Patent GB-852184-A (GB)
Title: Improvements in electric calculators
IPC: G06F7/52
Filed: 1955-12-19
Abstract: 852,184. Electronic decimal multiplying apparatus. DIRKS, G. March 19, 1957 [Dec. 19, 1955], No. 36266/55. Class 106 (1). A decimal digital multiplier (Fig. 1) comprises a rotating magnetic drum 1 with tracks 23-29, tracks 29, 25 and 24 storing the multiplicand, multiplier and partial product respectively, tracks 23, 28 and 27 having "start of revolution," " start of sector " and " end of sector " signals, and track 26 having ten signals recorded in each sector. The schematic blocks indicate amplifiers (such as 50), switched amplifiers (such as 49) and flip-flop switches (such as 48). Multiplication is effected by registering successively the multiplier digits, commencing with the least significant and one in each drum revolution, on a decimal counting tube 19, and multiplying the multiplier digit-by-digit by it, the partial product being accumulated in track 24. A part of the drum, and read and write heads are shown diagrammatically in Fig. 2; the drum surface is divided into n sectors 30/n-1 (for n decimal digits) with a blank sector 31, and each sector 30 is divided into three subsectors 32/1-32/3. In addition to the heads aligned at 33 further heads 5, 9 and 10 are provided for operation during different sub-sectors, and for tracks 23-25 for selecting different sectors (denominations). The operation will now be described assuming the multiplier and multiplicand to be recorded in tracks 25 and 29, and track 24 to be empty. Operation commences when switch 34 is closed, the next " start of revolution " pulse (23a) passing through amplifiers 35 and 37 to set counter 19 to 0 and set 40 to open 42 so that- 30/1; 32/1 the first multiplier digit is counted into 19. 28a switches 48 to open 49 and enter the first multiplicand digit into counter tube 16. Head 12/1 reads the lowest partial product digit and passes it to counter tube 20, but this is 0 at this time. At the end of the sub-sector 40 and 48 are switched off by recorded pulse 27a. 30/1; 32/2. Provided that 52 and 48 are switched on (i.e. that neither of the digits just read are zero) 54 will be open to supply 10 pulses from track 26 (head 8) to counter tube 18 and to a multiplier circuit 58 which delivers 100 pulses on line 59. For each pulse from head 8 until counter 18 is counted up to the multiplier digit registered in 19 ten pulses pass to counter tube 17; when 17 is counted up to the multiplicand digit registered there, one of the coincidence circuits 68/1-68/9 produces an output which acts through line 68a and flip-flop 61 to close amplifier 63 and cut off the rest of the ten, the next pulse from 8 re-opening 63. Amplifier 62 is closed by flip-flop 60 and coincidence circuits 64/1-64/9 when 18 has been counted up to the multiplier digit in 19 (a delay in this operation allows the ten pulses produced by 58 to pass 62 first), so that a number of pulses corresponding to the product of the digits passes via diode 67 to counter 20, the decimal carries being registered in counter 21. 30/1; 32/3. In this sub-sector the number registered in 20 is transferred to track 24, using head 13/1 to record it in 30/1; 32/1. For this the 10 signals 26a are sensed by head 9 and passed via amplifier 78 (opened by signal 28a read by head 5) to count up 20 until it registers 0, when 77 closes 78, and 82 opens 83 to pass the remaining pulses to 13/1. An " end-of-sector " signal then closes 42 and 82, and resets 16 to zero via amplifier 101 ready for- 30/2; 32/1-entry of the second multiplicand digit from head 4. Amplifier 42 has been closed so that 19 still registers the first multiplier digit. Head 10 reads the 10 pulses in track 26, but is placed so that the pulses it passes to amplifiers 95 and 96 are spaced between any partial product pulses read from track 24; they pass through 95 (95 has been opened and 96 closed by a " start-of-sector " pulse) to count up the partial product carry in 21 to 0, when a signal on line 98 closes 95 and opens 96 to enter this carry in 20 together with any partial product from 24 (although none is recorded there in this first revolution). 30/2; 32/2. The product of the first multiplier and second multiplicand digits is counted into 20 and 21 as in 30/1; 32/2 above. 30/2; 32/3. The new partial product digit is transferred from 20 to track 24 as in 30/1; 32/3 above. 30/3-30/n. The action continues as above, the track 24 registering the first partial product at the end of the revolution. For the next revolution the count in a counter tube 22 of n stages is advanced by a pulse from track 23, and a relay 39/2 is energized to switch from heads 11/1, 12/1, 13/1 and 14/1 to 11/2, 12/2, 13/2 and 15/2. Thus 11/2 reads the second multiplier digit into 19; 12/2 reads the second partial product digit in sector 30/1 into 20 and the new partial product digit obtained is entered by head 13/2 into track 24. Subsequent drum revolutions advance the count in 22 by 1 until the multiplication is complete. Specification 827,163 is referred to.