There are network structures you can choose from when implementing Windows NT Server.
The workgroup model can best be demonstrated by thinking of each Windows NT Server as an island. Each Windows NT Server has its own security database, resource listings and users. The Windows NT Servers do not share this information among each other nor do they request permission when clients access different servers. You can consider the workgroup model as the peer to peer implementation of Windows NT Server.
Providing centralized security is an important function of a network operating system. Windows NT Server uses a domain model as a directory service to implement security.