If you thought non-volatile memory (NVM) was that one time in grade school when you had three snow days in a row, that’s not quite right. Or, if you thought NVM was data storage, it’s technically not that either. But you’re warm and getting warmer.
At its core, non-volatile memory is “byte addressable,” random access memory (RAM) for computers that retains data even in the absence of power. Byte-addressable memories facilitate access to data at the individual byte level. Computer memory involves the “devices used to store information for use in a computer.”
Conversely, volatile memory requires continuous power to retain data or stored information, and some forms, such as dynamic random-access memory (DRAM), need periodic refreshing to prevent loss of data. While volatile random-access memory (RAM) continues to be the key player in primary memory for computer storage systems, non-volatile memory is most commonly used in secondary memory for program and data storage or long-term storage applications.
NVM: Electrically Addressed vs. Mechanically Addressed Systems
Non-volatile memory falls into two main categories as either electrically addressed or mechanically addressed systems. Electrically addressed systems are further categorized by write mechanism and tend to be more expensive, faster and have less capacity than their mechanically addressed counterparts. Examples of electrically addressed systems include flash memory and FRAM.
Mechanically addressed systems have larger storage capacity than electrically addressed systems and use a recording head or contact structure to read and write on an appointed storage medium. Examples include hard disks, magnetic tape and optical disks.
Examples of Non-Volatile Memory Chips
- Read-only memory (ROM)
- Erasable programmable ROM (EPROM)
- Electrically erasable programmable ROM (EEPROM)
- Ferroelectric RAM (FRAM)
- Flash memory (e.g., NOR and NAND flash memory and solid-state drives (SSD)
- Magnetic storage devices (e.g., hard disks, magnetic tape, floppy disks, etc.)
- Optical disks
- Punched tape and cards (early computer storage)
Here’s a sampling of non-volatile memory uses and applications:
- To hold boot code when a computer is turned on
- In memory chips for USB memory sticks and digital cameras
- As NOR flash memory in smartphones for the operating system and default applications
- In solid-state memory or flash memory (typically the less expensive and higher capacity NAND) in smartphones to store photos, videos, text messages or SMS, and call logs
Comparisons & Interactions of Volatile & Non-Volatile Memory
The memory hierarchy in computer systems employs volatile and non-volatile memory for different operations and processes for which each memory type is best suited. In many cases, volatile memory relies on non-volatile memory to initiate or buttress a shared process. In this sense, as well as countless other applications, they are simultaneously complementary and individually necessary in complex systems and applications, such as computers.
- Speed: Volatile memory is typically faster than nonvolatile memory
- Cost: Volatile memory typically costs less
- Performance: Volatile memory is considered to have higher performance
- Lifetime: Non-volatile memory has a limited lifetime due to its re-write capabilities.
- Energy Use: Many forms of volatile memory require repeated data refreshes, which consume additional power.
Looking Ahead
As with most technology, the uses and applications for non-volatile memory continue to evolve and expand. Demand for and subsequent growth in memory for storage and other applications will increase, as this technology is becoming ubiquitous in the digital world—think smartphones, cloud servers, etc..
Recent developments in the NVM space include:
- CBRAM: Conductive-bridging RAM
- DWM: Domain-wall or racetrack memory
- FeRAM: Ferroelectric RAM
- Millipede non-volatile memory
- MRAM: Magnetoresistive RAM
- NRAM: Nano-RAM
- PCM / PRAM: Phase-change memory
- ReRAM / RRAM: Resistive random-access memory
- SONOS: Silicon-oxide-nitride-oxide-silicon, a cross-sectional structure of MOSFET for NVM
Resources
The digital computer: Martin Plonus in Electronics and Communications for Scientists and Engineers (Second Edition)
Emerging Non-volatile Memories: Jalil Boukhobza, Pierre Olivier in Flash Memory Integration
PCMagazine: https://www.pcmag.com/encyclopedia/term/non-volatile-memo
Technopedia: https://www.techopedia.com/definition/2793/non-volatile-memory-nvm
Mobile Device Forensics: https://mobileforensics.wordpress.com/2010/09/01/non-volatile-memory-in-cell-phones/