This book is intended for two principle classes of readers: those interested in applying program behavior models in their systems modeling efforts, and those interested in program behavior, per se, for research or study purposes. Chapter 1 motivates program behavior modeling and measurement, and introduces several philosophical distinctions to be used later. Chapter 2 deals with those features of paging and paging systems relevant to later discussions: hardware, paging, algorithms, and a more detailed examination of the properties of locality. Chapter 3 presents several basic models, and chapter 4 elaborates on one of the most important modules - the lRU stack model and its extensions. Chapter 5 covers techniques for program measurement and model validation, including an introduction to spectral analysis. Some of the more advanced of these techniques are applied in chapter 6 to two sophisticated program models. Finally, the various models and measurements methods are summarized in chapter 7.