Oracle control file:

binary file
start of instance, file is checked
database has 1 control file each
modifiable only by oracle
editing prohibited, even by DBA

Keeps track of:

datafile names and locations
redo log names and locations
table-space information
name of database
time-stamp of database creation

Usage:

on start of oracle instance control file is checked for
redo log
datafile
database
that must be used for operation

Control file keeps track of database changes (e.g. new datafile or table-space)