Processor Licensing Model
A license is required for each physical or virtual processor accessed by an operating system environment running SQL Server. This license does not require any device or user client access licenses (CALs). Under this structure, a customer acquires a separate Processor license for each processor that is located in the server running the SQL Server software. If you have made a processor inaccessible to all operating system copies on which the SQL Server software is set up to run, you do not need a software license for that processor.
Server Plus User CALs Licensing Model
Server plus user client access license (CAL) licensing requires a separate Server license for each server on which the software is installed, plus a user CAL for each user accessing the server.
A SQL Server CAL is required for a user to access or use the services or functionality of either edition of SQL Server. For more information on the requirements for devices that use SQL Server functionality without directly accessing the database, please see the SQL Server 2005 licensing Special Considerations page.