Method of determining and preprogramming over-erases groups of memory cells

A method of controlling a nonvolatile memory device, the method comprising:

• determining, based on a write address, whether selected memory cells of the nonvolatile memory device corresponding to the write address are included in an over-erased group;
• based on the selected memory cells being included in the over-erased group, performing a preprogram operation to increase threshold voltages of an over-erased state of the selected memory cells;
• and
• after completion of the preprogram operation, performing a data program operation to store write data in the selected memory cells, wherein a time point of starting the data program operation is uniform regardless of whether the preprogram operation is performed or omitted.

A nonvolatile memory device comprising:

• a memory cell array comprising a plurality of memory cells;
• and
• a control circuit configured to:
• based on selected memory cells corresponding to a write address being included in an over-erased group, perform a preprogram operation to increase threshold voltages of an over-erased state of the selected memory cells, and
• after performing the preprogram operation, performing a data program operation to store write data in the selected memory cells,
• wherein the preprogram operation comprises decreasing a preprogram voltage applied to a selected wordline corresponding to the write address during the preprogram operation, as a distance between a selected string selection line corresponding to the selected memory cells and a wordline cut area decreases.