This book covers the organization, design, and architecture of computers. Architecture is the ‘‘art or science of building; a method or style of building,’’ according to Webster’s. A computer architect develops the functional and performance specifications for the various blocks of a computer system and defines the interfaces between those blocks, in consultation with hardware and software designers. A computer designer, on the other hand, refines those building-block specifications and implements those blocks with an appropriate mix of hardware, software, and firmware. It is my belief that the capabilities of an architect are greatly enhanced if he=she is exposed to the design aspects of a computer system. Computer organization deals with providing just enough details on the operation of the computer system for a sophisticated user and programmers. The backbone of this book is a description of the complete design of a simple but complete hypothetical computer. The book describes the architectural features of contemporary computer systems as enhancements to the structure of the simple computer.

Books on digital systems’ architecture fall into four categories: logic design books that cover the hardware logic design in detail but fail to provide the details of computer hardware design; books on computer organization that deal with the computer hardware from a programmer’s viewpoint; books on computer hardware design that are suitable for an electrical engineering curriculum; and books on computer system architecture with no detailed treatment of hardware design aspects. I have tried to capture the important attributes of the four categories of books to come up with a comprehensive text that includes pertinent hardware, software, and system aspects.

The first edition of the book, published in 1985, was a result of my teaching a sequence of computer architecture courses at the senior undergraduate and beginning graduate levels for several years to both computer science and electrical engineering students. The second edition, published in 1991, expanded the book to 11 chapters and included several additional topics in response to the comments from the users of the first edition. The third edition published in 2000 expanded the topical coverage of the second edition and contained additional contemporary architectures as examples. This fourth edition expands the book to include organization aspects, embedded systems, and performance evaluation. The book does not assume prior knowledge of computers, although exposure to programming with high-level and assembly languages makes the reading easier. Exposure to electronics is not required as a prerequisite for understanding this book.