Concepts are presented using intuitive descriptions. Important theoretical results are covered, but formal proofs are largely omitted. In place of proofs, figures and examples are used to suggest why i should expect the result in question to be true. The fundamental concepts and algorithms covered in the book are often based on those used in both commercial and open-source operating systems. My aim is to present these concepts and algorithms in a general setting that is, not tied to one particular operating system. However, i present a large number of examples that pertain to the most popular and the most innovative operating systems, including Linux, Microsoft Windows, Apple Mac OS X, and Solaris and Android also. The organization of the text reflects my many years of teaching courses on operating systems. Consideration was also given to the feedback provided by the reviewers of the text, along with the many comments and suggestions i received from readers of our previous editions and from our current and former students. The book, which provides a detailed overview of the Operating System, has been carefully designed so that a reader who is not familiar with details of computer architecture can start from scratch with ease. Every next chapter provides a very lucid and comprehensive introduction to the functioning of OS from inside. I believe that this understanding is crucial for a better appreciation of this book. However, for the reading of the book, no specific sequence is needed for reading, since the various topics covered are that independent in nature, and the reader can grasp them depending on how the book is designed or also depending on what he/she exactly wants to know.