Q: What is the maximum number of processor sockets supported by Windows Server 2012?

A: Both Windows Server 2012 and Windows Server 2008 R2 support 64 sockets, which means 64 physical processors. Each of these processors can have multiple processing cores and even hyperthreading to increase the logical processor count.

Windows Server 2012 supports 640 logical processors (or 320, if Hyper-V Role is enabled). This is confirmed by Microsoft. Note that as processors have more and more cores on them, many systems are focusing less on adding more sockets and more on adding processors with more cores, especially as Windows is licensed by socket and not core. Also note that in Windows Server 2012, both Standard and Datacenter have the same limits.

You might also be interested in the answer to this FAQ "Q: Why are only 64 logical processors being used on my Hyper-V-enabled Windows Server 2012 server in the parent partition?"