An “execution server” manages {HEAD ~ requests} from client machines based on priorities assigned to {TAIL ~ the requests} 
An “ execution server ” manages { HEAD ~ requests } from client machines based on priorities assigned to { TAIL ~ the requests }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL