The "empty root domain" is an AD design element that has become increasingly popular at organizations with decentralized IT authority such as universities.
The empty root domain acts as a placeholder for the root of Active Directory, and does not typically contain any users or resources that are not required to fulfill this roll [sic]. [...] Only those privileges that have tree or forest-wide scope are restricted to the empty root domain administrators. Departmental administrators can work independently of other departments.
This politically neutral root domain provides a central source of authority and policy enforcement, and provides a single schema and global catalog that allows users to find resources anywhere in the university/district/state system. Individual IT departments retain a significant degree of independence and can control their own users and resources without having to worry that actions by administrators in other departments will disrupt their domain.
Allows domain controllers running both Windows 2000 and earlier versions of Windows NT to co-exist in the domain. In mixed mode, the domain features from previous versions of Windows NT Server are still enabled, while some Windows 2000 features are disabled. Windows 2000 Server domains are installed in mixed mode by default. In mixed mode the domain may have Windows NT 4.0 backup domain controllers present. Nested groups are not supported in mixed mode.
When all the domain controllers in a given domain are running Windows 2000 Server. This mode allows organizations to take advantage of new Active Directory features such as Universal groups, nested group membership, and inter-domain group membership.
LDAP is the directory service protocol that is used to query and update AD. LDAP naming
paths are used to access AD objects and include the following:
1. Windows Server, Advanced Server, Datacenter Server
2. Minimum Disk space of 200MB for AD and 50MB for log files
3. NTFS partition
4. TCP/IP Installed and Configured to use DNS
5. Administrative privilege for creating a domain in existing network