Arguably the most important invention of the modern world is the microprocessor. Arm claims to have sold 30 billion of its microprocessors. Microchip sells 1 billion of its microprocessors per year. Yes, that's "billion" with a "b." Where in the world are all these things? The numbers tell us they must be in many more places than just our computers. Microprocessors run smart phones, networks, web sites, cars, laptops, appliances, factories, etc. We are often unaware that, at the heart of devices we use every day, a hidden, or "embedded," microprocessor controls the device. It might be in a toy or in a coffeemaker. Your car may have 12, or 50, or 100 microprocessors. For example, one may be dedicated to collecting the air pressure in each tire. And yet, even though we use all these devices, we don't understand how they work. They seem like magic. That's because we don't understand how microprocessors work. We don't understand digital electronics. It's time to stop being ignorant. This book purports to lift the veil of secrecy, the clouds of ignorance hiding this wonderful device. I have every confidence that, when you learn how these microprocessors work, you will find them to be even more wonderful than before. When you learn the secret of how a magic trick works, it often becomes mundane, as in, "is that all there is to it?" When you learn how microprocessors work, I believe you will be even more in awe of them.