the quality of data stored in a memory system is assessed by different methods , and the memory system is operated according to the assessed quality . the data quality can be assessed during read operations . subsequent use of an error correction code can utilize the quality indications to detect and reconstruct the data with improved effectiveness . alternatively , a statistics of data quality can be constructed and digital data values can be associated in a modified manner to prevent data corruption . in both cases the corrective actions can be implemented specifically on the poor quality data , according to suitably chosen schedules , and with improved effectiveness because of the knowledge provided by the quality indications . these methods can be especially useful in high - density memory systems constructed of multi - level storage memory cells .