Why Active Directory

You may have heard Directory Service. A directory is similar to a database for storing, grouping, managing, administering, and organizing entries. Entries can be users, groups, files, devices, email addresses, phone numbers, etc. Each resource in the directory is considered an object. An object can have multiple attributes such as multiple computers for "Work PC" and "Test PC" to find resources more conveniently.

Unlike databases, directory services read data more frequently than written. This is because directory servers usually store user and computer entries, and many applications use LDAP to read their attributes to determine if have the corresponding permissions to grant or deny access. Administrators only need to maintain and grant account or computer permissions in one place without having to create accounts or add items repeatedly.

There are many directory service implementations. But for Windows OS, Active Directory is the only choice.

1. Active Directory Domain Services (AD DS) implemented the directory service function, which works well with Windows' enterprise features by configuring group policies.
2. Active Directory Certificate Services (AD CS) can be used as a Certificate authority (CA) to issue certificates for internal devices or users.
3. Active Directory Rights Management Services (AD RMS) can be used to limit operations on documents such as prohibiting reading or editing by protecting documents using information rights management (IRM).
4. Active Directory Federation Services (AD FS) extends the ability to use single sign-on (SSO) functionality, which allows users to authenticate once and access multiple resources without being prompted for more credentials.

Did you find that Active Directory is more than just a directory service? It is a complete identity and access management solution with more exclusive features than directory service applications. Considering that Windows is the most used OS including enterprises, Active Directory and Microsoft Entra ID (formerly Azure Active Directory, the cloud version of Active Directory) have the largest market share and are supported by many applications, thus forming a complete ecosystem.