In addition to providing abstractions such as processes, address spaces, and files, an operating system also controls all the computer’s I/O (Input/Output) devices. It must issue commands to the devices, catch interrupts, and handle errors. It should also provide an interface between the devices and the rest of the system that is simple and easy to use. To the extent possible, the interface should be the same for all devices (device independence). The I/O code represents a significant fraction of the total operating system. How the operating system manages I/O is the subject of this chapter.
This chapter is organized as follows. We will look first at some of the principles of I/O hardware and then at I/O software in general. I/O software can be structured in layers, with each having a well-defined task. We will look at these layers to see what they do and how they fit together.
Next, we will look at several I/O devices in detail: disks, clocks, keyboards, and displays. For each device, we will look at its hardware and software. Finally, we will consider power management.