Patent GB-873624-A (GB)
Title: Data storage devices
IPC: H01L39/00
Filed: 1957-10-14
Abstract: 873,624. Superconductive currents. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 14, 1957 [Oct. 15, 1956], No. 32000/57. Class 40 (9). Binary digits are stored in superconducting rings, a persistent current representing " 1 " and zero current representing "0." A superconducting ring is returned to normal by a magnetic field of more than a critical strength and the current therein falls to zero. The field is applied to a portion of the ring, normal conductivity being restored in that portion. A current is started in the ring by removing the controlling magnetic field to establish a superconducting state whilst flux is linked with the ring. Removal of the flux then induces a current which persists indefinitely if the temperature is kept constant at about 4 K. In one arrangement, electrical connection to a ring are used to start a circulating current. Writing.-In a matrix, the row and column conductors 52. 53, Fig. 4, cross at a point 51A on the circumference of a ring 51. The control currents are chosen so that current in one conductor alone is insufficient to restore the adjacent part of the ring to normal conductivity. Control currents on both row and column conductors make the part normally conducting and thereby attenuate any current flowing in the ring. The currents I1, I2 indicated in conductors 52, 53 produce no resultant flux through the ring. The flux necessary for storage purposes is produced by a loop in conductor 54 carrying current 13. The pulse sequencies necessary to write the digits " 0 " and " 1 " in the ring are shown in Figs. 4A, 4B. Alternative arrangements of conductors and cores are shown in Figs. 5, 6. In another arrangement, Figs. 7A, 7B, a rectangular loop 61 includes an inset 62 of material with a low critical field. The inset 62 may be changed from a superconductive state to a normally conducting state and vice versa while 61 remains superconductive. The row and column conductors 59, 60 run along two sides of the loop 61 and the inset lies at the intersection. Control currents in the directions shown in Fig. 8A produce a resultant flux linked with the loop and termination of the control currents leaves a persistent current in the loop to store the digit "1." If the control currents are as shown in Fig. 8B, there is no resultant flux linked with the loop and the digit " 0 " is stored. One limb 63 of the loop is reduced in cross-section to increase the magnetic field at the surface for control purposes. Reading.-A sensing tape 38, Fig. 3, common to all the cores 36 &c. of a matrix is divided into three strips adjacent each core by apertures 39, 40. The strips include insets 42, 43, 44 of material with a low critical field, the tape itself having a high critical field and being always superconductive. An inset 44 is rendered normal by current in a core 36. When core 36 is addressed by currents in conductors 48, 50, rendering insets 42, 43 normal a test signal from read gate 38B produces a volt drop across tape 38 only if there is current in ring 36 and inset 44 is normal. Matrices.-The matrix shown in part in Fig. 3 includes separate sets (not shown) of row and column conductors and of control circuits for writing information into the cores. The conductors may be linked with the cores as shown in Fig. 4, 5 or 6. A field conductor (not shown) corresponding to 54 of Figs. 4-6 includes a separate loop for each storage ring. Modified cell, Fig. 2.-Conductor 18 and inductor 19 form a closed loop of superconductor material. When switch 27 is closed, conductor 18 becomes resistive and on closure of switch 28 current flows through superconductor 19. When switch 27 is opened current continues to flow through 19 but not through 18 which is again superconductive. Current circulates in the loop 18, 19 when switch 28 is opened. If switch 28 is closed again a signal is transmitted to the read gate 30. The condenser 18 may have a lower critical field than the inductor 19. The modifier cells may be used in a matrix like the matrix shown in Fig. 3.