Normal database operation means that an instance is started and the database is mounted and open. This mode allows any valid user to connect to the database and perform data access operations. The following command starts an instance, reads the initialization parameters from the default location, and then mounts and opens the database. (You can optionally specify a PFILE clause.)
STARTUP
You can start an instance without mounting a database. Typically, you do so only during database creation. Use the STARTUP command with the NOMOUNT clause:
STARTUP NOMOUNT
The instance starts, but does not mount the control file or open the database. This status of the instance enables the following tasks:
1. To create a new database or
2. A new control file or
3. To recover control file.
When you start an instance at nomount stage it reads initialization parameter file determine the values of initialization parameters. Then, it allocates an SGA, which is a shared area of memory used for database information, and start background processes. At this point, no database is associated with these memory structures and processes.
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