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92-447: Above figures are approximate and do not include input-output devices. Decimal point occurs at the right of the sign digit. Addition, subtraction, and multiplication times given below include reading and executing the instruction. The time includes formation of the result in the accumulator. All instructions, however are performed at minimum latency rates. All users utilize a 2,000-word, 24,000-digit magnetic-core storage unit. Each of

184-412: A single magnetic domain . Next the powder is pressed into a shape, dried, and re-sintered. The shaping may be performed in an external magnetic field, in order to achieve a preferred orientation of the particles ( anisotropy ). Small and geometrically easy shapes may be produced with dry pressing. However, in such a process small particles may agglomerate and lead to poorer magnetic properties compared to

276-481: A backing sheet "patch" that supported them during manufacture and later use. Threading needles were butt welded to the wires, the needle and wire diameters were the same, and efforts were made to eliminate the use of needles. The most important change, from the point of view of automation, was the combination of the sense and inhibit wires, eliminating the need for a circuitous diagonal sense wire. With small changes in layout, this also allowed much tighter packing of

368-406: A body-centered cubic or hexagonal crystal structure . Like most of the other ceramics , ferrites are hard, brittle , and poor conductors of electricity . They are typically composed of α- iron(III) oxide (e.g. hematite Fe 2 O 3 ) with one, or more additional, metallic element oxides, usually with an approximately stochiometric formula of M O·Fe 2 O 3 such as Fe(II) such as in

460-487: A component of radar-absorbing materials or coatings used in stealth aircraft and in the absorption tiles lining the rooms used for electromagnetic compatibility measurements. Most common audio magnets, including those used in loudspeakers and electromagnetic instrument pickups , are ferrite magnets. Except for certain "vintage" products, ferrite magnets have largely displaced the more expensive Alnico magnets in these applications. In particular, for hard hexaferrites today

552-502: A considerable voltage across the whole line due to the superposition of the voltage at each single core. This potential risk of "misread" limits the minimum number of Sense wires. Increasing Sense wires also requires more decode circuitry. Core memory controllers were designed so that every read was followed immediately by a write (because the read forced all bits to 0, and because the write assumed this had happened). Instruction sets were designed to take advantage of this. For example,

644-511: A converted aspirin press in 1949. Rajchman later developed versions of the Williams tube and led development of the Selectron . Two key inventions led to the development of magnetic core memory in 1951. The first, An Wang's, was the write-after-read cycle, which solved the problem of how to use a storage medium in which the act of reading erased the data read, enabling the construction of

736-584: A data word. For instance, a machine might use 32 grids of core with a single bit of the 32-bit word in each one, and the controller could access the entire 32-bit word in a single read/write cycle. Core memory is non-volatile storage —it can retain its contents indefinitely without power. It is also relatively unaffected by EMP and radiation. These were important advantages for some applications like first-generation industrial programmable controllers , military installations and vehicles like fighter aircraft , as well as spacecraft , and led to core being used for

828-471: A fuse blows, power is shut off and an indicator circuit shows in which bay the blown fuse is located, and a "flag" indicates the specific fuse. An automatic voltage-monitoring system continuously monitors all critical DC potentials giving an alarm if any moves outside the prescribed limits. Magnetic-core memory In computing , magnetic-core memory is a form of random-access memory . It predominated for roughly 20 years between 1955 and 1975, and

920-507: A high coercivity and high remanence after magnetization. Iron oxide and barium carbonate or strontium carbonate are used in manufacturing of hard ferrite magnets. The high coercivity means the materials are very resistant to becoming demagnetized, an essential characteristic for a permanent magnet. They also have high magnetic permeability . These so-called ceramic magnets are cheap, and are widely used in household products such as refrigerator magnets . The maximum magnetic field B

1012-465: A magnetic uniaxial anisotropy. This can be done by magnetic annealing, magnetic field assisted compaction, or reaction under uniaxial pressure. This last solution has the advantage to be ultra fast (20 min) thanks to the use of spark plasma sintering . The induced magnetic anisotropy in cobalt ferrite is also beneficial to enhance the magnetoelectric effect in composite. In contrast, permanent ferrite magnets are made of hard ferrites , which have

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1104-425: A metal or plastic plate. The term "core" comes from conventional transformers whose windings surround a magnetic core . In core memory, the wires pass once through any given core—they are single-turn devices. The properties of materials used for memory cores are dramatically different from those used in power transformers. The magnetic material for a core memory requires a high degree of magnetic remanence ,

1196-542: A number of years after availability of semiconductor MOS memory (see also MOSFET ). For example, the Space Shuttle IBM AP-101B flight computers used core memory, which preserved the contents of memory even through the Challenger ' s disintegration and subsequent plunge into the sea in 1986. Another characteristic of early core was that the coercive force was very temperature-sensitive;

1288-405: A one and a zero, these diagnostics tested the core memory with worst-case patterns and had to run for several hours. As most computers had just a single core-memory board, these diagnostics also moved themselves around in memory, making it possible to test every bit. An advanced test was called a " Shmoo test " in which the half-select currents were modified along with the time at which the sense line

1380-534: A serial, one-dimensional shift register (of 50 bits), using two cores to store a bit. A Wang core shift register is in the Revolution exhibit at the Computer History Museum . The second, Forrester's, was the coincident-current system, which enabled a small number of wires to control a large number of cores enabling 3D memory arrays of several million bits. The first use of magnetic core was in

1472-601: A single cycle. A typical machine's register set usually used only one small plane of this form of core memory. Some very large memories were built with this technology, for example the Extended Core Storage (ECS) auxiliary memory in the CDC 6600 , which was up to 2 million 60-bit words. Core rope memory is a read-only memory (ROM) form of core memory. In this case, the cores, which had more linear magnetic materials, were simply used as transformers ; no information

1564-523: A spinel crystalline form and is widely used a magnetic recording substrate. However the structure is not an ordinary spinel structure , but rather the inverse spinel structure: One eighth of the tetrahedral holes are occupied by B cations, one fourth of the octahedral sites are occupied by A cations. and the other one fourth by B cation. It is also possible to have mixed structure spinel ferrites with formula [ M (1− δ )  Fe δ  ] [ M δ  Fe (2− δ )  ] O 4 , where δ

1656-423: A value – or written – is selected by powering one X and one Y wire to half of the required power, such that only the single core at the intersection is written. Depending on the direction of the currents, the core will pick up a clockwise or counterclockwise magnetic field, storing a 1 or 0. This writing process also causes electricity to be induced into nearby wires. If the new pulse being applied in

1748-498: A value in memory could be read and modified almost as quickly as it could be read and written. In the PDP-6 , the AOS* (or SOS* ) instructions incremented (or decremented) the value between the read phase and the write phase of a single memory cycle (perhaps signaling the memory controller to pause briefly in the middle of the cycle). This might be twice as fast as the process of obtaining

1840-402: Is a stored 1 , while the other is a stored 0 . The toroidal shape of a core is preferred since the magnetic path is closed, there are no magnetic poles and thus very little external flux. This allows the cores to be packed closely together without their magnetic fields interacting. The alternating 45-degree positioning used in early core arrays was necessitated by the diagonal sense wires. With

1932-434: Is about 0.35  tesla and the magnetic field strength H is about 30–160 kiloampere turns per meter (400–2000  oersteds ). The density of ferrite magnets is about 5 g/cm . The most common hard ferrites are: Ferrites are produced by heating a mixture of the oxides of the constituent metals at high temperatures, as shown in this idealized equation: In some cases, the mixture of finely-powdered precursors

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2024-413: Is applied to each bit sense/write line for a bit to be set. In some designs, the word read and word write lines were combined into a single wire, resulting in a memory array with just two wires per bit. For write, multiple word write lines could be selected. This offered a performance advantage over X/Y line coincident-current in that multiple words could be cleared or written with the same value in

2116-427: Is detected, and the computer stalls. Other types of checking circuits cause Univac to stall when other types of errors occur. An error occurs if reference to a non-existent memory address is attempted. An odd-even error in the transfer rI to rM will result in a transfer stop and the location of the error (rI address) will be indicated. The 720 character count will be displayed on a modulus 100 counter. In addition to

2208-470: Is made of semiconductors, particularly by people who had worked with machines having actual core memory. The files that result from saving the entire contents of memory to disk for inspection, which is nowadays commonly performed automatically when a major error occurs in a computer program, are still called " core dumps ". Algorithms which work on more data than the main memory can fit are likewise called out-of-core algorithms . Algorithms which only work inside

2300-468: Is normally associated with three independent teams. Substantial work in the field was carried out by the Shanghai -born American physicists An Wang and Way-Dong Woo , who created the pulse transfer controlling device in 1949. The patent described a type of memory that would today be known as a delay-line or shift-register system. Each bit was stored using a pair of transformers, one that held

2392-410: Is often just called core memory , or, informally, core . Core memory uses toroids (rings) of a hard magnetic material (usually a semi-hard ferrite ). Each core stores one bit of information. Two or more wires pass through each core, forming an X-Y array of cores. When an electrical current above a certain threshold is applied to the wires, the core will become magnetized. The core to be assigned

2484-475: Is pressed into a mold. For barium and strontium ferrites, these metals are typically supplied as their carbonates, BaCO 3 or SrCO 3 . During the heating process, these carbonates undergo calcination : After this step, the two oxides combine to give the ferrite. The resulting mixture of oxides undergoes sintering . Having obtained the ferrite, the cooled product is milled to particles smaller than 2 μm , sufficiently small that each particle consists of

2576-548: Is the degree of inversion. The magnetic material known as "Zn Fe" has the formula Zn Fe 2 O 4 , with Fe occupying the octahedral sites and Zn occupying the tetrahedral sites, it is an example of normal structure spinel ferrite. Some ferrites adopt hexagonal crystal structure, like barium and strontium ferrites BaFe 12 O 19 ( BaO  : 6 Fe 2 O 3 ) and SrFe 12 O 19 ( Sr O  : 6 Fe 2 O 3 ). In terms of their magnetic properties,

2668-471: The IBM 7090 , early IBM 7094s , and IBM 7030 . Core was heated instead of cooled because the primary requirement was a consistent temperature, and it was easier (and cheaper) to maintain a constant temperature well above room temperature than one at or below it. Diagnosing hardware problems in core memory required time-consuming diagnostic programs to be run. While a quick test checked if every bit could contain

2760-507: The PDP-6 at the MIT Artificial Intelligence Laboratory by 1967. This was considered "unimaginably huge" at the time, and nicknamed the "Moby Memory". It cost $ 380,000 ($ 0.04/bit) and its width, height and depth was 175 cm × 127 cm × 64 cm (69 in × 50 in × 25 in) with its supporting circuitry (189 kilobits/cubic foot = 6.7 kilobits/litre). Its cycle time

2852-409: The memory density of core slowly increased. By the late 1960s a density of about 32 kilobits per cubic foot (about 0.9 kilobits per litre) was typical. The cost declined over this period from about $ 1 per bit to about 1 cent per bit. Reaching this density requires extremely careful manufacturing, which was almost always carried out by hand in spite of repeated major efforts to automate the process. Core

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2944-479: The spinel chemical structure with the formula A B 2 O 4 , where A and B represent various metal cations , one of which is usually iron (Fe). Spinel ferrites usually adopt a crystal motif consisting of cubic close-packed (fcc) oxides ( O ) with A cations occupying one eighth of the tetrahedral holes, and B cations occupying half of the octahedral holes, i.e., A B 2 O 4 . An exception exists for ɣ-Fe 2 O 3 which has

3036-519: The spinel group) include those with nickel (NiFe 2 O 4 ) which occurs as the mineral trevorite , magnesium containing magnesioferrite (MgFe 2 O 4 ), cobalt ( cobalt ferrite ), or manganese (MnFe 2 O 4 ) which occurs naturally as the mineral jacobsite . Less often bismuth , strontium , zinc as found in franklinite , aluminum , yittrium , or barium ferrites are used In addition, more complex synthetic alloys are often used for specific applications. Many ferrites adopt

3128-682: The Whirlwind computer, and Project Whirlwind's "most famous contribution was the random-access, magnetic core storage feature." Commercialization followed quickly. Magnetic core was used in peripherals of the ENIAC in 1953, the IBM 702 delivered in July 1955, and later in the 702 itself. The IBM 704 (1954) and the Ferranti Mercury (1957) used magnetic-core memory. It was during the early 1950s that Seeburg Corporation developed one of

3220-512: The X-Y wires is the same as the last applied to that core, the existing field will do nothing, and no induction will result. If the new pulse is in the opposite direction, a pulse will be generated. This is normally picked up in a separate "sense" wire, allowing the system to know whether that core held a 1 or 0. As this readout process requires the core to be written, this process is known as destructive readout , and requires additional circuitry to reset

3312-404: The ability to stay highly magnetized, and a low coercivity so that less energy is required to change the magnetization direction. The core can take two states, encoding one bit . The core memory contents are retained even when the memory system is powered down ( non-volatile memory ). However, when the core is read, it is reset to a "zero" value. Circuits in the computer memory system then restore

3404-506: The chain. Wang and Woo were working at Harvard University 's Computation Laboratory at the time, and the university was not interested in promoting inventions created in their labs. Wang was able to patent the system on his own. The MIT Project Whirlwind computer required a fast memory system for real-time aircraft tracking. At first, an array of Williams tubes —a storage system based on cathode-ray tubes —was used, but proved temperamental and unreliable. Several researchers in

3496-482: The circuitry assumes there has been a read operation and the bit is in the 0 state. The Sense wire is used only during the read, and the Inhibit wire is used only during the write. For this reason, later core systems combined the two into a single wire, and used circuitry in the memory controller to switch the function of the wire. However, when Sense wire crosses too many cores, the half select current can also induce

3588-442: The combined magnetic field generated where the X and Y lines cross (the logical conjunction ) is sufficient to change the state; other cores will see only half the needed field ("half-selected"), or none at all. By driving the current through the wires in a particular direction, the resulting induced field forces the selected core's magnetic flux to circulate in one direction or the other (clockwise or counterclockwise). One direction

3680-428: The common mineral magnetite composed of Fe(II)-Fe(III) 2 O 4 . Above 585 °C Fe(II)-Fe(III) 2 O 4 transforms into the non-magnetic gamma phase. Fe(II)-Fe(III) 2 O 4 is commonly seen as the black iron(II) oxide coating the surface of cast-iron cookware). The other pattern is M ·Fe(III) 2 O 3 , where M is another metallic element. Common, naturally occurring ferrites (typically members of

3772-484: The core to its original value if the process flipped it. When not being read or written, the cores maintain the last value they had, even if the power is turned off. Therefore, they are a type of non-volatile memory . Depending on how it was wired, core memory could be exceptionally reliable. Read-only core rope memory , for example, was used on the mission-critical Apollo Guidance Computer essential to NASA 's successful Moon landings. Using smaller cores and wires,

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3864-467: The cores in each patch. By the early 1960s, the cost of core fell to the point that it became nearly universal as main memory , replacing both inexpensive low-performance drum memory and costly high-performance systems using vacuum tubes , and later discrete transistors as memory. The cost of core memory declined sharply over the lifetime of the technology: costs began at roughly US$ 1.00 per bit and dropped to roughly US$ 0.01 per bit. Core memory

3956-544: The cores of RF transformers and inductors in applications such as switched-mode power supplies and loopstick antennas used in AM radios. The most common soft ferrites are: For use with frequencies above 0.5 MHz but below 5 MHz, Mn Zn ferrites are used; above that, Ni Zn is the usual choice. The exception is with common mode inductors , where the threshold of choice is at 70 MHz. Moreover, cobalt ferrite's magnetostrictive properties can be tuned by inducing

4048-524: The data in the identical units give an indication of faulty operation, and stall the computer. At this point, the instruction may be repeated. The pulse code used in the Univac System is so designed that all characters contain an odd number of pulses. At several strategic points within Univac, every character is checked for an odd number of pulses. An indication is given whenever an even number of pulses

4140-941: The day. Ferrite (magnet)#Semi-hard ferrites A ferrite is one of a family of iron oxide -containing magnetic ceramic materials. They are ferrimagnetic , meaning they are attracted by magnetic fields and can be magnetized to become permanent magnets . Unlike many ferromagnetic materials, most ferrites are not electrically conductive , making them useful in applications like magnetic cores for transformers to suppress eddy currents . Ferrites can be divided into two groups based on their magnetic coercivity , their resistance to being demagnetized: "Hard" ferrites have high coercivity , so are difficult to demagnetize. They are used to make permanent magnets for applications such as refrigerator magnets , loudspeakers , and small electric motors . "Soft" ferrites have low coercivity, so they easily change their magnetization and act as conductors of magnetic fields. They are used in

4232-442: The different ferrites are often classified as "soft", "semi-hard" or "hard", which refers to their low or high magnetic coercivity , as follows. Ferrites that are used in transformer or electromagnetic cores contain nickel , zinc , and/or manganese compounds. Soft ferrites are not suitable to make permanent magnets. They have high magnetic permeability so they conduct magnetic fields and are attracted to magnets, but when

4324-435: The early 1970s, and by the mid-70s it was down to 600  ns (0.6 μs). Some designs had substantially higher performance: the CDC 6600 had a memory cycle time of 1.0 μs in 1964, using cores that required a half-select current of 200 mA. Everything possible was done in order to decrease access times and increase data rates (bandwidth), including the simultaneous use of multiple grids of core, each storing one bit of

4416-583: The electronics industry to make efficient magnetic cores called ferrite cores for high-frequency inductors , transformers and antennas , and in various microwave components. Ferrite compounds are extremely low cost, being made mostly of iron oxide, and have excellent corrosion resistance. Yogoro Kato and Takeshi Takei of the Tokyo Institute of Technology synthesized the first ferrite compounds in 1930. Ferrites are usually ferrimagnetic ceramic compounds derived from iron oxides , with either

4508-413: The elimination of these diagonal wires, tighter packing was possible. The access time plus the time to rewrite is the memory cycle time . To read a bit of core memory, the circuitry tries to flip the bit to the polarity assigned to the 0 state, by driving the selected X and Y lines that intersect at that core. The detection of such a pulse means that the bit had most recently contained a 1. Absence of

4600-431: The equipment; these types of ferrites are made with lossy materials to not just block (reflect), but also absorb and dissipate as heat, the unwanted higher-frequency energy. Early computer memories stored data in the residual magnetic fields of hard ferrite cores, which were assembled into arrays of core memory . Ferrite powders are used in the coatings of magnetic recording tapes . Ferrite particles are also used as

4692-486: The external magnetic field is removed, the remanent magnetization does not tend to persist. This is due to their low coercivity . The low coercivity also means the material's magnetization can easily reverse direction without dissipating much energy ( hysteresis losses ), while the material's high resistivity prevents eddy currents in the core, another source of energy loss. Because of their comparatively low core losses at high frequencies, they are extensively used in

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4784-399: The ferrite material used to make the toroids. An electric current in a wire that passes through a core creates a magnetic field. Only a magnetic field greater than a certain intensity ("select") can cause the core to change its magnetic polarity. To select a memory location, one of the X and one of the Y lines are driven with half the current ("half-select") required to cause this change. Only

4876-444: The first and 43rd, for example, or the 9th and 52nd. Physically the memory is a rectangular prism 7.25×10×12.75 inches (18.4×25.4×32.4 cm). A memory location thus always implies two cores in all 42 planes. The two cores are determined by the intersection of one column of fifty possible columns with two rows of the 80 possible rows. One row is in each section of the plane. All 42 planes are used twice for each word. Associated with

4968-510: The first commercial applications of coincident-current core memory storage in the "Tormat" memory of its new range of jukeboxes , starting with the V200 developed in 1953 and released in 1955. Numerous uses in computing, telephony and industrial process control followed. Wang's patent was not granted until 1955, and by that time magnetic-core memory was already in use. This started a long series of lawsuits, which eventually ended when IBM bought

5060-431: The follow-on core memory systems built by DEC for their PDP line of air-cooled computers. Another method of handling the temperature sensitivity was to enclose the magnetic core "stack" in a temperature controlled oven. Examples of this are the heated-air core memory of the IBM 1620 (which could take up to 30 minutes to reach operating temperature , about 106 °F (41 °C) and the heated-oil-bath core memory of

5152-429: The full current is applied to one or more word read lines; this clears the selected cores and any that flip induce voltage pulses in their bit sense/write lines. For read, normally only one word read line would be selected; but for clear, multiple word read lines could be selected while the bit sense/write lines ignored. To write words, the half current is applied to one or more word write lines, and half current

5244-473: The full plane of cores in a "nest" and then pushed an array of hollow needles through the cores to guide the wires. Use of this machine reduced the time taken to thread the straight X and Y select lines from 25 hours to 12 minutes on a 128 by 128 core array. Smaller cores made the use of hollow needles impractical, but there were numerous advances in semi-automatic core threading. Support nests with guide channels were developed. Cores were permanently bonded to

5336-494: The information in an immediate re-write cycle. The most common form of core memory, X/Y line coincident-current , used for the main memory of a computer, consists of a large number of small toroidal ferrimagnetic ceramic ferrites ( cores ) held together in a grid structure (organized as a "stack" of layers called planes ), with wires woven through the holes in the cores' centers. In early systems there were four wires: X , Y , Sense , and Inhibit , but later cores combined

5428-421: The late 1940s conceived the idea of using magnetic cores for computer memory, but MIT computer engineer Jay Forrester received the principal patent for his invention of the coincident-current core memory that enabled the 3D storage of information. William Papian of Project Whirlwind cited one of these efforts, Harvard's "Static Magnetic Delay Line", in an internal memo. The first core memory of 32 × 32 × 16 bits

5520-404: The latter two wires into one Sense/Inhibit line. Each toroid stored one bit (0 or 1). One bit in each plane could be accessed in one cycle, so each machine word in an array of words was spread over a "stack" of planes. Each plane would manipulate one bit of a word in parallel , allowing the full word to be read or written in one cycle. Core relies on the square hysteresis loop properties of

5612-437: The main memory are sometimes called in-core algorithms. The basic concept of using the square hysteresis loop of certain magnetic materials as a storage or switching device was known from the earliest days of computer development. Much of this knowledge had developed due to an understanding of transformers , which allowed amplification and switch-like performance when built using certain materials. The stable switching behavior

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5704-479: The memory has been adjusted to the speed of the arithmetic portion of the Univac which permits the transfer into or out of the memory of 12 characters in 40 microseconds. Word pulses flow from or to the high speed bus and the insertion register via a mechanism which converts from serial to parallel and vice versa, in 42-bit modules. Whenever feasible, registers and other circuits appear in duplicate. Their contents are continuously compared so that inconsistencies between

5796-401: The memory is a half-word insertion register of 42-bit capacity. Each bit is temporarily stored in a magnetic core of this register during a memory reference. Each of these register cores is associated with one of the 42 memory planes. To write into the memory, the first half of the word is placed in the insertion register and the address selector alerts the appropriate column and the proper row of

5888-543: The most common uses are still as permanent magnets in refrigerator seal gaskets, microphones and loud speakers, small motors for cordless appliances and in automobile applications. Ferrite magnets find applications in electric power steering systems and automotive sensors due to their cost-effectiveness and corrosion resistance. Ferrite magnets are known for their high magnetic permeability and low electrical conductivity , making them suitable for high-frequency applications. In electric power steering systems, they provide

5980-556: The necessary magnetic field for efficient motor operation, contributing to the system's overall performance and reliability. Automotive sensors utilize ferrite magnets for accurate detection and measurement of various parameters, such as position, speed, and fluid levels. Due to ceramic ferrite magnet’s weaker magnetic fields compared to superconducting magnets , they are sometimes used in low-field or open MRI systems. These magnets are favored in certain cases due to their lower cost, stable magnetic field , and ability to function without

6072-552: The need for complex cooling systems. Ferrite nanoparticles exhibit superparamagnetic properties. Yogoro Kato and Takeshi Takei of the Tokyo Institute of Technology synthesized the first ferrite compounds in 1930. This led to the founding of TDK Corporation in 1935, to manufacture the material. Barium hexaferrite (BaO•6Fe 2 O 3 ) was discovered in 1950 at the Philips Natuurkundig Laboratorium ( Philips Physics Laboratory ). The discovery

6164-419: The next transformer pair. Those that did not contain a value simply faded out. Stored values were thus moved bit by bit down the chain with every pulse. Values were read out at the end, and fed back into the start of the chain to keep the values continually cycling through the system. Such systems have the disadvantage of not being random-access, to read any particular value one has to wait for it to cycle through

6256-740: The parity bits check on the high-speed bus, a second checker establishes that the invalid "all ones" character is not inadvertently created by a system fault. Input and output checkers also detect the invalid "all ones" character. Built-in checking features are contained in the Card-to-Tape Converter, the Tape-to-Card Converter and the High Speed Printer. Univac is completely fused in order that faults may be isolated. Each bay has its own set of fuses in addition to main fuses on all DC and AC potentials. If

6348-500: The patent outright from Wang for US$ 500,000 . Wang used the funds to greatly expand Wang Laboratories , which he had co-founded with Dr. Ge-Yao Chu, a schoolmate from China. MIT wanted to charge IBM $ 0.02 per bit royalty on core memory. In 1964, after years of legal wrangling, IBM paid MIT $ 13 million for rights to Forrester's patent—the largest patent settlement to that date. In 1953, tested but not-yet-strung cores cost US$ 0.33 each. As manufacturing volume increased, by 1970 IBM

6440-402: The planes is divided into two sections of 50 by 40 cores, making 2,000 cores in each section. Each section contains one core - for one binary position (bit) - of every one of the 2,000 words. The same relative binary position of the other half-word is held in a core in the same physical location in the other section of the plane. Thus each plane contains two binary positions in each of 2,000 words;

6532-405: The proper half-select current at one temperature is not the proper half-select current at another temperature. So a memory controller would include a temperature sensor (typically a thermistor ) to adjust the current levels correctly for temperature changes. An example of this is the core memory used by Digital Equipment Corporation for their PDP-1 computer; this strategy continued through all of

6624-401: The pulse means that the bit had contained a 0. The delay in sensing the voltage pulse is called the access time of the core memory. Following any such read, the bit contains a 0. This illustrates why a core memory access is called a destructive read : Any operation that reads the contents of a core erases those contents, and they must immediately be recreated. To write a bit of core memory,

6716-404: The sintered product. To allow efficient stacking of product in the furnace during sintering and prevent parts sticking together, many manufacturers separate ware using ceramic powder separator sheets. These sheets are available in various materials such as alumina, zirconia and magnesia. They are also available in fine, medium and coarse particle sizes. By matching the material and particle size to

6808-420: The top section in each of the 42 planes. At the appropriate instant the information is transferred from each core of the insertion register to the selected core in the corresponding plane of the memory. Forty-two pulse times later, the second half word has been placed in the insertion register and the process is repeated in the lower section of the memory. Read-outs are accomplished in a reverse manner. The speed of

6900-425: The value and a second used for control. A signal generator produced a series of pulses which were sent into the control transformers at half the energy needed to flip the polarity. The pulses were timed so the field in the transformers had not faded away before the next pulse arrived. If the storage transformer's field matched the field created by the pulse, then the total energy would cause a pulse to be injected into

6992-449: The value with a read-write cycle, incrementing (or decrementing) the value in some processor register, and then writing the new value with another read-write cycle. Word line core memory was often used to provide register memory. Other names for this type are linear select and 2-D . This form of core memory typically wove three wires through each core on the plane, word read , word write , and bit sense/write . To read or clear words,

7084-487: The ware being sintered, surface damage and contamination can be reduced while maximizing furnace loading. Ferrite cores are used in electronic inductors , transformers , and electromagnets where the high electrical resistance of the ferrite leads to very low eddy current losses. Ferrites are also found as a lump in a computer cable, called a ferrite bead , which helps to prevent high frequency electrical noise ( radio frequency interference ) from exiting or entering

7176-413: The wet pressing process. Direct calcination and sintering without re-milling is possible as well but leads to poor magnetic properties. Electromagnets are pre-sintered as well (pre-reaction), milled and pressed. However, the sintering takes place in a specific atmosphere, for instance one with an oxygen shortage. The chemical composition and especially the structure vary strongly between the precursor and

7268-465: Was 2.75 μs. In 1980, the price of a 16 kW ( kiloword , equivalent to 32 kB) core memory board that fitted into a DEC Q-bus computer was around US$ 3,000 . At that time, core array and supporting electronics can fit on a single printed circuit board about 25 cm × 20 cm (10 in × 8 in) in size, the core array was mounted a few mm above the PCB and was protected with

7360-461: Was actually stored magnetically within the individual cores. Each bit of the word had one core. Reading the contents of a given memory address generated a pulse of current in a wire corresponding to that address. Each address wire was threaded either through a core to signify a binary [1], or around the outside of that core, to signify a binary [0]. As expected, the cores were much larger physically than those of read-write core memory. This type of memory

7452-420: Was almost universal until the introduction of the first semiconductor memory chips in the late 1960s, and especially dynamic random-access memory (DRAM) in the early 1970s. Initially around the same price as core, DRAM was smaller and simpler to use. Core was driven from the market gradually between 1973 and 1978. Although core memory is obsolete, computer memory is still sometimes called "core" even though it

7544-447: Was dominated by the cost of stringing the wires through the cores. Forrester's coincident-current system required one of the wires to be run at 45 degrees to the cores, which proved difficult to wire by machine, so that core arrays had to be assembled under microscopes by workers with fine motor control. In 1956, a group at IBM filed for a patent on a machine to automatically thread the first few wires through each core. This machine held

7636-622: Was exceptionally reliable. An example was the Apollo Guidance Computer used for the NASA Moon landings. The performance of early core memories can be characterized in today's terms as being very roughly comparable to a clock rate of 1  MHz (equivalent to early 1980s home computers, like the Apple II and Commodore 64 ). Early core memory systems had cycle times of about 6  μs , which had fallen to 1.2 μs by

7728-449: Was expensive and complicated. As I recall, which may not be entirely correct, it used two cores per binary bit and was essentially a delay line that moved a bit forward. To the extent that I may have focused on it, the approach was not suitable for our purposes." He describes the invention and associated events, in 1975. Forrester has since observed, "It took us about seven years to convince the industry that random-access magnetic-core memory

7820-431: Was further refined via 5 additional patents and ultimately used in the first industrial robot . Frederick Viehe applied for various patents on the use of transformers for building digital logic circuits in place of relay logic beginning in 1947. A fully developed core system was patented in 1947, and later purchased by IBM in 1956. This development was little-known, however, and the mainstream development of core

7912-563: Was installed on Whirlwind in the summer of 1953. Papian stated: "Magnetic-Core Storage has two big advantages: (1) greater reliability with a consequent reduction in maintenance time devoted to storage; (2) shorter access time (core access time is 9 microseconds: tube access time is approximately 25 microseconds) thus increasing the speed of computer operation." In April 2011, Forrester recalled, "the Wang use of cores did not have any influence on my development of random-access memory. The Wang memory

8004-633: Was made obsolete by semiconductor integrated circuit memories in the 1970s, though remained in use for mission-critical and high-reliability applications in the IBM System/4 Pi AP-101 (used in the Space Shuttle until an upgrade in early 1990s, and the B-52 and B-1B bombers). An example of the scale, economics, and technology of core memory in the 1960s was the 256K 36-bit word (1.2  MiB ) core memory unit installed on

8096-423: Was producing 20 billion cores per year, and the price per core fell to US$ 0.0003 . Core sizes shrank over the same period from around 0.1 inches (2.5 mm) diameter in the 1950s to 0.013 inches (0.33 mm) in 1966. The power required to flip the magnetization of one core is proportional to the volume, so this represents a drop in power consumption by a factor of 125. The cost of complete core memory systems

8188-447: Was somewhat accidental—due to a mistake by an assistant who was supposed to be preparing a sample of hexagonal lanthanum ferrite for a team investigating its use as a semiconductor material. On discovering that it was actually a magnetic material, and confirming its structure by X-ray crystallography , they passed it on to the magnetic research group. Barium hexaferrite has both high coercivity (170 kA/m) and low raw material costs. It

8280-479: Was tested ("strobed"). The data plot of this test seemed to resemble a cartoon character called " Shmoo ," and the name stuck. In many occasions, errors could be resolved by gently tapping the printed circuit board with the core array on a table. This slightly changed the positions of the cores along the wires running through them, and could fix the problem. The procedure was seldom needed, as core memory proved to be very reliable compared to other computer components of

8372-423: Was the solution to a missing link in computer technology. Then we spent the following seven years in the patent courts convincing them that they had not all thought of it first." A third developer involved in the early development of core was Jan A. Rajchman at RCA . A prolific inventor, Rajchman designed a unique core system using ferrite bands wrapped around thin metal tubes, building his first examples using

8464-471: Was well known in the electrical engineering field, and its application in computer systems was immediate. For example, J. Presper Eckert and Jeffrey Chuan Chu had done some development work on the concept in 1945 at the Moore School during the ENIAC efforts. Robotics pioneer George Devol filed a patent for the first static (non-moving) magnetic memory on 3 April 1946. Devol's magnetic memory

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