The book is good, no doubt about it. And it covers a big gap in the Unix world. It helped me numerous times to understand how things work in the kernel of FreeBSD. But, and there is a big but here, the book does not contain even a single line of code. Strange for a book that is supposed to describe a kernel. There are a few instances of pseudo-code here and there but nothing more. The book gives you the big picture, describes the various parts of the kernel like virtual memory, scheduling, filesystems but it is too descriptive in my opinion. I would like to see instead of long descriptions some real kernel code. Ofcourse you may argue that you can find all the source code in the world in FreeBSD, but thats different. Its not a book for beginners, you should already have read some other Operating System book first before you dig in this one as the authors themselves agree. Bottomline: good book but too theoretical for my taste. I recommend it only to the serious reader. Its not a bed time book. You need to work your brain to make the connection.