Overview#Forest Root Domain, in Microsoft Active Directory, is the first AD DOMAIN created in a AD Forest, it is the root domain in the domain namespace hierarchy.
Although the distinguished name of the Configuration Directory Partition indicates that it is a child of the Forest Root Domain object, the Configuration Directory Partition is not physically part of the Forest Root Domain directory partition but is a separate directory partition that is replicated to all Domain Controllers in the AD Forest; in contrast to the configuration directory partition, the forest root domain directory partition is replicated to only domain controllers in that domain.
Similarly, the topmost object in the Schema Directory Partition is the child of the Configuration Directory Partition. The distinguished name of the Schema Directory Partition (cn=schema,cn=configuration,dc= forestRootDomain ) shows the location of the schema to be within the forest root domain. Although the Schema Directory Partition is a child of the Configuration Directory Partition, the Schema Directory Partition is not physically part of the Configuration Directory Partition nor part of the forest Root Domain Directory Partition.