Subtitled 'A guide to the QL Operating System', this book is not intended as an introduction for beginners. The sleeve notes quite specifically describe the intended reader, for the book is aimed at those who want to understand the workings of the QL ROM [Which one? - Ed] and this requires a full working knowledge of 68000/8 machine code.

Andrew Pennel, the author, also wrote Assembly Language Programming For The Sinclair QL, however, he has not simply rehashed that book but now takes a look at the QL's Operating System with an emphasis on functionality rather than simple description. The book goes beyond the supplied operating manual to provide a broader understanding of QDOS and how to use it.

The one hundred and seventy pages are split into nine chapters, along with a number of appendices and index. There are chapters on multi-tasking, the second processor, and interrupts, among others. Each chapters, along with a number headings detailing aspects of the topic under discussion.

Understanding the QL's Operating System is no easy task, but the author has done well to keep each chapter in clearly defined and comprehensible sections, which are further clarified by the use of diagrams, tables and example where appropriate. Having said that though, readers will still require a knowledge of Operating System principles and machine code as well as a few ideas on how they wish to use their knowledge in order to get the best from the book, and my only criticism of it is, that while concentrating on functionality it could also have given a few constructive suggestions on how to use all that knowledge.

The Sinclair QDOS Companion is written by Andrew Pennell. Published by Sunshine Books, it is reasonable value for money at £6.95 (ISBN 0-940408-90-0).