The fact that you're reading this book means you want to learn about the Linux operating system (OS). To begin this journey, you must first understand what Linux is and what an OS is. This chapter is therefore devoted to these basic issues. I describe what an OS is, how users interact with an OS, how Linux compares to other OSs with which you may be familiar, and how specific Linux implementations vary. Understanding these issues will help you make your way as you learn about Linux and switch between Linux-based systems and other computers.