A computer generally means a programmable machine. The two principal characteristics of a computer are: it responds to a specific set of instructions in a well-defined manner and it can execute a pre-recorded list of instructions (a program).

Modern computers are electronic and digital. The actual machinery — wires, transistors, and circuits — is called hardware; the instructions and data are called software.

All general-purpose computers require the following hardware components:

Memory: enables a computer to store, at least temporarily, data and programs.
Mass storage device: allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.
Input device: usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.
Output device: a display screen, printer, or other device that lets you see what the computer has accomplished.
Central processing unit (CPU): the heart of the computer, this is the component that actually executes instructions.



In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.


HISTORY OF COMPUTER

The computer as we know it today had its beginning with a 19th century English mathematics professor named Charles Babbage. He designed the Analytical Engine and it was this design that the basic framework of the computers of today are based on.

Generally speaking, computers can be classified into three generations. Each generation lasted for a certain period of time, and each gave us either a new and improved computer or an improvement to the existing computer.

First generation: 1937 – 1946 – In 1937 the first electronic digital computer was built by Dr. John V. Atanasoff and Clifford Berry. It was called the Atanasoff-Berry Computer (ABC). In 1943 an electronic computer named the Colossus was built for the military. Other developments continued until in 1946 the first general–purpose digital computer, the Electronic Numerical Integrator and Computer (ENIAC) was built. It is said that this computer weighed 30 tons, and had 18,000 vacuum tubes which was used for processing. When this computer was turned on for the first time lights dim in sections of Philadelphia. Computers of this generation could only perform single task, and they had no operating system.

Second generation: 1947 – 1962 – This generation of computers used transistors instead of vacuum tubes which were more reliable. In 1951 the first computer for commercial use was introduced to the public; the Universal Automatic Computer (UNIVAC). In 1953 the International Business Machine (IBM) 650 and 700 series computers made their mark in the computer world. During this generation of computers over 100 computer programming languages were developed, computers had memory and operating systems. Storage media such as tape and disk were in use also were printers for output.

Third generation: 1963 – present – The invention of integrated circuit brought us the third generation of computers. With this invention computers became smaller, more powerful more reliable and they are able to run many different programs at the same time. In 1980 Microsoft Disk Operating System (MS-Dos) was born and in 1981 IBM introduced the personal computer (PC) for home and office use. Three years later Apple gave us the Macintosh computer with its icon driven interface and the 90s gave us Windows operating system.

As a result of the various improvements to the development of the computer we have seen the computer being used in all areas of life. It is a very useful tool that will continue to experience new development as time passes.


CATEGORIES OF COMPUTER

Since the advent of the first computer different types and sizes of computers are offering different services. Computers can be as big as occupying a large building and as small as a laptop or a microcontroller in mobile & embedded systems. The four basic types of computers are:
SUPERCOMPUTER

The most powerful computers in terms of performance and data processing are the supercomputers. These are specialized and task specific computers used by large organizations. These computers are used for research and exploration purposes, like NASA uses supercomputers for launching space shuttles, controlling them and for space exploration purpose. The supercomputers are very expensive and very large in size. It can be accommodated in large air-conditioned rooms; some supercomputers can span an entire building. In 1964, Seymour Cray designed the first supercomputer CDC 6600.
MAINFRAME COMPUTER

Although Mainframes are not as powerful as supercomputers, but certainly they are quite expensive nonetheless, and many large firms & government organizations uses Mainframes to run their business operations. The Mainframe computers can be accommodated in large air-conditioned rooms because of its size. Supercomputers are the fastest computers with large data storage capacity, Mainframes can also process & store large amount of data. Banks, educational institutions & insurance companies use mainframe computers to store data about their customers, students & insurance policyholders.
MINICOMPUTER

Minicomputers are used by small businesses & firms. Minicomputers are also called as “Midrange Computers”. These are small machines and can be accommodated on a desk with not as processing and data storage capabilities as Supercomputers & Mainframes. These computers are not designed for a single user. Individual departments of a large company or organizations use Mini-computers for specific purposes. For example, a production department can use Mini-computers for monitoring certain production process.
MICROCOMPUTER

Desktop computers, laptops, personal digital assistant (PDA), tablets & smartphones are all types of microcomputers. The micro-computers are widely used & the fastest growing computers. These computers are the cheapest among the other three types of computers. The Micro-computers are specially designed for general usage like entertainment, education and work purposes. Well known manufacturers of Micro-computer are Dell, Apple, Samsung, Sony and Toshiba. Desktop computers, Gaming consoles, Sound & Navigation system of a car, Netbooks, Notebooks, PDAs, Tablet PCs, Smartphones, Calculators are all type of Microcomputers.


COMPONENTS OF COMPUTER

Hardware is generic term used to describe any component of a computer system with a physical presence and which can, therefore, been seen and touched.

Hardware components are often categorised as being input, output, storage or processing components. Devices which are not an integral part of the CPU are referred to as being peripherals. Peripherals are usually used for input, storage or output (such as a hard disk, keyboard or printer). A device does not necessarily have to be outside the same physical box as the CPU. The best example of this is the hard disk, which is a peripheral even though it is not usually housed within the main case. The main components of a computer are:

Input devices: They are hardware devices which take information from the user of the computer system, convert it into electrical signals and transmit it to the processor. The primary function of input devices is to allow humans to interact with the computer system. For instance a mouse allows the user to control the movement of the pointer (a common element in user interface design).
Output devices: They take data from the computer system and convert it to a form that can be interpreted by humans. For instance a monitor creates a visual electronic display to output information created by the processor to the user.
Processing devices: They are the components responsible for the processing of information within the computer system. This includes devices such as the CPU, memory and motherboard.
Storage devices: They are components which allow data to be stored within a computer system. This includes devices such as hard disk drives and compact disk drives.

Source: http://www.inyavic.com/2015/03/13/computer/

Dude, the first computing device was the abacus invented by the chinese sometime in the fiftren century.

lomprico:
Dude, the first computing device was the abacus invented by the chinese sometime in the fiftren century.

An abacus is not like a modern computer. People think of a computer as an electronic, programmable device that can store, retrieve, and process data. There were many computing devices prior to the electronic computer that had processing capabilities. They were mechanical devices and are computers. There are many different kinds of computing devices and an abacus is one of them.
Source: http://www.answers.com/Q/Is_Abacus_a_computer

computer system could be define as an electronic device that accepting data, performing certain operations and presenting the results of those operations. A functional unit, consisting of one or more computers and associated software, that (a) uses common storage for all or part of a program and also for all or part of the data necessary for the execution of the program, (b) executes user-written or user-designated programs, and (c) performs user-designated data manipulation, including arithmetic and logic operations. Note: A computer system may be a stand-alone system or may consist of several interconnected systems.