UNIX is a kernel implementation.
Wikipedia page about UNIX.
Standardizing UNIX, an article by David Chisnall.
The first in the series, Neil Brown's 2010-10-27 article Ghosts of Unix Past: a historical search for design patterns introduces the concepts of file descriptors and the single, hierarchical .
Next, Neil Brown's 2010-11-04 article Ghosts of Unix past, part 2: Conflated designs discusses issues with conflated designs such as the
mountcommand (a problem we have partly solved / solved differently with our translator approach and the virtual file system), and the plethora of flags that can be passed to the
In Neil Brown's 2010-11-16 article Ghosts of Unix past, part 3: Unfixable designs, he deals with unfixable designs, such as UNIX signals and the UNIX permission model (which is clearly inferior to a capability-based system).