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

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

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

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

Model Question For Computer Science Class 11

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

HSEB question model of computer science

Grade : 11

For : 2070

Time : 3hrs
F.M. : 75
P.M : 27

Group A (long answer question)

Attempt all the questions. [3 X 10 = 30]

1. 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.
1. What is an operating system ? Explain any three function of an operating system.
2. The “WiMP” environment is much more user-friendly, why ?
OR
1. What is cell addressing and explain different types of cell addressing used in spreadsheet.
2. Write a tag to design your personal web page to link photo family, background and banner page using frame. [5+5]

Define flowchart and pseudocode. Explain their significance in programming. [5]
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 X 5 = 45]**

4. Classify the computers according to their generation based on the technology used. [5]

5. Differentiate between analogue and digital computer, explain with examples. [5]

6. What do you mean by number system? Why do digital computers use binary numbers for their operation ? [2 + 3]

7. Convert these numbers. [5]

1. (126)10 = (?)2
2. (11011)2 = (?)10
3. (57)8 = (?)2

Perform following operations.

4. 1011 – 1001
5. 1110 + 1110

8. State the Demorgan’s theorem and verify it. [5].

9. What are logic gates? Construct the truth table of NOR operation. [5]

10. Write short notes on (any two) : [5]

IDE 2. SCSI 3. Wave Camera

11. What are uses of internet ? Write any five search engine name. [5]

12. Differentiate between System Software and Application Software with examples. [5]

13. What are DPT features in MS-Words? Write three features of Presentation Packages. [2 + 3]

14. Write an algorithm and flowchart to print the word “Hello” ten times using “while loop” [5]

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.

Types of Programming Languages

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

There are two types of programming languages, which can be categorized into the following ways:

1. Low level language

Machine language (1GL)
Assembly language (2GL)

2. High level language

Procedural-Oriented language (3GL)
Problem-Oriented language (4GL)
Natural language (5GL)

1. Low level language
This language is the most understandable language used by computer to perform its operations. It can be further categorized into:

- Machine language (1GL)
Machine language consists of strings of binary numbers (i.e. 0s and 1s) and it is the only one language, the processor directly understands. Machine language has an Merits of very fast execution speed and efficient use of primary memory.

Merits:

It is directly understood by the processor so has faster execution time since the programs written in this language need not to be translated.
It doesn’t need larger memory.

Demerits:

It is very difficult to program using 1GL since all the instructions are to be represented by 0s and 1s.
Use of this language makes programming time consuming.
It is difficult to find error and to debug.
It can be used by experts only.

- Assembly language
Assembly language is also known as low-level language because to design a program programmer requires detailed knowledge of hardware specification. This language uses mnemonics code (symbolic operation code like ‘ADD’ for addition) in place of 0s and 1s. The program is converted into machine code by assembler. The resulting program is referred to as an object code.

Merits:

It is makes programming easier than 1GL since it uses mnemonics code for programming. Eg: ADD for addition, SUB for subtraction, DIV for division, etc.
It makes programming process faster.
Error can be identified much easily compared to 1GL.
It is easier to debug than machine language.

Demerits:

Programs written in this language is not directly understandable by computer so translators should be used.
It is hardware dependent language so programmers are forced to think in terms of computer’s architecture rather than to the problem being solved.
Being machine dependent language, programs written in this language are very less or not protable.
Programmers must know its mnemonics codes to perform any task.

2. High level language
Instructions of this language closely resembles to human language or English like words. It uses mathematical notations to perform the task. The high level language is easier to learn. It requires less time to write and is easier to maintain the errors. The high level language is converted into machine language by one of the two different languages translator programs; interpreter or compiler.

High level language can be further categorized as:

Procedural-Oriented language (3GL) Procedural Programming is a methodology for modeling the problem being solved, by determining the steps and the order of those steps that must be followed in order to reach a desired outcome or specific program state. These languages are designed to express the logic and the procedure of a problem to be solved. It includes languages such as Pascal, COBOL, C, FORTAN, etc.

Merits:

Because of their flexibility, procedural languages are able to solve a variety of problems.
Programmer does not need to think in term of computer architecture which makes them focused on the problem.
Programs written in this language are portable.

Demerits:

It is easier but needs higher processor and larger memory.
It needs to be translated therefore its execution time is more.

- Problem-Oriented language (4GL)
It allows the users to specify what the output should be, without describing all the details of how the data should be manipulated to produce the result. This is one step ahead from 3GL. These are result oriented and include database query language.
Eg: Visual Basic, C#, PHP, etc.

The objectives of 4GL are to:
Increase the speed of developing programs.
Minimize user’s effort to botain information from computer.
Reduce errors while writing programs.

Merits:

Programmer need not to think about the procedure of the program. So, programming is much easier.

Demerits:

It is easier but needs higher processor and larger memory.
It needs to be translated therefore its execution time is more.

- Natural language (5GL)
Natural language are stil in developing stage where we could write statrments that would look like normal sentences.

Merits:

Easy to program.
Since, the program uses normal sentences, they are easy to understand.
The programs designed using 5GL will have artificial intelligence (AI).
The programs would be much more interactive and interesting.

Demerits:

It is slower than previous generation language as it should be completely translated into binary code which is a tedious task.
Highly advanced and expensive electronic devices are required to run programs developed in 5GL. Therefore, it is an expensive approach.

These are the different types of programming languages with their merits and demerits.

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

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.

Classification Of Computer

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

Classification of computer

1. On the basis of Purpose of Use

General Purpose Computer
Special Purpose Computer

2. On the basis of speed/size

Super Computer
Mainframe Computer
Mini Computer
Micro Computer: Portable micro computer and non-portable micro computer

3. On the basis of Working Principle

Analog Computer
Digital Computer
Hybrid Computer

4. On the basis of Brand

IBM Computer: IBM computer and IBM compartable
Apple Computer

5. On the basis of Model

XT Computer
AT Computer
PS/2 Computer

& Difference Between Digital and Analog Computer