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