Directory services and Active Directory

In the context of a computer network, a directory is a hierarchical structure that stores information about objects on the network. A directory service stores directory data and makes it available to network users, administrators, services, and applications.

Active Directory (AD) is a set of directory services developed by Microsoft as part of Windows 2000 for on-premises domain-based networks. The best-known service of this kind is Active Directory Domain Services (AD DS). It stores information about members of the domain, including devices and users, verifies their credentials, and defines their access rights. A server running AD DS is a domain controller (DC).

AD DS is a central component in organizations with on-premises IT infrastructure. AD DS gives organizations the ability to manage multiple on-premises infrastructure components and systems using a single identity per user. AD DS doesn't, however, natively support mobile devices, SaaS applications, or line of business apps that require modern authentication methods.

The growth of cloud services, SaaS applications, and personal devices being used at work, has resulted in the need for modern authentication, and an evolution of Active Directory-based identity solutions.

Microsoft Entra ID, previously referred to as Azure Active Directory (Azure AD), is the next evolution of identity and access management solutions. It provides organizations with an Identity as a Service (IDaaS) solution for all their apps across cloud and on-premises.