This is a book about the Universal Serial Bus, or USB. The USB was designed by the computer industry to replace the ailing and ancient RS-232 serial-port technology. The USB is bigger, faster, and better. It's built to handle the demands of audio and video. It's built to be hot pluggable. It's built to be plug-n-play. It's built to host a hundred or more devices at the same time, though it works wonderfully well with just a single device or two. Finally, it's built to be inexpensive enough to seamlessly become a part of the personal computer without burdening the PC owners.

This book explains exactly what the USB is and how it works. It does not explain how to write software for the USB. We'll leave it up to Sun, Apple, and Microsoft to tell us how to write code for their platforms. This is a "concepts" book. If you want to know how it works under the hood, then you picked up the right book. You will get a lot of detail about how the bus and its devices all communicate and keep things straight, but you won't see any state or timing diagrams that require an engineering degree to understand.