It has been suggested that this article or section be merged with Non-volatile memory. (Discuss)

Non-volatile random access memory (NVRAM) is the general name used to describe any type of random access memory which does not lose its information when power is turned off. This is in contrast to the most common forms of random access memory today, DRAM and SRAM, which both require continual power in order to maintain their data. NVRAM is a subgroup of the more general class of non-volatile memory types, the difference being that NVRAM devices offer random access, as opposed to sequential access like hard disks. The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ... Volatile memory refers to computer memory that must be powered to maintain its data. ... Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. ... eDRAM stands for embedded DRAM, a capacitor-based dynamic random access memory usually integrated on the same die or in the same package as the main ASIC or processor, as opposed to external DRAM modules and transistor-based SRAM typically used for caches. ... Static random access memory (SRAM) is a type of semiconductor memory. ... 1T-SRAM is MoSyss implementation of embedded-DRAM on a conventional digital-logic (standard-cell) ASIC process. ... Z-RAM, short for zero capacitor DRAM is a new type of computer memory in development by Innovative Silicon Inc. ... TTRAM, short for Twin Transistor RAM is new type of computer memory in development by Renesas. ... The Williams tube or (more accurately) the Williams-Kilburn tube (after Freddie Williams and coworker Tom Kilburn), developed about 1946 or 1947, was a cathode ray tube used to store electronic data. ... Mercury memory of UNIVAC I (1951) Delay line memory was a form of computer memory used on some of the earliest digital computers, such as the EDSAC and UNIVAC I. The basic concept of the delay line originated with World War II radar research, specifically to reduce clutter from reflections... The Selectron was an early form of computer memory developed by RCA. Development started in 1946 with a planned production of 200 by the end of the year, but production problems meant that they were still not available by the middle of 1948. ... It has been suggested that this article or section be merged with NVRAM. (Discuss) Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... D23128C PROM on the board of ZX Spectrum A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory where the setting of each byte is locked by a fuse or antifuse. ... Read-only memory (ROM) is used as a storage medium in computers. ... EPROM. The small quartz window admits UV light during erasure. ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ... A USB flash drive. ... Ferroelectric RAM (FRAM or FeRAM) is a type of non-volatile computer memory, similar to EEPROM but based on electric field orientation and with near-unlimited number (exceeding 1010 for 5V devices and even more for 3. ... Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ... Phase-change memory (also known as PCM, PRAM, Ovonic Unified Memory and Chalcogenide RAM [C-RAM]) is a type of non-volatile computer memory. ... Wikipedia does not have an article with this exact name. ... RRAM or Resistive Random Access Memory is a new non-volatile memory type begin developed by Sharp, Samsung, Fujitsu, Spansion, Macronix, Winbond and other companies. ... Nano-RAM, is a proprietary computer memory technology from the company Nantero. ... hi i am cool xbox is all most as cool as me hi again ... A 16×16 cm area core memory plane of 128×128 bits, i. ... Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles, which each store one bit of data. ... Wikipedia does not have an article with this exact name. ... It has been suggested that this article or section be merged with NVRAM. (Discuss) Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... Non-Volatile Random Access Memory (NVRAM) is a computer memory chip which will not lose its information when the power is lost. ... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... Dram can mean several things: For the imperial unit of volume see dram (unit), commonly used to describe a measure of Scotch whisky For the imperial unit of weight or mass see avoirdupois and apothecaries system (of mass) For the Armenian monetary unit see dram (currency) DRAM is a type... Static random access memory (SRAM) is a type of semiconductor memory. ... In computer science, random access is the ability to access a random element of a group in equal time. ... In computer science sequential access means that a group of elements (e. ... Typical hard drives of the mid-1990s. ...

The best-known form of NVRAM memory today is flash memory. Some claim flash memory 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. A USB flash drive. ...

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. A 16×16 cm area core memory plane of 128×128 bits, i. ...

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 alternately 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. NASAs Glenn Research Center cleanroom. ... In physics, the solid state is one of the three phases of matter (solid, liquid, and gas). ... Dram can mean several things: For the imperial unit of volume see dram (unit), commonly used to describe a measure of Scotch whisky For the imperial unit of weight or mass see avoirdupois and apothecaries system (of mass) For the Armenian monetary unit see dram (currency) DRAM is a type... Primary storage is a category of computer storage, often called main memory. ...

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 diodes permanently wired to return the required data, the diodes being built in this configuration when they are being fabricated. Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... Types of diodes. ...

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. This article or section does not cite any references or sources. ... Look up fuse in Wiktionary, the free dictionary. ... The Nintendo GameCube is an example of a popular video game console. ...

For those who required real RAM-like performance and non-volatility typically have to use conventional RAM devices and a battery backup. This 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 caches for high-speed databases, requiring a performance level newer NVRAM devices have not yet managed to meet. The first Macintosh computer, introduced in 1984, upgraded to a 512K Fat Mac. The Macintosh or Mac, is a line of personal computers designed, developed, manufactured, and marketed by Apple Computer. ... Look up cache in Wiktionary, the free dictionary. ... This article does not cite any references or sources. ...

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 EPROM. EPROM consists of a grid of transistors whose base terminal (the "switch") is protected by a high-quality insulator. By "pushing" electrons onto the base with the application of higher-than-normal power, 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 photons 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. It has been suggested that this article or section be merged into Floating_Gate_MOSFET. (Discuss) A cross-section of a floating-gate transistor The floating-gate transistor is a kind of transistor that is commonly used for non-volatile storage such as flash, EPROM and EEPROM memory. ... EPROM. The small quartz window admits UV light during erasure. ... “UV” redirects here. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...

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 basically 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 generally have short write-lifetimes, on the order of 10⁵ writes to any particular bit. An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ...

The basis of Flash RAM 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. Areal 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. Flash memory is a form of EEPROM that allows multiple memory locations to be erased or written in one programming operation. ... Computer storage density is a measure of the quantity of information bits that can be stored on a given length of track, area of surface, or in a given volume; of a computer storage medium. ...

Newer Approaches

Flash and EEPROM's limited write-cycles are a serious problem for any real RAM-like role, however. Additionally, 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 pump, 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. A charge pump is an electronic circuit that uses capacitors as energy storage elements to create either a higher or lower voltage power source. ...

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. Ferroelectric RAM (FRAM or FeRAM) is a type of non-volatile computer memory, similar to EEPROM but based on electric field orientation and with near-unlimited number (exceeding 1010 for 5V devices and even more for 3. ... In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. ...

Another approach to see major development effort is Magnetoresistive Random Access Memory, or MRAM, which uses magnetic elements and generally operates in a fashion similar to core. Only one MRAM chip has entered production to date, Freescale Semiconductor's 4 Mbit part, and using the techniques in this particular design it is unlikely to grow any time soon. Another technique, known as STT-MRAM, appears to allow for much higher densities, but is falling behind Flash for the same reasons as FeRAM – enormous competitive pressures in the Flash market. Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ... Freescale Semiconductor, Inc. ...

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 DVDs, 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. It has been suggested that RRAM be merged into this article or section. ... CD redirects here; see Cd for other meanings of CD. Image of a compact disc (pencil included for scale) A compact disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. ... DVD (Digital Versatile Disc or Digital Video Disc) is an optical disc storage media format that can be used for data storage, including movies with high video and sound quality. ... Samsung Group is one of the largest South Korean business groupings. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... STMicroelectronics is an international leading supplier of semiconductors. ... Intel Developer Forum (IDF), is a twice yearly gathering of technologists to discuss Intel products and products based around Intel products. ...

Also seeing renewed interest is silicon-oxide-nitride-oxide-silicon (SONOS) memory. Wikipedia does not have an article with this exact name. ...

Perhaps one of the more unique solutions is millipede memory, developed by IBM. Millipede is essentially a punch 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. 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. ... IBM redirects here. ... Punched cards (or Hollerith cards, or IBM cards), are pieces of stiff paper that contain digital information represented by the presence or absence of holes in predefined positions. ... Buckminsterfullerene C60, also known as the buckyball, is the simplest of the carbon structures known as fullerenes. ... Typical hard drives of the mid-1990s. ... Perpendicular recording (or Perpendicular Magnetic Recording, PMR) is a recently implemented technology for data recording on hard disk. ...

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. Nano-RAM, is a proprietary computer memory technology from the company Nantero. ... 3D model of three types of single-walled carbon nanotubes. ... A quantum dot is a potential well that confines electrons in three dimensions to a region of the order of the electrons de Broglie wavelength in size, a few nanometers in a semiconductor. ... An electronic device known as a diode can be formed by joining two nanoscale carbon tubes with different electronic properties. ... Nanowires are structures that have a lateral size constrained to tens of nanometers or less and an unconstrained longitudinal size (a nanometer is 10^-9 meters). ...

See also

• RAM
• Static RAM (SRAM)
• Dynamic RAM (DRAM)
• MRAM
• Flash RAM
• EEPROM

Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... Static random access memory (SRAM) is a type of semiconductor memory. ... Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. ... Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ... Flash memory is a form of EEPROM that allows multiple memory locations to be erased or written in one programming operation. ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ...

External links

• NVRAM vs. Other Memory Types