The bulk of the storage allocated to any Oracle database is dedicated to (no surprise here) data. Data storage is arguably the most important component of the Oracle database, and it may be the most complex as well.

Oracle differs from other database management systems in many ways: one of the most important differences is the way Oracle allocates and manages data storage. In many systems, storage is maintained by the operating system and allocated to a database as required. In an Oracle database, the DBA allocates one or more blocks of storage to Oracle in the form of one or more operating system files, and Oracle itself then manages the allocation of this storage. In fact, the physical operating system files that make up the database are invisible to database user—only the DBA knows the physical makeup of the database. In order to control storage allocation, Oracle manages the physical disk space by dividing it into Oracle blocks , and uses logical constructs called tablespaces, described in some detail in the next section. Figure 11.1 illustrates the relationships within Oracle’s data storage structure.

Figure 11-1. Data storage components of an Oracle database