Global Catalogs contain commonly-searched attributes from all Naming Contexts of a forest. An attribute is included in the Global Catalog if the partialAttributeSet property of attribute is set to TRUE in the schema Naming Context. When this property is first marked True, the attribute is replicated to each schema Naming Context. Each Domain Controller must make its Naming Contexts consistent with the schema by doing a full sync on the Global Catalogs. If the partialAttributeSet property is blank, the attribute is not included in the global catalog. If the partialAttributeSet property is set to FALSE, the attribute is marked to be removed from the Global Catalog. When the property is FALSE, the PartialAttributeDeletionList is set to TRUE until the attribute is removed from the Global Catalog. The PartialAttributeDeletionList is cleared on a per domain controller basis and does not update the USN number.

The global catalog is a service and store that contains folder information from all domains in a forest. The global catalog is queried to find common objects irrelevant of their originating domain in the forest. The global catalog is used to speed searches by resolving queries for all domains in the forest locally by keeping a partial replica of the all the forest domain attributes including the schema and configuration naming context. A domain controller holds at least three naming contexts by default: Schema, Configuration, and Domain. If the domain controller is a global catalog, it will hold additional naming contexts. The list of naming contexts is contained in the following container on each domain controller:

CN=Partitions
CN=Configuration
DC=domain
DC=root
DC=com (or net,us,etc)