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1. Introduction: A computer is a machine that manipulates data according to a set of instructions called program. It is a set of interacting elements, responding to input so as to produce desire output. It is an electronic device that can perform a variety of operations according to a set of instructions or program. According to McGraw Hill Encyclopaedia (1997), it is “a device that receives, processes and presents information” (p. 270). According to Encyclopaedia Britannica (1991), a computer is a device that solves problems by applying prescribed operation on data entered into it (p. 638).

2. Types of Computers: Computers can be classified in many different ways; some of them are discussed bellow

A) Based on Technology / Design: Based on technology computer can of the following types-

a) Analog Computer: An analog computer receives inputs that are instantaneous representation of variable quantities and produce output results dynamically to a graphical display device, a virtual display device or, in case of a control system, a device which causes mechanical motion. Example includes Analog clock, Speedometer, etc.

b) Digital Computer: The digital computer works with numbers, words, and symbols expressed as digits which it manipulates and counts discretely. Example includes Calculators, Digital watches, etc.

c) Hybrid Computer: The flexibility of the electronic analog computer has allowed it to be augmented with interface channels to the electronic digital computer, so that during 1960s a third type of general computer i.e. the hybrid computer came into being. The hybrid computers combine the features of the other two types and utilize both analog and discrete representation of data. Example includes the computer used in hospitals to measure the heartbeat of the patient, computer used in petrol pump, etc..

B) Based on Size: Modern computer system varies in physical size from those that used to fill a room to those with CPUs that can rest on the nail of a person’s little finger. Generally, the larger the systems the greater are its processing speed, storage capacity, cost and ability to handle large number of powerful input and output devices. This classification is arbitrary. The fact is that the size, cost, and performance capabilities of machines in different classifications are likely to overlap.

a) Micro Computer: Micro computers are popularly known as Desktop computer. Microcomputers are the smallest unit. They may be tiny, special purpose devices dedicated to carrying out a single task or they may be the more visible and familiar personal computer ranging from note book size to desktop size that we can use in countless ways. The performance of some newer micros surpasses the capabilities of some older minis. Eg. Acer’s, Aspire, Compaq, etc.

b) Mini Computer: They are generally more powerful and more expensive than Micros. In physical size mini computers vary from desktop models to unit that has the size of a small cabinet. Eg. IBM-6000 model 580, CDC 4360, etc.

c) Mainframe Computer: Mainframe computers are the system that offers faster processing speeds and greater storage capacity than a typical mini. The Mainframe computers can be accommodated in large air-conditioned rooms because of its size. Eg. CDC 2000, IBM ES-2, etc.

d) Super Computer: These are the largest, fastest and more expensive system in the world. Super computer is designed to process complex scientific jobs, to analyze large commercial databases, produce animated movies and play games such as Chess. A super computer is very expensive, prices range from about $ 4 million to over $ 17 million. Eg. Cray -1, Cray-2, Cray-3, ETA-10, X-MP, etc.

C) Based on Purpose and Use: Depending upon the purpose for which computers are used, it can be classified as follows

a) General Purpose Computer: This type of computer is so designed that it can be used to solve many kinds of problem or it permits the development of different stimulated models as needed. Eg. Model EA1-2000 (Electronic Association Inc).

b) Special Purpose Computer: It has a fixed programme with a few or no permitted adjustment. It is generally built into or appended to the physical system it serves. Examples: Special Purpose Pneumatic Analog Computer, Model Foxboro 516 (Foxboro Co.).

D) Based on Programme: Based on programme computer can be-

a) Embedded Computer: Embedded computers are small, simple devices that are used to control other devices. These are embedded within the circuitry of appliances such as fighter aircraft, industrial robots, digital cameras, children’s toys, washing machines, wrist watches, etc. These computers are typically preprogrammed for a specific task.

b) Programmable Computer: The user can create a new program for his/her specific purpose in these types of computers. It can be used as notepads, scheduling system and address books. If equipped with a cellular phone it can also be connected to World Wide computer networks for exchanging information regardless of location.

E) Home Computer / Personal Computer: A personal computer (PC) is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator. A personal computer may be a desktop computer, a laptop computer or a tablet computer.

Home computer was a class of personal computer entering the market in 1977 and becoming common during the 1980s. They were marketed to consumers as accessible personal computers, more capable than video game consoles. These computers typically cost much less than business, scientific or engineering-oriented desktop personal computers of the time, and were generally less powerful in terms of memory and expandability. Personal computers, in various forms, are icons of the Information Age and are what most people think of as “a computer”; however, the most common form of computer in use today is the embedded computer.

a) Desktop Computer: A desktop computer is a personal computer (PC) in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. It can indicate a horizontally-oriented computer case usually intended to have the display screen placed on top to save space on the desk top. Most modern desktop computers have separate screens and keyboards.

b) Laptop Computer: A laptop is a personal computer designed for mobile use and is small enough to sit on one’s lap. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device (a touchpad, also known as a trackpad, and/or a pointing stick), speakers, and often including a battery, into a single small and light unit. Laptop computer is also known as Notebook Computer or Portable computer.

c) Handheld Computer: A handheld computer is a pocket-sized computing device, typically having a display screen with touch input or a miniature keyboard.

d) Personal Digital Assistance (PDA): A Personal Digital Assistant (PDA) is a handheld computer, also known as a palmtop computer. Newer PDAs commonly have color screens and audio capabilities, enabling them to be used as mobile phones (smartphones), web browsers, or portable media players.

F) Others: A few more computers are being made all over the world, which are in their developmental stages. They include

a) Optical Computer: Optical or photonic computing uses photons produced by lasers or diodes for computation. This was first achieved with the photonic transistor, invented in 1989 at the Rocky Mountain Research Center.

b) DNA Computer: DNA computing is a branch of computing which uses DNA, biochemistry, and molecular biology hardware, instead of the traditional silicon-based computer technologies.

c) Biological Computer: Biocomputers use systems of biologically derived molecules—such as DNA and proteins—to perform computational calculations involving storing, retrieving, and processing data.

d) Chemical Computer: A chemical computer, also called reaction-diffusion computer, BZ computer (stands for Belousov–Zhabotinsky computer) or gooware computer is an unconventional computer based on a semi-solid chemical "soup" where data are represented by varying concentrations of chemicals.

e) Quantum Computer: Quantum computing studies theoretical computation systems (quantum computers) that make direct use of quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data. Quantum computers are different from binary digital electronic computers based on transistors.

3. Advantages and Disadvantages of Computers: Computers have some strength, which makes them immensely useful and popular and also adorable for all. Some of its main characteristics are given below-

a) Accuracy: Computers can perform all the calculation and comparison accurately provided the hardware does not malfunction.

b) Automaticity: Computers are capable of doing certain level of automation provided they are programmed in that order. In the computer, once a task is initiated, it can perform on its own till its completion. It will execute the program in the correct sequence i.e. it will switch on/off the machine at the appropriate time, monitor the operational parameter, send warning signals or take corrective actions if the parameters exceed the control level and so on.

c) Diligence / Reliability: The human being suffers from weaknesses like tiredness, lack of concentration, etc. being constant and earnest in efforts and application. Humans also have feelings, so they become sad, depressed, bored and negligent and virtually it is reflected in the work they do. But the computers can perform the task repetitively for n numbers of times without any degradation in quality. So computers are more reliable than human beings.

d) Speed: Computers can calculate at a very high speed. A modern computer can execute millions of instructions in one second.

e) Storage: Computers can store a large amount of information in a very small space. The storage capacity of a computer is virtually unlimited.

f) Versatility: The computer can perform activities ranging from simple calculation to performing complex tasks in any field of knowledge and in different environment conditions, i.e. they can do hazardous jobs even in hospital environment.

Being an electronic device the computers have certain limitations also, which can be summarized as follows.

a) Lack of Decision Making Power: Computers cannot decide on their own; they are dependent on human instruction. Computers can only do what they are told to do.

b) Zero IQ: Computers are dumb machines with zero IQ. They need to be told in each and every step, however minute it may be.

c) No Heuristic: Heuristic refers broadly to learning from past experiences. If a computer commits an error once and the similar situation / event occurs again, the computer will commit the same error again. i.e. it cannot learn from the past experiences.

4. Uses of Computers: Computer is used everywhere in the world in every field of life. It has a very big impact on our day-to-day life and increasingly it is becoming an integral part of our life. It is enhancing our efficiency and productivity in all activities. It is used for a number of applications like education, research and development, entertainment, medical treatment, business, military services, space, etc.. The uses of computers in human life are virtually endless. A cursory account of it is given below:

a) Education: There are many uses of computer in schools, colleges and universities. For example, student details are stored into the computer system for subsequent operation on them. Multimedia, animations, graphics and charts could be used to teach the students and many boring topics can be made interesting by using multimedia. Students again could access internet for online help and courses for more information.

b) Health and Medicine: Computers are helping immensely to monitor the extremely ill in the intensive care unit and provide cross-sectional views of the body. This eliminates the need for hired nurses to watch the patient twenty-four hours a day, which is greatly tiring and error prone. Doctors use computers in diagnosing certain diseases. Computers are now able to map, in exquisite details, the structure of the human cold virus - the first step towards the common cold. Furthermore, computers are used greatly in managing patients, doctors, wards and medicine records, as well as for making appointments, scheduling surgeries, etc.

c) Agriculture: Farmers use small computers to help themselves with billing, crop information, and cost per acre, feed combinations, and market price checks.

d) Banking:  Every bank is now using a computerized system because it is very fast and user friendly. ATM cards, credit cards, are used everywhere now which let us bank any time we want. PC banking (Personal Computer banking), mobile banking allows us to see our bank balance, request transfers between accounts and pay bills electronically, etc.

e) Entertainment: Computers are used to make cartoon movies, animated and special effects in movies, games, and so on.

f) Sports: In sports computers are used widely in conjunction with video cameras. These are used to record the motion of all the sports men. 3D programs are used later on to help the trainers see their movements and to improve their style of playing.

g) Communication: Internet is becoming an information superhighway with lots of facilities to communicate by Email, chat, Voice over Internet Protocol (VoIP), Video Conferencing, etc.

h) Traffic Light Control: In traffic light control the computer is being employed to drive the traffic signals. There are some programmed codes like “turn off the red light” or “turn on the red light” to control the traffic signal and to carry out the instructions that follows.

i) Day to Day Life: It is used in Railway ticket booking, air ticket booking, and so on. In simple it can be said that now-a-days we are surrounded by the computer system and it is not possible to live without them.

5. Conclusion: Experts don’t agree on computer classification because computer technology is changing so fast that within the span of a month, when a new system comes out, it is faced with two potential factors- one costs the same and has a much higher performance and the other has the same performance but costs much less. Thus, a recently introduced smaller system can outcome (outperform) the large model of a few years ago and a new PC can do the work of an earlier mini at a much lower cost.

This is the Computer Age and these machines are beginning to affect our lives in many ways. There are so many applications of computers that it becomes virtually impossible to mention their applications in our day to day life. The computer era appears before us with the promise of new and improved ways of thinking, living and working. Computers are all around us and avoiding them is virtually impossible. We have been exposed to the world of computer hype, computer advertisements and computer headlines. We interact with computers in our daily lives - whether we are at the cinemas, the school, or the public library or anywhere in between.
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