To understand a computer system, you must understand the software that manages and coordinates its pieces. The operating system of a computer is the glue that holds the hardware and software together. It is the software foundation on which all other software rests, allowing us to write programs that interact with the machine. This chapter and the next one explore the way in which an operating system manages computer resources. Just as a policeman organizes the efficient flow of cars through an intersection, an operating system organizes the efficient flow of programs through a computer system.