Patent GB-1133200-A (GB)
Title: Semi-permanent memory
IPC: G11C17/02
Filed: 1966-12-09
Abstract: 1,133,200. Magnetic data storage apparatus. INTERNATIONAL STANDARD ELECTRIC CORP. 9 Dec., 1966 [15 Dec., 1965], No. 55220/66. Heading H3B. A memory matrix comprises a conductive substrate 1 having a thin magnetic film 2, 3 on each side, word and digit conductors M, C adjacent to one film 2, and interrogation, inhibit and sense conductors I, E and L, adjacent to the other film, the inhibit conductors having a crenellated configuration. The films are preferably uniaxially anisotropic thin films, the storage film 2 having a higher anisotropy field than the read film 3. Data is stored in a word organized manner using conductors M, C, the stray fields from film 2 being, however, insufficient to switch regions of film 3. After writing, a pulse is applied to interrogate conductors I to switch the read film 3 to the hard direction, so that when the pulse terminates the storage regions in the film each relax to a remanent state determined by the data stored in the corresponding region in film 2. For readout, operation is in a random-access mode, being initiated by applying pulses to all the inhibit conductors E except that coupled to the storage region to be read. Before these pulses terminate a pulse is applied to the interrogation conductor coupled to the selected region, to produce magnetic field having the same direction as those generated by the inhibit pulses. As a result an output pulse is induced in conductor L and supplied to a sense amplifier strobed at the instant of application of the interrogation pulse. In order to reduce the amplitude of noise voltages induced in conductor L, the leading and trailing edges of the inhibit pulse and the trailing edge of the interrogation pulse have low slopes. The conductive substrate shields each film from varying magnetic fields applied to the other film and acts as a return conductor for all except the inhibit conductors. In a modification the inhibit current flows continuously and is terminated in a selected inhibit line during read-out. Multiplane matrix.-Corresponding interrogation and inhibit conductors in respective planes are connected in series. The store is wordorganized, having a digit from each word in a corresponding position in each plane. An auxiliary matrix is necessary for writing data and may comprise ferrite cores arranged in as many rows as there are conductors C and as many columns as there are planes in the thin film memory. Data is first written row by row into the auxiliary store, simultaneously in all the cores of a row, and is then read column by column, each column being read simultaneously with energization of a conductor M. If a single word is to be modified in the thin film memory, data is first read out from the memory and stored in the auxiliary memory, and the appropriate word is then modified before returning the data to the main store. The storage capacity of the store may be doubled by providing additional word and interrogation conductors positioned between adjacent conductors M and between adjacent conductors I (Fig. 6, not shown). The storage film 2 may be of isotropic material having a coercive field higher than the anisotropy field of the read film. Data is written by current coincidence on column, row and writing conductors, the magnetic fields generated by the writing conductors either assisting or opposing those due to the other conductors, depending on the digit to be stored.