Abstract: A flash memory stores current and past BPTs (Block Pointer Tables) indicating correspondence between physical addresses and logical addresses of blocks. At the time of writing of user data, which requires that a new current BPT after this writing be written in a vacant block, a controller updates the current BPT to the new current BPT to include information indicating the order at which that vacant block is used for storing the BPT, the location of the BPT older by one, whether or not the block previously used for storing the BPT is a defective block. At the next initialization, the controller performs correction, etc. of a current BPT based on these pieces of information. In a case where any of these pieces of information is missing, the controller specifies the content of a current BPT based on the other available pieces of information.

Abstract: A controller stores a BSI (Block Search Index) to specify an empty block of a lash memory. The controller determines whether a pointer indicating a physical block address of an empty block is stored. If no such pointer is stored, the controller generates a random number based on the BSI, determines the initial value of the pointer based on the generated random number, and stores a pointer indicating this initial value. When supplied with user data, which is the objective of writing, the controller writes the user data in the empty block indicated by the pointer. The controller updates the pointer to indicate an empty block having a physical block address which appears next to the address of that block, and updates the BSI such that it no longer indicates that the block in which the user data has been written is an empty block.