Every Oracle database contains a control file.
The control file gives Oracle a place to store important information about the physical state of the database. It contains the following information:

1. The database name
2. Information about tablespaces
3. The names and locations of all the datafiles
4. The names and locations of all the redo log files
5. The current log sequence number
6. Checkpoint information
7. Information about redo logs and the current state of archiving

Perhaps the most significant use of the control file is to keep track of all the other files that make up the database. When you start an instance and open a database, Oracle reads the initialization file to find the name and location of the control file. Then it reads the control file to find the names and locations of all the datafiles and redo log files. Finally it opens all those files, making the database available for you to use.

The control file is so critical to the proper operation of an Oracle database that Oracle encourages you to keep at least three copies of the control file at all times. These should be on separate disks, and preferably separate controllers .
That's why the initialization file that you saw in the last lesson listed three control file names. The Oracle database software always writes the same information to all control files, thus keeping them in sync with one another.

Before you move on to the next lesson, click the Exercise link below to test your knowledge of the control and initialization files.
Data Control Files