This book has 253 A4 size pages, which sounds a lot, but you should be aware that 136 pages are simply re-prints of manufacturers' IC data sheets. The remaining 117 pages are reproduced from a computer printout done on a daisywheel printer, but using a fairly large text format. This means that there are about 400-500 words per page. The following summary gives an idea of the contents of each chapter, plus some indication of its length.

Chapter 1 (five pages) is a general introduction giving an overview of the BBC microcomputer system as a whole. The aim of the book, it says, it to give 'a detailed understanding of the internal workings of the BBC Micro'.

Chapter 2 (six pages) is entitled 'Attitudes to work and disciplines required'. It conveys some general ideas of the technical skills needed if you want to start playing with the hardware: how to handle ICs that might be damaged by static, and information on how to solder, de-solder and de-flux PCBs.

Chapter 3 (23 pages), which contains a 'complete description of the circuitry', is where the real meat of the book begins. This number of pages may seem ample space to describe the circuit, but it is an extremely complex machine, and in places the description is a little superficial. Also, the last six pages of the chapter deal with the use and applications of the 1MHz bus.

Chapter 4 (21 pages) is a very full survey of the link selections. The first four pages explain how to remove the main PCB and re-assemble it and give a warning about breaking warranty by doing soldering on the board. I was interested to see that the authors have been unable to find out what link S7 really does. While writing the new service manual I spent some time asking engineers at Acorn what it was for, and no-one there knew either. (Anyone got any ideas?)

These is one notable omission, presumably accidental. When talking about line S23 the reader is referred to the data sheet for the 88LS120 (RS423 driver IC) which it says is included in the book - unfortunately it's not there.

Chapter 5 contains 34 pages of detailed information about how to upgrade the machine from A to B, how to add the disc, Econet and speech interfaces, and some indication about adding second processors.

An interlude between chapters 5 and 6 consists of four full-page photographs of the computer indicating the positions of various ICs, fixing screws and so on.

Chapter 6, 'Hints, tips and modifications' (13 pages) contains many ideas which, on the authors' own admission, have been published elsewhere. Nevertheless, it makes a useful compilation. The chapter contains a section about the analogue port which has a number of mistakes. The pin numbering of the plug is incorrect in two of the diagrams, and it gives a method of supposed over-voltage protection which, in certain circumstances, would not only fail to protect the chip but would blow the protecting devices - LEDs. This is because they have forgotten to put current limiting resistors in series with each input - 1000 ohms would do.

There are one or two other omissions, apart from the lack of the 88LS120 data sheet. The first is that, except for the cassette interface, no circuit diagram is provided. This reduces the value of the circuit description. Acorn would not give permission for Wise-Owl Publications to reproduce the diagram (despite the fact that it had already been released to the general public in the Advanced User Guide). The other omission is that, although the preface refers to 'system fault-finding', there seems to be no more than a passing reference to this in the text.

There's quite a lot of useful information in this book, and generally speaking it is of a good technical standard. It is also helpful to have all the datasheets in the one document, but the real question is whether or not it is worth the money (£13.45 inc P&P). Owners of the Advanced User Guide may feel it is not since they already have a link selection survey and a limited description of the hardware. In general though this is a useful text, if a little overpriced.