Memory Interfaces: Past, Present, and Future

Over the last few decades, the bandwidth of dynamic random-access memory (DRAM) has increased significantly through innovative architectures and circuit-level techniques to overcome the well-known "memory wall" problem. We can understand the past challenges of DRAM input/output (I/O) by investigating the technologies utilized for DRAM I/O in the transition from single-data-rate (SDR) synchronous DRAM (SDRAM)to double-data-rate (DDR) SDRAM. Recently developed versions of low-power DDR four (LPDDR4) and synchronous graphics DDR five (GDDR5) employ new I/O features for further bandwidth increase. Looking beyond LPDDR4 and GDDR5, what should be done to make another jump in bandwidth increase for DRAM?