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1st Year Computer Notes CH#08 Computer Network
Computer Network
In connection with the information technology and computers a network is a way to connect computers together so that they can communicate, exchange information and pool resources or a network is a communicating system connecting two or more computers. Network connects people as close as the next office and as for as halfway around the world.
In business networks have revolutionized the use of computer technology. Many businesses that used to relay on a centralized system with mainframe and a collection of terminals now use computer networks in which every employee who needs a computer has personal computer connected to the network. In education, schools, colleges and universities have also shifted to strategies built around networked personal computers.
Configurations or Topologies Networks
A network can be arranged or configured in several different ways. This arrangements is called the network's topology. The four principal network topologies are
1. Star Network
2. Bus Network
3. Ring Network
4. Hierarchical Network
1. Star Network
In a star network small computers or peripheral devices are linked to a central unit. This central unit may be a host computer or a file server. All the communications pass through this central unit. Control is maintained by polling. Each device is in turn allowed to send the message.
One particular advantage of the star form of network is that it can be used to provide a time-sharing system. i.e several users can share resources (time) on a central computer. The star is a common arrangement for linking several microcomputers to a mainframe that allows access to an organizations database.
2. Bus Network
In a bus network each device in the network handles its own communication control. There is no host computer. All communications control travel along a common connecting cable called a bus. As the information passes along the bus it is examined by each device to see if the information is intended for it.
The bus network is typically used when only a few microcomputers are to be linked together. The bus network is not as efficient as the star network for sharing common resources. However it is less expensive and is in very common use.
3. Ring Network
In a ring network, each device is connected with two other devices forming a ring. There is no central file server or computer. Messages are passed around the ring until they reach correct destination. With microcomputers ring network is the least frequently used arrangement. However it is often used to link mainframes specially over wide geographical areas.
A ring network is useful in a decentralized organization because it makes possible a distributed data processing system i.e. computers can perform processing tasks at their own dispersed locations.
4. Hierarchical Network
This type of networks are also called hybrid network. It consist of several computers linked to a central host computer just like a star network. However these computers are also hosts to other smaller computers or to peripheral devices. The host at the top of the hierarchical network could be mainframe. The computers below the mainframe could be minicomputers and those below microcomputers. This network allows various computers to share database processing programs and different output devices. It is useful in a centralized organizations.
Strategies of Networks
Every network has a strategy or a way of coordinating the sharing of the information and resource. The most common network strategies are terminal, peer-to-peer and client/server systems, terminal network system. In this system processing power is centralized in one large computer, usually the mainframe. The nodes (a node is any device connected to network) connected to this host computer are terminals (a terminal is a input or output device) with little or no processing capability. Most airline reservation systems are terminal systems.
Peer-to-Peer Network System
In a peer-to-peer network, nodes can act both as servers and clients. There are several advantages of using this type of strategy. The networks as inexpensive and easy to install and they usually work well for smaller systems with less than ten nodes. As the number of nodes increases, however the performance of the network declines.
Client/Server Network System
Client/Server network system uses to coordinate and supply services to all other nodes on the network. The server provides access to centralized resources such as databases, applications software and hardware. This strategy is based on specialization. Server nodes coordinate and supply specialized services and client nodes request services.
One advantage of client/server network system is its ability to handle very large networks efficiently. Another advantage is the powerful management software that monitors and controls networks activities. The major disadvantage of it is the high cost of installation and maintenance.
Advantages of Network
Networks provide tremendous benefits. The most compelling advantages of network are as follows.
1. Networks allow users simultaneous access to shared programs and data.
2. Network also allows users to share peripheral devices such as printers and hard disks.
3. Network usually includes the capacity to send e-mail and many e-mail systems let users to attach files to their messages.
4. Connecting computers to form a network makes it easier to perform backups of the data on all the network hard disks.
Types of Networks
Communications differ in geographical size. Three important types are LANs, MANs, WANs.
Local Area Networks (LANs)
Network with computers and peripherals devices in close proximity within the same building are called local area networks (LANs).
The figure shows an example of a LAN. This type of arrangement has two benefits.
1. People can share different equipment, which lowers the cos of equipment.
2. LAN also features a network gateway. i.e. a LAN may be linked to other LANs or to large networks in this manner.
Metropolitan Area Network (MANs)
These network are used as links between office buildings in a city. Cellular phone systems expand the flexibility of MANs by allowing links to car phones and portable phones.
Wide Area Network (WANs)
Wide area networks are countrywide and worldwide networks. Among other kinds of channels they use microwave relays and satellites to reach users over long distances. One of the most widely used WANs is Internet. Which allows users to connect to other users and facilities worldwide.
Uses of Internet
The most common uses of Internet are
1. Communicating
Sending and receiving e-mail is the most popular internet activity. You can send and receive e-mail to and from you friends and family located almost anywhere in the world. You can join an listen to discussions and debates on a wide variety of special interest topics.
2. Shopping
One of the fastest growing applications of Interest is electronic commerce. You can visit a cyber mall for making purchases.
3. Researching
Internet provides you to have one of the world's largest libraries available from home.
4. Entertainment
Do you like music, the moves and reading or playing computer games? You can find them all on Internet waiting for you to locate and enjoy.
In connection with the information technology and computers a network is a way to connect computers together so that they can communicate, exchange information and pool resources or a network is a communicating system connecting two or more computers. Network connects people as close as the next office and as for as halfway around the world.
In business networks have revolutionized the use of computer technology. Many businesses that used to relay on a centralized system with mainframe and a collection of terminals now use computer networks in which every employee who needs a computer has personal computer connected to the network. In education, schools, colleges and universities have also shifted to strategies built around networked personal computers.
Configurations or Topologies Networks
A network can be arranged or configured in several different ways. This arrangements is called the network's topology. The four principal network topologies are
1. Star Network
2. Bus Network
3. Ring Network
4. Hierarchical Network
1. Star Network
In a star network small computers or peripheral devices are linked to a central unit. This central unit may be a host computer or a file server. All the communications pass through this central unit. Control is maintained by polling. Each device is in turn allowed to send the message.
One particular advantage of the star form of network is that it can be used to provide a time-sharing system. i.e several users can share resources (time) on a central computer. The star is a common arrangement for linking several microcomputers to a mainframe that allows access to an organizations database.
2. Bus Network
In a bus network each device in the network handles its own communication control. There is no host computer. All communications control travel along a common connecting cable called a bus. As the information passes along the bus it is examined by each device to see if the information is intended for it.
The bus network is typically used when only a few microcomputers are to be linked together. The bus network is not as efficient as the star network for sharing common resources. However it is less expensive and is in very common use.
3. Ring Network
In a ring network, each device is connected with two other devices forming a ring. There is no central file server or computer. Messages are passed around the ring until they reach correct destination. With microcomputers ring network is the least frequently used arrangement. However it is often used to link mainframes specially over wide geographical areas.
A ring network is useful in a decentralized organization because it makes possible a distributed data processing system i.e. computers can perform processing tasks at their own dispersed locations.
4. Hierarchical Network
This type of networks are also called hybrid network. It consist of several computers linked to a central host computer just like a star network. However these computers are also hosts to other smaller computers or to peripheral devices. The host at the top of the hierarchical network could be mainframe. The computers below the mainframe could be minicomputers and those below microcomputers. This network allows various computers to share database processing programs and different output devices. It is useful in a centralized organizations.
Strategies of Networks
Every network has a strategy or a way of coordinating the sharing of the information and resource. The most common network strategies are terminal, peer-to-peer and client/server systems, terminal network system. In this system processing power is centralized in one large computer, usually the mainframe. The nodes (a node is any device connected to network) connected to this host computer are terminals (a terminal is a input or output device) with little or no processing capability. Most airline reservation systems are terminal systems.
Peer-to-Peer Network System
In a peer-to-peer network, nodes can act both as servers and clients. There are several advantages of using this type of strategy. The networks as inexpensive and easy to install and they usually work well for smaller systems with less than ten nodes. As the number of nodes increases, however the performance of the network declines.
Client/Server Network System
Client/Server network system uses to coordinate and supply services to all other nodes on the network. The server provides access to centralized resources such as databases, applications software and hardware. This strategy is based on specialization. Server nodes coordinate and supply specialized services and client nodes request services.
One advantage of client/server network system is its ability to handle very large networks efficiently. Another advantage is the powerful management software that monitors and controls networks activities. The major disadvantage of it is the high cost of installation and maintenance.
Advantages of Network
Networks provide tremendous benefits. The most compelling advantages of network are as follows.
1. Networks allow users simultaneous access to shared programs and data.
2. Network also allows users to share peripheral devices such as printers and hard disks.
3. Network usually includes the capacity to send e-mail and many e-mail systems let users to attach files to their messages.
4. Connecting computers to form a network makes it easier to perform backups of the data on all the network hard disks.
Types of Networks
Communications differ in geographical size. Three important types are LANs, MANs, WANs.
Local Area Networks (LANs)
Network with computers and peripherals devices in close proximity within the same building are called local area networks (LANs).
The figure shows an example of a LAN. This type of arrangement has two benefits.
1. People can share different equipment, which lowers the cos of equipment.
2. LAN also features a network gateway. i.e. a LAN may be linked to other LANs or to large networks in this manner.
Metropolitan Area Network (MANs)
These network are used as links between office buildings in a city. Cellular phone systems expand the flexibility of MANs by allowing links to car phones and portable phones.
Wide Area Network (WANs)
Wide area networks are countrywide and worldwide networks. Among other kinds of channels they use microwave relays and satellites to reach users over long distances. One of the most widely used WANs is Internet. Which allows users to connect to other users and facilities worldwide.
Uses of Internet
The most common uses of Internet are
1. Communicating
Sending and receiving e-mail is the most popular internet activity. You can send and receive e-mail to and from you friends and family located almost anywhere in the world. You can join an listen to discussions and debates on a wide variety of special interest topics.
2. Shopping
One of the fastest growing applications of Interest is electronic commerce. You can visit a cyber mall for making purchases.
3. Researching
Internet provides you to have one of the world's largest libraries available from home.
4. Entertainment
Do you like music, the moves and reading or playing computer games? You can find them all on Internet waiting for you to locate and enjoy.
1st Year Computer Notes CH#07 Data Presentation
Data Presentation
The set of symbols to express quantities as the basis of counting is referred to be a number system. There has been various number systems under human use for the purpose of counting and measurement. For instance decimal number system, octal number system, binary number system and hexadecimal number system have been most popular number systems which human beings have been utilizing for the purpose of counting and measurement.
Though a computer can process only binary numbers i.e. only 0 and 1, we give a brief account of each of the number system mentioned above. Inter conversion of these number systems would also be discussed in this chapter.
Decimal Number System
This is the most commonly used number system and which is very natural to man, hence very easy to use and remember. It consists of ten digits, i.e. from 0 to 9. As the total number of digits used in a number system is called its base or radix, hence base of radix of decimal number system is said to be ten.
Binary Number System
The base or radix of binary number is two, implying that there are only two digits 0 and 1 used in binary number system. This number system has become most popular system because of its use by the computers for processing data.
Octal Number System
This number system is consist of eight i.e. 0,1,2,3,4,5,6 and 7. Hence the base or the radix of octal number system is eight. Actually this number is a short hand version of binary numbers, Hence one octal represents three binary digits.
Hexadecimal Number System
Hexadecimal numbers are extensively used in microcomputers. As they are much shorter than binary numbers, hence easy to write and remember. They are also a short hand version of binary numbers. The hexadecimal also called Hex is equivalent to four binary digits. This number system consists of 0,1,2,3,4,5,6,7,8,9, A,B,C,D,E and F. The base of this number system is 16. The symbol A........F stand respectively for 10.....15.
Binary to Decimal Conversion
All the number system may be easily converted into other number systems. In order to convert binary numbers into decimal numbers we multiply each bit of a particular binary number with (n-1) power of 2.
Add all the resultant multiplied bits.
Example No. 1
To convert the binary number 10010 to a decimal number we proceed as follows:
100102 = (1 x 24) + (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 16) + (0 x 8) + (0 x 4) + (1 x 2) + (0 x 1)
= 16 + 0 + 2 + 0
= 18
It should be kept in the mind that any number raised to the power 0 equals 1.
Example No. 2
Similarly in order to convert the binary number 110111 to a decimal number we may proceed as follows:
1101112 = (1 x 25) + (1 x 24) + (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 32) + (1 x 16) + (1 x 8) + (1 x 4) + (1 x 2) + (1 x 1)
= 32 + 16 + 0 + 0 + 4 + 2 + 1
= 56
Example No. 3
If there is a period (.) in the binary number e.g. (1011.10). Then the conversion of such binary number can be illustrated as follows:
(10112) = (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 8) + (0 x 4) + (1 x 2) + (1 x 1)
= 8 + 0 + 2 + 1
= 11
AND
(.102) = (1 x 2-4) + (1 x 2-2)
= (1 x 1/2) + (1 x 1/4)
= 1/2 + 0 = 0.5
Hence (1011.102) = 11.5
Decimal to Binary Conversion
A decimal number can easily be converted to a binary number. For this purpose we take following steps.
1. Divide the decimal number by 2 and note down the remainder.
2. Take the quotient and again divide by 2, then note down the remainder again.
3. Repeat the 2nd step unit you get 1 as the quotient.
4. The remainders in the reverse order would be our required binary number.
Example No. 4
For example in order to convert decimal number 15 to binary number. we may proceed as follows.
15/2 = 7 and the remainder is 1
7/2 = 3 and the remainder is 1
3/2 = 1 and the remainder is 1
1/2 = 0 and the remainder is 1
Hence the required binary number is 1111
Converting Decimal Fractions to Binary Numbers
The most simple method of converting fractional decimal numbers to binary number is repeated multiplication by two. In this method numbers to the right of the decimal point are repeatedly multiplied by 2 till we get a whole number. The product in fractions is assigned as 0 bit while in whole number it is assigned as 1 bit.
The process of converting a fractional decimal number to binary number would be explained by the following example.
Example No. 5
Let us suppose the we want to convert 0.125 in a binary numbers then proceed as follow.
0.125 x 2 = 0.250 it carries 0
0.250 x 2 = 0.500 it carries 0
0.500 x 2 = 1.00 it carries 1
Hence we can conclude that (0.125)10 = (0.001)2
Addition to Binary Numbers
In order to add binary number below given table should be kept in mind
0 + 0 = 0
0 + 1 + 1
1 = 0 = 1
1 + 1 = 0 with a carry of 1
The following example will illustrate the addition of binary numbers.
Example No.6
Add 1001 and 1010
1001 + 1010 = 11011
Subtraction of Binary Numbers
In order to subtract a binary number from another binary number you must keep the following table in your mind.
0 - 0 = 0
1 - 0 = 1
1 - 1 = 0
0 - 1 = 1 with a barrow of 1
The process of binary subtraction an be illustrated with the help of example given below
Example No. 7
For subtracting binary number 101 from 1001 we proceed as follows
1001 - 100.1 = 1.11
Octal to Decimal Conversion
For converting an octal number to a decimal number we use the same sort of polynomial as was used in the binary case. However in octal to decimal conversion the base or radix is 8 instead of 2.
The process of converting an octal number into a decimal number would be clarified with the help of following example.
Example No. 9
The Octal number 2134 can be converted into decimal number by proceeding as follows
(2134)8 = (2 x 83) + (2 x 82) + (2 x 81) + (2 x 80)
= (2 x 512) + (1 x 64) + (3 x 8) + (4 x 1)
= 1024 + 64 + 24 + 4
= 1116
Hence (2134)8 = (1116)10
Example No. 10
The octal number 1.123 can be converted to decimal number as follows
(1.123)8 = (1 x 80) + (1 x 8-1) + (1 x 8-2) + (1 x 8-3)
= (1 x 1) + (1 x 1/8) + (1 x 1/64) + (3 x 1/512)
= 1 + 1/8 + 2/64 + 3/512
= 1 83/512
Decimal to Octal Conversion
For converting decimal number to octal number. we apply a method of repeatedly dividing decimal by 8 and use each reminder as a digit in the octal number. The process of converting decimal to octal number may be illustrated by the following example.
Example No. 11
To convert the decimal number 429 to octal number we process as follows
429/8 = 53 Reminder is 5
53/8 = 6 Reminder is 5
6/8 = 0 Reminder is 6
Hence (429)8 = (655)10
Octal to Binary Conversion
As we have mentioned earlier that octal number system is a short hand version of binary numbers and one octal represents three binary digits as shown by the following table
Equivalent Octal and Binary Number
Octal 0
1
2
3
4
5
6
7
Binary
000
001
010
011
100
101
110
111
In order to convert an octal number to a binary number we just replace each octal digit with the appropriate three bits. This produce an be explained with the help of following example
Example No. 12
(25)8 = (010101)2
Because (2)8 = (010)2 and (5)8 = (101)2 as shown by the above table.
The set of symbols to express quantities as the basis of counting is referred to be a number system. There has been various number systems under human use for the purpose of counting and measurement. For instance decimal number system, octal number system, binary number system and hexadecimal number system have been most popular number systems which human beings have been utilizing for the purpose of counting and measurement.
Though a computer can process only binary numbers i.e. only 0 and 1, we give a brief account of each of the number system mentioned above. Inter conversion of these number systems would also be discussed in this chapter.
Decimal Number System
This is the most commonly used number system and which is very natural to man, hence very easy to use and remember. It consists of ten digits, i.e. from 0 to 9. As the total number of digits used in a number system is called its base or radix, hence base of radix of decimal number system is said to be ten.
Binary Number System
The base or radix of binary number is two, implying that there are only two digits 0 and 1 used in binary number system. This number system has become most popular system because of its use by the computers for processing data.
Octal Number System
This number system is consist of eight i.e. 0,1,2,3,4,5,6 and 7. Hence the base or the radix of octal number system is eight. Actually this number is a short hand version of binary numbers, Hence one octal represents three binary digits.
Hexadecimal Number System
Hexadecimal numbers are extensively used in microcomputers. As they are much shorter than binary numbers, hence easy to write and remember. They are also a short hand version of binary numbers. The hexadecimal also called Hex is equivalent to four binary digits. This number system consists of 0,1,2,3,4,5,6,7,8,9, A,B,C,D,E and F. The base of this number system is 16. The symbol A........F stand respectively for 10.....15.
Binary to Decimal Conversion
All the number system may be easily converted into other number systems. In order to convert binary numbers into decimal numbers we multiply each bit of a particular binary number with (n-1) power of 2.
Add all the resultant multiplied bits.
Example No. 1
To convert the binary number 10010 to a decimal number we proceed as follows:
100102 = (1 x 24) + (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 16) + (0 x 8) + (0 x 4) + (1 x 2) + (0 x 1)
= 16 + 0 + 2 + 0
= 18
It should be kept in the mind that any number raised to the power 0 equals 1.
Example No. 2
Similarly in order to convert the binary number 110111 to a decimal number we may proceed as follows:
1101112 = (1 x 25) + (1 x 24) + (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 32) + (1 x 16) + (1 x 8) + (1 x 4) + (1 x 2) + (1 x 1)
= 32 + 16 + 0 + 0 + 4 + 2 + 1
= 56
Example No. 3
If there is a period (.) in the binary number e.g. (1011.10). Then the conversion of such binary number can be illustrated as follows:
(10112) = (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
= (1 x 8) + (0 x 4) + (1 x 2) + (1 x 1)
= 8 + 0 + 2 + 1
= 11
AND
(.102) = (1 x 2-4) + (1 x 2-2)
= (1 x 1/2) + (1 x 1/4)
= 1/2 + 0 = 0.5
Hence (1011.102) = 11.5
Decimal to Binary Conversion
A decimal number can easily be converted to a binary number. For this purpose we take following steps.
1. Divide the decimal number by 2 and note down the remainder.
2. Take the quotient and again divide by 2, then note down the remainder again.
3. Repeat the 2nd step unit you get 1 as the quotient.
4. The remainders in the reverse order would be our required binary number.
Example No. 4
For example in order to convert decimal number 15 to binary number. we may proceed as follows.
15/2 = 7 and the remainder is 1
7/2 = 3 and the remainder is 1
3/2 = 1 and the remainder is 1
1/2 = 0 and the remainder is 1
Hence the required binary number is 1111
Converting Decimal Fractions to Binary Numbers
The most simple method of converting fractional decimal numbers to binary number is repeated multiplication by two. In this method numbers to the right of the decimal point are repeatedly multiplied by 2 till we get a whole number. The product in fractions is assigned as 0 bit while in whole number it is assigned as 1 bit.
The process of converting a fractional decimal number to binary number would be explained by the following example.
Example No. 5
Let us suppose the we want to convert 0.125 in a binary numbers then proceed as follow.
0.125 x 2 = 0.250 it carries 0
0.250 x 2 = 0.500 it carries 0
0.500 x 2 = 1.00 it carries 1
Hence we can conclude that (0.125)10 = (0.001)2
Addition to Binary Numbers
In order to add binary number below given table should be kept in mind
0 + 0 = 0
0 + 1 + 1
1 = 0 = 1
1 + 1 = 0 with a carry of 1
The following example will illustrate the addition of binary numbers.
Example No.6
Add 1001 and 1010
1001 + 1010 = 11011
Subtraction of Binary Numbers
In order to subtract a binary number from another binary number you must keep the following table in your mind.
0 - 0 = 0
1 - 0 = 1
1 - 1 = 0
0 - 1 = 1 with a barrow of 1
The process of binary subtraction an be illustrated with the help of example given below
Example No. 7
For subtracting binary number 101 from 1001 we proceed as follows
1001 - 100.1 = 1.11
Octal to Decimal Conversion
For converting an octal number to a decimal number we use the same sort of polynomial as was used in the binary case. However in octal to decimal conversion the base or radix is 8 instead of 2.
The process of converting an octal number into a decimal number would be clarified with the help of following example.
Example No. 9
The Octal number 2134 can be converted into decimal number by proceeding as follows
(2134)8 = (2 x 83) + (2 x 82) + (2 x 81) + (2 x 80)
= (2 x 512) + (1 x 64) + (3 x 8) + (4 x 1)
= 1024 + 64 + 24 + 4
= 1116
Hence (2134)8 = (1116)10
Example No. 10
The octal number 1.123 can be converted to decimal number as follows
(1.123)8 = (1 x 80) + (1 x 8-1) + (1 x 8-2) + (1 x 8-3)
= (1 x 1) + (1 x 1/8) + (1 x 1/64) + (3 x 1/512)
= 1 + 1/8 + 2/64 + 3/512
= 1 83/512
Decimal to Octal Conversion
For converting decimal number to octal number. we apply a method of repeatedly dividing decimal by 8 and use each reminder as a digit in the octal number. The process of converting decimal to octal number may be illustrated by the following example.
Example No. 11
To convert the decimal number 429 to octal number we process as follows
429/8 = 53 Reminder is 5
53/8 = 6 Reminder is 5
6/8 = 0 Reminder is 6
Hence (429)8 = (655)10
Octal to Binary Conversion
As we have mentioned earlier that octal number system is a short hand version of binary numbers and one octal represents three binary digits as shown by the following table
Equivalent Octal and Binary Number
Octal 0
1
2
3
4
5
6
7
Binary
000
001
010
011
100
101
110
111
In order to convert an octal number to a binary number we just replace each octal digit with the appropriate three bits. This produce an be explained with the help of following example
Example No. 12
(25)8 = (010101)2
Because (2)8 = (010)2 and (5)8 = (101)2 as shown by the above table.
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