SCCS
From Just Solve the File Format Problem
Source Code Control System (SCCS) is a per-file revision control system, originally developed by Marc Rochkind at Bell Labs, and later incorporated into AT&T's System III and System V versions of Unix, and licensed to commercial vendors for inclusion in their OSes based on those releases.
For each file checked into SCCS control, a file storing the history and changes in each version of the file is created, usually with the file's normal name with "s." prepended, either in the same directory or under a subdirectory named "SCCS".
