GB880383A - Improvements in or relating to magnetic data storage apparatus - Google Patents

Abstract

880,383. Magnetic core storage devices. INTERNATIONAL COMPUTERS & TABULATORS Ltd. Dec. 4, 1958 [Dec. 23, 1957], No. 39905/57. Class 38 (2). [Also in Group XXXIX] A bi-stable magnetic device has an elementary area of an isotropic magnetic thin film, storage being effected by magnetizing the film in one or other direction along the easy axis of magnetization. The setting is arranged to take place mainly by domain rotation. The film may be deposited in vacuo from a 83/17 nickel-iron vapour in the presence of a magnetic field which produces the anisotropy. Write-in may be affected by applying a large magnetizing field perpendicular to the easy axis and a small field in the required direction along the easy axis, or alternatively merely a larger current in the direction of the easy axis. Alternatively a single field slightly at an angle to the difficult axis may be used. As shown, Fig. 3, the magnetic film 7 and the conductors 9, 10 are separated from each other by vacuum deposited insulating layers of magnesium fluoride. The conductors may be deposited by printed circuit techniques. In one arrangement the conductor 9 is placed at a small angle to the easy direction of magnetization 3-5. In one direction of current flow through the conductor 9, a sufficiently high current will take the direction of magnetizaton past the difficult direction of magnetization, so that when the current ceases the flux will relapse to the opposite easy direction. Thus the magnetization can be set to either of the directions 3 or 5 according to the direction of the current in the conductor 9. Destructive read-out may be effected by applying current to the conductor 9 in such a direction as to return the flux to the direction 3 (corresponding to storage of the digit " zero "). If the film was already in the " zero " condition then two equal and opposite changes of flux occur at the onset and termination of the current in conductor 9, so producing a negative pulse followed by a positive pulse in conductor 10. If the film was in the " one " condition, both changes are in the same direction so producing two positive pulses. In a second embodiment. Fig. 4, half current switching may be used, two write-in conductors 10, 13 being provided which when energized together can switch the direction of magnetization from one easy direction to the opposite one. Alternatively a simultaneous current in conductor 9 providing a field in the difficult direction may also be used so reducing the value of the currents necessary in conductors 10, 13. The conductor 9 is at right angles to conductors 10, 13 which themselves may be along the easy direction of magnetization, or may be at a small angle to it. Non-destructive read-out may be effected by applying a small current to the conductor 9 and using conductor 10 to sense the changes in flux. In this case the store will not be switched, but the conductor 10 will receive a positive pulse followed by a negative pulse or vice versa in accordance with the existing direction of the flux in the easy direction.