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