All of the objects in the Active Directory forest are represented in the Directory Tree. A Directory Tree is a hierarchy of objects and containers in a directory that can be viewed graphically as an upside-down tree, with the root object at the top. A tree shows how objects are connected in terms of the path from one object to another.
The Directory Tree of Active Directory tree is partitioned to allow sections to be distributed (replicated) to domain controllers in different domains within the forest. Each domain controller stores a copy of a specific part of the directory tree, called a “Naming Context” also know as Directory Partition. “Naming Context” is replicated as a unit to other domain controllers in the forest that contain a replica of the same sub tree. A “Naming Context” is also called a Directory Partition.
In Active Directory, a single server always holds at least three naming contexts:
Schema Naming Context
Schema Naming Context contains definitions of objects that can be created in the forest and the attributes those objects can have. Objects in the schema partition must be replicated to all domain controllers in all domains in the forest.
Configuration Naming Context
Configuration Naming Context contains objects that represent the logical structure of the forest, including the domain structure and replication topology. Objects in the configuration partition must be replicated to all domain controllers in all domains in the forest.
Domain Naming Context
Domain Naming Context contains all of the objects stored in a domain. Objects in the domain partition can be replicated only to domain controllers within the domain.