Overview of Datafiles (62)

A tablespace in an Oracle database consists of one or more physical datafiles. A
datafile can be associated with only one tablespace and only one database.
Oracle creates a datafile for a tablespace by allocating the specified amount of disk
space plus the overhead required for the file header. When a datafile is created, the
operating system under which Oracle runs is responsible for clearing old information
and authorizations from a file before allocating it to Oracle. If the file is large, this
process can take a significant amount of time. The first tablespace in any database is
always the SYSTEM tablespace, so Oracle automatically allocates the first datafiles of
any database for the SYSTEM tablespace during database creation.[@more@]