Patent GB-920696-A (GB)
Title: Cryogenic memory systems
IPC: G11C11/44
Filed: 1959-06-22
Abstract: 920,696. Superconductive devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. June 22, 1959 [June 24, 1958], No. 21305/59. Class 40 (9). [Also in Group XIX] Words and associated tags are stored in word and tag registers respectively, each register comprising a plurality of groups of storage devices, one group to each word or tag, and means are provided to interrogate the tag register, the presence or absence of a required tag controlling read-out means associated with the word register. As described non-comparison between interrogation signals and the tag register contents switches a trigger to inhibit response by the word register to a read-out pulse. Wire-wound or thin film cryotrons are used in the preferred embodiments. Components.-A trigger AT or A (Fig. 2) comprises cryotrons K1 to K4 and provides a superconductive path to a D.C. signal on line 46 to the coils 50 or 52 of output cryotrons K5 or K6 according as lines 40 or 42 are energized. K3 and K4 are cross-coupled to K1 and K2 to render the trigger stable. The coils of cryotrons K7 and K8 must be energized by a signal on line 44 to enable the state of the circuit to be changed, although these cryotrons may be dispensed with. The state of a trigger AT may be determined by a comparison circuit CC (Fig. 5). The output of trigger AT controls the resistive state of cryotrons K15, K16 and an interrogation signal on line 70 or 72 renders K17 or K18 resistive respectively. It is assumed if K15 is resistive the trigger is in state " 0 " and that if line 70 is energized a zero is sought. With the arrangement shown if the state of the trigger is that represented by the interrogation signal there is a superconductive path from input 70 to output 76 through either K15, K17 or K16, K18. Non-comparison creates a superconductive path through the coils of K19 which is thus rendered resistive. By exchanging the significance of signals on lines 70 and 72 a circuit is created which sends K19 resistive if comparison between trigger state and interrogation signal occurs. Other comparison circuits are described including (Fig. 8, not shown) one in which a superconductive path for an input signal is provided to one of two output leads according as the interrogation signal matches the trigger state or not. A read-out circuit is shown in Fig. 9 in which the state of triggers AT-1, AT-2 is indicated by the resistivity of cryotrons K31 to K34. A read-enable signal on line 110 sends K35 and K36 resistive and results in a signal on line 114 being gated to output 117 if AT-1 is in the " 1 " state or to output 119 if AT-1 is in the " 0 " state. Word storage.-As shown in Figs. 10A to 10D 3-bit words are stored in triggers AT-13 to AT-15 and AT-23 to AT-25, and associated 2- bit tags in AT-10, AT-11 and AT-21, AT-22. With each tag trigger is associated a compare circuit CC and with each word trigger a readout circuit RO. Information is read in to the memory by providing a D.C. current from source 140 at the input leads 46 of the triggers, energizing the enable line 44 from source 150A or 150B feeding the row in which the word and tag is to be stored, and energizing the appropriate lines 40 or 42 from storage inputs S1 to S5. For tag interrogation a reset pulse is applied to row compare triggers T-A and T-B. These are similar to the triggers described above with C indicating the cryotrons which are resistive after a successful interrogation of a row and #C those cryotrons which are conductive. Incorporated in one of the possible current paths of the row compare triggers are the cryotrons K19 of the compare circuits. The reset impulse is also applied to the lines 42 of a register compare trigger T-2 and then to lines 40 of output triggers T-3 to T-5. These triggers are similar to the trigger shown in Fig. 2 save that the cryotrons K7 and K8 are omitted. Interrogation pulses thus issue from sources I1 and 12 on the input lines 70 or 72 of the compare circuits, after which a first compare pulse is sent through the compare circuits from source 160. If the value of the interrogate input is not the same as the stored tag value then at least one of the cryotrons K19 in the row storing the tag will become resistive switching the row compare trigger. A second compare pulse issues from source 170 sensing the state of the row compare triggers. If all have been switched the second pulse switches trigger T-2 to zero indicating that the required tag is not in the register. If a row trigger has not been switched the compare pulse is diverted by resistive cryotron K41 or K43 through conductive cryotron K42 or K44 to provide a read enable signal for the appropriate row of the word register. Where both tags compare with the interrogation only the top row of the word register is prepared for read out. A read-out pulse is supplied by source 200 and is gated through cryotron K45 to the input of RO-13. If it is assumed that the contents of the top row are to be read out, energization of the read enable line 110 will result in the provision of a superconductive path to one of the outputs 117 or 119. If on output 117, indicating that At-13 is in the " 1 " state, the signal continues through R0-23 to input 42 of output trigger T-3 switching it to the " 1 " state. By similar means triggers T-4 and T-5 register the contents of the selected row of the word register. It should be noted that if the required tag is not in the tag register the read-out signal is shunted through conductive cryotron K46 since T-2 is not switched from its initial " 1 " state. Modifications of the tag register are described (Figs. 12 to 16, not shown) utilizing different types of compare circuits. Specifications 862,178 and 920,697 are referred to.