What is System R? What are its two major subsystems?
System R was intended and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to illustrate 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.