The Massbus is a high-performance computer input/output bus designed in the 1970s by Digital Equipment Corporation (DEC). The architecture development was sponsored by Gordon Bell and John Levy was the principal architect.
67-463: The bus was used by Digital to interconnect its highest-performance computers with magnetic disk and magnetic tape storage equipment. The use of a common bus was intended to allow a single controller design to handle multiple peripheral models, and allowed the PDP-10 , PDP-11 , and VAX computer families to share a common set of peripherals. At the time there were multiple operating systems for each of
134-475: A bit pattern to each character , digit , or multimedia object. Many standards exist for encoding (e.g. character encodings like ASCII , image encodings like JPEG , and video encodings like MPEG-4 ). By adding bits to each encoded unit, redundancy allows the computer to detect errors in coded data and correct them based on mathematical algorithms. Errors generally occur in low probabilities due to random bit value flipping, or "physical bit fatigue", loss of
201-493: A computer a brief window of time to move information from primary volatile storage into non-volatile storage before the batteries are exhausted. Some systems, for example EMC Symmetrix , have integrated batteries that maintain volatile storage for several minutes. Utilities such as hdparm and sar can be used to measure IO performance in Linux. Full disk encryption , volume and virtual disk encryption, andor file/folder encryption
268-424: 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
335-702: A drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library. Tertiary storage is also known as nearline storage because it is "near to online". The formal distinction between online, nearline, and offline storage is: For example, always-on spinning hard disk drives are online storage, while spinning drives that spin down automatically, such as in massive arrays of idle disks ( MAID ), are nearline storage. Removable media such as tape cartridges that can be automatically loaded, as in tape libraries , are nearline storage, while tape cartridges that must be manually loaded are offline storage. Off-line storage
402-479: A drum. In 1928, Fritz Pfleumer developed the first magnetic tape recorder . Early magnetic storage devices were designed to record analog audio signals. Computers and now most audio and video magnetic storage devices record digital data . In 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 . Unlike modern computers, magnetic tape
469-549: A halfway position that weakens the readability of the domain and relieves the magnetic stresses. A write head magnetises a region by generating a strong local magnetic field, and a read head detects the magnetisation of the regions. Early HDDs used an electromagnet both to magnetise the region and to then read its magnetic field by using electromagnetic induction . Later versions of inductive heads included Metal In Gap (MIG) heads and thin film heads. As data density increased, read heads using magnetoresistance (MR) came into use;
536-400: A relatively simple processor may keep state between successive computations to build up complex procedural results. Most modern computers are von Neumann machines. A modern digital computer represents data using the binary numeral system . Text, numbers, pictures, audio, and nearly any other form of information can be converted into a string of bits , or binary digits, each of which has
603-424: A single true magnetic domain . Each magnetic region in total forms a magnetic dipole which generates a magnetic field . In older hard disk drive (HDD) designs the regions were oriented horizontally and parallel to the disk surface, but beginning about 2005, the orientation was changed to perpendicular to allow for closer magnetic domain spacing. Older hard disk drives used iron(III) oxide (Fe 2 O 3 ) as
670-574: A source to read instructions from, in order to start the computer. Hence, non-volatile primary storage containing a small startup program ( BIOS ) is used to bootstrap the computer, that is, to read a larger program from non-volatile secondary storage to RAM and start to execute it. A non-volatile technology used for this purpose is called ROM, for read-only memory (the terminology may be somewhat confusing as most ROM types are also capable of random access ). Many types of "ROM" are not literally read only , as updates to them are possible; however it
737-436: A type of air bearing . Analog recording is based on the fact that remnant magnetisation of a given material depends on the magnitude of the applied field. The magnetic material is normally in the form of tape, with the tape in its blank form being initially demagnetised. When recording, the tape runs at a constant speed. The writing head magnetises the tape with current proportional to the signal. A magnetisation distribution
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#1732855920654804-490: A value of 0 or 1. The most common unit of storage is the byte , equal to 8 bits. A piece of information can be handled by any computer or device whose storage space is large enough to accommodate the binary representation of the piece of information , or simply data . For example, the complete works of Shakespeare , about 1250 pages in print, can be stored in about five megabytes (40 million bits) with one byte per character. Data are encoded by assigning
871-558: A wire—was publicized by Oberlin Smith in the Sept 8, 1888 issue of Electrical World . Smith had previously filed a patent in September, 1878 but found no opportunity to pursue the idea as his business was machine tools. The first publicly demonstrated (Paris Exposition of 1900) magnetic recorder was invented by Valdemar Poulsen in 1898. Poulsen's device recorded a signal on a wire wrapped around
938-427: Is a form of volatile memory that also requires the stored information to be periodically reread and rewritten, or refreshed , otherwise it would vanish. Static random-access memory is a form of volatile memory similar to DRAM with the exception that it never needs to be refreshed as long as power is applied; it loses its content when the power supply is lost. An uninterruptible power supply (UPS) can be used to give
1005-425: Is a level below secondary storage. Typically, it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; such data are often copied to secondary storage before use. It is primarily used for archiving rarely accessed information since it is much slower than secondary storage (e.g. 5–60 seconds vs. 1–10 milliseconds). This
1072-410: Is a technology consisting of computer components and recording media that are used to retain digital data . It is a core function and fundamental component of computers. The central processing unit (CPU) of a computer is what manipulates data by performing computations. In practice, almost all computers use a storage hierarchy , which puts fast but expensive and small storage options close to
1139-434: Is achieved along the magnetic tape. Finally, the distribution of the magnetisation can be read out, reproducing the original signal. The magnetic tape is typically made by embedding magnetic particles (approximately 0.5 micrometers in size) in a plastic binder on polyester film tape. The most commonly-used of these was ferric oxide, though chromium dioxide, cobalt, and later pure metal particles were also used. Analog recording
1206-504: Is also called bubble memory . The basic idea is to control domain wall motion in a magnetic medium that is free of microstructure. Bubble refers to a stable cylindrical domain. Data is then recorded by the presence/absence of a bubble domain. Domain propagation memory has high insensitivity to shock and vibration, so its application is usually in space and aeronautics. Magnetic storage media can be classified as either sequential access memory or random access memory , although in some cases
1273-423: Is also widely used in some specific applications, such as bank cheques ( MICR ) and credit/debit cards ( mag stripes ). A new type of magnetic storage, called magnetoresistive random-access memory or MRAM, is being produced that stores data in magnetic bits based on the tunnel magnetoresistance (TMR) effect. Its advantage is non-volatility, low power usage, and good shock robustness. The 1st generation that
1340-410: Is computer data storage on a medium or a device that is not under the control of a processing unit . The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction. Off-line storage
1407-441: Is conceptually divided into many small sub- micrometer -sized magnetic regions, referred to as magnetic domains, (although these are not magnetic domains in a rigorous physical sense), each of which has a mostly uniform magnetisation. Due to the polycrystalline nature of the magnetic material, each of these magnetic regions is composed of a few hundred magnetic grains . Magnetic grains are typically 10 nm in size and each form
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#17328559206541474-408: Is done before deciding whether to keep certain data compressed or not. For security reasons , certain types of data (e.g. credit card information) may be kept encrypted in storage to prevent the possibility of unauthorized information reconstruction from chunks of storage snapshots. Generally, the lower a storage is in the hierarchy, the lesser its bandwidth and the greater its access latency
1541-609: Is estimable using S.M.A.R.T. diagnostic data that includes the hours of operation and the count of spin-ups, though its reliability is disputed. Flash storage may experience downspiking transfer rates as a result of accumulating errors, which the flash memory controller attempts to correct. The health of optical media can be determined by measuring correctable minor errors , 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 support error scanning. As of 2011 ,
1608-1109: Is from the CPU. This traditional division of storage to primary, secondary, tertiary, and off-line storage is also guided by cost per bit. In contemporary usage, memory is usually fast but temporary semiconductor read-write memory , typically DRAM (dynamic RAM) or other such devices. Storage consists of storage devices and their media not directly accessible by the CPU ( secondary or tertiary storage ), typically hard disk drives , optical disc drives, and other devices slower than RAM but non-volatile (retaining contents when powered down). Historically, memory has, depending on technology, been called central memory , core memory , core storage , drum , main memory , real storage , or internal memory . Meanwhile, slower persistent storage devices have been referred to as secondary storage , external memory , or auxiliary/peripheral storage . Primary storage (also known as main memory , internal memory , or prime memory ), often referred to simply as memory ,
1675-410: Is from the starting point. The case of ferrite-core memory is the opposite. Every core location is immediately accessible at any given time. Hard disks and modern linear serpentine tape drives do not precisely fit into either category. Both have many parallel tracks across the width of the media and the read/write heads take time to switch between tracks and to scan within tracks. Different spots on
1742-416: Is primarily useful for extraordinarily large data stores, accessed without human operators. Typical examples include tape libraries and optical jukeboxes . When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place it in
1809-700: Is readily available for most storage devices. Hardware memory encryption is available in Intel Architecture, supporting Total Memory Encryption (TME) and page granular memory encryption with multiple keys (MKTME). and in SPARC M7 generation since October 2015. Distinct types of data storage have different points of failure and various methods of predictive failure analysis . Vulnerabilities that can instantly lead to total loss are head crashing on mechanical hard drives and failure of electronic components on flash storage. Impending failure on hard disk drives
1876-488: Is slow and memory must be erased in large portions before it can be re-written. Some embedded systems run programs directly from ROM (or similar), because such programs are rarely changed. Standard computers do not store non-rudimentary programs in ROM, and rather, use large capacities of secondary storage, which is non-volatile as well, and not as costly. Recently, primary storage and secondary storage in some uses refer to what
1943-442: Is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in a uniform manner. Historically, early computers used delay lines , Williams tubes , or rotating magnetic drums as primary storage. By 1954, those unreliable methods were mostly replaced by magnetic-core memory . Core memory remained dominant until
2010-417: Is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory . The information is accessed using one or more read/write heads . Magnetic storage media, primarily hard disks , are widely used to store computer data as well as audio and video signals. In the field of computing,
2077-409: Is typically magneto-resistive while the write element is typically thin-film inductive. The heads are kept from contacting the platter surface by the air that is extremely close to the platter; that air moves at or near the platter speed. The record and playback head are mounted on a block called a slider, and the surface next to the platter is shaped to keep it just barely out of contact. This forms
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2144-405: Is typically automatically fenced out, taken out of use by the device, and replaced with another functioning equivalent group in the device, where the corrected bit values are restored (if possible). The cyclic redundancy check (CRC) method is typically used in communications and storage for error detection . A detected error is then retried. Data compression methods allow in many cases (such as
2211-505: Is typically measured in milliseconds (thousandths of a second), while the access time per byte for primary storage is measured in nanoseconds (billionths of a second). Thus, secondary storage is significantly slower than primary storage. Rotating optical storage devices, such as CD and DVD drives, have even longer access times. Other examples of secondary storage technologies include USB flash drives , floppy disks , magnetic tape , paper tape , punched cards , and RAM disks . Once
2278-496: Is used to transfer information since the detached medium can easily be physically transported. Additionally, it is useful for cases of disaster, where, for example, a fire destroys the original data, a medium in a remote location will be unaffected, enabling disaster recovery . Off-line storage increases general information security since it is physically inaccessible from a computer, and data confidentiality or integrity cannot be affected by computer-based attack techniques. Also, if
2345-399: Is useful in applications where moderate amounts of storage with a need for very frequent updates are required, which flash memory cannot support due to its limited write endurance. Six state MRAM is also being developed, echoing four bit multi level flash memory cells, that have six different bits, as opposed to two . Research is also being done by Aleksei Kimel at Radboud University in
2412-476: The disk read/write head on HDDs reaches the proper placement and the data, subsequent data on the track are very fast to access. To reduce the seek time and rotational latency, data are transferred to and from disks in large contiguous blocks. Sequential or block access on disks is orders of magnitude faster than random access, and many sophisticated paradigms have been developed to design efficient algorithms based on sequential and block access. Another way to reduce
2479-466: The 16-bit, 32-bit, and 36-bit computer lines. The 18-bit PDP-15 /40 connected to Massbus peripherals via a PDP-11 front end. An engineering goal was to reduce the need for a new driver per peripheral per operating system per computer family. Also, a major technical goal was to place any magnetic technology changes (data separators) into the storage device rather than in the CPU-attached controller. Thus
2546-690: The 1970s, when advances in integrated circuit technology allowed semiconductor memory to become economically competitive. This led to modern random-access memory (RAM). It is small-sized, light, but quite expensive at the same time. The particular types of RAM used for primary storage are volatile , meaning that they lose the information when not powered. Besides storing opened programs, it serves as disk cache and 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. Spare memory can be utilized as RAM drive for temporary high-speed data storage. As shown in
2613-463: The CPU I/O or memory bus to Massbus adapter needed no changes for multiple generations of storage technology. A business objective was to provide a subsystem entry price well below that of IBM storage subsystems which used large and expensive controllers unique to each storage technology and processor architecture and were optimized for connecting large numbers of storage devices. The first Massbus device
2680-501: The CPU and slower but less expensive and larger options further away. Generally, the fast technologies are referred to as "memory", while slower persistent technologies are referred to as "storage". Even the first computer designs, Charles Babbage 's Analytical Engine and Percy Ludgate 's Analytical Machine, clearly distinguished between processing and memory (Babbage stored numbers as rotations of gears, while Ludgate stored numbers as displacements of rods in shuttles). This distinction
2747-508: The I/O bottleneck is to use multiple disks in parallel to increase the bandwidth between primary and secondary memory. Secondary storage is often formatted according to a file system format, which provides the abstraction necessary to organize data into files and directories , while also providing metadata describing the owner of a certain file, the access time, the access permissions, and other information. Most computer operating systems use
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2814-522: The Netherlands towards the possibility of using terahertz radiation rather than using standard electropulses for writing data on magnetic storage media. By using terahertz radiation, writing time can be reduced considerably (50x faster than when using standard electropulses). Another advantage is that terahertz radiation generates almost no heat, thus reducing cooling requirements. Primary storage Computer data storage or digital data storage
2881-510: The architecture was a Master Massbus drive and slave tape drives. DEC also developed the Massbus RS03/04, a head per track disk drive for high performance swapping. The last Massbus disk drive was the DEC designed RM80 as DEC shifted to internal development of large disks. The bus is logically implemented as two separate sections: Magnetic disk Magnetic storage or magnetic recording
2948-524: The concept of 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 ) to a swap file or page file on secondary storage, retrieving them later when needed. If a lot of pages are moved to slower secondary storage, the system performance is degraded. The secondary storage, including HDD , ODD and SSD , are usually block-addressable. Tertiary storage or tertiary memory
3015-430: 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 (HDDs) or solid-state drives (SSDs) are usually used as secondary storage. The access time per byte for HDDs or SSDs
3082-491: The desired location of data. Then it reads or writes the data in the memory cells using the data bus. Additionally, a memory management unit (MMU) is a small device between CPU and RAM recalculating the actual memory address, for example to provide an abstraction of virtual memory or other tasks. As the RAM types used for primary storage are volatile (uninitialized at start up), a computer containing only such storage would not have
3149-400: The diagram, traditionally there are two more sub-layers of the primary storage, besides main large-capacity RAM: Main memory is directly or indirectly connected to the central processing unit via a memory bus . It is actually two buses (not on the diagram): an address bus and a data bus . The CPU firstly sends a number through an address bus, a number called memory address , that indicates
3216-436: The distinction is not perfectly clear. The access time can be defined as the average time needed to gain access to stored records. In the case of magnetic wire, the read/write head only covers a very small part of the recording surface at any given time. Accessing different parts of the wire involves winding the wire forward or backward until the point of interest is found. The time to access this point depends on how far away it
3283-425: The electrical resistance of the head changed according to the strength of the magnetism from the platter. Later development made use of spintronics ; in read heads, the magnetoresistive effect was much greater than in earlier types, and was dubbed "giant" magnetoresistance (GMR). In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element
3350-477: The former using standard MOSFETs and the latter using floating-gate MOSFETs . In modern computers, primary storage almost exclusively consists of dynamic volatile semiconductor random-access memory (RAM), particularly dynamic random-access memory (DRAM). Since the turn of the century, a type of non-volatile floating-gate semiconductor memory known as flash memory has steadily gained share as off-line storage for home computers. Non-volatile semiconductor memory
3417-568: The information stored for archival purposes is rarely accessed, off-line storage is less expensive than tertiary storage. In modern personal computers, most secondary and tertiary storage media are also used for off-line storage. Optical discs and flash memory devices are the most popular, and to a much lesser extent removable hard disk drives; older examples include floppy disks and Zip disks. In enterprise uses, magnetic tape cartridges are predominant; older examples include open-reel magnetic tape and punched cards. Storage technologies at all levels of
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#17328559206543484-443: The magnetic material, but current disks use a cobalt -based alloy. For reliable storage of data, the recording material needs to resist self-demagnetisation, which occurs when the magnetic domains repel each other. Magnetic domains written too close together in a weakly magnetisable material will degrade over time due to rotation of the magnetic moment of one or more domains to cancel out these forces. The domains rotate sideways to
3551-458: The magnetic medium is heated locally by a laser , which induces a rapid decrease of coercive field. Then, a small magnetic field can be used to switch the magnetisation. The reading process is based on magneto-optical Kerr effect . The magnetic medium are typically amorphous R-Fe-Co thin film (R being a rare earth element). Magneto-optical recording is not very popular. One famous example is Minidisc developed by Sony . Domain propagation memory
3618-641: The most commonly used data storage media are semiconductor, magnetic, and optical, while paper still sees some limited usage. Some other fundamental storage technologies, such as all-flash arrays (AFAs) are proposed for development. Semiconductor memory uses semiconductor -based integrated circuit (IC) chips to store information. Data are typically stored in metal–oxide–semiconductor (MOS) memory cells . A semiconductor memory chip may contain millions of memory cells, consisting of tiny MOS field-effect transistors (MOSFETs) and/or MOS capacitors . Both volatile and non-volatile forms of semiconductor memory exist,
3685-408: The physical bit in the storage of its ability to maintain a distinguishable value (0 or 1), or due to errors in inter or intra-computer communication. A random bit flip (e.g. due to random radiation ) is typically corrected upon detection. A bit or a group of malfunctioning physical bits (the specific defective bit is not always known; group definition depends on the specific storage device)
3752-444: The recording of analog audio and video works on analog tape . Since much of audio and video production is moving to digital systems, the usage of hard disks is expected to increase at the expense of analog tape. Digital tape and tape libraries are popular for the high capacity data storage of archives and backups. Floppy disks see some marginal usage, particularly in dealing with older computer systems and software. Magnetic storage
3819-530: The result. It would have to be reconfigured to change its behavior. This is acceptable for devices such as desk calculators , digital signal processors , and other specialized devices. Von Neumann machines differ in having a memory in which they store their operating instructions and data. Such computers are more versatile in that they do not need to have their hardware reconfigured for each new program, but can simply be reprogrammed with new in-memory instructions; they also tend to be simpler to design, in that
3886-413: The storage hierarchy can be differentiated by evaluating certain core characteristics as well as measuring characteristics specific to a particular implementation. These core characteristics are volatility, mutability, accessibility, and addressability. For any particular implementation of any storage technology, the characteristics worth measuring are capacity and performance. Non-volatile memory retains
3953-654: The storage media take different amounts of time to access. For a hard disk this time is typically less than 10 ms, but tapes might take as much as 100 s. Magnetic disk heads and magnetic tape heads cannot pass DC (direct current), so the coding schemes for both tape and disk data are designed to minimize the DC offset . Most magnetic storage devices use error correction . Many magnetic disks internally use some form of run-length limited coding and partial-response maximum-likelihood . As of 2021 , common uses of magnetic storage media are for computer data mass storage on hard disks and
4020-422: The stored information even if not constantly supplied with electric power. It is suitable for long-term storage of information. Volatile memory requires constant power to maintain the stored information. The fastest memory technologies are volatile ones, although that is not a universal rule. Since the primary storage is required to be very fast, it predominantly uses volatile memory. Dynamic random-access memory
4087-401: The term magnetic storage is preferred and in the field of audio and video production, the term magnetic recording is more commonly used. The distinction is less technical and more a matter of preference. Other examples of magnetic storage media include floppy disks , magnetic tape , and magnetic stripes on credit cards. Magnetic storage in the form of wire recording —audio recording on
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#17328559206544154-456: Was also often used for secondary storage. Information is written to and read from the storage medium as it moves past devices called read-and-write heads that operate very close (often tens of nanometers) over the magnetic surface. The read-and-write head is used to detect and modify the magnetisation of the material immediately under it. There are two magnetic polarities, each of which is used to represent either 0 or 1. The magnetic surface
4221-505: Was developed was produced by Everspin Technologies , and utilized field induced writing. The 2nd generation is being developed through two approaches: thermal-assisted switching (TAS) which is currently being developed by Crocus Technology , and spin-transfer torque (STT) on which Crocus , Hynix , IBM , and several other companies are working. However, with storage density and capacity orders of magnitude smaller than an HDD , MRAM
4288-461: Was extended in the Von Neumann architecture , where the CPU consists of two main parts: The control unit and the arithmetic logic unit (ALU). The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and logical operations on data. Without a significant amount of memory, a computer would merely be able to perform fixed operations and immediately output
4355-441: Was historically called, respectively, secondary storage and tertiary storage . The primary storage, including ROM , EEPROM , NOR flash , and RAM , are usually byte-addressable . Secondary storage (also known as external memory or auxiliary storage ) differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfer
4422-816: Was the RP04, based on Sperry Univac Information Storage Systems's (ISS) clone of the IBM 3330. Subsequently, DEC offered the RP05 and RP06, based on Memorex 's 3330 clone. Memorex modified the IBM compatible interface to DEC requirements and moved the data separator electronics into the drive. DEC designed the rest which was mounted in the "bustle" attached to the drive. This set the pattern for future improvements of disk technology to double density 3330, CDC SMD drives, and then "Winchester" technology. Drives were supplied by ISS/Univac, Memorex, and Control Data. Multiple generations of tape technology and performance were also Massbus connected although
4489-645: Was the most popular method of audio and video recording. Since the late 1990s, however, tape recording has declined in popularity due to digital recording. Instead of creating a magnetisation distribution in analog recording, digital recording only needs two stable magnetic states, which are the +Ms and −Ms on the hysteresis loop . Examples of digital recording are floppy disks , hard disk drives (HDDs), and tape drives . HDDs offer large capacities at reasonable prices; as of 2024 , consumer-grade HDDs offer data storage at about US$ 15–20 per terabyte. Magneto-optical recording writes/reads optically. When writing,
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