Patent ID: 8171205

Claim:
An apparatus, comprising: a non-volatile memory; and a memory controller configured to; control reads, writes, and erases of contents of the memory; write a sequence number value into metadata of each sub-unit of a block if data is written into the sub-unit; increment the sequence number value each time a new sub-unit is written into, and to wrap the sequence number around to a minimum value after a maximum value of the sequence number is reached, wherein a range of values from the minimum value to the maximum value comprises of a first range and a non-overlapping second range; and select a one of the first range and the second range containing a newest active sequence number as a top range, and to select the other of the first range and the second range as a bottom range; wherein all active sequence numbers in the top range are designated to have a larger effective value than all active sequence numbers in the bottom range.