Magnetic core memory

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.

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.

Related Topics:
Shanghai - American - Physicist - An Wang - Harvard University - MIT

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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.

Related Topics:
Jay Forrester - Whirlwind - MIT - Realtime - Flight simulator - Williams tube

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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).

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Core arrays were manually assembled; the work was performed under microscopes and required fine motor control. Initially garment workers were used.

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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 had become 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.

Related Topics:
Main memory - Drum memory - Vacuum tube

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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 $0.01 per bit. Core was in turn replaced by silicon memory chips (RAM) in the early 70s.

Related Topics:
Moore's Law - RAM

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Dr. Wang's patent was not granted until 1955, and by this 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.

Related Topics:
IBM - Wang Laboratories

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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 1950's, 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 U. S. Army Signal Corps in the late fifties.

Related Topics:
Transistor - MOBIDIC

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