{HEAD ~ processor} means for reading {TAIL ~ data} from said main memory means and writing data into said main memory means 
for reading
{ HEAD ~ processor } means for reading { TAIL ~ data } from said main memory means and writing data into said main memory means
HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH