Patent GB-771764-A (GB)
Title: An improved electronic means for carrying out algebraic calculations
IPC: G06F7/48
Filed: 1954-09-23
Abstract: 771,764. Digital electric calculating apparatus. COMPAGNIE DES MACHINES BULL. Sept. 23, 1954 [Sept. 24, 1953], No. 27590/54. Class 106 (1). An electronic computer having several circulatory stores for storing data in the form of binary-coded decimal, series-mode, pulse trains, one store being equipped with an arithmetic operator, and an order transmitter for signalling the type of operation to be effected, is characterized by means for introducing a sign code into the decimal position following the highest allocated digit position of a number in a store, a device for detecting the presence of a sign code during transfer of a number from an ordinary store to the arithmetic store, a signdetermining device comprising first and second sign-signal registers controlled by the sign detector, the second register being controlled also by the order transmitter, and means for comparing the contents of the two registers to determine the nature of subsequent operations. The computer is basically the same as that described in Specification 764,523 but is adapted for carrying out algebraic calculations. Data is introduced into the storage memories S1, S2, &c., either from the accumulator of a tabulating machine or from the card sensing unit, in the form of binary-coded decimal signals. Except in the case of the first store S1, zeros to the right of the highest significant digit of a number are " coded ", i.e. they are represented by " ten " in binary code (2 + 8 = 1010). If the number concerned is negative, a minus sign, also represented by a coded ten, is registered in the place immediately left of the highest permissible digit, the position of which is registered in the order transmitter OF; a positive sign code is implied by the absence of any pulse in this position. Detection of sign code. The sign code is detected during transfer of a number from an ordinary store (S2, for example) defined by the order transmitter AD (not shown) to the arithmetic store MO. The store MO and an auxiliary memory MD (not shown) are zeroized immediately before the new number enters MO and its beginning order is passed from an order transmitter OD (not shown) into MD. A comparator R (not shown) compares the number in OD with the number of pulses registered by a decimal period counter K and, as soon as equality is detected, initiates a train of gating pulses H which are applied to an input of the store MO and allow numerical pulses from S2 to enter. Since the numeral stored in order transmitter OF defines the highest available digit position for the number, therefore by increasing this numeral by unity the position of the sign signal is defined. A comparator N feeding into a quadrupler 1221 signals the arrival of this latter position and if a " coded ten " is detected in the signal train passing from S2 to MO at this instant, a signal is emitted by a regenerator 515 (forming part of the " tens detector," Fig. 12a, not shown) which is gated through into a first sign signal storage loop or register 1222 (MSB). Sign-determining arrangements. If the type of operation set up on the control panel is an addition or a subtraction involving terms A and B, account must be taken not only of the signs of the two terms but also of the type of operation called for, changing this if necessary. The number 10 set up in the order transmitter TO (not shown) represents " addition " while number 11 represents " subtraction " ; so that the type of operation is easily changed by adding or subtracting unity. The following eight cases are possible:- In cases 2, 3, 6 and 7 the type of operation must be changed. In a case of subtraction regard must also be paid to the relative magnitudes of the two numbers A and B. The result C of a subtraction (B - A) performed by the decimal adder/subtractor is incorrect when A > B. The general comparator is used to compare the absolute values, and the correct value is obtained by performing a second subtraction O - C = D. In the cases of multiplication or division the apparatus must arrange for a positive result if the two numbers are of like sign and a negative result if of opposite sign. In the case of multiplication the multiplier is lodged in MO and its sign is stored in a second sign signal storage loop or register 1224 (MSMO) and the multiplicand is in the store defined by the number stored in the order transmitter AD (not shown). In the course of a multiplication the sign of the multiplicand will be stored in the first sign signal storage MSB in the manner described above. If the signs are identical, gates 1226 and 1256, forming a comparator, will remain non-conductive and a value " zero " representing a positive sign will be left in the second sign signal register MSMO. If the signs are different the regenerator 1241 emits a pulse to store a representation of the minus sign in register MSMO. Similar arrangements apply to an operation of division. When a number is returned from the arithmetic store to an ordinary store the sign code of the number is inserted in the appropriate decimal digit position. U.S.A. Specification 2,557,729 also is referred to.