A memory device is provided. The memory device includes: a buffer memory; a nonvolatile backup memory; and a memory controller configured to: store map data corresponding to an external storage device in the buffer memory; provide, in response to a request from the external storage device, an address pair corresponding to the request, from among address pairs of the map data, to the external storage device; and back up, in response to a sudden power-off event, the map data to the nonvolatile backup memory.