaller in size as compares to 1st generation.
2. Much more reliable.
3. Less heat generated.
4. Computation was performing in micro second.
5. Less hardware and maintenance problem.
6. Could be used for commercial use.

Disadvantages of Second Generation
1. Very costly for commercial use.
2. It still required frequent maintenance.
3. Frequent cooling also required.

Third Generation of Computers (1965-1970)

Main Features
Major Innovation – Integrated circuit (ICs) as basic electronic component.
Main Memory – PROM and DRAM.
External Storage – Improve disk (Floppy Disk)
Input and Output Devices – Keyboard for input, monitor for output.
Languages – More high level languages.
Operating System – Complete operating systems were introduced.
Size – Mini, for example: IBM SYSTEM / 360, ICH-360, HONEY WELL-316 etc.
In this generation the integrated circuits (IC) were used. Integrated circuits contain many electronic components on a single chip. The disk oriented systems wee made at the end of this generation. The size of computer became very small with better performance and reliability. High level programming languages were extensively used. In 1969 the first microprocessor chip INTEL 4004 was developed but it was used only in calculators. The faster input/output devices made possible multi-processing and multi programming. Where by a number of input terminals could be run virtually at the same time on a single centrally located computer. The famous computer were IBM-360, IBM-370, UNIVAC 9000 series etc.

Advantages of Third Generation
1. Smaller in size as compared to second generation.
2. More reliable.
3. Portable
4. Less electricity consumption.
5. Heat generation was rare.
6. General purpose computer.

Disadvantages of Third Generation
1. Air conditioning was required in many cases due to ICs.
2. Very advance technology was required to make the ICs.

Fourth Generation of Computers (1971-1981)

Main Features
Major Innovation – LSIC and VLSIC (Micro Processor)
Main Memory – EPROM and SRAM.
External Storage – Floppy Disk and Hard Disk.
Input and Output Devices – Monitor for output.
Languages – Languages and application softwares.
Operating System – MS-DOS and PC-DOS
Size – Micro computer e.g. IBM-PC, Apple Macintosh etc.
The Integrated circuits were more developed and called Small scale integration (SSI), after some time the SSI were more developed and termed as Large scale integration (LSI). There was a great versatility of input/output devices. In 1971, a powerful microprocessor chip INTEL 8008 was introduced. The first microprocessor which is used in personal computers (PC) was INTEL 8080. The 8 inch floppy disk was also introduced in 1971, while hard disk was introduced in 1973. The 5.25 floppy disk was first time used in 1978. The optical disk was developed in 1980. First portable computer “Osborne I” was marketed in 1981. IBM-3033, IBM-370, IBM system 34, IBM system 36, Cray-I, CP/M etc were introduced in this generation.

Advantages of Fourth Generation
1. Smaller in size and much reliable.
2. No cooling system required in many cases.
3. Much faster computation.
4. Portable and cheap.
5. The heat generated was negligible.
6. Totally general purpose computer.

Disadvantages of Fourth Generation
1. Very advanced technology was required to fabricate to the ICs.

Fifth Generation (1981-Onward)

Main Features
Major Innovations – ULSIC (Ultra large scale integrated circuit)
Main Memory – EEPROM, SIMM and DIMM.
External Storage – Modified magnetic and Optical disks.
Input/output Devices – Keyboard, Pointing Device, Scanner as input and Monitor as main output.
Languages – AI (Artificial Intelligence) Expert systems.
Operating System – GUI based e.g. Windows 95, Windows NT.
Size – Very small in size example: Laptop, Note book, Digital Diary, Palm top and Pocket PC.
This generation is started from 1981 and still continued, new technologies are adopted to fabricate IC chips, such as electron beam, X-rays or laser rays. The Very Large Scale Integration
(VLSI) was developed, so the computer became much smaller than ever before. New memory storage device like bubble memory, optical or memory are being designed. the new computer will be controlled by using human voice and will work by giving command in our own language. Future computer will in some way to be intelligent and capable of making decision.

Advantages of Fifth Generation
1. Very large storage capacity.
2. Long bit processor builds.
3. Artificial Intelligence Language developed.

Short Notes

1. Super Computer

These are the largest and fastest machines today where numerical computations are carried out speeds of up to 50 millions operation per second. Super computers are very sophisticated machines designed to perform complex calculations at fastest speeds. Super computers are used to model very large dynamic systems, such as weather patterns national or global weather forecasting, satellite tracking, cold-testing of atomic and nuclear weapon etc. Carry research and Intel are well known producers of Super Computers.

2. Main Frames

A main frame originally meant the cabinet containing the central processor unit of a very large computer. After mini computer became available, the word main-frame comes to refers to the large computer itself.
Mainframes, the biggest and the most productive general purpose systems, that are made to model large dynamic computing need of a big organizations that serve hundreds of terminals all at the same time. A terminal consists of a monitor and keyboard that allow a person to enter information and retrieve it from the computer. These computers are the ultimate in sophistication, flexibility and speed.

3. Mini-Computer

Mini computer are increasingly powerful and do almost any thing that large computers do, only more slowly and at much lower cost than mainframes. This makes it ideal for small companies where capacity and speed of operations in not highly critical. These computers are smaller than mainframe and larger than micro computer in size. A mini computer is a multiprocessing system having terminals attached to it and is capable of supporting 4 to 200 users simultaneously. DEC VAX and IBM AS/400 are commonly used mini-computers.

4. Micro-Computer

Micro-Computers are computers that are powered by microprocessors. Sometimes they are referred as SINGLE CHIP PROCESSOR a SYSTEM-ON-A-CHIP. Micro-computers or personal computers are the smallest computers, designed to be used by individuals for writing, illustrating, budgeting, playing games and communicating with other computers.

Programming Language

A programming language is a type of software. A program is a set of step by step instruction that directs the computer to do the tasks you want it to do and produce the result you want. A set of rules that provides a way of telling a computer when operations to perform is called a Programming Language.

Machine Language (Low Level Language)

Every creation of this universe has its own language. Like wise, computer has a language that is called Machine Language (machine level language) for instructing computer to perform specific task. It is also called binary language because it is the language of 0s and 1s, means every instruction in Machine language consists of a series of 0s and 1s (binary code) that a computer can understand and execute directly. Each machine language statement corresponds to one machine action. An operation that requires one machine language instruction in one computer may require several instructions in another computer. Each computer has its own unique machine language.

Assembly Language

In assembly language, the statements are written in symbolic codes (termed as mnemonics) that are easier for human to read and write as compared to machine language. Each assembly language statement corresponds to one machine language statement.

Advantages of Assembly Language

1. Operation codes of machine language are mnemonics, which are easy to remember.
2. An Assembly language program may be written easily as compared to machine language.
3. The memory addresses are used in machine language which is replaced by the variable names in this language.
4. Revision of complete program is quite easy.
5. The insertion and deletion of the instructions in the program are quite easy.

Disadvantages of Assembly Language

1. As compared to machine language assembly language is less efficient.
2. An assembly language program cannot be executed on small size computers.

High Level Language

High level languages are closer to human languages than low-level language and include statement like GOTO and PRINT which are regular words. Unlike the assembly language, the program of high level languages do not have to be written for a particular computer, but it can be execute on any machine that has a compiler for that language.

Internet

Internet is the largest network of the world that connects computers located t different parts of the world. The Internet has had a huge impact on society. The Internet provides information and service, as well as the ability to communicate to people all around the world in a variety of ways. These range from bulletin boards and chat rooms to voice conversations and video conferencing.
The Internet creates new ways for citizens to communicate, congregate and share information. It is obvious that the Internet has and will continue to change the way we live.
All in all, the Internet is affecting so many people’s lives in most welcome, exciting and challenging ways.

Advantages of Internet

1. It gives information about every field of life.
2. You may take advantages from encyclopedias and dictionaries with the help of Internet.
3. You my get information according to your need through Internet.
4. It gives a co-ordination with whole world and its interests.
5. It helps to exchange views with the person of same mental attitude.
6. Internet brings the world closer.
7. Current happening incident can be discovered by the use of Internet.
8. Any kind of topic related with politics, fashion, science etc can be discovered by use of Internet.

Disadvantages of Internet

1. The student waste their precious hours on sitting on Internet without taking any positive and constructive benefit.
2. Most of the people using Internet to satisfy their negative desires.
3. Adult material is easily available through Internet which destroys the moral values of young boys and girls.
4. Computer hacking is very common by the use of Internet some extreme minded people can digest the money through the use of credit cards of others.
5. The students waste their time in useless talking with each other.
6. Several hours on Internet without any purpose produce wrong effects on a person.

Compiler

A compiler is complex system software that automatically converts a program written in some high-level language into an equivalent low-level machine language. The compiler or the language processor converts the entire program into machine code before execution. A program written by a programmer in a language other than machine language is called a Source Program. The output from a compiler or an assembler, which consists of machine language instructions, is called the Object Program.

Interpreter

An interpreter is another type of translator that converts each statement of a program written in a high level language into machine code and executes it before translating the next statement of the source program. It differs from a compiler that translates the entire source program into object program without undergoing its execution.

Short Notes

BASIC – Beginner’s All-Purpose Symbolic Instruction Code)

John Kemeny and Thomas Kurtz developed BASIC in 1964 for beginners. BASIC is a very simple language to use and understand. It uses simple English words. Even a person with a little knowledge of computer programming can learn it and utilize it for business and scientific purpose. It is a powerful language that has grasped millions of users. The biggest problem with it is that it has no standard version and different manufacturers modified it into different versions.

PASCAL

A French mathematician Blaise Pascal introduced a programming language by the name of PASCAL. It is a highly structured programming language. It was developed in 1970’s after the concept of structured programming.

FORTRAN (Formula Translation)

It was developed in 1957 for IBM computers to solve mathematical, scientific and engineering problems. It was one of the first languages to introduce the concept of “Modular Programming”. It has been revised so many times.

Advantages and Disadvantages of Computers

Following are some advantages and disadvantages of computer in our life.

Advantages

1. Computers make us more productive in many of our jobs.
2. In education they can help us for better understanding faster learning and broaden our thinking.
3. In hospitals we have better diagnosis, proper treatment and better healthcare.
4. In business, they are used to record stocks of raw materials as well as finished products, making customer’s bill, analyzing sales of various products etc.
5. In banks, they are used for day-to-day processing of customer’s accounts and payments.
6. In manufacturing, they provide ways to develop a representation of the product and to test it in a variety of simulated environments.

Disadvantages

1. Unemployment due to automation.
2. Wastage of time and energy in useless computer activities.
3. Data security.
4. Privacy
5. Computer Crimes.

 

Data Processing

 

Data Processing

Data processing often referred as D.P is a process of collecting the data together and converting the data into information. The method used for collecting the data may be manual, mechanical or electronic.
Data processing is a term mostly associated with business and commercial work. Since computers are being used in the processing of data the term “electronic data processing” may also be used.

Electronic Data Processing

Data processing means transformation of data into more meaningful results for carrying out scientific, business activities. The result of data processing is called “information”. The transformation of data consist of a sequence of operations. The sequence is called “procedure”.
Input -> Processing -> Output
Data processing is a system which takes data as an input, carries out the required processing on the data and produces the information. The system is called “MANUAL” when processing is performed by human beings and “AUTOMATIC” when machines are used. When computers are used for data processing the system is called “Electronic Data Processing”.

Elements of EDP

There are five basic elements in a processing system which uses a computer for processing data. These are hardware, software, user program, procedure and personnels.

1. HARDWARE

All the physical parts which makes up a computer system called hardware i.e. all the devices or peripherals which performs the data processing operations.

2. SOFTWARE

Software consists of programs and routines whose purpose is to make the computer useable for the user. These software normally supplied by computer manufacturers or software manufacturers.

3. USER PROGRAM

A program consist of a related instructions to perform operations. A data processing job may require a number of programs.

4. PROCEDURE

The operations of data processing system requires procedure for use, in preparing data, for operating the computer and distributing the output after processing.

5. PERSONNELS

E.D.P basically needs three kinds of skilled personnels.
a) System Analyst
b) Progammer
c) Operator

a) SYSTEM ANALYST
System Analyst studies information needs and data processing requirements, design a data processing system and prepare specification.

b) PROGRAMMER
A Programmer writes a programmer on specification by System Analyst.

c) OPERATOR
An Operator is a person who operates the computer system.

 

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)

 

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
<= 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

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.

 

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.

 

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.

 

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.

 

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.

 

9th Class Computer Science Important Questions & Notes For Exam 2013

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