With Windows NT domains, you can make changes only on the PDC's copy of the directory. But as you know, Windows 2000 doesn't have PDCs and BDCs—just domain controllers. All the domain controllers retain read/write copies of the directory, so you can make changes on any of them. The system then uses multimaster replication to ensure that all domain controllers receive the changes you made. To prevent you from making conflicting changes at different domain controllers within a domain, Active Directory (AD) performs conflict resolution using update sequence numbers (USNs) and time stamps that it associates with every AD object change.

How...