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Encyclopedia > Random access memory
Dynamic RAM (DRAM) modules

Two 512 MB DRAM Modules
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Random access memory (usually known by its acronym, RAM) is a type of computer data storage. It takes the form of integrated circuits that allow the stored data to be accessed in any order — that is, at random and without the physical movement of the storage medium or a physical reading head. RAM is a volatile memory as the information or instructions stored in it will be lost if the power is switched off. Look up RAM, Ram, ram in Wiktionary, the free dictionary. ... Image File history File links Size of this preview: 800 × 600 pixel Image in higher resolution (2304 × 1728 pixel, file size: 1. ... ReBoot character, see Megabyte (ReBoot). ... Part of a 1983 Sinclair ZX Spectrum computer board. ... A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... SDRAM means synchronous dynamic random access memory which is a type of solid state computer memory. ... Direct Rambus DRAM or DRDRAM (sometimes just called Rambus DRAM or RDRAM) is a type of synchronous dynamic RAM, designed by the Rambus Corporation. ... Micron Technology (Micron) NYSE: MU is a multinational company based in Boise, Idaho, USA, best known for producing many forms of semiconductor devices. ... Samsung Group is one of the largest South Korean business groupings. ... ‹ The template below (Expand) is being considered for deletion. ... Corsair Memory is a company which produces computer memory, primarily for the computer enthusiast crowd, although they also produce a value line called Value Select. ... Mushkin Enhanced Memory Systems Founded in 1994, provides customers with specialized semiconductor technology from their headquarters in Denver, CO. Mushkin is a subsidiary of ISO certified Ramtron International Corporation (NASDAQ: RMTR). ... It has been suggested that this article or section be merged with Backronym and Apronym (Discuss) Acronyms and initialisms are abbreviations, such as NATO, laser, and ABC, written as the initial letter or letters of words, and pronounced on the basis of this abbreviated written form. ... This article or section does not cite its references or sources. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... For other uses, see Data (disambiguation). ... In computer science, random access is the ability to access a random element of a group in equal time. ... Look up volatile in Wiktionary, the free dictionary. ...


The word "random" refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.[1] This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs, which rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than the data transfer, and the retrieval time varies depending on the physical location of the next item. Compact audio cassette Magnetic tape is a non-volatile storage medium consisting of a magnetic coating on a thin plastic strip. ... “Optical media” redirects here. ...

Contents

RAM

Originally, RAM referred to a type of solid-state memory, and the majority of this article deals with that, but physical devices which can emulate true RAM (or, at least, are used in a similar way) can have "RAM" in their names: for example, DVD-RAM. RAM is usually writable as well as readable, so "RAM" is often used interchangeably with "read-write memory". The alternative to this is "ROM", or Read Only Memory. Most types of RAM lose their data when the computer powers down. "Flash memory" is a ROM/RAM hybrid that can be written to, but which does not require power to maintain its contents. RAM is not strictly the opposite of ROM, however. The word random indicates a contrast with serial access or sequential access memory. You can recognize a DVD-RAM immediately because visually there are lots of little rectangles distributed on the surface of the data carrier. ... Read-write memory is a type of computer memory that may be relatively easily be written-to as well as read from. ... Rom is also the name of a toy and comic book character Rom (Spaceknight). ... A USB flash drive. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... In telecommunication, the term serial access has the following meanings: 1. ... In computer science sequential access means that a group of elements (e. ...


"Random access" is also the name of an indexing method: hence, disk storage is often called "random access" because the reading head can move relatively quickly from one piece of data to another, and does not have to read all the data in between. However the final "M" is crucial: "RAM" (provided there is no additional term as in "DVD-RAM") always refers to a solid-state device.


Many CPU-based designs actually have a memory hierarchy consisting of registers, on-die SRAM caches, DRAM, paging systems, and virtual memory or swap space on a hard-drive. This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different access times, violating the original concept behind the "random access" term in RAM. Even within a hierarchy level such as DRAM, the specific row/column/bank/rank/channel/interleave organization of the components make the access time variable, although not to the extent that rotating storage media or a tape is variable. Static random access memory (SRAM) is a type of semiconductor memory. ...

1 Module of 128Mb NEC SD-RAM
1 Module of 128Mb NEC SD-RAM

Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (2272 × 1704 pixel, file size: 797 KB, MIME type: image/jpeg) Photographed by Liam P Adlen NEC 128Mb RAM I, the creator of this work, hereby release it into the public domain. ... Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (2272 × 1704 pixel, file size: 797 KB, MIME type: image/jpeg) Photographed by Liam P Adlen NEC 128Mb RAM I, the creator of this work, hereby release it into the public domain. ...

Overview

The key benefit of RAM over types of storage which require physical movement is that retrieval times are short and consistent. Short because no physical movement is necessary, and consistent because the time taken to retrieve a piece of data does not depend on its current distance from a physical head; it requires practically the same amount of time to access any piece of data stored in a RAM chip. Most other technologies have inherent delays for reading a particular bit or byte. The disadvantage of RAM over physically moving media is cost, and the loss of data when power is turned off. BIT is an acronym for: Bannari amman Institute of Technology Bangalore Institute of Technology Beijing Institute of Technology Benzisothiazolinone Bilateral Investment Treaty Bhilai Institute of Technology - Durg Birla Institute of Technology - Mesra Battles in Time (Doctor Who magazine) BIT International College, formerly the Bohol Institute of Technology in Bohol, Philippines... In computer science a byte (pronounced bite) is a unit of measurement of information storage, most often consisting of eight bits. ...


Because of this speed and consistency, RAM is used as 'main memory' or primary storage: the working area used for loading, displaying and manipulating applications and data. In most personal computers, the RAM is not an integral part of the motherboard or CPU—it comes in the easily upgraded form of modules called memory sticks or RAM sticks about the size of a few sticks of chewing gum. These can quickly be removed and replaced should they become damaged or too small for current purposes. A smaller amount of random-access memory is also integrated with the CPU, but this is usually referred to as "cache" memory, rather than RAM. Primary storage, or internal memory, is computer memory that is accessible to the central processing unit of a computer without the use of computers input/output channels. ... A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ... For other uses, see cache (disambiguation). ...


Modern RAM generally stores a bit of data as either a charge in a capacitor, as in dynamic RAM, or the state of a flip-flop, as in static RAM. Some types of RAM can detect or correct random faults called memory errors in the stored data, using RAM parity and error correction codes. Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... See Capacitor (component) for a discussion of specific types. ... 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. ... In digital circuits, the flip-flop, latch, or bistable multivibrator is an electronic circuit which has two stable states and thereby is capable of serving as one bit of memory. ... Static random access memory (SRAM) is a type of semiconductor memory. ... RAM parity determines whether a random access memory unit stores a parity bit for error detection purposes. ... It has been suggested that this article or section be merged with SEC-DED. (Discuss) In mathematics, computer science, telecommunication, and information theory, error detection and correction has great practical importance in maintaining data (information) integrity across noisy channels and less-than-reliable storage media. ...


Many types of RAM are volatile, which means that unlike some other forms of computer storage such as disk storage and tape storage, they lose all data when the computer is powered down. For these reasons, nearly all PCs use disks as "secondary storage". Small PDAs and music players (up to 8 GB in Jan 2007) may dispense with disks, but rely on flash memory to maintain data between sessions of use. Disk storage is a category of data storage mechanisms for computers; data is recorded on planar surfaces or disks for temporary or permanent storage. ... Magnetic tape has been used for data storage for over 50 years. ... Look up PDA in Wiktionary, the free dictionary. ...


Software can "partition" a portion of a computer's RAM, allowing it to act as a much faster hard drive that is called a RAM disk. Unless the memory used is non-volatile, a RAM disk loses the stored data when the computer is shut down. However, volatile memory can retain its data when the computer is shut down if it has a separate power source, usually a battery. Typical hard drives of the mid-1990s. ... A RAM-Disk, Ramdisk or Ramdrive is a virtual solid state disk that uses a segment of active computer memory, RAM, as secondary storage, a role typically filled by hard drives. ... Symbols representing a single Cell (top) and Battery (bottom), used in circuit diagrams. ...


If a computer becomes low on RAM during intensive application cycles, the computer can resort to swapping. In this case, the computer temporarily uses hard drive space as additional memory. Constantly relying on this type of backup memory is called thrashing, which is generally undesirably because it lowers overall system performance. In order to reduce the dependency on swapping, more RAM can be installed. Swapping is the increasingly prevalent informal bartering system in which persons on internet communities trade items of comparable value on a trust basis. ... Typical hard drives of the mid-1990s. ... In computer science, thrash is the poor performance of a virtual memory (or paging) system, when the same pages are being loaded repeatedly due to a lack of main memory. ...


Recent developments

Currently, several types of non-volatile RAM are under development, which will preserve data while powered down. The technologies used include carbon nanotubes and the magnetic tunnel effect. It has been suggested that this article or section be merged with Non-volatile memory. ... 3D model of three types of single-walled carbon nanotubes. ... If two ferromagnets are separated by a thin (about 1 nm) insulator, the resistance of the tunneling current changes with the relative orientation of the two magnetic layers. ...


In summer 2003, a 128 KB magnetic RAM chip manufactured with 0.18 µm technology was introduced. The core technology of MRAM is based on the magnetic tunnel effect. In June 2004, Infineon Technologies unveiled a 16 MB prototype again based on 0.18 µm technology. A kilobyte (derived from the SI prefix kilo-, meaning 1,000) is a unit of information or computer storage equal to either 1,000 bytes or 1,024 bytes (210), depending on context. ... Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ... If two ferromagnets are separated by a thin (about 1 nm) insulator, the resistance of the tunneling current changes with the relative orientation of the two magnetic layers. ... Infineon Technologies AG (ISIN: DE0006231004, FWB: IFX, NYSE: IFX) was founded in April 1999 when the semiconductor operations of parent company, Siemens AG, were spun off to form a separate legal entity. ... ReBoot character, see Megabyte (ReBoot). ...


Nantero built a functioning carbon nanotube memory prototype 10 GB array in 2004. This article does not cite its references or sources. ... This article is about the unit of measurement. ...


In 2006, Solid state memory came of age, especially when implemented as "Solid state disks", with capacities exceeding 150 gigabytes and speeds far exceeding traditional disks. This development has started to blur the definition between traditional random access memory and disks, dramatically reducing the difference in performance.


Memory wall

The "memory wall" is the growing disparity of speed between CPU and memory outside the CPU chip. An important reason of this disparity is the limited communication bandwidth beyond chip boundaries. From 1986 to 2000, CPU speed improved at an annual rate of 55% while memory speed only improved at 10%. Given these trends, it was expected that memory latency would become an overwhelming bottleneck in computer performance. [2] CPU redirects here. ... In engineering, bottleneck is a phenomenon where the performance or capacity of an entire system is severely limited by a single component. ...


Currently, CPU speed improvements have slowed significantly partly due to major physical barriers and partly because current CPU designs have already hit the memory wall in some sense. Intel summarized these causes in their Platform 2015 documentation (PDF):

“First of all, as chip geometries shrink and clock frequencies rise, the transistor leakage current increases, leading to excess power consumption and heat (more on power consumption below). Secondly, the advantages of higher clock speeds are in part negated by memory latency, since memory access times have not been able to keep pace with increasing clock frequencies. Third, for certain applications, traditional serial architectures are becoming less efficient as processors get faster (due to the so-called Von Neumann bottleneck), further undercutting any gains that frequency increases might otherwise buy. In addition, resistance-capacitance (RC) delays in signal transmission are growing as feature sizes shrink, imposing an additional bottleneck that frequency increases don't address.” Design of the Von Neumann architecture For the robotic architecture also named after Von Neumann, see Von Neumann machine The von Neumann architecture is a computer design model that uses a single storage structure to hold both instructions and data. ... A resistor-capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors driven by a voltage or current source. ...

The RC delays in signal transmission were also noted in Clock Rate versus IPC: The End of the Road for Conventional Microarchitectures which projects a maximum of 12.5% average annual CPU performance improvement between 2000 and 2014. The data on Intel Processors clearly shows a slowdown in performance improvements in recent processors. However, Intel's new processors, Core 2 Duo (codenamed Conroe) show a significant improvement over previous Pentium 4 processors; due to a more efficient architecture, performance increased while clock rate actually decreased. Core 2 Duo brand logo Core 2 Extreme brand logo Core 2 is an eighth-generation x86 architecture microprocessor produced by Intel based on an all-new CPU architecture called the Intel Core Microarchitecture, which is the successor of NetBurst microarchitecture that has powered most Intel processors since 2000. ... The Pentium 4[1] brand refers to Intels mainstream desktop and mobile single-core CPUs (introduced on November 20, 2000[2]) with the seventh-generation NetBurst architecture, which was the companys first all-new design since the Intel P6 of the Pentium Pro branded CPUs of 1995. ...


DRAM packaging

Main article: DRAM packaging

For economic reasons, the large (main) memories found in personal computers, workstations, and non-handheld game-consoles (such as Playstation and Xbox) normally consists of dynamic RAM (DRAM). Other parts of the computer, such as cache memories and data buffers in hard disks, normally use static RAM (SRAM). Dram can mean several things: Dram (unit), an imperial unit of volume Dram, an imperial unit of weight or mass, see avoirdupois and apothecaries system Ottoman dram, a unit of weight, see dirhem Armenian dram, a monetary unit DRAM, a type of RAM Category: ... 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. ... This article is about the computer term. ... Static random access memory (SRAM) is a type of semiconductor memory. ...


See also

Wikimedia Commons has media related to:
RAM

Image File history File links Commons-logo. ... This article or section is in need of attention from an expert on the subject. ... Two types of DIMMs: a 168-pin SDRAM module (top) and a 184-pin DDR SDRAM module (bottom). ... You can recognize a DVD-RAM immediately because visually there are lots of little rectangles distributed on the surface of the data carrier. ... Dual-channel architecture DDR/DDR2 SDRAM describes a motherboard technology that effectively doubles data throughput from RAM to the memory controller. ... It has been suggested that this article or section be merged with SEC-DED. (Discuss) In mathematics, computer science, telecommunication, and information theory, error detection and correction has great practical importance in maintaining data (information) integrity across noisy channels and less-than-reliable storage media. ... Registered (sometimes called buffered) memory modules have additional components between the SDRAM modules and the systems memory controller. ... CompactFlash (CF) was originally a type of data storage device, used in portable electronic devices. ... The PCMCIA is the Personal Computer Memory Card International Association, an industry trade association that creates standards for notebook computer peripheral devices. ... Static random access memory (SRAM) is a type of semiconductor memory. ... Spin torque transfer writing technology is a technology in which data is written by aligning the spin direction of the electrons flowing through a TMR (tunneling magneto-resistance) element. ... It has been suggested that this article or section be merged with Non-volatile 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. ... DRAM is a type of random access memory that stores each bit of data in a separate capacitor. ... 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. ... XDR DRAM is a high performance RAM Interface like SDR-SDRAM and DDR-SDRAM. The XDR solution was engineered to be effective in small high-bandwidth consumer systems, high-performance main memory applications, and flagship GPUs. ... SDRAM means synchronous dynamic random access memory which is a type of solid state computer memory. ... DDR SDRAM or double-data-rate synchronous dynamic random access memory is a type of memory integrated circuit used in computers. ... “DDR2” redirects here. ... Direct Rambus DRAM or DRDRAM (sometimes just called Rambus DRAM or RDRAM) is a type of synchronous dynamic RAM, designed by the Rambus Corporation. ... This article is about the company. ...

Notes and references

  1. ^ Strictly speaking, modern types of DRAM are therefore not truly (or technically) random access, as data are read in burst; the name DRAM has stuck however.
  2. ^ The term was coined in Hitting the Memory Wall: Implications of the Obvious (PDF).

External links


  Results from FactBites:
 
Random access memory - Wikipedia, the free encyclopedia (1133 words)
Most RAM can be both written to and read from, so "RAM" is often used interchangeably with "read-write memory." In this sense, RAM is the opposite of Sequential Access Memory.
The basic concepts of tube and core memory are used in modern RAM implemented with integrated circuits.
Modern RAM generally stores a bit of data as either a charge in a capacitor, as in dynamic RAM, or the state of a flip-flop, as in static RAM.
  More results at FactBites »

 
 

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