Patent ID: 7472251

Claim:
A removable data storage device detachably mounted to a host apparatus, comprising: a non-volatile semiconductor memory in which data recorded thereon is erased in batches, wherein a batch is a block of a predetermined data volume, wherein the non-volatile semiconductor memory comprises a system area having information of the data storage device recorded therein; and a user area having data recorded by a user therein; and file management data corresponding to a logical format supervising the recorded data by setting logical addresses from one sector as a data read or write unit to another and also supervising the relationship of interconnection of the recorded data based on a cluster, composed of a predetermined number of physically consecutive sectors, is recorded in said system area, wherein the number of sectors in one block and the information indicating the logical address of the sector of the block boundary position are stored in said system area, wherein information showing relationship between logical block numbers and corresponding physical block numbers is recorded in a redundant area that cannot be accessed from the host apparatus, wherein said host apparatus accesses the data storage device based on said logical format.