Welcome to my book “Simplified way to understand OPERATING SYSTEM. I have tried to cover all issues regarding operating system in a simplified notes form. The book offers a proper guidance to understanding Operating System in notes form within a short time. It focuses on the most important areas of Computer Science including ways of building your Computer System, important services provided by an Operating System and how the Computer Operating System performs these services etc. The book contains several chapters as units. The units are the key to helping you improve your skills as a student. By reading this book, you’ll find that you are enjoying learning more than ever before. As a result, you will feel more confident in your classes and be better prepared to demonstrate your acquired knowledge. I invite you to use this book “Simplified way to understand OPERATING SYSTEM” at undergraduate level. As you go through each unit, you will open the doors to success in University level as well as to many other areas in your life. Good luck and enjoy the journey! God bless you.