It would be unappropriate to differentriate between DBMS & RDBMS. As RDBMS is nothing different but a part of DBMS.
DBMS (Database Management System):- is the way you organize your data. Or how you store/process that.
RDBMS (Relational Database Management System):- is a classification under DBMS where you organize data in relational way.
There are 3 classifications of DBMS:-
1> Hierarchical- Where you organize data in hierarchical fashion. e.g. IMS
2> Relational- Where data is stored in relational fashion like tables. e.g. DB2
3> Network Database- Used in networking.