We have long felt that the traditional approach to teaching about Operating Systems can make (OSs) was not the best approach. The purpose of this book is to support a differen approach to this task When studying any complex domain of knowledge, the onder in which one learns the hierarchy of principles, laws, ideas, and concepts the process casier or more difficult. The most common technique is to partition the subject into major topics and then study each one in great detail For OS this has traditionally meant that after a brief introduction to some terms and an overview, a student studied isolated topics in depth-processes and process management, then memory management, then tile systems, and so on. We can call this a depth-oriented approach or a vertical approach. After learning a great mass of unrelated details in these isolated topic areas, the student then examined case studies, examples of real OSs, and finally saw how the different topics fit together to make a real 05