A refresh method for a volatile memory device includes refreshing memory cells of a first set of rows of an array at a first refresh rate having a first refresh period, the first refresh rate being a lower rate having a longer refresh period than a second refresh rate having a second refresh period, wherein each memory cell in the first set of rows of the array has a retention time longer than the first refresh period; and refreshing memory cells of a second set of rows of the array at a third refresh rate having a third refresh period, the third refresh rate being a higher rate having a shorter refresh period than the second refresh rate having the second refresh period, wherein at least one memory cell of each row of the second set of rows has a retention time longer than the third refresh period and shorter than the first refresh period. The second refresh period corresponds to a refresh period defined in a standard for the volatile memory device.