Unit 2 Fundamentals of Computers Bcom Notes

Unit 2 Fundamentals of Computers Bcom Notes:- In this post, you will get the notes of B.com 3rd year Information Technology, by reading this post you can score well in the exam, hope that this post has helped you with this post to all your friends and all groups right now I must share it so that every student can read this post and it can also be helped in this post. Fundamentals of Computers Notes

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Fundamentals of Computer

“Data is the name given to basic facts and entities such as names, numbers, graphs, images, icons, addresses, text codes, registration. mark etc.” This term is used to describe basic facts about the activities of the system, may be a corporate house, manufacturing unit, educational institute etc. Data are generally in the form of names, numbers, times, dates, prices, employees names, product name, names of the books, schools, students, teachers, roll numbers etc.

Types of data

(i) Alphabetic: Such data items may contain only alphabets, both upper and lower case and spaces. For example name of a person. (ii) Numeric: Such data items may contain only digits. The value may have an optional sign and a decimal point to give the fractional part. The data items which do not have any fractional portion are called integers. The ones which have a fractional part are known as real numbers. These numeric data items can be used in various arithmetical operations. For example: The Basic pay, Rate, Amount, Roll number etc.

(iii) Alpha-numeric: Such data items may have any character from the complete character set i.e. alphabates, digits and symbols. For example the address of a person or an organisation.

Meaning of Information

Information are data which have been converted or organised into a more useful or intelligible for direct utilization of mankind, as information help human beings in decision making process. After going through the different components of the data processing cycle, one is in a better position to deal with the concept of Data Processing Cycle, more commonly termed as Input-Process-Output cycle (I-P-O Cycle).

The Input-Process-Output Cycle

Processing of data does not just involve arithmetical operation, but it involves data comparison & decision-making.

The I-P-O cycle is the cycle that begins with providing and storing the data and instructions. Further, processing of the data as per the instruction given in a logical sequence one by one, gives an outcome commonly called the ‘OUTPUT’. This output which is the outcome of one process, can be further fed as an ‘INPUT’ along with the instructions required, to a second process & so on. PROCESSING could take in various forms like:

• Data processing,
• Text processing,
• Graphical processing,
• Arithmetical processing,
• Decision making etc.

Fundamentals of Computers Notes

Meaning of Data Processing

Data processing is the process of restructuring, manipulating or reordering of data by people or machines, to increase their usefulness and value for some particular purpose. These are described below.

(a) Capturing: The data needs to be captured first from the

source of its origination. It is collected from an event or occurrences, in some form such as sales made by a salesman, money deposited by a customer, orders received by a store etc.

(b) Verifying: The captured data needs to be verified for its accuracy before starting the process of manipulating it.

(c) Classifying: Classifying involves, grouping of like items of transactions. It places data elements into specific categories which provide meaning for the user.

(d) Sorting: It is the process of arranging the various records within a file in a given order or sequence. The order may be ascending or descending.

(e) Summarising: Summarising involves consolidation of data. For example a summary may give the total number of students who appeared in the examination, the number of students who have passed/failed etc.

Fundamentals of Computers Notes

Techniques/Methods of Data Processing

The different methods of carrying out data processing are as follows:

(1) Manual Data Processing: When all the stages of a data processing system starting with collection of data to the generation of final output are handled manually without the help of any machine, it is termed as a manual data processing system.

(2) Mechanical Data Processing: When we start taking the help of some mechanical machines in carrying out the data processing jobs, it is known as mechanical data processing.

The first known mechanical aid was ABACUS the machine using beads in different wires helping to count and carry out calculations. Then there were a whole machines handling punched cards and punched paper tapes. We have calculators using gears for carrying out arithmetical operations. A slide rule is another popular device where one logarithmic scale is made to slide over the other to again help in the arithmetic calculations.

(3) Electrical & Electronic Data Processing: After came the era of electrical and electronic data processing, the mechanical systems were broke down by the speed of the persons operating them.

Then came the wonder machine the “COMPUTER”. It revolutionised the complete processing methodology. It can offer a true completely automated system. The input device can capture the data right from the source of the origination and pass it on to the central processing unit. The real revolution is the STORED PROGRAM t CONCEPT. The processing logic is separated from the data being processed and is written in the form of various instructions making a program. This program can be written only once and stored on the computer.

A computer is a device that accepts information in the form of n digital data and manipulates it for some results based on a program or a sequence of instructions on how data are to be processed.

Fundamentals of Computers Notes

Levels of Information

The type of information needs of an organisation depends upon a number of facts. Accordingly one can decide the level of information needed by the people at different levels. The information needs mainly can be met by internal and external sources.

The level of information needed by an organisation thus depends upon its size and the area of its operation and, of course, the nature of its work. We may divide these levels in the following way:

(1) International Information: For example currency states, weather, market demands, political and economic data, foreign politics of various countries, Defence information and war information etc.

(2) National Information: For example industrial output, demand and supply of products, weather, interest rates, financial institution policies, political activity, census data etc.

(3) Corporate Information: For example: Balance Sheet, Manpower, Production, Diversification Plans, Research and Development, Budget, Sales forecast etc.

(4) Departmental information: For example: Turnover of a branch or regional office, Funds collection, Expenses, Monthly plans etc.

(5) Individual information: For example Salary, Hours worked, Leave, Bonus Overtime etc.

Fundamentals of Computers Notes

Types of Information

The categories of management information can be broadly given as follows.

(a) Strategic Information

(b) Tactical Information

(c) Operational Information

Each category of information is needed by the management at three different levels. These levels can be defined as follows.

(a) Top level Management

(b) Middle level Management

(c) Lower (operational) level Management

The strategic information is needed by the persons at the top level management, Tactical information by the middle level management and Operational information by the lower or operational level management.

Fundamentals of Computers Notes

Number System

We may define a number system as a system which consists of,

• a set of symbol used for formation of numbers,
• a set of rules which may be used to form numbers from these symbols and assign values to them.
• a set of rules for performing common arithmetic operations on this system.

There are the following different number system:

(1) Decimal number system

(2) Binary number system

(3) Octal number system

(4) Hexadecimal number system

(1) Decimal Number System: Most commonly used number system is decimal number system. This number system involves ten symbols, which are used to form numbers. These symbols are 0, 1,2,3, 4, 5, 6, 7, 8 and 9. These symbols are known as digits. Any combination of these digits is a number in this number system.

Number of digits used tells the base of that number system. The decimal number system involves 10 symbols for the formation of numerals. So, decimal number system has the base 10. The digit 5, 4, 5 and 8 are called face values. 10 is base and power of 10 are called place values. Decimal number system is known to everybody. It is the number system which knowingly or unknowingly we have used through out our life in day-to-day routine.

(2) Binary Number System: The binary number system uses only two symbols 0 and 1. That is why this is called binary because bi means two. Since, only two symbols are used by the binary number system, the base of this number system is 2. Each digit of this number system is called binary digit or bit.

(3) Octal Number System: In many special purpose computers such as IBM 7090, PDP 7, PDP 8, etc., octal numbers are used for easy and direct input-output operations. Octal number system is the number system with base 8. This means in this number system, there are 8 symbols or digits which are used for formation of the numbers. These symbols are 0, 1, 2, 3, 4, 5, 6 and 7. The place values are calculated as we have calculated in earlier number systems. Here place values are the powers of 8.

(4) Hexadecimal Number System: The hexadecimal number system is abbreviated to hex. The numbers are written to the base 16 (hex-6, deci= 10) using the symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, r D, E and F. This type of number system is presently used in the computers such as IBM system 360, 370, 1130, HONEYWELL 200, RCA spectra 70 etc.

Fundamentals of Computers Notes

I. Conversion between various Number Systems

The following conditions can be occured to change the one number system into another number system Decimal to Binary & Binary to Decimal To convert the Decimal number to Binary number & Binary number to Decimal number, we have to use the following steps: Decimal to Binary: For converting decimal number system to binary number system, step by step process of conversion is:

Step 1. Divide the number by 2.

Step 2. Note down the quotient and remainder. Remainder will be either 0 or 1.

Step 3. If quotient is not 0, then divide the quotient by 2. Go to Step 2.

Step 4. If quotient is 0, then stop the process of division.

Step 5. The first remainder of the process is called Least Significant bit (LSB) and the last remainder is called Most Significant bit (MSB).

Step 6. Write all the remainders from MSB to LSB in a sequence from left to right. The combination of 0 and 1 thus obtained is the required binary equivalent of number.

Example: Convert (108), from decimal to binary.

2	108
2	54 – 0LSB
2	27 – 0
2	13 – 1
2	6 – 1
2	3 – 0
2	1 – 1
2	0 – 1MSB

The remainders taken from MSB to LSB are 1101100.

This implies, (108)_10­ → (1101100)₂

Binary to Decimal: To convert the binary number to decimal number, we follow the following steps.

Step 1. Multiply the bits of whole binary number with powers of 2.

These powers are positive for integral part of number and negative for fractional part of number. Magnitude of these powers depend on the position of bit in the number. If integral part is n bits long, then powers are 0 to n-1 from right to left. If fractional part is n bits long, then powers are -1 to -n from left to right.

Step 2. Add the partial results obtained by multiplying the powers with digits. The final result thus obtained after addition is the desired result. Consider the following examples to understand the conversion.

Example: Convert (1011)₂ from binary to decimal.

(1011)₂

Binary number           1         0         1        1

Powers of 2     =        2³        2²        2¹        2⁰

=        8         4         2        1

=     (8×1)+(4×0) + (2×1) + (1×1)

=      8+0+2+1

=      11

So (11)₁₀          =      (1011)₂

Fundamentals of Computers Notes

II. Decimal to Octal & Octal to Decimal

To convert the decimal number to octal number & octal number to decimal number, we have to use the following steps.

Decimal to Octal: Any number in decimal number system can be converted to octal number system, step by step process of conversion is:

Step 1. Divide the number by 8.

Step 2. Note down the quotient and remainder. Remainder will be any digit from 0 to 7.

Step 3. If quotient is not 0, then divide the quotient again by 8. Go to Step 2.

Step 4. If quotient is 0, then stop the process of division.

Step 5. The first remainder of the process is called Least Significant digit (LSD) and the last remainder is called Most Significant digit.

Step 6. Write all the remainders from MSD to LSD, from left to right. The combination of digits 0 to 7 thus obtained is the required Octal equivalent of number.

Example: (256)₁₀ Convert into Octal.

8	256 remainders
8	32-    0     LSD
8	4 –     0
	0 –     4     MSD

Writing remainders from MSD to LSD, we get (256)₁₀ → (400)₈

Octal to Decimal: Conversion of octal number to decimal number is not a very tedious job. To accomplish this task we follow the following steps:

Step 1. Multiply the whole octal number with powers of 8. These powers are. positive for integral part of number and negative for fractional part of number. If integral part is n digits long. then powers are 0 to n-1 from right to left. If fractional part is n digits long, then powers are -1 to -n from left to right. Consider the following examples to understand the conversion.

Examples: Convert (542)₈ from octal to decimal.

Powers of 8     =        8³        8¹        8⁰

=        64       8         1

=     (64×5)+(8×4) +(1×2)

=      320+32+2

=      354

Thus  (542)₈    =      (354)₁₀

Fundamentals of Computers Notes

III Decimal to Hexadecimal & Hexadecimal to Decimal

To convert the Decimal number to Hexadecimal number & Hexadecimal number to Decimal number, we have to use the following steps.

Decimal to Hexadecimal: For converting the number in decimal number system to the number in hexadecimal number system Step by step process of conversion is:

Step 1. Divide the number by 16.

Step 2. Note down the quotient and remainder. Remainder will be any digit from 0 or 9 or symbol from A to F.

Step 3. If quotient is not 0, then divide the quotient by 16. Go to step 2.

Step 4. If quotient is 0 or any digit or symbol less than 16, then stop the process of division.

Step 5. The first remainder of the process is called lest Significant digit (LSD) and the last remainder is called Most Significant digit (MSD).

Step 6. Write all the remainders from MSD to LSD, from left to right. The combination of any digit from 0 or 9 or symbol from A to F thus obtained is the required Hexadecimal equivalent of number.

Example: Convert (1498), from decimal to hexadecimal.

16	1498  remainders
16	93 –   A    LSD
16	5-      0
	0-      5     MSD

Writing remainders from MSD to LSD, we get

(1498)₁₀ (5DA)₁₆

Hexadecimal to Decimal: Steps to convert the number from Hexadecimal to decimal are:

Step 1. Conversion of hexadecimal number to decimal number is similar to other conversions. This time multiply the whole hexadecimal number with powers of 16. These powers are positive for integral part of number and negative for fractional part of number. If integral part is n bits long, then powers are 0 to n-1 from right to left. If fractional part is n digits long, then powers are -1 to-n from left to right. Consider the following examples to understand the conversion.

Example: Convert (4E6), from Hexadecimal to Decimal.

Powers of 16:  =        16²     16¹      16⁰

=        256       16         1

=     (256×4)+(16xE) +(1×6)

=      1024+224+6

=      1254

Thus (4E6)₁₆    =      (1254)₁₀

Fundamentals of Computers Notes

IV. Binary to Octal & Octal to Binary

To convert the binary number to octal number & octal number to binary number, we have to use the following steps:

Binary to Octal: Conversion of data from binary number system to the data of the other number system except decimal is very easy. Steps to convert binary number to octal number system are:

Step 1. For conversion divide all binary digits of the number to be converted in the groups of three bits cach. Start grouping from right to left.

Step 2. Now each of these groups of three bits each will be converted to decimal number system.

Suppose, b₁ b₂ b₃ b₄ b₅ b₆ is a binary number which is to be converted to octal number system. Proceeding according to step one we divide it into the groups of three bits starting from right to left. Thus we get two groups

b₁ b₂ b₃ and b₄ b₅ b₆

Now these groups will be converted to decimal separately. If O₁ and O₂ are two numbers:

such that (0₁)₈ (b₁ b₂ b₃), and (O₂)₈ (b₄ b₅ b₆)₂ then (b₁ b₂ b₃ b₄ b₅ b₆), = (0₁ 0₂)₈ For conversion, we use the following table which shows the binary equivalent of each octal digit.

Octal digit	Binary Equivalent
0	000
1	001
2	010
3	011
4	100
5	101
6	110
7	111

Example: Convert (110010011011)₂ from binary to octal.

Sol.

110	010	011	011
6	2	3	3

Therefore (110010011011)₂ = (6233)₈

Octal to Binary: Like binary to octal, this conversion is also very easy.

Step 1. Every digit of the number which is to be converted from octal to binary, is individually converted to the 3-bit binary equivalent using the table. The combination of 0 and 1 thus obtained is the desired result.

To understand it, let us consider a fictitious number say ABCD. Now suppose binary equivalent of A is aaa, B is bbb, binary equivalent of C is ccc and binary equivalent of D is ddd. Then

(ABCD)₈ = (aaabbbcccddd)₂

Example: Convert (275)₉ from octal to binary.

Sol. (275)₈ = 010 111 101

Thus, (275)₈ = (010111101)₂

Fundamentals of Computers Notes

V. Binary to Hexadecimal & Hexadecimal to Binary

To convert the binary number to Hexadecimal number & Hexadecimal number to binary number, we have to use the following steps:

Binary to Hexadecimal: Steps to convert the number from binary to hexadecimal are:

Step 1. For conversion divide all binary digits of the number to be converted in the groups of four bits each. Start the grouping from right to left.

Step 2. Now each of these groups of four bits each will be converted to decimal number system. Suppose, b₁ b₂ b₃ b₄ b₅ b₆ b₇ b₈ is a binary number which is to be converted to hexadecimal number system. Proceeding according to step one we divide it into the groups of four bits. starting from right to left. Thus we get two groups: b₁ b₂ b₃ b₄ and b₅ b₆ b₇ b₈.

Now these groups will be converted to decimal separately. If H₁ and H₂ are two numbers such that (H₁)₁₀ (b₁ b₂ b₃ b₄)₂ and (H₂)₁₆ = (b₁ b₂ b₃ b₄)₂, then (b₁ b₂ b₃ b₄ b₅ b₆ b₇ b₈), = (H₁H₂)₁₆

For conversion we use the following table which shows the binary equivalent of each hexadecimal digit.

Hexadecimal digit	Binary Equivalent
0	0000
1	0001
2	0010
3	0011
4	0100
5	0101
6	0110
7	0111
8	1000
9	1001
10 (A)	1010
11 (B)	1011
12 (C)	1100
13 (D)	1101
14 (E)	1110
15 (F)	1111

Example: Convert (110010011011)₂ from binary to Hexadecimal.

Sol.      1100     1001    1011

12         9          11

= (12, 9, 11)₁₆

Thus, (110010011011)₂ = (C9B)₁₆

Hexadecimal to Binary: Like octal to binary, this conversion is also very easy.

Every digit of the number which is to be converted from hexadecimal to binary, is individually converted to the 4-bit binary equivalent using the table. The combination of 0 and I thus obtained is the desired result.

To understand it let us consider a fictitious number say H₁ H₂ H₃ H₄ Now suppose 4-bit binary equivalent of H₁ is a₁ a₂ a₃ a₄ H₂ is b₁ b₂ b₃ b₄ binary equivalent of H₃ is c₁ c₂ c₃ c₄ and binary equivalent of H₄ is d₁ d₂ d₃ d₄ Then (H₁ H₂ H₃ H₄)₁₆ = (a₁ a₂ a₃ a₄ b₁ b₂ b₃ b₄ c₁ c₂ c₃ c₄ d₁ d₂ d₃ d₄)₂

Example: Convert (AB86), from hexadecimal to binary.

Sol.    1010    1011     1000     0110

= (1010101110000110)₂

Thus (AB86)₁₆ = (1010101110000110)₂

Example: (5D)₁₆ = (?)₂

Sol.          0101     1101

(01011101)₂

Fundamentals of Computers Notes

VI. Octal to Hexadecimal & Hexadecimal to Octal

To convert the Octal number to Hexadecimal number & Hexadecimal number to Octal number, we have to use the following steps:

Octal to Hexadecimal: For converting an octal number to hexadecimal equivalent, we have to use the following steps.

Step 1. Convert the octal number to its binary equivalent.

Step 2. Now convert this binary equivalent to hexadecimal number.

Example: Convert (375)₈ from Octal to Hexadecimal.

Sol.                            3            7          5

Binary value             011        111      101

4-4 pairs of digit       0000     1111    1101

Thus (375)₈ = (FD)₁₆

Hexadecimal to Octal: For converting any hexadecimal number to octal number system equivalent, we have to use the following steps:

Step 1. Convert the hexadecimal number to its binary equivalent.

Step 2. Now convert this binary equivalent to octal number system.

Example: Convert (18A), from Hexadecimal to Octal.

Sol.                            1            8          A

Binary value              001     1000      1010

3-3 pairs of digit        000       110        001      010

= (612)₈ Ans.

Example: Convert (24AB) 16 from Hexadecimal to Octal.

Sol.                             2           4          A             B

Binary value              010     100       1010      1011

3-3 pairs of digit        001      010        010       101       011

= (12253)₈ Ans.

Fundamentals of Computers Notes

Binary Addition

The binary number system contains two symbols 0 and 1. The rules for adding these two bits are as follows:

(i) 0     +     0     =      0

i.e. When zero is added to zero, we get zero.

(ii) 0    +     1     =      1

i.e. When one is added to zero, we get one.

(iii) 1    +     0     =      1

i.e. When zero is added to one, we get one,

(iv) 1    +     1     =      10

i.e When one is added to one, we get one-zero or we can say 2 as decimal equivalent of 10 (one-zero) is 2,

Binary Multiplication

The process of multiplication is nothing but repeated addition. In binary number system, the rules for multiplication are:

(i) 0  x  0  =  0

i.e. when zero is multiplied by zero, we get zero.

(ii) 0  ×  1  =  0

i.e. when zero is multiplied by one, we get zero.

(iii) 1  x  0  =  0

i.e. When one is multiplied by zero, we get zero.

(iv) 1  x  1  =  1

i.e. when one is multiplied by one, we get one.

Fundamentals of Computers Notes

Boolean Algebra

Boolean algebra is an attempt of representing the true-false logics of humans in mathematical form. George bole proposed the principles of boolean algebra in 1854 and hence the name Boolean Algebra. Boolean Algebra is used for designing and analysing digital circuits.

Meaning of Logic Gates

All operations within a computer are carried out by means of combinations of signals passing through standard blocks of built in circuits that are known as logic gates. In other words, a logic gate in simply an electronic circuit which operates on one or more input signals to produce standard output signals.

Computer circuits are built up using combinations of different types of logic gates to perform the necessary operations. The output signal of a gate is a simple boolean operation of its input signal. So gates are the basic logic elements. A boolean function can be represented in the form of gates.

There are seven types of gates.

AND, OR, and NOT are called basic gates.

AND Gate: An And gate is the physical realization of the logical multiplication (AND) operation. That is, it is an electronic circuit that generates an output signal of I only if all the input signals are also I.

OR Gate: An OR gate is the physical realization of the logical addition (OR) operation. That is, it is an electronic circuit that generates an output signal of 1 if any of input signals is also 1.

NOT Gate: A NOT gate is the physical realization of the complementation operation. It is an electronic circuit that generates an output signal which is the reverse of the input signal. A NOT gate is also known as an inverter because it inverts the input.

NAND Gate: It is a complemented AND gate, i.e. the output of NAND gate will be a 1 if any one of the input is 0 and output will be a 0 only when all the input are 1.

The NAND gate is said to be universal gate because it is alone sufficient to implement any Boolean function.

To show that any Boolean function can be implemented with the sole use of NAND gates, We need only show that the logical operations AND, OR and NOT can be implemented with NAND gates. A NOT operation is obtained from a one input NAND gate.

Thus we find that a single input NAND gate behaves as an inverter.

The AND operation requires two NAND gates. The first one produces the inverted AND and the second one being a single input NAND gate, acts as an inverter to obtain the normal AND output.

For the OR operation the normal inputs A and B are first. complemented using two single input NAND gate. Now the complemented variable are fed as input to another NAND gate which produces the normal OR output.

NOR Gate: It is a complemented OR gate. i.e. the output of NOR gate will be a 1 when all inputs are 0 and it will be a 0 if any input represents a 1.

To show that any boolean function can be implemented with the sole use of NAND gates, We need only show that the logical operations AND, OR and NOT can be impiemented with NOR gates.

The NOT operation is obtained from a one-input NOR gate. Thus a single input NOR gate is yet another inverter circuit. The OR operation requires two NOR gates. The first one produces the inverted OR and the second one being a single input NOT gate acts as an inverter to obtain the normal OR output.

The AND operation is achieved through a NOR gate with additional invertors in each input. So NAND and NOR gate are known as universal gate.

Fundamentals of Computers Notes

Application of Logic Gates

Multiplexer: Multiplexer is one of the basic building of a computer system which allows sharing of a common line by more than one input lines. It connects multiple input lines to a single output line,

At a specific time one of the input lines selected and the selected input is passed on to the output line.

The selection of a particular input line is controlled by a set of selection lines. Normally, there are 2 input lines and n selection lines whose bit combinations determine which input is selected.

Decoders: Much of the information in computers is handled in a highly encoded form. In an instruction, an n-bit field may be used to denote 1 out of 2″ possible choice for the action to be taken. To perform the desired action, the encoded instruction must first be decoded. A circuit capable of accepting an n-variable input and generating the corresponding output signal one out of 2″ output lines is called a decoder.

Encoders: An encoder is a combinational logic circuit that essentially performs a ‘reverse’ decoder function. An encoder accepts an active level on one of its inputs representing a digit, such as a decimal or octal digit, and converts it to a coded output, such as binary or BCD. The output lines generate the binary code for the 2″ input variables, for example:

Fundamentals of Computers Notes

A Decimal-to- BCD Encoder

This type of encoder has ten inputs-one for each decimal digit and four outputs corresponding to the BCD code. This is a basic 10-line-to-4 line encoder.

Karnaugh Map

Karnaugh maps is a convenient way of representing and simplifying boolean function of 2 to 6 variables. The stepwise procedure for karnaugh map is:

Step 1: Create a simple map depending on the no. of variables in the function. A map of 2 variables contain 4 value positions or elements, while for 3 variables it has 2¹ = 8 elements similarly for 4 variable it is 2¹ = 16 elements and so on.

Step 2: The next step in karnaugh map is to map the truth table into the map. The mapping is done by putting a 1 in the respective square belonging to the I value in the truth table. This mapped map is used to arrive at simplified boolean expressions which can be used for dreaming up the optimal logical circuits.

Step 3: Now, create simple algebraic expressions from the karnaugh map. These expressions are created by using adjacency of we have two adjacent I’s then the expression for those can be simplified together since they differ in only one variable. Similarly we search for adjacent pairs of 4, 8 and so on. A 1 can appear in more than one adjacent pairs.

Fundamentals of Computers Notes

Minimization of Boolean Expressions

Boolean Expression are formed using different variables and numbers. These are simplified by the following four methods:

1. Algebric expression
2. K-Map
3. Tabular method of minimization
4. Tree reduction

Here, we will study only K-maps.

K-Map: A graphical means to spot these adjacent terms was proposed by Karnaugh, hence the name Karnaugh Maps.

There are many types of K-Map

Two Variable Map: A K-Map is similar to the truth table in that all possible input combinations are enumerated. A K-Map is constructed by rearranging the truth table in a 2 dimensional format.

Three Variable Map: With three variables, there are a total of eight combinations. Each min-term must be adjacent to three cells.

The K-Maps for 3 variables is constructed with two columns of four rows are used here.

Four Variable Map: With four variables, there are a total of sixteen combinations.

Each min-term must be adjacent to four cells. The K-Maps for 4 variables is constructed with four columns of four rows.

Note that two variables define the labels on the four rows and two more variables define the labels of the two columns.

Computer

It is an electronic device or a flexible machine, which can manipulate data. These manipulations may or may not be mathematical. More accurately a computer may be defined as a device that operates upon data. Data can be anything like bio-data of various applicants when the computer is used for recruiting personnel, or the marks obtained by candidates in a competitive exams such as medical entrance, engineering entrance, civil service examination etc. Data comes in various shapes depending upon the type of computer application. A computer can store, process and retrieve data as when required. Due to the fact that computers process data is so fundamental that many people have started calling is a data processor.

Fundamentals of Computers Notes

Characteristics of Computer

The important factors that lead a person to use a computer are: Speed: Computers are very fast. They can process millions of instructions per second. Today, computers can perform 1000 million computations in 1 second.

Accuracy: Computers are accurate. They do not make mistakes in calculations. The probability of computer error is quite small and often traceable to faulty data.

Storage: Computers are having enormous storage capacity. Versatility: This is one of the most wonderful things about the computer. Computers can do a variety of jobs depending upon the instructions fed to them and their hardware characteristics. Modern computers can be used in railway, air reservations systems, process controls, nuclear reactors, manufacturing plants, scientific laboratories, hospitals and hotels etc. They can also act as controlling devices in children toys. Briefly, a computer is capable of performing any task provided that the task can be reduced to a series of logical steps.

Diligence: Computers are diligent in nature as they can perform complicated and respective tasks very well with full concentration, without committing any error, for long periods of time. Computers do not suffer from carelessness, boredom or tiredness.

Reliability: Computer systems are widely accepted due to their exceptional reliability. Computers are very reliable. Memory

Capability: Computer systems have the capability to recall the total data instantly and an almost unlimited capacity to store this data.

The above characteristics of computers enhance human capabilities of doing analytical work at high speed. They have no I.Q. They have no feelings and cannot work like human beings. Classification on the Basis of their Electronics

1. Analog Computers: These computers operate on inputs of continuously varying electrical voltage. They represent numbers by a physical quantity; i.e., they assign numeric values by physically measuring some actual property such as length of an object, angle or amount of voltage passing through a point in an electric circuit.
2. Digital Computers: These computers represent data as numbers or separate units. The digital computer can represent data accurately using as many positions and numbers as required. Adding machines and calculators are common examples of devices based on principles of digital computers.
3. Hybrid Computers: These computers are based on the best features of analog and digital computers. They are having the speed of analog computers and the accuracy of digital computers. Classification of computers on the basis of memory size and storage capacity.
4. Supercomputers (256 MB onwards): Supercomputers are basically designed for complex scientific applications. Therefore, there is a substantial increase in the speed of computation. The first supercomputer was built in 1960s for the U.S department of defence.

The speed of modern supercomputers is measured in nanoseconds and gigaflop. A nanosecond is 1 billionth of a second. A gigaflop is 1 billion floating-point arithmetic operations per second. Supercomputers can perform 128 gigaflop.

Cray’s XMP -1, 2, 3, CDC’s 205, ETA GF-10, NEC’s SX-25 Fujitsu’s VP-200 and 400 and Hitachi’s S-810/20 are some of the most popular supercomputers. Out of these ETA-10 is the fastest supercomputer.

The CRAY T3E supercomputer, configurable with 6 to 2048 processors, provides the computing power to tackle the world’s most challenging computing problems.

ILLIAC-IV was the first supercomputer. 64 different calculations could be made at a time i.e., it is equivalent to 64 different computers. It can execute instructions at the rate of 300 millions per second.

2. Mainframe (80-128 MB onwards): The earliest computers were called mainframes due to their enormous size. The term is still in use for the large computers of today but the models of mainframes are far more powerful. The storage capacity of these computers is very high and data can be processed very quickly. Big companies banks, government departments use mainframes.
3. Mini computers (20 MB onwards): These computers are at least 5 times faster than microcomputers having CPU speed of approximately 500 instructions per second.
4. Microcomputers (Up to 64MB): Microcomputer is the smallest type of computer available. It is called micro for two reasons (i) it is million times smaller in size than a unit quantity, (ii) it uses microprocessor.

Fundamentals of Computers Notes

Generations of Computer

1. The First Generation Computers: The first generation computer control was centralized in a single CPU, and all operations required direct intervention of the CPU. Use of ferrite-core main memory was started during this time. It uses virtual memory and index register. Punched cards were used as input device. Magnetic tapes and magnetic drums were used as secondary memory. Binary code or machine language was used for programming.
2. The Second Generation Computers: The transistor, an electronic device, was invented by Bardeen, Bratain and Shockley in 1951. Semi-conducting materials like silicon are used in manufacturing transistors. These devices are more reliable, cheaper and much smaller in size than vacuum tubes.
3. The Third Generation Computers: The advances in electronics technology continued and the advent of micro-electronics technology started the method of integrating large number of circuit elements into very small (less than 5 mm square) surface of silicon known as ‘chips’. This new invention of integrated circuits (ICS) defines the third generation of computers.
4. The Fourth Generation Computers: With the rapid advancement of IC technology, it became possible to integrate 30,000 components on a single chip. This technology was known as Large Scale Integration (LSI).
5. The Fifth Generation Computers: Unlike the human brain a computer cannot think on its own, but has to be given a very explicit, step-by-step, instructions to make it perform a task. There is a lack of creativity and imagination and the ability to reason logically. It does not have intuition and cannot draw conclusion without going through all the intermediate steps.

Fundamentals of Computers Notes

Parts of a Computer

Computers can be divided into Input Device, Central Processing Unit, Memory and Output Device.

Computers are known for their speed and accuracy. But to do some work i.e., to process it requires some data. Raw data is to be given to the computer which is expected to be converted into information after processing.

(A) Input Devices

To process, the computers need raw data. This raw data is to be input to the computers using certain devices known as input devices. Input devices transfer data into a computerized information system so that it can be processed. Remember, that the computer does not process information it processes data. The main input devices are as follows:

1. Keyboard: This device resembles a typewriter and is today the most widely used device to input information in the form of words and numbers. This layout of keys is called QWERTY because Q-W-E-R-T-Y is the order in which the letters occur on the top row of the keyboard.

Along with normal expected keys the special keys include, Control, Shift, Alt, Return, Escape, Arrow keys and Function keys. Applications make use of the keys according to their requirement. For example,

F2 is used by many applications to save data permanently.

FI is frequently used to provide context sensitive help to the users.

Page Up, Page Down, Home and End keys are used for cursor movements.

Caps Lock is used to type in capital letters.

Num Lock is used to toggle the use of numeric keypad available on the keyboard.

Shift keys can also be used to type in uppercase or lowercase according to the on or off state of the Caps Lock key.

2. Pointing Devices: When the interface is graphical one easier way of selection and feeding information to the system is the pointing device. Various pointing devices available are:

(1) Mouse: It comes in different sizes slightly bigger than Indian Match box. It rolls over a bearing. When the user rolls the mouse across a flat surface, such as desk, the screen cursor moves in the direction of the mouse’s movement.

(ii) Track Ball: It is something similar to the mouse but less complicated and designed for use by children. This has got a spherical ball, which can be rotated by fingers in various directions to affect screen movements.

(iii) Touch Pad: This is a small device, which can be embedded directly into various systems like laptops and notebooks. Pointing devices like mouse does not find place with such devices because they are mainly used for mobile computing.

(iv) Joystick: Joystick resembles a stick and is used as input device, specially, in game and multimedia software. The type of input from this device mainly comprise of the movement of cursor on the screen or movement of screen output in various game software.

(v) Touch sensitive screens: Small touch sensitive boxes are provided on the screen of the monitor itself, which act something like the function keys present on the keyboard.

(vi) Pen based systems: A light pen is another pointing device similar to any normal pen and can be used effectively to input data.

3. Data scanning devices: There may be need that the input is not to be given in words or numbers but through already available data typed on a page. Various available data scanning devices can be used to scan and input data through available documents.

Fundamentals of Computers Notes

Optical Recognition Systems

(a) Bar code reader (BCR) scans a set of vertical bars of different widths for specific data and are used to read tags and merchandise in stores, medical records, library books etc.

(b) Optical mark reader (OMR) this device is used mainly to recognize marks made by pencil or pen. The device can be used in various competitive exams where the method of examination is objective type and the candidates are required to fill the answer sheets with pencils.

(c) Optical scanners can be used to scan images, posters, magazine pages, other physical objects like ornaments etc., and can be directly stored into computers memory.

4. Magnetic Ink Character Recognition (MICR): The MICR system reads characters printed in a special magnetic ink into the computer. The main users of MICR are banks.
5. Optical Character Recognition (OCR): An optical character recognition system consists of a scanner and some software. The scanner is used to scan an image of a page of text to be read into the computer.
6. Voice recognition systems: These devices can directly take input in the form of human voice and translate it in digital form understandable by the computers.

(B) Processing Device

Central Processing Unit (CPU): Central Processing Unit is the main part of the computer. In other words, it is referred to as brain of the computer. This part of the computer controls all the functions of the computer.

Processor is an integrated circuit that contains millions and millions of transistors and other electrical components. The CPU is a mere small silicon chip, and yet it runs the whole computer. A processor is the heart component in a computer system.

Fundamentals of Computers Notes

Functions of CPU

1. Getting & Following the instruction: The central processing unit performs a couple of basic functions. First of all, in order for a computer to operate, it needs instructions to tell it what to do. It gets these instructions in the form of software. Software can come in two forms. Operating system software tells the computer how it is to be run, while application software are applications such as games, word processors, and media players. It is up to the CPU to decode what exactly the software instructions are telling the computer to do.
2. To Perform Arithmetical Operations: The Arithmetic/Logic Unit (ALU) is the part of the central processing unit that performs various calculations and comparisons. Some of its tasks are as simple as the basic operations of addition, subtraction, multiplication, and division, while others are so complex that it would take human beings years to complete.
3. Moving Data: In addition to interpreting and executing instructions, the CPU can also move data from one memory location to another. When data is stored in the RAM, the main memory of a computer, it is given an address.
4. Making Decisions: Another of the CPU’s basic functions is that it can make certain decisions about how the computer is operated, and based on these decisions, the CPU can jump from one instruction to another. It does not necessarily have to execute the instructions. The central processing unit also has a pipelining technology that allows it to perform many different instructions simultaneously. This technology helps to make the CPU extremely powerful.

Fundamentals of Computers Notes

Factors Affecting the Performance of CPU

There are many factors that influence the performance of a processor.

1. Data bus width, 2. Processor Clock rate, 3. I/O bus speed, 4.Internal CPU architecture, 5. Cache memory.

The details about the above factors are as under:

1. Data Bus Width: This refers to the size of the data bus in bits. The processor uses the data bus to transfer data between it and system memory and the secondary devices. The size in bits thus determines how many characters it can transfer at any one time. An eight-bit data bus transfers one character at a time, a 16-bit data bus transfers 2 characters at a time and a 32-bit data bus transfers 4 characters at a time.
2. Processor Clock Rate: This refers to the speed of the clock that drives the processor. Originally, the 8088 processor was released at 4.77 MHz. In general, a faster clock signal (higher) means the processor will perform operations faster. Today, Pentium processors run at speeds of 3200MHz or greater.
3. Input/Output (I/O) Bus Speed: This refers to the speed at which the Input/Output bus (to which peripheral devices like video displays and hard disks are connected) can run. The original IBM-PC ran the expansion I/O bus (called ISA) at 8MHz, but later units revised this to 10 or 12 MHz. The need for high bandwidth (lots of data in a short time) is necessary for high-resolution graphic displays, sound and video.
4. Internal CPU Architecture: Following are the various techniques to execute instructions faster than ever before.

(a) Branch Prediction: Branch prediction is a technique that attempts to provide proper next instruction address to the processor. Pipelined machines must obtain the next instruction before they have completely executed the previous instruction.

(b) Instruction Cache: I-Cache is a fast local memory that holds the instructions to be executed. When a program tries to access an instruction that is not yet in the cache, the CPU must wait until hardware obtains the desired instructions. This wastes the processor time. So larger cache enhance the performance.

(c) Pipelining: Pipelined machines have multiple instructions executing at the same time, but at different stages in the machine. This technique divides the execution of an instruction into sequential steps, using different micro architectural resources at each step.

(d) Speculative Execution: It is a mechanism that permits instructions to be started early. Results are collected in temporary storage. When required, these results are committed from temporary storage.

(e) Super Scaler: It is the ability to process more than one instruction per clock. The Pentium processors has two execution pipes. So it is super scalar level 2. The Pentium Pro processor can dispatch and retire 3 instructions per clock so it is superscalar level 3.

5. Cache Memory: To reduce the number of wait states, cache memory is used. The CPU can access the instructions stored inside cache at a faster rate than those stored in system memory. Cache memory allows the processor to run at full speed (zero-wait State). Most cache systems will run at about 98% efficiency. There are two level of cache system:

(a) Level One Cache: Level One (L1) cache is memory that is very high speed (can be accessed quickly with zero wait state) but small in size. The processor tries to read instructions or data from level one cache first. Early systems implemented L1 cache on the motherboard, with up to 128K or 256K of high-speed static memory.

(b) Level Two Cache: If the required data or instruction is not present in L1 cache, the L2 cache is tried next. L2 cache is a large size but slower speed than the LI cache. If the required data or instruction is not present in L2 cache, the system memory or L3 cache if there is one, is tried next.

Fundamentals of Computers Notes

Parts of the CPU

The main parts of the C.P.U. are as under:

1. Control Unit: The control unit supervises all of the CPU’s operations. It obtains the software instructions from the memory, and it also coordinates the times and order in which the instructions are carried out. For example, the control unit has a special feature known as the interrupt. An interrupt is a special signal that interrupts the task the central processing unit is currently performing. It will tell the CPU to put aside this operation and to instead begin work on another operation.
2. Instruction Decoder: The instruction decoder decode the instructions for CPU so that they can be executed & carried out.
3. Program Counter: The program counter is a special key. It advances by one whenever new instructions are picked up, and thus it sequentially goes through the tasks the CPU must perform. There may be certain instructions that can tell the CPU to jump to another set of instructions that are not next in the sequence.
4. Arithmetic/Logic Unit (ALU): As mentioned above, the arithmetic/logic unit is the part of the central processing unit that does the actual computing. Data is brought here, where it is operated on. The ALU cannot only do addition, subtraction, multiplication, and division, but it can also perform logical operations.
5. Registers: Registers are special storage location which located inside the CPU. The data contained here can be accessed much quicker than the data contained in other memory locations. Registers in different parts of the CPU are used for different functions. In the control unit, the registers are used to store the computer’s current instructions. Meanwhile, the registers found in the ALU, called accumulators, are used to store the results of the arithmetic or logical operations.
6. Clock: The clock is a timer that acts as a heartbeat for the central processing unit. Usually, small tasks might take up to several pulses before they can be finished. It is by this clock that we can calculate the speed of a processor. The speed of a CPU is measured in megahertz’s (MHz). Most modern computers have speeds of at least 3200 MHz.

Fundamentals of Computers Notes

(C) Memory

Memory is of two types –

(1) Internal memory: It is the primary memory or main memory. It is collection of registers with the associated circuits needed to transfer information in and out of the registers. These memories resides in the computer and forms the main part of CPU. These memories are very near to CPU, so the access time is very short. These memories are very compact in size and too costly as compared to other memories. So large volume of data cannot be stored in the internal memories.

Different types of internal or main or primary memories are RAM, ROM, PROM, EPROM.

Random Access Memory (RAM): RAM is an array of storage cell that stores information in binary form. This information can be randomly written into or read out of each storage element as required.

It is also known as read-write memory. This means that contents of this memory can be accessed, read and if needed can also be changed. This memory is volatile memory.

 Read Only Memory (ROM): ROM is that part of memory whose contents are permanently wired or sealed into the chip at the time of manufacturing. Any trial to change those contents is rejected by computer. That’s why it is known as Read only memory. This memory contains that information which is required every time necessarily when computer is on. ROM is a non-volatile memory.

(ii) External memory: It is also known as secondary or auxiliary memory. It is not the permanent part of a computer i.e. availability of these memories is optional in a computer. It is attached to the computer if required. These are located far from CPU within a computer, so access time is more. These memories are very spacious and can store bulky data. Also they are cheap as compared to primary memory. All backup storage devices are secondary memory.

Fundamentals of Computers Notes

Magnetic Disk

Magnetic disk is a rigid plastic disk coated with an oxide for easy magnetization. The operation principle is similar to the functioning of the gramophone records. There, the sound waves are converted to the electromagnetic signals and stored on the record surface and while playing reverse process occurs i.e. the electromagnetic signals are converted back to sound waves. In magnetic disk the data is stored in the form of magnetic spots.

Magnetic disk is infact a pack of many plastic disks. Many plastic disks are placed together one over each another to form an hard disk. One magnetic disk place i.e. hard disk may consist 5 or more disks which can be used from both the sides. All these disks are covered by a metallic shield to form one hard disk.

 

Magnetic Tapes

Magnetic tape is an another backup storage device. It is a plastic tape similar to a tape recorder cassette. Magnetic tape is 0.5 inches wide and 2400 feet long. The length of tape can vary but normally 2400 feet long tapes are available. This tape is coated with an oxide for easy magnetization. The tape is wound on a spool. All the things including read/write head are mounted on a tape unit. This tape passes through read/write head and wounds up on pickup tape reel.

Like magnetic disks, the magnetic tapes also have tracks. These tracks are linear and parallel to each other along the length of the tap.

This means for 2400 feet of tape, cach track is 2400 feet long. Their are either 9 or 7 tracks in a tape. If tape has seven tracks, then 6-bit BCD with one parity bit is used. If tape has 9 tracks then 8-bit EBCDIC code with one parity bit is used.

Compact Disk-read Only Memory (CD-ROM)

CD-ROM means Compact Disk-Read only memory. These ar known as optical disks also. Usually they consist of a single removable plastic or metal disk coated on one side with tellerium. They are protected by a 1 mm layer of transparent plastic. In this storage device the information is stored in compact form. The data is stored in the form of minute pits which are burned into the tellerium coating with a laser beam. These pits, which are too tiny to be visible by naked eyes (size is about one micron), are stored in the tracks on disk.

Fundamentals of Computers Notes

(D) Output Devices

The input data are to be processed and need to give certain output The devices used to take the output from the computer are known as output devices. An output device takes data from the computer and converts this into information in a form, which is normally understandable by humans. Various output devices available are:

Monitors: It is also known as video display units (VDU) or simply screen. This is the most widely used medium to view the output. An image displayed on the screen is made up of lots of dots called pixels. If you look closely at the screen you may be able to see these pixels. The resolution of the screen is “how many pixels there are up and down and from left right across the screen.”

SVGA is usually 800 x 600, Displays with lots of pixels are called high resolution. Displays with fewer pixels are called low resolution. High-resolution display can show much more detail than low resolution ones and are required for applications, such as Computer Aided Designing and Multimedia.

Audio output: This unit permits the computer to talk back to us This makes computer an excellent interactive medium to work with All the sounds needed to process the possible enquiries are pre-recorded on a storage media. Each sound is given a code when enquiries are received. The processor follows a set of rules to create a reply message in coded form.

Printers: The hardcopy of the data stored in the computer’s memory is taken through printers, which is also an output device like VDU. Printers can also be classified according to their nature. These are needed to produce a hard copy output. Unlike images on a screen hard copy can provide a permanent record of work and can be looked at away from the computer. Hard copy can be obtained using a printer or a plotter. There are lots of different types of printers and plotters available. They vary in the method they use to produce hard copy and the cost and the quality of the hard copy they produce. Different devices are suitable for different applications.

Printers can be divided into the following categories:

Impact printers: The technology uses the direct mechanical contact between the print head and the paper. These use variations of standard typewriter printing mechanism where hammer strikes paper through linked ribbon. Because of the hammering action impact printers are noisy when they are printing. Various types include solid font and dot matrix printer.

Other available impact printers are:

Daisy Wheel Printer: Daisy wheel printers are rarely used any more. A daisy wheel printer hammers character stamps (like those on typewriters) against a ribbon to produce high quality text output. The character patterns are all arranged around the edge of a wheel. When a letter is to be printed the wheel rotates so that the correct letter is against the ribbon. A hammer then hits the letter against the ribbon to print it on the paper. Daisy wheel printers are very slow and noisy. It is not possible to print graphics using a daisy wheel printer.

Line Printers: Dot matrix and daisy wheel printers both print only one character at a time. For that reason they are called Character Printers. In contrast a line printer prints a whole line (typically 80 or 132 characters) of text at a time. These printers are very fast. They are expensive to buy and are used when high volumes of output are required. Example applications include printing telephone bills or bank statements.

Non-impact printers: These printers use technology where there is no direct contact between the print and paper giving longer life to the print head. They print characters by spraying small drops of ink on to paper. Because there is no hammering action non-impact printers are very quite but cannot print multiple copies using carbon paper. Examples include inkjet, laser printer etc.

Laser Printer: Laser Printers are called Page Printers because they print a whole page at a time. A laser beam is used to draw the image to be printed onto a light sensitive Drum. After the image has been drawn on the drum, fine powder ink called Toner is put onto it. The toner only sticks where the laser has drawn the image. The paper then passes over the drum and the toner is transferred onto the paper. Laser printers produce very high quality output, are very quiet and very fast. Typical home laser printers can print 8 pages per minute (ppm). Some industrial versions print over 40 ppm and can print on both sides of a piece of paper at the same time. The main disadvantage of this type of printer is the high cost.

Inkjet Printers: Inkjet printers are the most popular type of printer for use at home or in a small business. This is because they are relatively cheap to purchase and can print in colour. Inkjet printers generate output by squirting tiny jets of ink at the paper to be printed on. Typically inkjet printers can produce 360 or 720 dots per inch (dpi) but these dots are larger than those that a laser printer makes so the quality, although very good, is not quite as perfect. Ink-jet printers can work in black and white or colour.

Plotters: Plotters use pen or inkjet approaches. It can be used in case of a computer system dedicated to design work where the CPU may send output directly to a plotter. Plotters are normally very slow in motion because of the excessive mechanical movement required during plotting. The computer program controls the colour and amount of ink placed on the paper.

A plotter can be used to produce very large drawings on paper sizes up to A0 (16 times as big as A4). A plotter draws onto the paper using very fine pens. There are two types of plotter. They differ in the way that pen can be moved about on the piece of paper to draw lines. Various types of plotters include drum and flatbed plotters.

Flatbed Plotters: The paper is fixed and the pen moves left and right up and down across the paper to draw lines.

Drum Plotter: The pen moves up and down on the paper and the paper is moved left and right by rotating a drum on which the paper is placed. Plotters can automatically change their pens and so can produce colour output. The lines drawn by a plotter are continuous and very accurate.

Plotters are very slow but produce high quality output. They are usually used for Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM) applications such as printing out plans for houses or car parts. The quality of the output produced by inkjet printers is now very good and large format (big) inkjet printers are steadily replacing plotters for most tasks.

Fundamentals of Computers Notes

Software

Software can be classified into three categories:

1. System software
2. Application software
3. Utility Software
4. System Software: These are the software which control the performance of a computer system. They help in controlling the various functions of a computer system like loading or unloading of any software in the main memory, creating new files, storing new files and so on. They control the various functions of the hardware connected to the system..

(i) Operating System: It is an interface between a computer and its user. An operating system controls all functioning of a computer. It works as a traffic manager. It acts as a medium between the user and the various hardware. An operating system is nothing but a set of programs with the specific task of managing the entire systems.

MS-DOS, Windows and Unix are the some examples of operating

Previously, MS-DOS was a very commonly used software, but now-a-days, Windows is the most popular. Earlier versions of Windows Windows 3.0, 3.1 and Win 3.11 were based on DOS environments. In 1995, Windows-95 was launched. The 95 version of Windows worked as an operating system as well as an environment.. We can work with DOS if required in this version.

After Windows-95; Windows-98, Windows 2000, Windows ME and Windows XP came up with various improvements.

(ii) Language Translator: You have learnt about some computer languages. You already know about Low Level and High Level Languages. You are also aware that computer only takes instruction in Machine Language, which is a Low Level Language while we mostly work with High Level Languages. Is coder to convert High Level Language programs to Low Level Languages instructions, the computer uses something called a translator Language translati a system software which translates a High Level or Assembly Language program into Machine Language (Machine Language is comprehensible to the computer).

These are of three types:

(a) Assembler (b) Interpreter (c) Compiler.

You have already learnt about these in detail. Here let us quickly discuss them in brief.

(a) Assembler: This is a translator that only works on Assembly Language. It converts Machine Language codes to Assembly Language instructions and vice versa.

(b) Interpreter: Interpreter converts High Level Language (HLL) programs to Machine Language. It works on one line of at program at a time. It translates one line of the program and then moves on to the next. If there is an error on the line, it reports the same and stops the execution of the program.

(c) Compiler: A compiler also works on a HLL program and converts it to Machine Language and vice versa. But unlike an interpreter, a compiler works on the program as a whole. If it encounters any error, it reports the same together with the line numbers where the error occurred. Once the errors are removed, an executable file is made to run the program.

2. Application Software: These are readymade software. They are designed for different purposes. These software may be written in any language. These days C is the most popular language for writing application software. All these software are available either for common applications like Word Processing or Database Management System.

There are the two types of application software.

(i) User Developed or Customized Application Software: These softwares are the programs written by the computer programmer in order to perform some specific job for some particular user. These packages are developed exactly according to the user’s requirement and generally with the intervention of user. These include packages for company payrolls, accounts related packages, inventory control system etc.

(ii) Standard Package or Standard Application Software: These are the collection of packages which have been designed to be used together. This package is an integrated set of package with different facilities for common user. These software is developed by the expert software developers.

Some application software are:

DBMS: A Database Management System organises various kinds of data and stores them for future use. Some popular DBMS are FoxPro, SQL Server, MS-Access, etc.

Word Processor: These software are used in offices and shops for writing letters, applications, reports, etc. Some word processors are MS-Word, WordPad, Notepad, etc.

Spreadsheet: These software are used for calculating numeric figures. Charts and tables can very easily be made with these software.

Some spreadsheet software are MS-Excel, LOTUS 1-2-3, etc.

Graphics: These software are used for computer designing. You can make any design with these software. Some graphics software are CAD, CAM, CorelDraw, Adobe Photoshop, etc.

There are some other application software which are developed in accordance with the needs of the users. For example: Inventory System, Airline Reservation System, Payroll System, Hotel Management System, Hospital Management System, School Management System, Library Management System, etc.

3. Utility Software or Service Programs: These programs are useful for maintaining software and hardware. These are requested by many application programs. For example, Virus Scanner, Disk Defragmenter, Disk Cleanup, Editors, Dump, Linker and Loader are used to enhance the working of the computer.

There are the two main program in utility software given below:

Disk Defragmenter: Defragmentation is a process that reduces the amount of fragmentation in file systems. It does this by physically organizing the contents of the disk to store the pieces of each file close together and continuously.

Virus Scanner and Remover: Virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. All computer viruses are manmade. A simple virus that can make a copy itself over and over again is relatively easy to produce.

Antivirus (or anti-virus) software is used to prevent, detect, and remove malware, including computer viruses, worms, and trojan horses. Such programs may also prevent and remove adware, spyware, and other forms of malware.

Fundamentals of Computers Notes

Operating System

An operating system is a set of programs that is used to manage the various resources and overall operations of a computer system. It provides a link between the user and computer software & hardware. It basically work as a resource manager. You can think of operating system as a policeman who directs traffic at a busy intersection.

Types of Operating System

There are two type of operating system:

Single User System: One such operating system is MS-DOS. This is Microsoft disk operating system. This is used on micro computers. MS is the registered trademark of Microsoft.

Multi User Systems: These are large computers which works in the multiprogramming or multiprocessing or time-sharing or any other multi-user mode. There are several common operating systems for various types of personal computers. Each operating system has a very different usage. Most common of them are: DOS, Windows, Unix, etc.

DOS: DOS stands for Disk Operating System. It is the second most widely used operating system. Although it is just DOS, yet there are two version of DOS, PC-DOS and MS-DOS. PC-DOS is a window based on Disk Operating System whereas MS-DOS stands for Microsoft Disk Operating System. The two operating systems are nearly identical but there are different utilities which make one different from the other.

Windows: In the early 1990s, a US based company known as Microsoft developed Windows. Windows is the most common and widely used operating system. Infact, now-a-days, almost all the computers have Windows as operating systems. The reason for Windows being so popular is its easy usage. The user does not have to remember thousands of commands while working in a software. Windows is considered to be the first GUI (Graphic User Interface) for computers where the user can communicate with the computer with text as well as graphics. ndows is also a mouse friendly operating system where the user can use a mouse alongwith the keyboard.

Unix: Unix is the short form of Uniplexed information and computing system. Unix is a large, complicated operating system which can run several programs at the same time. It also has an additional feature that many people with their keyboard and monitor can use the same computer at the same time. Basically Unix is installed on large computers, namely, mainframe and mini computers. Whereas another version of Unix, i.e., XENIX is installed on micro computers. The biggest drawback while using Unix is its text interface. You need to remember all the commands while using a Unix Operating System.

Linux: This is a more developed version. It is used in place of Unix.

Windows NT: This is developed by the Microsoft company. This type of operating system is used for providing the network facility.

OS/2: This system is developed by the IBM.

DOS

MS-DOS or Microsoft Disk Operating System provides you the facility of a text user interface, which means we can only make changes and work upon text using this OS. MS-DOS allows the user to interact with the computer by typing a set of commands in order to get the required job done. The main functions of MS-DOS is to manage the computer, execute programs and interpret commands. DOS is already installed in the memory of a computer. The user can start working by typing in commands and unprocessed data when you see the DOS prompt.

Types of DOS Commands

MS-DOS consist of three files 10.sys, MS-DOS.sys and command.com. MS-DOS has two types of commands.

1. Internal 2. External

Internal Commands: These are the simplest most commonly used commands. These are loaded into memory at the time of booting i.e. they are loaded when the three basic files IO.sys, MS-DOS sys, and COMMAND.COM are loaded because they are part of a file named COMMAND.COM. When you list the directory of your DOS Diskette the internal command are not seen. Because no such files are exist on Disk. Few internal commands are DATE, TIME, DIR, VOL, etc.

External Commands: These commands are stored on disk in the form of files. When we run any external command, we have to read its corresponding file each time. These files can be Copied, Deleted or Renamed. Few external commands are TREE, XCOPY, MODE, MORE.

Rules For Naming The File & Directories

The names of files are kept in a directory on disk. File and Directory name can be divided into two parts primary name and secondary name or extension.

In DOS, Primary name may contain maximum eight characters and secondary name may contain maximum three characters. Secondary name is optional. So file name may contain maximum 11 character. The primary name and secondary name is separated by (.) a dot. File name or Directory name may contain any of the following characters A-Z or a-z, 0-9, $, 4, #, @, !, (, ), {, }, ~ etc. User cannot include any space anywhere.

Some valid names are XYZ,  ABC, X.BAK,  A1.BAK, AB$, OBC etc.

Fundamentals of Computers Notes

Internal Commands

DATE: This command sets the system date. It displays the current date and allows you to enter new date. Syntax: DATE [mm/dd/yy]

VER: It displays the current version of DOS in which you are working.

Syntax: VER

VOL: It display the volume label of specified disk in a specified drive.

Syntax: VOL [Drive]

Examples: VOL: Display the volume label of current drive.

VOL A: Display the volume label of drive A.

CLS: This command clears the screen.

Syntax: CLS

DIR: This command lists the files and the subdirectories in a directory except the hidden system files such as IBM BIO.COM and IBMDOS.COM; even if present.

DIR [d:] [path] [file name] [/w] [/p]

Example: DIR C:

display the contents of the current working directory on drive C.

MKDIR: It creates a subdirectory in the specified disk.

Syntax: MKDIR [d:] path

or MD (d:] path

For example: MD/FORTRAN: It will create a subdirectory namely FORTRAN under the root directory.

CHDIR: It is used to change the directory.

Syntax: CHDIR [d:] [path]

OR

CD [d:] [path]

CD..→ To come to the parent directory of current directory

CD\→To come to the root directory.

CD F:\Batch New To go the the directory “NEW” which is created in the directory “batch” which itself presents in root directory of drive F.

RD Or RMDIR: It is used to remove the directory.

Syntax: RD [d:] [path]

To remove a directory, it is essential that directory must be empty and directory must be empty and directory must not be current. COPY CON: It is used to create a new text file.

Syntax: Copy Con [d:] [path] [file name]

We will close the file by using ^Z or F6 key. To cancel the creation of file we will use ^C i.e. it will not save on the disk.

DEL OR ERASE: This command is used to delete files which is present on disk. Wild cards can be used with this command.

DEL [d:] [path] <file name>

OR

ERASE

REN: This command change the name of file.

Syntax: REN [d:] [path] <Old name> <New name>

Copy: This command is used to make the copies of existing file. We can copy more than one file by using wild cards a literals instead of file name.

COPY [d1:] [Path 1]<Source file> [d2:] [Path 2] <Target file>

Path: This command is used to set a search path for program file having extensions EXE, COM, BAT.

Syntax: PATH [dl] [directory]; [d2][directory]……….n

Maximum length of command search path is [2] character.

Tree: This command displays all directories and subdirectories including files.

Syntax: Tree [d:] [/f]

where

d=specifies the drive

/F=displays all paths and file name in the directories

XCOPY: This command copies files, subdirectories and lower level directories of they exists.

Syntax: XCOPY [d :] [Path] [file name] [d] [path] [file name] [(/A)] [/D: date] [/E] [/M] [/P] [/S] [/V] [/W]

ATTRIB: This commands set or reset the file single file, for selected files or all files in a directory.

MODE: This command sets operation modes for devices. Its format for display modes is MODE n

where n-to, 80 and Mono

DISKCOPY: This command copies the contents of the diskette in the source drive to the diskette in the target drive.

FORMAT: This command formats the disk to the specified disk Formatting analyzes the entire disk for any objective tracks and prepare the disk to accept MS-DOS files. Be careful before formatting any disk, particularly a fixed disk because formatting destroys all data on the disk.

CHKDSK: It is used to check the disk and display Disk volume label, Total disk space, No. of bytes in hidden files, No. of bytes in directories, No. of bytes in user files, No. of bytes in bad sector, No. of bytes available on disk, Total bytes used by memory, Total bytes available for memory.

BACKUP: This command is used to make backup copies from one disk to another.

SORT: This command read sorts and sends the data to the screen, file or to another device. Sort to arrange data in an order. Syntax: SORT [d:] [path] [file name] [/r] [/+n]

More: This command is used to simply prints the data a screenful at a time and prints “more” at the bottom of the screen until you press a key.

Syntax: MORE

Pipe (:): You have seen already: (vertical bar) sign. It is known as pipe sign. A pipe is a command that directs the output of one function or program into another function or program.

Fundamentals of Computers Notes

Redirection of Output and Input

Redirection is ability to send output from a process to somewhere different from its usual destination. Greater than sign (>) and less than (<) sign are used for redirection.

> Redirects the output to a command to a file or to a device other than the monitor.

< Redirects the input to a command from a file or device other than the keyboard.

For example: DIR: SORT > PRN

print a directory listing in alphabetical order. So> Sign redirects the output. Output of the DIR; SORT command goes to the printer and print a list.

SORT<AL.TXT

The less than sign instructs SORT to take its input from the file instead of keyboard.

Fundamentals of Computers Notes

Creation of Batch File

Batch File: A batch file contains a series of commands that DOS executes sequentially whenever you enter the name of the batch file. The Batch file name must contain the extension.BAT to execute.

Creating Batch File: You can create a batch file using copy con command or any other editor or word processor. While saving the batch file. Use the extension.BAT to the file name.

Fundamentals of Computers Notes

Using COPYCON Command

COPYCON Filename.BAT

Where [file name] specifies the name you wish to assign to the batch file. After entering this you simply type each command statement in the order you wish it to be processed. Finally you shall terminate the line by pressing the ENTER key.

After you have entered all the command statements, you save on disk by pressing CTRL-Z or by pressing F6 and the Enter key. Various Batch File Commands

Any command that you can enter at the command prompt, you can put into a batch file. DOS offers several commands that are particularly useful in batch file. The CLS, REM, ECHO, PAUSE and CALL commands are almost always used in batch files rather than at the command prompt.

REM: This command creates notes or comments in your batch program. These notes help document what a program does for eg: REM: This program list all the .Fxp extension files.

ECHO: When you run a batch file its command are normally echoed (displayed) on the screen as they are expected. You can use the ECHO command to control the screen output of a batch file.

ECHO ON: Turns on echoing for all subsequent commands in a batch file.

ECHO OFF: Turns off echoing for all subsequent commands in a batch file.

ECHO: Display a blank line.

PAUSE: This command temporarily halts the execution of a batch file to give the user time to read on screen message. When you issue a Pause command in a batch file, the execution of that file is temporarily halted and the message.

CALL: You may need to run a batch file within another batch file. You can use the CALL command to call its batch file.

The syntax of the CALL command is:

CALL [d][path] file name

Fundamentals of Computers Notes

Windows

Windows is the operating system that controls the overall activity of a computer.

There are various types of operating system such as DOS, Windows, Unix, Linux, etc. Now-a-days Windows is the most popular operating system.

Ms-Windows is the Microsoft wide interactive network development for office-work solution.

Features of Windows

Windows is a user-friendly operating system. There are many features which make it very popular. Some features of Windows are given below:

1. It is a GUI (Graphical User Interface) based operating system. It allows you to work on a computer in an easy and interesting manner. A GUI means the use of pictures, menus, icons, sounds, messages, etc.
2. In Windows, you can give commands with the help of a mouse and do not need to remember the command.
3. Windows allows you to do multi-tasking on the computer i.e. it can run several programs simultaneously. You can type documents while listening to songs.
4. Windows is object-oriented. Every object has properties and behaviour. For example: My Computer, Recycle Bin etc.

Fundamentals of Computers Notes

Basic elements of windows

Basic elements of windows are as follows:

Desktop: The area on the display screen where icons are grouped is often referred to as the desktop because the icons are intended to represent real objects on a real desktop. It is the interface through which all of the programs are accessed.

Elements of DeskTop: While there may be more or less options enabled on a particular display, we would discuss the basic elements. The Windows desktop is comprised of three key elements:

1. Icons
2. Start Menu
3. Taskbar
4. Icons: Icons can be further classified into five categories:

(i) Folder Icons: When a folder icon is double clicked, a folder

window is opened displaying the contents of the folder.

(ii) Program Icons: When a Program icon is double clicked, the corresponding program is loaded into the memory of the computer and the application starts running in a Window.

(iii) Document Icons: When a document icon is double clicked, the document itself is opened. Windows starts the application (Word processing program, spreadsheet, database, etc.) in which the document was created, and then opens the document (data file) itself.

(iv) Shortcut Icons: Shortcut icons provide an alternate way to open programs, documents, and folders. Shortcut icons are indicated by a little curved arrow in a box in the lower left hand corner of the icon and their labels generally begin with “Shortcut to.” Deleting a shortcut icon does not delete the program or file; only the shortcut that leads to it is deleted.

(v) System Icons: System icons are mandatory programs or files that are located on your desktop: User is not allowed to delete the system icon, since deleting the system icon would mean deleting the actual program from the hard drive of the computer. Examples of System Icons are Recycle Bin, My Computer, Network Neighborhood etc.

(a) Recycle Bin: Any file that is deleted from the hard disk of the computer is moved to a separate folder called Recycle Bin. The files stored in the bin can be restored to their original location by using the “Restore’ option of Recycle Bin. ‘Restore’ option can be accessed by right clicking on Recycle Bin icon.

(b) My Computer: My computer displays icons representing various resources available to your computer. These includes floppy drives, CD-ROM drives, hard disk drives and also any network resources you are connected to such as printers and network drives. Double click these icons to see the contents.

(c) Internet Explorer: Double click the Internet Explorer icon to browse web pages on your local network and/or on the Internet.

(d) Network Neighborhood: If your computer is connected to a network then the “Network Neighborhood” icon will be displayed on the desktop. Double-clicking this icon will open a Windows that displays other computers and resources, like printers, connected to the network.

2. Start Menu/Button: The start button is located at the bottom of your screen when you start windows for the first time. By default this is always visible when windows is running. You will use the start button to start programs, open documents, change system settings. Find item on your computer, get help and more.

To see the start menu, which contains everything you need to begin using windows, click the Start button. The following list briefly describes each command on the start menu.

Program Manager: You can find your old program groups by clicking the Start button and then pointing to All Programs. Your groups appear as folders on the All Programs menu.

File Manager: To manage your files, click the Start button, point to All programs, and then click windows explorer, your directories appear as folders.

MS-Dos Prompt: To open as MS-Dos window clicks the Start button, point to All Programs Accessories, and then click Command Prompt.

Print Manager: To set up a printer or look at information about documents you click the Start button, point to Settings, and then click Printers and Faxes.

RUN Command: To use the Run command, click the Start button and then click Run. You can either type the name and path of the Programs that you want to start or you can just specify the name of the program. You can execute MS-DOS based and windows based programs, open folders and connect to network resources by using Run.

3. Taskbar: The Windows taskbar is located at the bottom of the desktop. The taskbar usually stays on the screen all the time. It is comprised of several elements. Start button is also an element of the taskbar. The other elements of Taskbar are Quick Launch Toolbar and System Tray.

Fundamentals of Computers Notes

Anatomy of A Window

The various parts, a user can see while working with Windows, are as below:

(i) Application Window: It contains a running application. Application Window have menu bars and may also contain one more document Window,

(ii) Document Window: It contains a document used by an application. Generally, document windows appear within application windows are often referred to as child windows. This is because document windows close when you exit the application.

(iii) Title bar: This is the area located at the top of a window (just inside the border) which displays a window name. You can move the window by dragging the title bar.

(iv) Menu bar: Menus provide access to available commands. Menu bar contains different menu items. Click menu name or press ALT and type the underscored character in the menu name to open a menu.

(v) Window border: This is the area framing the window. Note that the border is separated into vertical, horizontal, and corner segment. Click and drag the border to resize the window.

(vi) Corner border segment: Click and drag the corner border segment to resize the window.

(vii) Vertical scroll bar: This is the area located to the right of a window (just inside the border) which is used to scroll (up/down) through a window’s contents. Click and

(viii) Scroll box: This is located within the scroll bar. drag the scroll box to move with in the windows.

(ix) Minimize button: Minimize reduces a window to an icon. This puts aside the current window temporarily and includes it in the taskbar located at the bottom of the desktop. The program has not been cancelled but merely set aside.

(x) Maximize button: Maximize expands a window to fill the entire screen area. The current window is enlarged to take up the full screen.

(xi) Restore button: The Restore button restores an icon or document window to its previous size. This is the size of a window before being either maximized or minimized. This is the only time that the size of the window can be changed.

(xii) Close button: This button is located on right most position from the array of three buttons on the top right corner of the window. This button can be used to close the window.

(xiii) Control menu: This menu is found on the top left corner of the window. Some applications represent it with their icons. This menu contains commands for manipulating the windows such as, closing the window, restoring the window, moving the window, resizing the window, minimizing the window, maximizing the window.

Fundamentals of Computers Notes

Working With Windows

Opening a window: To open a window or to run a program, you have to double click your mouse on the icon. In Windows files and folders are also represented as icons. To view the contents of a folder or the file the same procedure can be followed. When you double click a file icon the application associated with the file will be launched automatically and that particular application will open the specified file.

Closing a window: To close a window you can do it in more than one way:

(a) Choose File menu item from the menu bar and choose Exit or Close for programs and folders respectively.

(b) Click the Close button found on top right corner of the window.

(c) By using the Control Menu found on the top right corner of the window.

Moving a window: The window can be moved if it is not in a maximised state. The window can be moved by dragging the Title bar of the window.

Sizing a window: This action can also be performed the window is not in a maximized state. You can size or resize the window by dragging the border of the window. The control menu also provides the option for sizing the window. This helps in sizing the window through keyboard. If you select the size option from the control menu. Windows will display the four-sided arrow. Press the arrow key that corresponds to the side of the window (Right arrow corresponds to right side and so on.). Windows will place a sizing arrow on the corresponding frame. Using your keyboard arrow keys, you can then increase or decrease the window’s size. When the size becomes according to your requirements press Enter key.

Fundamentals of Computers Notes

Windows Explorer

The windows explorer displays files and directories in the system and allows easy navigation through the directories. The folders and the files of the hard disk and floppy drive, network, Control panel, printers, Desktop and Recycle Bin are all displayed in the explorer.

Fundamentals of Computers Notes

Computer Network

A computer network is a collection of computers and peripheral devices connected together by communication links, cables so that they can exchange information and allow the network components to work together.

The network components may be located at many remote locations or within the same office of an organization. All the computers in the network are hooked together with cables. To make the system work, a special network adaptor is needed inside your computer, which connects your computer to the other computers and to the mainframe.

The inter-connection of the computers is done through a communication link also known as physical layer of the network. This link maintains the transparency of the network to the users sitting at far away places. For creating communication link some interfacing software are used which are known as protocols. These protocols enable any user to access another computer, database, application program in another location.

Fundamentals of Computers Notes

Need of Networks

Computer network has conquered the dimensions of time and space both. Computers can process data so quickly that it is justified to say that computer conquers time. Space constraints are removed by the computer networks. oday, network is a need of every office, organization, company, institute etc.

Computer networks are used for electronic mail, teleconferences etc. While sitting in front of a computer, you can collect information about any place, institute etc. This can be done with the help of a program called Netscape Navigator. You can talk to your friend through a special software sitting thousands of miles away from you and see his face on the screen.

Fundamentals of Computers Notes

Types of Networks

On the basis of geographical distances the Network can be categorized as LAN, MAN & WAN.

(1) LAN: The small Computer Network that are confined to a localized area like an Office, Building or a factory are called Local Area Network (i.e. LANs). The diameter of such Network is not more than few Kilometers.

It is a network of computers largely located in vicinity such as a floor of a building or a building itself. They developed from point-to-point connections, where single wire joined the two systems.

These typically have the following characteristics:

Cover small geographical area.

Cables with twisted-pair wire, Coaxial or fiber-optic cable.

(ii) MAN: When a Network is spread over a city, it is called Metropolitan Area Network (i.e. MAN). For example, a cable TV Network that is spread over a city.

(iii) WAN: WAN stands of Wide Area Network. When the organization is spread over a wide area, it is becomes more difficult and costly to link them through cables. For this situation the various units of the organisation are linked using Wide area networks.

Fundamentals of Computers Notes

LAN Topology

A network topology is defined as the physical layout of the network in which all the devices are connected. This includes all the hardware that makes up the network. The points of connection to the network by the stations are called Nodes or link stations. Several types of topographical design and strategies are used to implement LAN. The majority of these are based on three types of topologies given below.

1. Star Topology: Star topology comprises of a number of stations connected directly to a central station or controller. Communications on the connecting links between the stations and the central station of star topography can be bi-directional and are point-to-point. A station on this type of network passes an information frame to the central controller, which then forwards the information to the destination station. The central controller manages and controls all communications between stations on the network. Failure of station on a star network is easy to detect and can be removed from the network.
2. Bus Topology: Bus topology comprises of stations that are connected to a single communication line. This single communication line is referred to as a bus. Information frames originating to a station are propagated away from the station in ooth directions on the bus. Each station on the bus interrogates the information frame destination address field for its own address. If the destination field does not match the stations address, the station discards the information frame back on to the bus. If the destination address matches the station address, it accepts the information frame and processes the frame.
3. Ring Topology: Ring topology is a kind to an omni bus circuit. Local area networks that have each station attached to an adjacent station using point-to-point links form a physical ring. Each station attached and active to the ring regenerates the information frame, then re-transmits the information frame on the ring. The ring itself is logically circular and the flow of information is unidirectional.

Fundamentals of Computers Notes

Some Important Facts

You must know its related important facts. These are the following:

(i) Protocol: Data communication software actually contains certain procedures and rules that instruct how transfer of data should take place. These procedures and rules are known as protocols. Thus protocols provide a method for orderly and efficient exchange of data by establishing rules for the proper interpretation of controls and data transmitted as row bits and bytes.

(ii) Client: A computer which work on the network is known as client. It shares all the information and facilities with remote server.

(iii) Server: The main computer of the network is known as server. It is a central computer and all the computers are connected with it. Computer network program is run by the server.

(iv) Node: Every computer which is attached with the network server called as node. Every node has own identity or name.

(v) Cable: All computers are connected by the wires in network. These wires are called as cable. It may be type of twisted pair or coaxial and fibre optic.

(vi) N.O.S.: Network operating system is a group of programs which run the network. It controls the transaction of data in all the computers of network. This software is installed in the server.

(vii) Topology: The arrangement of connected computer in network is called Topology. It has many type.

Fundamentals of Computers Notes

Data communication

In data communications, four basic terms – Signalling and Transmission are frequently used. Data, Signal,

Data are entities that convey meaning. Data and information does not mean the same thing; data are a representation of something; whereas information refers to the content or interpretation of data.

Signals are electric or electromagnetic encoding of data, and signaling is propagation of signal along suitable communication medium.

Transmission is communication of data achieved by the propagation and processing of signals.

Fundamentals of Computers Notes

Communication Speed Rate

The speed at which two computers exchange or transmit data is called communication rate on transmission speed. The unit of measurement of the speed in measured using bps (bits per second) or band. Normal PC based communication station transferred using 300 to 9600 bps, whereas mainframe computers uses 19,200 band or more.

Fundamentals of Computers Notes

Private vs. Switched Channels

Private vs leased lines are permanently connected circuits between two or more points. These lihes are available for private use by the leasing party. Whereas switched lines, or dial up lines are available to any subscriber. For example telephone connection in our home or office is a dial up lines as we dial up a number to use a particular circuit.

Fundamentals of Computers Notes

Analog and Digital Transmission

One of the fundamentals concepts in data transmission is to understand the difference between analog and digital signals.

An analog signals is one that is continuous with respect to time, and may take on any value within a given range of values. Human voice, video and music when concerted to electrical signal using suitable devices produce analog signals.

A digital signal may take on only a discrete set of values within a given range. Most computers related equipment is digital. Irrespective of original form of the message, the actual transmission of signal could be either in analog or digital form.

Fundamentals of Computers Notes

Parallel and Serial Transmission

In parallel data transmission, there are multiple parallel lines concepting the transmitting and receiving units. Each wire carries a bit of information.

In serial data transmission, each bit is sent sequentially one after another and it requires only one pairs or wire conductors for connecting the receiving and transmitting units.

Serial transmission is slower than parallel transmission is used primarily for transferring data between devices at the same site. Communication between computers is almost always serial.

Fundamentals of Computers Notes

Communication Channels

The most basic hardware required for communication is the media through which data is transferred. There are several types of media, and the choice of the right media depends on many factors such as cost of transmission media, efficiency of data transmission and the transfer rate. We will describe some of these transmission media.

Fundamentals of Computers Notes

Two Wire Open

This is the simplest of all the transmission media. It consists of a simple pair of metallic wires made of copper or sometimes aluminium of between 0.4 and 1 mm diameter, and each wire is insulated from the other. There are variation to this simplest form with several pairs of wire enclosed in a single in a single protected cable called a multicore cable or moulded in the form of a flat ribbon. This type of media is used for communication with a a short distance, upto about 50 meters, and can achieve a transfer rate of upto 19200 bits per second.

Fundamentals of Computers Notes

Twisted Pair Cable

A twisted pair consists of a pair of insulated conductors that are twisted together. The advantage of a twisted pair cable over the two wire open lines is, it provides better immunity from spurious noise signals. As the two wires are close to each other, both pick equal interferences caused by extraneous signals sources and this reduces the differential signal added by the noise.

Fundamentals of Computers Notes

Coaxial Cable

A coaxial cable consists of a solid conductor running coaxially inside a solid or braided outer annular conductor. The space between the two conductors is filled with a dielectric insulating material. Larger the cable diameter, lower is the transmission loss, and higher transfer speeds can be achieved. A coaxial table can be used over a distance of about 1 Km, and can achieve a transfer rate upto 100 megabytes per second,

A coaxial cable is of two types- a 75 ohm cable which is used by the cable TV operators and the 50 ohm cable which is used in high speed broadband networks and are low loss cables,

Fundamentals of Computers Notes

Fiber Optic Cables

A fibre optic cable carries signals in the form of fluctuating light in a glass or plastic fibre. An optical fibre cable consists of a glass or plastic core surrounded by a cladding made of a similar material but with a lower refractive index. The core transmits the light while the change in refractive index between the core and the cladding causes total internal reflection, thus minimising the loss of light from fibre.

Fundamentals of Computers Notes

Radio, Microwave and Satellite Channels

Radio, microwave and satellite channels use electromagnetic propagation in open space. The advantage of these channels lie in their capability to cover large geographical areas and being inexpensive than the wired installation.

Radio frequencies transmission may be below 30 MHZ or above 30 MHZ and thus the techniques of transmission are different. Owing to the characteristics of the ionosphere, frequencies below 30 MHZ are reflected back towards the surface of the earth.

Microwave links would invariably use line-of-sight transmission with repeaters placed every 100-200 Kms.

Microwave links can achieve data transfer rates of about 1000 Mbps. Satellites links use microwave frequencies is the order of 4-12 Ghz with the satellite as a repeater. They can achieve data transfer rates of about 1000 bps.

Fundamentals of Computers Notes

 

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