Active Directory® is the Microsoft's implementation of Directory Services its purpose is to store information about users, resources, and other network components, and to provide that information according to access permissions of the entity who is requesting it.
Active Directory (AD) is meant for use in Microsoft Windows network environments and it provides central authentication and authorization services for Windows-based computers.
Active Directory uses Lightweight Directory Access Protocol (LDAP), which is derived from X.500 data model. Hence Active Directory is X.500 compliant.
The Directory Service should provide an efficient way to manage, find and access all the resources (computers, users, printers etc) in the network. The following are the features which should be provided by a good Directory Service implementation. Microsoft’s Directory implementation (Active Directory®) addresses all these issues.
Centralization: Active Directory is centralized directory implementation providing a single database of network resources.
Scalability: Active Directory allows its database to be partitioned and distributed across the domains that make the network. But still Active Directory can be managed as a single directory.
Standardization: Active Directory is standardized because it is made accessible through Lightweight Directory Access Protocol (LDAP), which is an IETF standard.
Extensible: Active Directory is extensible. It allows third-party developers to store the information of their own application inside Active Directory and make use of the features provided by the Active Directory.
Separation of physical network: Active Directory makes the physical structure of the network transparent and only the local structure is visible to the users.
Security: Active Directory is tightly integrated with the Windows 2003 server security and the major security protocols make it more secure.
Domain Name System (DNS) support: The Active Directory supports Domain Name System (DNS) and Active Directory requires DNS to function properly.
TCP/IP compatibility: Active Directory and Windows Server 2003 utilize the TCP/IP protocol stack as their primary method of communications.