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Encyclopedia > Computer data storage
1 GiB of SDRAM mounted in a personal computer. An example of primary storage.
40 GB hard disk drive (HDD); 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, computer memory, and often casually storage or memory refer to computer components, devices and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer, that of information retention. It is one of the fundamental components of all modern computers, and coupled with a central processing unit (CPU, a processor), implements the basic computer model used since the 1940s. Image File history File links Download high-resolution version (1600x1067, 614 KB) DDR2 Ram in socket File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Computer storage ... Image File history File links Download high-resolution version (1600x1067, 614 KB) DDR2 Ram in socket File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Computer storage ... A gibibyte is a unit of information or computer storage. ... SDRAM means synchronous dynamic random access memory which is a type of solid state computer memory. ... Image File history File links Seagate_Hard_Disk. ... Image File history File links Seagate_Hard_Disk. ... This article is about the unit of measurement. ... Image File history File links Size of this preview: 745 × 600 pixelsFull resolution‎ (800 × 644 pixels, file size: 63 KB, MIME type: image/jpeg)Moved image to a different wikiname. ... Image File history File links Size of this preview: 745 × 600 pixelsFull resolution‎ (800 × 644 pixels, file size: 63 KB, MIME type: image/jpeg)Moved image to a different wikiname. ... A Super DLT I tape cartridge Digital Linear Tape (DLT) (previously called CompacTape) is a magnetic tape data storage technology developed by Digital Equipment Corporation from 1984 onwards. ... A tape silo being loaded. ... This article is about the machine. ... A recording medium is a physical material that holds information expressed in any of the existing recording formats. ... In Computer Science, data is often distinguished from code, though both are represented in modern computers as binary strings. ... CPU redirects here. ...


In contemporary usage, memory usually refers to a form of semiconductor storage known as random access memory (RAM) and sometimes other forms of fast but temporary storage. Similarly, storage today more commonly refers to mass storage - optical discs, forms of magnetic storage like hard disks, and other types slower than RAM, but of a more permanent nature. Historically, memory and storage were respectively called primary storage and secondary storage. A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ... RAM redirects here. ... In computing, mass storage refers to storage of large amounts of information in a persisting and machine-readable fashion. ... “Optical media” redirects here. ... Magnetic storage is a term from engineering referring to the storage of data on a magnetised medium. ... Typical hard drives of the mid-1990s. ...


The contemporary distinctions are helpful, because they are also fundamental to the architecture of computers in general. As well, they reflect an important and significant technical difference between memory and mass storage devices, which has been blurred by the historical usage of the term storage. Nevertheless, this article uses the traditional nomenclature.

Contents

Purpose of storage

Various forms of storage, based on various natural phenomena, have been invented. So far, no practical universal storage medium exists, and all forms of storage have some drawbacks. Therefore a computer system usually contains several kinds of storage, each with an individual purpose.


A digital computer represents information 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 whose storage space is large enough to accommodate the binary representation of the piece of information, or simply data. For example, using eight million bits, or about one megabyte, a typical computer could store a small novel. ... The binary numeral system, or base-2 number system, is a numeral system that represents numeric values using two symbols, usually 0 and 1. ... This article is about the unit of information. ... For the computer industry magazine, see Byte (magazine). ... In Computer Science, data is often distinguished from code, though both are represented in modern computers as binary strings. ... ReBoot character, see Megabyte (ReBoot). ...


Traditionally the most important part of every computer is the central processing unit (CPU, or simply a processor), because it actually operates on data, performs any calculations, and controls all the other components. CPU redirects here. ...


Processor without a memory would not be a computer, merely a simple digital signal processing device, able to perform a fixed operation and immediately output the result. It would have to be re-built to change its behaviour, like in case of a calculator. The ability to store and change both instructions and data, the important von Neumann's idea, makes computers versatile. It basically introduces the concept of computer programming, as opposed to re-building the hardware. Digital signal processing (DSP) is the study of signals in a digital representation and the processing methods of these signals. ... For other uses, see Calculator (disambiguation). ... In computer science, an instruction typically refers to a single operation of a processor within a computer architecture. ... 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. ... Programming redirects here. ...


A computer can exist that uses the single type of storage for all the data. However, to provide acceptable computer performance at a lower cost, computers usually use a whole storage hierarchy. The traditional division of storage to primary, secondary, tertiary and off-line storage is based on the speed and cost per bit. The lower a storage is in hierarchy, the bigger is its distance from the CPU. The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. ...


Hierarchy of storage

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.

Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... CPU redirects here. ... ALU redirects here. ... A control unit is the part of a CPU or other device that directs its operation. ... Energy Input: The energy placed into a reaction. ... The home computer is a consumer-friendly word for the second generation of microcomputers (the technical term that was previously used), entering the market in 1977 and becoming common during the 1980s. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ...

Primary storage

Direct links to this section: Primary storage, Main memory.

Primary storage, presently known as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them. Any data actively operated on is also stored there in uniform manner. 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. ... Primary storage is a category of computer storage, often called main memory. ...


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, which was still rather cumbersome. Undoubtedly, a revolution was started with the invention of a transistor, that soon enabled then-unbelievable miniaturization of electronic memory via solid-state silicon chip technology. Computing hardware has been an important component of the process of calculation and computer data storage since it became useful for numerical values to be processed and shared. ... Mercury memory of UNIVAC I (1951) Delay line memory was a form of computer memory used on some of the earliest digital computers, such as the EDSAC and UNIVAC I. // The basic concept of the delay line originated with World War II radar research, as a system to reduce clutter... The Williams tube or (more accurately) the Williams-Kilburn tube (after Freddie Williams and coworker Tom Kilburn), developed about 1946 or 1947, was a cathode ray tube used to store electronic data. ... hi i am cool xbox is all most as cool as me hi again ... A 16×16 cm area core memory plane of 128×128 bits, i. ... Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. ... Solid state may refer to: In computing: Solid state devices are data storage device components that uses memory chips, such as SDRAMs, to store data. ... An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. ...


This led to a modern random access memory (RAM). It is small-sized, light, but quite expensive at the same time. It also loses the stored information when not electrically powered—it is volatile. RAM redirects here. ... Volatile memory refers to computer memory that must be powered to maintain its data. ...


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 every processor. Each of the registers holds only several bits of data, for example 64 bits. The arithmetic and logic unit uses this data to carry out the current instruction. Registers are technically the fastest of all forms of computer data storage, being switching transistors integrated on the CPU's chip, and functioning as electronic "flip-flops".
  • Processor cache is an intermediate stage between ultra-fast registers and much slower main memory. It's introduced solely to increase performance of the computer. 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 it is much slower, but much larger 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 connected to the CPU via a memory bus, or front side bus, a high-speed digital "superhighway". It is actually comprised of 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 itself 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. In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to frequently used values—typically, these values are involved in multiple expression evaluations occurring within a small region on the program. ... In computing, word is a term for the natural unit of data used by a particular computer design. ... ALU redirects here. ... An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. ... 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. ... Diagram of a CPU memory cache A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. ... The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. ... In personal computers, the front side bus (FSB) or system bus is the physical bi-directional bus that carries all electronic signal information between the central processing unit (CPU) and the northbridge. ... An address bus is (part of) a computer bus, used by CPUs or DMA-capable units for communicating the physical addresses of computer memory elements/locations that the requesting unit wants to access (read/write). ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers. ... In computer science, a memory address is a unique identifier for a memory location at which a CPU or other device can store a piece of data for later retrieval. ... This 68451 MMU could be used with the Motorola 68010 MMU, short for memory management unit or sometimes called paged memory management unit as PMMU, is a class of computer hardware components responsible for handling memory accesses requested by the CPU. Among the functions of such devices are the translation... The program thinks it has a large range of contiguous addresses; but in reality the parts it is currently using are scattered around RAM, and the inactive parts are saved in a disk file. ...


Any data stored in the RAM is cleared as soon as it receives no electricity. Therefore, if a computer contained only RAM, the CPU would not have a source to read any instructions from in order to start the computer. Hence, a non-volatile primary storage containing a small startup program (BIOS) is used, both to perform a hardware power-on self test, and to bootstrap, that is, to read the larger program from non-volatile secondary storage to RAM and execute it. A non-volatile technology used for this purpose is commonly, but somewhat confusingly, called read-only memory (ROM). Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... For other uses, see Bios. ... Power-on Self Test (POST) is the common term for a computers pre-boot sequence. ... In computing, Bootstrapping refers to a process where a simple system activates another more complicated system that serves the same purpose. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ...


Current ROM implementation, an EEPROM, is not literally read only, an update is possible; however it is slow and memory is completely erased before it can be re-written. Some embedded systems work without RAM, exclusively on ROM, because their programs and data are rarely changed. Standard computers do not store non-rudimentary programs in ROM, rather use large capacities of secondary storage, which is non-volatile as well, and not as costly. An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ... What is an Embedded System? Electronic devices that incorporate a computer(usually a microprocessor) within their implementation. ...


Recently, primary storage and secondary storage in some uses refer to what was historically called, respectively, secondary storage and tertiary storage.[1]


Secondary storage

A hard disk drive with protective cover removed.
Direct link to this section: Secondary storage.

Secondary storage, or storage in popular usage, 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 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 an order of magnitude less expensive than primary storage. Consequently, modern computer systems typically have an order of magnitude more secondary storage than primary storage and data is kept for a longer time there. Image File history File links Mergefrom. ... In computing, mass storage refers to storage of large amounts of information in a persisting and machine-readable fashion. ... Image File history File links Mergefrom. ... A mass-storage device is usually a very high capacity computer storage medium that is an order of magnitude less costly than a hard disk or other primary storage media. ... Image File history File links Hard_disk_platter_reflection. ... Image File history File links Hard_disk_platter_reflection. ... In computer storage, secondary storage, or external memory, is computer memory that is not directly accessible to the central processing unit of a computer, requiring the use of computers input/output channels. ... Energy Input: The energy placed into a reaction. ... In computing, a buffer is a region of memory used to temporarily hold output or input data, comparable to buffers in telecommunication. ...


In modern computers, hard disks 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 thousand-millionths of a second, or nanoseconds. This illustrates the very 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, typically have somewhat longer access times than hard disks. Typical hard drives of the mid-1990s. ... In computing, sound reproduction, and video, an optical disc is flat, circular, usually polycarbonate disc whereon data is stored. ... CD redirects here. ... DVD (also known as Digital Versatile Disc or Digital Video Disc) is a popular optical disc storage media format. ...


Some other examples of secondary storage technologies are: flash memory (e.g. USB sticks or keys), floppy disks, magnetic tape, paper tape, punch cards, standalone RAM disks, and Zip drives. A USB flash drive. ... Jumpdrive redirects here; for the unrelated science fiction concept, see Jump drive A USB flash drive, shown with a 24 mm U.S. quarter coin for scale. ... A floppy disk is a data storage device that is composed of a disk of thin, flexible (floppy) magnetic storage medium encased in a square or rectangular plastic shell. ... Magnetic tape has been used for data storage for over 50 years. ... A roll of punched tape Punched tape is an old-fashioned form of data storage, consisting of a long strip of paper in which holes are punched to store data. ... Punched cards (or Hollerith cards, or IBM cards), are pieces of stiff paper that contain digital information represented by the presence or absence of holes in predefined positions. ... 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. ... Iomega ZIP-100 Drive Logo An internal Zip drive. ...


The secondary storage is often formatted according to a filesystem 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. See Filing system for this term as it is used in libraries and offices In computing, a file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. ... A file in a computer system is a stream (sequence) of bits stored as a single unit, typically in a file system on disk or magnetic tape. ... This article is about the computing term. ... Metadata is data about data. ...


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. An operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. ... The program thinks it has a large range of contiguous addresses; but in reality the parts it is currently using are scattered around RAM, and the inactive parts are saved in a disk file. ... In a context of computer virtual memory, a page, memory page, or virtual page is a fixed-length block of main memory, that is contiguous in both physical memory addressing and virtual memory addressing. ... Virtual memory is intended to help the programmer by taking care of some memory housekeeping duties. ... In computer operating systems, paging memory allocation algorithms divide computer memory into small partitions, and allocates memory using a page as the smallest building block. ...


Tertiary storage

Large tape library. Tape cartridges placed on shelves in the front, robotic arm moving in the back. Visible height of the library is about 180 cm.

Tertiary storage or tertiary memory,[2] is a system where a robotic arm will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands. It is primarily used for archival of 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. Image File history File links Size of this preview: 450 × 600 pixelsFull resolution‎ (768 × 1,024 pixels, file size: 109 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 450 × 600 pixelsFull resolution‎ (768 × 1,024 pixels, file size: 109 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... A tape silo being loaded. ... A tape silo being loaded. ... An optical jukebox or autochanger is a computer device used for massive data storage. ...


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. This article is about computing. ... An industrial robot is officially defined by ISO[1] as an automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes. ...


Off-line storage

Off-line storage, also known as disconnected storage, is a computer data storage on a medium or a device that is not under the control of a processing unit.[3] 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. CPU redirects here. ...


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 be probably unaffected, enabling disaster recovery. Off-line storage increases a general information security, since it is physically unaccessible 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 accessed seldom or never, off-line storage is less expensive than tertiary storage. “Online” redirects here. ... The movement of data from one location to another is called data transfer. ... This article is about business continuity planning. ... Security is everyone’s responsibility. ...


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

A 1GB DDR RAM memory module

There are also other ways to characterize various types of storage. Image File history File links Metadata Size of this preview: 472 × 600 pixelsFull resolution (1926 × 2448 pixel, file size: 796 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Metadata Size of this preview: 472 × 600 pixelsFull resolution (1926 × 2448 pixel, file size: 796 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ...


Volatility of information

Main article: Volatile memory
  • Non-volatile memory will retain the stored information even if it is not constantly supplied with electric power. It is suitable for long-term storage of information. Nowadays used for most of secondary, tertiary, and off-line storage. In 1950s and 1960s, it was also used for primary storage, in the form of magnetic core memory.
  • Volatile memory requires constant power to maintain the stored information. The fastest memory technologies of today are volatile ones (not a universal rule). Since primary storage is required to be very fast, it predominantly uses volatile memory.
    • Dynamic memory, is a kind of volatile memory which also requires the stored information to be periodically re-read and re-written, or refreshed, otherwise it would vanish.

Volatile memory refers to computer memory that must be powered to maintain its data. ... Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... The 1950s decade refers to the years 1950 to 1959 inclusive. ... Year 1960 (MCMLX) was a leap year starting on Friday (link will display full calendar) of the Gregorian calendar. ... A 16×16 cm area core memory plane of 128×128 bits, i. ... Volatile memory refers to computer memory that must be powered to maintain its data. ... 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: ... Memory refresh is the process of periodically reading information from an area of computer memory, and immediately rewriting the read information to the same area with no modifications. ...

Ability to access non-contiguous information

  • Random access means that any location in storage can be accessed at any moment in approximately the same amount of time. Such characteristic is well suited for primary storage.
  • Sequential access means that the accessing a piece of information will take a varying amount of time, depending on which piece of information was accessed last. The device may need to seek (e.g. to position the read/write head correctly), or cycle (e.g. to wait for the correct location in a revolving medium to appear below the read/write head).

In computer science, random access is the ability to access a random element of a group in equal time. ... In computer science sequential access means that a group of elements (e. ... Microphotograph of a hard disk head. ...

Ability to change information

  • 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 (WORM) 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-R.
  • Slow write, fast read storage is 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.

For other uses, see Worm (disambiguation). ... This article does not cite any references or sources. ... Compact Disc ReWritable (CD-RW) is a rewritable optical disc format. ...

Addressability of information

  • In location-addressable storage, 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.
  • In file system storage, 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.
  • In content-addressable storage, each individually accessible unit of information is selected with a hash value, or a short identifier with number? pertaining to the memory address the information is stored on. Content-addressable storage can be implemented using software (computer program) or hardware (computer device), with hardware being faster but more expensive option.

In computer science, a memory address is a unique identifier for a memory location at which a CPU or other device can store a piece of data for later retrieval. ... For library and office filing systems, see Library classification. ... This article is about computer files and file systems in general terms. ... Human-readable refers to a representation of information that can be naturally read by humans. ... An operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. ... In computer science, abstraction is a mechanism and practice to reduce and factor out details so that one can focus on a few concepts at a time. ... Content-addressable memory (CAM) is a special type of computer memory used in certain very high speed searching applications. ... A hash function is a reproducible method of turning some kind of data into a (relatively) small number that may serve as a digital fingerprint of the data. ... Software redirects here. ... Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware. ...

Capacity and performance

  • Storage capacity is 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).
  • Storage density refers to 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).
  • Latency is 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, and in case of sequential access storage, minimum, maximum and average latency.
  • Throughput is 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 or 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.

This article is about the unit of information. ... For the computer industry magazine, see Byte (magazine). ... ReBoot character, see Megabyte (ReBoot). ... Computer storage density is a measure of the quantity of information bits that can be stored on a given length of track, area of surface, or in a given volume; of a computer storage medium. ... Latency is a time delay between the moment something is initiated, and the moment one of its effects begins. ... Measurement is the determination of the size or magnitude of something. ... To help compare orders of magnitude of different times this page lists times between 10−9 seconds and 10−8 seconds (1 nanosecond and 10 nanoseconds) See also times of other orders of magnitude. ... One millisecond is one-thousandth of a second. ... This article is about the unit of time. ... In communication networks, throughput is the amount of digital data per time unit that is delivered over a physical or logical link, or that is passing through a certain network node. ... In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ...

Fundamental storage technologies

Semiconductor storage

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. Semiconductor memory is a generic term referring to any computer storage method implemented on a semiconductor-based integrated circuit. ... A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ... 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. ... Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. ... 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. ... A USB flash drive. ...


Magnetic storage

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. Since the read/write head only covers a part of the surface, magnetic storage is sequential access and must seek, cycle or both. In modern computers, the magnetic surface will take these forms: Magnetic storage is a term from engineering referring to the storage of data on a magnetised medium. ... Magnetization is a property of some materials (e. ... In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. ... Microphotograph of a hard disk head. ...

In early computers, magnetic storage was also used for primary storage in a form of magnetic drum, or core memory, core rope memory, thin film memory, twistor memory or bubble memory. Also unlike today, magnetic tape was often used for secondary storage. Disk storage is a general category of a computer storage mechanisms, in which data is recorded on planar, round and rotating surfaces (disks, discs, or platters). ... A floppy disk is a data storage device that is composed of a disk of thin, flexible (floppy) magnetic storage medium encased in a square or rectangular plastic shell. ... Typical hard drives of the mid-1990s. ... Magnetic tape has been used for data storage for over 50 years. ... The Magnetic Drum was invented by G. Taushek in 1932 in Austria. ... A 16×16 cm area core memory plane of 128×128 bits, i. ... Core rope memory is a form of read-only memory (ROM) for computers, first used by early NASA Mars probes and then in the Apollo Guidance Computer (AGC) designed by MIT and built by Raytheon. ... Thin film memory is a high-speed variation of core memory developed by Sperry Rand in a government-funded research project. ... Twistor is a form of computer memory, similar to core memory, formed by wrapping magnetic tape around a current-carrying wire. ... Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles, which each store one bit of data. ...

Optical storage

Optical storage, in the case of typical Optical discs, uses tiny pits etched on the surface of a circular disc to store information, and reads this information by illuminating the surface with a laser diode and observing the reflection. Optical disc storage is non-volatile and sequential access. The following forms are currently in common use: [4] Optical Storage is made possible by data storage devices such as optical discs and holographic storage systems. ... “Optical media” redirects here. ... A packaged laser diode with penny for scale. ...

  • CD, CD-ROM, DVD: Read only storage, used for mass distribution of digital information (music, video, computer programs)
  • CD-R, DVD-R, DVD+R: Write once storage, used for tertiary and off-line storage
  • CD-RW, DVD-RW, DVD+RW, DVD-RAM: 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. CD may stand for: Compact Disc Canadian Forces Decoration Cash Dispenser (at least used in Japan) CD LPMud Driver Centrum-Demokraterne (Centre Democrats of Denmark) Certificate of Deposit České Dráhy (Czech Railways) Chad (NATO country code) Chalmers Datorförening (computer club of the Chalmers University of Technology) a 1960s... The CD-ROM (an abbreviation for Compact Disc Read-Only Memory (ROM)) is a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. ... DVD (also known as Digital Versatile Disc or Digital Video Disc) is a popular optical disc storage media format. ... This article does not cite any references or sources. ... A DVD+R disc The title given to this article is incorrect due to technical limitations. ... This article or section does not cite any references or sources. ... Compact Disc ReWritable (CD-RW) is a rewritable optical disc format. ... The title given to this article is incorrect due to technical limitations. ... This article or section does not cite its references or sources. ... You can recognize a DVD-RAM immediately because visually there are lots of little rectangles distributed on the surface of the data carrier. ... Magneto-optical disc. ... Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ...


3D optical data storage has also been proposed. Schematic representation of a cross-section through a 3D optical storage disc (yellow) along a data track (orange marks). ...

Other early methods

Paper data storage

Main article: Paper data storage

Paper tape and punch cards have been used to store information for automatic processing since the 1890s, long before general-purpose computers existed. Information was recorded by punching holes into the paper or cardboard medium, and was read by mechanically (or, later, optically) sensing whether a particular location on the medium was solid or contained a hole. Paper data storage refers to the storage, on paper, of data that can be interpreted by a machine or is the result of the functioning of a machine. ... A roll of punched tape Punched tape is an old-fashioned form of data storage, consisting of a long strip of paper in which holes are punched to store data. ... Punched cards (or Hollerith cards, or IBM cards), are pieces of stiff paper that contain digital information represented by the presence or absence of holes in predefined positions. ... The 1890s were sometimes referred to as the Mauve Decade, because William Henry Perkins aniline dye allowed the widespread use of that colour in fashion, and also as the Gay Nineties, under the then-current usage of the word gay which referred simply to merriment and frivolity, with no...

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 Selectron tube was expensive. The Williams tube or (more accurately) the Williams-Kilburn tube (after Freddie Williams and coworker Tom Kilburn), developed about 1946 or 1947, was a cathode ray tube used to store electronic data. ... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT: 1. ... The Selectron was an early form of computer memory developed by RCA. Development started in 1946 with a planned production of 200 by the end of the year, but production problems meant that they were still not available by the middle of 1948. ... Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ...


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. Mercury memory of UNIVAC I (1951) Delay line memory was a form of computer memory used on some of the earliest digital computers, such as the EDSAC and UNIVAC I. // The basic concept of the delay line originated with World War II radar research, as a system to reduce clutter... This article is about compression waves. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Standard atomic weight 200. ...


Proposed methods

Phase-change memory uses different mechanical phases of phase change material to store information, and reads the information by observing the varying electric 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. Phase-change memory (also known as PCM, PRAM, Ovonic Unified Memory and Chalcogenide RAM [C-RAM]) is a type of non-volatile computer memory. ... A Phase Change Material (PCM) is a substance with a high heat of fusion which, melting and solidifying at certain temperatures, is capable of storing or releasing large amounts of energy. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...


Holographic 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). It has been suggested that Holographic data storage be merged into this article or section. ... For other uses, see Crystal (disambiguation). ... A photopolymer is a polymer which is cured by exposure to light, often in the ultraviolet spectum. ... Picture of an HVD by Optware. ...


Molecular memory stores information in polymers that can store electric charge. Molecular memory might be especially suited for primary storage. Molecular memory is a type of experimental data storage technology which hopes to supplant DRAM memory as the lowest cost technology for high-speed computer memory. ... A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ...


Related technologies

Network connectivity

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 in a much lesser degree. A computer network is a system for communication among two or more computers. ...

  • Direct-attached storage (DAS) is a traditional mass storage, that does not use any network. This is still a most popular approach. This term was coined lately, 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.
    • Network computers are computers that do not contain internal mass storage devices. Instead, all data are stored exclusively on a NAS.
  • Storage area network (SAN) is a specialized network, that provides other computers with storage capacity. The crucial difference between NAS and SAN is the former presents and manages file systems to client computers, whilst a latter provides access at block-addressing (raw) level, leaving it to attaching systems to manage data or file systems within the provided capacity.

Direct Attached Storage (DAS) refers to a digital storage system directly attached to a server or workstation, without a storage network in between. ... Network-attached storage (NAS) is a file-level data storage connected to a computer network providing data access to heterogeneous network clients. ... A local area network (LAN) is a computer network covering a local area, like a home, office or small group of buildings such as a college. ... A wide area network or WAN is a computer network covering a wide geographical area, involving vast array of computers. ... It has been suggested that this article or section be merged with Online backup. ... A network computer is a lightweight computer system that operates exclusively via a network connection. ... In computing, a storage area network (SAN) is an architecture to attach remote computer storage devices such as disk array controllers, tape libraries and CD arrays to servers in such a way that to the operating system the devices appear as locally attached devices. ...

Robotic storage

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. A tape silo being loaded. ... An optical jukebox or autochanger is a computer device used for massive data storage. ... ADIC Scalar 100, Example of an Autoloader An Autoloader is a data storage device consisting of at least one tape drive (the drive), a method of loading tapes into the drive (the robot), and a storage area for tapes (the magazine). ... The term Autochanger may refer to: A device for playing multiple gramophone records in a predetermined sequence without user intervention. ...


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. For other uses of Backup, see Backup (disambiguation). ... Hierarchical Storage Management (HSM) is a data storage technique that automatically moves data between high-cost and low-cost storage media. ...


See also

Primary storage topics

Data proliferation refers to the unprecedented amount of data, structured and unstructured, that business and government continue to generate at an unprecedented rate and the usability problems that result from attempting to store and manage that data. ... Memory management is the act of managing computer memory. ... The program thinks it has a large range of contiguous addresses; but in reality the parts it is currently using are scattered around RAM, and the inactive parts are saved in a disk file. ... It has been suggested that this article or section be merged with Dynamic memory allocation. ... Dynamic Memory, often called heap memory, is one of the types of memory allocation that happens inside of a computer program. ... In computer science, a memory leak is a particular kind of unintentional memory consumption by a computer program where the program fails to release memory when no longer needed. ... Memory protection is a system that prevents one process from corrupting the memory of another process running on the same computer at the same time. ... 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. ... Static random access memory (SRAM) is a type of semiconductor memory. ...

Secondary, tertiary and off-line storage topics

Data proliferation refers to the unprecedented amount of data, structured and unstructured, that business and government continue to generate at an unprecedented rate and the usability problems that result from attempting to store and manage that data. ... For library and office filing systems, see Library classification. ... This is a list of file formats organized by type, as can be found on computers. ... A USB flash drive. ... For other uses, see Knowledge base. ... This article refers to both flash and DRAM-based solid state drives. ... Virtual Tape Library (VTL) is a data storage virtualization technology used typically for archival storage purposes. ... A wait state is a delay experienced by a computer processor when accessing external memory or another device that is slow to respond. ... Write protection, (also known as record protection) is a mechanism that prevents erasure of valuable data by the accidental recording or storing of new data. ...

Data storage conferences

Storage Networking World (commonly called SNW) is a business conference for data storage professionals in the United States. ... Storage World Conference (sometimes called SWC) is a business conference for data storage professionals in the United States. ...

References

  1. ^ http://searchstorage.techtarget.com/topics/0,295493,sid5_tax298620,00.html "Primary Storage or Storage Hardware" (shows usage of term "primary storage" meaning "hard disk storage")
  2. ^ A thesis on Tertiary storage
  3. ^ National Communications System (1996), Federal Standard 1037C - Telecommunications: Glossary of Telecommunication Terms, General Services Administration, FS-1037C, <http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm>. Retrieved on 2007-10-08 See also article Federal Standard 1037C.
  4. ^ The DVD FAQ is a comprehensive reference of DVD technologies.
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