In 1975, USC need to upgrade the System/360-58 from 1/2 MB of RAM to 1 MB.
The IBM 2361 core memory cost $1 million.
We bought Intel semiconductor memory for $1/4 million. We were pioneers.
I got an Intel LCD watch - last watch I ever had. The Intel office was on Rosecrans two blocks east of the Pacific movies.

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The thimble actually contains 50,000 cores.

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   Workmen mounting core memory unit into JOHNNIAC, c. 1957

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   MIT magnetic core memory
US
c. 1957

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   Magnetic core memory (IBM 360/91)
US
1969

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Core memory uses a 3-dimensional array of tiny ferrite rings to store data or programs. Each ring stores a single bit and is magnetized in either a clockwise or counterclockwise direction, representing a “0” or a “1” respectively. The cores are magnetized by a current flowing in wires that are threaded through each core. The direction of the current determines the direction of the magnetization.
  Elements of Core Memory
In 1953, Jay Forrester invented “coincident current addressing”, which made core memory practical. In this scheme, the current needed to magnetize the core is split between two wires (one horizontal, the other vertical). Only the core at the intersection of two electrified wires will change magnetization. In order to read a single core, a third wire is threaded through all the cores of a plane. When a core is magnetized to a “0,” a pulse occurs on this sense wire only if that core had been a “1” and not if it was already a “0.” This is destructive readout, since if it was a “1” it now needs to be rewritten. Consequently, it takes two cycles to read core memory, one to read the contents and another to reset it to its original state.

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   Early 16 x 16 ceramic core plane

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   Front face of a Williams Tube, bright spots were “1s”, faint spots were “0s”

 

(CRT storage - before Core Memory)