Designing Embedded Hardware, 2nd Edition

Chapter 1. An Introduction to Computer Architecture

Each machine has its own, unique personality which probably could be defined as the intuitive sum total of everything you know and feel about it. This personality constantly changes, usually for the worse, but sometimes surprisingly for the better...

—Robert M. Pirsig, Zen and the Art of Motorcycle Maintenance

This book is about designing and building specialized computers. We all know what a computer is. It's that box that sits on your desk, quietly purring away (or rattling if the fan is shot), running your programs and regularly crashing (if you're not running some variety of Unix). Inside that box is the electronics that runs your software, stores your information, and connects you to the world. It's all about processing information. Designing a computer, therefore, is about designing a machine that holds and manipulates data.

Computer systems fall into essentially two separate categories. The first, and most obvious, is that of the desktop computer. When you say "computer" to someone, this is the machine that usually comes to her mind. The second type of computer is the embedded computer, a computer that is integrated into another system for the purposes of control and/or monitoring. Embedded computers are far more numerous than desktop systems, but far less obvious. Ask the average person how many computers he has in his home, and he might reply that he has one or two. In fact, he may have 30 or more, hidden inside his TVs, ...