Active Directory Domain Services 

    Active Directory Domain Services (AD DS), formerly known as Active Directory Directory Services, is the central location for configuration information, authentication requests, and information about all of the objects that are stored within your forest. Using Active Directory, you can efficiently manage users, computers, groups, printers, applications, and other directory-enabled objects from one secure, centralized location. Enhancements to AD DS in Windows Server 2008 include:

     Auditing 
   Changes made to Active Directory objects can be recorded so that you know what was changed on the object, as well as the previous and current values for the changed attributes.

     Fine-Grained Passwords
   Password policies can be configured for distinct groups within the domain. No longer does every account have to use the same password policy within the domain.

     Read-Only Domain Controller
   A domain controller with a read-only version of the Active Directory database can be deployed in environments where the security of the domain controller cannot be guaranteed, such as branch offices where the physical security of the domain controller is in question, or domain controllers that host additional roles, requiring other users to log on and maintain the server. The use of Read-Only Domain Controllers (RODCs) prevents changes made at branch locations from potentially polluting or corrupting your AD forest via replication. RODCs also eliminate the need to use a staging site for branch office domain controllers, or to send installation media and a domain administrator to the branch location.

     Restartable Active Directory Domain Services
   Active Directory Domain Services can be stopped and maintained. Rebooting the domain controller and restarting it in Directory Services Restore Mode is not required for most maintenance functions. Other services on the domain controller can continue functioning while the directory service is offline.

     Database Mounting Tool
   A snapshot of the Active Directory database can be mounted using this tool. This allows a domain administrator to view the objects within the snapshot to determine the restore requirements when necessary.