What is a directory server

Directory server: The server that contains a lookup service that provides mapping between network resources and their network addresses

• It’s used to organize and look up organizational objects and ​entities ranging from things like user accounts, user groups, ​telephone numbers and network shares.
• The ideal enterprise quality directory server should support Replication: the store directory data is copied and distributed across a number of physically distributed servers but still appears as one unified data store for querying and administering
• Directory services: A lookup service contained in a network server that provides mapping between network resources and their network addresses  ​Directory services are useful for organizing data and ​making it searchable for an organization. This is achieved through the use of a hierarchical model of objects and ​containers.  - The containers are referred to as organizational units or ​OUs and they can contain objects or more organizational units.   - ​This is similar in organizational structure to a file system.   - ​OUs are like folders which can contain individual files or objects for ​directory service. ​OUs can also contain additional folders.