Oracle Database Concepts - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 80

Control File:

Every database has one control file and it basically contains the
information regarding the structure of database. Control file
doesn't contain any records. If you keep inserting records in your
tables using the INSERT statement, the size of your control file
will not change. Oracle Instance reads control file at the time of
startup to find out database name, location of data files and redo
log files. You can tell Oracle Instance to “Multiplex” control file
or in other words having a exact mirror copy of control file
sitting at some other disk. In case media failure occurs you
would always be having another copy available on the other
disk. Never place the mirror copy on the same disk.

Control File
Data Files
Redo Log Files

Main Oracle Database Files.

Oracle Instance reads it at
startup.

Parameter File (init.ora)

Archived Redo Log

Archiving of Redo Log Files

Files
Figure 3-3: Oracle physical files on the disk drive(s).

Data Files:

Data files are the files where the actual database's data resides. If
you keep inserting the records using the INSERT statement the
size of these files increases. Oracle database can have one or
more data files. The size of each data file is limited to OS
(operating system) maximum file size. But the size of the Oracle
Database can be whatever you like. There is no limit on the
maximum size of the database. If you are running out of space
you can always add more data files to the database by bringing in
hard drives into your system.