US Patent 9037947 Method of controlling a semiconductor storage device

A method of controlling a nonvolatile semiconductor memory includes checking a first group at a first interval period, the first group including a plurality of blocks, and when a first block in the first group satisfies a first condition, assigning the first block to a second group. The method includes checking, at a second interval period, an error count of data stored in the second group, and when a second block in the second group satisfies a second condition, moving data stored in the second block to an erased block in which stored data is erased among the plurality of blocks.