Q. What the heck is a Windows domain and how do you create one? 

A. A Windows Domain is a logical grouping of computers that share common
   security and user account information. This information is stored in a
   master directory database (SAM) which resides on a Windows server
   designated as a domain controller. 

   There are two kinds of controllers in a Windows NT domain; a single
   Primary Domain Controller (PDC), and --optionally-- one or more Backup
   Domain Controllers (BDC). The PDC automatically replicates it's master
   directory database to each of the BDC's.

   The word "Domain" does not refer to any particular computer, or network
   configuration. It is an administrative concept. A single domain
   constitutes a single administrative unit.

   Typically, one would choose whether or not to configure a computer as a
   domain controller during installation of the NT Server software. 

A. The domain database in Windows 2000 is now stored in the Active
   Directory, a distributed database which is served via a modified DNS
   server.

   PDC and BDC are no longer used except in the NT configuration.  The
   domain controllers are now peers in a Windows 2000 configuration.  They
   all replicate to each other.

A. The "NT configuration", usually referred to as a "Mixed Mode Domain", 
   remains a dominant force in what I see of the installed base. Ideally, 
   one should understand the role each type of controller plays in 
   either an NT or a W2K domain. 



   
Q. Do you have to have a box running a special (server) version of Windows 
   to be the domain server?  Or can a W2K workstation be a domain server?  

A. A domain requires any Server license. An NT Workstation cannot be a
   domain controller, nor can a W2K Workstation. W2K Server may emulate a
   domain controller, but domains are no longer the native administrative
   tool in a Windows 2000 network; they have been dropped in favour of
   Active Directory.

A. Domains are still the model in Windows networking.  While there have been
   some changes since NT 4.0, the basic concepts are the same and they are
   still referred to as domains.

A. While the name "domain" stays the same in the W2K model, the
   architecture of a domain in W2K changes significantly. In W2K, structure
   elements such as Domains and Trusts resemble their NT ancestors;
   however, there are many more design elements to consider during
   implementation. Forests, Trees, Child Domains, Organizational Units,
   Transitive Trusts; none of which existed under NT, all play an important
   role within Active Directory.

   ...the PDC/BDC/Domain concept is no longer the native 
   administrative/organizational model used by W2K.
   The Active Directory --in which Domains are one of the building blocks--
   is the new framework used to define and administer the logical structure
   of your network.





Q. Can a Linux box be a domain server?  Can an AS/400 (with no
   integrated PC card) be a domain server?

A. Yes to both. 

   Linux provides this functionality through the software known as "Samba".
   Samba, as of version 2.2, can be configured as a Primary Domain
   controller. Samba does not yet support BDC replication or domain trusts.
   The Samba TNG project is a fork of the original Samba project, created
   with the objective of providing a fully functional NT/2K  domain
   controller running on *nix.

   The AS/400 provides this functionality through the IPCS, or through
   Netserver. Netserver is equivalent to Samba. The IPCS is of course a PC
   installed on your AS/400, and therefore is able to run NT/2K Server
   itself.

   For additional information relevent to the AS/400 implementation, refer
   to the following links:

   Netserver: http://publib.boulder.ibm.com/iseries/v5r2/ic2924/info/rzahl/rzahldmnlogonspt.htm

   Windows Server on iSeries (aka IPCS): http://publib.boulder.ibm.com/iseries/v5r2/ic2924/info/rzahq/rzahqntspo.htm



Answers courtesy John Taylor and Andy Nolen-Parkhouse via Midrange-L