Under the term NVDIMM memory, various technical solutions for non-volatile data storage based on a DIMM memory are summarized. NVDIMM stands for Non-Volatile-Dual-Inline-Memory-Modules. This memory technology is used in specific servers.
The addressing of NVDIMM memory is done via the DDR interface, similar to a DDR4 or DDR5 DIMM module. Technically, the NVDIMM-F module is more similar to an SSD than to RAM.
Access to NVDIMM-F, NVDIMM-P, and NVDIMM-X memory is not as fast as with DDR4 or DDR5 LRDIMM, but faster than a conventional SSD solution.
In DDR4/DDR5 DIMM as RAM (Read Access Memory) based storage, the cell contents must be maintained through a permanent refresh. If the power supply to the memory is interrupted, the data is no longer available (volatile data storage).
The commonality among the various NVDIMM technologies is non-volatile data storage. If data on the NVDIMM is not actively deleted, it remains available even when no voltage is applied.
All NVDIMM memory uses the memory bus and standard DIMM sockets of DDR4 or DDR5 RAM, but they have completely different approaches to addressing and data storage:
NVDIMM-N memory “works” with DRAM memory. Additionally, there is a flash memory on the memory board. In the event of a power failure, the contents of the volatile DRAM memory are transferred to the non-volatile flash memory within the NVDIMM. An external battery and onboard capacitors are necessary for this. Upon system startup, the data is retrieved from the flash memory of the NVDIMM and loaded into the DRAM memory of the NVDIMM. An NVDIMM-N has a similar performance to RDIMM or LRDIMM memory. Due to the increased space requirements of the capacitors and the flash chip on the board, the space for the DRAM memory is physically limited. Compared to RDIMM or LRDIMM memory, the price of NVDIMM-N is higher, but the capacity is lower.
NVDIMM-F modules work with NAND flash memory. The data is stored non-volatile. Much larger capacities than with NVDIMM-N are possible. The DDR4 or DDR5-based main memory is externally used as fast cache memory through the NVDIMM-F technology to enhance performance. Nevertheless, the performance is significantly lower than that of an RDIMM or LRDIMM memory module.
NVDIMM-P modules utilize Intel Optane Persistent Memory technology (PMem) with non-volatile memory. The data is stored in 3D-Xpoint cells. Intel achieves better speeds with 3D-Xpoint memory than currently possible with other flash memories. In general, the NVDIMM-P standard is also intended to be usable for configurations with NAND flash, ReRAM, and other non-volatile memories.
NVDIMM-X uses NAND flash memory and additional DRAM memory as cache memory on the NVDIMM board. The name is derived from NVDIMM and the company name “Xitore,” which developed this technology.
The development of NVDIMM memory has brought innovation to the way data is processed and stored within systems. The non-volatile memory on a DIMM board, which is directly implemented on the fast system bus and directly addressed by the processor, promises interesting possibilities for combining large and secure storage capacities with the speed of RAM.