As a widely used textbook for introductory OS classes (Dragon Book), it tries to explain every crucial OS notion as clearly as possible. Many times very lengthy. Therefore it gets the benefit of being never ambiguous. However in real-world examples, this book is not very helpful. As I’m coming from a non-CS education, often times I find various OS notions hard to grasp, at least not transparent. This book fills my blanks very well.
Process and Memory managements are where this book shines. Various virtual memory models have existed, iterated and implemented in the discussions. It also provides many clear illustration about system layout and inter-process communications (IPC).