> the cover of Lions' book: After 20 years this is still the best exposition of the workings of a real operating system Fun fact: At one point in history, Lion

> the cover of Lions' book: After 20 years this is still the best exposition of the workings of a real operating system Fun fact: At one point in history, Lions' book had the status of being a forbidden book of knowledge due to copyright problems. After AT&T commercialized UNIX v7 in 1979, the permission for using the source code in classrooms was withdrawn, it could no longer be read without a UNIX license. But students continued to make illegal copies and study it illegally, who would later become the next generation of hackers and developers. This is also the initial motivation for Andrew Tanenbaum to write MINIX - as a classroom substitute. And he had to be as careful as possible not to derive anything from the original Unix code, such as Lions' book. https://upload.wikimedia.org/wikipedia/commons/5/50/Lions_Commentary_Unix.jpeg https://upload.wikimedia.org/wikipedia/commons/5/50/Lions_Co... This picture from an Unix history exhibition recreated the historical atmosphere by showing Lion's book in front of a huge legal warning [0]. I found this period of history was amusingly similar to the worldbuilding of some fantasy fictions - In the world of magic, the original magic scriptures are forbidden to be learned, the books are sealed, reading them is a taboo [i.e. UNIX source code]. Instead, one must read "safe" textbooks to learn magic. These textbooks are written by great wizards, and it basically contains a second-hand and distorted rehearsal of the knowledge in the original scriptures, sanitized to the level that deemed safe for human, but it is not as powerful [i.e. Tanenbaum's MINIX]. And there are outlaws who want power and they ignore the taboo, however, attempting to read the original magic scriptures will cause irreversible psychological injuries [i.e. cleanroom violation, AT&T lawsuits are coming]. [0] This document contains proprietary information of the Bell System. Use is restricted to authorized employees of the Bell System who have a job-related need-to-know. Duplication or disclosure to unauthorized persons is prohibited. Outside the Bell System, distribution of this document has been restricted to holders of a license for the UNIX Time Sharing Operating System, Sixth Edition from the Western Electric Company. Use, duplication, or disclosure of this document is subject to the restrictions stated in such license from Western Electric Company.