This translation of the second edition of the book "AS/400 Fundamentals" describes almost all aspects of the operation of this computer system: from the latest hardware and software technologies used in it to the history of its creation. The publication consists of a preface, introduction, 12 chapters, appendix and index; contains illustrations. The book's author, Frank Soltis, who has made an academic career in computer science starting with the System/38, is one of the leading experts on the philosophy and architecture of the AS/400. The book is intended for a wide range of readers: businessmen, managers, heads of departments who want to understand how an AS/400e system or server can be beneficial to their business. However, the publication will also be useful to specialists who want to understand the smallest details. Published in Russian for the first time.