Computer is an electronic device that receives input, stores and manipulates data, and provides output in a useful format at high speed. Computer performs tasks, such as calculations or electronic communication, under the control of a set of instructions called a program. Computers perform a wide variety of activities reliably, accurately, and quickly. The most versatile machine that man has ever created is computer. In the sectors of education, industries, government, medicine, scientific research, law and even in music and art computer has played a vital role. So without computers, life would certainly be difficult and different.

Today, computers are found everywhere in offices, homes, schools and many other
places. Much of the world runs on computers, and computers have changed our lives. Some of the characteristics of computers, which make them the most essential part of every emerging technology, are listed below:

Computers work at tremendous speed which process data at an extremely fast rate. At present a powerful computer can perform billions of operations in just a second.
Milli second = A thousandth of a second (1/1,000)
Micro second = A millionth of a second (1/1,000,000)
Nano second = A billionth of a second (1/1,000,000,000)
Pico second = A trillionth of a second (1/1,000,000,000,000)

The computers are very accurate. The level of accuracy depends upon the instructions and the type of machine being used. Computer is capable of doing only what it is instructe
d to do. Inaccurate instructions for processing lead to inaccurate results. This is known as GIGO (Garbage In Garbage Out). Errors may occur in the results due to human factors rather than the technological weaknesses.

Computers are automatic machines. Once a program is in the memory of a computer, no human intervention is needed; it allows the instructions step by step, executes them and terminates the execution when it receives the command to do so.

Storage capacity
Computers have got a main memory and the secondary storage systems. The main mem
ory of the computer is relatively small and it can hold only a certain amount of information. Therefore, the larger amount of data and information is stored in the secondary storage media such as magnetic disk and optical disk. Computers can also retrieve the information instantly when desired.

Computer, being a machine, does not suffer from the human problems of tiredness and lack of concentration. It can continuously work for hours without making mistakes. Even if millions of calculations are to be performed, it will perform the last calculation with the same accuracy and speed as it has done in the first one.

Computers have certain limitations too. As a machine, a computer can only perform what it is programmed to do. Computers lack decision-making power, computers cannot decide on their own. If an unanticipated situation arises, computers will either produce erroneous results or abandon the task altogether. They do not have the potential to work out an alternative solution

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An input device can be defined as an electromechanical device that allows the user to feed data and instructions into the computer for analysis, storage, and to give the commands to the computer. Data and instructions are entered into the computer’s main memory through an input device. Input device captures data and translates it into a form that can be broadly classified into the following categories:

Key board
A keyboard is the most common input device. Using a keyboard, the user can type the text and execute commands. Keyboard is designed to resemble a regular typewriter with a few additional keys. Data is entered into the computer by simply pressing various keys.
The layout of a keyboard comes in various styles but QWERTY is the most common layout. The layout of the keyboard has changed very little ever since it was introduced. In fact, the most common change in its technology has simply been the natural evolution of adding more keys that provide additional functionality. The number of keys on a keyboard varies from 82 keys to 108 keys. Portable computers such as laptops quite often have custom keyboards that have slightly different key arrangements from a standard keyboard.

Pointing Devices
Pointing devices are the input devices by which we can point out and select the items rapidly from the multiple options displayed on the screen. These devices can also be used to create graphic elements on the screen such as lines, curves and freehand shapes. The most common types of pointing devices available are;
a) Mouse b) Trackball c) Joystick
d) Touch Screen e) Light Pen d) Touch Pad

a) Mouse
A mouse is a small hand-held pointing device, which is used to create graphic elements on the screen such as lines, curves, and freehand shapes. It is also used to run a program and pull down a menu in GUI (Graphic User Interface) base computer system. It is rectangular shaped with a rubber ball embedded at its lower side and buttons on the top. Usually a mouse contains two or three buttons, whish can be used to input commands or instructions. The mouse may be classified into two categories:
I) Mechanical mouse II) Optical mouse

I) Mechanical mouse
A mechanical mouse uses a rubber ball at the bottom surface, which rotates as the mouse along a flat surface to move the cursor. It is the most common and expensive pointing device. Microsoft, IBM and Logitech are some well-known makers of the mechanical mouse.

II) Optical mouse
An optical mouse uses the light beam instead of rotating ball to detect the movement across a specially patterned mouse pad. As the mouse rolls the mouse on a flat surface, the cursor on the screen also moves in the direction of the mouse’s movement. It is more expensive in comparison with the mechanical mouse. Modern optical mouse are accurate and often do not need a mouse pad.

b) Track Ball
A track ball is another pointing device that uses a ball which is settled in a square cardle. In general, a track ball is just like a turned upside down a mouse. The ball is rolled by fingers to move the cursor around the screen. A track ball requires less space than a mouse for operation because the whole device is not moved for moving the curser. It is often attached to or inbuilt into the keyboard. The trackball built into the keyboard are commonly used in laptop computers, because the mouse is not practical for laptop users in a small space. This pointing device comes in various shapes but with the same functionality. It works like a mouse.

c) Joystick
Joystick is a device that moves in all directions and controls the movement of the cursor on the screen. The joystick offers three types of controls.
• Digital control
• Glide control
• Direct control
Digital control allows in a limited movement in a number of directions such as up,
down, left and right. Glid and direct controls allow movements in all directions (360 degree). The basic design of a joystick consists of a stick that is attached to plastic base with a flexible rubber sheath. It has some pushing buttons and a circuit board which is placed under the stick. Joysticks are mainly used for computer games, controlling industrial robots and for other applications such as flight simulators, training simulators, etc.

d) Light Pen
A light pen is a hand-held electro-optical pointing device which is connected to the computer by a cable. When it touches to a connected computer monitor, it will allow the computer to determine where on that screen the pen is pointed. It facilitates drawing images and selects objects on the display screen by directly pointing to the objects with the pen. Light pens give the user the full range of mouse capabilities, without using the pad and any horizontal surface. Using light pens, the user can interact more easily with applications in such modes as dragging and dropping or highlighting. It is very popular for graphic work in engineering like CAD (Computer Aided Design)

e) Touch Screen
A touch screen is a special kind of screen device, which is placed on the computer monitor in order to allow the direct selection or activation of the computer’s information, when somebody touches the screen. Essentially, it registers the input when a finger or other object to touch the screen. Touch screen is normally used to touch the screen. Touch screen is normally used to access the information with minimum effort. However, it is not suitable for input of large amount of data. Typically, they are used in information-providing systems like the hospital, airlines, railway reservation counters, amusement parks, etc.

f) Touch Pad
A touch pad is one of the latest pointing devices. It looks like a small gray window, about two inches wide. It is use din potable computer such as laptop and notebook to substitute the mouse. It has two buttons below or above the pads which work like the mouse buttons. You can move the cursor on the screen by making a finger or other object along the pad .And one can also click by tapping a finger on the touch pad, and drag with a tap in the continuous pointing scale.

Digital Camera
A digital camera is also an input device which stores pictures digitally rather than recording them on a film. Once a picture has been taken that stores on its chip memory. The picture can be downloaded to computer system and then manipulated with an image editing software. Then it can be printed. The major advantage of digital cameras is that making photos is both inexpensive and fast because there is no film processing.

A scanner scans an image and transforms the image to ASCII codes and graphics. This can be edited, manipulated, combined and then printed. Scanners use a light beam to scan the input data. If the data to be scanned is an image, it can be changed by using the special image editing software. If the image is a page of a text, then the special optical character recognition software must be used to convert the image of letters in the text and this can be edited by using a word processor. Most of the scanners come with a utility program that allows it to communicate with the computer and save the scanned image as a graphic file on the computer. Commonly scanners are classified in two types:
• Hand-Held scanner
• Flat-Bed scanner

A microphone is a speech recognition device. Speech recognition is one of the most interactive system to communicate with the computer. The user can simply instruct the computer about the task to be performed with the help of a microphone. It is the technology by which sounds, words or phrases spoken by humans are converted into digital signals, and these signals are transformed into the computer generated texts or commands. Most speech recognition systems are speaker-dependent so they must be separately trained for each individual user. The speech recognition systems system learns to voice of the user, who speaks isolated words repeatedly. Then, these voiced words are recognizable in the future. It is more popular in the corporate world among non-typists, people with disabilities, and business travelers who tap-record information for later transcription.

Graphic Digitizer
Graphic digitizer is an input device, which is used for converting pictures, maps and drawings into digital form for storage in computers. This enables re-creation of the drawing whenever required. It also facilitates any changes in the drawing whenever required.
A digitizer consists of a digital tablet (also known as graphics tablet) associated with a stylus. The digitizing tablet is a flat surface, which contains hundreds of fine copper wires forming a grid. Each copper wire receives electric pulses. The digitizing tablet can be spread over a working table, and is connected to computer.

Optical Scanners
New technologies have developed alternative methods to input data instead of entering data through keystrokes. Devices such as bar code reader can interpret machine printed marks or codes. Accordingly there are four types of optical recognition.
a) OCR (Optical Character Recognition)
b) OMR (Optical Mark Recognition)
c) MICR ( Magnetic-Ink Character Recognition)
d) BCR(Bar Code Reader)

Optical Character Recognition (OCR)
Optical Character Recognition is a process of scanning printed pages as image on a flatbed scanner using OCR software which recognizes the letters as ASCII text. The device used for this technology is called optical reader. In the OCR system book or a magazine article is fed directly into an electronic computer file, and then this file is edited by using a word processor. Advanced OCR systems can read the text large variety of fonts.

Optical Mark Recognition (OMR)
Optical Mark Recognition is the process of recognizing a pre-specified type of marks made by pencils or pen on the paper. This type of technology is used to evaluate the papers of competitive examination. Optical mark reading is done by special device called optical mark reader.

Magnetic-Ink Character Recognition (MICR)
Magnetic-Ink Character Recognition technology is used by the banking industry for faster processing of the large volume of cheques. This technology also ensures accuracy of data entry, because most of the information is pre-printed on the cheque and is directly fed to the computer. Magnetic ink character reader is a device used in the technology.

Bar Code Reader (BCR)
A bar code is a machine-readable code in the form of a pattern of parallel vertical lines. They are commonly used for labeling goods that are available in supermarkets, numbering books in libraries, etc. These codes/strips are sensed and read by a photoelectric device called bar code reader that reads the code by means of reflective light. The information recorded in a bar code reader is fed into the computer, which recognizes the information from the thickness and spacing of bars.

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During the period of 1940 to 1956 first generation of computers were developed. The first generation computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. The vacuum tube was developed by Lee DeForest. A vacuum tube is a device generally used to amplify a signal by controlling the movement of electrons in an evacuated space. First generation computers were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions.

1) First generation computers were based on vacuum tubes.
2) The operating systems of the first generation computers were very slow.
3) They were very large in size.
4) Production of the heat was in large amount in first generation computers.
5) Machine language was used for programming.
6) First generation computers were unreliable.
7) They were difficult to program and use.

UNIVAC, EDVAC, EDSAC and ENIAC computers are examples of first generation computing devices.

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During the period of 1956 to 1963 second generation of computers were developed. The second generation computers emerged with development of Transistors. The transistor was invented in 1947 by three scientists J. Bardeen, H.W. Brattain and W. Shockley. A transistor is a small device made up of semiconductor material like germanium and silicon. Even though the Transistor were developed in 1947 but was not widely used until the end of 50s. The transistor made the second generation computers faster, smaller, cheaper, more energy-efficient and more reliable than their first-generation computers. Even though the transistor used in the computer generated enormous amount of heat which ultimately would lead to the damage of the computers but was far better than vacuum tubes.
Second generation computers used the low level language i.e. machine level language and assembly language which made the programmers easier to specify the instructions. Later on High level language programming were introduced such as COBOL and FORTRAN. Magnetic core was used as primary storage. Second generation computer has faster input /output devices which thus brought improvement in the computer.
1) Transistors were used in place of vacuum tubes.
2) Second generation computers were smaller in comparison with the first generation computers.
3) They were faster in comparison with the first generation computers.
4) They generated less heat and were less prone to failure.
5) They took comparatively less computational time.
6) Assembly language was used for programming.
7) Second generation computers has faster input/output devices.

IBM 7000, NCR 304, IBM 650, IBM 1401, ATLAS and Mark III are the examples of second generation computers.

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During the period of 1964 to 1971 Third generation computers were developed. The third generation computers emerged with the development of IC (Integrated Circuits). The invention of the IC was the greatest achievement done in the period of third generation of computers. IC was invented by Robert Noyce and Jack Kilby in 1958-59. IC is a single component containing a number of transistors. Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of computers.
Keyboards and monitors developed during the period of third generation of computers. The third generation computers interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory.

1) IC was used instead of transistors in the third generation computers.
2) Third generation computers were smaller in size and cheaper as compare to the second generation computers.
3) They were fast and more reliable.
4) High level language was developed.
5) Magnetic core and solid states as main storage.
6) They were able to reduce computational time and had low maintenance cost.
7) Input/Output devices became more sophisticated.

PDP-8, PDP-11, ICL 2900, IBM 360 and IBM 370 are the examples of third generation computers.

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After 1971 the fourth generation computers were built. The fourth generation computers were the extension of third generation technology. The fourth generation computers emerged with development of the VLSI (Very Large Scale Integration).With the help of VLSI technology microprocessor came into existence. The computers were designed by using microprocessor, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The fourth generation computers became more powerful, compact, reliable and affordable. As a result, they give rise to personal computer (PC) revolution.
For the first time in 1981 IBM introduced its computer for the home user and in 1984 Apple introduced the Macintosh Microprocessor.

1) The fourth generation computers have microprocessor-based systems.
2) They are the cheapest among all the computer generation.
3) The speed, accuracy and reliability of the computers were improved in fourth generation computers.
4) Many high-level languages were developed in the fourth generation such as COBOL, FORTRAN, BASIC, PASCAL and C language.
5) A Further refinement of input/output devices was developed.
6) Networking between the systems was developed.

IBM 4341, DEC 10, STAR 1000, PUP 11 and APPLE II are the examples of fourth generation computers.

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Fifth generation computers are in developmental stage which is based on the artificial intelligence. The goal of the fifth generation is to develop the device which could respond to natural language input and are capable of learning and self-organization. Quantum computation and molecular and nanotechnology will be used in this technology. So we can say that the fifth generation computers will have the power of human intelligence.

1) The fifth generation computers will use super large scale integrated chips.
2) They will have artificial intelligence.
3) They will be able to recognize image and graphs.
4) Fifth generation computer aims to be able to solve highly complex problem including decision making, logical reasoning.
5) They will be able to use more than one CPU for faster processing speed.
6) Fifth generation computers are intended to work with natural language.

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Universal Automatic Computer (UNIVAC)

UNIVAC (Universal Automatic Computer) was the first commercially general purpose electronic computer. John Eckert and John Mauchly at the Moore School of Engineering, Pennsylvania developed it in 1951. It was used for the analysis of 1952 Presidential Election in the United States. It was 8 feet high, 15 feet long and weighed 5 tons. It contained 5600 tubes, 18000 crystal diodes, and 300 relays. A magnetic tape was used for data input and output.

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Electronic Delay Storage Automatic Calculator (EDSAC)

EDSAC (Electronic Delay Storage Automatic Calculator) was developed by a group of scientists, headed by Professor Maurice Wilkes at Cambridge University, England, in 1949. It was also based on the stored program concept and one of the first to use binary digits. The input and output were provided by a paper tape. It could do about 700 additions per second and 200 multiplications per second. The machine occupied a room, which measured 5/4 meters.

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Electronic Discrete Variable Automatic Computer (EDVAC)

John Mauchly and J.P. Eckert also proposed the development of EDVAC. The conceptual design for EDVAC electronic computer to use the stored program concept introduced by John Von Neumann. Unlike the ENIAC, it used binary number rather than decimal. The University of Pennsylvania built the EDVAC for the U.S. Army’s Ballistics Research Laboratory at the Aberdeen Proving Ground. EDVAC had almost 6000 vacuum tubes and 12000 diodes. It consumed 56kW of power. It covered 490 feet square of floor and weighed 7850kg.

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Electronic Numerical Integrator and Calculator (ENIAC)

Electronic Numerical Integrator and Calculator (ENIAC) was designed by John Mauchly and John Presper Eckert in 1946 at the Moore School of Electrical Engineering, University of Pennsylvania. It was the first electronic computer. ENIAC was initially built for the United States military to calculate the paths of artillery shells. It contained 18000 vacuum tubes, 7200 crystal diodes, 1500 relays, 70000 resistors, 10000 capacitors and around 5 million hand-soldered joints. It weighed nearly 30 tons and consumed 160 kW of power. Input was possible from an IBM card reader while an IBM punch card was used for output.

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