is there any percentage that is treated as system memory on esxi host.
VMKernel need 100MB+ of RAM (depending on the number of hosts devices)
also there is virtual machine memory overhead
http://www.vmware.com/support/pubs/vsphere-esxi-vcenter-server-pubs.html
But what i observed with 2.5gb ram it is 9.5mb and with 4gb ram it is 17.5mb.