According to one embodiment, a memory system includes a non-volatile semiconductor memory with a plurality of blocks. A controller in the system controls the writing of data to the non-volatile semiconductor memory and includes a host I/F control interface to receive write command information including file allocation information indicating a location for write data, a file information management unit to assign an erasure level to a file and output a file identifier in which a file name, a file size, and the erasure level of the file are combined, and a flash translation layer unit to allocate each file on a single file per block basis based on the write command information and the file identifier.