Microsoft Licensing

Every Installation of Windows requires a license. You also need a Client Access License (CAL) for all clients that attach to a server over the network. Licenses are not required for Internet Information Services (IIS), Telnet and File Transfer Protocol (FTP) connections.

Licensing Modes

Per Server Licensing Mode

The Per Server licensing mode requires a license for each concurrent connection to a server.

4 Client Access Licenses (CALs) required.

The key here is that the server holds the licenses. If it only held 3 licenses only 3 of the 4 clients could connect at any one time.

Per Seat Licensing Mode

The Per Seat Licensing Mode requires a license for each client accessing a server (This can be any Windows Server)

4 Per Seat Licenses (CALs) required or 12 Per Server Licenses.

The clients hold the licenses. A client with a per seat license can access any Windows 2003 Server