US Patent 9685218 Memory device and memory system having the same

A memory device includes a memory cell array, an intensively accessed row detection circuit, and a refresh control circuit. The memory cell array includes a plurality of memory cell rows. The intensively accessed row detection circuit generates an intensively accessed row address indicating an intensively accessed memory cell row among the plurality of memory cell rows based on an accumulated access time for each of the plurality of memory cell rows. The refresh control unit preferentially refreshes neighboring memory cell rows adjacent to the intensively accessed memory cell row indicated by the intensively accessed row address when receiving the intensively accessed row address from the intensively accessed row detection unit. The memory device effectively reduces a rate of data loss.