Modeling, Architecture, and Applications for Emerging Memory Technologies
IEEE Design & Test of Computers
MEMORY HIERARCHY DESIGN is a key component of modern computer systems. Memory hierarchy importance increases with advances in microprocessor performance. Traditional memory hierarchy design consists of embedded memory (such as SRAM and embedded DRAM [eDRAM]) for on-chip caches, commodity DRAM for main memory, and magnetic hard disk drives (HDDs) for storage. Recently, solidstate drives (SSDs) based on NAND-flash memory have also gained momentum to replace caches in traditional magnetic HDDs.
... closer the memory is placed to the microprocessor, the faster latency and higher bandwidth must be, along with the penalty of the memory's smaller capacity. Technology scaling of SRAM and DRAM, the common memory technologies used in the traditional memory hierarchy, are increasingly constrained by fundamental technology limits. In particular, the increasing leakage power for SRAM and DRAM and the increasing refresh dynamic power for DRAM have posed challenges to circuit and architecture designers of future memory hierarchy designs. Emerging memory technologiesÀ Àsuch as spintransfer torque RAM (STT-RAM), phase-change RAM (PCRAM), and resistive RAM (RRAM)À Àare being explored as potential alternatives to existing memories in future computing systems. Such emerging nonvolatile memory (NVM) technologies combine the speed of SRAM, the density of DRAM, and the nonvolatility of flash memory, and so become very attractive as alternatives for the future memory hierarchies. As emerging memory technologies mature, computer architects need to understand the benefits and limitations of such technologies so that they can better use them to improve the performance, power, and reliability of future computer architectures. Specifically, architecture designers should seek answers to the following questions: How should emerging NVM technologies be modeled at the architectural level? What will be the impacts of such NVMs on the future memory hierarchy? What will be the novel architectures and applications? What limitations must be overcome for this new memory hierarchy? This article examines two of the most promising memory technologies, STT-RAM and PCRAM, and reviews recent research efforts that seek to answer these questions. Although the review focuses chiefly on STT-RAM and PCRAM nonvolatile memory, much of the discussion can also apply to other emerging NVM, such as RRAM. Emerging memory technologies Many promising candidates, such as PCRAM, STT-RAM, RRAM, and memristor, have gained substantial attention of late and are being actively investigated by industry. Two of the most promising memory technologies are STT-RAM and PCRAM.