Like the Advanced User Guide, this publication from Dabs Press is aimed at the more serious user of the BBC range of machines. Written by David Atherton, formerly of the BBC's own software house, BBC Soft, it deals in the main with all aspects of the Master's operating system.

There are details of all new OS commands featured on the Master, the new 65C12 opcodes, all the new OSBYTE/OSWORD calls, sideways RAM programming, shadow RAM programming, paged ROM implementation, loading and saving of ROM images, driving the Tube in both directions, and filing system changes. The Tube section in particular deserves special mention as it really is excellent. There are a number of program listings provided in the book to illustrate various features and programming techniques. Some of these are quite useful utilities, especially the CMOS RAM editor and the clock ROM.

One of the most interesting and useful features of this book for me is the detailing of lists of differences between the various versions of the system software. For example, the 1770 DFS as supplied as an upgrade for the Model B, or as standard with the B+ and Master has suffered with a variety of bugs. In consequence, there have been many versions released. Here, at last, are details of the known bugs in each release which many will find of interest. Apart from the bug aspect of the software, having a detailed list of the differences in the software supplied for all the different machines will be a boon for many programmers who wish to make sure that their software will run on all machines.

The Master Operating System is a spiral-bound book and has 270 pages. The layout is good and there is a reasonable index and useful glossary too. At the back of the book there are several appendices providing lots of lists and quick look-up guides to the VDU commands, OS commands, memory map etc, all most useful to programmers. Along with this there are some hardware details such as pin-outs for the machines' various ports and sockets.

Although this book is called the Master Operating System, it is also claimed to be of interest to Model B, B+ and Electron owners. I would have to say that I find this only slightly true. Yes, there is information here that may be of interest to owners of Acorn machines other than the Master, but the book most certainly caters in the main for Master owners.

David Atherton's 'The Master Operating System' does contain a wealth of information for those who need it, and I think it is reasonably priced too. Check carefully, though, if contemplating the purchase of this book and you already have the Master Reference Manuals parts 1 and 2. I personally would consider it hard to justify buying the book in this case, but do decide this for yourself.