ferrite core memory - definizione. Che cos'è ferrite core memory
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Cosa (chi) è ferrite core memory - definizione

PREDOMINANT FORM OF RANDOM-ACCESS COMPUTER MEMORY FOR 20 YEARS BETWEEN ABOUT 1955 AND 1975
Ferrite core memory; Ferrite-core memory; Core store; Magnetic-Core Storage; Ferrite ram; Magnetic core storage; Core Memory; Main store; Magnetic core memory; Core memory; Core memories
  • Diagram of a 4×4 plane of magnetic core memory in an X/Y line coincident-current setup. X and Y are drive lines, S is sense, Z is inhibit. Arrows indicate the direction of current for writing.
  • A 10.8×10.8 cm plane of magnetic core memory with 64 x 64 bits (4 Kb), as used in a [[CDC 6600]]. Inset shows ''word line'' architecture with two wires per bit
  • A 32 x 32 core memory plane storing 1024 bits (or 128 [[byte]]s) of data. The small black rings at the intersections of the grid wires, organised in four squares, are the ferrite cores.
  • Close-up of a core plane. The distance between the rings is roughly 1 mm (0.04 in). The green horizontal wires are X; the Y wires are dull brown and vertical, toward the back. The sense wires are diagonal, colored orange, and the inhibit wires are vertical twisted pairs.
  • One of three inter-connected modules that make up an Omnibus-based PDP-8 core memory plane.  This is the middle of the three and contains the array of actual ferrite cores.
  • One of three inter-connected modules that make up an Omnibus-based (PDP 8/e/f/m) PDP-8 core memory plane.
  • One of three inter-connected modules that make up an Omnibus-based PDP-8 core memory plane.
  • [[Project Whirlwind]] core memory
  • Diagram of the [[hysteresis]] curve for a magnetic memory core during a read operation. Sense line current pulse is high ("1") or low ("0") depending on original magnetization state of the core.

ferrite core memory         
<storage> (Or "core") An early form of non-volatile storage built (by hand) from tiny rings of magnetisable material threaded onto very fine wire to form large (e.g. 13"x13" or more) rectangluar arrays. Each core stored one bit of data. These were sandwiched between printed circuit boards(?). Sets of wires ran horizontally and vertically and where a vertical and horizontal wire crossed, a core had both wires threaded through it. A single core could be selected and magnetised by passing sufficient current through its horizontal and vertical wires. A core would retain its magnetisation until it was re-magnetised. The two possible polarities of magnetisation were used to represent the binary values zero and one. A third "sense" wire, passed through the core and, if the magnetisation of the core was changed, a small pulse would be induced in the sense wire which could be detected and used to deduce the core's original state. Some core memory was immersed in a bath of heated oil to improve its performance. Core memory was rendered obsolete by semiconductor memory. For example, the 1970s-era NCR 499 had two boards, each with 16 kilobytes of core memory. (1996-03-04)
Magnetic-core memory         
Magnetic-core memory was the predominant form of random-access computer memory for 20 years between about 1955 and 1975.
main store         

Wikipedia

Magnetic-core memory

Magnetic-core memory was the predominant form of random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or, informally, core.

Core memory uses toroids (rings) of a hard magnetic material (usually a semi-hard ferrite) as transformer cores, where each wire threaded through the core serves as a transformer winding. Two or more wires pass through each core. Magnetic hysteresis allows each of the cores to "remember", or store a state.

Each core stores one bit of information. A core can be magnetized in either the clockwise or counter-clockwise direction. The value of the bit stored in a core is zero or one according to the direction of that core's magnetization. Electric current pulses in some of the wires through a core allow the direction of the magnetization in that core to be set in either direction, thus storing a one or a zero. Another wire through each core, the sense wire, is used to detect whether the core changed state.

The process of reading the core causes the core to be reset to a zero, thus erasing it. This is called destructive readout. 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.

Using smaller cores and wires, the memory density of core slowly increased, and by the late 1960s a density of about 32 kilobits per cubic foot (about 0.9 kilobits per litre) was typical. However, reaching this density required extremely careful manufacture, which was almost always carried out by hand in spite of repeated major efforts to automate the process. The cost declined over this period from about $1 per bit to about 1 cent per bit. The introduction of the first semiconductor memory chips in the late 1960s, which initially created static random-access memory (SRAM), began to erode the market for core memory. The first successful dynamic random-access memory (DRAM), the Intel 1103, followed in 1970. Its availability in quantity at 1 cent per bit marked the beginning of the end for core memory.

Improvements in semiconductor manufacturing led to rapid increases in storage capacity and decreases in price per kilobyte, while the costs and specs of core memory changed little. Core memory was driven from the market gradually between 1973 and 1978.

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.

Although core memory is obsolete, computer memory is still sometimes called "core" even though it 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".