Book excerpt: UNDERSTANDING OPERATING SYSTEMS provides a basic understanding of operating systems theory, a comparison of the major operating systems in use, and a description of the technical and operational tradeoffs inherent in each. The effective two-part organization covers the theory of operating systems, their historical roots, and their conceptual basis (which does not change substantially), culminating with how these theories are applied in the specifics of five operating systems (which evolve constantly). The authors explain this technical subject in a not-so-technical manner, providing enough detail to illustrate the complexities of stand-alone and networked operating systems. UNDERSTANDING OPERATING SYSTEMS is written in a clear, conversational style with concrete examples and illustrations that readers easily grasp.