Computers are changing almost every aspect of our lives. They're changing how we relate to one another and even changing how we think of ourselves. The very idea that my brain is a biological computer that could be, in some fundamental mathematical sense, no more powerful than the laptop on which I'm typing these words is mind-boggling. The fact that I can program a computer to control a robot, play chess, or find a cure for disease is tremendously empowering.

This book is organized as a series of essays that explore interesting and fundamental topics in computer science with the aim of showing how computers and computer programs work and how the various aspects of computer science are connected. Along the way I hope to convey to you some of my fascination with computers and my enthusiasm for working in a field whose explosive growth is fueled in no small measure by the ability of computers to support collaboration and information sharing.

While not meant to be exhaustive, this book examines a wide range of topics, from digital logic and machine language to artificial intelligence and searching the World Wide Web. These topics are explored by interacting with programs and experimenting with short fragments of code while considering such questions as:

• How can a computer learn to recognize junk email?

• What happens when you click on a link in a browser?

• […]