Dictionary.net

(Or "core") An early form of non-volatile storagebuilt (by hand) from tiny rings of magnetisable materialthreaded onto very fine wire to form large (e.g. 13"x13" ormore) 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 avertical and horizontal wire crossed, a core had both wiresthreaded through it.A single core could be selected and magnetised by passingsufficient current through its horizontal and vertical wires.A core would retain its magnetisation until it wasre-magnetised. The two possible polarities of magnetisationwere used to represent the binary values zero and one.A third "sense" wire, passed through the core and, if themagnetisation of the core was changed, a small pulse would beinduced in the sense wire which could be detected and used todeduce the core's original state.Some core memory was immersed in a bath of heated oil toimprove its performance.Core memory was rendered obsolete by semiconductor memory.For example, the 1970s-era NCR 499 had two boards, each with16 kilobytes of core memory.