This revised edition of the book has been designed for the students of B.Tech. (all branches of engineering)/MCA/MBA of Indian universities imparting technical education. A systematic presentation of principles and practices of Information Technology given would also be useful for all BCA/B.Sc. (Computer Science), 'A' level of DOEACC and IGNOU students. This book explains following in several details and contains more and revised examples, figures, illustrations, objective questions and a new chapter on Operating Systems.