This book is a real asset for professionals interested in operating systems architecture and implementation. It reveals a lot of implementation details together with the principles to organize this structure in an orderly and understandable manner.
The authors’ goal is to remove all the mystery that surrounds the operating system design and achievement, and they succeed in systematically presenting the construction of XINU, an operating system for the Apple Macintosh which can also run on the IBM PC, the DEC LSI-11, PDP 11, and VAX, the SUN 2 and SUN 3, and machines based on the NS 32000 processor.
The basic principle enunciated in the preface, and underlined in the book countless times, is hierarchical ordering, which makes it possible to clearly specify a complex operating system in terms of levels and components. The authors also emphasize the importance of the principles which underlie the design of the UNIX-like multiprocessing system, and they give the code for every piece of the operating system; the machine-dependent routines are written in assembly language and the others are written in C. Thus, the reader can clearly see how the ideas and design principles come to life.
Whenever necessary, the authors draw the less-experienced reader’s attention to the possibility of paying too much attention to the practical realization of some functions when the focus should be on understanding the basic ideas behind them. Equally important to the student is the way in which the authors justify their choice between alternative solutions to a problem, considering the advantages and disadvantages of each. The authors seek solutions that solve the problem as well as possible at minimal cost in terms of implementation and resource use. Remarkably, the authors always have their attention on the goal to be achieved, eliminating the generalizations and simplifications that have no place in the context of the proposed objective.
The exercises, questions, and selected references at the end of each chapter are very important and useful. Their purpose is to fix the ideas presented in the chapter and to point the reader to more detailed discussions of some material.
The 24 chapters of the book present all components of the XINU operating system. The first chapter is a good review of operating system facilities. Chapter 2 reviews the architecture of the Macintosh, describing the basic features of the processor, memory, and communications devices. The third chapter introduces a set of procedures that manipulate lists and queues. The other chapters describe the construction of a layered operating system capable of supporting multiple processes, network communication, and a file system. Each chapter describes one component of the XINU system (including memory management, process management, process coordination, process synchronization, clock management, interprocess communication, device management, device drivers, the file system, and the user interface) and explains its role. The details are illustrated with programs.
Chapter 24 discusses the ways a designer selects the procedures to provide a fixed set of system calls and to reconfigure the software to accommodate changes in hardware devices.
Chapter 14, “Window Management Using Devices,” is noteworthy. It deals with the problem of window management at the operating system level. This approach is a novelty for UNIX-like operating systems and eliminates the usual anarchy that surrounds the window field. It offers consistent and simple window primitives that are implemented easily and perform well.
The discussion of the material in chapter 19, “A Syntactic Namespace,” denotes the importance the authors place on a unified conceptual approach to the varied notions supported in the XINU environment. The solution generated by the “prefix patterns” is very elegant. It offers the user an efficient and simple tool for supporting file names almost transparently.
The authors’ exposition is clear and systematic and they link their material in a natural fashion. They are obviously concerned with the user friendliness of the presentation. The first appendix is an introduction to C which compares it with ALGOL, Pascal, and PL/I; this will be very useful for less-experienced readers. The presence in one book of both the theoretical exposition of some ideas and their implementations is also remarkable. This combination will encourage readers who want to run parts of the XINU system effectively.
Appendix 2 (pages 485–608) is the XINU Programmer’s Manual, which gives a terse description of XINU procedures. It is intended to serve as a quick reference for programmers, not to teach the operating system. It is arranged like the UNIX manual: each page describes one command, system call, or library routine. The book also contains a comprehensive list of references and an index.
Maybe the book should specify how the hardware influences the behavior of the operating system and discuss the conception of either XINU or some other operating system. While most readers would consider this a common sense question, this approach could sometimes be risky.
The reader has not previously been offered such a coherent, well-structured, and well-written book on this subject. It is primarily designed as a textbook for an advanced undergraduate or graduate course, but it is also suitable for designers of new operating systems. In addition, it contains a lot of useful information for all computer users. This book represents a significant contribution to the literature in this field.
