{HEAD ~ A second coding device} is located in the write path and removes {TAIL ~ runs} of zeros in interleaved subsequences in the scrambled user data 
removes
{ HEAD ~ A second coding device } is located in the write path and removes { TAIL ~ runs } of zeros in interleaved subsequences in the scrambled user data
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH