Patent GB-839244-A (GB)
Title: Improvements in or relating to electronic digital calculating equipment
Inventor: BIRD RAYMOND
IPC: G06F9/32
Filed: 1955-08-19
Abstract: 839,244. Electronic dividing apparatus. INTERNATIONAL COMPUTERS & TABULATORS Ltd., Aug. 17, 1956 [Aug. 19 1955], No. 23951/55. Class 106 (1). An electronic calculating-apparatus for performing calculations in a plurality of steps in response to a succession of different instructions applied thereto, includes a function control means adapted to be conditioned at each step by an instruction currently positioned at a predetermined position in a shifting register to control performance of the instruction, means operative at each step to replace a current instruction with the next in succession and means for inhibiting operation of the replacing means to permit the control means to cause repeated performance of a currently positioned instruction. The control means is described as applied to the binary calculator claimed in Specification 839,241 for dividing by repeated subtraction in which the dividend is entered in a first register and the divisor is subtracted from it to form a partial remainder which is re-entered in the first register, the dividend being meanwhile entered, with a shift of one place upward, in a second register. Thereafter the divisor is subtracted from the partial remainder in the first register if this is positive or, if it is negative, then from the dividend or the last positive partial remainder in the second store. The calculator operates with word lengths of forty binary digits representing either a number or a series of instructions. Initially all words are stored on a magnetic drum 2, Fig. 1, and the performance of a calculation is effected by reading out a first instruction from the drum into a shifting control register, this instruction including the address of the next instruction. The machine obeys this first instruction and prepares for the selection of the next instruction and so on. Different digits or groups of digits of an instruction word each have a different significance being used to determine the function to be performed, the register from which the numbers to be operated upon are to be taken, or the track from which they are to be read. The machine has four registers 17, 18, 19, 20, apart from the control register 16, which are used for storing initial, intermediate and terminal factors involved in the calculation. The drum 2 has sixty-two read-heads 1 and further heads 5, 7 used for providing clock pulses and a synchronizing pulse respectively. The track to be read is selected by a unit 3 which has a tree of relay contacts the relays of which are controlled by the control register through lines 33. The output from the selection unit is passed through amplifier 4 and gates 9, 10 to the input trigger 11 of the registers. There are sixteen forty-digit words on each track of the drum, the particular word required being selected by its address number. This address is set up in control register stages 10 to 13 and applied on lines 34 to a multiple coincidence gate 35, Fig. 2. The clock pulses from head 5 are applied to a counter 23 which counts up to forty and then passes an " end of word " pulse to a counter 24. The counter 24 therefore contains the number of the word being read at each moment. This number is applied on lines 36 to the gate 35 which opens when the number on line 36 and lines 34 are the same, to cause the selected word to be entered into one of the registers. The control register 16 and other registers 17, 19, 20 are connected to highway 21 through input gates 12, 13, 14, 15, which are opened to allow the pulses to pass into the registers, the digits being moved along by shift pulses applied to the registers. A number entered in a register is thereafter available both from the drum or from the register, the instruction in the control register determining the location from which the number is to be read and if it is to be from the register the drum read out circuit is blocked. The function to be performed by the calculating apparatus is registered in positions 14 to 18 of the control register, which positions are connected by lines 44 to a function matrix which, according to the input signals changes the voltage levels on different combinations of output lines which control the opening of various distribution gates so as to govern the function performed by the circuits. At the end of the performance of a calculation the control register is prepared to receive the next instruction by applying a signal on lines 57 to open gates 58. This causes the number registered in stages 28 to 31 of the register to be transferred to stages 10 to 13. The address of the next instruction is thereby applied to gate 35 over lines 34 to select the next instruction. Coincidence in gate 35 sets a trigger 28 at the end of the performance of one instruction this trigger is unset by an end of word pulse from counter 23 applied through line 25 and gates 26 and 56. The unsetting of trigger 28 causes a pulse on line 57 to transfer the next instruction word address to the operative positions of the register. In a division operation a repeated performance of a subtraction operation is necessary and in such a case the gate 56 is held closed by a potential on line 46w from the function matrix. This prevents the trigger 28 being unset and the machine is therefore not switched to the next operation but instead continues to repeat the same operation in each succeeding cycle. However, there is registered in a counter-stage of the control register a number which represents the number of subtraction operations to be made. This number is reduced by one by each operation by a pulse on line 95 until it becomes zero whereupon the counter gives an output pulse on line 123 which is applied through gate 121 to unset trigger 28 in place of the end of word pulse passing through gate 56. The division operation is thereby ended and the machine conditioned to enter the next instruction into the control register. Specification 738,269 also is referred to.