Are you trying to decide which domain model to use with your Windows NT system? Do you need to know the hardware requirements for use with your new domain model? In this article, I’ll examine the four primary domain models, server roles, trust relationships, and PDC/BDC hardware requirements.
To help everyone understand what is being discussed in this article, I will define a few of the terms that I will be using.Domain
A domain is a grouping of computers, users, and resources into groupsDomain Model
A domain model extends the core coverage to include the words and concepts needed for a particular application. In a database, the domain model must also supply the correspondence between the database relations and the linguistic concepts and predicates.Trust Relationship
A trust relationship describes the interaction between domains. A machine in one domain “trusts” the authority of another domain’s directory database.
The different types of domains
One of the first considerations when setting up a Windows NT-based network is the domain structure. Because of the architectural limitations inherent in the NT domain model, certain circumstances require that simple domains be split into multiple domains connected by trust relationships, which allow users in one domain to access resources in another.

In any domain model, a computer running Windows NT Server can participate in one of three roles. They are as follows:

  • Primary domain controller (PDC): The PDC contains the master copy of the security accounts manager (SAM) database. Each domain allows only one PDC.
  • Backup domain controller (BDC): A BDC contains a copy of the security accounts manager (SAM). If a PDC fails, the BDC can be promoted into the PDC slot. Microsoft Premier Support recommends having at least one BDC per domain.
  • Domain server (or resource server): A domain server can act as a file, print, applications, or communications server. However, the domain server can’t authenticate users.

The four primary domain models
Domain models consist of one or more of the controllers mentioned in the previous paragraph, and use trust relationships to interact with other domains. They are as follows:

  • Single domain model: A single PDC, along with its BDCs and resource servers, serves the needs of the entire organization. This particular domain model provides the easiest upgrade path to Windows 2000 and the Active Directory.
  • Single domains with trust: This model involves two or more independent domains, each of which is in a two-way trusting relationship with every other domain in the organization.
  • Single master domain: Like the single domain with trust, the single master domain involves at least two domains, but in this case, one domain serves as the master and the remaining domains trust the master domain.
  • Multiple master domains: This model is a hybrid of the single domain with trust and the single master domain.

Making a choice on your organization’s needs
When deciding which model to use, a consideration must be made regarding physical limitations. Every Windows NT 4.0 domain can contain 40,000 users maximum, and the recommended size limit for the SAM database is 40 MB. Below you will find Table 1 to help you determine which domain model best suits your organization’s needs.

Hardware requirements for PDC/BDCs
When choosing a computer for use as a PDC, use the hardware guideline in Table 2, seen below. The data in the table assumes three things: first, the computer will function only as a PDC; second, no other major Windows NT operations occur, such as SQL Server, SNA Server, and RAS operations; and third, the computer’s page file size is at least 250 MB.


What kind of domain models do you use within your organization? Do you prefer one kind of domain model to another? Let us know your thoughts by posting a message below, or send us a note.