This book should have been titled "SCO Internals", as it discusses different SCO versions (including Openserver R5) in a practical approach, as the title states. Besides that, it's a very good book, which takes you through the shell, processes, memory management, IPC, file services, I/O system, and many other areas typically found in this kind of books.
Again, the problem lies that the author expects you to have a SCO flavour installed for practicing. If that weren't the case, do not expect to practice (in most cases) the examples given in the book, as they rely on utilities found only in SCO, such as crash, adm, etc.
On the positive side, the book contains several screen dumps with captures of program output and code examples, which makes the above requisite dispensable. Recommended with reservations.