A memory system has a first memory to store first-granularity data having a granularity smaller than second-granularity data, the first memory having a memory capacity smaller than a memory capacity of a second memory storing the second-granularity data, a controller to read third-granularity data having a granularity equal to or greater than the first-granularity from the data stored in the second memory, and a data extractor to extract the first-granularity data from the third-granularity data read by the controller and to store the extracted data in the first memory.