Computers are now affecting every sphere of human activity and bringing about many changes in industry, government, education, medicine, scientific research, law, social sciences and even in arts like music and painting. Computers are built to carry out a small variety of instructions. A computer may thus be thought of as a servant who mould carry out instructions obediently, uncritically at a very high speed and without exhibiting any emotions. An algorithm expressed using a precise notation is called a computer program. The computer's processing unit interprets the instructions in the programs executes them and sends the results to the output unit. The areas of application of computers are confined only by limitations on human creativity and imagination; in fact any task that can be carried out systematically using a precise step by step method can be performed by a computer. Therefore it is essential for every educated person today to know about a computer, its strengths, its weakness and its internal structure. Computers are machines which can help mankind in many ways, but they do not threaten us.