Server parameter files are binary files that exist only on the server and are called from client locations to start up the database.
Server parameter files let you make persistent changes to individual parameters. When you use a server parameter file, you can specify in an ALTER SYSTEM SET parameter statement that the new parameter value should be persistent. This means that the new value applies not only in the current instance, but also to any instances that are started up subsequently. Traditional client-side parameter files do not let you make persistent changes to parameter values.
Server parameter files are located on the server, so they allow for automatic database tuning by Oracle Database and for backup by Recovery Manager (RMAN).
To use a server parameter file when starting up the database, you must create it from a traditional text initialization parameter file using the CREATE SPFILE statement.
All instances in an Real Application Clusters environment must use the same server parameter file. However, when otherwise permitted, individual instances can have different settings of the same parameter within this one file. Instance-specific parameter definitions are specified as SID.parameter = value, where SID is the instance identifier.