Using 12c multithread mode, one Operating System process can support multiple Oracle processes running in DB.

Multithreaded mode is not enabled with a new 12c database by default, to enable multi-threaded mode, the parameter THREADED_EXECUTION must be set to TRUE and the database restarted.   Some OS processes will still support only one oracle thread, while other OS processes may support multiple Oracle processes.   This can be viewed in V$PROCESS view by identifying OS process ID for each oracle process.

When running in multi-threaded mode, you must have an administration account controlled by a password file.  If a password file is not in use starting the system in multi-threaded mode will result in the error ORA-01017 invalid username/password; logon denied.

Larry Catt

OCP