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