Memory system

A memory system comprising:

• a first nonvolatile memory including a memory cell array which includes a plurality of cell units each including a plurality of memory cells;
• and
• a memory controller configured:
• to store, in a first buffer, a first data set read from a first cell unit of the cell units in the first nonvolatile memory, and a first expected data set generated by an error correction on the first data set;
• to count a number of first memory cells corresponding to a first combination of data in the first data set and the first expected data set, and a number of second memory cells corresponding to a second combination of the data in the first data set and the first expected data set, among the memory cells in the first cell unit;
• to calculate a shift amount of a read voltage which is used in a read operation of reading data from the first cell unit, based on the counted number of the first memory cells and the counted number of the second memory cells;
• and
• to apply the shift amount to a next read operation of reading data from the first cell unit.