Crossing over into general-interest non-fiction from his popular programming manuals, Charles Petzold has written Code: The Hidden Language of Computer Hardware and Software. It's a carefully written, carefully researched gem that will appeal to anyone who wants to understand computer technology at its most essential levels.

Readers learn about number systems(decimal, octal, binary and all that) through Petzold's patient (and frequently entertaining) prose, then discover the logical systems that are used to process them. There's loads of historical information, too. From Louis Braille's development of his eponymous raised-dot code to Intel Corporation's release of its early microprocessors, Petzold presents the stories of people trying to find ways to communicate with (and by means of) mechanical and electrical devices. It's a fascinating progression of technologies and the author presents a clear statement of how they fit together.

The real value of Code is in its explanations of technologies that have been obscured for years behind fancy user interfaces and programming environments that, in the name of rapid application development, insulate the programmer from the machine. In a section on machine language, Petzold dissects the instruction sets of the genre-defining Intel 8080 and Motorola6800 processors. He walks the reader through the process of performing various operations with each chip, explaining which op codes poke which values into which registers along the way. Petzold knows that the hidden language of computers exhibits real beauty. In Code, he helps his readers appreciate it.

--David Wall