Omitting Refresh: A Case Study for Commodity and Wide I/O DRAMs

Dynamic Random Access Memories (DRAM) have a big impact on performance and contribute significantly to the total power consumption in systems ranging from mobile devices to servers. Up to half of the power consumption of future high density DRAM devices will be caused by refresh commands. Moreover, not only the refresh rate does depend on the device capacity, but it strongly depends on the temperature as well. In case of 3D integration of MPSoCs with Wide I/O DRAMs the power density and thermal dissipation are increased dramatically. Hence, in 3D-DRAM even more DRAM refresh operations are required. To master these challenges, clever DRAM refresh strategies are mandatory either on hardware or on software level using new or already available infrastructures and implementations, such as Partial Array Self Refresh (PASR) or Temperature Compensated Self Refresh (TCSR). In this paper, we show that for dedicated applications refresh can be disabled completely without or with negligible impact on the application performance. This is possible if it is assured that either the lifetime of the data is shorter than the currently required DRAM refresh period or if the application can tolerate bit errors to some degree in a given time window.