Dan Stolts explains dynamic memory was introduced in Windows Server 2008 R2 with SP1.  It gave the Hyper-V hypervisor the capability to dynamically adjust the amount of memory assigned to a machine based on memory demand.  The reason we would want to do this is simple…read on…..

http://itproguru.com/expert/2013/03/virtual-memory-management-dynamic-memory-much-different-than-memory-over-commit-become-a-virtualization-expert-part-3-of-20/

Compare Vmware to Hyper at: http://aka.ms/hyperv2vmware and scroll to the bottom on the webpage and click on DATASHEET, this is a great comparison and stacks them up side by side.