Magnetic-core memory

Uncommon card · No. 118558

In computing, magnetic-core memory is a form of random-access memory. It predominated for roughly 20 years between 1955 and 1975, and 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. At least two wires pass through each core, forming a two-dimensional X-Y-wired 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 a value – or written – is selected by powering one X and one Y wire to half of the required current, 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...

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