Nsys

The 'nsys' kernel is the earliest extant version of the Unix kernel written in the C language. It pre-dates the release of Fourth Edition Unix by a few months.

The files here come from nsys.tar.gz, which was donated by Dennis Ritchie. He writes:

This is a tar archive derived from a DECtape labelled "nsys". What is contains is just the kernel source, written in the pre-K&R dialect of C. It is intended only for PDP-11/45, and has setup and memory-handling code that will not work on other models (it's missing things special to the later, smaller models, and the larger physical address space of the still later 11/70.) It appears that it is intended to be loaded into memory at physical address 0, and transferred to at location 0.

For more information about Fourth Edition Unix, see The Evolution of the Unix Time-sharing System by Dennis Ritchie.