On May 9, 2014, at 1:31 PM, erik quanstrom wrote: > the question is interesting, but i don't know the answer. > i don't know the origin of u.h, either. "The Design and Implementation of the 4.[X] Operating System" books (for X in 3 and 4) describe this in great detail. While not directly related to Plan9, they are required reading for anyone wanting to understand the legacy of the UNIX kernel(s). --lyndon P.S. abebooks.com :-)