Patent GB-836360-A (GB)
Title: Improvements in or relating to electrical signalling apparatus
IPC: G11B20/14
Filed: 1956-05-04
Abstract: 836,360. Self-clocking arrangements for data storage apparatus. INTERNATIONAL COMPUTERS & TABULATORS Ltd. May 4. 1956 [May 4, 1955],No. 13834/56. Class 106 ( 1 ). The apparatus described is for reading and interpreting digital data from a magnetic storage drum without the use of independently generated (e.g. from a clock pulse track) clock pulses. Data stored on the drum must be arranged in blocks, each block commencing with a block start pattern, Fig. 3A, and ending with a block-end pattern. A block is read-out by generating a start pulse, Fig. 3B, which must occur after the first zero and before the last zero of the block-start pattern and which, it appears, may be generated either by a block marker head 25, as in Fig. 2 (the tolerance in positioning this head with respect to the data reading head is thus almost 2 cells) or from the block-start signal itself. As described, the data shown in Fig. 1A is assumed to have been recorded on the drum by the pulses shown (Figs. 1B or 1C and 1D), and is read by head 11, Fig. 2, the signals from this head, Fig. 1E, being clipped, Fig. 1F, differentiated, Fig. 1G, and separated into positive-going pulses and negative-going pulses, the positive-going pulses, Fig. 3D, emerging from a device 17, Fig. 2, and the negative-going pulses, after inversion, Fig. 3C, emerging from a device 18, Fig. 2. Of these pulses those from device 17, Fig. 3D, contain pulses corresponding to all the recorded-zeros and those from device 18, Fig. 30, contain pulses corresponding to all the recorded ones. These pulses are applied to threshold 3 gates 21 and 22, through which they cannot pass until a start pulse, Fig. 3B, has occurred. On the occurrence of a start pulse, which in Fig. 2 is assumed to come from a lead 25, flip-flops 24 and 32 are both set on (the start pulse being positive does not pass through shapers 43, 44) and the signal from flip-flop 24 constituting the:block gate, Fig. 3E, is applied to one input of gates 21 and 22. The signal from flip-flop 33, constituting the start gate, Fig. 3F, is applied to agate 33 allowing the next zero representing signal of the block start pattern to pass and set a flip-flop 35 on, which applied a signal, Fig. 3G, to a delay line 23 having one output, Fig. 3H, applied to gates 21 and 22 and delayed by ¥-digit period, and a second output delayed by ¢-digit period, which is applied via diodes 36 and 37 to reset flip-flops 32 and 35. Flip-flop 35 is, however, set on again by the one representing or zero representing pulse which passes through gates 21 or 22, so that it continues to oscillate, the read ones appearing on terminal 47 and the read zeros on terminal 46. On the occurrence of a stop-pulse, Fig. 3B (which being negative does not pass shapers 26, 27) flip-flop 24 is reset, closing gates 21 and 22. It is stated that the pulses emerging from devices 17 and 18 which correspond to neither ones or zeros can be used for checking, since between two adjacent (i.e. successive) pulses representing the same bit there occurs an unwanted pulse on the other lead. The data read from the drum may be temporarily stored in a shift register using pulses from the delay line 23 as shift register advance pulses. Specification 772,102 is referred to.