TyroCity: Computer 11 Notes

Communication And Computer Network

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction to communication and computer network

Today computer is available in many offices and homes and therefore there is a need to share data and programs among various computers with the advancement of data communication facilities. The communication between computers has increased and it thus it has extended the power of computer beyond the computer room. Now a user sitting at one place can communicate computers of any remote sites through communication channel. The aim of this chapter is to introduce you the various aspects of computer network.

Objectives

After going through this lesson you will be in a position to:

explain the concept of data communication
understand the use of computer network
identify different components of computer network
identify different types of network
explain communication protocols
understand what is internet and email and its uses in modern communication
appreciate the use of satellite communication.

Data communication

We all are acquainted with some sorts of communication in our day to day life. For communication of information and messages we use telephone and postal communication systems. Similarly data and information from one computer system can be transmitted to other systems across geographical areas. Thus data transmission is the movement of information using some standard methods. These methods include electrical signals carried along a conductor, optical signals along an optical fibers and electromagnetic areas.

Suppose a manager has to write several letters to various clients. First he has to use his PC and Word Processing package to prepare his letter. If the PC is connected to all the client’s PCs through networking, he can send the letters to all the clients within minutes. Thus irrespective of geographical areas, if PCs are connected through communication channel, the data and information, computer files and any other program can be transmitted to other computer systems within seconds. The modern form of communication like e-mail and Internet is possible only because of computer networking.

Basic elements of a communication system

The following are the basic requirements for working of a communication system.

A sender (source) which creates the message to be transmitted.
A medium that carries the message.
A receiver(sink) which receives the message.

In data communication four basic terms are frequently used. They are:

- Data: A collection of facts in raw forms that become information after processing.
- Signals: Electric or electromagnetic encoding of data.
- Signaling: Propagation of signals across a communication medium.
- Transmission: Communication of data achieved by the processing of signals.

Communication protocols

You may be wondering how do the computers send and receive data across communication links. The answer is data communication software. It is this software that enables us to communicate with other systems. The data communication software instructs computer systems and devices as to how exactly data is to be transferred from one place to another. The procedure of data transformation in the form of software is commonly called protocol.

The data transmission software or protocols perform the following functions for the efficient and error free transmission of data.

Data sequencing: A long message to be transmitted is broken into smaller packets of fixed size for error free data transmission.

Data routing: It is the process of finding the most efficient route between source and destination before sending the data.

Flow control: All machines are not equally efficient in terms of speed. Hence the flow control regulates the process of sending data between fast sender and slow receiver.

Error control: Error detecting and recovering is the one of the main function of communication software. It ensures that data are transmitted without any error.

Data transmission modes

There are three ways for transmitting data from one point to another

1. Simplex: In simplex mode the communication can take place in one direction. The receiver receives the signal from the transmitting device. In this mode the flow of information is Uni.-directional. Hence it is rarely used for data communication.

2. Half-duplex: In half-duplex mode the communication channel is used in both directions, but only in one direction at a time. Thus a half-duplex line can alternately send and receive data.

3. Full-duplex: In full duplex the communication channel is used in both directions at the same time. Use of full-duplex line improves the efficiency as the line turn-around time required in half-duplex arrangement is eliminated. Example of this mode of transmission is the telephone line.

Digital and analog transmission

Data is transmitted from one point to another point by means of electrical signals that may be in digital and analog form. So one should know the fundamental difference between analog and digital signals. In analog signal the transmission power varies over a continuous range with respect to sound, light and radio waves. On the other hand a digital signal may assume only discrete set of values within a given range. Examples are computer and computer related equipment. Analog signal is measured in Volts and its frequency in Hertz (Hz). A digital signal is a sequence of voltage represented in binary form. When digital data are to be sent over an analog form the digital signal must be converted to analog form. So the technique by which a digital signal is converted to analog form is known as modulation. And the reverse process, that is the conversion of analog signal to its digital form, is known as demodulation. The device, which converts digital signal into analog, and the reverse, is known as modem.

Asynchronous and synchronous transmission

Data transmission through a medium can be either asynchronous or synchronous. In asynchronous transmission data is transmitted character by character as you go on typing on a keyboard. Hence there is irregular gaps between characters. However, it is cheaper to implement, as you do not have to save the data before sending. On the other hand, in the synchronous mode, the saved data is transmitted block by block. Each block can contain many characters. Synchronous transmission is well suited for remote communication between a computer and related devices like card reader and printers.

Following are the major communication devices used to day.

Wire pairs: Wire pairs are commonly used in local telephone communication and for short distance digital data communication. They are usually made up of copper and the pair of wires is twisted together. Data transmission speed is normally 9600 bits per second in a distance of 100 meter.

Coaxial cables: Coaxial cable is groups of specially wrapped and insulted wires that are able to transfer data at higher rate. They consist of a central copper wire surrounded by an insulation over which copper mesh is placed. They are used for long distance telephone lines and local area network for their noise immunity and faster data transfer.

Microwave: Microwave system uses very high frequency radio signals to transmit data through space. The transmitter and receiver of a microwave system should be in line-of-sight because the radio signal cannot bend. With microwave very long distance transmission is not possible. In order to overcome the problem of line of sight and power amplification of weak signal, repeaters are used at intervals of 25 to 30 kilometers between the transmitting and receiving end.

Communication satellite: The problem of line-sight and repeaters are overcome by using satellites which are the most widely used data transmission media in modern days. A communication satellite is a microwave relay station placed in outer space. INSAT-1B is such a satellite that can be accessible from anywhere in India. In satellite communication, microwave signal is transmitted from a transmitter on earth to the satellite at space. The satellite amplifies the weak signal and transmits it back to the receiver. The main advantage of satellite communication is that it is a single microwave relay station visible from any point of a very large area. In microwave the data transmission rate is 16 giga bits per second. They are mostly used to link big metropolitan cities.

In-text questions 1

1. What is communication protocol?

2. What is the difference between asynchronous and synchronous transmission?

3. State whether True or False

The basic requirements for working of a communication system are sender medium and receiver.
Electric or Electromagnetic encoding of data is called Transmission.
In full duplex the communication channel is used in both directions at the same time.
Analog signal is measured in Volts and its frequency in Hertz
The technique by which a digital signal is converted to analog form is known as modulation.

Computer network

A computer network is an interconnection of various computer systems located at different places. In computer network two or more computers are linked together with a medium and data communication devices for the purpose of communicating data and sharing resources. The computer that provides resources to other computers on a net
work is known as server. In the network the individual computers, which access shared network resources, are known as workstations or nodes.
Computer Networks may be classified on the basis of geographical area in two broad categories.

Local area network (LAN)
Wide area network (WAN)

Local area network

Networks used to interconnect computers in a single room, rooms within a building or buildings on one site are called Local Area Network (LAN). LAN transmits data with a speed of several megabits per second (106 bits per second). The transmission medium is normally coaxial cables.

LAN links computers, i.e., software and hardware, in the same area for the purpose of sharing information. Usually LAN links computers within a limited geographical area because they must be connected by a cable, which is quite expensive. People working in LAN get more capabilities in data processing, work processing and other information exchange compared to stand-alone computers. Because of this information exchange most of the business and government organizations are using LAN.

Major characteristics of LAN

Every computer has the potential to communicate with any other computers of the network
High degree of interconnection between computers
Easy physical connection of computers in a network
Inexpensive medium of data transmission
High data transmission rate

Advantages

The reliability of network is high because the failure of one computer in the network does not effect the functioning for other computers.
Addition of new computer to network is easy.
High rate of data transmission is possible.
Peripheral devices like magnetic disk and printer can be shared by other computers.

Disadvantages

If the communication line fails, the entire network system breaks down.

Use of LAN

Followings are the major areas where LAN is normally used

File transfers and Access
Word and text processing
Electronic message handling
Remote database access
Personal computing
Digital voice transmission and storage

Wide area network

The term Wide Area Network (WAN) is used to describe a computer network spanning a regional, national or global area. For example, for a large company the head quarters might be at Delhi and regional branches at Bombay, Madras, Bangalore and Calcutta. Here regional centers are connected to head quarters through WAN. The distance between computers connected to WAN is larger. Therefore the transmission medium used are normally telephone lines, microwaves and satellite links.

Characteristics of WAN

Followings are the major characteristics of WAN.

1. Communication facility: For a big company spanning over different parts of the country the employees can save long distance phone calls and it overcomes the time lag in overseas communications. Computer conferencing is another use of WAN where users communicate with each other through their computer system.

2. Remote data entry: Remote data entry is possible in WAN. It means sitting at any location you can enter data, update data and query other information of any computer attached to the WAN but located in other cities. For example, suppose you are sitting at Madras and want to see some data of a computer located at Delhi, you can do it through WAN.

3. Centralized information: In modern computerized environment you will find that big organizations go for centralized data storage. This means if the organization is spread over many cities, they keep their important business data in a single place. As the data are generated at different sites, WAN permits collection of this data from different sites and save at a single site.

Examples of WAN

1. Ethernet: Ethernet developed by Xerox Corporation is a famous example of WAN. This network uses coaxial cables for data transmission. Special integrated circuit chips called controllers are used to connect equipment to the cable.

2. Aparnet: The Aparnet is another example of WAN. It was developed at Advanced Research Projects Agency of U. S. Department. This Network connects more than 40 universities and institutions throughout USA and Europe.

Difference between LAN and WAN

LAN is restricted to limited geographical area of few kilometers. But WAN covers great distance and operate nationwide or even worldwide.
In LAN, the computer terminals and peripheral devices are connected with wires and coaxial cables. In WAN there is no physical connection. Communication is done through telephone lines and satellite links.
Cost of data transmission in LAN is less because the transmission medium is owned by a single organization. In case of WAN the cost of data transmission is very high because the transmission medium used are hired, either telephone lines or satellite links.
The speed of data transmission is much higher in LAN than in WAN. The transmission speed in LAN varies from 0.1 to 100 megabits per second. In case of WAN the speed ranges from 1800 to 9600 bits per second (bps).
Few data transmission errors occur in LAN compared to WAN. It is because in LAN the distance covered is negligible.

Network topology

The term topology in the context of communication network refers to the way the computers or workstations in the network are linked together. According to the physical arrangements of workstations and nature of work, there are three major types of network topology. They are star topology, bus topology and ring topology.

Star topology

In star topology a number of workstations (or nodes) are directly linked to a central node (see, Fig. 4.3). Any communication between stations on a star LAN must pass through the central node. There is bi-directional communication between various nodes. The central node controls all the activities of the nodes. The advantages of the star topology are:

It offers flexibility of adding or deleting of workstations from the network.
Breakdown of one station does not affect any other device on the network.

The major disadvantage of star topology is that failure of the central node disables communication throughout the whole network.

Bus topology

In bus topology all workstations are connected to a single communication line called bus. In this type of network topology there is no central node as in star topology. Transmission from any station travels the length of the bus in both directions and can be received by all workstations. The advantage of the bus topology is that:

It is quite easy to set up.
If one station of the topology fails it does not affect the entire system.

The disadvantage of bus topology is that any break in the bus is difficult to identify.

Ring topology

In ring topology each station is attached nearby stations on a point to point basis so that the entire system is in the form of a ring. In this topology data is transmitted in one direction only. Thus the data packets circulate along the ring in either clockwise or anti-clockwise direction. The advantage of this topology is that any signal transmitted on the network passes through all the LAN stations. The disadvantage of ring network is that the breakdown of any one station on the ring can disable the entire system.

In-text questions 2

1. Differentiate between LAN and WAN.

2. What are the different types of network topology?

3. State True or False

Networks used to interconnect computers in a single room, rooms within a building or buildings on one site are called Wide Area Network (WAN).
The term Wide Area Network (WAN) is used to describe a computer network spanning a regional, national or global area.
The speed of data transmission is much higher in WAN than in LAN.
In star topology a number of workstations (or nodes) are directly linked to a central node.
The advantage of the bus topology is that, If one station of the topology fails it does not affect the entire system.

Internet

The Internet is a network of networks. Millions of computers all over the world are connected through the Internet. Computer users on the Internet can contact one another anywhere in the world. If your computer is connected to the Internet, you can connect to millions of computers. You can gather information and distribute your data. It is very much similar to the telephone connection where you can talk with any person anywhere in the world.

In Internet a huge resource of information is accessible to people across the world. Information in every field starting from education, science, health, medicine, history, and geography to business, news, etc. can be retrieved through Internet. You can also download programs and software packages from anywhere in the world. Due to the tremendous information resources the Internet can provide, it is now indispensable to every organization.

Origin of internet

In 1969 Department of Defense (DOD) of USA started a network called ARPANET (Advanced Research Projects Administration Network) with one computer at California and three at Utah. Later on other universities and R & D institutions were allowed to connect to the Network. APARNET quickly grew to encompass the entire American continent and became a huge success. Every university in the country wanted to become a part of ARPANET. So the network was broken into two smaller parts MILNET for managing military sites and ARPANET (smaller) for managing non-military sites. Around 1980, NSFNET (National Science Foundation Network) was created. With the advancement of modern communication facilities, other computers were also allowed to be linked up with any computer of NSFNET. By 1990 many computers were looking up to NSFNET giving birth to internet.

How internet functions

Internet is not a governmental organization. The ultimate authority of the Internet is the Internet Society. This is a voluntary membership organization whose purpose is to promote global information exchange. Internet has more than one million computers attached to it.

E-mail

E-mail stands for electronic mail. This is one of the most widely used features of Internet. Mails are regularly used today where with the help of postage stamp we can transfer mails anywhere in the world. With electronic mail the service is similar. But here data are transmitted through Internet and therefore within minutes the message reaches the destination may it be anywhere in the world. Therefore the mailing system is excessively fast and is being used widely for mail transfer.

In-text questions 3

What is internet?
What is e-mail?
How does internet function?

What you have learnt

In this lesson we discussed the importance and modes of communication through computers. Computers can communicate with one another through computer networking. There are two types of computer network: LAN and WAN. We discussed about the physical arrangements of computer and peripherals in network topology. There are three types of network topology: star topology, bus topology and ring topology. Also we discussed about Internet and e-mail.

Terminal questions

What is computer Network? What are its main objectives?
Differentiate between analog and digital transmission of data.
Explain in brief different communication media.
What is the difference between simplex and full-duplex transmission?

Feedback to in-text questions

In-text questions 1

1. The data communication software instructs computer systems and devices as to how exactly data is to be transferred from one place to another. The procedure of data transformation in the form of software is commonly called protocol.

2. In asynchronous transmission data is transmitted character by character as you go on typing on a keyboard. On the other hand, in the synchronous mode, the saved data is transmitted block by block.

True
False
True
True
True

In-text questions 2

1. LAN is restricted to limited geographical area whereas WAN covers great distance. In LAN the computer terminals and peripheral devices are connected with wires and coaxial cables whereas in WAN communication is done through telephone lines and satellite links. The speed of data transmission is much higher in LAN than in WAN.

2. There are three major types of network topology. They are star topology, bus topology and ring topology.

False
True
False
True
True

In-text questions 3

1. The Internet is a network of networks. Information in every field starting from education, science, health, medicine, history, and geography to business, news, etc. can be retrieved through Internet.

2. E-mail stands for electronic mail. Through e-mail we can transfer data anywhere in the world within seconds.

3. Internet is not a governmental organization. The ultimate authority of the Internet is the Internet Society. This is a voluntary membership organization whose purpose is to promote global information exchange.

Buffer

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Buffer

It is a temporary memory located in different hardware devices mainly I/O devices. This memory is used to store data during I/O process. The process of using buffer for computer operation is known as buffering.

Input Devices

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Some of the input devices used in a computer are keyboard, mouse scanner, joystick, touch screen, touchpad, track ball, bar code reader, light pen, optical code reader (OCR), MICR, OMR, microphone, digital camera, webcam, card readers, digitizing tablets, etc.

Keyboard

Keyboard is the most basic input device. It is used for text input. It contains multiple keys. User can provide input by pressing the key. The different types of key found in keyboard are:

Alphanumeric keys (A-Z, 0-9)
Function keys (Ctrl, Alt, Caps lock, Enter, Tab, Shift)
Special function keys (F1, F2, F3,……..,F12)
Cursor movement keys (?, ?)
Punctuation keys (,, “” , ’’, ?, !)
Numeric pad
Multimedia keys

On the basis of keys, keyboard can be classified as

XT keyboard -83 keys
AT keyboard -101 keys
Enhanced keyboard -103 and more keys

A keyboard contains an electronic circuit known as keyboard encoder. This circuit detects the pressed key, generates its electronic signal and transmits towards CPU.
On the basis of connectivity, keyboard can be wire or wireless.

Mouse

Mouse is a most common pointing and selecting device. It is used in graphical user interface. Mouse contains buttons for providing inputs. User can provide inputs by moving the mouse and pressing the button. On the basis of buttons, mouse can be:

Two-buttoned mousse
Three-buttoned mouse

Usually, the left button of the mouse is for normal selection and the right button is used for special function and central button is used for scrolling a document.
On the basis of working mechanism and its architecture, mouse can be classified as:

Mechanical mouse
Opto-mechanical mouse
Optical mouse

Mechanical mouse contains a rubber ball and a pair of rotating wheels. When the mouse is moved on the table, the ball rotated which results in rotation of the wheels and generates electronic signal.
Optical mouse operates using reflection of light. It is easier to use but usually less reliable than mechanical mouse.
The opto-mechanical mouse contains both mechanical and electric component.

Track ball
Trackball is the modification of mechanical mouse. It contains rubber ball on its top. User can move the cursor by rotating the ball with finger. It also contains two buttons on the either sides similar to mouse. It was used in older laptops.

Track pad/Touch pad

Track pad is the modification of optical mouse, and touch pad is further modification making it touch sensitive. It contains a window with two buttons on the either sides. User can also provide left click option by tapping the window with the finger. It is mainly used in portable devices like laptops, notebook, palmtop, etc.

Joystick

Joystick is a hand held pointing device which is mainly used for playing games. It is used for controlling objects, their movement, direction and speed of movement. Modern joysticks handle can move in any direction. When the handle is moved, the electronic circuit in the base detects the movement and sends corresponding binary signals to CPU.

Light pen

Light pen is used for creating drawings, designs by directly touching the screen. It is mainly used by designers, architects, engineers, etc. it is used in monitor not having touch screen facility. It is a pen shaped structure containing photo sensitive tip which can capture light emitted from the monitor and mark the position on the monitor.

Touch screen

Touch screen is none of the common input device at present mainly for portable computers. User can provide inputs by directly touching the screen with the metallic pen (stylus), finger or any pointed object. Touch screen is developed by using either of the following technologies:
a) Pressure sensitive
b) Capacitive
c) Infrared

Scanner

Scanner digitizes hard copy or printed images which can be used in digital computers. Scanner copies the image and draws a new digital image in its memory similar to hard copy image.

OCR (Optical Character Reader)

OCR digitizes handwritten or printed text.
Printed text will have fewer errors than hand written. It directly converts hand written text into digital text which can be edited. OCR contains predefined format of all the characters. During digitizing process, it creates an image of the character and compares it with stored format to determine the character.

MICR

It stands for Magnetic Ink Character Reader. MICR is an OCR that can digitize text written or printed by using magnetic ink like iron oxide or barium ferrite. It is used in security systems and for processing cheque in bank.

OMR

It stands for Optical Mark Reader. It is used for answer sheet correction in multiple choice questions. With the use of OMR answer sheet correction will be faster and error free.

BCR

It stands for Bar Code Reader. Bar codes are the magnetic lines used for storing the information about the product like manufacturing date, expiry date, company name, etc. BCR is used to read the information stored in bar codes. Bar codes are also used in security system.

Microphone

It is an input device for sound. It captures sound wave, converts it into digital format and provides it to the CPU. Common mobile computing devices like PDA, smart phone contains microphone.

Digital camera, Web camera

Digital camera captures real time images and video and stores it in a digital format. The image captured by digital camera can be directly used in a digital camera.

Web camera is a digital camera used in internet. It usually captures low quality images so that it could be transmitted at a faster speed.

Card reader

It is used to read the information stored in cards like ATM card, Credit card, Smart card, etc.

Digitizing tablet

It is used to digitize large map or hardcopy images. It is also used to track the movements of living beings and capture them in digital format.

Generation Of Computer

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Generation of computer

The computers of electronic age are further divided into 5 generation on the basis of technology used by the computer. The different generations are:

First generation of computers
Second generation of computers
Third generation of computers
Fourth generation of computers
Fifth generation of computers

1. First generation of computers

Technology used: Vacuum tube
Operating speed: Millisecond range
Programming language used: Machine language
Memory used Primary memory: Magnetic core memory Secondary memory: Magnetic drum, Magnetic tape.
I/O device:
Punched card as input device, printing device as output device.
Use: Simple mathematical calculation.
Computers were extremely large in size, and they required special cooling system. e.g.: ENIVAC, EDVAC, UNIVAC, etc.

2. Second generation of computers:

Technology used: Transistor
Operation speed: Micro second range (10-6 sec)
Programming language used: Assembly language
Memory used Primary memory: Magnetic core memory. Secondary memory: Magnetic drum, Magnetic tape.
I/O: Punched card as input device, Printer as output device
Use: Computers were used for complex scientific calculations.
The size, cost, power requirement, heat generation decreased compared to previous generation.
Processing speed, storage capacity, use of the computer increased compared to previous generation.
E.g.: IBM 1620, IBM 7094, LEO MARK III, etc.

Advantages of transistor over vacuum tube:

One transistor could replace one thousand vacuum tubes.
Size of a transistor is 1/200 th times of a vacuum tube.
The power requirement of a transistor is 1/20 th times of a vacuum tube.
Transistors are more reliable than vacuum tube.

3. Third generation of computers

Technology used: IC (Integrated Circuit)
Operating speed: Nanosecond range (10 -9 sec)
Programming language used: HLL (High Level Language) Like FORTAN, COBOL, PASCAL, C, C++, etc.
Memory used: Primary memory: Semiconductor memory (silicon) Secondary memory: Magnetic tape, Magnetic disk like floppy disk, hard disk, etc)
I/O device: Keyboard as input device, monitor as output device.
Use: Computers were used for managing population census, bank, insurance company, etc.
Concept of database was developed and used.
Size, cost, power requirement, heat generation decreased compared to previous generations.
Processing speed, storage capacity, use of the computer increased compared to previous generations.
E.g.: IBM 360 series, ICL 900 series, Honeywell 200 series, etc.

IC and its types:
IC is a small silicon chip which contains large number of electronic components like transistor, resistor, capacitor, etc.
The process of creation of IC is called fabrication.
Types of IC on the basis of number of electronic components.

SSI (Small Scale Integration)(1-20 components)
MSI (Medium Scale Integration)(21-100 components)
LSI (Large Scale Integration)(101-1000 components)
VLSI (Very Large Scale Integration)(1001-10000 components)
ULSI ( Ultra Large Scale Integration)(More than 10000 components)

4. Fourth generation of computers:

Technology used:- VLSI (or Microprocessor)
Operating speed:- Pico second range
Programming language used: 4GL (Problem Oriented Language)
Memory used: Primary: Semi-conductor memory Secondary: Magnetic tape, Magnetic Disk, Optical memory (CD/DVD/ Blu ray), Flash memory(pen drive, memory card)
I/O device: Advanced I/O devices like mouse, touch screen, scanner, LCD, LED, color printer, etc are developed.
Use: Computers are used for different task in different areas like education, business, hospital, transportation, military, etc.
Microcomputers like desktop PC, laptop, notebook, etc, are developed.
The popular communication media like internet, email, mobile communication, etc were developed.
Advanced, user friendly, web based software, etc are developed.
Size, cost, power requirement, heat generation decreased compared to previous generation.
Operating speed, storage capacity, use of the computer increased compared to previous generation.
E.g.: IBM desktop PC, HP laptop, Acer notebook, Mac book, etc.

5. Fifth generation of computers:

Technology to be used:- Bio-chip
Operating speed:- Femto second range
(10 -15 second) / TIPS
Programming language to be used:- Natural language
The computers will have AI.
The computers will be used in complex calculation where intelligence of the computer is required.
The computers will have parallel processing in full fledge.
The computers will be based on KIPS (Knowledge based Information Processing System)

Disk Operating System (DOS)

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction to disk operating system

When the computer starts, it starts the operating system that takes the control of the machine. An Operating System is a set of programs that help in controlling and managing the Hardware and the Software resources of a computer system. A good operating system should have the following features:

Help in the loading of programs and data from external sources into the internal memory before they are executed.
Help programs to perform input/output operations, such as:

Print or display the result of a program on the printer or the screen.
Store the output data or programs written on the computer in storage device.
Communicate the message from the system to the user through the VDU.
Accept input from the user through the keyboard or mouse.

Objectives

At the end of this lesson, you would be able to:

Explain the concept operating system
Discuss the functions of operating system
Understand the procedures of loading operating system into the memory
Use file management features of operating system
Create separate locations for logically related files
Copy files from one computer to another
Use Windows for File Management

Disk operating system

As the name suggests, the operating System is used for operating the system or the computer. It is a set of computer programs and also known as DOS (Disk Operating System). The main functions are to manage disk files, allocate system resources according to the requirement. DOS provides features essential to control hardware devices such as keyboard, screen, disk devices, printers, modems and programs.
Basically, DOS is the medium through which the user and external devices attached to the system communicate with the system. DOS translate the command issued by the user in the format that is understandable by the computer and instruct computer to work accordingly. It also translates the result and any error message in the format for the user to understand.

1. Loading of DOS
The BOOT Record into the computer memory loads DOS (Disk Operating System). BOOT Record in turn is triggered by ROM program already there in the computer.
The system start-up routine of ROM runs a reliability test called Power On Self Test (POST) which initializes the chips and the standard equipment attached to the PC, and check whether peripherals connected to the computer are working or not. Then it tests the RAM memory. Once this process is over, the ROM bootstrap loader attempts to read the Boot record and if successful, passes the control on to it. The instructions/programs in the boot record then load the rest of the program. After the ROM boot strap loader turns the control over to boot record, the boot tries to load the DOS into the memory by reading the two hidden files IBMBIO.COM and IBMDOS.COM. If these two are found, they are loaded along with the DOS command interpreter COMMAND.COM. COMMAND.COM contains routines that interpret what is typed in through the keyboard in the DOS command mode. By comparing the input with the list of command, it acts by executing the required routines/commands or by searching for the required routine utility and loads it into the memory.

Computer files in DOS
A file may contain a program or any other kind of information. Generally, a file must be given a name that can be used to identify it. DOS (Disk Operating System) permits the user to assign a name consisting of two parts to a file – primary and secondary names. Primary name can be of a maximum of eight characters consisting of Characters, Alphabets, Number and Hyphen), and the Secondary name should consist of three characters, which is optional. The primary name and the secondary (or extension) name, if any, are to be separated by a dot (.).
Primary name can be linked to proper name, whereas extensions are like surnames of people. Using an extension with the file name is preferable, though optional. However, once the extension is specified, using the complete name (primary name and extension, with the period separating them can only refer the file). Using extensions can be an excellent way of naming a file so that it can be identified easily.

DOS (Disk Operating System) has a way of showing which disk drive is currently active. The floppy disk drives are assigned alphabets A and B, whereas the hard disk drive is assigned the alphabet C. If your PC has a single floppy drive, the drive would be A and if it has two, they would be termed as A and B. If your PC includes a hard disk, besides a FDD (Floppy Disk Drive), the drive names would be A and C. If the prompt is A, then it implies that the first floppy disk drive is active. Where as the DOS prompt would be C, if the hard disk is active. Data as well as instructions reside in a file stored in a disk.

Directory structure in DOS
The files in the computer come from various sources. Some files come with DOS, while other come with publications such as a word processor. These files contain codes and other information that is necessary to make the computer application operational. Before long, there will be hundreds or even thousands of files in the computer, which can make it difficult to locate specific files.
The names of all the files created in a disk are stored in its directory. Directory is just like a file folder, which contain all the logically related files. DOS files are organized in a hierarchical or an inverted tree-like structure. The general analogy is with a file cabinet containing a number of drawers, which in turn may contain folders. The content of these folders is the needed information.
The file cabinet here is the ROOT DIRECTORY, the drawer is INDIVIDUAL DIRECTORY, the folders are SUBDIRECTORYand the information in these folders may in turn be classified as FILES.
Otherwise, the large number of files that get created for various purposes in a disk can make the directory huge and difficult to view and manage. Therefore, DOS enables the user to organize the files in a disk into directories and sub-directories in a hierarchical structure. Directories can contain other directories. A directory within another directory is called a sub-directory.
Of course, there may be sub-directories of sub-directories, but a file name is the furthest you may descend down the (inverted) tree of directories and files. Thus, a file name corresponds to a tree leaf, a sub-directory to a branch, the directory to the trunk, and the root directory to the root of the tree, hence the name ROOT DIRECTORY.
Command.com (Personal) Autoexec.bat (Accounts) Pk.bat LEAVE INSURANCE GPF PENSION LOAN
The directory/sub-directory is represented in bold letters.

Directory command
The content of each of the sub-directory cannot be viewed unless it is made active, or a sub-directory is specified as part of the DIR command. Doing either of these requires an understanding of the concepts of navigating around the disk.
The directory, the user is in at any point of time, is called the WORKING/PRESENT/CURRENT directory. DOS indicates which directory you are in by displaying the directory’s name in the command prompt. For example, the following command prompt indicate that you are in the DOS directory: C:DOS>. Knowing which directory is current helps you find files, and to move from one directory to another more easily. Typically, the ROOT DIRECTORY () is the initial working directory. The entire specification of directory from root is called a PATH. By itself, the DIR command is applicable to the working/present directory. The names of the sub-directories at adjacent levels are separated by backslash (), while specifying the path to be followed while traveling to a sub-directory.

Using path to specify the location of files
A path is the route that leads from the root directory of a drive to the file you want to use.
For example, to access the NOS.LET file in the LETTER subdirectory of NOS directory, DOS must go from the ROOT () directory through the NOS directory to the LETTER directory.
To specify the same path at the command prompt, you would type it as shown in the following illustration:
C:NOSLETTERNOS.LET
This is the path or route to the file NOS.LET. The first letter and the colon (C:) represent the drive the file is on. The first back slash () represents the root directory. The second backslash separates the NOS directory from the LETTER sub-directory. The third backslash separates the LETTER sub-directories from the file name, NOS.LET.
Note: MS-DOS recognizes path up to 67 characters long (including the
Drive letter, colon, and backslash).

DIR command
The DIR command gives the list of is there on the disk that is mounted on the active drive.
Syntax : C:> DIR A:> DIR
Example
A:> DIR
Volume in drive A has no label
Directory of A:
COMMAND COM 23612 10-20-88 11.30a
DISKCOPY COM 4235 10-20-88 12.00p
FORMAT COM 15780 03-12-89 12.00p
3 file(s) 325013 bytes free
A:>
As can be seen, on typing DIR followed by key at DOS prompt, five columns of data followed by the number of files and bytes that are free in the disk are displayed. The first column contains the primary name of each file resident on the disk. However, most files are named with an extension, which appear in the second column. Whereas, the third column contains the size of the file in bytes, and the fourth and fifth columns show the date and time on which the files was created or last modified. The last line displays the number of file(s) and remaining disk space free in bytes. It is important to note that the DIR command only displays the names of the files and not their contents.

Changing a directory
All the names displayed using DIR command that have
besides them are directories. You can see the list of files in another directory by changing to that directory and then using the DIR command again.
The Change Directory (CHDIR) or CD command enables the user to travel around the directories in a disk. Type the CD command at the command prompt.
Syntax:
A:> CHDIR {path} or a:> CD {path}
Examples : (Refer to the figure)
1. A:>CD NOS
This command makes the NOS sub-directory under the root directory () active.
2. A:>CD NOSLETTERS
The backslash indicates the root, and LETTERS, which is a sub-directory under the NOS directory, becomes the working directory.
3. A:> CD
The root directory becomes the working directory; i.e. you will change back to the root or main directory. The slash typed in this command is a backslash (). No matter which directory you are in, this command always returns you to the root directory of a drive. The root directory does not have a name, it is simply referred to by a backslash ().

Making or creating directory
As the number of files increases in a disk, a need is felt to organize them in a meaningful way by creating sub-directories to store a group of logically related/similar files.
To create a directory, DOS provides the MKDIR (Make Directory) or MD command.
Syntax:
A:>MKDIR [drive:] {pathname} or A:>MD [drive:] {pathname}
Square brackets indicate that [drive:] entry is optional.
The MD or MKDIR command creates a new empty directory whose name is the last item specified in the pathname, in the specified drive. If active, the drive need not be specified. If the directory is to be created as a sub-directory of the working directory on the active drive, typing MD {directory name} at the DOS prompt or command prompt is sufficient.
Examples:
1. A:> MD ACCTSALARY
makes a SALARY directory in the: drive, under ACCT directory.
2. A:> MD C:> SALARY
Makes a salary directory in the C: drive, under root directory.
5.11 DELETING A DIRECTORY
You may want to delete or remove a directory to simplify your directory structure. DOS provides RD (Remove Directory) to delete a directory.
Example:
1. A:> RD ACCTSALARY
removes the SALARY sub-directory in ACCT directory.
NOTE: You cannot delete a directory if you are in it. Before you can delete a directory, you must type cd.. at the command prompt. At the same point of time, the directory to be deleted should be empty.

Copying files
To copy a file, DOS provides COPY’ command. When you usecopy’ command, you must use the following two parameters; the location and the name of the file you want to copy, or the source; and the location and the file name to which you want to copy the file or the target (destination). You separate the source and the destination or target with a space. The syntax of the `COPY’ command is
COPY {source} {destination} or,
COPY [drive:] [path] [filename] [drive:] [path] [filename]
i.e. the first set of drive, path and filename refers to the source file, and the second set of drive, path and filename
refers to the destination file.
(a) Copying Single File
To copy the DEBUG.EXE file from the DOS directory to the NOS
directory

Return to the root directory by typing the following command prompt: CD
Change to the DOS directory by typing the following commands at the DOS prompt: CD DOS
To copy the file DEBUG.EXE file from the DOS directory to the NOS, directory type the following at the command prompt: Copy c:dosdebug.exe c:nos and the following message appears: 1 file (s) copied Examples: 1. A:> copy a:letteroffice.doc letteroffice.bak makes a copy of the office.doc file in the current or working directory with a new name office.bak 2. A:> copy office.doc a:lettersnos.mem copy the file office.doc from the root directory to the sub-directory LETTER under root directory with a new name nos.mem. If the target drive is not specified, the copied file will reside in the disk mounted on the active drive. 5.13 USE OF WILDCARD CHARACTERS If you want to carry out a task for a group of files whose names have something in common, you can use wildcard characters to specify groups of files. DOS recognize two wildcard characters: asterisk () represents one or more characters that a group of files has in common; and the question mark (?) represents a single character that a group of files has in common. You can use wildcards to replace all or part of a file’s name or its extension. The following table shows examples of wildcards: Wildcard What it Represents Example *.TXT All files with a .TXT extension JULY.TXT LETTER.TXT REPORT. All files named REPORT with any REPORT.TXT extension REPORT.LET REPORT.WRI M*.* All files beginning with letter M MEMO.TXT regardless of their extension MARCH.XLI ???.* All files having 3 letter names, SUN.BMP with any or no extension WIN.LET You can include the wildcard in the command. Use of wildcard characters in COPY command 1. A:>COPY letters*.COB B: It means, copy all files with extension *.COB from the directory LETTERS under the ROOT directory to the working or ROOT directory of the `B’ drive.
A:> COPY B:COMPANYOPEL.* The command is to copy all files with primary name OPEL (irrespective extension) in the directory COMPANY under ROOT of the drive B’ into the current working directory of the disk mounted inA’ drive. Incase of one drive, the system will ask for the source and target drive. The command, 3.A:>COPY C:.

copies all files of the ROOT directory of the ‘C’ drive into the working directory of the ‘A’ drive.

A:> COPY LETTE?.* B: copies all files with primary name consisting of 6 characters in total and LETTE as the first five characters (irrespective of extension name) into drive `B’.
A:> COPY B:?.DOC copies all files having a primary name of one character with an extension .DOC from ROOT directory of ‘B’ to the ROOT directory of `A’ drive. 5.14 RENAMING FILES To rename a file, DOS provides REN command. The REN command stands for “Rename”. When you use the REN command, you must include two parameters. The first is the file you want to rename, and the second is the new name for the file. You separate the two names with a space. The REN command follows this pattern: REN oldname newname Example: REN NOS.DOC NOS.MEM Rename the old filename NOS.DOC to a new filename NOS.MEM.

Deleting files
This section explains how to delete or remove a file that is no longer required in the disk. DOS provides DEL command, which means to delete.
Syntax : DEL {drive:} {path} {filename}
Example:
1. DEL DOSEDIT.HLP
delete the EDIT.HLP from the DOS directory under ROOT directory.
5.16 PRINTING A FILE
The PRINT’ command of DOS works more or less likeTYPE’ com
mand, but at the same time, it enables the content of a text file
to be printed on a paper.
Syntax:
A:> PRINT [drive:] {path} {filename}
Example:
A:> PRINT AIAETLETTERAIAET.LET

In-text questions 1
1. The startup routine runs, when machine boots up is known as

POST
BOOT up
Operating Routine
I/O operation

2. Operating system is also known as:

database
System software
Hardware
Printer

3. What is the maximum length allowed for primary name of a computer file under DOS?

8
12
3
None of the above

4. Which of the following could be a valid DOS file specification?

NOSFILE.POST
NOSFILE.P.OST
NOSFILE.DOC
NOST.FILEDOC

5. How many characters form a secondary name for a file?

8
12
3
None of the above

6. What is the name given to something that the computer will automatically use unless you tell it otherwise?

a specification
a wildcard
a default
a rule

7. As per symbolic notation of DOS, which of the following indicates the ROOT directory
(a)*
(b) >
(c) /
(d) None of the above

8. In wildcard specification `?’ is used as replacement for

9. With DOS, you may use the *’ and?’:

When changing the default settings
To represent unspecified characters in a filename
Instead of wildcard characters
In the extension but not in the drive name or the file name

10. DOS system file consists of

IBMBIO.COM, IBMDOS.COM, COMMAND.COM
COMMAND.COM, IBMBIO.COM, FORMAT.COM
SYS.COM,IBMBIO.COM,IBMDOS.COM
None of the above

11. The batch file uses the extension

.BAT
.DOC
.PRG
.DOS

12. To display the list of all the file of the disk you would type

DIR
COPY
DIR FILES
DIR AUTOEXEC.BAT

13. State whether the following questions are True(T) or False(F).

Command.Com is hidden file.
Primary name of a file can be of 10 characters.
The command MKDIR and MD performs the same task.
Under DOS .EXE is not an executable file.
DIR command is used to see the content of a specific file.

What you have learnt
In this lesson you were introduced to one of the most popular desktop operating system and its working environment. It explained the directory structure, file naming conventions. It also talked in great length about the file management in terms of COPY, DEL, and MOVE. Here you learned the steps involved in loading of operating systems into computer.

Terminal questions

Explain in brief what do you understand by Operating system.
Explain the process involved in loading of Operating System.

Feedback to in-text questions 1

2.b3.a,4.b,5.b,6.c,7.d,8.a,9.b,10.a,11.a,12.a,13. F,F,T,F,F

Introduction To MS-Word

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction to Microsoft Word
Let us consider an office scene. Many letters are typed in the office. The officer dictates a letter. The typist first types a draft copy of the letter. The officer goes through it to check mistakes regarding spelling errors, missing words, etc. and suggests corrections. The typist changes the letter as suggested by the officer. This is a simple example of word processing.
There are many software packages to do the job of word processing. Some of them work in dos environment. Example are WordStar, Word Perfect and Professional Write. But in these days working in windows is becoming more and more popular. So let us consider software for word processing which works in windows. Our choice is Microsoft Word because it is the most popular software in these days.
MS-word is a part of the bigger package called Microsoft office, which can do much more than word processing. In fact when you open up Microsoft office you will find four main components in it. They are Microsoft Word (for word processing), Microsoft Excel (for spreadsheet), Microsoft Access (for database management) and Microsoft PowerPoint (for presentation purposes). However, we will limit ourselves to MS-word only in this lesson.

Objectives

After going through this lesson you should be in a position to:

Start the Microsoft Word package
Be familiar with the Microsoft Word screen
Advantages and Features of Word Processing
Some common Word Processing Packages
How to invoke Microsoft Word
Learn the capabilities of Microsoft Word

What is word processing?
Word Processor is a Software package that enables you to create, edit, print and save documents for future retrieval and reference. Creating a document involves typing by using a keyboard and saving it. Editing a document involves correcting the spelling mistakes, if any, deleting or moving words sentences or paragraphs.

Advantages of word processing
One of the main advantages of a word processor over a conventional typewriter is that a word processor enables you to make changes to a document without retyping the entire document.

Features of word processing
Most Word Processor available today allows more than just creating and editing documents. They have wide range of other tools and functions, which are used in formatting the documents. The following are the main features of a Word Processor:

Text is typing into the computer, which allows alterations to be made easily.
Words and sentences can be inserted, amended or deleted.
Paragraphs or text can be copied /moved throughout the document.
Margins and page length can be adjusted as desired.
Spelling can be checked and modified through the spell check facility.
Multiple document/files can be merged.
Multiple copies of letters can be generated with different addresses through the mail-merge facility.

Some Common Word processing packages
The followings are examples of some popular word processor available

Softword
WordStar
Word perfect
Microsoft word

Important feature of Microsoft Word
Microsoft word not only supports word processing features but also DTP features. Some of the important features of Microsoft Word are listed below:

Using word you can create the document and edit them later, as and when required, by adding more text, modifying the existing text, deleting/moving some part of it.
Changing the size of the margins can reformat complete document or part of text.
Font size and type of fonts can also be changed. Page numbers and Header and Footer can be included.
Spelling can be checked and correction can be made automatically in the entire document. Word count and other statistics can be generated.
Text can be formatted in columnar style as we see in the newspaper. Text boxes can be made.
Tables can be made and included in the text.
Word also allows the user to mix the graphical pictures with the text. Graphical pictures can either be created in word itself or can be imported from outside like from Clip Art Gallery.
Word also provides the mail-merge facility.
Word also has the facility of macros. Macros can be either attached to some function/special keys or to a tool bar or to a menu.
It also provides online help of any option.

In-text questions 1

1. State True or False

Word processor is Software Package that enables you to create, edit, print and save document.
WordStar is a popular Word processor.
Changing the size of the margins cannot reformat complete document or part of the text.
Word has the facility of Macros.
Word does not allow the user to mix the graphical pictures with text.

Getting started with Microsoft Word
We have already told you that for working in MS-Word you should be familiar with windows. If you have not covered windows so far then read that first and then go through MS-word. By now you must be aware of the fact that a software package is improved from time to time. These improvements are sold in the market as new versions of the same software. Thus you will find many versions of Microsoft Word being used in different offices. In this lesson we will cover the version Microsoft Word 97, which is latest in the market and contain many improvements over the older versions. However, you do not have to worry if you have an older version such as word 6.0 or word 95. All the commands available in these older versions are also available in word 97 and they are compatible.
While working in Microsoft Word you have to work with a mouse. Also one can work, to some extent, through the keyboard. The use of mouse is simpler as it is fully menu driven. In MS-word every command is available in the form of ‘icons’.

You can go inside MS-word by the following way:

Take the mouse pointer to start button on the task bar. Click the left mouse button.
Move the pointer to programs. You will notice another menu coming up to the right.
In that menu identify where Microsoft word is placed. Move the cursor horizontally to come out of programs.
Move into the rectangular area meant for Microsoft word. Click the left mouse button there. The computer will start MS-word.

Let us discuss the important components of the screen.

- Title bar
The title bar displays the name of the currently active word document. Like other windows applications, it can be used to alter the size and location of the word window.

- Tool bars
Word has a number of tool bars that help you perform task faster and with great ease. Two of the most commonly tool bars are the formatting tool bar and the standard tool bar. These two toolbars are displayed just below the title bar. At any point of time any tool bar can be made ON or OFF through the tool bar option of View Menu.

- Ruler bar
The Ruler Bar allows you to format the vertical alignment of text in a document.

- Status bar
The Status Bar displays information about the currently active document. This includes the page number that you are working, the column and line number of the cursor position and so on.

- Scroll bar
The Scroll Bar helps you scroll the content or body of document. You can do so by moving the elevator button along the scroll bar, or by click in on the buttons with the arrow marked on them to move up and down and left and right of a page.

- Workspace
The Workspace is the area in the document window were you enter/type the text of your document.

- Main menu
The Word main menu is displayed at the top of the screen as shown in the Fig. 9.1. The main menu further displays a sub menu. Some of the options are highlighted options and some of them appear as faded options. At any time, only highlighted options can be executed, faded options are not applicable. Infect if the option is faded you will not be able to choose it. You may not that any option faded under present situation may become highlighted under different situations.

In-text questions 2
1. Choose the best answer.

1. While working in MS-Word you have to work with

Mouse only
Keyboard only
Both mouse and keyboard

2. In Microsoft Word every command is available in

Print
Letter
Icons

3. You can go inside Microsoft Word by the following way

Take the mouse pointer to start button on the task bar and click the left mouse button.
Take the mouse pointer to start button and click the right mouse button.
Move the mouse pointer on the screen.

2. State True or False

The title bar displays the name of the currently active word document.
Two of the most commonly tool bars are the formatting tool bar and the standard tool bar.
The tool bar allows you to format the vertical alignment of text.
The scroll bar helps you to scroll the content or body of document.
The workspace is the area in the document window where you enter/type the text.

Main menu options

The overall functions of all the items of main menu are explained below.

- File
You can perform file management operations by using these options such as opening, closing, saving, printing, exiting etc.
New: Ctrl+N
Open: Ctrl+O
Close: ALT + F4
Save : Ctrl+S
Save Aa: CTL + A
Print: Ctrl+P

File sub menu

- Edit
Using this option you can perform editing functions such as cut, copy, paste, find and replace etc.
Undo Clear: Ctrl+Z
Repeat Clear: Ctrl+Y
Cut: Ctrl+X
Copy: Ctrl+C
Paste: Ctrl+V
Clear: Delete
Select All: Ctrl+A
Find: Ctrl+F
Replace: Ctrl+H
Go To: Ctrl+G

Edit sub menu

- View
Word document can be of many pages. The different pages may have different modes. Each mode has its limitations. For example in normal mode the graphical picture cannot be displayed. They can only be displayed in page layout mode. Using the option “View” you can switch over from one mode to other. It displays the following Sub menu.

Normal

Online Layout
Page Layout
Outline
Master Document

Tool Bars

Ruler

Header and Footer

Footnotes
Comments
Full Screen
Zoom

- Insert
Using this menu, you can insert various objects such as page numbers, footnotes, picture frames etc. in your document. It displays the following Sub menu.

Break
Page Numbers
Date and Time
AutoText 8

Field…
Symbol…
Comment
Footnote…
Caption…
Cross-reference…
Index & Tables…
Picture 8
Text Box…
File…
Object…
Bookmark Hyperlink… Ctrl+k

- Format
**Using this menu, you can perform various type of formatting operations, such as fonts can be changed, borders can be framed etc. It displays the following Sub menu.

Font…

Paragraph…
Bullets and Numbering
Borders and Shading…

Columns…

Tabs…
Drop Cap…
Text Direction…
Change Case…
Auto Format…
Style Gallery…
Style…
Background…

Object

- Tools
Using this menu, you can have access to various utilities/tools of Word, such as spell check, macros, mail merge etc. It displays the following Sub menu.
Spelling and Grammar…

Language…
Word count…
AutoSummarize
Auto correct..
Look up reference

Track change

Merge Documents…
Protect Document…
Mail Merge…

Envelops and Labels…

Letter wizard…
Macro…
Templates and add-ins…
Customize…
Options…

- Table
This menu deals with tables. Using this menu you can perform various types of operations on the table. It displays the following Sub menu.

Draw Table
Insert Table…

Delete cells…
Merge cells…
Split cells…

Select Row

Select column
Select table

Table Auto Format…

Distribute rows evenly
Distribute columns evenly
Cell height and width…
Headings

Convert Text to table…

Sort …
Formula…
Split table
Hide grid lines

- Window
This menu allows you to work with two documents simultaneously. This would require two windows to be opened so that each one can hold one document. Using this menu, you can switch over from one window to another. It displays the following Sub menu.

New Window

Arrange all
Split
1Document1.doc

- Help
Using this menu, you can get on-line help for any function.

In-text question 3

1. State True or False

Using View option you can perform editing functions such as cut, copy, paste, find and replace etc.
Using the Edit option you can switch over from Normal mode to Out line mode.
Using Insert menu you can insert various objects such as page numbers, footnotes, picture frames etc.
Using Tools menu you can access to various utilities of word such as spell check, macros and mail merge etc.
Window menu allows you to work with two documents simultaneously.

What you have learnt
At the end of this lesson you have learnt the important features of Ms-Word. We started with procedure to invoke Ms-Word. We identified toolbars available in the main menu of Ms-Word are discussed.

Terminal questions

What do you understand by Word processing? Give examples.
Describe the important features of Ms-Word.
Describe the various options available in the main menu bar of Ms-Word.
What are the different types of toolbar?
Define two methods to start Ms-Word.

Feedback to the in-text questions

In-text question 1

True
True
False
True
False

In-text question 2

3, 3,1
True, True, False, True, True

In-text question 3

False
False
True
True
True

Communication Port

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It is a hardware device used for connecting peripherals devices with the computer. It has major functions like:

Connecting peripheral devices.
Transmitting data to and fro from peripheral devices.
Providing electrical power to the small peripheral devices.

Some of the communication ports used are:

- Serial port
It is used for connecting slow speed devices like keyboard, mouse, etc. It also provides electrical power supply to these devices. It cam transmit 1 bit data at a time.

- Parallel port
It is used for connecting medium speed devices like monitor, printer, etc. It can transmit 8 bit data at a time.

- USB (Universal serial bus)
USB is the common interface developed by multiple hardware developers for supporting large variables of devices. It is used to connect keyboard, monitor, pen drive, etc. It is the most common user interface at present.

- SCSI
It is used for connecting external memory devices like magnetic tape, multiple hard disk, etc.

- IEEE 1394 interface
This interface is used for connecting high speed devices like connecting audio/video equipments, aeronautical devices, medical equipments, etc.

- PCI (Peripheral communications interface)
It is used for connecting peripheral devices like internal modem, internal TV card, sound card, graphics card, etc with the computer. It is available in the mother board.

Basic Concept Of Computer

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction to computer

Let us begin with the word ‘compute’. It means ‘to calculate’. We all are familiar with calculations in our day to day life. We apply mathematical operations like addition, subtraction, multiplication, etc. and many other formulae for calculations. Simpler calculations take less time. But complex calculations take much longer time. Another factor is accuracy in calculations. So man explored with the idea to develop a machine which can perform this type of arithmetic calculation faster and with full accuracy. This gave birth to a device or machine called ‘computer’.

The computer we see today is quite different from the one made in the beginning. The number of applications of a computer has increased, the speed and accuracy of calculation has increased. You must appreciate the impact of computers in our day to day life. Reservation of tickets in Air Lines and Railways, payment of telephone and electricity bills, deposits and withdrawals of money from banks, business data processing, medical diagnosis, weather forecasting, etc. are some of the areas where computer has become extremely useful.

However, there is one limitation of the computer. Human beings do calculations on their own. But computer is a dumb machine and it has to be given proper instructions to carry out its calculation. This is why we should know how a computer works.

Objectives

After going through this lesson you will be in a position to

Define a computer
Identify characteristics of computer
Know the origin and evolution of computer
Identify capability of computer in terms of speed and accuracy
Distinguish computer from human beings and calculator
Identify the role of computer
Appreciate the evolution of computer through five generations

Computers

Computer is an electronic device. As mentioned in the introduction it can do arithmetic calculations faster. But as you will see later it does much more than that. It can be compared to a magic box, which serves different purpose to different people. For a common man computer is simply a calculator, which works automatic and quite fast. For a person who knows much about it, computer is a machine capable of solving problems and manipulating data. It accepts data, processes the data by doing some mathematical and logical operations and gives us the desired output.

Therefore, we may define computer as a device that transforms data. Data can be anything like marks obtained by you in various subjects. It can also be name, age, sex, weight, height, etc. of all the students in your class or income, savings, investments, etc., of a country. Computer can be defined in terms of its functions. It can:

Accept data
Store data
Process data as desired
Retrieve the stored data as and when required
Print the result in desired format. You will know more about these functions as you go through the later lessons

Characteristics of computer

Let us identify the major characteristics of computer. These can be discussed under the headings of speed, accuracy, diligence, versatility and memory.

Speed

As you know computer can work very fast. It takes only few seconds for calculations that we take hours to complete. Suppose you are asked to calculate the average monthly income of one thousand persons in your neighborhood. For this you have to add income from all sources for all persons on a day to day basis and find out the average for each one of them. How long will it take for you to do this? One day, two days or one week? Do you know your small computer can finish this work in few seconds? The weather forecasting that you see every day on TV is the results of compilation and analysis of huge amount of data on temperature, humidity, pressure, etc. of various places on computers. It takes few minutes for the computer to process this huge amount of data and give the result.

You will be surprised to know that computer can perform millions (1,000,000) of instructions and even more per second. Therefore, we determine the speed of computer in terms of microsecond (10-6 part of a second) or nano-second (10-9part of a second). From this you can imagine how fast your computer performs work.

Accuracy

Suppose some one calculates faster but commits a lot of errors in computing. Such result is useless. There is another aspect. Suppose you want to divide 15 by 7. You may work out up to 2 decimal places and say the dividend is 2.14. I may calculate up to 4 decimal places and say that the result is 2.1428. Some one else may go up to 9 decimal places and say the result is 2.142857143. Hence, in addition to speed, the computer should have accuracy or correctness in computing.

The degree of accuracy of computer is very high and every calculation is performed with the same accuracy. The accuracy level is determined on the basis of design of computer. The errors in computer are due to human and inaccurate data.

Diligence

A computer is free from tiredness, lack of concentration, fatigue, etc. It can work for hours without creating any error. If millions of calculations are to be performed, a computer will perform every calculation with the same accuracy. Due to this capability it overpowers human being in routine type of work.

Versatility

It means the capacity to perform completely different type of work. You may use your computer to prepare payroll slips. Next moment you may use it for inventory management or to prepare electric bills.

Power of remembering

Computer has the power of storing any amount of information or data. Any information can be stored and recalled as long as you require it, for any numbers of years. It depends entirely upon you how much data you want to store in a computer and when to lose
or retrieve these data.

No IQ

Computer is a dumb machine and it cannot do any work without instruction from the user. It performs the instructions at tremendous speed and with accuracy. It is you to decide what you want to do and in what sequence. So a computer cannot take its own decision as you can.

No feeling

It does not have feelings or emotion, taste, knowledge and experience. Thus it does not get tired even after long hours of work. It does not distinguish between users.

Storage

The Computer has an in-built memory where it can store a large amount of data. You can also store data in secondary storage devices such as floppies, which can be kept outside your computer and can be carried to other computers.

In-text questions 1

What is a computer? Why is it known as data processor?
What are the important characteristics of computer?

History Of computer

History of computer could be traced back to the effort of man to count large numbers. This process of counting of large numbers generated various systems of numeration like Babylonian system of numeration, Greek system of numeration, Roman system of numeration and Indian system of numeration. Out of these the Indian system of numeration has been accepted universally. It is the basis of modern decimal system of numeration (0, 1, 2, 3, 4, 5, 6, 7, 8, 9). Later you will know how the computer solves all calculations based on decimal system. But you will be surprised to know that the computer does not understand the decimal system and uses binary system of numeration for processing.

We will briefly discuss some of the path-breaking inventions in the field of computing devices.

Calculating Machines

It took over generations for early man to build mechanical devices for counting large numbers. The first calculating device called ABACUS was developed by the Egyptian and Chinese people.

The word ABACUS means calculating board. It consisted of sticks in horizontal positions on which were inserted sets of pebbles. A modern form of ABACUS is given in Fig. 1.2. It has a number of horizontal bars each having ten beads. Horizontal bars represent units, tens, hundreds, etc.

Napier’s bones

English mathematician John Napier built a mechanical device for the purpose of multiplication in 1617 A D. The device was known as Napier’s bones.

Slide rule

English mathematician Edmund Gunter developed the slide rule. This machine could perform operations like addition, subtraction, multiplication, and division. It was widely used in Europe in 16th century.

Pascal’s adding and subtractory machine

You might have heard the name of Blaise Pascal. He developed a machine at the age of 19 that could add and subtract. The machine consisted of wheels, gears and cylinders.

Leibniz’s multiplication and dividing machine

The German philosopher and mathematician Gottfried Leibniz built around 1673 a mechanical device that could both multiply and divide.

Babbage’s analytical engine

It was in the year 1823 that a famous English man Charles Babbage built a mechanical machine to do complex mathematical calculations. It was called difference engine. Later he developed a general-purpose calculating machine called analytical engine. You should know that Charles Babbage is called the father of computer.

Mechanical and electrical calculator

In the beginning of 19th century the mechanical calculator was developed to perform all sorts of mathematical calculations. Up to the 1960s it was widely used. Later the rotating part of mechanical calculator was replaced by electric motor. So it was called the electrical calculator.

Modern electronic calculator

The electronic calculator used in 1960 s was run with electron tubes, which was quite bulky. Later it was replaced with transistors and as a result the size of calculators became too small.

The modern electronic calculator can compute all kinds of mathematical computations and mathematical functions. It can also be used to store some data permanently. Some calculators have in-built programs to perform some complicated calculations.

In-text questions 2

What is the first mathematical device built and when was it built?
Who is called the father of Computer Technology.

Computer generations

You know that the evolution of computer started from 16th century and resulted in the form that we see today. The present day computer, however, has also undergone rapid change during the last fifty years. This period, during which the evolution of computer took place, can be divided into five distinct phases known as Generations of Computers. Each phase is distinguished from others on the basis of the type of switching circuits used.

First generation computers

First generation computers used Thermion valves. These computers were large in size and writing programs on them was difficult. Some of the computers of this generation were:

ENIAC: It was the first electronic computer built in 1946 at University of Pennsylvania, USA by John Eckert and John Mauchy. It was named Electronic Numerical Integrator and Calculator (ENIAC). The ENIAC was 30´50 feet long, weighed 30 tons, contained 18,000 vacuum tubes, 70,000 registers, 10,000 capacitors and required 150,000 watts of electricity. Today your favorite computer is many times as powerful as ENIAC, still size is very small.

EDVAC: It stands for Electronic Discrete Variable Automatic Computer
and was developed in 1950. The concept of storing data and instructions inside the computer was introduced here. This allowed much faster operation since the computer had rapid access to both data and instructions. The other advantages of storing instruction was that computer could do logical decision internally.

Other Important Computers of First Generation

EDSAC: It stands for Electronic Delay Storage Automatic Computer and was developed by M.V. Wilkes at Cambridge University in 1949.

UNIVAC-1: Ecker and Mauchly produced it in 1951 by Universal Accounting Computer setup.

Limitations of First Generation Computer

Followings are the major drawbacks of First generation computers.

The operating speed was quite slow.
Power consumption was very high.
It required large space for installation.
The programming capability was quite low.

Second generation computers

Around 1955 a device called Transistor replaced the bulky electric tubes in the first generation computer. Transistors are smaller than electric tubes and have higher operating speed. They have no filament and require no heating. Manufacturing cost was also very low. Thus the size of the computer got reduced considerably.

It is in the second generation that the concept of Central Processing Unit (CPU), memory, programming language and input and output units were developed. The programming languages such as COBOL, FORTRAN were developed during this period. Some of the computers of the Second Generation were

IBM 1620: Its size was smaller as compared to First Generation computers and mostly used for scientific purpose.
IBM 1401: Its size was small to medium and used for business applications.
CDC 3600: Its size was large and is used for scientific purposes.

Third generation computers

The third generation computers were introduced in 1964. They used Integrated Circuits (ICs). These ICs are popularly known as Chips. A single IC has many transistors, registers and capacitors built on a single thin slice of silicon. So it is quite obvious that the size of the computer got further reduced. Some of the computers developed during this period were IBM-360, ICL-1900, IBM-370, and VAX-750. Higher level language such as BASIC (Beginners All purpose Symbolic Instruction Code) was developed during this period.

Computers of this generations were small in size, low cost, large memory and processing speed is very high.

Fourth generation computers

The present day computers that you see today are the fourth generation computers that started around 1975. It uses large scale Integrated Circuits (LSIC) built on a single silicon chip called microprocessors. Due to the development of microprocessor it is possible to place computer’s central processing unit (CPU) on single chip. These computers are called microcomputers. Later very large scale Integrated Circuits (VLSIC) replaced LSICs.

Thus the computer which was occupying a very large room in earlier days can now be placed on a table. The personal computer (PC) that you see in your school is a Fourth Generation Computer.

Fifth generation computer

The computers of 1990s are said to be Fifth Generation computers. The speed is extremely high in fifth generation computer. Apart from this it can perform parallel processing. The concept of Artificial intelligence has been introduced to allow the computer to take its own decision. It is still in a developmental stage.

Types of computers

Now let us discuss the varieties of computers that we see today. Although they belong to the fifth generation they can be divided into different categories depending upon the size, efficiency, memory and number of users. Broadly they can be divided it to the following categories.

1. Microcomputer: Microcomputer is at the lowest end of the computer range in terms of speed and storage capacity. Its CPU is a microprocessor. The first microcomputers were built of 8-bit microprocessor chips. The most common application of personal computers (PC) is in this category. The PC supports a number of input and output devices. An improvement of 8-bit chip is 16-bit and 32-bit chips. Examples of microcomputer are IBM PC, PC-AT .

2. Mini Computer: This is designed to support more than one user at a time. It possesses large storage capacity and operates at a higher speed. The mini computer is used in multi-user system in which various users can work at the same time. This type of computer is generally used for processing large volume of data in an organization. They are also used as servers in Local Area Networks (LAN).

3. Mainframes: These types of computers are generally 32-bit microprocessors. They operate at very high speed, have very large storage capacity and can handle the work load of many users. They are generally used in centralized databases. They are also used as controlling nodes in Wide Area Networks (WAN). Example of mainframes are DEC, ICL and IBM 3000 series.

4. Supercomputer: They are the fastest and most expensive machines. They have high processing speed compared to other computers. They have also multiprocessing technique. One of the ways in which supercomputers are built is by interconnecting hundreds of microprocessors. Supercomputers are mainly being used for whether forecasting, biomedical research, remote sensing, aircraft design and other areas of science and technology. Examples of supercomputers are CRAY YMP, CRAY2, NEC SX-3, CRAY XMP and PARAM from India.

In-text questions 3

Into how many generations the evolution of computer is divided?
What is VLSIC?
The personal computer that you see today is in which generation of computer?

What you have learnt

In this lesson we have discussed about the major characteristics of computer. The speed, accuracy, memory and versatility are some of the features associated with a computer. But the computer that we see to
day has not developed over night. It has taken centuries of human effort to see the computer in its present form today. There are five generations of computer. Over these generations the physical size of computer has decreased, but on the other hand the processing speed of computer has improved tremendously. We also discussed about the varieties of computers available today.

Terminal questions

1. Why is computer known as data processor?

2. Explain in brief the various generations in computer technology?

3. Write a short note on Fifth Generation of computer. What makes it different from Fourth generation computer?

4. Why did the size of computer get reduced in third generation computer?

5. Give short notes on the following:

Versatility
Storage
Slide Rule
Babbage’s Analytical Engine

6. Distinguish between Microcomputer and Mainframe computer.

Feedback to in-text questions

In-text questions 1

A computer is an electronic device, which is used to accept, store, retrieve and process the data. It is called as data processor because it is mainly used for processing data for producing meaningful information.
The characteristics of computer are speed, accuracy, diligence, versatility and storage.

In-text questions 2

Analytical engine, 1823.
Charles Babbage

In-text questions 3

Five generations
Very Large Scale Integrated Circuits
Fourth Generation

Terminal questions

Explain various types of computers.
Explain in brief the various generations in computer technology.
Write a short note on Fifth Generation of computer. What makes it different from Fourth Generation computer?
Why did the size of computer get reduced in Third Generation computer?

In-text questions 4

1. State True or False

Word processor is Software Package that enables you to create, edit, print and save document .
WordStar is a popular Word processor.
Changing the size of the margins cannot reformat complete document or part of the text.
Word has the facility of Macros.
Word does not allow the user to mix the graphical pictures with text.

In text questions 5

1. Choose the best answer.

1. While working in Microsoft Word you have to work with

Mouse only
Keyboard only
Both mouse and keyboard

2. In Ms- Word every command is available in

Print
Letter
Icons

3. You can go inside Microsoft Word by the following way

Take the mouse pointer to start button on the task bar and click the left mouse button.
Take the mouse pointer to start button and click the right mouse button.
Move the mouse pointer on the screen.

4. State True or False

The title bar displays the name of the currently active word document
The most commonly tool bars are the Formatting tool bar and the Standard tool bar.
The Tool bar allows you to format the vertical alignment of text.
The Scroll bar helps you to scroll the content or body of document.
The work space is the area in the document window where you enter/type the text.

In-text question 6

1. State True or False

Using View option you can perform editing functions such as cut, copy, paste, find and replace etc.
Using the Edit option you can switch over from Normal mode to Out line mode.
Using Insert menu you can insert various objects such as page numbers, footnotes, picture frames etc.
Using Tools menu you can access to various utilities of word such as spell check, macros and mail merge etc.
Window menu allows you to work with two documents simultaneously.

Application Package | Computer Science | HSEB Notes

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Detailed notes to follow:

1. Word processor

Use & Character
Examples
Some Important Terms Used: Thesaurus, speller, mail merge

2. Spread sheet

Use & Character
Examples
Some Important Terms Used: Relative cell reference, absolute cell reference

3. Presentation

Use & Character
Examples

Functions of Operating System

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Operating system supports the basic functions of the computer and is a low-level software. The functions of operating systems are as described below:

1. I/O management:
OS manages I/O devices and makes the I/O process effective. OS accepts the input from the input device, stores it in the main memory, ask the CPU to process it and finally provides the result to the output devices for output.

2. Command interpreter:
Command interpreter is one of the part of operating system which reads the commands that user types in at a terminal, interprets them and translate them into a detailed set of instructions that the computer hardware can understand. It varies widely from one OS to other OS. Every OS must provide command interpreter for its operation.

3. Memory management:
Memory is the large array of words or bytes, each with its own address. When user requests CPU for read/write operation, OS determines the amount of memory required for the program instructions and data. Then, OS allocates required memory to load the program and data into RAM. When program terminates its memory area is free and the same memory area is allocated for other programs.

4. Process management:
OS finds the status of processor and processes, chooses a job, chooses processer in the job, allocates the processor to the process and frees the processor when the process is executed.

5. Time sharing:
OS manages the time of CPU. The kernel OS checks frequency for other processes requesting CPU time. Time-sharing checks for CPU request from higher priority processes that are made every 10 milliseconds. When two or more processes at the same priority level are competing for the CPU time, CPU time is sliced into segments, defined by time slice and passed from process to process in a round robin fashion, preventing a single process from monopolizing the CPU until it blocks or terminates.

6. Security:
OS makes sure that only authorized users get access to the computer and its data and the users only do things they are authorized to do.

7. Deadlock prevention:
During processing, a situation can arise in which a resource shared by two or more processes cannot continue because the resource required by one process is held by the other. This situation is called deadlock. OS ensures that the above condition do not hold by carefully allocating resources.

8. Interrupt handling:
Interrupt is a signal generated from a device or program when they need attention of the CPU. OS determines the type of interrupt and priority of the interrupt, stops the execution process of CPU, preserves the initial state of the CPU, perform the requested operation and brings the CPU at the same state when it was stopped.

9. Virtual storage:
If there are programs larger than main memory (RAM) of the computer, OS uses the reserved space in the secondary memory which is termed as virtual memory. It makes the execution of larger program (than RAM) possible but at the same times the operation becomes slower.

Email Service

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Email service is used for transmitting electronic or soft-copy documents, message by using electronic devices like computer, computer network, internet, etc. present e-mail service is based on stored and forward concept i.e. email sent by the sender is stored in email server before forwarding it to the receiver. It doesn’t require the sender and receiver to be connected at the same time. Traditionally, the older concept of email required both sender and receiver to be connected at the same time.
It uses protocols like SMTP, POP, IMAP, etc.

Features of e-mail:

It is faster and cheaper medium of communication.
It is reliable.
It is secured communication.
It can be used for transmitting text, image, audio, video.
Same message can be sent to multiple users at the same time by using CC (Carbon Copy) and BCC (Blind Carbon Copy).
It may or may not use internet directly.

Types:

Web based email
POP email service

1. Web based email:
It is the internet based mailing system. It requires internet connection and a browser to send or receive the message. Email providers like hotmail.com, yahoo.com, gmail.com, etc. provide internet based email. It is the most widely used email service.

2. POP email service:
This email service is provided by local email or network providers. It requires connection to the e-mail provider and email client software like:

Outlook express
Thunderbird
Eudora
Kmail, etc.

It can be used from the system with email client software and proper setting to connect email providers.

Secondary Memory

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It is also known as external memory/S=storage memory/auxiliary memory/backup memory. It is used for storing data and instructions permanently. It is also used for carrying data from one computer to another. Secondary memory is not directly accessible to CPU. It is usually slower for read/write, cheaper and used in larger storage capacity.
Example: Hard disk, CD, DVD, Pen drive, etc.

Types of Secondary memory are:

Magnetic memory
Optical memory

1. Magnetic memory
Magnetic memory uses the property of magnet for storing data. It is in use since first generations of computer. It contains data storing surface coated by magnetic oxide. Magnetic memory is further divided as:

- Magnetic drum
Magnetic drum contains a metallic drum coated by magnetic oxide on the outer surface of the drum, data is stored in this surface. It was in use in first and second generations of computer.

- Magnetic tape
Magnetic tape contains thin plastic ribbon, only one side of the ribbon is used for storing data. The data storing side is coated by magnetic oxide. It is a sequential access memory. So, the data read/write speed is slower. It is mainly used for storing audio, video and back-up data. It is highly reliable. It requires magnetic tape drive for reading and writing data. It has the storage capacity of 100MB-200GB. The width of the ribbon also varies from 4mm-1inch.

- Magnetic disk
Magnetic disk contains a circular disc made of metal or plastic. Both side of the disc is usually used for storing data. The disc is coated by magnetic oxide. The disc is divided into multiple concentric circles known as track. Tracks are further divided into small area known as sectors. Data are stored in sectors.
Example: Hard disk, floppy disk, zip disk, super disk, Winchesterdisk, jaz disk.

- Hard disk
It is used as main storage device of the computer. It uses 2-4 metallic disk (platter). The disk is usually made of aluminum. Both sides of the disk is used for storing data except the upper side of the uppermost disk and lower side of the lowermost disk. The data storing surface is coated by magnetic oxide. Each data storing surface contains separate read/write head. During data read/write process platter rotates at the rate of 3600-15000rpm. Hard disk is also known as hard drive because both data storing disk and data read/write components are combined together. It has the storage capacity of few mega bytes to tera byte.

- Floppy disk
It contains single plastic disk. Initially it was used as a main storage device but nowadays it is used for carrying data from one computer to another. It requires floppy drive for its operation. It is not reliable as hard disk because the data storing surface is exposed. So, it may be affected by dust particles and magnetic field.

2. Optical memory
Optical memory uses light beam for its operation. It is developed in fourth generation of computer. It is mainly used for storing audio/video, backup as well as for carrying data. It requires optical drive for its operation. Its read/write speed is slower compared to hard disk and flash memories.
Example: CD, DVD, BD

CD
It stands for Compact Disk. It has storage capacity of 700 MB or approximately 90 minutes of standard audio. CD contains hard circular plastic, single side of this plastic is coated by aluminum alloy. This alloy stores data. It is protected by additional thin plastic covering. CD required CD drive for its operation. Types of CD are:
CD-R is a blank CD in which data can be stored once. After storing data it is converted into CD-ROM.
CD-ROM
It cannot be erased or updated
CD-RW
it can be erased and used for multiple times.
DVD
It stands for Digital Versatile Disk. It has the storage capacity of 4.7GB to 17GB. Its shape and size is similar to CD but the difference in storage capacity is due to different chemical component and data is compressed before storing. It requires DVD drive for its operation. Read/write speed of DVD is slower than that of CD. Types of DVD are:

DVD-R
DVD-ROM
DVD-RW

DVD can also be classified as:

Single sided single layered DVD (4.7GB)
Single sided dual layered DVD (7-8GB)
Dual sided single layered DVD (9GB)
Dual sided dual layered DVD (17GB)

BD
It stands for Bluray disk. It has the storage capacity of 25GB-50GB. It requires BD drive for its operation. Its shape and size is similar to CD and DVD. Types of BD are:

BD-R
BD-ROM
BD-RW

Working mechanism of CD
The surface of the CD contains land and pit. Land represents binary 1 and pit represents binary 0. During CD reading process a beam of light is emitted which strikes the surface of CD and gets reflected. The reflection is captured by lens in the CD drive. Difference in reflection from land and pit is identified to determine 1 and 0. Land is actually in a crystalline form and pit is in amorphous form. The size of land and pit is smaller in DVD compared to CD.
External memory devices:

1. Zip disk
It is a magnetic memory. It is thee modification of floppy disk. It has the storage capacity of 100MB and 250MB. It requires Zip disk drive for its operation.

2. Jaz disk
It is also a magnetic memory. It has the storage capacity of 2GB. It also requires separate Jaz disk drive for its operation.

3. Super disk
It is also a magnetic memory. It has the storage capacity of 120MB. It requires Super disk drive for its operation. Both floppy and super disk can be used in super disk drive.

4. Pen drive
It is a flash memory. It is a semi-conductor memory. It is mainly used for transferring data. It has faster read/write speed compared to magnetic memory. Pen drive has storage capacity of few MB-GB. A pen drive is a plug and play device. A pen drive can be connected with the computer through USB port.

5. Portable hard disk
it is a magnetic hard disk. It can be connected with the computer through the USB port. It is also a plug and play device. It is mainly used for storing backup. It has the storage capacity from few GB-TB