How does ESX determine MAX RAM permissible for a VM ?
I have two separate windows VMs showing different limits of max - memory - for - performance values..........
Do you have different Maximum numbers of RAM when configuring the VM?
Are the Windows servers different versions? Perhaps one Enterprise and one Standard? The host is aware to some degree of licensing rules for guest operating systems, that could limit you to use certain features.
How does ESX determine MAX RAM permissible for a VM ?
It depends by the guest OS that you have specify.