GB1076569A - Improvements in or relating to thin magnetic film storage devices - Google Patents

Abstract

1,076,569. Magnetic information storage apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. Sept. 2, 1964 [Sept. 27, 1963], No. 35903/64. Heading H3B. [Also in Division H1] Non-destructive read-out of a thin magnetic film store is achieved by providing a keeper member of magnetic material adjacent each storage cell, effective to return the cell to its original magnetization direction after it has been switched to the hard direction for a time less than the relaxation time constant of the field due to the keeper member. The member comprises soft magnetic material which may be of ferrite or a vapour deposited film and may be isotropic or anisotropic. The relaxation time constant is preferably between 5 and 10 nano-seconds. The member may be in the form of a sheet covering a plane matrix (Fig. 5, not shown) or may form the substrate upon which the film elements are deposited. In the latter case the sheet is provided with a copper coating to act as return conductor for the bit lines (Fig. 7, not shown). Eddy currents induced in the conductive layer tend to assist restoration of the film to its initial state after switching. In other embodiments a separate member is provided for each film and has a similar size and shape to the film. In Fig. 9, store cell 15 and read cell 14 are driven to opposite remanent states by a bit pulse in line B and a word pulse in line W. During read-out eddy currents tend to inhibit switching of store cell 15 so that on removing the read-out pulse cell 14 is restored by the fields due to cell 15 and to the eddy currents in line B. In a modification the sense line and bit line are separate (Fig. 10, not shown), while in a further modification inner and outer bit/sense lines are provided interconnected at one end by an impedance, and connected at the same end to the conductive substrate by a second impedance, while the other end of the outer conductor is connected directly to the substrate. Cells 14 and 15 may exhibit a different coercive force.