NVRAM

NVRAM – Non-Volatile RAM. This is a type of memory in which its contents are not lost when power is turned off, unlike DRAM.

NVRAM combines the speed of RAM with the persistence of storage, making it useful for caching, buffering, or storing critical data that must survive power cycles, such as system firmware, configuration settings, or write caches in storage arrays. It can be implemented using different hardware technologies and configurations, each suited to specific performance, cost, and durability needs:

Battery-Backed DRAM: A standard DRAM module is paired with a battery or supercapacitor. If power is lost, the battery provides temporary power to maintain the DRAM’s contents or copy them to a non-volatile mediym (e.g. flash memory). The hardware includes DRAM chips, a battery/supercapacitor, and, sometimes, a small flash chip for backup.

A controller manages data ransfer between DRAM and the backup medium during power outage events.

Flash-Backed DRAM (NVDIMM-F or NVDIMM-N): Combines DRAM for fast access with NAND flash for persistence. On power loss, a supercapacitor or battery powers the copying of DRAM contents to the flash memory. On power restoration, data is reloaded into DRAM.

• NVDIMM-N: Integrates DRAM and flash on the same module (DIMM form factor), with a supercapacitor for power backup. The DRAM handles normal operations, with flash only storing data during power loss.
• NVDIMM-F: Uses flash as the primary storage medium but with DRAM-like access speeds, often via a controller. It fits into standard DRAM slots on server motherboards, interfacing via the memory bus (e.g. DDR4/DDR5).

Newer technologies like MRAM (Magneto- Resistive RAM), PCM (Phase-Change Memory), or FeRAM (Ferro-Electric RAM) provide native non-volatility without needing backup mechanisms.