Removing the mystery from operating system design, this text guides readers through the construction of a conventional process-based operating system using practical, straightforward primitives. It reviews the major system components and imposes a hierarchical design paradigm that organizes the components in an orderly and understandable manner. The text begins with a bare machine and proceeds step by step through the design and implementation of a small, elegant system. Software and instructions for building a Linksys lab are available on the author'¬"s website.