Memory system and memory device

A memory system comprising:

• a first memory;
• a clock configured to measure time;
• a non-volatile memory that includes
• a plurality of memory cells each configured to store data in a non-volatile manner, and
• a control circuit configured to:
• write first data of n bits (where n is a real number of 1 or larger) to each of the plurality of memory cells by a first write operation;
• and
• write second data of m bits (where m is a real number larger than n), which includes the n bits of the first data, to each of the plurality of memory cells by a second write operation;
• and
• a memory controller electrically connected to the non-volatile memory and configured to:
• issue a first command sequence to the non-volatile memory to execute the first write operation;
• select one of first and second methods for preparing the second data for the second write operation;
• and
• issue a second command sequence to the non-volatile memory to execute the second write operation, the second command sequence indicating the selected method for preparing the second data, wherein
• the memory controller is further configured to:
• store in the first memory, a first management table having a plurality of entries respectively corresponding to the plurality of memory cells, each of the entries indicating a memory cell address and a first time related to the first write operation performed on a memory cell designated by the memory cell address;
• select the first method for performing the second write operation on a target memory cell among the plurality of memory cells when a difference value between a second time related to the second write operation to be performed on the target memory cell and the first time stored in the entry for the target memory cell is equal to or shorter than a second threshold value;
• and
• select the second method for performing the second write operation on the target memory cell when the difference value is longer than the second threshold value.