What is the difference between a CAL lisence and a Processor lisence?

Answer 1

A Device CAL - this permits one device (used by any number of users) to access or use the server software. Device CALs can be used in kiosks or shared computer environments where multiple employees use the same computer to access their e-mail and calendar information. For example, in a manufacturing environment where 100 factory floor workers each shift can use any of the 10 shared computers on the floor, the factory only needs to purchase 10 Device CALs. A User CAL - this permits one user using any device to gain access to or use the server software. Many Exchange users prefer the User CAL because it allows access to the server running Exchange from multiple devices, including computers, laptops, and mobile devices.

so to summarise, I device cal is good for multiple users of one device where as user cals are good for one user of multiple devices.