Non-volatile memory
Encyclopedia
Non-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 storage devices (e.g. hard disk
s, floppy disk
s, and magnetic tape
), optical disc
s, and early computer storage methods such as paper tape and punched card
s.
Non-volatile memory is typically used for the task of secondary storage, or long-term persistent storage. The most widely used form of primary storage today is a volatile form of random access memory (RAM), meaning that when the computer is shut down, anything contained in RAM is lost. Unfortunately, most forms of non-volatile memory have limitations that make them unsuitable for use as primary storage. Typically, non-volatile memory either costs more or performs worse than volatile random access memory.
Several companies are working on developing non-volatile memory systems comparable in speed and capacity to volatile RAM. For instance, IBM is currently developing MRAM
(Magnetoresistive RAM). Not only would such technology save energy, but it would allow for computers that could be turned on and off almost instantly, bypassing the slow start-up and shutdown sequence.
Non-volatile data storage can be categorized in electrically addressed systems (read-only memory
) and mechanically addressed systems (hard disk
s, optical disc
, magnetic tape
, holographic memory, and such). Electrically addressed systems are expensive, but fast, whereas mechanically addressed systems have a low price per bit, but are slow. Non-volatile memory may one day eliminate the need for comparatively slow forms of secondary storage systems, which include hard disks.
was prewired at the design stage to contain specific data; once the mask was used to manufacture the integrated circuit
s, the data was cast in stone (silicon, actually)
and could not be changed.
The mask ROM was therefore useful only for large-volume production, such as for
read-only memories containing the start up code in early microcomputers. This program
was often referred to as the "bootstrap
", as in pulling oneself up by
one's own bootstraps.
Due to the very high initial cost and inability to make revisions, the mask ROM is rarely, if ever, used in new designs.
s, which would be selectively "blown" or destroyed by a device programmer or PROM programmer in order to change 0s to 1s. Once the bits were changed, there was no way to restore them to their original condition. Non-volatile but still somewhat inflexible.
Early PAL programmable array logic
chips used a similar programming approach to that used in the fuse-based PROMs.
Newer Antifuse-based PROMs (which are also referred to as one-time-programmable (OTP) memory) are widely used in consumer and automotive electronics, radio-frequency identification devices (RFID), implantable medical devices, and high-definition multimedia interfaces(HDMI) due to their small footprint, reliability, fast read speed, and long data retention rates.
window in the center of the chip package. These operated by trapping an electrical charge on the gate of a field-effect transistor
in order to change a 1 to a 0 in memory. To remove the charge, one would place the chip under an intense short-wavelength
fluorescent ultraviolet
lamp for 20–30 minutes, returning the entire chip to its original blank (all ones) state.
The limited number of times a single location can be rewritten is usually in the 10000-100000 range; the capacity of an EEPROM also tends to be smaller than that of other non-volatile memories. Nonetheless, EEPROMs are useful for storing settings or configuration for devices ranging from dial-up modem
s to satellite receivers.
s and desktop PC BIOS
chips.
Flash memory devices use two different logical technologies—NOR and NAND—to map data.NOR flash provides high-speed random access, reading and writing data in specific memory locations; it can retrieve as little as a single byte. NAND flash reads and writes sequentially at high speed, handling data in small blocks called pages, however it’s slower on read when compared to NOR. NAND flash reads faster than it writes, quickly transferring whole pages of data. Less expensive than NOR flash at high densities, NAND technology offers higher capacity for the same-size silicon.
List of NOR Flash providers:
List of NAND Flash providers:
The 1st generation of MRAM, such as Everspin Technologies
' 4 Mbit, utilized field induced writing. The 2nd generation is being developed mainly through two approaches: Thermal Assisted Switching
(TAS) which is being developed by Crocus Technology
, and Spin Torque Transfer
(STT) which Crocus
, Hynix
, IBM
, and several other companies are developing.
ferroelectric memory.
Thin Film Electronics
("Thinfilm") produces rewriteable non-volatile organic memory based on ferroelectric polymers
. Thinfilm successfully demonstrated roll-to-roll printed
memories in 2009.
In Thinfilm's
organic memory the ferroelectric
polymer is sandwiched between two sets of electrodes in a passive matrix. Each crossing of metal lines is a ferroelectric capacitor
and defines a memory cell. This gives a non-volatile memory comparable to ferroelectric RAM
technologies and offer the same functionality as flash memory
.
Computer memory
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory
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...
, 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...
, ferroelectric RAM, most types of magnetic computer storage devices (e.g. hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
s, floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
s, and magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
), optical disc
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
s, and early computer storage methods such as paper tape and 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...
s.
Non-volatile memory is typically used for the task of secondary storage, or long-term persistent storage. The most widely used form of primary storage today is a volatile form of random access memory (RAM), meaning that when the computer is shut down, anything contained in RAM is lost. Unfortunately, most forms of non-volatile memory have limitations that make them unsuitable for use as primary storage. Typically, non-volatile memory either costs more or performs worse than volatile random access memory.
Several companies are working on developing non-volatile memory systems comparable in speed and capacity to volatile RAM. For instance, IBM is currently developing MRAM
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...
(Magnetoresistive RAM). Not only would such technology save energy, but it would allow for computers that could be turned on and off almost instantly, bypassing the slow start-up and shutdown sequence.
Non-volatile data storage can be categorized in electrically addressed systems (read-only memory
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...
) and mechanically addressed systems (hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
s, optical disc
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
, magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
, holographic memory, and such). Electrically addressed systems are expensive, but fast, whereas mechanically addressed systems have a low price per bit, but are slow. Non-volatile memory may one day eliminate the need for comparatively slow forms of secondary storage systems, which include hard disks.
Electrically addressed
Electrically addressed non-volatile memories based on charge storage can be categorized according to their write mechanism:Mask-programmed ROM
One of the earliest forms of non-volatile read-only memory, the mask-programmed ROMwas prewired at the design stage to contain specific data; once the mask was used to manufacture the integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s, the data was cast in stone (silicon, actually)
and could not be changed.
The mask ROM was therefore useful only for large-volume production, such as for
read-only memories containing the start up code in early microcomputers. This program
was often referred to as the "bootstrap
Booting
In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
", as in pulling oneself up by
one's own bootstraps.
Due to the very high initial cost and inability to make revisions, the mask ROM is rarely, if ever, used in new designs.
Programmable ROM
The next approach was to create a chip which was initially blank; the programmable ROM originally contained silicon or metal fuseFuse (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...
s, which would be selectively "blown" or destroyed by a device programmer or PROM programmer in order to change 0s to 1s. Once the bits were changed, there was no way to restore them to their original condition. Non-volatile but still somewhat inflexible.
Early PAL programmable array logic
Programmable Array Logic
The term Programmable Array Logic is used to describe a family of programmable logic device semiconductors used to implement logic functions in digital circuits introduced by Monolithic Memories, Inc. in March 1978. MMI obtained a registered trademark on the term PAL for use in "Programmable...
chips used a similar programming approach to that used in the fuse-based PROMs.
Newer Antifuse-based PROMs (which are also referred to as one-time-programmable (OTP) memory) are widely used in consumer and automotive electronics, radio-frequency identification devices (RFID), implantable medical devices, and high-definition multimedia interfaces(HDMI) due to their small footprint, reliability, fast read speed, and long data retention rates.
Erasable PROMs
There are two classes of non-volatile memory chips based on EPROM technology.UV-erase EPROM
The original erasable non-volatile memories were EPROM's; these could be readily identified by the distinctive quartzQuartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
window in the center of the chip package. These operated by trapping an electrical charge on the gate of a field-effect transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
in order to change a 1 to a 0 in memory. To remove the charge, one would place the chip under an intense short-wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
fluorescent 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...
lamp for 20–30 minutes, returning the entire chip to its original blank (all ones) state.
OTP (one-time programmable) EPROM
An OTP is electrically an EPROM, but with the quartz window physically missing. Like the fuse, PROM it can be written once, but cannot be erased.Electrically erasable PROM
Electrically erasable PROMs have the advantage of being able to selectively erase any part of the chip without the need to erase the entire chip and without the need to remove the chip from the circuit. While an erase and rewrite of a location appears nearly instantaneous to the user, the write process is slightly slower than the read process; the chip can be read at full system speeds.The limited number of times a single location can be rewritten is usually in the 10000-100000 range; the capacity of an EEPROM also tends to be smaller than that of other non-volatile memories. Nonetheless, EEPROMs are useful for storing settings or configuration for devices ranging from dial-up modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s to satellite receivers.
Flash memory
The flash memory chip is a close relative to the EEPROM; it differs in that it can only be erased one block or "page" at a time. It is a solid-state chip that maintains stored data without any external power source. Capacity is substantially larger than that of an EEPROM, making these chips a popular choice for digital cameraDigital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
s and desktop PC BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
chips.
Flash memory devices use two different logical technologies—NOR and NAND—to map data.NOR flash provides high-speed random access, reading and writing data in specific memory locations; it can retrieve as little as a single byte. NAND flash reads and writes sequentially at high speed, handling data in small blocks called pages, however it’s slower on read when compared to NOR. NAND flash reads faster than it writes, quickly transferring whole pages of data. Less expensive than NOR flash at high densities, NAND technology offers higher capacity for the same-size silicon.
List of NOR Flash providers:
- AtmelAtmelAtmel Corporation is a manufacturer of semiconductors, founded in 1984. Its focus is on system-level solutions built around flash microcontrollers...
- Intel
- Greenliant SystemsGreenliant SystemsGreenliant Systems is a manufacturer of flash memory, solid-state storage and controller semiconductors for embedded system, data center and mobile products. Greenliant was founded in 2010, when former Silicon Storage Technology CEO Bing Yeh acquired several flash memory assets from the company...
- Macronix
- Micron TechnologyMicron TechnologyMicron Technology, Inc. is an American multinational corporation based in Boise, Idaho, USA, best known for producing many forms of semiconductor devices. This includes DRAM, SDRAM, flash memory, SSD and CMOS image sensing chips. Consumers may be more familiar with its consumer brand Crucial...
(formerly Numonyx) - Silicon Storage TechnologySilicon Storage TechnologySilicon Storage Technology, Inc. is a Sunnyvale, California, USA, technology company producing non-volatile memory devices and related products.It was founded by Bing Yeh in 1989....
(SST) (now Microchip TechnologyMicrochip TechnologyMicrochip Technology is an American manufacturer of microcontroller, memory and analog semiconductors. Its products include microcontrollers , Serial EEPROM devices, Serial SRAM devices, KEELOQ devices, radio frequency devices, thermal, power and battery management analog devices, as well as...
) - SpansionSpansionSpansion Inc. is a Flash memory chip maker that designs, develops and manufactures NOR flash memory products. The company has over 3,400 employees and is headquartered in Sunnyvale, California. Spansion is a former joint-venture between AMD and Fujitsu....
- STMicroelectronicsSTMicroelectronicsSTMicroelectronics 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,...
List of NAND Flash providers:
- HynixHynixHynix 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...
- Intel
- Micron TechnologyMicron TechnologyMicron Technology, Inc. is an American multinational corporation based in Boise, Idaho, USA, best known for producing many forms of semiconductor devices. This includes DRAM, SDRAM, flash memory, SSD and CMOS image sensing chips. Consumers may be more familiar with its consumer brand Crucial...
- QimondaQimondaQimonda AG, was a memory company split out of Infineon Technologies on 1 May 2006, to form at the time the second largest DRAM company worldwide, according to the industry research firm Gartner Dataquest...
- Renesas Electronics Corporation
- SamsungSamsungThe Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
- SpansionSpansionSpansion Inc. is a Flash memory chip maker that designs, develops and manufactures NOR flash memory products. The company has over 3,400 employees and is headquartered in Sunnyvale, California. Spansion is a former joint-venture between AMD and Fujitsu....
- STMicroelectronicsSTMicroelectronicsSTMicroelectronics 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,...
- ToshibaToshibais a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
Magnetoresistive RAM (MRAM)
Magnetoresistive RAM is one of the newest approaches to non-volatile memory and stores data in magnetic storage elements called magnetic tunnel junctions (MTJ's). MRAM has an especially promising future as it seeks to encompass all the desirable features of the other popular types of memory (non-volatility, infinite endurance, high-speed reading/writing, low cost).The 1st generation of MRAM, such as 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, utilized field induced writing. The 2nd generation is being developed mainly through two approaches: 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) 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 developing.
Mechanically addressed systems
Mechanically addressed systems utilize a contact structure ('head') to read and write on a designated storage medium. Since circuitry layout is not a key factor for data density, the amount of storage is typically much larger than for electrically addressed systems.Organic
There are polymer printedPrinted electronics
Printed electronics is a set of printing methods used to create electrical devices on various substrates. Printing typically uses common printing equipment or other low-cost equipment suitable for defining patterns on material, such as screen printing, flexography, gravure, offset lithography and...
ferroelectric memory.
Thin Film Electronics
Thin Film Electronics ASA
Thin Film Electronics ASA is a Norwegian printed electronics company, headquartered in Oslo with its main R&D offices in Linköping, Sweden....
("Thinfilm") produces rewriteable non-volatile organic memory based on ferroelectric polymers
Ferroelectric polymers
Ferroelectric Polymersare a group of crystalline polar polymers that are also ferroelectric, meaning that they maintain a permanent electric polarization that can be reversed, or switched, in an external electric field....
. Thinfilm successfully demonstrated roll-to-roll printed
Printed electronics
Printed electronics is a set of printing methods used to create electrical devices on various substrates. Printing typically uses common printing equipment or other low-cost equipment suitable for defining patterns on material, such as screen printing, flexography, gravure, offset lithography and...
memories in 2009.
In Thinfilm's
Thin Film Electronics ASA
Thin Film Electronics ASA is a Norwegian printed electronics company, headquartered in Oslo with its main R&D offices in Linköping, Sweden....
organic memory the ferroelectric
Ferroelectricity
Ferroelectricity is a property of certain materials which possess a spontaneous electric polarization that can be reversed by the application of an external electric field. The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was...
polymer is sandwiched between two sets of electrodes in a passive matrix. Each crossing of metal lines is a ferroelectric capacitor
Ferroelectric capacitor
Ferroelectric capacitor is a capacitor based on a ferroelectric material. In contrast, traditional capacitors are based on dielectric materials. Ferroelectric devices are used in digital electronics as part of ferroelectric RAM, or in analog electronics as tunable capacitors .In memory...
and defines a memory cell. This gives a non-volatile memory comparable to 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...
technologies and offer the same functionality as 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...
.
Specifications
| Specification March 2007 | 2.5" HDD | 1" Microdrive | Flash Memory | Optical Disk | Tape | MRAM |
|---|---|---|---|---|---|---|
| Device Model: | Hitachi Travelstar 5k160 | Hitachi Microdrive 3k8 | Hynix HY27UH08AG5M | Blu-ray Blu-ray Disc Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs... |
HP Ultrium 960 | Everspin MR2A16A |
| Density (GBit/cm2) | 20.3 | 18.4 | 6.7 | 3.8 | 0.047 | 0.0021 |
| Capacity (GByte) | 160 | 8 | 2 | 50 | 400 | 0.004 |
| Price per bit (Eur/GByte) | 1.5 | 9.0 | 6.0 | 1.25 | 0.075 | 35000 |
| Price per unit (Eur) | 110 | 87 | 14 | 635 | 2340 | 17.4 |
| Price per medium (Eur) | nd | nd | nd | 40 | 30 | nd |
| Data rate (Mbit/s) | 540 | 80 | 23 | 144 | 640 | 436 |
| Access time (ms) | 11 | 12 | 0.025 | 180 | 72000 | 1.000035 |
| Power consumption (W) | 1.8 | 0.6 | 0.1 | 25 | 20 | 0.08 |
| Form factor h x w x d (cm) |
0.95x7x10 | 0.5x3x4 | 0.1x1.2x2 | 4x15x19 | 2x10x10 | 0.1x1x1.8 |