Is "CVS" the same thing as "PVCS" by Merant? I used that at the last employer for all mainframe source code storage. Worked pretty well. At the job before that we used something from MKS to store the source code files - can't remember the name anymore though.
Currently we use Visual Source Safe. It was in place but ignored until I started bitching loudly. I mean, the last checked-in source code module was at least 25 versions ago in some cases, and a few modules were checked out by a guy who quit in 2001, and nobody ever cleaned up after him. Only good thing about VSS is that it stores compiled object files.