Accelerating write by exploiting PCM asymmetries

To improve the write performance of PCM, this paper proposes a new write scheme, called two-stage-write, which leverages the speed and power difference between writing a zero bit and writing a one bit. Writing a one takes longer time but less electrical current than writing a zero. We propose to divide a write into stages: in the write-0 stage all zeros are written at an accelerated speed, and in the write-1 stage stage, all ones are written with increased parallelism, without violating power constraints. We also present a new coding scheme to improve the speed of the write-1 stage by further increasing the number of bits that can be written to PCM in parallel. Based on simulation experiments of a multi-core processor under various SPEC CPU 2006 workloads, our proposed techniques can reduce the memory latency of standard PCM by 68.3% and improve the system performance by 33.9% on average. In addition, the proposed two-stage-write shows 16.5% latency reduction and 9.2% performance improvement over Flip-N-Write.