Overview of Primary Components
The Oracle architecture includes many primary components, which are discussed below.
•Oracle instance: An Oracle instance is the combination of the background processes and the memory structures. The instance must be started to access the database. When instance started, a System Global Area (SGA) is allocated and Oracle background processes are started.
•Oracle database: An Oracle database consists of operating system files, also called database files, that provide the actual physical storage for database information. The database files are used to ensure that the data is kept consistent and can be recovered in the event of a failure of the instance.
•User and server processes: The user and server processes are the primary processes which involved when a SQL statement is executed, however, other processes can also help the server complete the processing of the SQL statement.