SCCS, the Source Code Control System, was created at Bell Telephone Laboratories by Marc Rochkind in the early 1970s. It is generally regarded as the first version-control system: instead of leaving programmers to manage loose copies of files, it kept the complete history of each source file in one controlled place.
Rochkind documented the system in “The Source Code Control System,” published in IEEE Transactions on Software Engineering in December 1975. According to that paper, SCCS could store, update, and retrieve every version of a module, control who was allowed to change a file, identify released versions by number, and record who made each change, along with when, where, and why it was made.
A key idea in SCCS was that it did not keep a separate full copy of every revision. It stored one file’s history as the original text plus the changes (deltas) needed to reconstruct any past or present version on demand. This made it practical to keep long histories without using enormous amounts of disk space.
SCCS worked on one file at a time rather than on a whole project as a unit, and programmers checked a file out to edit it and checked it back in to record a new revision. That checkout-and-check-in model, and the per-file history behind it, shaped RCS, CVS, and the long line of version-control tools that followed.