{HEAD ~ A read write circuit} has two data lines each of which is associated with {TAIL ~ a read circuit} 
{ HEAD ~ A read write circuit } has two data lines each of which is associated with { TAIL ~ a read circuit }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL