The general purpose of a database is to store and retrieve related information. An Oracle database has a logical and a physical structure. The physical structure of the database is the set of operating system files in the database. An Oracle database consists of three file types.
•1.Data files containing the actual data in the database
•2.Online redo log files containing a record of changes made to the database to enable recovery of the data in case of failures
•3.Control files containing information necessary to maintain and verify database integrity
The Oracle server also uses other files that are not part of the database:
•4.The parameter file defines the characteristics of an Oracle instance. For example, it contains parameters that size some of the memory structures in the SGA.
•5.The password file authenticates users privileged to start up and shut down an Oracle instance.
•6.Archived redo log files are offline copies of the online redo log files that may be necessary to recover from media failures.
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