Centralised SCM
A centralised ["SCM"] stores all of its metadata in a single authoritative (or "master") database that is not replicated. ["CVS"] follows this model, as does ["Subversion"].
["Mercurial"] is a distributed SCM, which is a more general model that's a proper superset of the centralised SCM model. If you want to change your development pattern as little as possible and switch from ["CVS"] or ["Subversion"] for reasons of non-brokenness (["CVS"] does not have atomic commits), speed, or future flexibility, ["Mercurial"] can be used in a way that's very similar to most centralised SCM systems. Instructions on how to do this can be found at CvsLikePractice.