DRAM refresh

Refresh interval

This frequent DRAM refresh consumes a third of the total power drawn by low-power electronics devices in standby mode. Researchers have proposed several approaches for extending battery run-time between charges by reducing the refresh rate, including temperature-compensated refresh (TCR) and retention-aware placement in DRAM (RAPID). Experiments show that in a typical off-the-shelf DRAM chip, only a few weak cells really require the worst-case 64 ms refresh interval, and even then only at the high end of its specified temperature range. At room temperature (e.g. 24 °C (75 °F)), those same weak cells need to be refreshed once every 500 ms for correct operation. If the system can avoid using the weakest 1% of pages, a typical DRAM only needs to be refreshed once a second, even at 70 °C (158 °F), for correct operation of the remaining 99% of the pages. Some experiments combine these two complementary techniques, giving correct operation at room temperature at refresh intervals of 10 seconds.