DRAM refresh power, which is consumed solely to preserve data, is rapidly increasing as capacity increases. A study predicts that the power will account for up to 35% of total DRAM power in the high capacity DRAM device. While various schemes were proposed to reduce the refresh power, those could not be adopted to commercial products due to cost overhead and design complexity issues. In this paper, we propose a simple refresh power saving scheme called TWW. We implement it with a much smaller amount of register size than previous works without modification on OS and DRAM controller. It eliminates unnecessary refresh operation of pre-activated rows in a specific timing window with optimum register size. We can save the refresh power up to 16% with only 6.2 KB registers in a DRAM device. This paper explains the implementation of the proposed scheme and shows the power saving effectiveness with gem5 full system simulator.