Mac OS X Internals [Englisch] [Gebundene Ausgabe]

I had the opportunity to review the draft manuscript of Amit Singh's Mac OS X Internals book. With so many different types of operating systems books out there, let me try to place the book to give a better idea what to expect. There are general introduction books that normally introduce the operating system to the reader, without explaining what is actually going on. We have concept books (I put "The Design and Implementation of the FreeBSD Operating System" in this category) which are usually a good introduction to a new system. I used to be a great fan of this type of books, and I still enjoy reading them, but I don't anticipate much new from them. The fact is that operating systems today differ not that much in concepts and abstractions but more in their implementation. Then we have the kernel programming books that either cover the kernel programming in general, like Linux Kernel Internals, or focus on specific parts of the kernel, like Linux Device Drivers.

The Mac OS X Internals book falls into a category that I call OS Internals books category. Books in this category (like the popular Inside Windows books) are similar to the concept books in the sense that they are not focusing on solving some predefined problems, but rather share knowledge. They differ from the concept books in that they approach the concepts from implementation point of view. In recent years I have become a great fan of this type of books. Books in this category are both very enjoyable for anyone interested in the OS but also very useful for application developers.

Actually Amit's book does start off as more of a concept book, and in the first part of the book he gives a great overview of the Mac OS X system, which should be an interesting read even for people not using Mac, but with general interest in operating systems. I found it particularly interesting to read because OS X is so different from other operating systems I know and love, like Linux and Solaris. We've all heard how Mac OS X is built on top of the Mach kernel, uses large parts from BSD, supports backward compatibility via the Carbon API, etc. Not until I had read the first part of this book I fully understood how all the pieces fit together.

In my opinion the first two chapters are rich enough in content and interesting and fun to read for me to recommend this book to anyone interested in operating systems, regardless if they will ever do any programming on a Mac.

The remaining parts of the book cover OS X in a logical order, from the bottom up. Since the book is more focused on educating the reader of how things work rather that trying to teach how to do some particular task (like a network programming book would do) it is important to realize that the book is covering a lot of content, which may not all be of interest to you. If you are more interested in some particular area it is probably wise to jump directly to the appropriate chapter.

The book covers a lot, including the xnu kernel, the boot process, and the role of the firmware. It covers typical OS topics, like processes, virtual memory management, IPC, file systems, and the I/O Kit. What made these chapters especially interesting was to see exactly what part the Mach kernel plays here.

While reading the book I have to say that I have become a great fan of Amit's style. He manages to find a good balance between breadth and depth in his coverage, while keeping the text interesting. Each chapter covers each topic to a reasonable level. He achieves the depth by carefully selecting parts where he drills in quite extensively. Here he uses examples to clarify things. His examples are almost all excellent, both usually short, and to the point. The examples both lend the reader a first hand experience with some low level concepts, but also work as a starting point for the reader to actually try out things for themselves. Amazingly the examples usually don't require anything special beyond the normal dev setup. Meaning, you don't have to do any kernel programming to run most of the examples, which is great for application programmers like me.

After reading this book, I can recommend this book to anybody interested in operating systems and to all developers for the OS X system. OS enthusiasts will get a great overview of the Mac OS X system which will allow them to compare OS X to their own system, be it Linux, Windows, or Solaris. OS X application developers will probably gain the most from this book. This is not a kernel programming book but a book that builds up a strong base for application programmers. Whereas the book is not directly covering any specific class of API, Cocoa, Carbon or POSIX, it builds up a very strong base. For example, after reading the IPC chapter, things like Cocoa notification, Cocoa tasks and threads, remote objects, all become very clear. It will also make it much easier for anyone familiar with for instance Carbon or POSIX to move to Cocoa, because you will understand the common part of the API you know and the new one. Finally, for anyone doing anything advanced in Mac OS X, this book is a must have.

This book is essential for anybody that wants to understand the inner workings of Mac OS X, which should include all serious OSX software developers. This book is also a must read for any technical users of OSX, in order for them to know what's really underneath the covers, even when they are not writing software for OSX.

I am the second type of reader: I am a researcher with Microsoft Research, where I work mostly on operating-systems related topics. However, at home, I've had machines running OSX since version 10.0, and I have been waiting for somebody to write this book since then. (In fact, I was eager enough to review portions of an early draft of this book.)

The published book is a bit daunting, at over 1600 pages (bound in a sturdy format, which should tolerate heavy use). However, as quickly becomes clear, it covers a complex topic in such substantial detail that it is hard to see how it could be shorter. Also, given the book's size, and the amount of material it covers, the price seems very reasonable.

Fortunately, despite its size, the book is well structured and has a good index, so information is easy to find. Also, the book is written in an highly readable style, which helps the reader maintain attention. As a result, the book is quite pleasant to browse and read a few dozen pages at a time (as I've been doing for a while, as light bed-side reading).

One of the reasons this book is so useful is that, even more so than other modern operating systems, OSX is a complex mix of new and legacy technologies, both proprietary and open source. So to understand OSX, one has to understand parts of Mac OS 9, Mach, BSD Unix, NextStep, GNU/Linux as well as technology novel to OSX. This book does a good job of covering all of these influences, and give enough historical background to understand why OSX is like it is. Of course, it is possible to successfully use OSX as a "Unix", without knowing about other APIs or subsystems---however, this makes it impossible to use much functionality, and to truly understand the entire system.

This book covers most essential OSX abstractions and concepts, much like the Magic Garden Explained does for System V, the "red daemon" books do for BSD, and the Windows Internals books do for NT. So, the reader will know how scheduling, memory management, synchronization and inter-process communication works, how Mach tasks relate to processes, and other such essentials.

Some of the other operating system books (e.g., the BSD books) relate what they discuss to particular files and functions of the source code. As far as I can tell, this book does this to an unprecedented extent, describing in detail the Darwin sources for OSX and how they implement the concepts being discussed. In particular, for important system aspects, such as booting and initialization, and scheduling, the data and control flow between source functions is given in complete detail. So, for anybody wanting to explore the Darwin sources, I would think this book would be an invaluable guide.

Another striking property of this book is its detailed "programming examples", for which full source code is usually given. These make the book feel much different than other concepts books, as the author clearly likes to get "down and dirty" and play with the aspects of the system that he describes. The examples range from the incredibly useful (such as user-mode install and control of device drivers) to the highly esoteric (a custom boot GUI in Open Firmware). Some of the examples, such as the one on OSX virtual-machine-monitor interfaces, are likely the only place one may find information and working code for powerful OSX features. These "examples" are typically the basis for interesting system utilities, and in combination with the book's website (osxbook.com), they remind me of how the SysInternals utilities and source code have helped make Windows internals much less mysterious, and enabled much advanced systems work for Windows.

It is worth stressing again that the book is amazingly detailed on a number of topics. For example, it covers the hardware and system initialization of OSX in great detail, in particular for PowerPC and Open Firmware. Also, one could say there is a "mini book" on filesystems, with around 250 pages dedicated to OSX filesystems and the detailed inner workings of HFS+. Much of this information is not available anywhere else in a accessible form for an OSX audience, as far as I know.

Finally, the book has the website http://osxbook.com (formerly kernelthread.com) that is frequently updated with interesting new stuff. There is already lots of bonus material (and sources) on this website. In fact, I keep seeing the website cited in slashdot postings, as the author releases new utilities etc. If you like the articles etc. on that site, you will almost certainly enjoy this book. Also, having the book will make it easier to understand the source for advanced OSX tricks and utilities, both those at osxbook.com and elsewhere.

A notable omission in the book is that it doesn't have much of a discussion of the internals of OSX networking (although it says it is much like that in BSD). I was somewhat surprised when I noticed this, but I guess that the book is as thick as it can be at 1600 pages. Hopefully the book's author will be posting bonus material about OSX networking on the book's webpage, which will make the treatment truly comprehensive.

This book has to be one of the most comprehensive treatments of any operating system ever. I read through the sections with which I am most familiar (file systems, Spotlight and HFS). The level of detail and understanding expressed in those sections is very impressive. I thought I might find some errors or at least niggling details that weren't quite right but I could not find any.

Perusing the other sections of the book I even found that I learned a few things. The depth and breadth of this book make it a must-have for anyone involved in MacOS X programming (IMHO). Even if you're not a kernel programmer, there are many details and pieces of information that explain how and why things work the way they do.