Physical and Logical Structures
An Oracle database system is made up of at least one instance of the application, along with data storage. An instance, identified by an instantiation number (or activation id: SYS.V_$DATABASE.ACTIVATION#), is made up of a set of operating system processes and memory-structures that work with the storage.
If an Oracle database administrator has employed Oracle RAC (Real Application Clusters), then multiple instances attach to a storage array. This implementation offers advantages such as better performance, scalability, and redundancy.
The Oracle DBMS can store and execute procedures and functions within itself. PL/SQL or the object-oriented language, Java, can use such code objects and/or provide the programming structures for writing them.