For those readers that are curious who Tannenbaum is, he wrote (the best IMHO) operating systems book [0]. This book contained the complete source of an operating system 'Minix'. At the same time Torvalds wanted to build a OS system. Did Torvalds use/steal or extend the Minix source? It is extremely controversial [1] amount CS types.

https://www.amazon.com/Modern-Operating-Systems-Andrew-Tanen... [0]

http://wiki.c2.com/?MinixOperatingSystem [1]