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Dynamic Random Access Memory (DRAM)
Published in Shimeng Yu, Semiconductor Memory Devices and Circuits, 2022
The DDR protocol has a family of variants including LPDDR and GDDR. LPDDR is for low-power mobile platforms, and it is optimized for low leakage with lower supply voltage and long refresh interval. GDDR is for high-performance graphics platforms, and it is optimized for fast internal clock frequency with a small mat array size. Figure 3.3 shows the trends of I/O bandwidth for different interface protocols, including DDR, LPDDR, and GDDR.
Challenges in Design, Data Placement, Migration and Power-Performance Trade-offs in DRAM-NVM-based Hybrid Memory Systems
Published in IETE Technical Review, 2023
Sadhana Rai, Basavaraj Talawar
Implementations of hybrid memory have used either DRAM alternatives such as High-Bandwidth Memory (HBM) or Hybrid Memory Cubes (HMC) developed using 3D-stacked technology [32,33] or NVM devices. In the case of mobile devices, alternatives like LPDDR and WideIO2 are used to operate within the power and bandwidth constraints [34]. These technologies provide higher bandwidth and better energy efficiency (LPDDR: 30–50% [33]), when compared to conventional DRAM. Integration of HBM-DDR4 provides acceptable efficiency, and it depends on cache hit rate [33]. NVM technologies successfully integrated into Hybrid memory systems are Phase Change Memory (PCM), Spin Transfer Torque RAM (STT RAM), Resistive RAM(Re-RAM) and 3D-XPOINT. Table 1 gives the details about different NVM devices and Table 2 gives details of devices that have emerged as alternatives to DRAM. STT-RAM is a variant of Magnetic RAM (MRAM) that has better load latency when compared to DRAM [44]. STT-RAM and ReRAM are also considered to be good emerging technologies in NVM because of the operational benefits they provide, but they suffer from low density and they are less mature when compared to other NVMs [45]. However, STT-RAM is considered as a potential candidate for processor cache because of its read latency and good write endurance when compared to other NVMs [44]. In our study, we found that various NVMs that have been used are STT-RAM (≈ 4%), 3D-XPoint (12.5%), ReRAM (≈ 2%), PCM (75%). PCM is used widely because of the benefits it provides, such as (1) higher bit density, (2) the cost per bit of PCM is much lower than DRAM and (3) lower leakage power. Moreover commercial availability of PCM-based devices has attracted many researchers to include PCM as non-volatile memory in hybrid memory [2,9,15,45–47].