How does an oracle database start ?

Here I'm giving the step by step procedure to show how does an Oracle database start.

1. Start up process looks for a server parameter file or parameter file in the default location.
2. If a parameter file is found,it then parse it and get the info about the initialization parameters.
3. Allocate the SGA and started the background process.If auditing, altering and tracing also brought up.
4. Till this point we can say that oracle instance is started in nomount mode.
5. The same can be achieved by issue the following command :
   STARTUP NOMOUNT
6. Then, control file is read to know about the the details of the database and its related data files like data files , redo log files.
7. At this point, the database has been started. But it can only accessed by the DBA's.
8. This is called the MOUNT mode.
9. The same can be achived by issue the following command :
   STARTUP MOUNT
10. Then once the database has mounted, it get opened for other users.
11. After this it can go the recovery mode if you have done hard shutdown or if there is power failure in order to do synchronization between redo files and data files.
12. Then database is open for business.There will be consistency check not at the time of OPEN mode but periodically through the up time. SMON is required to do this.
13. As the user connect, the PMON process come into picture and monitor those connections.
14. The same can be achived by issue the following command :
    STARTUP OPEN

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