3. Client Access Licensing Modes
After you have selected a licence type, Device CAL or User CAL, you have the option to use the software in two different modes: Per User/Per Device or Per Server mode. Both modes are available for either type of licence.
A separate CAL is required for each user or device that accesses or uses the server software on any of your servers. The number of CALs required equals the maximum number of users or devices that may access the server software. If you choose this licensing mode your choice is permanent. You can, however, reassign a CAL from one device to another device or from one user to another user, provided the reassignment is made either (a) permanently away from the one device or user or (b) temporarily to accommodate the use of the Windows CAL either by a loaner device, while a permanent device is out of service, or by a temporary worker, while a regular employee is absent.
A separate CAL (of either type) is required for each user or device that accesses or uses the server software on any of your servers. The number of Windows CALs required equals the maximum number of users or devices that may simultaneously access or use the server software installed on a particular server. The CALs you acquire are designated for use exclusively with a particular server. If you choose this licensing mode, you have a one-time right to switch to the other licensing mode - Per User/Per Device mode. Your CALs would then be used in Per User/Per Device mode instead.
Terminal Services, as found in Windows Server 2003, lets you remotely execute applications on a Windows-based server from a wide range of devices over virtually any type of network connection. When a server is configured in the Terminal Server role it can be referred to as a Terminal Server. The Terminal Services functionality is included with the acquisition of a Windows Server licence. However, when a user or device accesses a Terminal Server, that user or device is required to have a Terminal Server CAL (in addition to a Windows CAL) in order to be compliant with the licensing terms of the product.
TS CALs are required for Windows XP Professional licences because desktop equivalency has been removed by Microsoft. This also means that TS CALs are no longer included freely under the Microsoft Campus agreement and they must now be purchased separately under the Microsoft Select or Campus agreements, see below, Acquiring CALs.