It has become increasingly necessary to abandon the old, and somewhat rigid, boundaries which have until now existed between "hardware" and "software". Within industry this trend has already manifested itself in the shape of a growing demand for "software engineers". but who, or what, are these crusaders of the information technology movement? They are certainly not primarily programmers, nor are they exclusively electronic engineers. Their talents lie with the integration of software and hardware into fully functional and fully optimized systems. The precise skills required are hard to define in just a few workds but essentially they centre on an awareness of and familiarity with electronic and microelectronic circuitry, coupled with a detailed knowledge of programming in either assembly language or an appropriate high level language. In addition, some knowledge of computer interfacing and communications is highly desirable. This book aims to provide the sort of everyday information required by such individuals, but it should also be of value to hardware and software specialists. Indeed, anyone engaged in regular use of a computer of microcomputer system at more than just the applications level should find something of value contained herein. This book cannot replace standard texts or detailed specifications. It does, however, cover a vast range of subjects at a practical level with, where appropriate, some explanatory text. It has also not been designed with readability in mind; rather the aim has been that of presenting information in the most concise manner and in a form which can be readily accessed.