The book focuses on 'pre-networked computers' and does not cover concepts like distributed computing because Petzold thought that it would not be as useful for 'most people using the Internet', his intended audience. The book also covers more recent developments, including topics like floating point math, operating systems, and ASCII.

He noted that 'very smart people' had to go down the 'dead ends' of mechanical computers and decimal computing before reaching a scalable solution-namely, the electronic, binary computer with a von Neumann architecture.

Electricity is explained through the example of a basic flashlight, which is then expanded upon through the explanation of the electrical telegraph. Code is notable for its explanations of historical technologies in order to build the pieces for further understanding. Petzold begins Code by discussing older technologies like Morse code, Braille, and Boolean logic, which he uses to explain vacuum tubes, transistors, and integrated circuits. The idea of writing the book came to him in 1987 while writing a column called 'PC Tutor' for PC Magazine. On June 10, 2022, Petzold announced that an expanded second edition would be published on Augand he is building a companion interactive website. Petzold describes Code as being structured as moving 'up each level in the hierarchy' in which computers are constructed. In the preface to the 2000 softcover edition, Petzold wrote that his goal was for readers to understand how computers work at a concrete level that 'just might even rival that of electrical engineers and programmers' and that he 'went as far back' as he could go in regard to the history of technological development.

Code: The Hidden Language of Computer Hardware and Software (1999) is a book by Charles Petzold that seeks to teach how personal computers work at a hardware and software level.

Petzolds code