What is "nvdimm"

A Non-Volatile Dual In-line Memory Module (NVDIMM) is a computer memory RAM DIMM that retains data even when electrical power is removed either from an unexpected power loss, system crash or from a normal system shutdown. NVDIMMs can be used to improve application performance, data security, system crash recovery time and to enhance SSD endurance and reliability. Some consider having "non-volatile" in the name misleading as it is still uses volatile memory during normal operation, it just has a dedicated power source to allow the DIMM to dump memory into on board non-volatile memory in case of system powerloss.

There are two main types of NVDIMM cards: NVDIMM-F and NVDIMM-N. NVDIMM-F is a Flash-only device that resides on the memory interconnect. NVDIMM-F can be operated in two modes. In "storage" mode, it is accessed via a block driver and has NAND Flash attributes such as high capacity, but slower access times (when missing the small front-end cache). In "Memory" mode, it is deployed in conjunction with DRAM DIMMs making it byte-addressable and expanding application memory to multiple terabytes in a single system. NVDIMM-F has been available since 2014.

NVDIMM-N is a byte-addressable memory-mapped device, which is typically accessed at memory or near-memory speeds. DDR4 NVDIMM-N cards are being sold by multiple hardware vendors and support is getting wider. These NVDIMM-N devices utilize DRAM for performance and endurance, though are limited in capacity and result in higher costs due to the use of both DRAM and flash memory.