Patent GB-973866-A (GB)
Title: Improvements in and relating to memory systems
IPC: G11C15/02
Filed: 1961-09-29
Abstract: 973,866. Associative memory. INTERNATIONAL BUSINESS MACHINES CORPORATION. Sept. 29, 1961 [Oct. 7, 1960] No. 35316/61. Heading G4C. [Also in Division H3] In an associative magnetic core memory 50, after location of a word having the specified tag the whole word is read out to a register 90. Interrogation of a core, and the preferred non-destructive readout, is by means of a short pulse of high magnetic force which does not switch the core but produces a high voltage on a sense winding if it tends to switch the core from its present remanent state (a mismatch). In the matrix 50, words occupy columns with corresponding bits in the same row. Interrogation takes place in two steps: first the one bits of the tags are matched and then the zero bits. The switches 21 to 24 are closed which correspond to those bit positions occupied by the tag and the flip-flops 11 to 14 in those positions of the tag occupied by a one bit are set. Pulses are then applied serially to terminals 31c to 34c and mismatch signals are detected by circuits 60 1  to 60 N  to unset corresponding flip-flops FF 1  to FF N  previously in their set state. The flip-flops 11 to 14 are now complemented so that the lines 15 to 18 from zero-storing tag positions are now up. Interrogation pulses are now applied to terminals 31d to 34d and are inverted by circuits such as 45, 45b so as to test the storage cores for the zero-representing remanent state. Again, mismatch signals cause flip-flops from FF 1  to FF N  associated with words generating the mismatch signals to be unset. In order to counteract the effect of the interrogating pulses on the remanent states of the cores, circuits 60 1  to 60 N  are blocked and pulses are applied to terminals 31c to 34c. Since the flip-flops 11 to 14 remain as complemented for the zero interrogation, positive pulses are applied where negative interrogation pulses were previously. Flip-flops 11 to 14 are complemented and pulses applied to terminals 31d to 34d. The effect is to deliver negative pulses to cores which were interrogated by positive pulses. There now follows read-out of the tag matched words. Switches such as 41e, 41a, 41m are operated to convert the horizontal interrogation lines into sense lines, and the vertical sense lines into interrogation lines connected to doublet pulse generators 80 1  to 80 N  which supply in quick succession an interrogation pulse and a resetting pulse. Registering circuits 90 1  to 90 N  pick up mismatch signals generated by the interrogation pulses but are caused to ignore the effect of the resetting pulses. Assuming that the memory contains several words having the required tag corresponding flip-flops FF 1  to FF N  will be in the set state. If FF N  is one of these the first read-out pulse of a train will be passed by gate 61 N  to trigger pulse generator 80 n  and to unset FF n . Word W N  will be read out to register 90. The next readout pulse of the train will be passed by gate 62 N  to either gate 61 8  or 62 8  depending on the setting FF 8 . If only one word had matched the tag, the second pulse of the train will pass all the gates 62 N  to 62 1  to operate flip-flop 64 and shut gate 63 to the passage of further read-out pulses. If a second word matched the tag, the second read-out pulse would be passed by the corresponding gate 61 to trigger the pulse generator 80 1  at the same time opening gate 62. Destructive read-out may be used, employing half-select currents, in which case the output of each gate 61 is converted to the appropriate X and Y co-ordinates in matrix 70. The non-destructive read out preferably employed is as described in an article by Newhouse in Proc. I.R.E. November, 1957, page 1484. Specification 673,759 and U.S.A. Specification 2,404,918 are referred to.