What is a Directory Service ?

A directory service is a network service that identifies all resources on a network and makes that information available to users and applications. Directory services are important, because they provide a consistent way to name, describe, locate access, manage, and secure information about these resources.

When a user searches for shared folder on the network, it is the directory service that identifies and provides that information to the user.

Active Directory is the directory service in the Windows Server 2003 family. It extends the basic functionality of a directory service to provide the following benefits :

Domain Name System (DNS) integration 

Active directory uses DNS naming conventions to create a hierarchical structure that provides a familiar, orderly, and scalable view of network relationship. DNS also functions to map host name, such as www.microsoft.com, to numeric TCP/IP addresses, such as 192.168.19.2.

Scalability

Active Directory is organized into sections that can store a large number of objects. As a result, Active Directory can expand as an organization grows. An organizational that has a single server with a few hundred objects can grow to thousands of servers and millions of objects.

Centralized Management

Active Directory enables administrators to manage distributed desktops, network services, and applications from a central location, while using a consistent management interface. Active Directory also provides centralized control of access to network resources by enabling users to log on only once to gain full access to resources throughout Active directory.

Delegated administration

The hierarchical structure of Active Directory enables administrative control to be delegated for specific segments of the hierarchy. A user authorized by a higher administrative authority can perform administrative duties in their designated portion of the structure. For example, a users might have limited administrative control over their workstation settings, and a department manager might have the administrative rights to create new users in an organization unit.