Patent GB-742464-A (GB)
Title: Improvements in or relating to binary digital computing apparatus
Inventor: KILBURN TOM
IPC: G06F7/52
Filed: 1950-12-22
Abstract: 742,464. Digital electric calculating-apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Dec. 13, 1951 [Dec. 22, 1950], No. 31212/50. Class 106 (1). In an electronic digital computer, binary numbers are divided by an arrangement comprising a store SR, Fig. 1b, having a location for a dividend number " D," and read-out and write-in means 43, 45 disposed in a regenerative loop including an adding circuit ADC and a doubling circuit MU, a divisor number " Y " being repeatedly presented to the second input to ADC, directly or as a complement, by means CMP controlled by sign-testing means (including F1) supplied with the output of ADC at each addition, the quotient number " Q " being derived in accordance with the successive results of the sign-testing. The dividing arrangement may be included in computing machines as disclosed in Specifications 705,479, 731,341 and 742,522, including C.R.T. stores as described in Specifications 657,591 and 705,474, each having a regenerative loop including a pick-up plate, amplifier, read unit and write unit. The machine described operates with 40-digit words (numbers and instructions) represented in series mode with a negative pulse for " 1 " and no pulse for " 0," and each normal operation or " bar " comprises four minor cycles or beats," Fig. 3. A CI number stored on one line of C.R.T. 30 of control unit CL, Fig. 1a, to which " 1 " (pulse position P0) is repeatedly added through gate G10 and add unit 36 in the regeneration circuit, is used to select from the main store MS through the address portion of staticisor MST a present instruction P.I. which is stored on a second line of C.R.T. 30 and is in turn set up in MST to select a further address in MS and to perform the required function, by the selective opening and closing of gates G. The basic operating waveforms, including those defining the beats, Fig. 3, (e)-(h), are generated in unit WGU, and the machine also includes an accumulator A, having a single-line C.R.T. 20, and the dividing arrangement of Fig. 1b. The latter comprises a store SR in which the C.R.T. 40 has two lines R and Q, for storing the dividend or remainder and quotient, scanned during " action " (A1, A2) and " scan " (S1, S2) beats respectively due to the inputs to Y-shift-control trigger circuit SR-YSG. The regenerative loop including the read unit 43 and write unit 45 is normally completed through gate G1. Dividing operation. The dividend D and divisor Y are initially adjusted by programme steps (not described in detail) involving denominational shift to produce D*, Y*, where 2Y*>D*#Y*>O. An S.V. instruction, when set up in MST, Fig. 1a, produces during beat A2, through coding device CD1, operative potentials, Fig. 3, (i) and (j), which close gate G1 and open G3 to enter D* from MS into the R line of store SR, Fig. 1b. During beat A2 of the following BAR 0, Fig. 3, main dividing instruction S.Y. similarly produces through coding device CD2, potentials, Fig. 3, (k) and (l), which close gate G1 and open gates G2, G5 so that D* from SR and Y* from MS, complemented in CMP, are passed simultaneously in series mode form to adder ADC to produce a remainder R 0 =D*-T* which is doubled in unit delay circuit MU and written on the R line of SR in place of D*. Also, waveform S.Y., Fig. 3 (k), is differentiated to actuate bistable trigger circuit F2 which then applies an inhibiting potential, Fig. 3, (p), to gate G10, Fig. 1a, to prevent stepping to the next instruction. During beat A2 of the next BAR 1, the number Y* is similarly subtracted from 2R 0 . If the new remainder R1 is negative and therefore has a digit pulse representing " 1 " in the highest (p39) position, this pulse will pass through gate G6 and inverter N1 and reset sign-testing trigger F1 which will then apply a complementing-preventing potential DCO, Fig. 3, (m), to CMP during the next BAR 2. If the remainder produced by adding Y* during BAR 2 is positive, the potentials of Fig. 3, (m) and (n) will be returned to the initial values shown, since F1 is actuated at the end of each bar by a p39 pulse passed through gate G9. The sign-testing and control of complementer CMP continues through the subsequent BARS 3-39, and the quotient Q is obtained by entering " 1 " (pulse PO) in the Q line through gate G4, Fig. 1b, during every beat S1 except when potential DCO is changed by the detection of a negative remainder during the immediately preceding beat A2, and repeatedly shifting the Q number by passing it through MU. The dividing operation is completed by an initially inserted control digit pulse in the Q line which, when shifted to the highest (p39) position, passes through gate G8 and inverter N2 to reset trigger F2 at the end of beat S1 of BAR 39, Fig. 3, (o) and (p). The quotient is finally formed during the beat S1 of the next bar and fed through gate G7 to the accumulator A; also, " 1 " is added to the CI number through gate G10 to step the computer on to the next instruction which may be one to correct the quotient in accordance with the initial adjustment of D and Y, and at the end of the following beat A1 the S.Y. potentials, Fig. 3, (k) and (l), are returned to their initial inoperative conditions. Complementer: circuit details. The input to complementer CMP, Fig. 1b, is applied to " and " gates G10, G11, Fig. 4a, the latter of which is normally held open by a negative potential from inverting circuit N3 to reproduce the input directly on ouput lead 101. Unless, however, gate G13 is closed by a relatively positive potential DCO, Fig. 3, (m), indicating a negative remainder, the first " 1 " digit pulse in the input is circulated round the loop including G13, unit delay circuit DL and " or" gate G12 and applied during every subsequent digit period to G10, G11; thus if the input digit is " 0," a " 1 " digit output will be obtained from G11, and if the input digit is " 1," G11 will be inhibited by a pulse from G10 inverted in N3, thus producing a " 0 " output. A circuit diagram is given in which the gates are formed by diodes, the inverter by a normally-conducting valve coupled to a cathodefollower, and the delay circuit by valves having pulse-differentiating input circuits controlled by the basic " dash " pulses and by a further pulse p44 to clear the circuit at the end of a beat. The inverters N1, N2 and delay circuit MU, Fig. 1b, may be similarly formed. Specification 645,691 also is referred to in the Provisional Specification.