How Text Audio Image And Video Data Are Stored In A Computer's Memory

Device used on a figurer for storing information

Modern DDR4 SDRAM module, commonly constitute in desktop computers.

In computing, memory is a device or organisation that is used to store information for immediate use in a figurer or related computer hardware and digital electronic devices.^[1] The term memory is oft synonymous with the term chief storage or main memory. An primitive synonym for memory is shop.^[two]

Estimator memory operates at a high speed compared to storage that is slower only less expensive and higher in chapters. As well storing opened programs, estimator memory serves every bit deejay cache and write buffer to amend both reading and writing performance. Operating systems borrow RAM capacity for caching so long equally non needed by running software.^[3] If needed, contents of the computer memory tin can be transferred to storage; a common way of doing this is through a retentivity management technique called virtual memory.

Modern memory is implemented as semiconductor memory,^[four] ^[5] where data is stored within memory cells built from MOS transistors and other components on an integrated circuit.^[six] There are two main kinds of semiconductor retentivity, volatile and non-volatile. Examples of non-volatile retention are flash retentivity and ROM, PROM, EPROM and EEPROM memory. Examples of volatile retentiveness are dynamic random-access retention (DRAM) used for primary storage, and static random-access memory (SRAM) used for CPU enshroud.

Most semiconductor memory is organized into retention cells each storing 1 scrap (0 or 1). Flash retentivity organization includes both one bit per retentiveness cell and multi-level cell capable of storing multiple bits per cell. The memory cells are grouped into words of fixed word length, for example, 1, 2, 4, 8, 16, 32, 64 or 128 bits. Each word can be accessed by a binary address of N $.25, making it possible to store 2^Northward words in the retention.

History [edit]

In the early 1940s, memory technology often permitted a capacity of a few bytes. The showtime electronic programmable digital computer, the ENIAC, using thousands of vacuum tubes, could perform uncomplicated calculations involving twenty numbers of x decimal digits stored in the vacuum tubes.

The side by side meaning accelerate in figurer memory came with audio-visual delay-line retentiveness, developed by J. Presper Eckert in the early 1940s. Through the structure of a glass tube filled with mercury and plugged at each end with a quartz crystal, filibuster lines could store $.25 of information in the form of sound waves propagating through the mercury, with the quartz crystals acting as transducers to read and write bits. Delay-line memory was limited to a capacity of up to a few thousand $.25.

Two alternatives to the delay line, the Williams tube and Selectron tube, originated in 1946, both using electron beams in glass tubes as means of storage. Using cathode ray tubes, Fred Williams invented the Williams tube, which was the first random-access computer memory. The Williams tube was able to store more data than the Selectron tube (the Selectron was limited to 256 bits, while the Williams tube could store thousands) and less expensive. The Williams tube was nevertheless frustratingly sensitive to environmental disturbances.

Efforts began in the late 1940s to discover not-volatile memory. Magnetic-core memory allowed for recall of memory after power loss. It was developed by Frederick W. Viehe and An Wang in the tardily 1940s, and improved by Jay Forrester and Jan A. Rajchman in the early on 1950s, earlier being commercialised with the Cyclone figurer in 1953.^[vii] Magnetic-core memory was the dominant form of memory until the development of MOS semiconductor memory in the 1960s.^[8]

The first semiconductor retention was implemented as a flip-flop circuit in the early on 1960s using bipolar transistors.^[8] Semiconductor memory made from discrete devices was start shipped past Texas Instruments to the The states Air Forcefulness in 1961. The same year, the concept of solid-country retentivity on an integrated circuit (IC) chip was proposed by applications engineer Bob Norman at Fairchild Semiconductor.^[9] The first bipolar semiconductor memory IC chip was the SP95 introduced by IBM in 1965.^[8] While semiconductor retentivity offered improved operation over magnetic-core retention, information technology remain larger and more expensive and did non displace magnetic-cadre retentivity until the tardily 1960s.^[eight] ^[10]

MOS memory [edit]

The invention of the metal–oxide–semiconductor field-upshot transistor (MOSFET) enabled the practical use of metal–oxide–semiconductor (MOS) transistors as memory cell storage elements. MOS memory was developed by John Schmidt at Fairchild Semiconductor in 1964.^[11] In addition to higher performance, MOS semiconductor memory was cheaper and consumed less power than magnetic core retentivity.^[12] In 1965, J. Wood and R. Ball of the Majestic Radar Establishment proposed digital storage systems that use CMOS (complementary MOS) retentiveness cells, in add-on to MOSFET power devices for the power supply, switched cross-coupling, switches and filibuster-line storage.^[13] The development of silicon-gate MOS integrated excursion (MOS IC) technology past Federico Faggin at Fairchild in 1968 enabled the product of MOS memory chips.^[14] NMOS retentiveness was commercialized past IBM in the early on 1970s.^[15] MOS retention overtook magnetic core retentiveness as the ascendant memory engineering science in the early 1970s.^[12]

The 2 principal types of volatile random-admission memory (RAM) are static random-admission memory (SRAM) and dynamic random-access memory (DRAM). Bipolar SRAM was invented by Robert Norman at Fairchild Semiconductor in 1963,^[8] followed by the development of MOS SRAM by John Schmidt at Fairchild in 1964.^[12] SRAM became an alternative to magnetic-cadre retention, but requires six transistors for each flake of data.^[16] Commercial employ of SRAM began in 1965, when IBM introduced their SP95 SRAM fleck for the Arrangement/360 Model 95.^[viii]

Toshiba introduced bipolar DRAM retentiveness cells for its Toscal BC-1411 electronic calculator in 1965.^[17] ^[18] While it offered improved performance, bipolar DRAM could non compete with the lower price of the then dominant magnetic-core memory.^[19] MOS technology is the basis for modern DRAM. In 1966, Robert H. Dennard at the IBM Thomas J. Watson Research Center was working on MOS retentiveness. While examining the characteristics of MOS technology, he establish it was possible to build capacitors, and that storing a charge or no accuse on the MOS capacitor could represent the i and 0 of a fleck, while the MOS transistor could command writing the accuse to the capacitor. This led to his development of a single-transistor DRAM retentivity cell.^[16] In 1967, Dennard filed a patent for a single-transistor DRAM retention prison cell based on MOS technology.^[twenty] This led to the first commercial DRAM IC bit, the Intel 1103 in October 1970.^[21] ^[22] ^[23] Synchronous dynamic random-access memory (SDRAM) later debuted with the Samsung KM48SL2000 flake in 1992.^[24] ^[25]

The term memory is also often used to refer to non-volatile retentivity including read-merely memory (ROM) through modern flash memory. Programmable read-only memory (PROM) was invented past Wen Tsing Chow in 1956, while working for the Arma Sectionalisation of the American Bosch Arma Corporation.^[26] ^[27] In 1967, Dawon Kahng and Simon Sze of Bong Labs proposed that the floating gate of a MOS semiconductor device could exist used for the prison cell of a reprogrammable ROM, which led to Dov Frohman of Intel inventing EPROM (erasable PROM) in 1971.^[28] EEPROM (electrically erasable PROM) was developed past Yasuo Tarui, Yutaka Hayashi and Kiyoko Naga at the Electrotechnical Laboratory in 1972.^[29] Wink retentivity was invented by Fujio Masuoka at Toshiba in the early 1980s.^[30] ^[31] Masuoka and colleagues presented the invention of NOR wink in 1984,^[32] and then NAND flash in 1987.^[33] Toshiba commercialized NAND wink retention in 1987.^[34] ^[35] ^[36]

Developments in technology and economies of scale have made possible so-called very large retentivity (VLM) computers.^[36]

Volatile memory [edit]

Various retentivity modules containing unlike types of DRAM (from top to bottom): DDR SDRAM, SDRAM, EDO DRAM, and FPM DRAM

Volatile memory is computer memory that requires power to maintain the stored information. Most modern semiconductor volatile memory is either static RAM (SRAM) or dynamic RAM (DRAM).^[a] DRAM dominates for desktop system memory. SRAM is used for CPU cache. SRAM is also institute in small embedded systems requiring petty memory.

SRAM retains its contents equally long as the power is connected and may use a simpler interface, just requires six transistors per flake. Dynamic RAM is more complicated for interfacing and control, needing regular refresh cycles to prevent losing its contents, simply uses only one transistor and one capacitor per scrap, allowing it to reach much college densities and much cheaper per-flake costs.^[1] ^[22] ^[36]

Non-volatile retention [edit]

Not-volatile memory tin can retain the stored information even when not powered. Examples of non-volatile memory include read-just memory, flash memory, nearly types of magnetic computer storage devices (east.g. hd drives, floppy disks and magnetic record), optical discs, and early computer storage methods such every bit paper tape and punched cards.^[36]

Non-volatile retention technologies nether development include ferroelectric RAM, programmable metallization prison cell, Spin-transfer torque magnetic RAM, SONOS, resistive random-access memory, racetrack memory, Nano-RAM, 3D XPoint, and millipede memory.

Semi-volatile memory [edit]

A third category of memory is "semi-volatile". The term is used to depict a retentiveness which has some limited not-volatile duration after power is removed, just then data is ultimately lost. A typical goal when using a semi-volatile memory is to provide high performance/immovability/etc. associated with volatile memories, while providing some benefits of a truthful non-volatile memory.

For example, some non-volatile memory types can wear out, where a "worn" jail cell has increased volatility but otherwise continues to work. Data locations which are written oft can thus be directed to use worn circuits. Every bit long as the location is updated within some known retention fourth dimension, the data stays valid. If the memory time "expires" without an update, and so the value is copied to a less-worn circuit with longer memory. Writing first to the worn area allows a high write rate while avoiding wear on the not-worn circuits.^[37]

Equally a 2d example, an STT-RAM can exist made non-volatile by building large cells, just the toll per bit and write power go upwards, while the write speed goes downward. Using modest cells improves cost, power, and speed, but leads to semi-volatile beliefs. In some applications the increased volatility can be managed to provide many benefits of a non-volatile retention, for example past removing ability but forcing a wake-up before information is lost; or by caching read-only information and discarding the cached data if the ability-off time exceeds the not-volatile threshold.^[38]

The term semi-volatile is as well used to describe semi-volatile behavior constructed from other retention types. For case, a volatile and a non-volatile retentivity may be combined, where an external indicate copies data from the volatile memory to the not-volatile memory, but if power is removed without copying, the data is lost. Or, a bombardment-backed volatile retention, and if external power is lost in that location is some known period where the battery can continue to ability the volatile retentiveness, only if power is off for an extended time, the battery runs downward and data is lost.^[36]

Management [edit]

Proper management of retentivity is vital for a reckoner organisation to operate properly. Mod operating systems have complex systems to properly manage retentiveness. Failure to do so can lead to bugs, slow performance, and at worst case, takeover by viruses and malicious software.

Bugs [edit]

Improper direction of retentiveness is a common crusade of bugs, including the following types:

In an arithmetic overflow, a calculation results in a number larger than the allocated retentiveness permits. For example, a signed 8-fleck integer allows the numbers −128 to +127. If its value is 127 and information technology is instructed to add together 1, the computer tin can not store the number 128 in that space. Such a case will upshot in an undesired performance, such as changing the number'due south value to −128 instead of +128.
A memory leak occurs when a programme requests memory from the operating system and never returns the retentiveness when it's washed with it. A program with this bug volition gradually require more and more memory until the program fails as it runs out.
A segmentation fault results when a plan tries to access memory that it does not have permission to access. More often than not, a plan doing then will be terminated past the operating system.
A buffer overflow ways that a program writes information to the end of its allocated infinite so continues to write data to retentivity that has been allocated for other purposes. This may event in erratic program behavior, including retentivity access errors, incorrect results, a crash, or a breach of organisation security. They are thus the basis of many software vulnerabilities and tin be maliciously exploited.

Early reckoner systems [edit]

In early computer systems, programs typically specified the location to write retention and what data to put there. This location was a concrete location on the actual memory hardware. The deadening processing of such computers did not permit for the complex memory management systems used today. Also, as about such systems were single-task, sophisticated systems were non required as much.

This approach has its pitfalls. If the location specified is incorrect, this will cause the computer to write the data to some other part of the program. The results of an mistake similar this are unpredictable. In some cases, the incorrect data might overwrite memory used by the operating system. Computer crackers can take reward of this to create viruses and malware.

Virtual memory [edit]

Virtual retentiveness is a system where all physical retentivity is controlled by the operating organisation. When a program needs memory, information technology requests it from the operating system. The operating organization so decides in what physical location to place the program's code and data.

This offers several advantages. Computer programmers no longer need to worry about where their data is physically stored or whether the user's computer will take enough retention. It also allows multiple types of memory to be used. For example, some data can be stored in physical RAM chips while other information is stored on a hard drive (e.g. in a swapfile), functioning as an extension of the cache hierarchy. This drastically increases the amount of retentivity available to programs. The operating arrangement will place actively used data in physical RAM, which is much faster than difficult disks. When the amount of RAM is non sufficient to run all the electric current programs, it can result in a situation where the computer spends more time moving information from RAM to disk and dorsum than it does accomplishing tasks; this is known as thrashing.

Protected memory [edit]

Protected memory is a system where each program is given an area of retentivity to utilize and is not permitted to get outside that range. Use of protected memory greatly enhances both the reliability and security of a computer system.

Without protected retentiveness, it is possible that a bug in one program will alter the memory used past another program. This will crusade that other program to run off of corrupted memory with unpredictable results. If the operating organization'southward memory is corrupted, the entire computer system may crash and need to be rebooted. At times programs intentionally alter the retentivity used by other programs. This is done by viruses and malware to have over computers. It may also be used benignly by desirable programs which are intended to modify other programs; in the mod age, this is mostly considered bad programming exercise for application programs, only it may be used past system development tools such as debuggers, for example to insert breakpoints or hooks.

Protected memory assigns programs their own areas of retentivity. If the operating system detects that a program has tried to alter retentiveness that does not belong to it, the program is terminated (or otherwise restricted or redirected). This mode, just the offending program crashes, and other programs are not affected by the misbehavior (whether adventitious or intentional).

Protected memory systems almost always include virtual memory as well.

See too [edit]

Retentiveness geometry
Retention hierarchy
Retentiveness organization
Processor registers store data simply normally are not considered as retention, since they only store one word and practise not include an addressing mechanism.
Semiconductor memory
Units of data

Notes [edit]

^ Other volatile memory technologies that have attempted to compete or replace SRAM and DRAM include Z-RAM and A-RAM.

References [edit]

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