SYSTEM and SYSAUX Tablespaces

Each Oracle Database must contain a SYSTEM tablespace and a SYSAUX tablespace, which are
automatically created when the database is created. The system default is to create a smallfile
tablespace. You can also create bigfile tablespaces, which enable the Oracle database to manage ultra
large files (up to 8 exabytes in size).
A tablespace can be online (accessible) or offline (not accessible). The SYSTEM tablespace is always
online when the database is open. It stores tables that support the core functionality of the database,
such as the data dictionary tables.
The SYSAUX tablespace is an auxiliary tablespace to the SYSTEM tablespace. The SYSAUX
tablespace stores many database components, and it must be online for the correct functioning of all
database components.
Note: The SYSAUX tablespace may be taken offline for performing tablespace recovery, whereas
this is not possible in the case of the SYSTEM tablespace. Neither of them may be made read-only.