All changes to a file are stored in a file named
s.file, which is called an SCCS file.
Each time a file is “entered” into SCCS,
SCCS notes which lines have been changed or deleted since the
most recent version. From that information, SCCS can regenerate
the file on demand.
Each set of changes depends on all previous sets of changes.
Each set of changes is called a delta and is assigned an
SCCS
identification string (sid).
The sid consists of
either two components: release and level numbers (in the
form a.b) or of four components:
the release, level, branch, and sequence numbers (in the
form a.b.c.d).
The branches and sequences are for situations when two on-running
versions of the same file are recorded in SCCS.
For example, delta
3.2.1.1 refers to release 3, level 2, branch 1, sequence 1.