Removing the mystery from operating system design, this text guides readers through the construction of a traditional 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 the underlying machine and proceeds step by step through the design and implementation of a small, elegant system. The text provides code for each piece of the system. Software and instructions for building a laboratory are available on the author’s website.