Patent GB-727926-A (GB)
Title: Improvements in or relating to data storage apparatus
IPC: G06C25/00
Filed: 1952-12-11
Abstract: 727,926. Electric digital data storage apparatus ; recording-apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 11, 1952 [Dec. 31, 1951], No. 31381/52. Classes 106 (1) and 106 (4). A digital data store includes a movable magnetic medium, reading means and recording means therefor coupled by data transfer means, and control means for selectively shifting the position at which the read data is re-recorded. In the storage system shown in Fig. 1 which may be part of a computing- machine, two reading heads 24, 25 and two recording heads 26, 27, selectively operative under control of unit 30, are associated with a track (called " revolver track ") on a rotating magnetic drum 22. After the recorded data has been read it is erased by magnet 37. The track is divided into sections or " cycle groups," Fig. 3, each comprising 22 digital positions including series of " low order and " high order " positions, in each of which a 10-digit decimal number may be recorded, and two control positions 20 and 21. Each digital position is sub-divided into 14 cells, Fig. 4, a pulse being recorded in one of the cells 0-9 to represent the nines complement of a decimal digit. The cells 11-14 could be used for recording alphabetic characters or other symbols; in the particularly described embodiment, however, timing control pulses are applied during the times corresponding to these cells which are further sub-divided at mid-points B. (Reference is made also to the use of a code requiring the division of a digital position into only 7 cells, and to parallel multi-track recording.) The normal reading and recording heads 24, 26 are spaced around the track by 21 digital positions so that; in view of a one-digit delay in data transfer unit 34, the read data is re-recorded in corresponding positions in the next cycle group. The reading head 25 is spaced one digital position from head 24, so that its use in conjunction with recording head 26 causes a onedigit right shift so that, e.g., the digit in position 2 is recorded in position 1 of the next cycle group. The use of recording head 27 with reading head 24 similarly causes a one-digit left shift. The control unit 30 includes circuits 31 and 32 for determining which of the heads 24, 25 and 26, 27 respectively are operatively connected to the unit 34, and also a circuit 36 for producing zero-representing pulses to fill the spaces left vacant by shifts. The units 30 and 34 comprise electronic circuits (Figs. 8A and 8B, not shown) built up from bi-stable triode trigger pairs, polarity-inverting circuits, cathode followers and two-input coincidence gates or switches," and receive timing (" cycle digisynch.") and programme control pulses respect tively from timing and " data storage " tracks (not shown) on the drum 22. In the unit 34, a differentially tiined pulse corresponding to the decimal digit being read is received on line 40 and opens a gate to allow pulses coinciding with cell-division points A, Fig. 4, to be applied to a decade counter 33. Since the decimal digit was recorded as a nines complement, the counter receives a number of pulses corresponding to the true digit value. At the beginning of the next digital period, the value on counter 33 is transferred to counter 35, and counter 33 is reset so as to be ready to receive pulses corresponding to the next digit. The value on counter 35 is read out by applying pulses coinciding with points B, Fig. 4, to the counter until it reaches zero when a carry pulse is sent over line 41 to the recording control circuit 32. Each of the counters 33, 35 comprises four trigger pairs serially connected so as to operate in normal binary fashion-for the first nine pulses received, and a blocking stage connected between the second and fourth triggers whereby the tenth pulse causes a reset to the initial state. A further shift counter may be provided which can be preset so as to produce a control output pulse after a predetermined number of (right or left) shifts have been performed. In a modification (Fig. 14, not shown), two tracks (" regeneration " and " operation " " revolvers ") are used, each having a single reading head and recording head. Data is normally circulated with no delay between the heads of the regeneration revolver which are spaced by 22 digital positions. For left shift, the data is diverted through a one-digit delay, and for right shift the data is diverted to the operation revolver, where the heads are spaced by 21 digital positions, and back to the regeneration revolver. Reference is made to shifting for positioning a decimal point or effecting rounding off.