Non-volatile Memory

Nonvolatile storage is a broad collection of technologies and devices that do not require continuous power to maintain data or program code over short or long periods of time. Nonvolatile storage technologies and devices vary widely in how they transfer and retrieve data, whether communicating with applications, microprocessors, or other types of devices. They can also vary significantly in terms of cost, capacity, durability, and latency.

Nonvolatile storage is often categorized by the following two types of systems:

• Electrically addressed systems – These NVM systems use electrical mechanisms to program (write) and read data. Electrically addressed systems include flash memory, read-only memory (ROM), and variations of ROM.

• Mechanically handled systems – These NVM systems use heads to write and read data to magnetic storage media. Mechanically handled systems include hard-disk drives (HDD) and tape drives.

Three common examples of nonvolatile devices that continuously store data are tape drives, HDDs, and SSDs. The term nonvolatile storage also applies to semiconductor chips that store data or control program code within devices such as SSDs, HDDs, tape drives, and memory modules.

There are many types of nonvolatile memory chips used today. For example, SSDs in enterprise and personal computer systems typically use NAND flash memory chips to store data. Chips are also used in consumer devices such as mobile phones and digital cameras, in USB sticks and memory cards. Flash memory chips, NOR, typically store controller code in storage drives and personal electronic devices.

Trend of Nonvolatile Memory

The manufacturer is working on additional non-volatile storage types to try to reduce the cost per bit of storing data and program code, improve performance, increase durability, and reduce power consumption. For example, manufacturers are developing 3D NAND flash technology in response to the physical scaling limitations of two-dimensional, or planar, NAND flash. 3D NAND can provide higher density at a lower cost per bit by stacking memory cells vertically, rather than using a single layer of cells. Over the years, manufacturers have also increased the number of bits per cell in NAND flash storage.

• Single-level cell (SLC) – Each cell contains only one bit. This configuration is the fastest, most durable, and least susceptible to errors. It is also the most expensive. However, for mission-critical workloads, it may be worth the cost.
• Multi-level cell (MLC) – Each cell contains exactly two bits, although its name suggests otherwise. MLC devices are not as fast, reliable, or durable as SLC storage, but they are more affordable and suitable for a wide range of enterprise workloads. MLC devices enabled standard laptops and desktop computers to start using SSDs and are still widely used in business computers.
• Triple level cell (TLC) – Each cell contains three bits. TLC technology sacrifices speed, reliability, and durability even further, but also increases density and lowers storage cost per gigabyte. TLC devices are now the main type of SSD storage used in consumer systems. They are also used in many business systems and data centers, rather than MLC storage.
• Quad-level cell (QLC) – Each cell contains four bits. Once again, the additional bits affect speed, reliability, and durability, but also make SSD storage more affordable. However, due to durability issues, QLC devices are often better suited for intensive read workloads, such as analytics, video streaming, or big data analytics.

Source:

https://www.techtarget.com/searchstorage/definition/nonvolatile-storage

https://www.fierceelectronics.com/electronics/what-non-volatile-memory