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Encyclopedia > Magnetic core memory
A 16×16 cm area core memory plane of 128×128 bits, i.e. 2048 bytes (2 KB)
A 16×16 cm area core memory plane of 128×128 bits, i.e. 2048 bytes (2 KB)

Magnetic core memory, or ferrite-core memory, is an early form of computer memory. It uses small magnetic ceramic rings, the cores, to store information via the polarity of the magnetic field they contain. Such memory is often just called core memory, or, informally, core. scan of a core memory frame, 16x16 cm (I put an actual device on the scanner. ... scan of a core memory frame, 16x16 cm (I put an actual device on the scanner. ... The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ... Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικος (keramikos, having to do with pottery). The term covers inorganic non-metallic materials whose formation is due to the action of heat. ... The polarity of an object is, in general, its physical alignment of atoms. ... Current flowing through a wire produces a magnetic field (B, labeled M here) around the wire. ...

Contents


History

The earliest work on core memory 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 name referred to the way that the magnetic field of the cores could be used to control the switching of current in electro-mechanical systems. Wang and Woo were working at Harvard University's Computation Laboratory at the time, but unlike MIT, Harvard was not interested in promoting inventions created in their labs. Instead Wang was able to patent the system on his own while Woo took ill. Shanghai (Chinese: 上海; pinyin: ; Shanghainese: ), situated on the banks of the Yangtze River Delta in East China, is Chinas largest city by population. ... A physicist is a scientist trained in physics. ... Dr. An Wang (Chinese: 王安; Hanyu Pinyin: ; February 7, 1920 – March 24, 1990) was a Chinese American computer engineer and inventor, and co-founder of computer company Wang Laboratories. ... Harvard University campus (old map) Harvard University (incorporated as The President and Fellows of Harvard College) is a private university in Cambridge, Massachusetts. ... The Massachusetts Institute of Technology, or MIT, is a private research university located in the city of Cambridge, Massachusetts, USA. MIT is one of the worlds leading research institutions in science and technology. ...


Jay Forrester's group, working on the Whirlwind project at MIT, became aware of this work. This machine required a fast memory system for realtime flight simulator use. At first, Williams tubes (more accurately, Williams-Kilburn tubes) — a storage system based on cathode ray tubes — were used, but these devices were always temperamental and unreliable. Jay Wright Forrester (born 14 July 1918 Climax, Nebraska) is an American pioneer of computer engineering. ... The Whirlwind computer was developed at the Massachusetts Institute of Technology. ... Mapúa Institute of Technology (MIT, MapúaTech or simply Mapúa) is a private, non-sectarian, Filipino tertiary institute located in Intramuros, Manila. ... An operation within a larger dynamic system is called a real-time operation if the combined reaction- and operation-time of a task is shorter than the maximum delay that is allowed, in view of circumstances outside the operation. ... Interior Cockpit of a modern Flight Simulator A flight simulator is a system that tries to replicate, or simulate, the experience of flying an aircraft as closely and realistically as possible. ... The Williams tube or (more accurately) the Williams-Kilburn tube (after Freddie Williams and coworker Tom Kilburn), developed about 1946 or 1947, was a cathode ray tube used to store electronic data. ... The Williams tube or (more accurately) the Williams-Kilburn tube (after Freddie Williams and coworker Tom Kilburn), developed about 1946 or 1947, was a cathode ray tube used to store electronic data. ... The cathode ray tube or CRT, invented by Karl Ferdinand Braun, is the display device used in most computer displays, televisions and oscilloscopes. ...


Two key inventions led to the development of magnetic core memory, which enabled the development of computers as we know them. The first, An Wang's, was the write-after-read cycle, which solved the puzzle of how to use a storage medium in which the act of reading was also an act of erasure. The second, Jay Forrester's, was the coincident-current system, which enabled a small number of wires to control a large number of cores (see Description section below for details).


Forrester's coincident-current system required one of the wires to be run at 45 degrees to the cores, which proved impossible to wire mechanically. Thus core arrays were manually assembled; the work was performed under microscopes and required fine motor control. Initially, garment workers were used.


By the late 1950s, industrial plants had been set up in the Far East to build core. Inside, hundreds of low-paid workers strung cores for cents a day. This lowered the cost of core to the point where it became largely universal as main memory by the early 1960s, replacing both the low-cost/low-performance drum memory as well as the high-cost/high-performance systems using vacuum tubes as memory. Far East is an inexact term often used for East Asia and Southeast Asia combined, sometimes including also the easternmost territories of Russia, i. ... It has been suggested that this article or section be merged with Physical memory. ... hi i am cool xbox is all most as cool as me hi again ... In electronics, a vacuum tube (U.S. and Canadian English) or (thermionic) valve (outside North America) is a device generally used to amplify, or otherwise modify, a signal by controlling the movement of electrons in an evacuated space. ...


Although the manufacture of core memory was never automated, costs almost followed the not-yet-formulated Moore's Law; over the lifetime of the technology costs began at roughly a dollar a bit and eventually approached roughly US$0.01 per bit. Core was in turn replaced by silicon memory chips (RAM) in the 1970s. Growth of transistor counts for Intel processors (dots) and Moores Law (upper line=18 months; lower line=24 months) Moores law is the empirical observation that the complexity of integrated circuits, with respect to minimum component cost, doubles every 24 months[1]. It is attributed to Gordon E... A four-megabyte RAM hiyaacard for the VAX 8600 computer (circa 1986). ...


Dr. Wang's patent was not granted until 1955, and by that time core was already in use. This started a long series of lawsuits, which eventually ended when IBM paid Wang several million dollars to buy the patent outright. Wang used the funds to greatly increase the size of Wang Laboratories which he co-founded with Dr. Ge-Yao Chu, a school mate from China. International Business Machines Corporation (IBM, or colloquially, Big Blue) (NYSE: IBM) (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, New York, USA. The company manufactures and sells computer hardware, software, and services. ... Wang logo circa 1980. ...


Core memory was part of a family of related technologies, now largely forgotten, which exploited magnetic properties of materials to perform switching and amplification. By the 1950s, vacuum-tube electronics was well-developed and very sophisticated, but tubes were fragile, and the use of heated filaments made them short-lived, high in power consumption, and unstable in their operating characteristics. Magnetic devices had many of the virtues of the transistor and solid-state devices that would replace them, and saw considerable use in military applications. A notable example was the portable (truck-based) MOBIDIC computer developed by Sylvania for the United States Army Signal Corps in the late Fifties. Assorted transistors The transistor is a solid state semiconductor device that can be used for amplification, switching, voltage stabilization, signal modulation and many other functions. ... MOBIDIC MOBIDIC, for mobile digital computer, was part of a pioneering effort by the US Army Signals Corps to computerize the distribution of intelligence around the battlefield, known as Fieldata. ... Branch insignia of the U.S. Army Signal Corps, representing Myers Wigwag The U.S. Army Signal Corps was founded in 1861 by United States Army Major Albert J. Myer, a physician by training. ...


Description

Close-up of the device shown above. The distance between the rings is roughly 1 mm (0.04 in).The light color vertical and horizontal wires are X and Y wires, the diagonal wires are Sense wires, the dark colored horizontal wires are Inhibit wires.
Close-up of the device shown above. The distance between the rings is roughly 1 mm (0.04 in).
The light color vertical and horizontal wires are X and Y wires, the diagonal wires are Sense wires, the dark colored horizontal wires are Inhibit wires.

closeup of core memory This is a scan (not a scan of an image but of an actual device) done at 1200 dpi, then magnified by 1. ... closeup of core memory This is a scan (not a scan of an image but of an actual device) done at 1200 dpi, then magnified by 1. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ...

How core memory works

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 ferrite (ferromagnetic ceramic) rings, cores, held together in a grid structure (each grid called a plane), with wires woven through the holes in the cores' middle. In early systems there were four wires, X, Y, Sense and Inhibit, but later cores combined the latter two wires into one Sense/Inhibit line. Each ring stores one bit (a 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. Ferrites are ferromagnetic ceramic materials, compounds of iron, boron and barium or strontium or molybdenum. ... Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικος (keramikos, having to do with pottery). The term covers inorganic non-metallic materials whose formation is due to the action of heat. ... This article is about the unit of information. ... Parallel computing is the simultaneous execution of the same task (split up and specially adapted) on multiple processors in order to obtain results faster. ...


Core relies on the hysteresis of the magnetic material used to make the rings. Only a magnetic field over a certain intensity (generated by the wires through the core) 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 required to cause this change. Only the combined magnetic field generated where the X and Y lines cross is sufficient to change the state, other cores will see only half the needed field, 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 field to point in one direction or the other (north or south). Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state: that is, systems whose states depend on their immediate history. ... Current flowing through a wire produces a magnetic field (B, labeled M here) around the wire. ... Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux. ...


Other forms of core memory were used for other purposes.


Register memory was often provided using word line core memory. 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, 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 is applied to each bit sense/write line for a bit to be set. For write, multiple word write lines could be selected. This offered a speed advantage over X/Y line coincident-current in that multiple words could be cleared or written with the same value in a single cycle. A typical machine's register set usually used only one small plane of this form of core memory.


Another form of core memory called core rope memory provided read-only storage. In this case, the cores were simply used as transformers; no information was actually stored magnetically within the core. Core rope memory is a form of read-only memory (ROM) for computers, first used by early NASA Mars probes and then in the Apollo Guidance Computer (AGC) designed by MIT and built by Raytheon. ... Rom is also the name of a toy and comic book character Rom (Spaceknight). ... Three-phase pole-mounted step-down transformer. ...


Reading and writing

Reading from core memory is somewhat complex. Basically the read operation consists of doing a "flip to 0" operation to the bit in question, that is, driving the selected X and Y lines at half power in the direction that causes the core to flip to whatever polarity the machine considers to be zero. If the ring was already in the 0 state nothing will happen. However if the ring was in the 1 state it will flip to 0. If this flip occurs, a brief pulse of power will be induced into the Sense line, saying, in effect, that the memory location used to hold a 1. If the pulse is not seen that meant no flip occurred, so the ring must have already been in the 0 state. Note that every read forces the ring in question into the 0 state, so reading is destructive, which is one of the oddities of core memory.


Writing is similar in concept, but always consists of a "flip to 1" operation, relying the memory already having been set to the 0 state in a previous read. If the ring in question is to hold a 1, then the operation proceeds normally and the ring flips to 1. However if the ring is to instead hold a zero, a small amount of current is sent into the Inhibit line, enough to drop the combined field from the X and Y lines below the amount needed to make the flip. This leaves the core in the 0 state.


Note that the Sense and Inhibit wires are used one after the other, never at the same time. For this reason later core systems combined the two into a single wire, and used circuitry in the memory controller to switch the duty of the wire from Sense to Inhibit.


Because core always requires a write after read, many computers included instructions that took advantage of this. These instructions would be used when the same location was going to be read, changed and then written, such as an increment operation. In this case the computer would ask the memory controller to do the read, but then signal it to pause before doing the write that would normally follow. When the instruction was complete the controller would be unpaused, and the write would occur with the new value. For certain types of operations, this effectively doubled the speed.


Physical characteristics

The speed of early core memories can be characterized in today's terms as being very roughly comparable to a clock speed of 1 MHz (0.001 GHz) (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 the early 1970s, and by the mid-70s it was down to 600 ns (0.6 µs). Everything possible was done in order to speed access, including the simultaneous use of multiple grids of core, each storing one bit of 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. MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ... The Apple II was one of the most popular personal computers of the 1980s. ... For the hip hop group, see Commodore 64 (band). ... A microsecond is an SI unit of time equal to one millionth (10-6) of a second. ... To help compare orders of magnitude of different times this page lists times between 10−9 seconds and 10−8 seconds (1 nanosecond and 10 nanoseconds) See also times of other orders of magnitude. ... 32-bit is a term applied to processors, and computer architectures which manipulate the address and data in 32-bit chunks. ...


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 military installations and vehicles like fighter aircraft, as well as spacecraft, and led to core being used for a number of years after availability of semiconductor MOS memory (see also MOSFET). Non-volatile storage is a category of computer storage. ... It has been suggested that Electromagnetic bomb be merged into this article or section. ... An A-10 Thunderbolt II, F-86 Sabre, P-38 Lightning and P-51 Mustang fly in formation during an air show at Langley Air Force Base, Virginia. ... A spacecraft is designed to leave Earths atmosphere and operate beyond the surface of the Earth in outer space. ... A semiconductor is a material with an electrical conductivity that is intermediate between that of an insulator and a conductor. ... Example of a MOSFET The metal oxide semiconductor field-effect transistor (MOSFET), is by far the most common field-effect transistor in both digital and analog circuits. ...


A characteristic of core was that it is current-based, not voltage-based. The "half select current" was typically about 400 mA for later, smaller, faster cores. Earlier, larger cores required more current. In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ... International danger high voltage symbol. ... The ampere (symbol: A) is the SI base unit of electric current. ...


Another characteristic of core is that the hysteresis loop was temperature sensitive, the proper half select current at one temperature is not the proper half select current at another temperature. So the memory controllers could include temperature sensors (typically a thermistor) to check the temperature and adjust the current levels to correct 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 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 the IBM 709, IBM 7090, and IBM 7030. Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state: that is, systems whose states depend on their immediate history. ... A thermistor is a type of resistor used to measure temperature changes, relying on the change in its resistance with changing temperature. ... Digital Equipment Corporation was a pioneering company in the American computer industry. ... The PDP-1 (Programmed Data Processor-1) was the first computer in Digital Equipments PDP series and was first produced in 1960. ... Digital Equipment Corporation was a pioneering company in the American computer industry. ... Programmed Data Processor (abbreviated PDP) was the name of a series of computers, several of them ground-breaking and very influential, made by Digital Equipment Corporation. ... The IBM 1620 was announced by IBM on October 21, 1959 and marketed as an inexpensive scientific computer. It was withdrawn on November 19, 1970. ... The IBM 709 was an early computer system introduced by IBM in August, 1958. ... IBM 7090 console The IBM 7090 was a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computers and was designed for large-scale scientific and technological applications. The 7090 was the third member of the IBM 700/7000 series scientific computers. ... The IBM 7030, also known as Stretch, was IBMs first attempt at building a supercomputer. ...


Core trivia

  • Although computer memory long ago moved to silicon chips, memory is still occasionally called "core". This is most obvious in the naming of the core dump, a dump of memory produced after a program error.

A core dump is a record of the raw, unstructured contents of one or more regions of working memory at a specific time, generally used to debug a program that has terminated abnormally (crashed). ...

See also

Delay line memory was a form of computer memory used on some of the earliest digital computers, such as the EDSAC and UNIVAC I. The first such systems consisted of a column of mercury with piezo crystal transducers (a combination of speaker and microphone) at either end. ... Core rope memory is a form of read-only memory (ROM) for computers, first used by early NASA Mars probes and then in the Apollo Guidance Computer (AGC) designed by MIT and built by Raytheon. ... Twistor is a form of computer memory, similar to core memory, formed by wrapping magnetic tape around a current-carrying wire. ... Intel bubble memory module Bubble memory is a type of computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles, which each store one bit of data. ... Thin film memory is a high-speed variation of core memory developed by Sperry Rand in a government-funded research project. ... Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ... Ferroelectric RAM (FRAM or FeRAM) is a type of non-volatile computer memory, similar to EEPROM but based on electric field orientation and with near-unlimited number (exceeding 1010 for 5V devices and even more for 3. ...

External links

  • Core Memory
  • Navy Manual
  • Core Memory on the PDP-11
  • Core memory and other early memory types accessed April 15, 2006
  • Coincident Current Ferrite Core Memories Byte magazine, July 1976

April 15 is the 105th day of the year in the Gregorian calendar (106th in leap years). ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... The front cover of the April 1981 issue of BYTE (Vol 6. ...

Patents

  • U.S. Patent 2667542 "Electric connecting device" (matrix switch with iron cores), filed September 1951, issued January 1954
  • U.S. Patent 2708722 "Pulse transfer controlling devices", An Wang filed October 1949, issued May 1955
  • U.S. Patent 2736880 "Multicoordinate digital information storage device" (coincident-current system), Jay Forrester filed May 1951, issued February 28, 1956
  • U.S. Patent 3161861 "Magnetic core memory" (improvements) Ken Olsen filed November 1959, issued December 1964
  • U.S. Patent 4161037 "Ferrite core memory" (automated production), July 1979
  • U.S. Patent 4464752 "Multiple event hardened core memory" (radiation protection), August, 1984

  Results from FactBites:
 
Magnetic core memory - Wikipedia, the free encyclopedia (2026 words)
Core memory was part of a family of related technologies, now largely forgotten, which exploited magnetic properties of materials to perform switching and amplification.
Early core memory systems had cycle times of about 6 µs, which had fallen to 1.2 µs by the early 1970s, and by the mid-70s it was down to 600 ns (0.6 µs).
A characteristic of core was that it is current-based, not voltage-based.
Core rope memory - Wikipedia, the free encyclopedia (292 words)
Core rope memory is a form of read-only memory (ROM) for computers, first used by early NASA Mars probes and then in the Apollo Guidance Computer (AGC) designed by MIT and built by Raytheon.
Contrary to ordinary coincident-current magnetic core memory, which was used for RAM at the time, the ferrite cores in a core rope are just used as transformers.
The signal from a word line wire passing through a given core is coupled to the bit line wire and interpreted as a binary "one" while a word line wire that bypasses the core is not coupled to the bit line wire and is read as a "zero".
  More results at FactBites »

 
 

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