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