Choosing between native mode and mixed mode can be a big issue. It all comes down to one key point -- whether you want to use pre-Windows 2000 systems (e.g. Windows NT 4.0 Server) as domain controllers or not. If you can make a firm decision about using only Windows 2000 Server or Windows Server 2003 as your domain controllers, then you should elect to deploy a native mode domain. If you must leave open the possibility of using Windows...
NT 4.0 Server as a domain controller, you must stick with mixed mode.
With a mixed mode domain, you gain the benefit of using Windows NT 4.0 Server legacy domain controllers. However, you reap the limitations of mixed mode as well. These include a maximum of 40,000 objects in the domain, specialized AD security groups, such as universal groups, are not allowed, and you are restricted to using LanMan Replication. Don't forget you also get to keep the limitations of Windows NT 4.0 Server itself, which include no group policies, no Kerberos authentication and no OU administration.
With a native mode domain, the 40,000 objects per domain restriction climbs to 1,000,000, all AD security groups are supported and File Replication Service (FRS) replaces LanMan Replication.
Even after moving to a native mode domain, the PDC Emulator FSMO role remains. However, its primary purpose is altered. Now, the PDC Emulator serves as interface through which password changes occur. The PDC Emulator helps to ensure that password changes are properly distributed throughout the DC mesh.
When in native mode, all systems must have minimal Active Directory support to participate in the domain. This requires the installation of the Directory Services Client onto Windows 9x and Windows NT 4.0 systems. This software can be downloaded from Microsoft. Once the Directory Services Client is installed, Windows NT 4.0 Server systems can operate as member servers in the domain.
James Michael Stewart is a partner and researcher for Itinfopros, a technology-focused writing and training organization.