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A magnetic memory can be interrogated nondestructively by applying a perturbing field normal to the direction of remanent magnetization, and, at the same time, observing the sign of the reversible flux change. However, there may be a considerable irreversible flux change during the first few interrogations following magnetization. This irreversible component can be reduced by introducing magnetic anisotropy in a direction parallel to the direction of magnetization which is used to store binary information. The characteristics of the ideal memory is analyzed by means of domain theory. In an experimental memory a steel wire under tension was used for the memory material. A small solenoid was used to magnetize the wire locally and also to observe the flux change which was produced by an interrogative current pulsed through the wire itself. The general predictions of the theory were confirmed by experiment. Interrogation is non‐destructive and is completed in less than 1 μsec. The output is proportional to the square of the wire current, and discrimination is a matter of observing its polarity. A single bit can be written into a memory array by a coincidence of a wire current and a solenoid current. The wire current can be the same as that used for interrogation. A number of bits can be carried on one wire and interrogated simultaneously. The factors affecting the design of a memory array are discussed.