TyroCity: Computer Notes

Number System

TyroCity.com — Sat, 12 Jul 2014 05:41:42 +0000

Conversion Techniques

1. Decimal to
a. Binary

/2 (Integer Part)
*2 (Decimal Part)

b. Octal

/8 (Integer Part)
*8 (Decimal Part)

c. Hexadecimal

/16 (Integer Part)
*16 (Decimal Part)

2. Binary to
a. Octal

Table (3-bit)

b. Decimal

*2n For eg. (1011)2 =1*23+0*22 +1*21+1*20

c. Hexadecimal

Table (4-bit)

3. Octal to
a. Binary

Table (3-bit)

b. Decimal

*8n For eg. (2341)8 =2*83+3*82 +4*81+1*80

c. Hexadecimal

Construct table of:
- Octal-Binary (3Bit)
- Binary-hexadecimal (4Bit)

4. Hexadecimal to

a. Binary

Table (4-bit)

b. Octal

Construct table of:
- Hexa-Binary (4Bit)
- Binary-Octal (3Bit)

c. Decimal

*16n For eg. (12A8)2 =1*163+2*162 +10*161+8*160

1’s and 2’s Complement

9’s and 10’s Complement

Model Question for Computer Science Class 11

TyroCity.com — Sun, 18 Aug 2013 05:41:42 +0000

GRADE : 11
FOR : 2070
Time : 3hrs
F.M. : 75
P.M : 27

Group A (Long Answer Question)
Attempt ALL the questions. [3 × 10 = 30]

Draw a well-labeled diagram of typical architecture of a computer system and explain the main function of Control Unit and ALU. [4+3+3] 2.a. What is an operating system ? Explain any three function of an operating system. [1 + 6] 2.b. The “WiMP” environment is much more user-friendly, why ?

OR
2.a. What is cell addressing and explain different types of cell addressing used in spreadsheet. [5]
2.b. Write a tag to design your personal web page to link photo family, background and banner page using frame. [5]

3.a. Define flowchart and pseudocode. Explain their significance in programming. [5]

3.b. Write a pseudocode to accept any three numbers and output the largest among them. [5]

Group B (Short Answer Questions)
Attempt any NINE questions. [9 × 5 = 45]

Classify the computers according to their generation based on the technology used. [5]
Differentiate between analogue and digital computer, explain with examples. [5]
What do you mean by number system? Why do digital computers use binary numbers for their operation ? [2 + 3]
Convert these numbers. [5]
- (126)10 = (?) 2
- (11011)2 = (?) 10
- (57)8 = (?) 2
Perform following operations.
- 1011 – 1001
- 1110 + 1110
State the Demorgan’s theorem and verify it. [5]
What are logic gates? Construct the truth table of NOR operation. [5]
Write short notes on (any two) : [5]
- IDE
- SCSI
- Wave Camera
What are uses of internet ? Write any five search engine name. [5]
Differentiate between System Software and Application Software with examples. [5]
What are DPT features in MS-Words? Write three features of Presentation Packages. [2 + 3]
Write an algorithm and flowchart to print the word “Hello” ten times using “while loop” [5]

Computer XI Questions

TyroCity.com — Sun, 18 Aug 2013 05:41:42 +0000

Questions

Computer Science Grade-11 2069

TyroCity.com — Sun, 18 Aug 2013 05:41:42 +0000

Candidates are required to give their answers in their own words as far as practicable. The figures in the margin indicate full marks.

Full Marks:- 75
Pass Marks:- 27
Time:- 3hrs.

Group A
Long answer questions

Attempt any three questions. 3×10=30

What is an operating system? Explain the functions of operating system.
What is memory in the computer system? Explain primary and secondary memory.
What is programming? Differentiate between compiler and interpreter.
What is Boolean algebra? Describe AND gate, OR gate, NOT gate and NAND gate symbol and Truth Table.

Group B
Short answer questions
Attempt any nine questions. 9×5=45

Why computer is known as versatile and diligent device? Explain.
What is mobile computing? Explain. Or Differentiate between analog and digital computer.
Convert (110111101)2 binary number into octal number.
What is BUS in terms of computer architecture? Explain.
Differentiate between Impact and Non-impact printers with examples.
What is internet? Write down the uses of internet. Or Explain the features of word processor.
What is web page? List the features of web page. Or Write down the advantages and disadvantages of DBMS. (Old)
What is CPU? Write down the functions of CPU.
Explain the types of programming errors with examples.
Subtract (1100)2 from (1111)2 using 1st and 2nd complement method.
Write short notes on:
- Modem
- Trackball

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.

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)

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 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.

Computer XI Notes

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

General

Introduction to Computer

Classification of Computer

Language/Software

Language/Software

Communication and Computer Network

Communication and computer network

Generation of computer

Generation of computer

Classification of Computer

Number System

Boolean Algebra

Boolean Algebra

Computer System

Operating System

Programming Concept

Application Package

Spread Sheet

Features of Microsoft Excel

Presentation

Internet

Remaining/Extras:

Dot Matrix Printer

Computer 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It is an impact type character printer. It prints character by the combination of dots where each dot is printed when the hammer strikes the printing material. It can print both image and text of different font and size. It is appropriate for low volume printing. It is usually available in three operating modes: fast, medium and slow. Faster speed will have low printing quality.

Merits:

It can print both image and text of different font and size.
Its operating cost is low.
It can print multiple copies at the same time using carbon paper.

Demerits:

It is noisy, slower.
It has low printing quality.
It can print single color only.
It is not appropriate for large volume printing.

SPOOL (Simultaneous Peripheral Operation On-line)

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

It is a free space of secondary memory managed by OS for the communication with peripheral devices like printer. It is required because of the difference in the operating speed of the CPU and peripheral devices. Peripheral devices are slow in their operation. The process of using SPOOL is known as spooling.

Bus Architecture

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

Bus is a group of wires that connects different components of the computer. It is used for transmitting data, control signal and memory address from one component to another. A bus can be 8 bit, 16 bit, 32 bit and 64 bit. A 32 bit bus can transmit 32 bit information at a time. A bus can be internal or external.

Types of bus:

1) Data bus
Data bus carries data from on component to another. It is uni-directional for input and output devices and bi-directional for memory and CPU.

2) Control bus
Control bus carries control signal. CU of CPU uses control signal for controlling all the components. It is uni-directional from CPU to all other components.

3) Address bus
Address bus carries memory address. A memory address is a numerical value used for identifying a memory location. Computer performs all its task through the memory address. CU of CPU sends memory address to all the components. So, address bus is also uni-directional from CPU to all other components.