If you have only recently unpacked your Spectrum then take heed; enjoy what you are doing and the power a command of Basic gives you, and for a while steer clear of machine code. On the other hand, if you are already familiar with Spectrum Basic and are seeking to increase the power and speed of your machine by programming directly in machine code then Introducing Spectrum Machine Code by Ian Sinclair is a handy companion to have.

The 135 pages and seven appendices set out to give an extensive, if not always detailed, introduction to machine code and the operations and functions of the bits that lie below the keyboard. The book will not, and does not attempt to, turn the reader into a competent machine code programmer, but that is not a shortcoming, it is designed to introduce machine code to beginners (such is the nature and extent of the subject that no one book is sufficient to offer complete knowledge).

In the early chapters, Mr Sinclair (no relation to the obvious) introduces the RAM, the ROM, the MPU and with clear examples describes the relationship between them. Subsequent chapters take task with binary and hexadecimal notation, introduce assembly language and examine the use of registers. Each section is fully highlighted by worked examples that require and assume minimal previous knowledge. Finally, through the introduction of flow diagrams, simple machine code routines are developed.

Throughout, the book is, where possible, jargon free, the text is always conscious that it is aimed at newcomers and its strength is that it never attempts to go too far into this confusing subject too soon. However, where is is deficient is in the number of final machine code program examples that are included; but since a number of recommendations for further reading are made this is not such a great problem.

Whether it is your intention to become a master of machine code or simply to make some sense of more advanced Basic programs, if you are well acquainted with Basic then this book will make your understanding of the Spectrum, and most other micros, far deeper.

Published by Granada Publishing, Introducing Spectrum Machine Code is written by Ian Sinclair and costs £7.95. ISBN 0-246-120827.