A NVDIMM (pronounced "en-vee-dimm") or non-volatile DIMM is a type of persistent random-access memory for computers using widely used DIMM form-factors. Non-volatile memory is memory that retains its contents even when electrical power is removed, for example from an unexpected power loss, system crash, or normal shutdown. Properly used, NVDIMMs can improve application performance and system crash recovery time. They enhance solid-state drive (SSD) endurance and reliability. Many "non-volatile" products use volatile memory during normal operation and dump the contents into non-volatile memory if the power fails, using an on-board backup power source. Volatile memory is faster than non-volatile; it is byte-addressable; and it can be written to arbitrarily, without concerns about wear and device lifespan. However, including a second memory to achieve non-volatility (and the on-board backup power source) increases the product cost compared to volatile memory. There are many emerging non-volatile memories in development and a few that have been launched including

Magnetoresistive RAM Magnetoresistive random-access memory (MRAM) is a type of non-volatile random-access memory which stores data in magnetic domains. Developed in the mid-1980s, proponents have argued that magnetoresistive RAM will eventually surpass competing tech ...

(MRAM) and Intel's

3D XPoint 3D XPoint (pronounced ''three-D cross point'') is a discontinued non-volatile memory (NVM) technology developed jointly by Intel and Micron Technology. It was announced in July 2015 and is available on the open market under the brand name Optane ...

. Like MRAM, Nano-RAM based on

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s is one technology intended to come close to DRAM on the criteria of performance, byte-addressability and device lifespan; first products are expected in 2021 at moderate density, from fabrication partner Fujitsu. The goal of this technology is able to scale cost-effectively scale out so persistent memory could replace DRAM as the main system memory in enterprise systems.

Types

There are three types of NVDIMM implementations by JEDEC Standards org: *NVDIMM-F: DIMM with flash storage. System users will need to pair the storage DIMM alongside a traditional DRAM DIMM. While there's no official standard, NVDIMM-F type of modules have been available since 2014. *NVDIMM-N: DIMM with flash storage and traditional DRAM on the same module. The computer accesses the traditional DRAM directly during system runtime. In the event of a power failure, the module copies the data from the volatile traditional DRAM to the persistent flash memory, and copies it back when power is restored. It uses a small backup power source for the module while the data in DRAM is being copied to the flash storage. * NVDIMM-P: specification fully released by JEDEC in February 2021. It enables computer main memory to be persistent, using

persistent memory In computer science, persistent memory is any method or apparatus for efficiently storing data structures such that they can continue to be accessed using memory instructions or memory APIs even after the end of the process that created or last mo ...

technology and can share the

DDR4 Double Data Rate 4 Synchronous Dynamic Random-Access Memory (DDR4 SDRAM) is a type of synchronous dynamic random-access memory with a high bandwidth ("double data rate") interface. Released to the market in 2014, it is a variant of dynamic rando ...

or DDR5 DIMM interconnect with DRAM DIMMs. Non-Standard NVDIMM implementations: * NVDIMM-X: DDR4 DIMM with NAND Flash storage and volatile DRAM on the same module, developed by Xitore. As of November 2012, most NVDIMMs used NAND flash as the non-volatile memory. Emerging memory technologies aim to achieve NVDIMM without a cache or two separate memories. Intel and Micron have announced use of the

PCM Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amp ...

technology in NVDIMM-F. Sony and

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have announced an NVDIMM-N product based on the

ReRAM Resistive random-access memory (ReRAM or RRAM) is a type of non-volatile (NV) random-access (RAM) computer memory that works by changing the resistance across a dielectric solid-state material, often referred to as a memristor. ReRAM bears som ...

technology. In 2015, Samsung and Netlist announced a NVDIMM-P product, possibly based on Z-NAND.

Backup power

NVDIMMs evolved from the BBU (battery backed up) DIMM, which used a

backup battery A backup battery provides power to a system when the primary source of power is unavailable. Backup batteries range from small single cells to retain clock time and date in computers, up to large battery room facilities that power uninterruptible po ...

to sustain power to a volatile memory for up to 72 hours. However,

batteries Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

are disfavored in computer components because they have a limited lifespan, they may be regarded as

hazardous waste Hazardous waste is waste that has substantial or potential threats to public health or the environment. Hazardous waste is a type of dangerous goods. They usually have one or more of the following hazardous traits: ignitability, reactivity, co ...

, and may contain

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which violate RoHS compliance. When the module includes non-volatile memory, backup power is required for only a short time after the computer's main power fails, while the module copies the data from volatile to non-volatile memory. Therefore, modern NVDIMMs use on-board

supercapacitors A supercapacitor (SC), also called an ultracapacitor, is a high-capacity capacitor, with a capacitance value much higher than other capacitors but with lower voltage limits. It bridges the gap between electrolytic capacitors and Rechargeable ba ...

to store energy.

Interface

A few server vendors still make products using the DDR3 interface to the computer, but standardization work in 2014 and 2015, such as at JEDEC and

ACPI Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto con ...

, was based on the

interface.

Uses

The BBU DIMM was originally designed for use as the cache of RAID HBAs (host bus adapters) or systems, to enable data in the cache to survive a power failure. NVDIMMs have moved beyond RAID applications into fast storage appliances or in-memory processing for the

data center A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommunic ...

and cloud computing.

References

External links