The book uses a precise and systematic approach to present the subject of computer science and information technology for GATE (CS). The content of the book is built after thorough analysis of concepts asked in previous year question papers, and thus emerges as a fully competent book to cater to the needs of the GATE aspirants. Difficult topics such as theory of computation, compiler design, operating systems are clarified using simple steps and illustrations as well as supported by a large number of problems for practice; as these form the major portion of the GATE syllabus.