Licensing for the Microsoft BackOffice family of server products requires a Server License for each server and a Client Access License for each client computer to access the server. These licenses are acquired separately prior to using the product. For Windows NT Server, SQL Server, and SNA Server, the Client Access License can be used in one of two licensing modes (Per Server and Per Seat) offering customers the flexibility to choose the option that best meets their needs.
Which licensing mode to choose really depends on which applications you will be using. For example, if you use Windows NT Server mainly for file and print sharing and on multiple servers, you may be better off choosing the Per Seat option. However, if you use it as a dedicated Remote Access server, you may want to choose the Per Server concurrent connections option.
There are two rules of thumb for choosing between the two licensing modes:
For example, if you have three servers to which 50 users can connect concurrently and you have 200 computers or workstations, you should choose the Per Server option. If, however, you add an additional 50-user server without adding any more computers or workstations, you should convert to the Per Seat option. Additional examples of situations under which you would use each licensing mode are provided in the Windows NT Server Update Information for Version 3.51 book.
Notice that, within a single organization, you can also mix the Per Server and Per Seat modes, since your choice depends on how much the different server products are used in each department. You can also mix the Per Server and Per Seat modes on a single server if you are running multiple server products. However, a given server product, such as SQL Server, cannot be simultaneously run in two modes on the same server.
Finally, to determine which licensing mode to choose and how many licenses are needed, you need to know how many users and how many servers are, or will be, on your network. You do not need to determine which users are accessing which servers. You only need to determine how many users access each server.