Licensing reference

A student ask about the reference for Windows CAL Licensing
Here are some reference for that:

Licence FAQ’s
http://www.microsoft.com/licensing/resources/faq.mspx

CAL

http://www.microsoft.com/licensing/about-licensing/client-access-license.aspx
http://www.microsoft.com/licensing/about-licensing/client-access-license.aspx#tab=2

Windows 2008 R2
http://www.microsoft.com/windowsserver2003/howtobuy/licensing/caloverview.mspx