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Preface


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[Page xv]

Preface

Most books on operating systems are strong on theory and weak on practice. This one aims to provide a better balance between the two. It covers all the fundamental principles in great detail, including processes, interprocess communication, semaphores, monitors, message passing, scheduling algorithms, input/output, deadlocks, device drivers, memory management, paging algorithms, file system design, security, and protection mechanisms. But it also discusses one particular systemMINIX 3a UNIX-compatible operating system in detail, and even provides a source code listing for study. This arrangement allows the reader not only to learn the principles, but also to see how they are applied in a real operating system.

When the first edition of this book appeared in 1987, it caused something of a small revolution in the way operating systems courses were taught. Until then, most courses just covered theory. With the appearance of MINIX, many schools began to have laboratory courses in which students examined a real operating system to see how it worked inside. We consider this trend highly desirable and hope it continues.

It its first 10 years, MINIX underwent many changes. The original code was designed for a 256K 8088-based IBM PC with two diskette drives and no hard disk. It was also based on UNIX Version 7 As time went on, MINIX evolved in many ways: it supported 32-bit protected mode machines with large memories and hard disks. It also changed from being based on Version 7, to being based on the international POSIX standard (IEEE 1003.1 and ISO 9945-1). Finally, many new features were added, perhaps too many in our view, but too few in the view of some other people, which led to the creation of Linux. In addition, MINIX was ported to many other platforms, including the Macintosh, Amiga, Atari, and SPARC. A second edition of the book, covering this system, was published in 1997 and was widely used at universities.


[Page xvi]

The popularity of MINIX has continued, as can be observed by examining the number of hits for MINIX found by Google.

This third edition of the book has many changes throughout. Nearly all of the material on principles has been revised, and considerable new material has been added. However, the main change is the discussion of the new version of the system, called MINIX 3. and the inclusion of the new code in this book. Although loosely based on MINIX 2, MINIX 3 is fundamentally different in many key ways.

The design of MINIX 3 was inspired by the observation that operating systems are becoming bloated, slow, and unreliable. They crash far more often than other electronic devices such as televisions, cell phones, and DVD players and have so many features and options that practically nobody can understand them fully or manage them well. And of course, computer viruses, worms, spyware, spam, and other forms of malware have become epidemic.

To a large extent, many of these problems are caused by a fundamental design flaw in current operating systems: their lack of modularity. The entire operatng system is typically millions of lines of C/C++ code compiled into a single massive executable program run in kernel mode. A bug in any one of those millions of lines of code can cause the system to malfunction. Getting all this code correct is impossible, especially when about 70% consists of device drivers, written by third parties, and outside the purview of the people maintaining the operating system.

With MINIX 3, we demonstrate that this monolithic design is not the only possibility. The MINIX 3 kernel is only about 4000 lines of executable code, not the millions found in Windows, Linux, Mac OSX, or FreeBSD. The rest of the system, including all the device drivers (except the clock driver), is a collection of small, modular, user-mode processes, each of which is tightly restricted in what it can do and with which other processes it may communicate.

While MINIX 3 is a work in progress, we believe that this model of building an operating system as a collection of highly-encapsulated user-mode processes holds promise for building more reliable systems in the future. MINIX 3 is especially focused on smaller PCs (such as those commonly found in Third-World countries and on embedded systems, which are always resource constrained). In any event, this design makes it much easier for students to learn how an operating system works than attempting to study a huge monolithic system.

The CD-ROM that is included in this book is a live CD. You can put it in your CD-ROM drive, reboot the computer, and MINIX 3 will give a login prompt within a few seconds. You can log in as root and give the system a try without first having to install it on your hard disk. Of course, it can also be installed on the hard disk. Detailed installation instructions are given in Appendix A.


[Page xvii]

As suggested above, MINIX 3 is rapidly evolving, with new versions being issued frequently. To download the current CD-ROM image file for burning, please go to the official Website: www.minix3.org. This site also contains a large amount of new software, documentation, and news about MINIX 3 development. For discussions about MINIX 3, or to ask questions, there is a USENET newsgroup: comp.os.minix. People without newsreaders can follow discussions on the Web at http://groups.google.com/group/comp.os.minix.

As an alternative to installing MINIX 3 on your hard disk, it is possible to run it on any one of several PC simulators now available. Some of these are listed on the main page of the Website.

Instructors who are using the book as the text for a university course can get the problem solutions from their local Prentice Hall representative. The book has its own Website. It can be found by going to www.prenhall.com/tanenbaum and selecting this title.

We have been extremely fortunate in having the help of many people during the course of this project. First and foremost, Ben Gras and Jorrit Herder have done most of the programming of the new version. They did a great job under tight time constraints, including responding to e-mail well after midnight on many occasions. They also read the manuscript and made many useful comments. Our deepest appreciation to both of them.

Kees Bot also helped greatly with previous versions, giving us a good base to work with. Kees wrote large chunks of code for versions up to 2.0.4, repaired bugs, and answered numerous questions. Philip Homburg wrote most of the networking code as well as helping out in numerous other useful ways, especially providing detailed feedback on the manuscript.

People too numerous to list contributed code to the very early versions, helping to get MINIX off the ground in the first place. There were so many of them and their contributions have been so varied that we cannot even begin to list them all here, so the best we can do is a generic thank you to all of them.

Several people read parts of the manuscript and made suggestions. We would like to give our special thanks to Gojko Babic, Michael Crowley, Joseph M. Kizza, Sam Kohn Alexander Manov, and Du Zhang for their help.

Finally, we would like to thank our families. Suzanne has been through this 16 times now. Barbara has been through it 15 times now. Marvin has been through it 14 times now. It’s kind of getting to be routine, but the love and support is still much appreciated. (AST)

Al’s Barbara has been through this twice now. Her support, patience, and good humor were essential. Gordon has been a patient listener. It is still a delight to have a son who understands and cares about the things that fascinate me. Finally, step-grandson Zain’s first birthday coincides with the release of MINIX 3. Some day he will appreciate this. (ASW)

Andrew S. Tanenbaum

Albert S. Woodhull

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