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Computer data storage
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"Memory device" redirects here. For tricks used to aid human memory, see mnemonic.
Main article: Data storage
1 GiB of SDRAM mounted in a personal computer. An example of primary storage.
15 GiB PATA hard disk drive (HDD) from 1999; when connected to a computer it serves as secondary storage.
160 GB SDLT tape cartridge, an example of off-line storage. When used within a robotic tape library, it is classified as tertiary storage instead.
Computer data storage, often called storage or memory, is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.[1]:15-16
The central processing unit (CPU) of a computer is what manipulates data by performing computations. In practice, almost all computers use a storage hierarchy,[1]:468-473 which puts fast but expensive and small storage options close to the CPU and slower but larger and cheaper options farther away. Generally the fast volatile technologies (which lose data when off power) are referred to as "memory", while slower persistent technologies are referred to as "storage".
In the Von Neumann architecture, the CPU consists of two main parts: The control unit and the arithmetic logic unit (ALU). The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and logical operations on data.
Contents
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1 Functionality
2 Data organization and representation
3 Hierarchy of storage
3.1 Primary storage
3.2 Secondary storage
3.3 Tertiary storage
3.4 Off-line storage
4 Characteristics of storage
4.1 Volatility
4.2 Mutability
4.3 Accessibility
4.4 Addressability
4.5 Capacity
4.6 Performance
4.7 Energy use
5 Storage media
5.1 Semiconductor
5.2 Magnetic
5.3 Optical
5.4 Paper
5.5 Other storage media or substrates
6 Related technologies
6.1 Redundancy
6.2 Network connectivity
6.3 Robotic storage
7 See also
7.1 Primary storage topics
7.2 Secondary, tertiary and off-line storage topics
7.3 Data storage conferences
8 References
9 Further reading
Functionality[edit]
Without a significant amount of memory, a computer would merely be able to perform fixed operations and immediately output the result. It would have to be reconfigured to change its behavior. This is acceptable for devices such as desk calculators, digital signal processors, and other specialized devices. Von Neumann machines differ in having a memory in which they store their operating instructions and data.[1]:20 Such computers are more versatile in that they do not need to have their hardware reconfigured for each new program, but can simply be reprogrammed with new in-memory instructions; they also tend to be simpler to design, in that a relatively simple processor may keep state between successive computations to build up complex procedural results. Most modern computers are von Neumann machines.
Data organization and representation[edit]
A modern digital computer represents data using the binary numeral system. Text, numbers, pictures, audio, and nearly any other form of information can be converted into a string of bits, or binary digits, each of which has a value of 1 or 0. The most common unit of storage is the byte, equal to 8 bits. A piece of information can be handled by any computer or device whose storage space is large enough to accommodate the binary representation of the piece of information, or simply data. For example, the complete works of Shakespeare, about 1250 pages in print, can be stored in about five megabytes (40 million bits) with one byte per character.
Data are encoded by assigning a bit pattern to each character, digit, or multimedia object. Many standards exist for encoding (e.g., character encodings like ASCII, image encodings like JPEG, video encodings like MPEG-4).
By adding bits to each encoded unit, redundancy allows the computer to both detect errors in coded data and correct them based on mathematical algorithms. Errors generally occur in low probabilities due to random bit value flipping, or "physical bit fatigue", loss of the physical bit in storage of its ability to maintain a distinguishable value (0 or 1), or due to errors in inter or intra-computer communication. A random bit flip (e.g., due to random radiation) is typically corrected upon detection. A bit, or a group of malfunctioning physical bits (not always the specific defective bit is known; group definition depends on specific storage device) is typically automatically fenced-out, taken out of use by the device, and replaced with another functioning equivalent group in the device, where the corrected bit values are restored (if possible). The cyclic redundancy check (CRC) method is typically used in communications and storage for error detection. A detected error is then retried.
Data compression methods allow in many cases (such as a database) to represent a string of bits by a shorter bit string ("compress") and reconstruct the original string ("decompress") when needed. This utilizes substantially less storage (tens of percents) for many types of data at the cost of more computation (compress and decompress when needed). Analysis of trade-off between storage cost saving and costs of related computations and possible delays in data availability is done before deciding whether to keep certain data compressed or not.
For security reasons certain types of data (e.g., credit-card information) may be kept encrypted in storage to prevent the possibility of unauthorized information reconstruction from chunks of storage snapshots.
Hierarchy of storage[edit]
Main article: Memory hierarchy
This article appears to contradict the article Memory hierarchy. Please see discussion on the linked talk page. (March 2013) (Learn how and when to remove this template message)
Various forms of storage, divided according to their distance from the central processing unit. The fundamental components of a general-purpose computer are arithmetic and logic unit, control circuitry, storage space, and input/output devices. Technology and capacity as in common home computers around 2005.
Generally, the lower a storage is in the hierarchy, the lesser its bandwidth and the greater its access latency is from the CPU. This traditional division of storage to primary, secondary, tertiary and off-line storage is also guided by cost per bit.
In contemporary usage, "memory" is usually semiconductor storage read-write random-access memory, typically DRAM (dynamic RAM) or other forms of fast but temporary storage. "Storage" consists of storage devices and their media not directly accessible by the CPU (secondary or tertiary storage), typically hard disk drives, optical disc drives, and other devices slower than RAM but non-volatile (retaining contents when powered down).[2]
Historically, memory has been called core memory, main memory, real storage or internal memory. Meanwhile, non-volatile storage devices have been referred to as secondary storage, external memory or auxiliary/peripheral storage.
Primary storage[edit]
Main article: Computer memory
Primary storage (also known as main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner.
Historically, early computers used delay lines, Williams tubes, or rotating magnetic drums as primary storage. By 1954, those unreliable methods were mostly replaced by magnetic core memory. Core memory remained dominant until the 1970s, when advances in integrated circuit technology allowed semiconductor memory to become economically competitive.
This led to modern random-access memory (RAM). It is small-sized, light, but quite expensive at the same time. (The particular types of RAM used for primary storage are also volatile, i.e. they lose the information when not powered).
As shown in the diagram, traditionally there are two more sub-layers of the primary storage, besides main large-capacity RAM:
Processor registers are located inside the processor. Each register typically holds a word of data (often 32 or 64 bits). CPU instructions instruct the arithmetic logic unit to perform various calculations or other operations on this data (or with the help of it). Registers are the fastest of all forms of computer data storage.
Processor cache is an intermediate stage between ultra-fast registers and much slower main memory. It was introduced solely to improve the performance of computers. Most actively used information in the main memory is just duplicated in the cache memory, which is faster, but of much lesser capacity. On the other hand, main memory is much slower, but has a much greater storage capacity than processor registers. Multi-level hierarchical cache setup is also commonly used—primary cache being smallest, fastest and located inside the processor; secondary cache being somewhat larger and slower.
Main memory is directly or indirectly connected to the central processing unit via a memory bus. It is actually two buses (not on the diagram): an address bus and a data bus. The CPU firstly sends a number through an address bus, a number called memory address, that indicates the desired location of data. Then it reads or writes the data in the memory cells using the data bus. Additionally, a memory management unit (MMU) is a small device between CPU and RAM recalculating the actual memory address, for example to provide an abstraction of virtual memory or other tasks.
As the RAM types used for primary storage are volatile (uninitialized at start up), a computer containing only such storage would not have a source to read instructions from, in order to start the computer. Hence, non-volatile primary storage containing a small startup program (BIOS) is used to bootstrap the computer, that is, to read a larger program from non-volatile secondary storage to RAM and start to execute it. A non-volatile technology used for this purpose is called ROM, for read-only memory (the terminology may be somewhat confusing as most ROM types are also capable of random access).
Many types of "ROM" are not literally read only, as updates to them are possible; however it is slow and memory must be erased in large portions before it can be re-written. Some embedded systems run programs directly from ROM (or similar), because such programs are rarely changed. Standard computers do not store non-rudimentary programs in ROM, and rather, use large capacities of secondary storage, which is non-volatile as well, and not as costly.
Recently, primary storage and secondary storage in some uses refer to what was historically called, respectively, secondary storage and tertiary storage.[3]
Secondary storage[edit]
A hard disk drive with protective cover removed
It has been suggested that Auxiliary memory be merged into this article. (Discuss) Proposed since November 2017.
Main article: Auxiliary memory
Secondary storage (also known as external memory or auxiliary storage), differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. Per unit, it is typically also two orders of magnitude less expensive than primary storage. Modern computer systems typically have two orders of magnitude more secondary storage than primary storage and data are kept for a longer time there.
In modern computers, hard disk drives are usually used as secondary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds. By contrast, the time taken to access a given byte of information stored in random-access memory is measured in billionths of a second, or nanoseconds. This illustrates the significant access-time difference which distinguishes solid-state memory from rotating magnetic storage devices: hard disks are typically about a million times slower than memory. Rotating optical storage devices, such as CD and DVD drives, have even longer access times. With disk drives, once the disk read/write head reaches the proper placement and the data of interest rotates under it, subsequent data on the track are very fast to access. To reduce the seek time and rotational latency, data are transferred to and from disks in large contiguous blocks.
When data reside on disk, accessing them in large blocks to hide latency offers an opportunity to design efficient external memory algorithms. Sequential or block access on disks is orders of magnitude faster than random access, and many sophisticated paradigms have been developed to design efficient algorithms based upon sequential and block access. Another way to reduce the I/O bottleneck is to use multiple disks in parallel in order to increase the bandwidth between primary and secondary memory.[4]
Some other examples of secondary storage technologies are flash memory (e.g. USB flash drives or keys), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks, and Iomega Zip drives.
The secondary storage is often formatted according to a file system format, which provides the abstraction necessary to organize data into files and directories, providing also additional information (called metadata) describing the owner of a certain file, the access time, the access permissions, and other information.
Most computer operating systems use the concept of virtual memory, allowing utilization of more primary storage capacity than is physically available in the system. As the primary memory fills up, the system moves the least-used chunks (pages) to secondary storage devices (to a swap file or page file), retrieving them later when they are needed. As more of these retrievals from slower secondary storage are necessary, the more the overall system performance is degraded.
Tertiary storage[edit]
See also: Nearline storage and Cloud storage
A large tape library, with tape cartridges placed on shelves in the front, and a robotic arm moving in the back. Visible height of the library is about 180 cm.
Tertiary storage or tertiary memory[5] provides a third level of storage. Typically, it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; such data are often copied to secondary storage before use. It is primarily used for archiving rarely accessed information since it is much slower than secondary storage (e.g. 5–60 seconds vs. 1–10 milliseconds). This is primarily useful for extraordinarily large data stores, accessed without human operators. Typical examples include tape libraries and optical jukeboxes.
When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place it in a drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library.
Tertiary storage is also known as nearline storage because it is "near to online". The formal distinction between online, nearline, and offline storage is:[6]
Online storage is immediately available for I/O.
Nearline storage is not immediately available, but can be made online quickly without human intervention.
Offline storage is not immediately available, and requires some human intervention to become online.
For example, always-on spinning hard disk drives are online storage, while spinning drives that spin down automatically, such as in massive arrays of idle disks (MAID), are nearline storage. Removable media such as tape cartridges that can be automatically loaded, as in tape libraries, are nearline storage, while tape cartridges that must be manually loaded are offline storage.
Off-line storage[edit]
Off-line storage is a computer data storage on a medium or a device that is not under the control of a processing unit.[7] The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction.
Off-line storage is used to transfer information, since the detached medium can be easily physically transported. Additionally, in case a disaster, for example a fire, destroys the original data, a medium in a remote location will probably be unaffected, enabling disaster recovery. Off-line storage increases general information security, since it is physically inaccessible from a computer, and data confidentiality or integrity cannot be affected by computer-based attack techniques. Also, if the information stored for archival purposes is rarely accessed, off-line storage is less expensive than tertiary storage.
In modern personal computers, most secondary and tertiary storage media are also used for off-line storage. Optical discs and flash memory devices are most popular, and to much lesser extent removable hard disk drives. In enterprise uses, magnetic tape is predominant. Older examples are floppy disks, Zip disks, or punched cards.
Characteristics of storage[edit]
A 1 GB DDR RAM module (detail)
Storage technologies at all levels of the storage hierarchy can be differentiated by evaluating certain core characteristics as well as measuring characteristics specific to a particular implementation. These core characteristics are volatility, mutability, accessibility, and addressability. For any particular implementation of any storage technology, the characteristics worth measuring are capacity and performance.
Volatility[edit]
Non-volatile memory retains the stored information even if not constantly supplied with electric power.[8] It is suitable for long-term storage of information. Volatile memory requires constant power to maintain the stored information. The fastest memory technologies are volatile ones, although that is not a universal rule. Since the primary storage is required to be very fast, it predominantly uses volatile memory.
Dynamic random-access memory is a form of volatile memory that also requires the stored information to be periodically reread and rewritten, or refreshed, otherwise it would vanish. Static random-access memory is a form of volatile memory similar to DRAM with the exception that it never needs to be refreshed as long as power is applied; it loses its content when the power supply is lost.
An uninterruptible power supply (UPS) can be used to give a computer a brief window of time to move information from primary volatile storage into non-volatile storage before the batteries are exhausted. Some systems, for example EMC Symmetrix, have integrated batteries that maintain volatile storage for several minutes.
Mutability[edit]
Read/write storage or mutable storage
Allows information to be overwritten at any time. A computer without some amount of read/write storage for primary storage purposes would be useless for many tasks. Modern computers typically use read/write storage also for secondary storage.
Read only storage
Retains the information stored at the time of manufacture, and write once storage (write once read many) allows the information to be written only once at some point after manufacture. These are called immutable storage. Immutable storage is used for tertiary and off-line storage. Examples include CD-ROM and CD-R.
Slow write, fast read storage
Read/write storage which allows information to be overwritten multiple times, but with the write operation being much slower than the read operation. Examples include CD-RW and swayne memory
Accessibility[edit]
Random access
Any location in storage can be accessed at any moment in approximately the same amount of time. Such characteristic is well suited for primary and secondary storage. Most semiconductor memories and disk drives provide random access.
Sequential access
The accessing of pieces of information will be in a serial order, one after the other; therefore the time to access a particular piece of information depends upon which piece of information was last accessed. Such characteristic is typical of off-line storage.
Addressability[edit]
Location-addressable
Each individually accessible unit of information in storage is selected with its numerical memory address. In modern computers, location-addressable storage usually limits to primary storage, accessed internally by computer programs, since location-addressability is very efficient, but burdensome for humans.
File addressable
Information is divided into files of variable length, and a particular file is selected with human-readable directory and file names. The underlying device is still location-addressable, but the operating system of a computer provides the file system abstraction to make the operation more understandable. In modern computers, secondary, tertiary and off-line storage use file systems.
Content-addressable
Each individually accessible unit of information is selected based on the basis of (part of) the contents stored there. Content-addressable storage can be implemented using software (computer program) or hardware (computer device), with hardware being faster but more expensive option. Hardware content addressable memory is often used in a computer's CPU cache.
Capacity[edit]
Raw capacity
The total amount of stored information that a storage device or medium can hold. It is expressed as a quantity of bits or bytes (e.g. 10.4 megabytes).
Memory storage density
The compactness of stored information. It is the storage capacity of a medium divided with a unit of length, area or volume (e.g. 1.2 megabytes per square inch).
Performance[edit]
Latency
The time it takes to access a particular location in storage. The relevant unit of measurement is typically nanosecond for primary storage, millisecond for secondary storage, and second for tertiary storage. It may make sense to separate read latency and write latency (especially for non-volatile memory[8]) and in case of sequential access storage, minimum, maximum and average latency.
Throughput
The rate at which information can be read from or written to the storage. In computer data storage, throughput is usually expressed in terms of megabytes per second (MB/s), though bit rate may also be used. As with latency, read rate and write rate may need to be differentiated. Also accessing media sequentially, as opposed to randomly, typically yields maximum throughput.
Granularity
The size of the largest "chunk" of data that can be efficiently accessed as a single unit, e.g. without introducing additional latency.
Reliability
The probability of spontaneous bit value change under various conditions, or overall failure rate.
Energy use[edit]
Storage devices that reduce fan usage, automatically shut-down during inactivity, and low power hard drives can reduce energy consumption by 90 percent.[9]
2.5-inch hard disk drives often consume less power than larger ones.[10][11] Low capacity solid-state drives have no moving parts and consume less power than hard disks.[12][13][14] Also, memory may use more power than hard disks.[14] Large caches, which are used to avoid hitting memory wall, may also consume a large amount of power.[15]
Storage media[edit]
As of 2011[update], the most commonly used data storage media are semiconductor, magnetic, and optical, while paper still sees some limited usage. Some other fundamental storage technologies have been used in the past or are proposed for development.
Semiconductor[edit]
Semiconductor memory uses semiconductor-based integrated circuits to store information. A semiconductor memory chip may contain millions of tiny transistors or capacitors. Both volatile and non-volatile forms of semiconductor memory exist. In modern computers, primary storage almost exclusively consists of dynamic volatile semiconductor memory or dynamic random-access memory. Since the turn of the century, a type of non-volatile semiconductor memory known as flash memory has steadily gained share as off-line storage for home computers. Non-volatile semiconductor memory is also used for secondary storage in various advanced electronic devices and specialized computers that are designed for them.
As early as 2006, notebook and desktop computer manufacturers started using flash-based solid-state drives (SSDs) as default configuration options for the secondary storage either in addition to or instead of the more traditional HDD.[16][17][18][19][20]
Magnetic[edit]
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Magnetic storage media
Wire (1898)
Tape (1928)
Drum (1932)
Ferrite core (1949)
Hard disk (1956)
Stripe card (1956)
MICR (1956)
Thin film (1962)
CRAM (1962)
Twistor (~1968)
Floppy disk (1969)
Bubble (~1970)
MRAM (1995)
Racetrack (2008)
Magnetic storage uses different patterns of magnetization on a magnetically coated surface to store information. Magnetic storage is non-volatile. The information is accessed using one or more read/write heads which may contain one or more recording transducers. A read/write head only covers a part of the surface so that the head or medium or both must be moved relative to another in order to access data. In modern computers, magnetic storage will take these forms:
Magnetic disk
Floppy disk, used for off-line storage
Hard disk drive, used for secondary storage
Magnetic tape, used for tertiary and off-line storage
Carousel memory (magnetic rolls)
In early computers, magnetic storage was also used as:
Primary storage in a form of magnetic memory, or core memory, core rope memory, thin-film memory and/or twistor memory.
Tertiary (e.g. NCR CRAM) or off line storage in the form of magnetic cards.
Magnetic tape was then often used for secondary storage.
Optical[edit]
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Optical storage media
Blu-ray (2003)
BD-R (2006)
BD-RE (2006)
BD-R XL (2010)
BD-RE XL (2010)
DVD (1995)
DVD-R (1997)
DVD-RW (1999)
DVD+RW (2001)
DVD+R (2002)
DVD+R DL (2004)
DVD-R DL (2005)
Compact disc (1982)
CD-R (1988)
CD-RW (1997)
Discontinued
Microform (1870)
Optical tape (20th century)
Optical disc (20th century)
LaserDisc (1978)
WORM (1979)
UDO (2003)
ProData (2003)
UMD (2004)
HD DVD (2006)
Magneto-optic Kerr effect (1877)
MO disc (1980s)
MiniDisc (1992)
Hi-MD (2004)
Optical Assist
Laser turntable (1986)
Floptical (1991)
Super DLT (1998)
Optical storage, the typical optical disc, stores information in deformities on the surface of a circular disc and reads this information by illuminating the surface with a laser diode and observing the reflection. Optical disc storage is non-volatile. The deformities may be permanent (read only media), formed once (write once media) or reversible (recordable or read/write media). The following forms are currently in common use:[21]
CD, CD-ROM, DVD, BD-ROM: Read only storage, used for mass distribution of digital information (music, video, computer programs)
CD-R, DVD-R, DVD+R, BD-R: Write once storage, used for tertiary and off-line storage
CD-RW, DVD-RW, DVD+RW, DVD-RAM, BD-RE: Slow write, fast read storage, used for tertiary and off-line storage
Ultra Density Optical or UDO is similar in capacity to BD-R or BD-RE and is slow write, fast read storage used for tertiary and off-line storage.
Magneto-optical disc storage is optical disc storage where the magnetic state on a ferromagnetic surface stores information. The information is read optically and written by combining magnetic and optical methods. Magneto-optical disc storage is non-volatile, sequential access, slow write, fast read storage used for tertiary and off-line storage.
3D optical data storage has also been proposed.
Light induced magnetization melting in magnetic photoconductors has also been proposed for high-speed low-energy consumption magneto-optical storage.[22]
Paper[edit]
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Paper data storage media
Antiquity
Writing on papyrus (c. 3000 BCE)
Paper (105 CE)
Modern
Railroad/Transit Punch Photograph (1880s)
Punched card (1890)
Edge-notched card (1896)
Optical mark recognition
Optical character recognition (1929)
Barcode (1948)
Paper data storage, typically in the form of paper tape or punched cards, has long been used to store information for automatic processing, particularly before general-purpose computers existed. Information was recorded by punching holes into the paper or cardboard medium and was read mechanically (or later optically) to determine whether a particular location on the medium was solid or contained a hole. A few technologies allow people to make marks on paper that are easily read by machine—these are widely used for tabulating votes and grading standardized tests. Barcodes made it possible for any object that was to be sold or transported to have some computer readable information securely attached to it.
Other storage media or substrates[edit]
Vacuum tube memory
A Williams tube used a cathode ray tube, and a Selectron tube used a large vacuum tube to store information. These primary storage devices were short-lived in the market, since Williams tube was unreliable and the Selectron tube was expensive.
Electro-acoustic memory
Delay line memory used sound waves in a substance such as mercury to store information. Delay line memory was dynamic volatile, cycle sequential read/write storage, and was used for primary storage.
Optical tape
is a medium for optical storage generally consisting of a long and narrow strip of plastic onto which patterns can be written and from which the patterns can be read back. It shares some technologies with cinema film stock and optical discs, but is compatible with neither. The motivation behind developing this technology was the possibility of far greater storage capacities than either magnetic tape or optical discs.
Phase-change memory
uses different mechanical phases of phase-change material to store information in an X-Y addressable matrix, and reads the information by observing the varying electrical resistance of the material. Phase-change memory would be non-volatile, random-access read/write storage, and might be used for primary, secondary and off-line storage. Most rewritable and many write once optical disks already use phase change material to store information.
Holographic data storage
stores information optically inside crystals or photopolymers. Holographic storage can utilize the whole volume of the storage medium, unlike optical disc storage which is limited to a small number of surface layers. Holographic storage would be non-volatile, sequential access, and either write once or read/write storage. It might be used for secondary and off-line storage. See Holographic Versatile Disc (HVD).
Molecular memory
stores information in polymer that can store electric charge. Molecular memory might be especially suited for primary storage. The theoretical storage capacity of molecular memory is 10 terabits per square inch.[23]
Magnetic photoconductors
store magnetic information which can be modified by low-light illumination.[22]
DNA
stores information in DNA nucleotides. It was first done in 2012 when researchers achieved a rate of 1.28 petabytes per gram of DNA. In March 2017 scientists reported that a new algorithm called a DNA fountain achieved 85% of the theoretical limit, at 215 petabytes per gram of DNA.[24][25][26][27]
Related technologies[edit]
Redundancy[edit]
Main articles: Disk mirroring and RAID
See also: Storage replication
While a group of bits malfunction may be resolved by error detection and correction mechanisms (see above), storage device malfunction requires different solutions. The following solutions are commonly used and valid for most storage devices:
Device mirroring (replication) – A common solution to the problem is constantly maintaining an identical copy of device content on another device (typically of a same type). The downside is that this doubles the storage, and both devices (copies) need to be updated simultaneously with some overhead and possibly some delays. The upside is possible concurrent read of a same data group by two independent processes, which increases performance. When one of the replicated devices is detected to be defective, the other copy is still operational, and is being utilized to generate a new copy on another device (usually available operational in a pool of stand-by devices for this purpose).
Redundant array of independent disks (RAID) – This method generalizes the device mirroring above by allowing one device in a group of N devices to fail and be replaced with the content restored (Device mirroring is RAID with N=2). RAID groups of N=5 or N=6 are common. N>2 saves storage, when comparing with N=2, at the cost of more processing during both regular operation (with often reduced performance) and defective device replacement.
Device mirroring and typical RAID are designed to handle a single device failure in the RAID group of devices. However, if a second failure occurs before the RAID group is completely repaired from the first failure, then data can be lost. The probability of a single failure is typically small. Thus the probability of two failures in a same RAID group in time proximity is much smaller (approximately the probability squared, i.e., multiplied by itself). If a database cannot tolerate even such smaller probability of data loss, then the RAID group itself is replicated (mirrored). In many cases such mirroring is done geographically remotely, in a different storage array, to handle also recovery from disasters (see disaster recovery above).
Network connectivity[edit]
A secondary or tertiary storage may connect to a computer utilizing computer networks. This concept does not pertain to the primary storage, which is shared between multiple processors to a lesser degree.
Direct-attached storage (DAS) is a traditional mass storage, that does not use any network. This is still a most popular approach. This retronym was coined recently, together with NAS and SAN.
Network-attached storage (NAS) is mass storage attached to a computer which another computer can access at file level over a local area network, a private wide area network, or in the case of online file storage, over the Internet. NAS is commonly associated with the NFS and CIFS/SMB protocols.
Storage area network (SAN) is a specialized network, that provides other computers with storage capacity. The crucial difference between NAS and SAN, is that NAS presents and manages file systems to client computers, while SAN provides access at block-addressing (raw) level, leaving it to attaching systems to manage data or file systems within the provided capacity. SAN is commonly associated with Fibre Channel networks.
Robotic storage[edit]
Large quantities of individual magnetic tapes, and optical or magneto-optical discs may be stored in robotic tertiary storage devices. In tape storage field they are known as tape libraries, and in optical storage field optical jukeboxes, or optical disk libraries per analogy. Smallest forms of either technology containing just one drive device are referred to as autoloaders or autochangers.
Robotic-access storage devices may have a number of slots, each holding individual media, and usually one or more picking robots that traverse the slots and load media to built-in drives. The arrangement of the slots and picking devices affects performance. Important characteristics of such storage are possible expansion options: adding slots, modules, drives, robots. Tape libraries may have from 10 to more than 100,000 slots, and provide terabytes or petabytes of near-line information. Optical jukeboxes are somewhat smaller solutions, up to 1,000 slots.
Robotic storage is used for backups, and for high-capacity archives in imaging, medical, and video industries. Hierarchical storage management is a most known archiving strategy of automatically migrating long-unused files from fast hard disk storage to libraries or jukeboxes. If the files are needed, they are retrieved back to disk.
See also[edit]
Wikimedia Commons has media related to Computer memory.
Wikiversity has learning resources about Computer data storage
Primary storage topics[edit]
Aperture (computer memory)
Dynamic random-access memory (DRAM)
Memory latency
Mass storage
Memory cell (disambiguation)
Memory management
Dynamic memory allocation
Memory leak
Virtual memory
Memory protection
Page address register
Static random-access memory (SRAM)
Stable storage
Secondary, tertiary and off-line storage topics[edit]
Cloud storage
Data deduplication
Data proliferation
Data storage tag used for capturing research data
File system
List of file formats
Flash memory
Information repository
Removable media
Solid-state drive
Spindle
Virtual tape library
Wait state
Write buffer
Write protection
Noise-predictive maximum-likelihood detection
Object(-based) storage
Data storage conferences[edit]
Storage Networking World
Storage World Conference
USENIX Conference on File and Storage Technologies
References[edit]
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
^ Jump up to: a b c Patterson, David A.; Hennessy, John L. (2005). Computer Organization and Design: The Hardware/Software Interface (3rd ed.). Amsterdam: Morgan Kaufmann Publishers. ISBN 1-55860-604-1. OCLC 56213091.
Jump up ^ Storage as defined in Microsoft Computing Dictionary, 4th Ed. (c)1999 or in The Authoritative Dictionary of IEEE Standard Terms, 7th Ed., (c) 2000.
Jump up ^ "Primary Storage or Storage Hardware" (shows usage of term "primary storage" meaning "hard disk storage") Archived 10 September 2008 at the Wayback Machine.. Searchstorage.techtarget.com (2011-06-13). Retrieved on 2011-06-18.
Jump up ^ J. S. Vitter, Algorithms and Data Structures for External Memory Archived 4 January 2011 at the Wayback Machine., Series on Foundations and Trends in Theoretical Computer Science, now Publishers, Hanover, MA, 2008, ISBN 978-1-60198-106-6.
Jump up ^ A thesis on Tertiary storage Archived 27 September 2007 at the Wayback Machine.. (PDF) . Retrieved on 2011-06-18.
Jump up ^ Pearson, Tony (2010). "Correct use of the term Nearline". IBM Developerworks, Inside System Storage. Retrieved 2015-08-16.
Jump up ^ National Communications System (1996). "Federal Standard 1037C – Telecommunications: Glossary of Telecommunication Terms". General Services Administration. FS-1037C. Archived from the original on 24 October 2011. Retrieved 8 October 2007. See also article Federal Standard 1037C.
^ Jump up to: a b "A Survey of Software Techniques for Using Non-Volatile Memories for Storage and Main Memory Systems Archived 25 December 2015 at the Wayback Machine.", IEEE TPDS, 2015
Jump up ^ Energy Savings Calculator Archived 21 December 2008 at the Wayback Machine. and Fabric website
Jump up ^ Mike Chin (8 March 2004). "IS the Silent PC Future 2.5-inches wide?". Archived from the original on 20 July 2008. Retrieved 2 August 2008.
Jump up ^ Mike Chin (18 September 2002). "Recommended Hard Drives". Archived from the original on 5 September 2008. Retrieved 2 August 2008.
Jump up ^ Super Talent's 2.5" IDE Flash hard drive – The Tech Report – Page 13 Archived 26 January 2012 at the Wayback Machine.. The Tech Report. Retrieved on 2011-06-18.
Jump up ^ Power Consumption – Tom's Hardware : Conventional Hard Drive Obsoletism? Samsung's 32 GB Flash Drive Previewed. Tomshardware.com (2006-09-20). Retrieved on 2011-06-18.
^ Jump up to: a b Aleksey Meyev (23 April 2008). "SSD, i-RAM and Traditional Hard Disk Drives". X-bit labs. Archived from the original on 18 December 2008.
Jump up ^ "A Survey of Architectural Techniques For Improving Cache Power Efficiency Archived 8 January 2016 at the Wayback Machine.", SUSCOM, 2014
Jump up ^ New Samsung Notebook Replaces Hard Drive With Flash Archived 30 December 2010 at the Wayback Machine.. ExtremeTech (2006-05-23). Retrieved on 2011-06-18.
Jump up ^ Welcome to TechNewsWorld Archived 18 March 2012 at the Wayback Machine.. Technewsworld.com. Retrieved on 2011-06-18.
Jump up ^ Mac Pro – Storage and RAID options for your Mac Pro Archived 6 June 2013 at the Wayback Machine.. Apple (2006-07-27). Retrieved on 2011-06-18.
Jump up ^ MacBook Air – The best of iPad meets the best of Mac Archived 27 May 2013 at the Wayback Machine.. Apple. Retrieved on 2011-06-18.
Jump up ^ MacBook Air Replaces the Standard Notebook Hard Disk for Solid State Flash Storage Archived 23 August 2011 at the Wayback Machine.. News.inventhelp.com (2010-11-15). Retrieved on 2011-06-18.
Jump up ^ The DVD FAQ Archived 22 August 2009 at the Wayback Machine. is a comprehensive reference of DVD technologies.
^ Jump up to: a b Náfrádi, Bálint (24 November 2016). "Optically switched magnetism in photovoltaic perovskite CH3NH3(Mn:Pb)I3". Nature Communications. 7: 13406. doi:10.1038/ncomms13406. PMC 5123013  . Archived from the original on 28 November 2016.
Jump up ^ New Method Of Self-assembling Nanoscale Elements Could Transform Data Storage Industry Archived 1 March 2009 at the Wayback Machine.. Sciencedaily.com (2009-03-01). Retrieved on 2011-06-18.
Jump up ^ Yong, Ed. "This Speck of DNA Contains a Movie, a Computer Virus, and an Amazon Gift Card". The Atlantic. Archived from the original on 3 March 2017. Retrieved 3 March 2017.
Jump up ^ "Researchers store computer operating system and short movie on DNA". Phys.org. Archived from the original on 2 March 2017. Retrieved 3 March 2017.
Jump up ^ "DNA could store all of the world's data in one room". Science Magazine. 2 March 2017. Archived from the original on 2 March 2017. Retrieved 3 March 2017.
Jump up ^ Erlich, Yaniv; Zielinski, Dina (2 March 2017). "DNA Fountain enables a robust and efficient storage architecture". Science. 355 (6328): 950–954. doi:10.1126/science.aaj2038. Archived from the original on 2 March 2017. Retrieved 3 March 2017.
Further reading[edit]
Goda, K.; Kitsuregawa, M. (2012). "The History of Storage Systems". Proceedings of the IEEE. 100: 1433–1440. doi:10.1109/JPROC.2012.2189787.
Memory & Storage, Computer History Museum
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.223 Wylde chamber
From Wikipedia, the free encyclopedia
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Diagram of an AR type rifle showing the location of the chamber
A .223 Wylde chamber is used on .223 caliber rifle barrels to allow them to safely fire either .223 Remington or 5.56x45mm NATO ammunition.
Contents
[hide]
1 History and rationale
1.1 Chamber dimensions
2 References
3 External links
History and rationale[edit]
In 1957 during research into development of a military .22 caliber rifle the Remington .222 Special was created. Due to there being several .222 caliber cartridges under development, the .222 Special was renamed to .223 Remington. The cartridge became the standard for the US Army in 1962 as the M193 Cartridge.[1]
In 1972 Fabrique Nationale (FN) created a new class of ammunition for NATO. It was based on the .223 Remington cartridge which was being used by the US Army that had greater range and effectiveness. The first iteration of this ammunition was type designated SS109.[2]
Due to differences in the chamber dimensions between the .223 Rem and 5.56 x 45mm NATO (SS109, M-855), the two cannot be used interchangeably, however .223 Remington can safely be fired from firearms chambered for 5.56 mm NATO.[1] As most rifle makers moved to support the 5.56mm NATO specification the reduced accuracy was considered a problem.[3]
Chamber dimensions[edit]
Bill Wylde of Greenup, Illinois compared the two cartridges and changed the chamber of the rifle's barrel to a specification which is called 223 Wylde chamber or 22 Wylde chamber. The chamber is made with the external dimensions and lead angle as found in the military 5.56×45mm NATO cartridge and the 0.2240 inch free bore diameter as found in the civilian SAAMI .223 Remington cartridge.[4] Rifles with a .223 Wylde chamber will typically accept both .223 Remington and 5.56×45mm NATO ammunition.[4] Note that while the .223 Remington and 5.56×45mm NATO chambers have slightly different dimension, the cartridges themselves are identical in dimension.[4] The chamber dimension differences are often confused with the cartridge dimensions and so it is often erroneously thought that the cartridges have different dimensions. The cartridges are loaded to different pressure levels (with the 5.56 being greater), however.[5] (The NATO dimensions offset the higher pressure with a longer throat - often confusing some to think the cartridge itself is longer). This chamber allows the use of both pressure levels safely while also increasing accuracy potential across the range of potential pressures.[3]
Wylde's hybrid chamber was designed to exploit the accuracy advantages of the .223 Remington chambering without problems concerning over pressure or compromising the functional reliability of semi-auto firearms like the AR-15 family when using 5.56×45mm NATO military ammunition.[6] Coincidentally, it shoots the relatively long and heavy 80-grain (5.18 g) bullets commonly used in the Sport Rifle Competition very well and is one of the preferred chambers for that use.[7] The Wylde chamber is used by rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels, and upper receivers.[8]
References[edit]
^ Jump up to: a b Barnes, Frank C. (19 December 2014). Cartridges of the World: A Complete and Illustrated Reference for Over 1500 Cartridges. Iola, Wisconsin: "F+W Media, Inc.". p. 88. ISBN 978-1-4402-4265-6.
Jump up ^ Walter, John (25 March 2006). Rifles of the World. Iola, Wisconsin: Krause Publications. p. 124. ISBN 0-89689-241-7.
^ Jump up to: a b Sweeney, Patrick (23 February 2010). Gunsmithing - The AR-15. Iola, Wisconsin: Gun Digest Books. pp. 49, 139. ISBN 1-4402-1457-3.
^ Jump up to: a b c Fitzpatrick, Brad (29 October 2015). "Clearing the Caliber Confusion: .223 Wylde vs. 5.56 NATO". AWC.
Jump up ^ McAdams, John (12 May 2014). "The dangers of mixing up 5.56x45mm NATO and .223 Remington rounds". Multi Briefs.
Jump up ^ Muramatsu, Kevin (21 November 2014). Gun Digest Guide to Customizing Your AR-15. Iola, Wisconsin: "F+W Media, Inc.". p. 231. ISBN 978-1-4402-4279-3.
Jump up ^ Wormley, Stanton (14 August 2014). "The AR-15 for Home Defense: Reliability". American Rifleman.
Jump up ^ Towsley, Bryce (17 June 2014). "JP Enterprises JP-15". Shooting Illustrated.
External links[edit]
Brownells Tech Tip: AR-15 5.56/.223/.223 Wylde
Chamber Choices ('Guns Magazine')
Retrieved from "https://en.wikipedia.org/w/index.php?title=.223_Wylde_chamber&oldid=804931820"
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5.56 × 45 mm NATO
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Article 8 of the European Convention on Human Rights
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Article 8 of the European Convention on Human Rights provides a right to respect for one's "private and family life, his home and his correspondence", subject to certain restrictions that are "in accordance with law" and "necessary in a democratic society". The European Convention on Human Rights (ECHR) (formally the Convention for the Protection of Human Rights and Fundamental Freedoms) is an international treaty to protect human rights and fundamental freedoms in Europe.
Contents
[hide]
1 Right
1.1 Private life
1.2 Family life
1.3 Home
2 Case law
2.1 Cases involving LGBT rights
3 Violation of the convention by mass surveillance
4 See also
5 Notes
6 External links
Right[edit]
Article 8 – Right to respect for private and family life
1. Everyone has the right to respect for his private and family life, his home and his correspondence.
2. There shall be no interference by a public authority with the exercise of this right except such as is in accordance with the law and is necessary in a democratic society in the interests of national security, public safety or the economic well-being of the country, for the prevention of disorder or crime, for the protection of health or morals, or for the protection of the rights and freedoms of others.
Article 8 is considered to be one of the Convention's most open-ended provisions.[1]
Private life[edit]
For better understanding of perception of "private life" case law should be analyzed. In Niemietz v. Germany, the Court held that it "does not consider it possible or necessary to attempt an exhaustive definition of the notion of 'private life'. However, it would be too restrictive to limit the notion to an 'inner circle' in which the individual may live his own personal life as he choose and to exclude therefrom entirely the outside world not encompassed within that circle. Respect for private life must also compromise to a certain degree the right to establish and develop relationship and develop relationship with other human beings."
Family life[edit]
In X, Y, and Z v. UK, the Court recalls that "the notion of 'family life' in Article 8 is not confined solely so the families based on marriage and may encompass other de facto relationship. When deciding whether a relationship can be said to amount to 'family life', a number of factors may be relevant, including whether the couples live together, the length of their relationship and whether they have demonstrated their commitment to each other by having children together or by any other means."
Home[edit]
In Niemietz v Germany case the Court gave broader meaning to the 'home' notion including professional/business premises such as a lawyer's office.[2]
Case law[edit]
Article 8 clearly provides a right to be free of unlawful searches, but the Court has given the protection for "private and family life" that this article provides a broad interpretation, taking for instance that prohibition of private consensual homosexual acts violates this article. This may be compared to the jurisprudence of the United States Supreme Court, which has also adopted a somewhat broad interpretation of the right to privacy. Furthermore, Article 8 sometimes comprises positive obligations: whereas classical human rights are formulated as prohibiting a State from interfering with rights, and thus not to do something (e.g. not to separate a family under family life protection), the effective enjoyment of such rights may also include an obligation for the State to become active, and to do something (e.g. to enforce access for a divorced father to his child).
Golder v. United Kingdom (1975) 1 EHRR 524 – A prisoner requested a lawyer because he said he wanted to sue a guard for defamation. Access was denied. This violated the right to a fair trial (Article 6 ECHR) and client confidentiality.
Silver v. United Kingdom (1981) 3 EHRR 475 – Censorship of a prisoner's correspondence regarding conditions in prison breached Article 8.
R v Brown [1994] 1 AC 212 – Article 8 was deemed not to "[invalidate] a law which forbids violence which is intentionally harmful to body and mind" (specifically, assault occasioning actual bodily harm as part of consensual sadomasochistic sex acts) by the UK House of Lords.[3]
Rotaru v. Romania [2000] ECHR 192 – Public information that is systematically collected and stored in files held by a state or its agents falls within the scope of private life.[4]
Pretty v. United Kingdom [2002] Article 8 extends to protect the right to die. Like with articles 9, 10 and 11, it can be interfered with provided there's valid justification, as there was in Pretty.
Mosley v News Group Newspapers [2008] EWHC 1777 (QB) — Per Eady J, equitable breach of confidence is extended to protect Art. 8 rights.
S and Marper v United Kingdom [2008] ECHR 1581 – Retention of DNA information in respect of persons arrested but not convicted of an offence was held to breach Article 8.
A, B and C v Ireland [2010] ECHR 2032 – Article 8 does not confer a "right to abortion", but the Republic of Ireland breached it by making it difficult for a woman to establish whether she qualifies for a legal abortion.
Gillan and Quinton v United Kingdom [2010] ECHR 28 – Stop and search powers granted to police under ss. 44–47 of the Terrorism Act 2000 were neither sufficiently circumscribed nor subject to adequate legal safeguards against abuse. As such, the Court found the powers not to be "in accordance with the law", in violation of Article 8.[5]
Birmingham City Council v Clue (2010) EWCA Civ 460 29/4/2010 – A challenge to the decision to refuse to provide Ms Clue and her family with essential support pending the UK Border Agency's determination of her application for indefinite leave to remain in the UK. In a ground-breaking decision of the Court of Appeal, the judgment extends the scope of community care provision for families subject to immigration control who seek to remain in the UK on Article 8 ECHR grounds.
Plantagenet Alliance v Ministry of Justice and others (2014) EWHC 1662 – Article 8 did not entitle modern-day descendants of the House of Plantagenet to be consulted on the place of re-interment of Richard III.
Zakharov v. Russia (2015) – The Court examined Russian surveillance legislation in abstracto, finding unanimously that the existence of inadequate legislation and its application in practice themselves amounted to a violation of the applicant's rights under Article 8.[6]
The Northern Ireland Human Rights Commission's Application [2015] NIQB 96 – Northern Ireland's criminalization of abortion in cases of fatal foetal abnormality, rape or incest declared incompatible with Article 8[7]
The notion of private life in the Article 8 is also interpreted as including some duty of environmental protection.[8]
Cases involving LGBT rights[edit]
The following cases deal with the applicability of Article 8 to issues related to LGBT people including the recognition of same-sex marriage, laws prohibiting sodomy, and access to health services for transgender people.
Modinos v. Cyprus (1993) – Ruling invalidating Section 171 of the Criminal Code of Cyprus under which male homosexual acts were banned, finding that there had been a breach under Article 8 of the applicant's right to respect for private life.
Smith and Grady v United Kingdom (1999) 29 EHRR 493 – The investigation into and subsequent discharge of personnel from the Royal Navy on the basis of sexual orientation was a breach of the right to a private life under Article 8.
Van Kück v. Germany [2003] ECHR 285 – Inadequate access to a fair hearing in a case involving reimbursement by a private medical insurer for costs of hormone replacement therapy and gender reassignment surgery by a transsexual woman, where undue burden had been placed upon her to prove the medical necessity of the treatment, was a violation under Article 8 and Article 6 § 1.[9]
Oliari and Others v Italy (2015) – Italy violated Article 8 by not providing legal recognition to same-sex couples.
Violation of the convention by mass surveillance[edit]
Mass surveillance, such as by the programs revealed in Edward Snowden's global surveillance disclosures, is often accused of violating the 8th article of the European Convention on Human Rights.[10][11][12][13][14]
A 2014 report to the UN General Assembly by the United Nations' top official for counter-terrorism and human rights condemned mass electronic surveillance as a clear violation of core privacy rights guaranteed by multiple treaties and conventions and makes a distinction between "targeted surveillance" – which "depend[s] upon the existence of prior suspicion of the targeted individual or organization" – and "mass surveillance", by which "states with high levels of Internet penetration can [] gain access to the telephone and e-mail content of an effectively unlimited number of users and maintain an overview of Internet activity associated with particular websites". Only targeted interception of traffic and location data in order to combat serious crime, including terrorism, is justified, according to a decision by the European Court of Justice.[15]
See also[edit]
Article 10 ECHR
Entick v Carrington
Semayne's case
Notes[edit]
Jump up ^ Elizabeth Wicks; Bernadette Rainey; Clare Ovey (12 June 2014). Jacobs, White and Ovey: the European Convention on Human Rights. Oxford University Press. p. 334. ISBN 978-0-19-965508-3.
Jump up ^ Mowbray, Alastair (2007). Cases and Materials on the European Convention on Human Rights. Oxford University Press. ISBN 978-0-19-920674-2.
Jump up ^ "R v Brown [1993] UKHL 19(11 March 1993)". Retrieved 8 March 2016.
Jump up ^ Rotaru v. Romania (2000) ECHR 28341/95, paras. 43–44: "Moreover, public information can fall within the scope of private life where it is systematically collected and stored in files held by the authorities. That is all the truer where such information concerns a person's distant past ... In the Court's opinion, such information, when systematically collected and stored in a file held by agents of the State, falls within the scope of 'private life' for the purposes of Article 8(1) of the Convention."
Jump up ^ "Gillan and Quinton v United Kingdom". Retrieved 9 February 2011.
Jump up ^ "HUDOC Press Release: Arbitrary and abusive secret surveillance of mobile telephone communications in Russia". hudoc.echr.coe.int. 2015-12-04. Retrieved 2016-04-15.
Jump up ^ The Northern Ireland Human Rights Commission's Application [2015] NIHC 96 (QB), [2015] NIQB 96 (30 November 2015), High Court (Northern Ireland)
Jump up ^ Antoine Buyse (2009-04-08). "Nuisance From Outside the Prison". Echrblog.blogspot.com. Retrieved 2013-09-01.
Jump up ^ "Courts' refusal to order reimbursement of top-up costs of transsexual's gender re-assignment treatment". Archived from the original on 7 August 2011. Retrieved 9 January 2010.
Jump up ^ Harding, Luke (26 January 2015). "Mass surveillance is fundamental threat to human rights, says European report". The Guardian. Retrieved 2 January 2017.
Jump up ^ Greenwald, Glenn. "UN Report Finds Mass Surveillance Violates International Treaties and Privacy Rights". The Intercept. Retrieved 2 January 2017.
Jump up ^ McCarthy, Kieren. "European human rights court rules mass surveillance illegal". The Register.
Jump up ^ "UN Says Mass Surveillance Violates Human Rights". Techdirt. Retrieved 2 January 2017.
Jump up ^ "Does government spying violate human rights law? - Right Now". Right Now. 11 March 2014. Retrieved 2 January 2017.
Jump up ^ Asthana, Anushka (25 December 2016). "Revealed: British councils used Ripa to secretly spy on public". The Guardian. Retrieved 2 January 2017.
External links[edit]
A guide to the implementation of Article 8 of the European Convention on Human Rights (PDF)
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