Friday, 8 July 2016

photoshop unit-1


1.    High speed: Computers have the ability to perform routine tasks at a greater speed than human beings. They can perform millions of calculations in seconds.

2.    Accuracy:  The computer accepts large amount of data and performs specified calculations and produces accurate results. Some people comment that computers also make mistakes. But it is not. It is the mistake on the part of human beings. The mistake might have happened because of wrong input or wrong program given by the human beings.

3.    Storage: Computers can store large amount of information. Any item of data or any instruction stored in the memory can be retrieved by the computer at lightning speeds.

4.    Automation: Computers are capable of executing the programs without the need of human intervention, the computer execute programs one by one automatically.  

5.    Diligence: Computers can perform the same task repeatedly & with the same accuracy without getting tired. A computer will work with same tempo from beginning to end.

6.    Cost effectiveness: Computers reduce the amount of paper work and human effort, thereby reducing costs.

Limitations of computers:

1.    Computer is not an intelligent machine of its own

2.    It requires human skills to operate
3.    It does not work on its own, it requires instructions to operate.
4.    It is not a decision making system.
5.    A program has to be written to take action


 Definition: A Computer is an electronic device for storing data, processing information and displays the desired (want) output in human readable form.
Especially computer is used to type documents, send email, play games, and browse the Web. You can also use it to edit or create spreadsheets, presentations, and even videos.


A set of values used to represent different quantities is known as Number System". 
Some important number systems are as follows.
·         Decimal number system
·         Binary number system
·         Octal number system
·         Hexadecimal number system
Decimal number System
The Decimal Number System consists of ten digits from 0 to 9 (i.e 0 1 2 3 4 5 6 7 8 9 ). These digits can be used to represent any numeric value. The base of decimal number system is 10. It is the most widely used number system.


The value of digit 4     =          4x102    =          400
The value of digit 5     =          5x101 =          50       
The value of digit 3     =          3x100 =          3
The actual number can be found by adding the values obtained by the digits as follows:
400 + 50 + 3    =45310

Binary Number System

Digital computer represents all kinds of data and information in the binary system. Binary Number System consists of two digits 0 and 1. Its base is 2. Each digit or bit in binary number system can be 0 or 1. A combination of binary numbers may be used to represent different quantities like 1001.

Example: Convert 101112 to decimal number

101112             =          1 x 24 + 0 x 23 + 1 x 22 + 1 x 21 + 1 x 20
                        =          1 x 16 + 0 + 1 x 4 + 1 x 2 + 1 x 1
                        =          16 + 0 + 4 2 + 1
                        =          2310

Octal Number System

Octal Number System consists of eight digits from 0 to 7. The base of octal system is 8. Each digit position in this system represents a power of 8. Any digit in this system is always less than 8. Octal number system is used as a shorthand representation of long binary numbers.

Example: convert 458 to decimal number

458       =          4 x 81 + 5 x 80
            =          4 x 8 + 5 x 1
            =          32 + 5
            =          3710    

Hexadecimal number system

The Hexadecimal Number System consists of 16 digits from 0 to 9 and A to F. The alphabets A to F represent decimal numbers from 10 to 15. The base of this number system is 16. Each digit position in hexadecimal system represents a power of 16. The number 76416 is valid hexadecimal number. It is different from 76410 which is seven hundred and sixty four.

Example: Convert 3A16 to decimal number

3A16     =          3 x 161 + A x 16                                              
            =          3 x 16 + 10 x 1
            =          48 + 10
            =          5810


Computer can be classified according to two different ways. They are                 
1.      According to the logic used by the computer.
2.      According to the size of the computer.
According to the logic used by the computer. It can be classified into 3 types. They are
1.      Analgo Computers    2. Digital Computers 3. Hybrid Computers
Analgo Computers:  The computers which accept the data in the form of voltage (v) or current signals  and convert  them to numeric values  are called Analog Computers.
These Computers can measure physical quantities like temperature, speed etc..These Computers give only approximate results.
Ex: . A speedometer which measures the speed of vehicle, and thermometer which measures the temperature of the body etc...
Digital Computers:   The computer which accepts the data in the form of binary digits (bits) representing ZERO (0) and ONE (1) are called as Digital Computers. Each one is called as a bit. Logically 0 indicates false and 1 indicates true.
            Digital Computers give more accurate and very faster results than analog computers.
            Digital Computers deal with counting rather than physical measurement. They accept the input data and instructions in the form of digits 0 to 9, alphabets ( A to Z) or special symbols like + , * ,- ,/ ,$ ,% etc….   In this there are TWO purposes of digital computers. They are
1.      General Purpose Digital Computer 2.     Special Purpose Digital Computer
General Purpose Digital Computers are designed to perform of different jobs or applications. These computers can be used in solving a business problem as well as mathematical problem with same accuracy and consistency.
Special Purpose Digital Computers are designed to meet the need of special application. They are designed, made and used for only a single job. So they execute their tasks quickly and efficiently.
Hybrid Computers:   The computers which accept the data in the form of combination of voltage or signals or binary digits are known as Hybrid Computers. So, these computers are computers which have the features of both digital and analog computers.
These computers are very useful in scientific research and to perform specific job etc….
Ex:       In a hospital ICU (Intensive Care Unit) , Analog devices may measure a patient’s heart function, temperature and other vital signs. These measurements may then be converted into numbers and supplied to the digital device which may send as immediate signal to the nurses’ station if any abnormal reading is detected.
According to the SIZE , the computers are classified as follows:
1. Super computers  2. Mainframe computers     3.Mini computers     4. Micro computers
Super computers:     Super computers are large size computers and  these computers can be processed  billions of instructions per second. These systems are multiprocessor system  and it is used to do parallel processing. These systems are very expensive and powerful and used in the complex tasks. It is typically used for following applications.
·        Weather Information
·        Medicine
·        Real-time Animation etc…..
Mainframe computers:                   Mainframe computers are large size computers and these computers can be processed hundreds of millions of instructions per second. In this computer, RAM is much more than micro computers as well as mini computers and it supports 100 users in time sharing mode. These computers are used in large organizations like…
·        Railway reservations
·        Airlines reservations
·        Banking applications etc…..
Mini computers:       Mini computers are also large size computers and these computers and it supports multiuser environment. These computers are expensive as compare to micro computers. The main memory RAM can be 1MB to 16 MB.These computers also used in large organizations like..
·        Reservation system
·        Banking and industries.
Micro computers  :   Micro computers are smallest category of digital computers in which a microprocessor performs the function of ALU and Control Unit. These computers are single user systems which mean that a single user can operate only one system at a time. These computers are also classified into types. They are
1.      Desktop computers  2. Laptop computers            3. Handheld computers
Desktop computers  ( Personal computers):             Desktop computers are also called as Personal computers or simply PC’s. Today the Desktop computers are most popular computer systems. They are usually easier to use and more affordable.
Laptop computers:                     Laptop computers are portable computers. They are light weight computers with a thin screen. They are also called as notebook computers because of their small size. It can be easily carried from one place to another place. It has battery also.
Handheld computers:    Handheld computers are also called as Personal Digital Assistants (PDA’s). These computers are pen based and battery – powered. These systems are small size and carried easily from one place to another place.

Initially, the generation term was used to distinguish between varying hardware technologies. But nowadays, generation includes both hardware and software, which together make up an entire computer system.
Following are the main five generations of computers
Generation & Description
The period of first generation: 1946-1959. Vacuum tube based.
The period of second generation: 1959-1965. Transistor based.
The period of third generation: 1965-1971. Integrated Circuit based.
The period of fourth generation: 1971-1980. VLSI (Very Large Scale Integration) microprocessor based.
The period of fifth generation: 1980-onwards. ULSI ( Ultra )microprocessor based

The computers of first generation used vacuum tubes as the basic components for memory and circuitry for CPU (Central Processing Unit). In this generation mainly batch processing operating system were used. Punched cards, paper tape, and magnetic tape were used as input and output devices. The computers in this generation used machine code as programming language.
The main features of first generation are:
·         Vacuum tube technology
·         Supported machine language only
·         Very costly
·         Generated lot of heat
·         Slow input and output devices
·         Huge size
·         Need of A.C.
·         Non-portable
In this generation transistors were used that were cheaper, consumed less power, more compact in size, more reliable and faster than the first generation machines made of vacuum tubes. In this generation, magnetic cores were used as primary memory and magnetic tape and magnetic disks as secondary storage devices. In this generation assembly language and high-level programming languages like FORTRAN, COBOL were used. The computers used batch processing and multiprogramming operating system.
The main features of second generation are:
·        Use of transistors
·        Smaller size as compared to first generation computers
·        Generated less heat as compared to first generation computers
·        Faster than first generation computers
·        Still very costly
·        A.C. needed
·        Supported machine and assembly languages
The computers of third generation used integrated circuits (IC's) in place of transistors. A single IC has many transistors, resistors and capacitors along with the associated circuitry. The IC was invented by Jack Kilby. This development made computers smaller in size, reliable and efficient. In this generation remote processing, time-sharing, multi-programming operating system were used. High-level languages (FORTRAN-II TO IV, COBOL, PASCAL PL/1, BASIC, ALGOL-68 etc.) were used during this generation.
The main features of third generation are:
·         IC used
·         Smaller size
·         Generated less heat
·         Faster
·         Lesser maintenance
·         Still costly
·         A.C needed
·         Supported high-level language
The computers of fourth generation used Very Large Scale Integrated (VLSI) circuits. VLSI circuits having about 5000 transistors and other circuit elements and their associated circuits on a single chip made it possible to have microcomputers of fourth generation. Fourth generation computers became more powerful, compact, reliable, and affordable. As a result, it gave rise to personal computer (PC) revolution. In this generation time sharing, real time, networks, distributed operating system were used. All the high-level languages like C, C++, DBASE etc., were used in this generation.
The main features of fourth generation are:
·         VLSI technology used
·         Very cheap
·         Use of PC's
·         Very small size
·         No A.C. needed
·         Concept of internet was introduced
·         Computers became easily available

In the fifth generation, the VLSI technology became ULSI (Ultra Large Scale Integration) technology, resulting in the production of microprocessor chips having ten million electronic components. This generation is based on parallel processing hardware and AI (Artificial Intelligence) software. All the high-level languages like C and C++, Java, .Net etc., are used in this generation.
The main features of fifth generation are:
·        ULSI technology
·        Development of true artificial intelligence
·        Advancement in Parallel Processing
·         More user friendly interfaces with multimedia feature


The computer system consists of three units:

1.  Input Unit
2. Central Processing Unit (CPU)
 3. Output Unit
Block diagram of a Computer:

Working Process of above diagram:
·        The program or data is entered through input unit like keyboard and that data is controlled by C .U.
·        The control unit sends this data to the memory unit (M.U) for temporary storage i.e. in RAM (Random Access Memory).
·        This temporary stored data is then sent to A.L.U (Arithmetic Logical Unit) for processing through C.U.
·        A.L.U processes this data and then this processed data sent it back to Memory Unit for permanent storage i.e. in hard disk, again through C.U.
·        This processed data can also be sent to output unit directly through control unit or it can also sent from permanently stored memory i.e. M.U to the output unit.
·        Finally, this output unit will give the result

1.     Input: This is the process of entering data and programs in to the computer system. You should know that computer is an electronic machine like any other machine which takes as inputs raw data and performs some processing giving out processed data. Therefore, the input unit takes data from us to the computer in an organized manner for processing.

2.     Central Processing Unit: It is the part of the computer that carries out the instructions of a computer program. It is the unit that reads and executes program instructions. Hence it is known as the Brain of the computer. The CPU consists of storage or memory unit, Arithmetic Logic Unit (ALU) and control unit.
(a). Memory Unit: It is also known as the primary storage or main memory. It stores data, program instructions, internal results and final output temporarily before it is sent to an appropriate output device. It consists of thousands of cells called ―storage locations‖. These cells activate with ―off-on‖ or binary digits (0,1) mechanism. Thus a character either a letter or numerical digit is stored as a string of (0, 1) Binary digits (BITS). These bits are used to store instructions and data by their combinations.
(b) Arithmetic and Logical Unit(ALU): It is the unit where all Arithmetic operations (addition, subtraction etc.) and logical functions such as true or false, male or female are performed. Once data are fed into the main memory from input devices, they are held and transferred as needed to ALU where processing takes place. No process occurs in primary storage. Intermediate generated results in ALU are temporarily placed in memory until needed at later time. Data may move from primary memory to ALU and back again to storage many times before the process is finalized.

(c).Control Unit : The control unit controls all the activities of the computer.

3.         Output: This is the process of producing results from the data for getting useful information. Similarly the output produced by the computer after processing must also be kept somewhere inside the computer before being given to you in human readable form. Again the output is also stored inside the computer for further processing.

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