# Computer data storage

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Storage of digital data readable by computers

For broader coverage of this topic, see [Data storage](/source/Data_storage).

1 [GiB](/source/Gibibyte) of [SDRAM](/source/SDRAM) mounted in a [computer](/source/Computer). An example of *primary storage*.

15 [GB](/source/Gigabyte) [PATA](/source/Parallel_ATA) hard disk drive (HDD) from 1999. When connected to a computer it serves as *secondary* storage.

Computer memory and data storage types General Memory cell Memory coherence Cache coherence Memory hierarchy Memory access pattern Memory map Secondary storage MOS memory floating-gate Continuous availability Areal density (computer storage) Block (data storage) Object storage Direct-attached storage Network-attached storage Storage area network Block-level storage Single-instance storage Data Structured data Unstructured data Big data Metadata Data compression Data corruption Data cleansing Data degradation Data integrity Data security Data validation Data validation and reconciliation Data recovery Storage Data cluster Directory Shared resource File sharing File system Clustered file system Distributed file system Distributed file system for cloud Distributed data store Distributed database Database Data bank Data storage Data store Data deduplication Data structure Data redundancy Replication (computing) Memory refresh Storage record Information repository Knowledge base Computer file Object file File deletion File copying Backup Core dump Hex dump Data communication Information transfer Temporary file Copy protection Digital rights management Volume (computing) Boot sector Master boot record Volume boot record GUID Partition Table Disk array Disk image Disk mirroring Disk aggregation Disk partitioning Memory segmentation Locality of reference Logical disk Storage virtualization Virtual memory Memory-mapped file Software entropy Software rot In-memory database In-memory processing Persistence (computer science) Persistent data structure RAID Non-RAID drive architectures Memory paging Bank switching Grid computing Cloud computing Cloud storage Fog computing Edge computing Dew computing The law Martiels law Volatile RAM Hardware cache CPU cache Scratchpad memory DRAM eDRAM SDRAM SGRAM DDR GDDR LPDDR QDRSRAM EDO DRAM XDR DRAM RDRAM HBM SRAM 1T-SRAM ReRAM QRAM Content-addressable memory (CAM) Computational RAM VRAM Dual-ported RAM Video RAM (dual-ported DRAM) Historical DC3MWCP (1946–1947) Delay-line memory (1947) Mellon optical memory (1951) Selectron tube (1952) Dekatron T-RAM (2009) Z-RAM (2002–2010) Non-volatile ROM Diode matrix MROM PROM EPROM EEPROM ROM cartridge Solid-state storage (SSS) Flash memory is used in: Solid-state drive (SSD) Solid-state hybrid drive (SSHD) USB flash drive IBM FlashSystem Flash Core Module Memory card Memory Stick CompactFlash PC Card MultiMediaCard SD card SIM card SmartMedia Universal Flash Storage SxS MicroP2 XQD card Programmable metallization cell NVRAM Memistor Memristor PCM (3D XPoint) MRAM Electrochemical RAM (ECRAM) Nano-RAM CBRAM Early-stage NVRAM FeRAM ReRAM FeFET memory Analog recording Phonograph cylinder Phonograph record Quadruplex videotape Vision Electronic Recording Apparatus Magnetic recording Magnetic storage Magnetic tape Magnetic-tape data storage Tape drive Tape library Digital Data Storage (DDS) Videotape Cassette tape Linear Tape-Open Betamax 8 mm video format DV MiniDV MicroMV U-matic VHS S-VHS VHS-C D-VHS Hard disk drive Optical 3D optical data storage Optical disc LaserDisc Compact Disc Digital Audio (CDDA) CD CD Video CD-R CD-RW Video CD Super Video CD Mini CD Nintendo optical discs CD-ROM Hyper CD-ROM DVD DVD+R DVD-Video DVD card DVD-RAM MiniDVD HD DVD Blu-ray Ultra HD Blu-ray Holographic Versatile Disc WORM In development CBRAM Racetrack memory NRAM Millipede memory ECRAM Patterned media Holographic data storage Electronic quantum holography 5D optical data storage DNA digital data storage Universal memory Time crystal Quantum memory UltraRAM Historical Paper data storage (1725) Punched card (1725) Punched tape (1725) Plugboard Drum memory (1932) Magnetic-core memory (1949) Plated-wire memory (1957) Core rope memory (1960s) Thin-film memory (1962) Disk pack (1962) Twistor memory (~1968) Bubble memory (~1970) Floppy disk (1971) v t e

**Computer data storage** or **digital data storage** is the retention of [digital data](/source/Digital_data) via [technology](/source/Technology) consisting of [computer](/source/Computer) components and [recording media](/source/Data_storage). Digital data storage is a core function and fundamental component of computers.[1]: 15–16

Generally, the faster and volatile storage components are referred to as "[memory](/source/Computer_memory)", while slower persistent components are referred to as "storage". This distinction was extended in the [Von Neumann architecture](/source/Von_Neumann_architecture), where the [central processing unit](/source/Central_processing_unit) (CPU) consists of two main parts: The [control unit](/source/Control_unit) and the [arithmetic logic unit](/source/Arithmetic_logic_unit) (ALU). The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and [logical operations](/source/Bitwise_operation) on data. In practice, almost all computers use a [memory hierarchy](/source/Memory_hierarchy),[1]: 468–473 which puts memory close to the CPU and storage further away.

In modern computers, [hard disk drives](/source/Hard_disk_drive) (HDDs) or [solid-state drives](/source/Solid-state_drive) (SSDs) are usually used as storage.

## Data

A modern [digital computer](/source/Computer) represents [data](/source/Data) using the [binary numeral system](/source/Binary_numeral_system). The [memory cell](/source/Memory_cell_(computing)) is the fundamental building block of [computer memory](/source/Computer_memory), storing stores one bit of binary information that can be set to store a 1, reset to store a 0, and accessed by reading the cell.[2][3]

Text, numbers, pictures, audio, and nearly any other form of information can be converted into a string of [bits](/source/Bit), or binary digits, each of which has a value of 0 or 1. The most common unit of storage is the [byte](/source/Byte), equal to 8 bits. [Digital data](/source/Digital_data) comprises the binary representation of a piece of information, often being [encoded](/source/Code) by assigning a bit pattern to each [character](/source/Character_(computing)), [digit](/source/Numerical_digit), or [multimedia](/source/Multimedia) object. Many standards exist for encoding (e.g. [character encodings](/source/Character_encoding) like [ASCII](/source/ASCII), image encodings like [JPEG](/source/JPEG), and video encodings like [MPEG-4](/source/MPEG-4)).

### Encryption

For [security reasons](/source/Data_security), certain types of data may be [encrypted](/source/Encrypted) in storage to prevent the possibility of unauthorized information reconstruction from chunks of storage snapshots. Encryption in transit protects data as it is being transmitted.[4]

### Compression

[Data compression](/source/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 percent) for many types of data at the cost of more computation (compress and decompress when needed). Analysis of the 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.

### Vulnerability and reliability

Distinct types of data storage have different points of failure and various methods of [predictive failure analysis](/source/Predictive_failure_analysis). Vulnerabilities that can instantly lead to total loss are [head crashing](/source/Head_crash) on mechanical hard drives and [failure of electronic components](/source/Failure_of_electronic_components) on flash storage.

#### Redundancy

[Redundancy](/source/Redundancy_(information_theory)) allows the computer to detect errors in coded data (for example, a random [bit flip](/source/RAM_parity) due to random [radiation](/source/Radiation)) and correct them based on mathematical algorithms. The [cyclic redundancy check](/source/Cyclic_redundancy_check) (CRC) method is typically used in communications and storage for [error detection](/source/Error_detection). Redundancy solutions include [storage replication](/source/Replication_(computing)), [disk mirroring](/source/Disk_mirroring) and RAID ([Redundant Array of Independent Disks](/source/RAID)).

#### Error detection

[Error rate measurement](/source/Optical_disc#Surface_error_scanning) on a [DVD+R](/source/DVD%2BR). The minor errors are correctable and within a healthy range.

Impending failure on [hard disk drives](/source/Hard_disk_drive) is estimable using [S.M.A.R.T.](/source/S.M.A.R.T) diagnostic data that includes the [hours of operation](/source/Power-on_hours) and the count of spin-ups, though its reliability is disputed.[5] The health of [optical media](/source/Optical_media) can be determined by [measuring correctable minor errors](/source/Optical_disc#Surface_error_scanning), of which high counts signify deteriorating and/or low-quality media. Too many consecutive minor errors can lead to data corruption. Not all vendors and models of [optical drives](/source/Optical_disc_drive) support error scanning.[6]

## Architecture

Without a significant amount of memory, a computer would only be able to perform fixed operations and immediately output the result, thus requiring hardware [reconfiguration](/source/Reconfiguration) for a new program to be run. This is often used in devices such as desk [calculators](/source/Calculator), [digital signal processors](/source/Digital_signal_processing), and other specialized devices. [Von Neumann machines](/source/Von_Neumann_architecture) differ in having a memory in which operating [instructions](/source/Instruction_set_architecture#Instructions) and data are stored,[1]: 20 such that they do not need to have their hardware reconfigured for each new program, but can simply be [reprogrammed](/source/Computer_programming) with new in-memory instructions. They also tend to be simpler to [design](/source/Computer_architecture), in that a relatively simple [processor](/source/Processor_(computing)) may keep [state](/source/State_(computer_science)) between successive computations to build up complex procedural results. Most modern computers are von Neumann machines.

### Storage and memory

In contemporary usage, the term "storage" typically refers to a subset of computer data storage that comprises storage devices and their media not directly accessible by the [CPU](/source/CPU), that is, [secondary](/source/Secondary_storage) or [tertiary storage](/source/Tertiary_storage). Common forms of storage include [hard disk drives](/source/Hard_disk_drive), [optical disc](/source/Optical_disc) drives, and [non-volatile](/source/Non-volatile_memory) devices (i.e. devices that retain their contents when the computer is powered down).[7] On the other hand, the term "[memory](/source/Random-access_memory)" is used to refer to [semiconductor](/source/Semiconductor_memory) [read-write](/source/Read%E2%80%93write_memory) data storage, typically [dynamic random-access memory](/source/Dynamic_random-access_memory) (DRAM). [Dynamic random-access memory](/source/Dynamic_random-access_memory) is a form of volatile memory that also requires the stored information to be periodically reread and rewritten, or [refreshed](/source/Memory_refresh); [static RAM](/source/Static_random-access_memory) (SRAM) is similar to DRAM, albeit it never needs to be refreshed as long as power is applied.

In contemporary usage, the [memory hierarchy](/source/Memory_hierarchy) of primary storage and secondary storage in some uses refer to what was historically called, respectively, *secondary storage* and *tertiary storage*.[8]

#### Primary

Various forms of storage, divided according to their distance from the [central processing unit](/source/Central_processing_unit). The fundamental components of a general-purpose computer are [arithmetic and logic unit](/source/Arithmetic_and_logic_unit), [control circuitry](/source/Control_unit), storage space, and [input/output](/source/Input%2Foutput) devices. Technology and capacity as in common [home computers](/source/Home_computer) around 2005.

**Main memory** (also known as **primary memory**, **internal memory** or **primary storage**), often referred to simply as *memory*, is storage 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 a uniform manner. Historically, [early computers](/source/History_of_computing_hardware) used [delay lines](/source/Delay-line_memory), [Williams tubes](/source/Williams_tube), or rotating [magnetic drums](/source/Drum_memory) as primary storage. By 1954, those unreliable methods were mostly replaced by [magnetic-core memory](/source/Magnetic-core_memory). Core memory remained dominant until the 1970s, when advances in [integrated circuit](/source/Integrated_circuit) technology allowed [semiconductor memory](/source/Semiconductor_memory) to become economically competitive.

This led to modern [random-access memory](/source/Random-access_memory), which is small-sized, light, and relatively expensive. RAM used for primary storage is [volatile](/source/Volatile_memory), meaning that it loses the information when not powered for a specific [time](/source/Time). Besides storing opened programs, it serves as [disk cache](/source/Page_cache) and [write buffer](/source/Write_buffer) to improve both reading and writing performance. Operating systems borrow RAM capacity for caching so long as it's not needed by running software.[9] Spare memory can be utilized as [RAM drive](/source/RAM_drive) for temporary high-speed data storage. Besides main large-capacity RAM, there are two more sub-layers of primary storage:

- [Processor registers](/source/Processor_register) are the fastest of all forms of data storage, being located inside the processor, with each register typically holding a [word](/source/Word_(computer_architecture)) of data (often 32 or 64 bits). CPU instructions instruct the [arithmetic logic unit](/source/Arithmetic_logic_unit) to perform various calculations or other operations on this data.

- [Processor cache](/source/Processor_cache) is an intermediate stage between faster registers and slower main memory, being faster than main memory but with much less capacity. Multi-level [hierarchical cache](/source/Memory_hierarchy) setup is also commonly used, such that primary cache is the smallest and fastest, while secondary cache is larger and slower.

Primary storage, including [ROM](/source/Read-only_memory), [EEPROM](/source/EEPROM), [NOR flash](/source/NOR_flash), and [RAM](/source/Random_access_memory),[10] is usually [byte-addressable](/source/Byte-addressable). Such memory is directly or indirectly connected to the central processing unit via a [memory bus](/source/Bus_(computing)), comprising an [address bus](/source/Address_bus) and a [data bus](/source/Data_bus). The CPU firstly sends a number called the [memory address](/source/Memory_address) through the address bus that indicates the desired location of data. Then it reads or writes the data in the [memory cells](/source/Memory_cell_(computing)) using the data bus. Additionally, a [memory management unit](/source/Memory_management_unit) (MMU) is a small device between CPU and RAM recalculating the actual memory address. Memory management units allow for [memory management](/source/Memory_management); they may, for example, provide an [abstraction](/source/Abstraction_(computer_science)) of [virtual memory](/source/Virtual_memory) or other tasks.

#### BIOS

[Non-volatile primary storage](/source/Non-volatile_memory) containing a small startup program ([BIOS](/source/BIOS)) is used to [bootstrap](/source/Bootstrapping#Computing) 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 [read-only memory](/source/Read-only_memory) (ROM). Most types of "ROM" are not literally read only but are difficult and slow to write to*.* Some [embedded systems](/source/Embedded_system) run programs directly from ROM, because such programs are rarely changed. Standard computers largely do not store many programs in ROM, apart from [firmware](/source/Firmware), and use large capacities of secondary storage.

#### Secondary

**Secondary storage** (also known as *external memory* or *auxiliary storage*) differs from primary storage in that it is not directly accessible by the CPU. Computers use [input/output](/source/Input%2Foutput) channels to access secondary storage and transfer the desired data to primary storage. Secondary storage is non-volatile, retaining data when its power is shut off. Modern computer systems typically have two orders of magnitude more secondary storage than primary storage because secondary storage is less expensive.

In modern computers, [hard disk drives](/source/Hard_disk_drive) (HDDs) or [solid-state drives](/source/Solid-state_drive) (SSDs) are usually used as secondary storage. The [access time](/source/Access_time) per byte for HDDs or SSDs is typically measured in [milliseconds](/source/Millisecond), while the access time per byte for primary storage is measured in [nanoseconds](/source/Nanosecond). Rotating [optical storage](/source/Optical_disc_drive) devices, such as [CD](/source/CD) and [DVD](/source/DVD) drives, have even longer access times. Other examples of secondary storage technologies include [USB flash drives](/source/USB_flash_drive), [floppy disks](/source/Floppy_disk), [magnetic tape](/source/Magnetic-tape_data_storage), [paper tape](/source/Paper_tape), [punched cards](/source/Punched_card), and [RAM disks](/source/RAM_drive).

To reduce the seek time and rotational latency, secondary storage, including [HDD](/source/Hard_disk_drive), [ODD](/source/Optical_disc_drive) and [SSD](/source/Solid_state_drive), are transferred to and from [disks](/source/Disk_formatting) in large contiguous blocks. Secondary storage is [addressable](/source/Address_space) by block; once the [disk read/write head](/source/Disk_read%2Fwrite_head) on HDDs reaches the proper placement and the data, subsequent data on the track are very fast to access. Another way to reduce the I/O bottleneck is to use multiple disks in parallel to increase the bandwidth between primary and secondary memory, for example, using [RAID](/source/RAID).[11]

Secondary storage is often formatted according to a [file system](/source/File_system) format, which provides the abstraction necessary to organize data into [files](/source/Computer_file) and [directories](/source/Directory_(computing)), while also providing [metadata](/source/Metadata) describing the owner of a certain file, the access time, the access permissions, and other information. Most computer [operating systems](/source/Operating_system) use the concept of [virtual memory](/source/Virtual_memory), allowing the 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](/source/Page_(computer_memory))) to a swap file or page file on secondary storage, retrieving them later when needed.

#### Tertiary

A large [tape library](/source/Tape_library), with tape cartridges placed on shelves in the front, and a robotic arm moving in the back. The visible height of the library is about 180 cm.

**Tertiary storage** or **tertiary memory** typically involves a [robotic arm](/source/Industrial_robot) which mounts and dismount removable mass storage media from a catalog [database](/source/Database) into a storage device according to the system's demands. 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](/source/Tape_libraries), [optical jukeboxes](/source/Optical_jukebox), and massive arrays of idle disks ([MAID](/source/Non-RAID_drive_architectures#MAID)). Tertiary storage is also known as [nearline storage](/source/Nearline_storage) because it is "near to online".[12] [Hierarchical storage management](/source/Hierarchical_storage_management) is an archiving strategy involving automatically migrating long-unused files from fast hard disk storage to libraries or jukeboxes.

#### Offline

**Offline storage** is computer data storage on a medium or a device that is not under the control of a [processing unit](/source/Central_processing_unit).[13] The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. Unlike tertiary storage, it cannot be accessed without human interaction. It is used to [transfer information](/source/Data_communication) since the detached medium can easily be physically transported. In modern personal computers, most secondary and tertiary storage media are also used for offline storage.

### Network connectivity

A secondary or tertiary storage may connect to a computer utilizing [computer networks](/source/Computer_network). This concept does not pertain to the primary storage.

- [Direct-attached storage](/source/Direct-attached_storage) (DAS) is a traditional mass storage, that does not use any network.

- [Network-attached storage](/source/Network-attached_storage) (NAS) is mass storage attached to a computer which another computer can access at file level over a [local area network](/source/Local_area_network), a private [wide area network](/source/Wide_area_network), or in the case of [online file storage](/source/File-hosting_service), over the [Internet](/source/Internet). NAS is commonly associated with the [NFS](/source/Network_File_System) and [CIFS/SMB](/source/CIFS%2FSMB) protocols.

- [Storage area network](/source/Storage_area_network) (SAN) is a specialized network, that provides other computers with storage capacity. SAN is commonly associated with [Fibre Channel](/source/Fibre_Channel) networks.

## Cloud

[Cloud storage](/source/Cloud_storage) is based on highly [virtualized](/source/Virtualization) infrastructure.[14] A subset of [cloud computing](/source/Cloud_computing), it has particular cloud-native interfaces, near-instant elasticity and [scalability](/source/Scalability), [multi-tenancy](/source/Multi-tenancy), and [metered](/source/Metered) resources. Cloud storage services can be used from an off-premises service or deployed on-premises.[15]

### Deployment models

Cloud deployment models define the interactions between cloud providers and customers.[16]

- [Private clouds](/source/Private_cloud_computing_infrastructure), for example, are used in [cloud security](/source/Cloud_security) to mitigate the increased [attack surface area](/source/Attack_surface) of [outsourcing](/source/Outsourcing) data storage.[17] A private cloud is cloud infrastructure operated solely for a single organization, whether managed internally or by a third party, or hosted internally or externally.[18]

- [Hybrid cloud storage](/source/Hybrid_cloud_storage) are another cloud security solution, involving storage infrastructure that uses a combination of on-premises storage resources with cloud storage. The on-premises storage is usually managed by the organization, while the public cloud storage provider is responsible for the management and security of the data stored in the cloud.[19][20] Using a hybrid model allows data to be ingested in an encrypted format where the key is held within the on-premise infrastructure and can limit access to the use of on-premise [cloud storage gateways](/source/Cloud_storage_gateway), which may have options to encrypt the data prior to transfer.[21]

- Cloud services are considered "public" when they are delivered over the public Internet.[22] - A [virtual private cloud](/source/Virtual_private_cloud) (VPC) is a pool of shared resources within a public cloud that provides a certain level of isolation between the different users using the resources. VPCs achieve user isolation through the allocation of a private IP [subnet](/source/Subnet) and a virtual communication construct (such as a [VLAN](/source/VLAN) or a set of [encrypted communication](/source/Encrypted_communication) channels) between users as well as the use of a [virtual private network](/source/Virtual_private_network) (VPN) per VPC user, securing, by means of authentication and encryption, the remote access of the organization to its VPC resources.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

### Types

There are three types of cloud storage:

- [Object storage](/source/Object_storage)[23][24]

- [File storage](/source/File_storage)

- [Block-level storage](/source/Block-level_storage) is a concept in cloud-hosted [data persistence](/source/Persistent_data_structure) where [cloud services](/source/Cloud_computing) emulate the behaviour of a traditional [block device](/source/Device_file#Block_devices), such as a physical [hard drive](/source/Hard_disk_drive),[25] where storage is organised as [blocks](/source/Block_(data_storage)). Block-level storage differs from [object stores](/source/Object_storage) or 'bucket stores' or to [cloud databases](/source/Cloud_database). These operate at a higher level of abstraction and are able to work with entities such as files, documents, images, videos or database records.[26] At one time, block-level storage was provided by [SAN](/source/Storage_area_network), and NAS provided file-level storage.[27] With the shift from on-premises hosting to cloud services, this distinction has shifted.[28] - Instance stores are a form of cloud-hosted block-level storage, being provided as part of a cloud [instance](/source/Instance_(computer_science)).[29] Unlike other forms of block storage, instance store data will be lost the cloud instance is stopped.[30]

## Characteristics

A 1 GiB module of [laptop](/source/SO-DIMM) [DDR2](/source/DDR2_SDRAM) [RAM](/source/RAM)

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](/source/Volatile_memory) - An [uninterruptible power supply](/source/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](/source/EMC_Symmetrix), have integrated batteries that maintain volatile storage for several minutes.

- [Mutability](/source/Immutable_object) - Storage can be classified into read/write, slow-write/fast-read (e.g. [CD-RW](/source/CD-RW), [SSD](/source/Solid-state_drive)), [write-once/read-many](/source/Write_once_read_many) or WORM (e.g. [programmable read-only memory](/source/Programmable_read-only_memory), [CD-R](/source/CD-R)), read-only storage (e.g. [mask ROM ICs](/source/Read-only_memory#Factory-programmed), [CD-ROM](/source/CD-ROM)).

- Accessibility - Types of access include [random access](/source/Random_access) and [sequential access](/source/Sequential_access). In random access, any location in storage can be accessed at any moment in approximately the same amount of time. In 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.

- [Addressability](/source/Addressing_mode) - Storage can be location accessible (i.e. selected with its numerical [memory address](/source/Memory_address)), [file addressable](/source/File_system), or [content-addressable](/source/Content-addressable_memory).

- Capacity and [density](/source/Density_(computer_storage))

- Performance - Storage performance metrics include [latency](/source/Latency_(engineering)), [throughput](/source/Network_throughput), granularity and reliability.

- Energy - Low capacity [solid-state drives](/source/Solid-state_drive) have no moving parts and consume less power than hard disks.[31][32][33] Also, memory may use more power than hard disks.[33] Large caches, which are used to avoid hitting the [memory wall](/source/Memory_wall), may also consume a large amount of power.

- Security[34]

Overview Characteristic Hard disk drive Optical disc Flash memory Random-access memory Linear tape-open Technology Magnetic disk Laser beam Semiconductor Magnetic tape Volatility No No No Volatile No Random access Yes Yes Yes Yes No Latency (access time) ~15 ms (swift) ~150 ms (moderate) None (instant) None (instant) Lack of random access (very slow) Controller Internal External Internal Internal External Failure with imminent data loss Head crash — Circuitry — Error detection Diagnostic (S.M.A.R.T.) Error rate measurement Indicated by downward spikes in transfer rates (Short-term storage) Unknown Price per space Low Low High Very high Very low (but expensive drives) Price per unit Moderate Low Moderate High Moderate (but expensive drives) Main application Mid-term archival, routine backups, server, workstation storage expansion Long-term archival, hard copy distribution Portable electronics; operating system Real-time Long-term archival

## Media

### Semiconductor

Main article: [Semiconductor memory](/source/Semiconductor_memory)

[Semiconductor memory](/source/Semiconductor_memory) uses [semiconductor](/source/Semiconductor)-based [integrated circuit](/source/Integrated_circuit) (IC) chips to store information. Data are typically stored in [metal–oxide–semiconductor](/source/Metal%E2%80%93oxide%E2%80%93semiconductor) (MOS) [memory cells](/source/Memory_cell_(computing)). A semiconductor memory chip may contain millions of memory cells, consisting of tiny [MOS field-effect transistors](/source/MOSFET) (MOSFETs) and/or [MOS capacitors](/source/MOSFET#MOS_capacitor_and_band_diagrams). Both *volatile* and *non-volatile* forms of semiconductor memory exist, the former using standard MOSFETs and the latter using [floating-gate MOSFETs](/source/Floating-gate_MOSFET).

In modern computers, primary storage almost exclusively consists of dynamic volatile semiconductor [random-access memory](/source/Random-access_memory) (RAM), particularly [dynamic random-access memory](/source/Dynamic_random-access_memory) (DRAM). Since the turn of the century, a type of non-volatile [floating-gate](/source/Floating-gate) semiconductor memory known as [flash memory](/source/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](/source/Laptop) and [desktop computer](/source/Desktop_computer) manufacturers started using flash-based [solid-state drives](/source/Solid-state_drive) (SSDs) as default configuration options for the secondary storage either in addition to or instead of the more traditional HDD.[35][36][37][38][39]

### Magnetic

[Magnetic storage](/source/Magnetic_storage) uses different patterns of [magnetization](/source/Magnetization) on a [magnetically](/source/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](/source/Disk_storage); - [Floppy disk](/source/Floppy_disk), used for off-line storage; - [Hard disk drive](/source/Hard_disk_drive), used for secondary storage.

- [Magnetic tape](/source/Magnetic-tape_data_storage), used for tertiary and off-line storage;

- [Carousel memory](/source/Carousel_memory) (magnetic rolls).

In early computers, magnetic storage was also used as:

- [Microcode](/source/Microcode) storage in [transformer read-only storage](/source/Transformer_read-only_storage);

- Primary storage in a form of [magnetic memory](/source/Drum_memory), or [core memory](/source/Core_memory), [core rope memory](/source/Core_rope_memory), [thin-film memory](/source/Thin-film_memory) and/or [twistor memory](/source/Twistor_memory);

- Magnetic-tape was often used for secondary storage;

- Tertiary (e.g. [NCR CRAM](/source/NCR_CRAM)) or off line storage in the form of magnetic cards.

Magnetic storage does not have a definite limit of rewriting cycles like flash storage and re-writeable optical media, as altering magnetic fields causes no physical wear. Rather, their life span is limited by mechanical parts.[40][41]

### Optical

[Optical storage](/source/Optical_storage), the typical [optical disc](/source/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](/source/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 in common use as of 2009[\[update\]](https://en.wikipedia.org/w/index.php?title=Computer_data_storage&action=edit):[42]

- [CD](/source/CD), [CD-ROM](/source/CD-ROM), [DVD](/source/DVD), [BD-ROM](/source/BD-ROM): Read only storage, used for mass distribution of digital information (music, video, computer programs);

- [CD-R](/source/CD-R), [DVD-R](/source/DVD-R), [DVD+R](/source/DVD%2BR), [BD-R](/source/BD-R): Write once storage, used for tertiary and off-line storage;

- [CD-RW](/source/CD-RW), [DVD-RW](/source/DVD-RW), [DVD+RW](/source/DVD%2BRW), [DVD-RAM](/source/DVD-RAM), [BD-RE](/source/BD-RE): Slow write, fast read storage, used for tertiary and off-line storage;

- [Ultra Density Optical](/source/Ultra_Density_Optical) or UDO is similar in capacity to [BD-R or BD-RE](/source/Blu-ray_Disc_recordable) and is slow write, fast read storage used for tertiary and off-line storage.

[Magneto-optical disc storage](/source/Magneto-optical_drive) is optical disc storage where the magnetic state on a [ferromagnetic](/source/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](/source/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.[43]

### Paper

[Paper data storage](/source/Paper_data_storage), typically in the form of [paper tape](/source/Paper_tape) or [punched cards](/source/Punched_card), 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. [Barcodes](/source/Barcode) make it possible for objects that are sold or transported to have some computer-readable information securely attached.

Relatively small amounts of digital data (compared to other digital data storage) may be backed up on paper as a [matrix barcode](/source/Matrix_barcode) for very long-term storage, as the longevity of paper typically exceeds even magnetic data storage.[44][45]

### Other

- Vacuum-tube memory: - A [Williams tube](/source/Williams_tube) used a [cathode ray tube](/source/Cathode_ray_tube), and a [Selectron tube](/source/Selectron_tube) used a large [vacuum tube](/source/Vacuum_tube) to store information.

- Electro-acoustic memory: [Delay-line memory](/source/Delay-line_memory) used [sound waves](/source/Longitudinal_wave) in a substance such as [mercury](/source/Mercury_(element)) to store information.

- [Optical tape](/source/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.

- [Phase-change memory](/source/Phase-change_memory) uses different mechanical phases of [phase-change material](/source/Phase-change_material) to store information in an X–Y addressable matrix and reads the information by observing the varying [electrical resistance](/source/Electrical_resistance) of the material.

- [Holographic data storage](/source/Holographic_data_storage) stores information optically inside [crystals](/source/Crystal) or [photopolymers](/source/Photopolymer), for example, in HVDs ([Holographic Versatile Discs](/source/Holographic_Versatile_Disc)). 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.

- Magnetic photoconductors store magnetic information, which can be modified by low-light illumination.[43]

- [Molecular memory](/source/Molecular_memory) stores information in [polymers](/source/Polymer) that can store electric charge.[46]

- [DNA](/source/DNA_digital_data_storage) stores digital information in DNA [nucleotides](/source/Nucleotide).[47][48][49][50]

## See also

Wikiversity has learning resources about ***[Computer data storage](https://en.wikiversity.org/wiki/Computer_data_storage)***

- [Aperture (computer memory)](/source/Aperture_(computer_memory))

- [Mass storage](/source/Mass_storage)

- [Memory leak](/source/Memory_leak)

- [Memory protection](/source/Memory_protection)

- [Page address register](/source/Page_address_register)

- [Stable storage](/source/Stable_storage)

### Secondary, tertiary and off-line storage topics

- [Data deduplication](/source/Data_deduplication)

- [Data proliferation](/source/Data_proliferation)

- [Data storage tag](/source/Data_storage_tag) used for capturing research data

- [Disk utility](/source/Disk_utility)

- [File system](/source/File_system)

- [Flash memory](/source/Flash_memory)

- [Geoplexing](/source/Geoplexing)

- [Information repository](/source/Information_repository)

- [Noise-predictive maximum-likelihood detection](/source/Noise-predictive_maximum-likelihood_detection)

- [Removable media](/source/Removable_media)

- [Spindle](/source/Hard_disk_drive#Spindle)

- [Virtual tape library](/source/Virtual_tape_library)

- [Wait state](/source/Wait_state)

- [Write buffer](/source/Write_buffer)

- [Write protection](/source/Write_protection)

- [Cold data](/source/Cold_data)

## Notes

## References

This article incorporates [public domain material](/source/Copyright_status_of_works_by_the_federal_government_of_the_United_States) from [*Federal Standard 1037C*](https://web.archive.org/web/20220122224547/https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm). [General Services Administration](/source/General_Services_Administration). Archived from [the original](https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm) on 22 January 2022.

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1. **[^](#cite_ref-50)** Erlich, Yaniv; Zielinski, Dina (2 March 2017). ["DNA Fountain enables a robust and efficient storage architecture"](https://zenodo.org/record/889697). *Science*. **355** (6328): 950–954. [Bibcode](/source/Bibcode_(identifier)):[2017Sci...355..950E](https://ui.adsabs.harvard.edu/abs/2017Sci...355..950E). [doi](/source/Doi_(identifier)):[10.1126/science.aaj2038](https://doi.org/10.1126%2Fscience.aaj2038). [PMID](/source/PMID_(identifier)) [28254941](https://pubmed.ncbi.nlm.nih.gov/28254941). [S2CID](/source/S2CID_(identifier)) [13470340](https://api.semanticscholar.org/CorpusID:13470340).

## Further reading

- Amelia Acker. 2025. *[Archiving Machines: From Punch Cards to Platforms](https://mitpress.mit.edu/9780262553247/archiving-machines/)*. MIT Press.

- Goda, K.; Kitsuregawa, M. (2012). ["The history of storage systems"](https://doi.org/10.1109%2FJPROC.2012.2189787). *[Proceedings of the IEEE](/source/Proceedings_of_the_IEEE)*. **100**: 1433–1440. [doi](/source/Doi_(identifier)):[10.1109/JPROC.2012.2189787](https://doi.org/10.1109%2FJPROC.2012.2189787).

- [Memory & storage](https://www.computerhistory.org/revolution/memory-storage/8), Computer history museum

v t e Basic computer components Input devices Pointing devices Graphics tablet Game controller Light pen Mouse Optical Optical trackpad Pointing stick Touchpad Touchscreen Trackball Other Keyboard Image scanner Graphics card GPU Microphone Refreshable braille display Sound card Sound chip Webcam Softcam Output devices Monitor Screen Refreshable braille display Printer Plotter Speakers Sound card Graphics card Removable data storage Disk pack Floppy disk Optical disc CD DVD Blu-ray Flash memory Memory card USB flash drive Computer case Central processing unit Microprocessor Motherboard Memory RAM BIOS Data storage HDD SSD (SATA / NVMe) SSHD Power supply SMPS MOSFET Power MOSFET VRM Network interface controller Fax modem Expansion card Ports Current Ethernet USB Thunderbolt Analog audio jack DisplayPort HDMI Obsolete FireWire (IEEE 1394) Parallel port Serial port Game port PS/2 port eSATA DVI VGA Related History of computing hardware History of computing hardware (1960s–present) List of pioneers in computer science

v t e Primary computer data storage technologies Volatile memory Current DRAM SDRAM DDR SDRAM DDR LPDDR HBM EDO DRAM RDRAM XDR DRAM QDR eDRAM Dual-ported RAM SRAM 1T-SRAM Experimental Z-RAM T-RAM Historical Delay-line memory Selectron tube Dekatron Non-volatile memory Current RRAM (3D XPoint) EAROM EEPROM EPROM Flash memory PROM ROM Future FeRAM MRAM NRAM PRAM SONOS Historical Bubble memory Drum memory Magnetic-core memory Twistor memory

v t e 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)

v t e Optical storage media Blu-ray (2006) BD-R (2006) BD-RE (2006) BD-R XL (2010) BD-RE XL (2010) Professional Disc (2003) PDD (2004) 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-i (1991) CD-RW (1997) Discontinued Microform (1870) Optical tape (20th century) Optical disc (20th century) LaserDisc (1978) WORM (1979) GD-ROM (1997) MIL-CD (1999) DataPlay (2002) UDO (2003) ProData (2003) UMD (2004) HD DVD (2006) Magneto-optic Kerr effect (1877) MO disc (1980s) MiniDisc (1992) MD Data (1993) Hi-MD (2004) Optical Assist Laser turntable (1986) Floptical (1991) Super DLT (1998)

v t e Paper data storage media Antiquity Writing on papyrus (c. 3000 BCE) Paper (105 CE) Modern Index card (1640s) Punched tape (mid-1800s) Punched card (1880s) Edge-notched card (1904) Optical mark recognition (1930s) Barcode (1948)

Authority control databases International GND National Czech Republic Other Yale LUX

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Adapted from the Wikipedia article [Computer data storage](https://en.wikipedia.org/wiki/Computer_data_storage) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Computer_data_storage?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.