Oracle Database 12c Release 1 (12.1) introduces the multitenant architecture.

This database architecture has a multitenant container database (CDB) that includes a root container, CDB$ROOT, a seed database, PDB$SEED, and multiple pluggable databases (PDBs).

Each pluggable database is equivalent to a separate database instance in Oracle Database release 11g.

The root container, CDB$ROOT, holds common objects that are accessible to every PDB utilizing metadata links or object links.

The seed database, PDB$SEED, is used when creating a new PDB to seed the new database.

The key benefit of the Oracle Database 12c multitenant architecture is that the database resources, such as CPU and memory, can be shared across all of the PDBs. This architecture also enables many databases to be treated as one for tasks such as upgrades or patches, and backups.