A global catalog is a directory service that contains information about every object in an Active Directory forest. This information includes the object’s name, distinguished name, object type, and other attributes. Global catalogs are used by clients to find objects in the forest, and they are also used by administrators to manage the forest. To check if a server is a global catalog, you can use the following steps:
The global catalog was introduced in Windows 2000 Server. Prior to Windows 2000 Server, clients had to contact each domain controller in the forest to find objects. This could be a slow and inefficient process, especially in large forests. The global catalog provides a single point of contact for clients to find objects in the forest. This makes it much faster and more efficient to find objects, and it also reduces the load on domain controllers.