The original Advanced User Guide found its way on to the bookshelf of almost every BBC Micro programmer in the country. It filled all the gaps left by Acorn's documentation, and it brought together in one place all the technical information programmers need to get every ounce of performance out of the machine.

The problem with the old version, however, was that Acorn insisted on bringing out new micros. While nearly all of the information in the guide was still relevant to the machines, there was so much extra that needed to be covered.

This new version puts that right. It covers all the BBC Micros, from the B to the Compact, plus the Electron.

If you're programming quite happily in Basic and still don't know what an OSBYTE is, then you're unlikely to need this book. It will sell to machine code programmers and those people wanting to utilise the special features of the machines - there are sections, for example, on controlling Shadow RAM, programming video circuitry and utilising paged ROMs. There are complete reference sections for the assembler, the 65CO2 chip and OSBYTE calls.

The book is, of course, intended as a reference work, and as such is very comprehensive, though for the newcomer to the computer's inner workings it can be confusing. You need a good grasp of the jargon and a fair understanding of how the machine works before you can use, or even understand, much of this information.

As a wirehead's bible, full of arcane and detailed information, the new guide is excellent, if somewhat expensive. However, if you want to learn about how the machine works, look elsewhere.