Patent GB-692912-A (GB)
Title: Improvements in or relating to magnetic data recording and playback device
IPC: G06F3/023
Filed: 1951-11-19
Abstract: 692,912. Digital electric calculating-apparatus. MONROE CALCULATING MACHINE CO. Nov. 19, 1951 [Nov. 17, 1950; Nov. 9, 1951], No. 27097/51. Class 106 (i). The apparatus comprises a magnetic storage system which includes a magnetic drum having a plurality of recording paths and recording and play-back means for at least a pair of paths, wherein the play-back means for each path are connected to the recording means for the other, to form a continuous loop. The apparatus is further characterized by the provision of input means for operating one of the recording means to enter information items into the loop during a particular period of a drum cycle, and means in the loop to delay the rerecording of the item one item space irrespective of the drum cycles. In this manner items are entered first on one track singly, each item being then transferred to the second track, each item being displaced forward one item space at each entry to make room for the next entry in sequence. Fig. 1 shows a magnetic drum in diagrammatic form mounted on a shaft 4 rotating at constant speed in the direction shown. Mounted on the same shaft coaxial with the drum is a toothed wheel 9 which co-operates with a magnetic pick-up head 8 to produce a regular train of pulses which serve as a time-base for the correct spacing of the items and their constituent magnetic marks on the drum. A similar wheel 6 having only one tooth 10 serves, with its magnetic pick-up 11 to provide a zero signal for controlling an electronic counter 13. The electronic counter 13 shown in detail in Fig. 2 comprises a binary system of hard valve trigger pairs of triodes. These trigger pairs have two stable states and represent from right to left 2‹, 2<SP>1</SP>, 2<SP>2</SP> 2<SP>3</SP>, 2<SP>4</SP>, 2<SP>5</SP>, 2<SP>6</SP>, 2<SP>7</SP>. The electronic counter counts in binary fashion the pulses from the toothed wheel generator 8, 9, which number, in the example given, is 180. On the 180th pulse the counter is reset by a dominating pulse from the toothed wheel generator 10, 11. In each case the toothed wheel generator provides a sinusoidal output which is passed through an amplifier and shaper unit 12 or 17 to provide a suitable shaped pulse for operating the counter circuits. A crystal diode matrix 15 distributes four sequentially generated timing pulses to circuits labelled t 0 , t 1 , t 2 , t 3  according to the sequence necessary for recording each four unit code signal. Four unit spaces on the drum track are allocated for each digit to be recorded and the code is a binary one, as shown below, where the letter P indicates a magnetic mark. Four gate tubes 19, 20, 21, 22 of the twin-triode type are provided to control the output of the crystal diode matrix along the conductors t 0 , t 1 , t 2 , t 3 . The gate tubes are so arranged that they will deliver a positive timing pulse in response to the blocking of both triode sections simultaneously, thus the four timing pulses which are required for the system are derived, i.e. the first four pulses of the binary counter 13, and subsequent pulses are suppressed. The output of the four gating valves 19, 20, 21, 22 is fed via four conductors 16 to a manual keyboard 1. The keys are provided with contact pairs 25, 30, as shown in Fig. 3. Depression of each key closes one pair of contacts 25 for transmission of a gating control or " G " signal. The contact keys when selectively closed by key manipulation produce via contacts 30 code signals which conform to that shown in the table above. The keyboard is also provided with a " clear " key 31 for removing previouslyrecorded data. The code signals are fed to the input circuits of two recording amplifiers 2 and 37, amplifier 37 is gated " off " and the code signal is recorded by amplifier 2 on to track A. When the key is lifted the code signal is played back from track A by the same magnetic recording-head into play-back amplifier 38 and thence via gate tube 41 to recording amplifier 37 and on to one of the tracks B<SP>1</SP>, B<SP>2</SP>, &c. The gate tubes 40, 41 are of the twin triode type and respond to " G impulses when a key is depressed to route the code signal on to track A and further respond to "G<SP>1</SP>" " signals when a key is released to route the recorded signal in track A to be re-recorded in track B. The speed of the drum is such that it makes at least two revolutions in the time taken to depress and release a key at the most rapid manual keying speed. If a second digit is now recorded on track A the first digit is played back from track B to track A but will be delayed by four pulse times in the delay circuit 7, so that a series of digits may be recorded in sequence on track A using the four-unit code for each digit independently of the manual keying speed. Each recording of a digit effects a wipe-out of the previously-recorded digit in track A, but only after it has been transcribed to track B. Each play-back from track B is delayed by the delay circuit 7 so that the record is precessed on its subsequent recording on track A and then the entire recording is transcribed back to track B. Thus the entire array of code signals for a plural digit number is stored along the track B, the code signals for any number of digits being precessed step-by-step as they are recorded. In a modification shown in Fig. 4 a separate recording and playback head is provided for each recording track, the displacement between the two being equivalent to 92 time positions in the case where there are 180 time positions in all around each recording track for one revolution of the drum. Thus a digit is recorded by the magnetic head 3<SP>1</SP> on to track A<SP>1</SP> and is played back at times t 92 , t 93 , t 94  and t 95 . A similar displacement exists between the heads 51 and 56 associated with track B<SP>1</SP> so that the signal played back from track A at t 92 , t 93 , t 94  and t 95  is recorded into track B<SP>1</SP> by the head 5<SP>1</SP> at these times but is played back by the head 56 at t 184 , t 185 , t 186  and t 187 , that is at actual times t 4 , t 5 , t 6 , t 7  of the following cycle. In this manner the recording from track A1 to track B<SP>1</SP> and back to track A<SP>1</SP> and again to track B<SP>1</SP> is carried out as before with the digits being displaced one digit space to make room for the incoming digit without the necessity for a delay network as in the previous embodiment. With this modified example the code signals are recorded on track A<SP>1</SP> while any of the keys of the keyboard 1<SP>1</SP> is held depressed, and on track B<SP>1</SP> when all the keys are in their restored positions.