Code: The Hidden Language of Computer Hardware and Software.

Petzold introduces us to the inner workings of computers (both in regards to hardware and software) without a need to resort to overly complex concepts for the initiated. As a matter of fact, he starts with a brief explanation of what is code and uses both Morse code and Braille to illustrate it.

The author also maintains an errata on his own website.

Technical description:
Title: Code. The Hidden Language of Computer Hardware and Software.
Author: Charles Petzold.
Publisher: Microsoft Press.
Edition: Redmond (USA), 1999.
Pages: 392 pages, including indexes.
ISBN: 0-7356-0505-X