This book describes how all these kinds of support are provided both by operating systems and by additional software layered on top of operating systems, which is known as middleware. The objective of this book is to make the students understand the basic operating system concepts such as processes, threads, scheduling, synchronization, deadlocks, memory management, file and I/O subsystems and protection.This note explains the following topics: OS Internals, C Programming, Bit-wise Operators, File Systems, Processes, File Descriptors, Threads, File Systems Internals, Synchronization, Deadlock.Also provides a solid theoretical foundation for understanding operating systems. The ninth edition has been thoroughly updated to include contemporary examples of how operating systems function. The text includes content to bridge the gap between concepts and actual implementations. End-of-chapter problems, exercises, review questions, and programming exercises help to further reinforce important concepts. A new Virtual Machine provides interactive exercises to help engage students with the material.