This book introduces the fundamental concepts and practical simulation te- niques for modeling different aspects of operating systems to study their g- eral behavior and their performance. The approaches applied are obje- oriented modeling and process interaction approach to discrete-event simu- tion. The book depends on the basic modeling concepts and is more specialized than my previous book: Practical Process Simulation with Object-Oriented Techniques and C++, published by Artech House, Boston 1999. For a more detailed description see the Web location: http://science.kennesaw.edu/~jgarrido/mybook,html. Most other books on performance modeling use only analytical approaches, and very few apply these concepts to the study of operating systems. Thus, the unique feature of the book is that it concentrates on design aspects of operating systems using practical simulation techniques. In addition, the book illustrates the dynamic behavior of different aspects of operating systems using the various simulation models, with a general hands-on approach.