Exploring high-performance and energy proportional interface for phase change memory systems

Phase change memory is emerging as a promising candidate for building up future energy efficient memory systems. To achieve high-performance and energy proportional design, phase change memory devices need to be reorganized so that (1) the relatively long latency of phase change memory devices should be hidden; (2) unnecessary power waste of phase change memory need to be preserved. Previous studies show that conventional memory ranks could be broken down into multiple smaller ranks for increased concurrency and lower power consumption. Nevertheless, the conventional electrical bus is incapable of supporting a large number of memory chips due to its insufficient load capacity and signal traversing speed. In this paper, we propose a phase change memory system design that leverages the state-of-art photonic links to overcome this issue. Moreover, thanks to the flexibility of photonic links, it is possible to amortize the small-rank penalty (e.g. the rank-to-rank switch overhead) by partitioning the channels either statically or dynamically. Our experimental results show that photonically interconnected phase change memory can increase the system performance (IPC) by up to 19% while saving 35% memory system power.