For the most part this book is informative. If you have no idea of how a basic Operating System functions, or what it's responsibilities are, then this book will definitely clue you in. However, this book seemed to fall short of what the writers promised. For example, the version of XINU described in this book boots from DOS. I am suspicious of any operating system that boots from another operating system and then uses the services of it...it reminds me of Microsoft Windows 3.1. The OS also uses and relies on some of the PC's BIOS routines and services. While that technique makes the OS portable on different PCs, it limits its use only to PCs and hides a lot of operations that (in my opinion) should be shown. After reading it a few times, I found that the book was quite helpful after all. The OS has been ported to many other CPU's. The full source code can be found on the internet. The OS is quite powerful but still is simple (I was able to port the code to run on a 68010 project of mine; seeing the ported versions and the book's theory was enough to guide me). A decent book, it doesn't describe an operating system 'from the ground up', but comes close to it. Sure there are other operating systems out there with open source, but how many of those tell you what each function of the code does and what role these functions play in a OS?