If the local CPU addresses a memory module which is different from {HEAD ~ the last accessed memory module}, then the subsystem monitoring circuit initiates {TAIL ~ a request} to maintain control of the system bus 
If the local CPU addresses a memory module which is different from { HEAD ~ the last accessed memory module } , then the subsystem monitoring circuit initiates { TAIL ~ a request } to maintain control of the system bus
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH