A removable memory card detachably mounted to a host device. The memory card includes a non-volatile semiconductor memory in which data recorded in the memory is erased as a block of a predetermined data volume. An interface for inputting/outputting data between the data storage device and said host device, and a controller for controlling file management in the semiconductor memory in response to a command from said host device over said interface is also used. Parameters for recording file management data are stored in a system information storage unit. The controller records the file management data in the semiconductor memory when supplied with an initialization command from said host device.