Directory is a specialized database optimized for reading, browsing and searching entities in an enterprise. Besides, directory services tend to contain descriptive, attribute-based information and support sophisticated filtering capabilities. And directories are tuned to give quick response to high-volume lookup or search operations. Moreover, directory services have the ability to replicate information widely in order to increase availability and reliability, while reducing response time. And there are many different ways to provide a directory service to organizations. Different methods allow different kinds of information to be stored in the directory, place different requirements on how that information can be referenced, queried and updated, and how it is protected from unauthorized access.
Active Directory (AD) is a special purpose database designed for Microsoft Windows networks and systems in organizations. And it is provides as a set of processes and services embedded with most Microsoft Windows server operating systems (OS). Furthermore, a Windows server that runs the AD domain services is the domain controller (DC) that validates and verifies all entities in the domain.
Some alternatives to Microsoft Windows AD include the following: