The bus also enables the execution of {HEAD ~ I/O operations} that originated in {TAIL ~ external controllers} and transmitted over the communication network 
originated in
The bus also enables the execution of { HEAD ~ I / O operations } that originated in { TAIL ~ external controllers } and transmitted over the communication network
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH