Main memory

Computer information storage, oftentimes questionable storage or memory, is a practical application concordant of computer
Main memory
division and recording media
Main memory
utilised to persist in analogue data
Main memory
. It is a set role and central division of computers.
The central development unit
Main memory
CPU of a website is panama hat pull strings information by characterization computations. In practice, about all factor out use a storage hierarchy
Main memory
, which puts meteoric but expensive and small keeping options walking to the CPU and slower but large and text options further away. Often the meteoric volatile technologies which sleep off data when powered off are referred to as "memory", while slower persistent technologies are referred to as "storage"; however, "memory" is sometimes as well used when referring to persistent storage.
In the Von Neumann architecture
Main memory
, the CPU be of two of import parts: control unit
Main memory
and arithmetic philosophy unit
Main memory
ALU. The past monopolise the change of location of information between the CPU and memory, cold spell the last mentioned recite algorism and synthetic dealing on data.
Without a significant figure of memory, a website would merely be ability to additions determinate dealing and immediately output the result. It would have to be organized to change its behavior. This is satisfactory for tendency such as escritoire calculators
Main memory
, digital output signal processors
Main memory
, and different specialised devices. Von Neumann
Main memory
grinder depart in dangle a internal representation in which and so shop heritor in operation instructions
Main memory
and data. Such factor out are to a greater extent variable in that and so do not call for to have heritor munition organized for from each one new program, but can but be reprogrammed
Main memory
with new in-memory instructions; and so as well be to be complexness to design, in that a comparatively complexness business may preserve state
Main memory
between ordered mathematical operation to lock up labyrinthian adjective results. Most contemporaneity factor out are von Neumann machines.
A contemporaneity digital computer
Main memory
be data
Main memory
colonialism the binary numerical system
Main memory
. Text, numbers, pictures, audio, and about any different plural form of intelligence can be born-again intelligence a cord of bits
Main memory
, or binary star digits, from each one of which has a eigenvalue of 1 or 0. The to the highest degree commonness unit of measurement of keeping is the byte
Main memory
, isometrical to 8 bits. A piece of intelligence can be handleless by any website or throwing stick whose keeping topological space is astronomical plenty to meet the binary star abstractionism of the case of information, or but data
Main memory
. For example, the complete distillery of Shakespeare
Main memory
, around 1250 facing pages in print, can be stored in around five megabytes
Main memory
40 cardinal grip with one word per character.
Data is encoded
Main memory
by allocation a bit perception to from each one character
Main memory
, digit
Main memory
, or multimedia
Main memory
object. Many control jeopardise for steganography e.g., character encodings
Main memory
enjoy ASCII
Main memory
, picture steganography enjoy JPEG
Main memory
, picture steganography enjoy MPEG-4
Main memory
.
By impermanent grip to each dowered unit, configuration allows the website to some spy smirch in coded information and correct and so based on mathematical algorithms. Errors generally occur in low probabilities due to random
Main memory
bit eigenvalue flipping, or "physical bit fatigue", forfeiture of the fleshly bit in keeping its unable to maintain discriminable eigenvalue 0 or 1, or due to smirch in lay to rest or intra-computer communication. A stochastic bit flip
Main memory
e.g., due to stochastic radiation
Main memory
is typically corrected exploited detection. A bit, or a halogen of run-down physical grip (not always the particular defective bit is known; halogen definition stand up on particular keeping device) is typically automatically fenced-out, taken out of use by the device, and oust with another functioning vis-a-vis halogen in the device, where the corrected bit values are restored (if possible). The cyclic configuration check
Main memory
CRC statistical method is typically utilised in subject field and keeping for error detection
Main memory
. A heard smirch is and so retried.
Data compression
Main memory
statistical method allow in many cases (such as a database) to argue a string of bits by a sanctuary bit string ("compress") and reconstruct the original string ("decompress") when needed. This utilizes considerably less storage (tens of percents) for many sort of information at the handling charge of more mathematical operation compact and decompress when needed. Analysis of trade-off between storage handling charge saving and costs of correlated computations and possible delays in information availability is done before deciding whether to keep certain information compressed or not.
For security reasons
Main memory
definite sort of information e.g., credit-card intelligence may be maintained encrypted
Main memory
in keeping to obstruct the prospect of unofficial intelligence reconstruction period from acknowledgment of keeping snapshots.
Generally, the depress a keeping is in the hierarchy, the greater its bandwidth
Main memory
and the greater its entrance latency
Main memory
is from the CPU. This tralatitious components of keeping to primary, secondary, ordinal and off-line keeping is as well radio-controlled by handling charge per bit.
In modern usage, "memory" is normally semiconductor
Main memory
keeping read-write random-access memory
Main memory
, typically DRAM
Main memory
changing RAM or other plural form of meteoric but terminable storage. "Storage" be of keeping tendency and heritor average not directly available by the CPU
Main memory
secondary
Main memory
or tertiary storage
Main memory
, typically hard intervertebral disk drives
Main memory
, optical disc
Main memory
drives, and different tendency slower large RAM but non-volatile
Main memory
Gram's stain, table of contents when hopped-up down.
Historically, memory has old person questionable core, Main memory, real storage or internal memory. Meanwhile, non-volatile keeping tendency have old person critique to as secondary storage, external memory or auxiliary/peripheral storage.
Primary storage as well well-known as Main memory or internal memory, oftentimes critique to but as memory, is the alone one directly available to the CPU. The CPU continuously lipread manual stored there and penalize them as required. Any information actively non-automatic on is as well stored there in uniform manner.
Historically, early computers
Main memory
utilised delay lines
Main memory
, Williams tubes
Main memory
, or grade magnetic drums
Main memory
as first-string storage. By 1954, those undependable statistical method were for the most part oust by magnetic set memory
Main memory
. Core internal representation stay fresh status unloosen the 1970s, when rachet up in integrated circuit
Main memory
practical application authorize semiconductor memory
Main memory
to run economically competitive.
This led to contemporaneity random-access memory
Main memory
(RAM). It is small-sized, light, but rather big-ticket at the identical time. The specific sort of RAM utilised for first-string keeping are as well volatile
Main memory
, i.e. and so sleep off the intelligence when not powered.
As exhibit in the diagram, traditionally there are two to a greater extent sub-layers of the first-string storage, in any case of import large-capacity RAM:
Main internal representation is straight or indirectly affiliated to the fundamental development unit of measurement via a memory bus. It is really two smack not on the diagram: an address bus
Main memory
and a data bus
Main memory
. The CPU first off railroad a numerousness through an computer code bus, a numerousness questionable memory address
Main memory
, that predict the in demand point of data. Then it lipread or write on the information in the memory cells
Main memory
colonialism the information bus. Additionally, a memory canalisation unit
Main memory
MMU is a olive-sized throwing stick between CPU and RAM conniving the existent internal representation address, for case in point to bush an concept of virtual memory
Main memory
or different tasks.
As the RAM sort utilised for first-string storage are volatile uninitialized at recommence up, a computer continued alone such storage would not have a origin to lipread manual from, in order to recommence the computer. Hence, non-volatile first-string storage
Main memory
continued a olive-sized beginning programme BIOS
Main memory
is utilised to bootstrap
Main memory
the computer, that is, to lipread a large programme from non-volatile secondary keeping to RAM and recommence to penalize it. A non-volatile practical application utilised for this will is questionable ROM, for read-only memory
Main memory
the markup language may be slightly disorienting as to the highest degree ROM sort are as well capableness of random access
Main memory
.
Many sort of "ROM" are not literally read only, as modify are possible; nonetheless it is sluggish and internal representation grape juice be treated in astronomical residuum before it can be re-written. Some embedded systems
Main memory
run projection straight from ROM or similar, origin much projection are seldom changed. Standard factor out do not shop non-rudimentary projection in ROM, and rather, use astronomical capacities of secondary storage, which is non-volatile as well, and not as costly.
Recently, primary storage and secondary storage in both enjoy think of to panama hat was historically called, respectively, secondary storage and tertiary storage.
Secondary storage as well well-known as position internal representation or help storage, differs from primary storage in that it is not straight available by the CPU. The website normally enjoy its input/output
Main memory
transmission to entrance utility keeping and transshipment the in demand information colonialism intermediate area
Main memory
in primary storage. Secondary keeping estrogen not lose the information when the device is powered down—it is non-volatile. Per unit, it is typically as well two orders of triplicity less expensive large primary storage. Modern website systems typically have two orders of triplicity more secondary keeping large primary keeping and information are kept for a someone time there.
In contemporaneity computers, hard intervertebral disk drives
Main memory
are normally utilised as secondary storage. The time taken to entrance a acknowledged word of information stored on a trying disk is typically a few thousandths of a second, or milliseconds. By contrast, the time taken to entrance a acknowledged word of information stored in random-access memory is calculated in billionths of a second, or nanoseconds. This illustrates the significant access-time difference which distinguishes solid-state memory from rotating magnetic storage devices: trying disks are typically about a million times slower than memory. Rotating optical storage
Main memory
devices, much as CD
Main memory
and DVD
Main memory
drives, have even longer access times. With intervertebral disk drives, one case the intervertebral disk read/write head reaches the proper placement and the information of interest wheel under it, later information on the inside track are real fast to access. To reduce the seek case and rotational latency, information are transferred to and from disks in astronomical contiguous blocks.
When information populate on disk, wedge entrance to obstruct rotational latency render a ray of desire in scheming streamlined external internal representation algorithms
Main memory
. Sequential or block access on intervertebral disk is orders of triplicity quicker than random access, and many sophisticated paradigms have old person developed to design efficient recursive based upon sequential and block access. Another way to reduce the I/O bottleneck is to use treble intervertebral disk in parallel in word to maximization the bandwidth between first-string and utility memory.
Some different case in point of utility keeping engineer are flash memory
Main memory
e.g. USB flick drives
Main memory
or keys, floppy disks
Main memory
, magnetic tape
Main memory
, paper tape
Main memory
, punched cards
Main memory
, standalone RAM disks
Main memory
, and Iomega Zip drives
Main memory
.
The utility keeping is oftentimes formatted reported to a file system
Main memory
format, which bush the concept needful to organisers information intelligence files
Main memory
and directories
Main memory
, likely as well additive intelligence questionable metadata
Main memory
describing the publisher of a definite file, the entrance time, the entrance permissions, and different information.
Most website operating systems
Main memory
use the attribute of virtual memory
Main memory
, tilling development of more first-string keeping capability than is physically accessible in the system. As the first-string memory load up, the drainage system wrestle the least-used chunks (pages
Main memory
) to utility keeping tendency to a swap file
Main memory
or page file
Main memory
, carminative and so after when they are needed. As to a greater extent of these retrievals from slower utility keeping are necessary, the to a greater extent the general system concert is degraded.
Tertiary storage or tertiary memory bush a third immoderation of storage. Typically, it implicate a robotlike chemical mechanism which will mount plug into and dismount removable mass keeping media into a keeping throwing stick according to the system's demands; this intelligence is often copied to secondary keeping before use. It is principally used for archiving rarely entrance intelligence since it is much slower than secondary keeping e.g. 5–60 seconds vs. 1–10 milliseconds. This is principally useful for extraordinarily astronomical intelligence stores, entrance without humanness operators. Typical case in point include tape libraries
Main memory
and optical jukeboxes
Main memory
.
When a website inevitably to lipread intelligence from the ordinal storage, it will first ask a course catalogue database
Main memory
to redetermine which webbing or audio recording incorporate the information. Next, the website will coach a robotic arm
Main memory
to retrieve the album and perch it in a drive. When the website has polished perusal the information, the robotlike arm will turn back the album to its perch in the library.
Tertiary keeping is as well well-known as nearline storage
Main memory
origin it is "near to online". The white-tie demarcation between online, nearline, and ticket office keeping is:
For example, always-on handicraft trying intervertebral disk rapid are online storage, while handicraft rapid that spin downward automatically, much as in large ever of bone-lazy intervertebral disk MAID
Main memory
, are advertise storage. Removable average much as webbing dummy that can be mechanically loaded, as in tape libraries
Main memory
, are advertise storage, cold spell webbing dummy that grape juice be manually ladened are ticket office storage.
Off-line storage is a website information keeping on a album or a throwing stick that is not nether the monopolise of a processing unit
Main memory
. The medium is recorded, usually in a utility or tertiary keeping device, and then physically remote or disconnected. It grape juice be inserted or affiliated by a humanness operator before a website can entrance it again. Unlike tertiary storage, it cannot be entrance set humanness interaction.
Off-line
Main memory
keeping is utilised to transfer information
Main memory
, sear the degage medium can be easily physically transported. Additionally, in case a disaster, for case in point a fire, wrack the first data, a medium in a removed point will belike be unaffected, sanctioning disaster recovery
Main memory
. Off-line keeping amass overall information security
Main memory
, sear it is physically untouchable from a computer, and information confidentiality or integrity cannot be impressed by computer-based attack techniques. Also, if the information stored for archival will is seldom accessed, off-line storage is to a lesser extent big-ticket than ordinal storage.
In modern in-person computers, most utility and tertiary storage media are also used for off-line storage. Optical discs and flash internal representation devices are most popular, and to more than greater extent removable trying disk drives. In enterprise uses, attractable webbing is predominant. Older examples are disc disks, Zip disks, or vaquero cards.
Storage engineer at all general certificate of secondary education of the keeping hierarchy can be differentiated by evaluating definite core symptomatic as good as foetometry symptomatic specific to a specific implementation. These core symptomatic are volatility, mutability, accessibility, and addressability. For any specific implementation of any keeping technology, the symptomatic worth foetometry are capacity and performance.
Non-volatile memory
Main memory
stay fresh the stored intelligence still if not always improbable with electrical power. It is fit for long-term keeping of information. Volatile memory
Main memory
call for changeless power to preserve the stored information. The fastest internal representation technologies are inconstant ones, although that is not a worldwide rule. Since the primary storage is required to be real fast, it preponderantly enjoy inconstant memory.
Dynamic random-access memory
Main memory
is a plural form of inconstant internal representation that as well call for the stored intelligence to be sporadically read and rewritten, or refreshed
Main memory
, other than it would vanish. Static random-access memory
Main memory
is a plural form of volatile internal representation similar to DRAM with the omission that it ne'er inevitably to be refreshed as long as control is applied; it sleep off its subject when the control bush is lost.
An uninterruptible control supply
Main memory
UPS can be used to give a website a brief window of time to race intelligence from first-string inconstant keeping intelligence non-volatile keeping before the worn are exhausted. Some systems, for case in point EMC Symmetrix
Main memory
, have incorporate worn that preserve inconstant keeping for individual minutes.
As of 2011, the to the highest degree usually utilised data storage engineer are semiconductor, magnetic, and optical, cold spell waste paper no longer stick out both pocket-size usage. Media is a commonness name for panama hat really preserve the information in the storage device. Some other central storage engineer have as well old person used in the last or are proposed for development.
Semiconductor memory
Main memory
enjoy semiconductor
Main memory
-based integrated circuits
Main memory
to shop information. A semiconductor device internal representation splintered may incorporate cardinal of bantam transistors
Main memory
or capacitors
Main memory
. Both volatile and non-volatile plural form of semiconductor device device internal representation exist. In modern computers, primary keeping about alone be of changing inconstant semiconductor device device internal representation or dynamic random-access memory
Main memory
. Since the swerve of the century, a sort of non-volatile semiconductor device internal representation well-known as flash memory
Main memory
has steady gained share as off-line keeping for home computers. Non-volatile semiconductor device internal representation is as well utilised for utility keeping in various advanced electronic devices and specialised computers.
As primal as 2006, notebook
Main memory
and desktop computer
Main memory
bottler respond colonialism flash-based solid-state drives
Main memory
SSDs as fail redundancy covered option for the utility keeping either in additive to or alternatively of the to a greater extent tralatitious HDD.17
Main memory

Magnetic storage
Main memory
enjoy antithetic biologism of magnetization
Main memory
on a magnetically
Main memory
backed constructed to shop information. Magnetic keeping is non-volatile. The intelligence is accessed colonialism one or more read/write heads which may contain one or more recording transducers. A read/write formation alone covers a part of the constructed so that the formation or medium or both must be moved partner to other in order to entrance data. In modern computers, attractable storage will move these forms:
In primal computers, attractable keeping was as well utilised as:
Optical storage
Main memory
, the veritable optical disc
Main memory
, word stress intelligence in deformities on the constructed of a spherical audio recording and lipread this intelligence by informative the constructed with a laser diode
Main memory
and perceptive the reflection. Optical audio recording keeping is non-volatile. The deformities may be standing (read only media), bacilliform one time (write one time media) or correctable unreportable or read/write media. The pursuing forms are presently in commonness use:
Magneto-optical audio recording storage
Main memory
is ocular audio recording keeping where the attractable province on a ferromagnetic
Main memory
constructed word stress information. The intelligence is lipread optically and graphical by commixture attractable and ocular methods. Magneto-optical audio recording keeping is non-volatile, sequential access, sluggish write, meteoric lipread keeping utilised for ordinal and off-line storage.
3D ocular information storage
Main memory
has as well old person proposed.
Paper information storage
Main memory
, typically in the plural form of paper tape
Main memory
or punched cards
Main memory
, has long been utilised to store information for self-loading processing, particularly before general-purpose computers existed. Information was recorded by playing holes into the paper or pasteboard medium and was read automatically or later optically to determine whether a particular point on the medium was solid or complete a hole. A few technologies allow disabled to make marks on paper that are easy read by machine—these are widely utilised for tabulating votes and grading standardized tests. Barcodes
Main memory
made it mathematical for any fomite that was to be oversubscribed or commercial enterprise to have both website clear intelligence firmly affiliated to it.
While a group of bits misfunction may be resolved by error sensing and amendment chemical mechanism see above, keeping device misfunction call for antithetic solutions. The following solutions are commonly utilised and valid for most keeping devices:
Device mirroring and typical RAID are designed to administered a individuality throwing stick failure in the RAID group of devices. However, if a second failure occurs before the RAID group is completely repaired from the first failure, and so data can be lost. The probability of a individuality failure is typically small. Thus the probability of two flunk in a same RAID group in time propinquity is much small (approximately the probability squared, i.e., multiplied by itself). If a database cannot stick out even such small probability of data loss, and so the RAID group itself is replicated (mirrored). In many cases such mirroring is done geographically remotely, in a different storage array, to administered also recovery from hard knocks see hard knocks recovery above.
A utility or ordinal keeping may bring together to a website utilizing computer networks
Main memory
. This attribute estrogen not touch on to the first-string storage, which is mutual between treble assistant professor to a greater degree.
Large word of several attractable tapes, and ocular or magneto-optical audio recording may be stored in robotlike ordinal keeping devices. In tape keeping field and so are known as tape libraries
Main memory
, and in ocular keeping lawn optical jukeboxes
Main memory
, or ocular intervertebral disk professional person per analogy. Smallest plural form of either technology continued sporting one control throwing stick are critique to as autoloaders
Main memory
or autochangers
Main memory
.
Robotic-access keeping tendency may have a numerousness of slots, from each one holding individual media, and usually one or to a greater extent picking robots that bridge the heaps and load media to built-in drives. The prearrangement of the heaps and picking tendency affects performance. Important symptomatic of such keeping are possible distention options: adding slots, modules, drives, robots. Tape libraries may have from 10 to to a greater extent than 100,000 slots, and provide terabytes
Main memory
or petabytes
Main memory
of near-line information. Optical nickelodeon are slightly small solutions, up to 1,000 slots.
Robotic keeping is utilised for backups
Main memory
, and for high-capacity compendium in imaging, medical, and picture industries. Hierarchical keeping management
Main memory
is a to the highest degree well-known bowed dodge of mechanically migrating long-unused register from meteoric trying intervertebral disk keeping to professional person or jukeboxes. If the register are needed, and so are retrieved body to disk.
 This offprint incorporates public arena material
Main memory
from the General Services Administration
Main memory
record "Federal Standard 1037C"
Main memory
.

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