Patent GB-816500-A (GB)
Title: Check number generating equipment
IPC: G06F11/10
Filed: 1957-10-25
Abstract: 816,500. Digital electric calculating-apparatus; electric digital-data-storage apparatus. STANDARD TELEPHONES & CABLES Ltd. Oct. 25, 1957 [Oct. 26, 1956], No. 33383/57. Class 106 (1). In electrical equipment for generating from a multi-digit number a remainder-modulo-three check number expressed as a binary code combination, a first circuit receives the number digit by digit and, for each digit, generates in binary form a ternary digit representing the remainder modulo three for that digit, and a second circuit connected to outputs of the first circuit and of storage means controls the setting of the storage means, whereby after the whole number has been received the storage means is. set to represent the required check number. Computing check numbers.-As shown in Fig. 3, the first circuit comprises two groups of AND gates 56-58 and 59-61 which receive each decimal digit of a number in excess -3 binarycoded form on lines 1 to 8<SP>1</SP>. The outputs of the groups of gates are connected via OR gates 62, 63 to lines A2, A1 respectively, these lines being marked when the remainder mod. 3 for the digit is " 2 " or " 1 " respectively; if, e.g., the digit 7 is entered by marking lines 8, 4<SP>1</SP>, 2 and 1<SP>1</SP> (representing 10=7+3), gate 59 will be actuated, thus marking line A, to indicate a remainder of " 1." The second circuit comprises AND gates 64-67 controlled as shown by lines A1, A2 and by the outputs of bistable devices 68, 69 which store the binary digits of the check number, the " 1 " outputs, controlling gates 65, 66, being previously combined in OR gate 70. The setting of devices 68, 69 is changed through OR gates 71, 72 when gates 64 or 65 and 66 or 67 respectively are actuated. The final check number is obtained from outputs P1, P2, the devices 68, 69 being reset to " 0 " before a further check number is computed. Data storage checking system.-As a number is passed, e.g. from magnetic or paper tape or punched cards in input device 10, Fig. 1, via channel 13 to storage device 12, a check number is computed in device 21 (Fig. 3) and appended to the number. When a number is read out on channel 14, a further check number is computed and compared in device 22 with the first check number, any disagreement causing actuation of error indicator 23. Reference is made to magnetic drum and tape storage. Computer checking system.-The computer system shown in Fig. 1 includes, as well as the data storage system, an arithmetic section for performing multiplication, addition and subtraction, one of the operands being obtained from accumulator 17 and the other from storage device 12 or, for multiplication, from register 19. The check numbers of the operands are applied over lines A, B to unit 26 comprising gating circuits (Fig. 2, not shown) conditioned by a signal " + ", "-" or "X" so as to obtain the correct check number for the result. This number is applied (after being held in register 29 in the case of multiplication) together with the check number computed from the result number in device 28 (Fig. 3), to comparator 27 which provides an arithmetic error indication for any disagreement.