Since the eighth edition of this book was published, the field of operating systems has seen continuous innovations and improvements. In this new edition, I have tried to capture these changes while maintaining a comprehensive coverage of the entire field. To begin the process of revision, the eighth edition of this book was extensively reviewed by a number of professors who teach the subject and by professionals working in the field. The result is that, in many places, the narrative has been clarified and tightened, and illustrations have been improved. Beyond these refinements to improve pedagogy and user friendliness, the technical content of the book has been updated throughout to reflect the ongoing changes in this exciting field, and the instructor and student support has been expanded.