Active Directory Question:

It is a role that only one DC can (or should) hold at any given time within its boundary.
Schema Master - Use MMC "Active Directory Schema Snap-in". The schema master domain controller controls all updates and modifications to the schema. Once the Schema update is complete, it is replicated from the schema master to all other DCs in the directory.
Domain Naming Master - Use "Active Directory Domains and Trusts". It controls the addition or removal of domains in the forest.
Primary Domain Controller (PDC) Emulator - Use the "ADUC" . The PDC emulator is necessary to synchronize time in an enterprise.
Relative ID Master (RID Master) - Use "ADUC". All objects have a SID and a domain SID. The RID assigns relative IDs to each domain controller.
Infrastructure Master - Use the "ADUC". Updates group membership information when users from other domains are moved or renamed.
The Infrastructure Master (IM) role should be held by a domain controller that is not a Global Catalog server (GC). If the Infrastructure Master runs on a Global Catalog server it will stop updating object information because it does not contain any references to objects that it does not hold.