With Windows Server 2012 and Windows Server 2012 R2 there are some changes to versions and licensing that you should be aware of. For years Microsoft has been saying that licensing is getting easier and with WS2012 it really has with only two editions being released.
- Windows Server 2012 Standard Edition
- Windows Server 2012 Datacenter Edition
And with these two editions the features and functionality is identical. Standard Edition has the same memory support (4TB) the same physical processor support (64 CPUs) and the same feature set including Failover Clustering. When it comes time to load the OS on to a server you simply need to determine if the server will run a standalone workload or if it will be a virtualization host.
Standalone workload = Standard Edition
Virtualization host = Datacenter Edition
Both are licensed per physical CPU (number of cores is irrelevant) now with the base license including support for 2 CPU. If your server has 4 CPU you will need two licenses.
For more information on licensing WS2012, downgrade rights and more please review the Windows Server 2012 Licensing and Pricing FAQ (PDF).