Memory system

A memory system comprising a memory portion including a memory cell for storing n-level data (n is an integer equal to or larger than 3), wherein

• said memory cell is operated as an n-level data storing memory cell until the number of times a write-erase sequence has been performed reaches an n-th number of times, said memory cell is operated as an (n-1) level data storing memory cell after the write-erase sequence has been performed the n-th number of times and until the number of times the write-erase sequence has been performed reaches an (n-1)th number of times, and said memory cell is operated as an i-level data storing memory cell (i is an integer equal to or larger than 2) after the write-erase sequence has been performed an (i+1)th number of times and until the number of times the write-erase sequence has been performed reaches an i-th number of times.

A memory system comprising a memory portion including a memory cell for storing n-level data (n is an integer equal to or larger than 3), said memory system further comprising

• a level holding portion for storing information of the level of data stored in said memory cell.

A memory system comprising a memory portion including memory cells comprising

• a first memory cell operating as an n-level data storing memory cell (n is an integer greater than or equal to 3);
• and
• a second memory cell operating as an m-level data storing memory cell (m is an integer smaller than n), wherein said second memory cell operated as an n-level data storing memory cell until the number of times data was written to or erased from said second memory cell exceeded a predetermined number.

A memory system comprising a memory portion including a memory cell for storing n-level data (n is an integer equal to or greater than 3), wherein

• said memory cell is operated as an n-level data storing memory cell until the number of times a writing/erasing operation has been performed reaches a predetermined number, and said memory cell is operated as an m-level data storing memory cell (m is an integer smaller than n) when the number of times the writing/erasing operation has been performed exceeds the predetermined number of times.

A memory system comprising a memory portion including a memory cell for storing n-level data (n is an integer equal to or larger than 3), wherein

• said memory cell is operated as an n-level data storing memory cell until the number of times a writing/erasing operation has been performed reaches an n-th number of times, said memory cell is operated as an (n-1) level data storing memory cell after the writing/erasing operation has been performed the n-th number of times and until the number of times the writing/erasing operation has been performed reaches an (n-1)th number of times, and said memory cell is operated as an i-level data storing memory cell (i is an integer equal to or greater than 2) after the writing/erasing operation has been performed an (i+1)th number of times and until the number of times the writing/erasing operation has been performed reaches an i-th number of times.

A memory system comprising memory cells, each memory cell capable of storing any one of "n" threshold levels, the threshold levels designating respective states corresponding to the storage of "n"-level data, wherein "n" is an integer equal to or larger than 3 and "n" is decreased for said memory cells when the number of times data is written to or erased from said memory cells exceeds a predetermined number.