MEMORY SYSTEM

A controller assigns a first plurality of blocks among a plurality of blocks provided in a non-volatile memory to a first area, assigns a second plurality of blocks to a second area, and assigns a third plurality of blocks to a third area. The controller uses each block assigned to the first area in a first mode, uses each block assigned to the second area in a second mode in which the number of bits of data written in each memory cell is larger than that in the first mode, and uses each block assigned to the third area in the first mode or the second mode. The controller writes data received from a host device to an area that corresponds to a designation from the host device out of the first area and the third area. The controller transcribes valid data written to the first area and the third area to the second area.