An obsolete type of nonvolatile memory in which binary information is stored in an array of toroidal magnetic cores. The cores had two stable magnetic states and were switched from one to the other by imposing a magnetic flux. The principle of the core store was discovered in 1949 by J. W. Forrester of MIT. Widely used as main storage for processors from the mid-1950s to the late 1970s, core store was superseded by semiconductor memory.