Microsoft Knowledge Base Article 305476 contains the following summary:
This article describes the initial synchronization requirements for domain controllers that host operations master roles
and that are running Microsoft Windows Server 2003 or Microsoft Windows 2000 Service Pack 3 (SP3) or later.
Initial synchronization must occur before dependent operations can occur in an Active Directory domain or forest.
Note The operations master roles are also known as flexible single master operations or FSMO roles.