Definition of Windows NT Directory Services (NTDS) in The Network Encyclopedia.

What is NTDS (Windows NT Directory Services)?

Windows NT Directory Services, or NTDS, is the directory services used by Microsoft Windows NT to locate, manage, and organize network resources. Windows NT Directory Services (NTDS) uses domains, trusts, and directory synchronization to provide users of enterprise-level Windows NT networks with the following advanced capabilities:

• Single-logon capability: Users can log on anywhere in the enterprise using only one account. 
• Centralized administration: Administrators can manage the entire network from a single location. 
• Universal resource access: Users can access resources anywhere in the enterprise if they have the appropriate permissions. 

To build effective enterprise-level directory services using Windows NT domains, you should consider the following factors:

• The number of domains needed (the domain model used)
• The number of domain controllers needed to support the number of users
• The placement of backup domain controllers (BDCs) to assure efficient directory synchronization of directory services
• The placement of BDCs to assure effective logon and resource authentication over slow WAN links