Before Oracle9i, Oracle instances were always started using a text file called 
an init<SID>.ora. This file is by default located in the "$ORACLE_HOME/dbs"
directory.

In Oracle9i, Oracle has also introduced the 'SPFILE', which is a binary file 
stored on the database Server. Changes which are applied to the instance 
parameters may be persistent accross all startup/shutdown procedures.

In Oracle9i, you can startup the instance using either an spfile or an init.ora
file.

An Oracle9i instance may be started by:

    - default spfile          --> spfile<SID>.ora 
    - default init.ora file   --> init<SID>.ora 
    - specified init.ora file 
    - specified spfile