This book is about compressing data to make digital systems work more effi­ ciently. According to the dictionary, when something is compressed, it is con­ densed, squeezed, constricted, or pressed together to fit into less space. Air is compressed for a variety of useful purposes. Businesses are downsized to make them more efficient. We pack our daily schedules tighter and tighter to accomplish more. Who has not crushed an empty soda can for recycling? Many different things can be compressed, including the data in computers, communications links, consumer-electronics gear, and all sizes and shapes of digital systems. Are you curious about how data compression squeezes the "air" out of digital bits? Would you like to know where it is used and, increasingly, why the marketplace demands it be used? Would you like to learn the right way to build data compres­ sion into your products? Then, this book is for you. This exciting technology and its importance for current and future digital systems are explained in easy to understand terms. No previous knowledge of data compression is required because the necessary technical background is carefully developed. Neither is an extensive understanding of mathematics because there are few equations and important ideas are graphically illustrated. If you read any of the popular or professional monthly magazines that cover the latest advances in digital systems, your background is adequate. If you understand this preface, you are ready to tackle this book.