A memory system includes a nonvolatile memory, a memory controller included in a first package, and a memory interface circuit included in a second package that is different from the first package. The memory controller includes an encoder for performing encoding for error correction. The memory controller is configured to encode first data into second data using the encoder, and program the second data into a location in the nonvolatile memory. The memory interface circuit is interposed between the memory and the memory controller. The memory interface circuit includes a decoder for performing decoding for error correction. The memory interface circuit is configured to read third data from a first location in the nonvolatile memory, diagnose the third data by decoding the third data using the decoder, and convey a result of the diagnosis to the memory controller.