A server parameter file can be thought of as a repository for initialization parameters
that is maintained on the machine running the Oracle Database server. It is, by design,
a server-side initialization parameter file. Initialization parameters stored in a server
parameter file are persistent, in that any changes made to the parameters while an
instance is running can persist across instance shutdown and startup. This
arrangement eliminates the need to manually update initialization parameters to make
persistent any changes effected by ALTER SYSTEM statements. It also provides a basis
for self-tuning by the Oracle Database server.

A server parameter file is initially built from a text initialization parameter file using
the CREATE SPFILE statement. (It can also be created directly by the Database
Configuration Assistant.) The server parameter file is a binary file that cannot be
edited using a text editor. Oracle Database provides other interfaces for viewing and
modifying parameter settings in a server parameter file.

When you issue a STARTUP command with no PFILE clause, the Oracle instance
searches an operating system–specific default location for a server parameter file from
which to read initialization parameter settings. If no server parameter file is found, the
instance searches for a text initialization parameter file. If a server parameter file exists
but you want to override it with settings in a text initialization parameter file, you
must specify the PFILE clause when issuing the STARTUP command.