Potassium nitrate

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Potassium_nitrate 

Potassium nitrate

Names
IUPAC name Potassium nitrate
Other names Saltpeter Saltpetre Nitrate of potash
Identifiers
CAS Number	7757-79-1
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL1644029
ChemSpider	22843
ECHA InfoCard	100.028.926
EC Number	231-818-8
E number	E252 (preservatives)
KEGG	D02051
PubChem CID	24434
RTECS number	TT3700000
UNII	RU45X2JN0Z
UN number	1486
CompTox Dashboard (EPA)	DTXSID4029692

InChI

SMILES
Properties
Chemical formula	KNO3
Molar mass	101.1032 g/mol
Appearance	white solid
Odor	odorless
Density	2.109 g/cm3 (16 °C)
Melting point	334 °C (633 °F; 607 K)
Boiling point	400 °C (752 °F; 673 K) (decomposes)
Solubility in water	133 g/1000 g water (0 °C) 316 g/1000 g water (20 °C) 383 g/1000 g water (25 °C) 2439 g/1000 g water (100 °C)
Solubility	slightly soluble in ethanol soluble in glycerol, ammonia
Basicity (pKb)	15.3
Magnetic susceptibility (χ)	−33.7·10−6 cm3/mol
Refractive index (nD)	1.335, 1.5056, 1.5604
Structure
Crystal structure	Orthorhombic, Aragonite
Thermochemistry
Heat capacity (C)	95.06 J/mol K
Std enthalpy of formation (ΔfH⦵298)	-494.00 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Oxidant, harmful if swallowed, inhaled, or absorbed on skin. Causes irritation to skin and eye area.
GHS labelling:
Pictograms
Hazard statements	H272, H315, H319, H335
Precautionary statements	P102, P210, P220, P221, P280
NFPA 704 (fire diamond)	1 0 0 OX
Flash point	non-flammable (oxidizer)
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1901 mg/kg (oral, rabbit) 3750 mg/kg (oral, rat)
Safety data sheet (SDS)	ICSC 0184
Related compounds
Other anions	Potassium nitrite
Other cations	Lithium nitrate Sodium nitrate Rubidium nitrate Caesium nitrate
Related compounds	Potassium sulfate Potassium chloride
Supplementary data page
Potassium nitrate (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Potassium nitrate is a chemical compound with the chemical formula KNO
₃. It is an ionic salt of potassium ions K⁺ and nitrate ions NO₃⁻, and is therefore an alkali metal nitrate. It occurs in nature as a mineral, niter (or nitre in the UK). It is a source of nitrogen, and nitrogen was named after niter. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpetre (or saltpeter in North America).

Major uses of potassium nitrate are in fertilizers, tree stump removal, rocket propellants and fireworks. It is one of the major constituents of gunpowder (black powder). In processed meats, potassium nitrate reacts with hemoglobin and myoglobin generating a red color.

Properties

Potassium nitrate has an orthorhombic crystal structure at room temperature, which transforms to a trigonal system at 129 °C (264 °F).

Potassium nitrate is moderately soluble in water, but its solubility increases with temperature. The aqueous solution is almost neutral, exhibiting pH 6.2 at 14 °C (57 °F) for a 10% solution of commercial powder. It is not very hygroscopic, absorbing about 0.03% water in 80% relative humidity over 50 days. It is insoluble in alcohol and is not poisonous; it can react explosively with reducing agents, but it is not explosive on its own.

Thermal decomposition

Between 550–790 °C (1,022–1,454 °F), potassium nitrate reaches a temperature-dependent equilibrium with potassium nitrite:

2 KNO₃ ⇌ 2 KNO₂ + O₂

History of production

See also: Nitre § Availability

From mineral sources

In Ancient India, saltpeter manufacturers formed the Nuniya caste. Saltpeter finds mention in Kautilya's Arthashastra (compiled 300BC - 300AD), which mentions using its poisonous smoke as a weapon of war, although its use for propulsion did not appear until medieval times.

A purification process for potassium nitrate was outlined in 1270 by the chemist and engineer Hasan al-Rammah of Syria in his book al-Furusiyya wa al-Manasib al-Harbiyya (The Book of Military Horsemanship and Ingenious War Devices). In this book, al-Rammah describes first the purification of barud (crude saltpeter mineral) by boiling it with minimal water and using only the hot solution, then the use of potassium carbonate (in the form of wood ashes) to remove calcium and magnesium by precipitation of their carbonates from this solution, leaving a solution of purified potassium nitrate, which could then be dried. This was used for the manufacture of gunpowder and explosive devices. The terminology used by al-Rammah indicated a Chinese origin for the gunpowder weapons about which he wrote.

At least as far back as 1845, nitratite deposits were exploited in Chile and California.

From caves

Major natural sources of potassium nitrate were the deposits crystallizing from cave walls and the accumulations of bat guano in caves. Extraction is accomplished by immersing the guano in water for a day, filtering, and harvesting the crystals in the filtered water. Traditionally, guano was the source used in Laos for the manufacture of gunpowder for Bang Fai rockets.

Nitraries

See also: Nitrary

Potassium nitrate is produced in a nitrary. The process involved burial of excrements (human or animal) in a field beside the nitraries, watering them and waiting until leaching allowed saltpeter to come to the ground surface by efflorescence. Operators then gathered the resulting powder and transported it to be concentrated by ebullition in the boiler plant.

Besides "Montepellusanus", during the thirteenth century (and beyond) the only supply of saltpeter across Christian Europe (according to "De Alchimia" in 3 manuscripts of Michael Scot, 1180–1236) was "found in Spain in Aragon in a certain mountain near the sea."

In 1561, Elizabeth I of England at war with Philip II of Spain, became unable to import the saltpeter (of which the Kingdom of England had no home production), and had to pay "300 pounds gold" to the German captain Gerrard Honrik for the manual "Instructions for making salpeter to growe" (the secret of the "Feuerwerkbuch" -the nitraries-).

Nitre bed

A nitre bed is a similar process used to produce nitrate from excrement. Unlike the leaching-based process of the nitrary, however, one mixes the excrements with soil and wait for soil microbes to convert amino-nitrogen into nitrates by nitrification. The nitrates are extracted from soil with water and then purified into saltpeter by adding wood ash. The process was discovered in the early 15th century and was very widely used until the Chilean mineral deposits were found.

The Confederate side of the American Civil War had a significant shortage of saltpeter. As a result, the Nitre and Mining Bureau was set up to encourage local production, including by nitre beds and by providing excrement to government nitraries. On November 13, 1862, the government advertised in the Charleston Daily Courier for 20 or 30 “able bodied Negro men” to work in the new nitre beds at Ashley Ferry, S.C. The nitre beds were large rectangles of rotted manure and straw, moistened weekly with urine, “dung water,” and liquid from privies, cesspools and drains, and turned over regularly. The National Archives published payroll records that account for more than 29,000 people compelled to such labor in the state of Virginia. The South was so desperate for saltpeter for gunpowder that one Alabama official reportedly placed a newspaper ad asking that the contents of chamber pots be saved for collection. In South Carolina, in April 1864, the Confederate government forced 31 enslaved people to work at the Ashley Ferry Nitre Works, outside Charleston.

Perhaps the most exhaustive discussion of the niter-bed production is the 1862 LeConte text. He was writing with the express purpose of increasing production in the Confederate States to support their needs during the American Civil War. Since he was calling for the assistance of rural farming communities, the descriptions and instructions are both simple and explicit. He details the "French Method", along with several variations, as well as a "Swiss method". N.B. Many references have been made to a method using only straw and urine, but there is no such method in this work.

French method

Turgot and Lavoisier created the Régie des Poudres et Salpêtres a few years before the French Revolution. Niter-beds were prepared by mixing manure with either mortar or wood ashes, common earth and organic materials such as straw to give porosity to a compost pile typically 4 feet (1.2 m) high, 6 feet (1.8 m) wide, and 15 feet (4.6 m) long. The heap was usually under a cover from the rain, kept moist with urine, turned often to accelerate the decomposition, then finally leached with water after approximately one year, to remove the soluble calcium nitrate which was then converted to potassium nitrate by filtering through potash.

Swiss method

LeConte describes a process using only urine and not dung, referring to it as the Swiss method. Urine is collected directly, in a sandpit under a stable. The sand itself is dug out and leached for nitrates which were then converted to potassium nitrate using potash, as above.

From nitric acid

From 1903 until the World War I era, potassium nitrate for black powder and fertilizer was produced on an industrial scale from nitric acid produced using the Birkeland–Eyde process, which used an electric arc to oxidize nitrogen from the air. During World War I the newly industrialized Haber process (1913) was combined with the Ostwald process after 1915, allowing Germany to produce nitric acid for the war after being cut off from its supplies of mineral sodium nitrates from Chile (see nitratite).

Production

Potassium nitrate can be made by combining ammonium nitrate and potassium hydroxide.

NH₄NO₃ (aq) + KOH (aq) → NH₃ (g) + KNO₃ (aq) + H₂O (l)

An alternative way of producing potassium nitrate without a by-product of ammonia is to combine ammonium nitrate, found in instant ice packs, and potassium chloride, easily obtained as a sodium-free salt substitute.

NH₄NO₃ (aq) + KCl (aq) → NH₄Cl (aq) + KNO₃ (aq)

Potassium nitrate can also be produced by neutralizing nitric acid with potassium hydroxide. This reaction is highly exothermic.

KOH (aq) + HNO₃ → KNO₃ (aq) + H₂O (l)

On industrial scale it is prepared by the double displacement reaction between sodium nitrate and potassium chloride.

NaNO₃ (aq) + KCl (aq) → NaCl (aq) + KNO₃ (aq)

Uses

Potassium nitrate has a wide variety of uses, largely as a source of nitrate.

Nitric acid production

Historically, nitric acid was produced by combining sulfuric acid with nitrates such as saltpeter. In modern times this is reversed: nitrates are produced from nitric acid produced via the Ostwald process.

Oxidizer

The most famous use of potassium nitrate is probably as the oxidizer in blackpowder. From the most ancient times until the late 1880s, blackpowder provided the explosive power for all the world's firearms. After that time, small arms and large artillery increasingly began to depend on cordite, a smokeless powder. Blackpowder remains in use today in black powder rocket motors, but also in combination with other fuels like sugars in "rocket candy" (a popular amateur rocket fuel). It is also used in fireworks such as smoke bombs. It is also added to cigarettes to maintain an even burn of the tobacco and is used to ensure complete combustion of paper cartridges for cap and ball revolvers. It can also be heated to several hundred degrees to be used for niter bluing, which is less durable than other forms of protective oxidation, but allows for specific and often beautiful coloration of steel parts, such as screws, pins, and other small parts of firearms.

Meat processing

Potassium nitrate has been a common ingredient of salted meat since antiquity or the Middle Ages. The widespread adoption of nitrate use is more recent and is linked to the development of large-scale meat processing. The use of potassium nitrate has been mostly discontinued because of slow and inconsistent results compared to sodium nitrite compounds such as "Prague powder" or pink "curing salt". Even so, potassium nitrate is still used in some food applications, such as salami, dry-cured ham, charcuterie, and (in some countries) in the brine used to make corned beef (sometimes together with sodium nitrite). When used as a food additive in the European Union, the compound is referred to as E252; it is also approved for use as a food additive in the United States and Australia and New Zealand (where it is listed under its INS number 252).

Food preparation

In West African cuisine, potassium nitrate (saltpetre) is widely used as a thickening agent in soups and stews such as okra soup and isi ewu. It is also used to soften food and reduce cooking time when boiling beans and tough meat. Saltpetre is also an essential ingredient in making special porridges, such as kunun kanwa literally translated from the Hausa language as 'saltpetre porridge'. In the Shetland Islands (UK) it is used in the curing of mutton to make reestit mutton, a local delicacy.

Fertilizer

Potassium nitrate is used in fertilizers as a source of nitrogen and potassium – two of the macronutrients for plants. When used by itself, it has an NPK rating of 13-0-44.

Pharmacology

• Used in some toothpastes for sensitive teeth. Recently, the use of potassium nitrate in toothpastes for treating sensitive teeth has increased.
• Used historically to treat asthma. Used in some toothpastes to relieve asthma symptoms.
• Used in Thailand as main ingredient in kidney tablets to relieve the symptoms of cystitis, pyelitis and urethritis.
• Combats high blood pressure and was once used as a hypotensive.

Other uses

• Electrolyte in a salt bridge
• Active ingredient of condensed aerosol fire suppression systems. When burned with the free radicals of a fire's flame, it produces potassium carbonate.
• Works as an aluminium cleaner.
• Component (usually about 98%) of some tree stump removal products. It accelerates the natural decomposition of the stump by supplying nitrogen for the fungi attacking the wood of the stump.
• In heat treatment of metals as a medium temperature molten salt bath, usually in combination with sodium nitrite. A similar bath is used to produce a durable blue/black finish typically seen on firearms. Its oxidizing quality, water solubility, and low cost make it an ideal short-term rust inhibitor.
• To induce flowering of mango trees in the Philippines.
• Thermal storage medium in power generation systems. Sodium and potassium nitrate salts are stored in a molten state with the solar energy collected by the heliostats at the Gemasolar Thermosolar Plant. Ternary salts, with the addition of calcium nitrate or lithium nitrate, have been found to improve the heat storage capacity in the molten salts.
• As a source of potassium ions for exchange with sodium ions in chemically strengthened glass.
• As an oxidizer in model rocket fuel called Rocket candy.
• As a chemical that hastens the decay process of tree stumps.

Etymology

Potassium nitrate, because of its early and global use and production, has many names. Hebrew and Egyptian words for it had the consonants n-t-r, indicating likely cognation in the Greek nitron, which was Latinised to nitrum or nitrium. Thence Old French had niter and Middle English nitre. By the 15th century, Europeans referred to it as saltpetre, specifically Indian saltpetre (sodium nitrate is chile saltpetre) and later as nitrate of potash, as the chemistry of the compound was more fully understood.

The Arabs called it "Chinese snow" (Arabic: ثلج الصين thalj al-ṣīn). It was called "Chinese salt" by the Iranians/Persians or "salt from Chinese salt marshes" (Persian: نمک شوره چينی namak shūra chīnī).

In folklore and popular culture

Potassium nitrate was once thought to induce impotence, and is still rumored to be in institutional food (such as military fare) as an anaphrodisiac; however, there is no scientific evidence for such properties.

In Bank Shot, El (Joanna Cassidy) propositions Walter Ballantine (George C. Scott), who tells her that he has been fed saltpeter in prison. "You know why they feed you saltpeter in prison?" Ballantine asks her. She shakes her head no. They kiss. He glances down at his crotch, making a gesture that reveals his body has not responded to her advances, and says, "That's why they feed you saltpeter in prison."

In One Flew Over the Cuckoo's Nest, Randle is asked by the nurses to take his medications, but not knowing what they are, he mentions he does not want anyone to 'slip me saltpeter'. He then proceeds to imitate the motions of masturbation in reference to its supposed effects as an anaphrodisiac.

In 1776, John Adams asks his wife Abigail to make saltpeter for the Continental Army. She, eventually, is able to do so in exchange for pins for sewing.

In the Star Trek episode "Arena", Captain Kirk injures a gorn using a rudimentary cannon that he constructs using potassium nitrate as a key ingredient of gunpowder.

In 21 Jump Street, Jenko, played by Channing Tatum, gives a rhyming presentation about potassium nitrate for his chemistry class.

In Eating Raoul, Paul hires a dominatrix to impersonate a nurse and trick Raoul into consuming saltpeter in a ploy to reduce his sexual appetite for his wife.

In the Simpsons episode "El Viaje Misterioso de Nuestro Jomer (The Mysterious Voyage of Homer)", Mr. Burns is seen pouring saltpeter into his chili entry, titled Old Elihu's Yale-Style Saltpeter Chili.

In the Sharpe (novel series) by Bernard Cornwell numerous mentions are made of an advantageous supply of saltpeter from India being a crucial component of British military supremacy in the Napoleonic Wars. In Sharpe's Havoc The French Captain Argenton laments that France need to scrape their supply from cesspits.

In the Dr Stone anime and manga series, the struggle for control over a natural saltpeter source from guano features prominently in the plot.

In the farming lore from the Corn Belt of the 1800s, drought-killed corn in manured fields could accumulate saltpeter to the extent that upon opening the stalk for examination it would “fall as a fine powder upon the table”.

Semiconductor memory

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Semiconductor_memory 

Semiconductor memory is a digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to MOS memory, where data is stored within metal–oxide–semiconductor (MOS) memory cells on a silicon integrated circuit memory chip. There are numerous different types using different semiconductor technologies. The two main types of random-access memory (RAM) are static RAM (SRAM), which uses several MOS transistors per memory cell, and dynamic RAM (DRAM), which uses a MOS transistor and a MOS capacitor per cell. Non-volatile memory (such as EPROM, EEPROM and flash memory) uses floating-gate memory cells, which consist of a single floating-gate MOS transistor per cell.

Most types of semiconductor memory have the property of random access, which means that it takes the same amount of time to access any memory location, so data can be efficiently accessed in any random order. This contrasts with data storage media such as hard disks and CDs which read and write data consecutively and therefore the data can only be accessed in the same sequence it was written. Semiconductor memory also has much faster access times than other types of data storage; a byte of data can be written to or read from semiconductor memory within a few nanoseconds, while access time for rotating storage such as hard disks is in the range of milliseconds. For these reasons it is used for primary storage, to hold the program and data the computer is currently working on, among other uses.

As of 2017, semiconductor memory chips sell $124 billion annually, accounting for 30% of the semiconductor industry. Shift registers, processor registers, data buffers and other small digital registers that have no memory address decoding mechanism are typically not referred to as memory although they also store digital data.

Description

See also: Computer memory

In a semiconductor memory chip, each bit of binary data is stored in a tiny circuit called a memory cell consisting of one to several transistors. The memory cells are laid out in rectangular arrays on the surface of the chip. The 1-bit memory cells are grouped in small units called words which are accessed together as a single memory address. Memory is manufactured in word length that is usually a power of two, typically N=1, 2, 4 or 8 bits.

Data is accessed by means of a binary number called a memory address applied to the chip's address pins, which specifies which word in the chip is to be accessed. If the memory address consists of M bits, the number of addresses on the chip is 2^M, each containing an N bit word. Consequently, the amount of data stored in each chip is N2^M bits. The memory storage capacity for M number of address lines is given by 2^M, which is usually in power of two: 2, 4, 8, 16, 32, 64, 128, 256 and 512 and measured in kilobits, megabits, gigabits or terabits, etc. As of 2014 the largest semiconductor memory chips hold a few gigabits of data, but higher capacity memory is constantly being developed. By combining several integrated circuits, memory can be arranged into a larger word length and/or address space than what is offered by each chip, often but not necessarily a power of two.

The two basic operations performed by a memory chip are "read", in which the data contents of a memory word is read out (nondestructively), and "write" in which data is stored in a memory word, replacing any data that was previously stored there. To increase data rate, in some of the latest types of memory chips such as DDR SDRAM multiple words are accessed with each read or write operation.

In addition to standalone memory chips, blocks of semiconductor memory are integral parts of many computer and data processing integrated circuits. For example, the microprocessor chips that run computers contain cache memory to store instructions awaiting execution.

Types

Volatile memory

RAM chips for computers usually come on removable memory modules like these. Additional memory can be added to the computer by plugging in additional modules.

Volatile memory loses its stored data when the power to the memory chip is turned off. However it can be faster and less expensive than non-volatile memory. This type is used for the main memory in most computers, since data is stored on the hard disk while the computer is off. Major types are:

RAM (Random-access memory) – This has become a generic term for any semiconductor memory that can be written to, as well as read from, in contrast to ROM (below), which can only be read. All semiconductor memory, not just RAM, has the property of random access.

• DRAM (Dynamic random-access memory) – This uses metal–oxide–semiconductor (MOS) memory cells consisting of one MOSFET (MOS field-effect transistor) and one MOS capacitor to store each bit. This type of RAM is the cheapest and highest in density, so it is used for the main memory in computers. However, the electric charge that stores the data in the memory cells slowly leaks out, so the memory cells must be periodically refreshed (rewritten) which requires additional circuitry. The refresh process is handled internally by the computer and is transparent to its user.
  • FPM DRAM (Fast page mode DRAM) – An older type of asynchronous DRAM that improved on previous types by allowing repeated accesses to a single "page" of memory to occur at a faster rate. Used in the mid-1990s.
  • EDO DRAM (Extended data out DRAM) – An older type of asynchronous DRAM which had faster access time than earlier types by being able to initiate a new memory access while data from the previous access was still being transferred. Used in the later part of the 1990s.
  • VRAM (Video random access memory) – An older type of dual-ported memory once used for the frame buffers of video adapters (video cards).
  • SDRAM (Synchronous dynamic random-access memory) – This added circuitry to the DRAM chip which synchronizes all operations with a clock signal added to the computer's memory bus. This allowed the chip to process multiple memory requests simultaneously using pipelining, to increase the speed. The data on the chip is also divided into banks which can each work on a memory operation simultaneously. This became the dominant type of computer memory by about the year 2000.
    • DDR SDRAM (Double data rate SDRAM) – This could transfer twice the data (two consecutive words) on each clock cycle by double pumping (transferring data on both the rising and falling edges of the clock pulse). Extensions of this idea are the current (2012) technique being used to increase memory access rate and throughput. Since it is proving difficult to further increase the internal clock speed of memory chips, these chips increase the transfer rate by transferring more data words on each clock cycle
      • DDR2 SDRAM – Transfers 4 consecutive words per internal clock cycle
      • DDR3 SDRAM – Transfers 8 consecutive words per internal clock cycle.
      • DDR4 SDRAM – Transfers 16 consecutive words per internal clock cycle.
    • RDRAM (Rambus DRAM) – An alternate double data rate memory standard that was used on some Intel systems but ultimately lost out to DDR SDRAM.
      • XDR DRAM (Extreme data rate DRAM)
    • SGRAM (Synchronous graphics RAM) – A specialized type of SDRAM made for graphics adaptors (video cards). It can perform graphics-related operations such as bit masking and block write, and can open two pages of memory at once.
      • GDDR SDRAM (Graphics DDR SDRAM)
        • GDDR2
        • GDDR3 SDRAM
        • GDDR4 SDRAM
        • GDDR5 SDRAM
        • GDDR6 SDRAM
    • HBM (High Bandwidth Memory) – A development of SDRAM used in graphics cards that can transfer data at a faster rate. It consists of multiple memory chips stacked on top of one another, with a wider data bus.
  • PSRAM (Pseudostatic RAM) – This is DRAM which has circuitry to perform memory refresh on the chip, so that it acts like SRAM, allowing the external memory controller to be shut down to save energy. It is used in a few game consoles such as the Wii.
• SRAM (Static random-access memory) – This stores each bit of data in a circuit called a flip-flop, made of 4 to 6 transistors. SRAM is less dense and more expensive per bit than DRAM, but faster and does not require memory refresh. It is used for smaller cache memories in computers.
• CAM (Content-addressable memory) – This is a specialized type in which, instead of accessing data using an address, a data word is applied and the memory returns the location if the word is stored in the memory. It is mostly incorporated in other chips such as microprocessors where it is used for cache memory.

Non-volatile memory

Non-volatile memory (NVM) preserves the data stored in it during periods when the power to the chip is turned off. Therefore, it is used for the memory in portable devices, which don't have disks, and for removable memory cards among other uses. Major types are:

• ROM (Read-only memory) – This is designed to hold permanent data, and in normal operation is only read from, not written to. Although many types can be written to, the writing process is slow and usually all the data in the chip must be rewritten at once. It is usually used to store system software which must be immediately accessible to the computer, such as the BIOS program which starts the computer, and the software (microcode) for portable devices and embedded computers such as microcontrollers.
  • MROM (Mask programmed ROM or Mask ROM) – In this type the data is programmed into the chip when the chip is manufactured, so it is only used for large production runs. It cannot be rewritten with new data.
  • PROM (Programmable read-only memory) – In this type the data is written into an existing PROM chip before it is installed in the circuit, but it can only be written once. The data is written by plugging the chip into a device called a PROM programmer.
  • EPROM (Erasable programmable read-only memory) – In this type the data in it can be rewritten by removing the chip from the circuit board, exposing it to an ultraviolet light to erase the existing data, and plugging it into a PROM programmer. The IC package has a small transparent "window" in the top to admit the UV light. It is often used for prototypes and small production run devices, where the program in it may have to be changed at the factory.
    

• • 4M EPROM, showing transparent window used to erase the chip
  • EEPROM (Electrically erasable programmable read-only memory) – In this type the data can be rewritten electrically, while the chip is on the circuit board, but the writing process is slow. This type is used to hold firmware, the low level microcode which runs hardware devices, such as the BIOS program in most computers, so that it can be updated.
• NVRAM (Non-volatile random-access memory)
  • FRAM (Ferroelectric RAM) – One type of nonvolatile RAM.
• Flash memory – In this type the writing process is intermediate in speed between EEPROMS and RAM memory; it can be written to, but not fast enough to serve as main memory. It is often used as a semiconductor version of a hard disk, to store files. It is used in portable devices such as PDAs, USB flash drives, and removable memory cards used in digital cameras and cellphones.

History

See also: Computer memory and Memory cell (computing)

Early computer memory consisted of magnetic-core memory, as early solid-state electronic semiconductors, including transistors such as the bipolar junction transistor (BJT), were impractical for use as digital storage elements (memory cells). The earliest semiconductor memory dates back to the early 1960s, with bipolar memory, which used bipolar transistors. Bipolar semiconductor memory made from discrete devices was first shipped by Texas Instruments to the United States Air Force in 1961. The same year, the concept of solid-state memory on an integrated circuit (IC) chip was proposed by applications engineer Bob Norman at Fairchild Semiconductor. The first bipolar semiconductor memory IC chip was the SP95 introduced by IBM in 1965. While bipolar memory offered improved performance over magnetic-core memory, it could not compete with the lower price of magnetic-core memory, which remained dominant up until the late 1960s. Bipolar memory failed to replace magnetic-core memory because bipolar flip-flop circuits were too large and expensive.

MOS memory

See also: MOSFET

The advent of the metal–oxide–semiconductor field-effect transistor (MOSFET), invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959, enabled the practical use of metal–oxide–semiconductor (MOS) transistors as memory cell storage elements, a function previously served by magnetic cores in computer memory. MOS memory was developed by John Schmidt at Fairchild Semiconductor in 1964. In addition to higher performance, MOS memory was cheaper and consumed less power than magnetic-core memory. This led to MOSFETs eventually replacing magnetic cores as the standard storage elements in computer memory.

In 1965, J. Wood and R. Ball of the Royal Radar Establishment proposed digital storage systems that use CMOS (complementary MOS) memory cells, in addition to MOSFET power devices for the power supply, switched cross-coupling, switches and delay-line storage. The development of silicon-gate MOS integrated circuit (MOS IC) technology by Federico Faggin at Fairchild in 1968 enabled the production of MOS memory chips. NMOS memory was commercialized by IBM in the early 1970s. MOS memory overtook magnetic core memory as the dominant memory technology in the early 1970s.

The term "memory" when used with reference to computers most often refers to volatile random-access memory (RAM). The two main types of volatile RAM are static random-access memory (SRAM) and dynamic random-access memory (DRAM). Bipolar SRAM was invented by Robert Norman at Fairchild Semiconductor in 1963, followed by the development of MOS SRAM by John Schmidt at Fairchild in 1964. SRAM became an alternative to magnetic-core memory, but required six MOS transistors for each bit of data. Commercial use of SRAM began in 1965, when IBM introduced their SP95 SRAM chip for the System/360 Model 95.

Toshiba introduced bipolar DRAM memory cells for its Toscal BC-1411 electronic calculator in 1965.  While it offered improved performance over magnetic-core memory, bipolar DRAM could not compete with the lower price of the then dominant magnetic-core memory. MOS technology is the basis for modern DRAM. In 1966, Dr. Robert H. Dennard at the IBM Thomas J. Watson Research Center was working on MOS memory. While examining the characteristics of MOS technology, he found it was capable of building capacitors, and that storing a charge or no charge on the MOS capacitor could represent the 1 and 0 of a bit, while the MOS transistor could control writing the charge to the capacitor. This led to his development of a single-transistor DRAM memory cell. In 1967, Dennard filed a patent under IBM for a single-transistor DRAM memory cell, based on MOS technology. This led to the first commercial DRAM IC chip, the Intel 1103, in October 1970. Synchronous dynamic random-access memory (SDRAM) later debuted with the Samsung KM48SL2000 chip in 1992.

The term "memory" is also often used to refer to non-volatile memory, specifically flash memory. It has origins in read-only memory (ROM). Programmable read-only memory (PROM) was invented by Wen Tsing Chow in 1956, while working for the Arma Division of the American Bosch Arma Corporation. In 1967, Dawon Kahng and Simon Sze of Bell Labs proposed that the floating gate of a MOS semiconductor device could be used for the cell of a reprogrammable read-only memory (ROM), which led to Dov Frohman of Intel inventing EPROM (erasable PROM) in 1971. EEPROM (electrically erasable PROM) was developed by Yasuo Tarui, Yutaka Hayashi and Kiyoko Naga at the Electrotechnical Laboratory in 1972. Flash memory was invented by Fujio Masuoka at Toshiba in the early 1980s. Masuoka and colleagues presented the invention of NOR flash in 1984, and then NAND flash in 1987. Toshiba commercialized NAND flash memory in 1987.

Applications

See also: List of MOSFET applications

 

MOS memory applications

MOS memory type	Abbr.	MOS memory cell	Applications
Static random-access memory	SRAM	MOSFETs	Cache memory, cell phones, eSRAM, mainframes, multimedia computers, networking, personal computers, servers, supercomputers, telecommunications, workstations, DVD disk buffer, data buffer, nonvolatile BIOS memory
Dynamic random-access memory	DRAM	MOSFET, MOS capacitor	Camcorders, embedded logic, eDRAM, graphics card, hard disk drive (HDD), networks, personal computers, personal digital assistants, printers, main computer memory, desktop computers, servers, solid-state drives, video memory, framebuffer memory
Ferroelectric random-access memory	FRAM	MOSFET, MOS capacitor	Non-volatile memory, radio-frequency identification (RF identification), smart cards
Read-only memory	ROM	MOSFET	Character generators, electronic musical instruments, laser printer fonts, video game ROM cartridges, word processor dictionary data
Erasable programmable read-only memory	EPROM	Floating-gate MOSFET	CD-ROM drives, embedded memory, code storage, modems
Electrically erasable programmable read-only memory	EEPROM	Floating-gate MOSFET	Anti-lock braking systems, air bags, car radios, cell phones, consumer electronics, cordless telephones, disk drives, embedded memory, flight controllers, military technology, modems, pagers, printers, set-top box, smart cards
Flash memory	Flash	Floating-gate MOSFET	ATA controllers, battery-powered applications, telecommunications, code storage, digital cameras, MP3 players, portable media players, BIOS memory, USB flash drive, digital TV, e-books, memory cards, mobile devices, set-top box, smartphones, solid-state drives, tablet computers
Non-volatile random-access memory	NVRAM	Floating-gate MOSFETs	Medical equipment, spacecraft