Lions Book

Definitions

1. John Lions' 'A Commentary on the Sixth Edition UNIX Operating System', paired with a full source listing of the V6 kernel. Because AT&T's licensing forbade its use in teaching, the book became the most photocopied document in computing history, passed hand to hand as increasingly degraded reproductions for nearly two decades. It taught a generation to read an operating system as a text, and its famous annotation of the context-switch code, 'You are not expected to understand this', became one of the most quoted comments in software. It was finally published openly in 1996 once the licensing obstacle was cleared.