Oracle Server Organization

Oracle Server is organized into databases that are subdivided into database objects. An Oracle database contains the following types of objects:

Tablespaces that contain data. Tablespaces can consist of multiple data files.
Data files that contain the database data. Data files are the physical files that define a tablespace.
Online redo log files that contain records of transactions applied to the tablespaces.
Control files that describe the structure of the database, including the tablespaces. There can be more than one control file copy for the database.
Parameter files that contain the various initialization parameters the database uses when it starts up.
Recovery area (for latest Oracle versions) that organizes all recovery-related files and activities for an Oracle database.