linking the original value of the data unit to the update data before transferring the update data to the storage layer if transferring {HEAD ~ the update data} to {TAIL ~ the storage layer results} in updating a value of the data unit 
linking the original value of the data unit to the update data before transferring the update data to the storage layer if transferring { HEAD ~ the update data } to { TAIL ~ the storage layer results } in updating a value of the data unit
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH