In Windows NT (and 2000), a domain combines some of the advantages of a workgroup (a group of users who exchange access to each others' resources on different computers) and a directory (a group of users who are managed centrally by an administrator). The domain concept not only allows a user to have access to resources that may be on different servers, but it also allows one domain to be given access to another domain in a trust relationship. In this arrangement, the user need only log in tothe first domain to also have access to the second domain's resources as well.
In a Windows NT network, not all servers need to be a PDC or BDC. A server can be designated as a member server whose resources become part of a domain without havinga role in the logon process.
Setting up and maintaining PDCs and BDCs and domain information is a major activity for the administrator of a Windows NT network. In Windows 2000, the domain controller concept is retained but the PDC and BDC serverroles are generally replaced by the Active Directory.
See the following articles for a lot of useful information:
“Understanding User Accounts, Groups, Domains, and Trust Relationships” – a Microsoft article.
http://www.microsoft.com/technet/treeview/default.asp?url=/TechNet/prodtechnol/winntas/maintain/featusability/acctgrps.asp
Windows2000 magazine article, “Understanding PDCs and BDCs: Domain controllers made easy”
http://www.winntmag.com/Articles/Index.cfm?ArticleID=7738
Windows2000.com – a large index of articles.
http://searchwin2000.techtarget.com/
REMOVE SPACES from the pasted URL.
Good luck,
Maxwell