The Fifth Edition of Unix was released by Bell Laboratories in June 1974. It was designed to run on the PDP-11s with 18-bit addressing and without separate Instruction and Data spaces, for example the PDP-11/40. The kernel's image size was around 26 Kbytes. At this stage in the development of Unix, neither the Standard I/O library nor the Bourne shell existed, and the editor was ed.
The files here come from v5root.tar.gz, donated by Dennis Ritchie.