Windows NT has several licensing
models. For the
Windows NT Workstation operating system, the local
machine is usually licensed individually or is covered by a
site license, where
X number of
computers are licensed within one
enterprise entity.
Windows NT Server has two different licensing models.
Per-Server Licensing
The traditional method of securing a license for Windows NT Server is to license the server to handle X number of concurrent connections. If you had three servers and 100 users who would be accessing the servers virtually at the same time, you would have to have three Windows NT Server operating systems licensed to accomodate 100 users each. This method is heavily relied upon in systems that are webservers and in small businesses. You do not know how many connections have pre-existing licensed operating systems, so you can set it up to allow 100 concurrent connections. This is another reason why Linux is making huge inroads into the internet server market.
Per-Seat Licensing
Most large enterprises use the per-seat license model. The IT department basically buys a Client Access License (CAL) for each terminal/machine. The server allows unlimited connections because the license is carried by the client operating system. The Windows NT License Manager collects and records the CALs from the connecting machines. In a nutshell, the server is licensed for the server operating system alone, and the license to connect to the server is covered under the client operating system.