Active Directory also has a global catalog (GC), which contains a partial replica of all objects in the directory. It also contains partial replicas of the schema and configuration containers. One or more domain controllers in a domain can hold a copy of the global catalog. For more information about binding to a global catalog, see Binding to the Global Catalog.
The global catalog holds a replica of every object in Active Directory, but with only a small number of their attributes. The attributes in the global catalog are those most frequently used in search operations, such as a user's first and last names, login names, and so on. The global catalog attributes also include those required to locate a full replica of the object. The global catalog allows users to quickly find objects of interest without knowing what domain holds them and without requiring a contiguous extended namespace in the enterprise; that is, you can search the entire forest.
So, if you bind to an object in the global catalog, you will search that object and the entire hierarchy below it — without having to go to any other server. However, the search can only use a query filter containing properties in the global catalog and can retrieve only properties in the global catalog.
Searching the global catalog has the following benefits:
Searching the global catalog has the following disadvantages: