Patent GB-656139-A (GB)
Title: Improvements in electronic calculating machines
IPC: G06F7/52
Filed: 1947-10-22
Abstract: 656,139. Statistical apparatus. BRITISH TABULATING MACHINE CO., Ltd. Oct. 22, 1947, No. 28236. Convention date, Oct. 22, 1946. [Class 106 (i)] An electronic calculating machine settable to perform either multiplication or division by the repeating methods, has a divisor storage unit, a single accumulator for registering both the dividend and the quotient, each denomination of which comprises a group of trigger circuits operable by pulses, column shifting means controlling groups of pulse gating devices related to accumulator orders, and a source of operating pulses, and is characterized by means for applying repeatedly through the pulse gates to the accumulator numbers of pulses determined by the divisor so as to add repeatedly to the dividend value the complement of the divisor and " no go " detection means for determining when the addition no longer produces a carry from the highest denomination and terminating the complemental addition during the computing step when a carry is no longer produced. The trigger. The computing section comprises a large number of double-stability electronic trigger circuits. A typical trigger is shown in Fig. 3. In the OFF condition valve a is conducting and valve b is blocked. A negative pulse applied simultaneously to condensers 16a, 16b causes a reversal of this state : the lowering of voltage on the grid of valve a reduces its anode current and thus causes a positive pulse to be applied through a condenser 14a to the grid of valve b. As current starts to flow through valve b its anode voltage falls and so causes a further negative pulse to be applied through condenser 14b to the grid of valve b. Thus valve a becomes blocked and valve b conducting. This is known as the ON condition of the trigger. The next negative pulse to be applied to the condensers 16a, 16b will reverse the trigger again to its OFF condition. Positive pulses of similar magnitude do not produce this effect. The amount registers are built up from triggers, and each order is arranged to count ten input pulses to each output pulse. The circuit of the 5th order of the Dividend/ Product/Quotient Register is shown in Fig. 6j. It consists of four triggers designated 1, 2, 4 and 8 which, during the count, are in ON or OFF conditions according to the values they represent. Thus 6 is represented when trigger 1 is OFF, trigger 2 ON, trigger 4 ON and trigger 8 OFF. Each input pulse is applied simultaneously to both the grids in the first trigger and reverses it as described above. Each time trigger 1 is turned OFF a negative pulse from a tapping in the anode resistance of its valve a is passed to both grids of the next trigger 2 and also to the grid of valve b in trigger 8. When trigger 2 returns to OFF on the count of four a pulse passes to trigger 4 turning it ON, and so on up to the count of seven when triggers 1, 2 and 4 are all ON. The eighth input pulse causes these three triggers to be turned OFF in succession and a negative pulse from the anode resistance of valve a in trigger 4 passes to the grid of valve a only in trigger 8 switching this trigger to the ON position. The consequent rise in potential on the anode of the valve a is communicated to the grid of an extra valve X and causes this valve to start conducting. The ninth input pulse merely switches trigger 1 to the ON position to represent, with trigger 8, the count of nine. The tenth input pulse returns trigger 1 to OFF in the usual way but the effect of the consequent negative inpulse to trigger 2 is now counteracted by the lowered voltage on the anode of valve X which is applied to the anode of the a valve and the grid of the b valve in trigger 2. Thus, trigger 2 is not switched over in this case. However, the negative impulse from trigger 1 also passes along a wire 48 to the grid of valve b in trigger 8, switching OFF this trigger. Consequent upon this, the lowered voltage on the anode of valve a is transmitted to the grid of valve X causing this valve to cease conducting. Thus the circuit is returned to its initial state on receipt of the tenth input pulse, and a carry impulse passes along the " OUT " line. Entry of data. Cards are fed one by one and in an intermittent manner from a hopper P, Fig. 1, and past sensing brushes 17. The dividend and divisor (or multiplicand and multiplier), are represented in separate groups of card columns, Fig. 2, and the corresponding sensing brushes are connected by plugboard accordingly. As a card passes under the sensing brushes the occurrence of a data perforation causes a circuit to be completed through the usual cam and card lever contacts, plug connections, &c. to the appropriate plug socket PD, Fig. 6j, and causes a positive impulse at the grid of valve b of an entry control trigger such as N(5) (that associated with the fifth order being shown in detail). This causes the trigger to be switched ON, and the rise in potential on the grid of its valve b is communicated to the control grid of a pentode 97 which, however, does not conduct until the voltage on its suppressor grid is raised. Positive pulses for this purpose are supplied by cam contacts P2, P3, CB3, CB4 and P6, P7, CB1, CB2, Fig. 6d, which are operated in synchronism with the passage of the card data positions under the sensing brushes to switch a trigger B23 ON and then OFF again at each of the nine index points. Each time the trigger B23 is switched ON the drop in voltage at the anode of its valve b is communicated to the control grid of a valve B24 causing it to become momentarily non-conductive, thus giving rise to a positive pulse on line 101. These positive pulses are transmitted to all the entry control circuits, Fig. 6j &c. and to the suppressor grids of all the pentodes 97. They have no effect on the pentodes 97 until the potential on the control grid has been stepped up, as described above, upon sensing of a card perforation. Thereafter, each positive pulse causes the pentode concerned to conduct momentarily whereby the drop in potential in its anode circuit provides a negative input pulse for entry into the register. Thus each pentode 97 acts as a gate and allows negative pulses equal in number to the value of the digit sensed to pass to the counter. Entry of data into the other registers takes place in a similar manner. The computing stage. Initiation of the computing operations is by the closure of cam contacts between the " 11 " and " 12 " points in the machine cycle. This brings into operation a multivibrator which produces pulses at a frequency of approximately 50 kc,/s. Suitable circuits clip the output of the multivibrator and produce square-topped so-called " A " pulses and, 180 degrees out of phase with these, " B " pulses. These pulses are counted by a group of trigger circuits operating in binary fashion to give a scale of 16 count which forms the basis of the computing cycle. By means of further triggers and like devices, the equivalent of a commutator, supplying controlling voltages at pre-arranged periods in the computing cycle, is obtained. The arrangement and operation of the apparatus will be described with reference to the example set out in Fig. 8, i.e. the division of 99105 by 66. The dividend is entered in the first six orders of the accumulator DD-PQ, and the divisor in the first five orders of a register MC-DR, in the manner described above. The accumulator DD-PQ comprises twelve orders in all, and the quotient appears in orders 7 to 12 of this accumulator as a result of transfers from the lower orders during the process of division. Division is performed by repeatedly adding the complement of the divisor. When a " no go " condition occurs the last divisor subtraction is cancelled by adding the true divisor, the carry through, in this case, being suppressed ; after which column shift means operates to prepare for the next entry of the divisor complement moved one order to the right. If the divisor is equal to or less than the dividend or dividend remainder, then the addition of its complement produces a carry out of the highest order of the accumulator- DD-PQ signalling a " go " condition, and causes a " 1 " to be added in the appropriate order of the quotient section of the accumulator. The divisor is picked up from the register MC-DR by supplying ten pulses to the input of each denomination, pulses also going into the appropriate orders of the accumulator DD-PQ until blocked by output pulses from corresponding denominations of the register MC-DR. This gating is accomplished by pentode valves. A "go" condition in the accumulator DD-PQ is signalled by a transfer out of the highest denomination which prevents reversal of a trigger under the influence of the commutator circuit. In the absence of..this signal, reversal of the trigger occurs and conditions the read-out circuits to cause the true divisor to be entered into DD-PQ in the next cycle. The carry from the highest denomination is suppressed and the equivalent of a column shift takes place preparatory to the second stage of the division. Column shift is controlled by a group of triggers only one of which is in the " ON " condition at any particular stage. The ON state is passed on to the trigger after each " no go " condition and, by changing the conditions of a further group of pentodes the next reading from the register MC-DR is transmitted to the accumulator with the equivalent of a column shift. The apparatus continues to operate in this manner throughout six dividing stages. During the seventh stage " rounding off " of the last digit is performed. If the carries into the sixth order total 5 or more, then one unit is added into the seventh order. This rounding off is provided for by an initial entry of five pulses into the sixth order at the commencement of the seventh dividing step. The apparatus is set for multiplication by plugging the socket MPY to COM, Fig. 6d, whereby an electronic multiplier commutator