NVRAM
Encyclopedia
Non-volatile random-access memory (NVRAM) is random-access memory
that retains its information when power is turned off, which is described technically as being non-volatile. This is in contrast to the most common forms of random access memory today, dynamic random-access memory (DRAM) and static random-access memory (SRAM), which both require continual power in order to maintain their data.
The best-known form of NVRAM memory today is flash memory
. Some drawbacks to flash memory include the requirement to write it in larger blocks than many computers can automically address, and the relatively limited longevity of flash memory due to its finite number of write-erase cycles (most consumer flash products at the time of writing can withstand only around 100,000 rewrites before memory begins to deteriorate). Another drawback is the performance limitations preventing flash from matching the response times and, in some cases, the random addressability offered by traditional forms of RAM. Several newer technologies are attempting to replace flash in certain roles, and some even claim to be a truly universal memory
, offering the performance of the best SRAM devices with the non-volatility of flash. To date these alternatives have not yet become mainstream.
Rapid advances in semiconductor fabrication
in the 1970s led to a new generation of solid state
memories that core simply could not compete with. Relentless market forces have dramatically improved these devices over the years, and today the low-cost and high-performance DRAM
forms the vast majority of a typical computer's main memory. However there are many roles where non-volatility is important, either in cases where the power will be removed for periods of time or where the constant power needs of DRAM conflicts with low-power devices. For many years, there was no practical RAM-like device to fill this niche, and many systems used a combination of RAM and some form of ROM for these roles.
Custom ROM
was the earliest solution, but had the disadvantage of being able to be written to only once, when the chip was initially designed. ROMs consist of a series of diode
s permanently wired to return the required data, the diodes being built in this configuration when they are being fabricated.
PROM
improved on this design, allowing the chip to be written to electrically by the end-user. PROM consists of a series of diodes that are initially all set to a single value, "1" for instance. By applying higher power than normal, a selected diode can be "burned out" (like a fuse
), thereby permanently setting that bit to "0". PROM was a boon to companies who wished to update the contents with new revisions, or alternately produce a number of different products using the same chip. For instance, PROM was widely used for game console cartridges in the 1980s.
For those who required real RAM-like performance and non-volatility typically have to use conventional RAM devices and a battery backup. This Nonvolatile BIOS memory
, often called CMOS RAM or Parameter RAM, was a common solution in earlier computer systems like the original Apple Macintosh, which used a small amount of memory powered by a watch "button" battery
for storing basic setup information like the selected boot volume. Much larger battery backed memories are still used today as cache
s for high-speed database
s, requiring a performance level newer NVRAM devices have not yet managed to meet.
. EPROM consists of a grid of transistors whose gate terminal (the "switch") is protected by a high-quality insulator. By "pushing" electrons onto the base with the application of higher-than-normal voltage, the electrons become trapped on the far side of the insulator, thereby permanently switching the transistor "on" ("1"). EPROM can be re-set to the "base state" (all "1"s or "0"s, depending on the design) by applying ultraviolet
light (UV). The UV photon
s have enough energy to push the electrons through the insulator and return the base to a ground state. At that point the EPROM can be re-written from scratch.
An improvement on EPROM, EEPROM
, soon followed. The extra "E" stands for electrically, referring to the ability to reset EEPROM using electricity instead of UV, making the devices much easier to use in practice. The bit are re-set with the application of even higher power through the other terminals of the transistor (source and drain). This high power pulse, in effect, sucks the electrons through the insulator, returning it to the ground state. This process has the disadvantage of mechanically degrading the chip, however, so memory systems based on floating-gate transistors in general have short write-lifetimes, on the order of 105 writes to any particular bit.
One approach to overcoming the rewrite count limitation is to have a standard SRAM where each bit is backed up by an EEPROM bit. In normal operation the chip functions as a fast SRAM and in case of power failure the content is quickly transferred to the EEPROM part, from where it gets loaded back at the next power up. Such chips were called NOVRAMs by their manufacturers.
The basis of flash memory
is identical to EEPROM, and differs largely in internal layout. Flash allows its memory to be written only in blocks, which greatly simplifies the internal wiring and allows for higher densities. Memory storage density is the main determinant of cost in most computer memory systems, and due to this flash has evolved into one of the lowest cost solid-state memory devices available. Starting around 2000, demand for ever-greater quantities of flash have driven manufacturers to use only the latest fabrication systems in order to increase density as much as possible. Although fabrication limits are starting to come into play, new "multi-bit" techniques appear to be able to double or quadruple the density even at existing linewidths.
, which makes writing dramatically slower than reading, often as much as 1,000 times. A number of new memory devices have been proposed to address these shortcomings.
To date, the only such system to enter widespread production is ferroelectric RAM
, or FeRAM. FeRAM uses a ferroelectric layer in a cell that is otherwise similar to conventional DRAM, this layer holding the charge in a 1 or 0 even with the power removed. To date, FeRAM has been produced on very old fabs, and even the most advanced research samples are still twice the linewidth of most flash devices. Although this difference might be addressable under normal circumstances, as flash moves to multi-bit cells the difference in memory density appears to be growing, rather than shrinking.
Another approach to see major development effort is Magnetoresistive Random Access Memory
, or MRAM, which uses magnetic elements and in general operates in a fashion similar to core, at least for the first-generation technology. Only one MRAM chip has entered production to date: Everspin Technologies
' 4 Mbit part, which is a first-generation MRAM that utilizes cross-point field induced writing. Two second-generation techniques are currently in development: Thermal Assisted Switching
(TAS), which is being developed by Crocus Technology
, and Spin Torque Transfer
(STT) on which Crocus
, Hynix
, IBM
, and several other companies are working. STT-MRAM appears to allow for much higher densities than the those of the first generation, but is lagging behind flash for the same reasons as FeRAM – enormous competitive pressures in the flash market.
Another solid-state technology to see more than purely experimental development is Phase-change RAM, or PRAM. PRAM is based on the same storage mechanism as writable CDs and DVD
s, but reads them based on their changes in electrical resistance rather than changes in their optical properties. Considered a "dark horse" for some time, in 2006 Samsung
announced the availability of a 512 Mb part, considerably higher capacity than either MRAM or FeRAM. The areal density of these parts appears to be even higher than modern flash devices, the lower overall storage being due to the lack of multi-bit encoding. This announcement was followed by one from Intel and STMicroelectronics
, who demonstrated their own PRAM devices at the 2006 Intel Developer Forum
in October. One of the most attended sessions in the IEDM December 2006 was the presentation by IBM of their PRAM technology.
Also seeing renewed interest is silicon-oxide-nitride-oxide-silicon (SONOS
) memory.
Perhaps one of the more innovative solutions is millipede memory
, developed by IBM
. Millipede is in essence a punched card
rendered using nanotechnology
in order to dramatically increase areal density. Although it was planned to introduce millipede as early as 2003, unexpected problems in development delayed this until 2005, by which point it was no longer competitive with flash. In theory the technology offers storage densities on the order of 1 Tbit/in², far greater than even the best hard drive technologies currently in use (perpendicular recording
offers about 230 Gbit/in²) . However, slow read and write times for memories this large seem to limit this technology to hard drive replacements as opposed to high-speed RAM-like uses, although to a very large degree the same is true of flash as well. It remains to be seen if this technology will ever become practical.
A number of more esoteric devices have been proposed, including Nano-RAM
based on carbon nanotube technology
, but these are currently far from commercialization. The advantages that nanostructures such as quantum dots, carbon nanotubes and nanowires offer over their silicon-based predecessors include their tiny size, speed and their density. Several concepts of molecular-scale memory devices have been developed recently.
Random-access memory
Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
that retains its information when power is turned off, which is described technically as being non-volatile. This is in contrast to the most common forms of random access memory today, dynamic random-access memory (DRAM) and static random-access memory (SRAM), which both require continual power in order to maintain their data.
The best-known form of NVRAM memory today is flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
. Some drawbacks to flash memory include the requirement to write it in larger blocks than many computers can automically address, and the relatively limited longevity of flash memory due to its finite number of write-erase cycles (most consumer flash products at the time of writing can withstand only around 100,000 rewrites before memory begins to deteriorate). Another drawback is the performance limitations preventing flash from matching the response times and, in some cases, the random addressability offered by traditional forms of RAM. Several newer technologies are attempting to replace flash in certain roles, and some even claim to be a truly universal memory
Universal memory
Universal memory may mean:* any memory device combining cost benefits of DRAM, speed of SRAM, and non-volatility of flash memory** magnetoresistive random-access memory ** Bubble memory** Racetrack memory** ferroelectric random-access memory...
, offering the performance of the best SRAM devices with the non-volatility of flash. To date these alternatives have not yet become mainstream.
Early NVRAMs
Early computers used a variety of memory systems, some of which happened to be non-volatile, although not typically by design but simply as a side-effect of their construction. The most common form of memory through the 1960s was magnetic-core memory, which stored data in the polarity of small magnets. Since the magnets held their state even with the power removed, core memory was also non-volatile.Rapid advances in semiconductor fabrication
Semiconductor fabrication
Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer...
in the 1970s led to a new generation of solid state
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
memories that core simply could not compete with. Relentless market forces have dramatically improved these devices over the years, and today the low-cost and high-performance DRAM
Dram
Dram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
forms the vast majority of a typical computer's main memory. However there are many roles where non-volatility is important, either in cases where the power will be removed for periods of time or where the constant power needs of DRAM conflicts with low-power devices. For many years, there was no practical RAM-like device to fill this niche, and many systems used a combination of RAM and some form of ROM for these roles.
Custom ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
was the earliest solution, but had the disadvantage of being able to be written to only once, when the chip was initially designed. ROMs consist of a series of diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
s permanently wired to return the required data, the diodes being built in this configuration when they are being fabricated.
PROM
Programmable read-only memory
A programmable read-only memory or field programmable read-only memory or one-time programmable non-volatile memory is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. Such PROMs are used to store programs permanently...
improved on this design, allowing the chip to be written to electrically by the end-user. PROM consists of a series of diodes that are initially all set to a single value, "1" for instance. By applying higher power than normal, a selected diode can be "burned out" (like a fuse
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
), thereby permanently setting that bit to "0". PROM was a boon to companies who wished to update the contents with new revisions, or alternately produce a number of different products using the same chip. For instance, PROM was widely used for game console cartridges in the 1980s.
For those who required real RAM-like performance and non-volatility typically have to use conventional RAM devices and a battery backup. This Nonvolatile BIOS memory
Nonvolatile BIOS memory
Nonvolatile BIOS memory refers to a small memory on PC motherboards that is used to store BIOS settings. It was traditionally called CMOS RAM because it used a low-power Complementary metal-oxide-semiconductor SRAM powered by a small battery when system power was off...
, often called CMOS RAM or Parameter RAM, was a common solution in earlier computer systems like the original Apple Macintosh, which used a small amount of memory powered by a watch "button" battery
Button cell
A watch battery or button cell is a small single cell battery shaped as a squat cylinder typically 5 to 12 mm in diameter and 1 to 6 mm high—like a button on a garment, hence the name. Button cells are used to power small portable electronics devices such as wrist watches, pocket...
for storing basic setup information like the selected boot volume. Much larger battery backed memories are still used today as cache
Cache
In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
s for high-speed database
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
s, requiring a performance level newer NVRAM devices have not yet managed to meet.
The floating-gate transistor
A huge advance in NVRAM technology was the introduction of the floating-gate transistor, which led to the introduction of erasable programmable read-only memory, or EPROMEPROM
An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...
. EPROM consists of a grid of transistors whose gate terminal (the "switch") is protected by a high-quality insulator. By "pushing" electrons onto the base with the application of higher-than-normal voltage, the electrons become trapped on the far side of the insulator, thereby permanently switching the transistor "on" ("1"). EPROM can be re-set to the "base state" (all "1"s or "0"s, depending on the design) by applying ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light (UV). The UV photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s have enough energy to push the electrons through the insulator and return the base to a ground state. At that point the EPROM can be re-written from scratch.
An improvement on EPROM, EEPROM
EEPROM
EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration...
, soon followed. The extra "E" stands for electrically, referring to the ability to reset EEPROM using electricity instead of UV, making the devices much easier to use in practice. The bit are re-set with the application of even higher power through the other terminals of the transistor (source and drain). This high power pulse, in effect, sucks the electrons through the insulator, returning it to the ground state. This process has the disadvantage of mechanically degrading the chip, however, so memory systems based on floating-gate transistors in general have short write-lifetimes, on the order of 105 writes to any particular bit.
One approach to overcoming the rewrite count limitation is to have a standard SRAM where each bit is backed up by an EEPROM bit. In normal operation the chip functions as a fast SRAM and in case of power failure the content is quickly transferred to the EEPROM part, from where it gets loaded back at the next power up. Such chips were called NOVRAMs by their manufacturers.
The basis of flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
is identical to EEPROM, and differs largely in internal layout. Flash allows its memory to be written only in blocks, which greatly simplifies the internal wiring and allows for higher densities. Memory storage density is the main determinant of cost in most computer memory systems, and due to this flash has evolved into one of the lowest cost solid-state memory devices available. Starting around 2000, demand for ever-greater quantities of flash have driven manufacturers to use only the latest fabrication systems in order to increase density as much as possible. Although fabrication limits are starting to come into play, new "multi-bit" techniques appear to be able to double or quadruple the density even at existing linewidths.
Newer approaches
Flash and EEPROM's limited write-cycles are a serious problem for any real RAM-like role, however. In addition, the high power needed to write the cells is a problem in low-power roles, where NVRAM is often used. The power also needs time to be "built up" in a device known as a charge pumpCharge pump
A charge pump is a kind of DC to DC converter that uses capacitors as energy storage elements to create either a higher or lower voltage power source. Charge pump circuits are capable of high efficiencies, sometimes as high as 90–95% while being electrically simple circuits.Charge pumps use some...
, which makes writing dramatically slower than reading, often as much as 1,000 times. A number of new memory devices have been proposed to address these shortcomings.
To date, the only such system to enter widespread production is ferroelectric RAM
Ferroelectric RAM
Ferroelectric RAM is a random-access memory similar in construction to DRAM but uses a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-volatile memory technologies that offer the same functionality as Flash memory...
, or FeRAM. FeRAM uses a ferroelectric layer in a cell that is otherwise similar to conventional DRAM, this layer holding the charge in a 1 or 0 even with the power removed. To date, FeRAM has been produced on very old fabs, and even the most advanced research samples are still twice the linewidth of most flash devices. Although this difference might be addressable under normal circumstances, as flash moves to multi-bit cells the difference in memory density appears to be growing, rather than shrinking.
Another approach to see major development effort is Magnetoresistive Random Access Memory
MRAM
Magnetoresistive Random-Access Memory is a non-volatile computer memory technology that has been under development since the 1990s. Continued increases in density of existing memory technologies – notably flash RAM and DRAM – kept it in a niche role in the market, but its proponents...
, or MRAM, which uses magnetic elements and in general operates in a fashion similar to core, at least for the first-generation technology. Only one MRAM chip has entered production to date: Everspin Technologies
Freescale Semiconductor
Freescale Semiconductor, Inc. is a producer and designer of embedded hardware, with 17 billion semiconductor chips in use around the world. The company focuses on the automotive, consumer, industrial and networking markets with its product portfolio including microprocessors, microcontrollers,...
' 4 Mbit part, which is a first-generation MRAM that utilizes cross-point field induced writing. Two second-generation techniques are currently in development: Thermal Assisted Switching
Thermal Assisted Switching
Thermal Assisted Switching, or TAS, is one of the new 2nd generation approaches to MRAM currently being developed. A few different designs have been proposed, but all rely on the idea of reducing the required switching fields by heating...
(TAS), which is being developed by Crocus Technology
Crocus Technology
Crocus Technology, founded in 2004, is a venture-capital-backed semiconductor startup company developing next generation magnetoresistive random access memory technology. The company's products originated in a Grenoble-based Spintec laboratory...
, and Spin Torque Transfer
Spin torque transfer
Spin-transfer torque is an effect in which the orientation of a magnetic layer in a tunnel magnetoresistance or spin valve can be modified using a spin-polarized current....
(STT) on which Crocus
Crocus Technology
Crocus Technology, founded in 2004, is a venture-capital-backed semiconductor startup company developing next generation magnetoresistive random access memory technology. The company's products originated in a Grenoble-based Spintec laboratory...
, Hynix
Hynix
Hynix Semiconductor Inc. chips and flash memory chips. Founded in 1983, Hynix is the world's second-largest memory chipmaker, the largest being Samsung Electronics. Formerly known as Hyundai Electronics, the company has manufacturing sites in Korea, the U.S., China and Taiwan...
, IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
, and several other companies are working. STT-MRAM appears to allow for much higher densities than the those of the first generation, but is lagging behind flash for the same reasons as FeRAM – enormous competitive pressures in the flash market.
Another solid-state technology to see more than purely experimental development is Phase-change RAM, or PRAM. PRAM is based on the same storage mechanism as writable CDs and DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
s, but reads them based on their changes in electrical resistance rather than changes in their optical properties. Considered a "dark horse" for some time, in 2006 Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
announced the availability of a 512 Mb part, considerably higher capacity than either MRAM or FeRAM. The areal density of these parts appears to be even higher than modern flash devices, the lower overall storage being due to the lack of multi-bit encoding. This announcement was followed by one from Intel and STMicroelectronics
STMicroelectronics
STMicroelectronics is an Italian-French electronics and semiconductor manufacturer headquartered in Geneva, Switzerland.While STMicroelectronics corporate headquarters and the headquarters for EMEA region are based in Geneva, the holding company, STMicroelectronics N.V. is registered in Amsterdam,...
, who demonstrated their own PRAM devices at the 2006 Intel Developer Forum
Intel Developer Forum
Intel Developer Forum , is a gathering of technologists to discuss Intel products and products based around Intel products. The first IDF was in 1997...
in October. One of the most attended sessions in the IEDM December 2006 was the presentation by IBM of their PRAM technology.
Also seeing renewed interest is silicon-oxide-nitride-oxide-silicon (SONOS
SONOS
SONOS, short for "Silicon-Oxide-Nitride-Oxide-Silicon", is a type of non-volatile computer memory closely related to Flash RAM. It is distinguished from mainstream flash by the use of silicon nitride instead of polysilicon for the charge storage material. A further variant is "SHINOS"...
) memory.
Perhaps one of the more innovative solutions is millipede memory
IBM Millipede
Millipede is a non-volatile computer memory stored on nanoscopic pits burned into the surface of a thin polymer layer, read and written by a MEMS-based probe...
, developed by IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
. Millipede is in essence a punched card
Punched card
A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...
rendered using nanotechnology
Nanotechnology
Nanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
in order to dramatically increase areal density. Although it was planned to introduce millipede as early as 2003, unexpected problems in development delayed this until 2005, by which point it was no longer competitive with flash. In theory the technology offers storage densities on the order of 1 Tbit/in², far greater than even the best hard drive technologies currently in use (perpendicular recording
Perpendicular recording
Perpendicular recording is a technology for data recording on hard disks. It was first proven advantageous in 1976 by Shun-ichi Iwasaki, then professor of the Tohoku University in Japan, and first commercially implemented in 2005.-Advantages:Perpendicular recording can deliver more than three...
offers about 230 Gbit/in²) . However, slow read and write times for memories this large seem to limit this technology to hard drive replacements as opposed to high-speed RAM-like uses, although to a very large degree the same is true of flash as well. It remains to be seen if this technology will ever become practical.
A number of more esoteric devices have been proposed, including Nano-RAM
Nano-RAM
Nano-RAM is a proprietary computer memory technology from the company Nantero. It is a type of nonvolatile random access memory based on the mechanical position of carbon nanotubes deposited on a chip-like substrate. In theory, the small size of the nanotubes allows for very high density memories...
based on carbon nanotube technology
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
, but these are currently far from commercialization. The advantages that nanostructures such as quantum dots, carbon nanotubes and nanowires offer over their silicon-based predecessors include their tiny size, speed and their density. Several concepts of molecular-scale memory devices have been developed recently.
See also
- RAM
- Static RAMStatic random access memoryStatic random-access memory is a type of semiconductor memory where the word static indicates that, unlike dynamic RAM , it does not need to be periodically refreshed, as SRAM uses bistable latching circuitry to store each bit...
(SRAM) - Dynamic RAMDynamic random access memoryDynamic random-access memory is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1...
(DRAM) - Non-volatile memoryNon-volatile memoryNon-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
- MRAMMRAMMagnetoresistive Random-Access Memory is a non-volatile computer memory technology that has been under development since the 1990s. Continued increases in density of existing memory technologies – notably flash RAM and DRAM – kept it in a niche role in the market, but its proponents...
- EEPROMEEPROMEEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration...