A computer may be defined as “An electronic device that accepts data and instructions, processes it and gives the output in a desired manner.” According to A.S. Hornby, “A computer is an electronic device which stores information on disks or magnetic tape, analyses it and produces information as required from the data on the tape etc.” According to Sampath, “A computer is a power-driven machine equipped with keyboards, electronic circuits and recording devices for the high speed performance of mathematical operations.” In Oxford Dictionary, a computer is defined as, “An automatic electronic apparatus for making calculations or controlling operations that are expressible in numerical or logical terms.” In the words of Donald H. Sanders, “Computer is an electronic symbol manipulating system that is designed and organized to automatically accept and store input data, process them and produce output results under the direction of a detailed step by step stored program of instructions. A computer has the ability to perform the following: 1) Accepts the data and instructions given by user (Input) 2) Processes the data according to given set of instructions (Processing) 3) Displays the output according to the requirements of the user (Output) In figure, input devices such as keyboard, mouse, scanner, smart card etc. are used to provide input to the computer. In processing, computer performs sequence of actions required to be performed on data to convert it into result or information. Finally, computer gives output on output devices such as printer, monitor or plotter etc. Main storage is used to place the data and an instruction currently being processed and secondary storage is used to store the final or intermediate results for future use on storage devices like floppy disk, hard disk, optical disk etc.
1.1 Characteristics of Computer:
A computer is capable of performing all types of works ranging from simple to complex ones. The following characteristics make computer a very powerful machine. 1. Speed: Computers work at amazing speed and that too without mistakes. Complex calculations can be solved within fractions of a second. A computer can
perform about 3 to 4 million simple arithmetical operations per second. Speed of a computer is measured in milliseconds (10-3), micro-seconds (10-6), nano-seconds (10-9) and Pico-seconds (10-12). Due to its marvelous speed, time and effort of a human being is saved. The speed of computer varies from computer to computer, the speed is increasing day by day with fast processing devices and other devices connected to it. Accuracy: Results calculated by a computer are always accurate. Even complex instructions can be performed with high degree of accuracy. Computer does not commit mistakes in processing of data. Errors are produced only when inaccurate input is provided to the computer. For example, computer will produce inaccurate results if you try to divide a number by 0. The degree of accuracy depends upon the design of a computer. Reliability: The results obtained by a computer are more reliable, because computers do not get tired even after long hours of work, so the results computed are dependable. Computer systems are widely accepted due to their exceptional reliability. Versatility: A computer can perform versatile jobs. It can perform a number of jobs depending upon the instructions fed to them and their hardware characteristics. You can surf the internet, play games, and do typing while listening songs. Computers are not only capable of handling complex arithmetic operations but also are able to perform a number of jobs at the same time. Storage capacity: A computer can store huge amount of data. It can store various files, articles, pictures, documents; sound etc. in its memory, the required data can be retrieved whenever required. The data stored in computer is enormous. Primary memory, secondary memory- Registers RAM, Magnetic disks, CDs, DVDs etc. can store several GBs of data. That is why a computer is also called a store house.