How to restrict SQL Server to use limited cores.

Hi,

I have Windows Server 2012 with 20 cores, Windows Server 2008 R2 with 4 core and SQL Server 2014 core License is for 20 cores only.
I want to restrict SQL Server to use only 16 cores on Windows server 2012 because I want to install SQL Server on Windows Server 2008 R2 also.

Please let me know how can I restrict SQL Server to use 16 cores only on Windows Server 2012 with 20 cores


Regards,
Nikhil P Desai