Patent GB-951860-A (GB)
Title: Magnetic memory
IPC: G11C19/10
Filed: 1962-06-12
Abstract: 951,860. Magnetic storage devices. HUGHES AIRCRAFT CO. June 12, 1962 [July 28, 1961], No. 22511/62. Heading H1T. [Also in Divisions G4 and H3] Two adjacent domains of opposite polarity with the common boundary wall in a neutral position are established in part of a magnetic wire, the wall being moved in one or the other direction to record binary information, and restored to its neutral position for reading out the information stored. As shown in Fig. 1, a magnetic wire 10 is continuously magnetized by domain forming windings 12, 14 to establish opposing fluxes 103, 105 having a boundary wall in a neutral position 32. This wall is moved in one or the other direction when current is passed through a control or digit winding 46, depending on the current direction and hence the digit value to be recorded. To read out the digit stored, reading windings 24, 26 are energized and produce opposing magnetic fluxes 100, 101 sufficient to restore the boundary wall to the neutral position. As a result an output voltage having a polarity determined by the direction of movement of the boundary wall is induced in the control winding 46. To prevent information stored from being influenced by further pulses through the control winding, as occurs in an array of storage units, the displaced boundary wall is held in position by continuously energized detent windings 34, 36 producing fields 85, 87 in opposition to the adjacent domain magnetizations 103, 105. Each operating cycle is effected by a clock 67 producing spaced pulses C 1  and C 2 , the pulse C 1  initiating a read operation by energizing a read pulse generator 27 so that the boundary wall is restored to the neutral position. The induced output in the control winding 46 is applied by way of a transformer 49 to a sense amplifier 52, and if a binary one is read out, a pulse is passed to an output AND gate 54 at the same time as a stroke pulse obtained from the read pulse generator over a delay 56 and differentiating circuit 59 is applied to the gate. Writing takes place when clock pulse C 2  is applied to a write pulse source, the control winding 46 then being appropriately energized depending on the digit to be stored. A nickel iron alloy wire 10 is used which may be maintained under tension. Several digits may be stored along a single wire, the principle being shown in Fig. 6 in which the limits of a first storage element are defined by domain forming coils 164, 166 and the second storage element limits by domain forming coils 166, 168, the shared coil 166 necessitating a pattern of opposing domain magnetizations 397, 405 and 405, 413 which alternate in sense in successive elements. Such an arrangement having two storage elements for each magnetic wire 142, 142a ... is shown in Figs. 5 and 5a. A two bit word is stored in each magnetic wire and is selectively read out by applying a positive pulse from a read pulse generator 214 to a column address driver 242 or 248 and a negative pulse to a row address driver 222 or 234. The combined pulses in the selected read windings 138, 140, 150, 152 are sufficient to switch the boundary walls in a single wire to the neutral position and so induce bits outputs in respective control windings 160, 162. These outputs are applied over transformers 206, 212 to gating circuits 272, 318 each comprising a transistor amplifier 270, transformer 280 and an output AND gate the other input of which is obtained from a strobe circuit 296. Each gating circuit also includes a checking arrangement comprising an inhibit gate 310 controlled by the strobe pulses which operates an error flip-flop 314 if no output from transformer 284 is detected in any strobe period. Positive or negative inputs from pulse forming circuits 330, 360 are applied to the transformers 206, 212 to write a word into the magnetic wire previously read out, the input pulses being applied to the upper and lower control windings 160, 162, respectively, of all the magnetic wires. Since the magnetizations of all the wires already recording a word is sustained by the detent windings 170, 172, 176, 178, the reading and writing currents have not effect on the wire magnetizations. Thus only the boundary walls in the previously read out wire are moved to recording positions. The pulse forming circuits 330, 360 each coil comprises a flip-flop 334 which is set to a first state if outputs from either of AND gates 336, 337 are received by way of OR gate 335, and is set to a second state if a differentiated pulse from a write pulse generator 326 is the only signal received. If a read out word is to be rewritten, a pulse is applied from lead 339 to the AND gate 336 in coincidence with a signal on lead 338 derived from the gating circuit output leads 300, 324. If new information is to be entered, this is applied to lead 341 in coincidence with a control signal in lead 340. The write pulse generator 326 is controlled from clock source 220 and energizes flip-flop output transistors 342, 343, the first or second state of the flip flop respectively causing a positive or negative writing pulse to be applied to a transformer 208, 212 by way of transistors 345 and 350 or transistor 355. The detent coils are omitted from the embodiment shown in Fig. 7 which is also modified by the use of transistor address drivers 536, 550, 512, 526 The detent action is provided by a continuous bias in the reading windings 430, 432, 434, 436 which is reversed in polarity only when a selected wire is subjected to a reading pulse by energizing a row and a column transistor. Constructional details are also disclosed in which each magnetic wire 628, 690, 694, 698, Fig. 10, has a control or digit winding 646, 666, 674, 684 extending the whole length of the wire, and common overlaid domain forming windings 700, 725, 739 and read windings 708, 710, 736, 738. The overlaid windings may be formed by a weaving technique in which a shuttle carrying insulated wire is passed between the parallel magnetic wires. The position of the detent coils, if provided, is shown by broken line 792 for one bit position. When weaving is completed, the magnetic wires are bent at spaced intervals in alternate directions so as to form a compact plated assembly. The various windings are then interconnected. It is stated that the detent and domain forming windings may be replaced by permanent magnets.