Patent ID: 7145801

Claim:
An external storage device comprising: a flash memory having a plurality of blocks for storing data; a block management register and n operation gates provided at each of the blocks of the flash memory; n control circuits; block selection unit; and storage unit that stores data to the blocks of the flash memory, wherein the block management register includes a use possibility register for indicating the use status of the block, and n (n is an integer of 2 or greater) erase count registers for indicating the erase count value of the block data; the n operation gates output result values that indicate erase count value of the usable blocks based on logical product of a value of use possibility register and each of the erase count register values; the n control circuits classify the usable blocks into n groups according to the erase count value based on the outputted result values of the operation gates; each of the control circuits has: a first circuit for outputting signals for indicating the usable block among the blocks included in one of the groups in a constitution sequence; and a second circuit for outputting signals for indicating that there are no usable blocks within the one group; the block selection unit specifies one group among n groups in a cyclic sequence for each output timing of the second circuit of the control circuit and selects the usable block based on the output signal of the first circuit; and the storage unit stores the data in the selected block.