Ghosts of Unix Past: a historical search for design patterns

Part 2 of the article is here: http://lwn.net/Articles/412131/

Part 4 http://lwn.net/Articles/416814/ (but not freely available till Dec 2, unless a subscriber chooses to share it)

Part 3 http://lwn.net/Articles/414618/

Tiny nitpick: CP/M had a fixed, two-level hierarchy with 16 different areas of the disk, accessible via the "user" command.