The Instance and the Database (285)

After starting an instance, Oracle associates the instance with the specified database.
This is a mounted database. The database is then ready to be opened, which makes it
accessible to authorized users.

Multiple instances can run concurrently on the same computer, each accessing its own
physical database. In large-scale cluster systems, Real Application Clusters enables
multiple instances to mount a single database.

Only the database administrator can start up an instance and open the database. If a
database is open, then the database administrator can shut down the database so that
it is closed. When a database is closed, users cannot access the information that it
contains.

Security for database startup and shutdown is controlled through connections to
Oracle with administrator privileges. Normal users do not have control over the
current status of an Oracle database.

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