Updated: January 21, 2005
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
The Active Directory® directory service is compatible with Microsoft® Windows NT® and supports a mix of operations that support domain controllers running Windows NT 4.0, Windows® 2000, and Windows Server 2003. This allows you to upgrade domains and computers at your own pace, based on your organization's needs.
Active Directory supports the NTLM protocol used by Windows NT. This enables authorized users and computers from a Windows NT domain to log on and access resources in Windows 2000 or Windows Server 2003 domains. To clients running Windows 95, Windows 98, or Windows NT that are not running Active Directory client software, a Windows 2000 or Windows Server 2003 domain appears to be a Windows NT 4.0 domain. For more information, see Active Directory clients.
The upgrade to Active Directory can be gradual and performed without interrupting operations. If you follow domain upgrade recommendations, it should never be necessary to take a domain offline to upgrade domain controllers, member servers, or workstations. When upgrading a Windows NT domain, you must upgrade the primary domain controller first. You can upgrade member servers and workstations at any time after this. For more information, see Upgrading from a Windows NT domain.
Active Directory allows upgrading from any Windows NT 4.0 domain model and supports both centralized and decentralized models. The typical master or multiple-master domain model can be easily upgraded to an Active Directory forest.