What is Magnetic-core memory?
+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 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 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 the core to + its original value if the process flipped it. +
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