Infrastructure master

Domain

Updates and changes if a user or group is renamed. There can be only one infrastructure master per domain. If a user moves across domains, the two infrastructure masters will replicate the change during the next multi-master replication between domains.

Primary domain controller (PDC) emulator

Domain

If the network is running in mixed mode, the PDC emulator acts like a Windows NT PDC and replicates with the NT backup domain controllers. If the network is running in native mode, the PDC emulator will be the first DC to get replication of password changes. If replication hasn’t occurred on a recent password change, a DC can check with the PDC emulator to see if it received the password change. This is especially important if a network has a lot of domain controllers and frequent password changes. There can be only one PDC emulator per domain.

Relative ID master

Domain

The relative ID master has two main functions. It assigns a group of consecutive IDs to domain controllers so that they can assign unique IDs to objects created on the DC. To move any Active Directory object between domains, you have to move it from the computer that is currently acting as the relative ID master. You can change which computer is the relative ID master, but there can be only one relative ID master at a time in a domain.

Domain naming master

Forest

Keeps track of domains that are added or removed from the forest. There can be only one domain naming master in the forest.

Schema master

Forest

Changes to the Active Directory Schema can only be made from the schema master. There can be only one schema master in the forest.