From: Bill Wohler
SCCS is supported by AT&T. RCS is supported by the Free Software
Foundation. Therefore RCS runs on many more platforms, including
PCs.
Most make programs recognize SCCS's "s." prefix while GNU make
is one of the few that handles RCS's ",v" suffix.
Some tar programs have a -F option that ignores either RCS
directories, or SCCS directories or both.