What is System R? What are its two major subsystems? | RDBMS Interview Questions

System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be
used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.
Its two subsystems are
? Research Storage
? System Relational Data System.