Software-Defined Memory (SDM) is an evolving concept for the convergence of Storage and Memory, which for decades were two separate computing domains. Storage is a multi-layer software implementation outside of the realm of Computer Architecture (i.e. I/O subsystem). The memory subsystem is the exact opposite, it is an integral part of Computer Architecture & Microarchitecture and implemented by hardware engineers.
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History
The term SDM was originally coined in 2014 by SanDisk to describe the software which leveraged their SSD and persistent memory devices. Both devices located on the processor's peripheral I/O subsystem, i.e. on PCIe-based cards.
The following year (2015) was a crucial year for the standardization of plug-and-play DDR4-based NVDIMM cards. These persistent memory devices reside on the processor's memory subsystem, which requires broader platform support, but is a better fit, because it was designed for memory-like latencies and cache-line granular access. 2015 also saw several key announcements of new storage-class memory (SCM) based devices, such as Intel & Micron 3D XPoint, HPE & SanDisk memristors, Samsung & Netlist NVDIMM-P and Sony & Viking Technology.
To reflect this richer hardware environment and its pros and cons, Plexistor has taken the next attempt to better define the term SDM in late 2015. Plexistor is world first persistent memory-based distributed storage solution delivering ultra-low latency storage and millions of IOPS using a commodity server.This time taking a hardware agnostic view and trying to stay close to definition of a related term: software-defined storage or SDS. SDS, which may be viewed as a subset of SDM, describes storage software that virtualizes traditional block-based storage hardware and often also mixes different storage tiers and provides data services.
Description
SDM is a software solution that can utilize standard heterogeneous off-the-shelf persistent memory devices and present them using standard APIs in a way that hides the internal complexity. It may support multi tiers (e.g. NVDIMM, SSD and HDD) in order to allow flexible price points, as well as other data services.