Since SDS controls the DRAM commands and power modes selectively, power state transitions and activate/ precharge operations can be avoided in those chips which are not involved in writes. Figure 10 shows net power consumption and its breakdown of conventional DRAM system and our SDS. Specifically, average 8.4%, 30%, and 25% of background (BG), read/write (RD/WR), and activate/ precharge (ACT/PRE) power consumptions are reduced by SDS for the write-back cache with x8 chips. Average refresh power consumption is same in both conventional and SDS because refresh power is consumed periodically in all DRAM chips even when DRAM is not used. Therefore, SDS reduces all factors of DRAM power consumption except refresh power.