Source Code Control System is on old version control systems. It predates RCS which predates SVN. It can see how old it is now. Some companies still use in their legacy systems. To remind myself I have made a cheat sheet.
All commands start with a call to the sccs binary. For example "sccs edit".
Check out a new version of a file in SCCS
Just like uncheckout
Will get the latest file from the SCCS directory to your current location
Add a file to SCCS
This will remove all files in the current directory that you are able to retrieve again from SCCS. This is better then delete the file using a linux or unix command because you might delete files that are not under SCCS control.