Hyper-V Host Server RAM Utilization

Hi,

We are running Hyper-V Environment on a Dell Power Edge R720 Server which has 128GB RAM.

Installed Windows Hyper-V Server 2012 R2 on the Host and created 7 VM's.

Total RAM assigned for 7 VM's is 116GB and remaining available is 12GB. But when i am trying to create a new VM on this host,it says you don't have sufficient RAM to create a VM. what could be the reason ?

How much memory does the Host server occupy and what factors does this take into consideration ?

11GB for a Server Core installation of OS ? i am stuck here ?

Thanks .