Patent attributes
A memory system includes a nonvolatile semiconductor memory including memory cells storing data, and a controller configured to control a read operation of the nonvolatile semiconductor memory to read data from the nonvolatile semiconductor memory. The controller is configured to determine a read voltage to be used for reading data from the nonvolatile semiconductor memory depending on whether the read operation is performed during a first period after an end of a write operation of the data or during a second period following the first period, upon determining that the read operation is performed during the first period, change the read voltage in accordance with an elapsed time after the end of the write operation of the data, and upon determining that the read operation is performed during the second period, determine the read voltage regardless of the elapsed time after the end of the write operation of the data.
