Patent GB-792520-A (GB)
Title: Apparatus for effecting the transfer of data between the data storage unit of an electronic digital computer and an auxiliary data storage unit
IPC: G06F3/06
Filed: 1956-02-06
Abstract: 792,520. Electric digital-data-storage apparatus. NATIONAL CASH REGISTER CO. Feb. 6, 1956 [Feb. 14, 1955], No. 3578/56. Class 106 (1). Selected data is transferred between an electronic digital computer storage unit, including a rotatable magnetic drum having word-periodidentifying signals recorded thereon, and an auxiliary store including tape units, by electrical transfer apparatus including a one-wordperiod recirculating register synchronized with the rotatable drum and adapted to store a computer command applicable to the selected data, a tape selector device for selecting the tape unit specified in the command, and logical transfer circuitry for effecting the transfer of the data between the selected tape unit and a multiword-period recirculating register synchronized with the drum, the circuitry including logical components which produce output signals in accordance with the command in the one-word register, and the sequence of operations being controlled by a sequentially stepping programme control device. The apparatus described is for transferring data between the magnetic drum memory 101, Fig. 1, of a computer similar to that described in Specification 770,952 and a selected one of seven magnetic tape units similar to the unit described in Specification 780,749. The drum 101 has a clock pulse channel 108 controlling binary and octal digit-period-defining counters 117, 118, an arc address channel 109 containing 64 successive octal numbers 0-77 defining the addresses of words stored in the main memory channels 111, and channels forming with the arithmetic unit 114 one-word recirculating registers E, F, G, H. A further 8-word recirculating register J forms a buffer store between the memory channels 111 and the tapes. The unit 114 comprises bi-stable hard valve trigger circuits (called " flip-flops ") and a logical diode gating network. The operating sequence to carry out a computer command, set up in register H, is determined by programme counter 115 controlled by flip-flop K1 so as either to step on to the next value, or to skip-or stay in the same condition, at the end of each word period. Figs. 3a-3c show the three commands, " search," " record " and " read," related to the tape units. Each tape (Fig. 5,. not shown) is similar to that of Specification 780,749 and comprises five pairs of duplicate channels, one pair for clock pulses, and the other four for recording binary coded decimal digits; a block of information comprises 16 11-decimaldigit words (W1-W16) in addition to the blank and address words (W9 and W0). A search operation is effected as described in Specification 780,749, except that selection circuits 182, Figs. 2 and 11, are controlled by the binary digits in position 06, Fig. 3a, to select the required tape unit. These digits are set up in flip-flops A9- A11 which supply relatively positive potentials on outputs A9-A11 when registering " 1." Each circuit 182 comprises terminals 1a, 2a, 3a and 1b, 2b, 3b, Fig. 11, across which a diode is placed in the number of the associated tape unit has a " 1 '' or " 0 " respectively in the corresponding position (A9-A11). The diodes across 1a-3a form AND gates such as 188, and the diodes across 1b-3b form OR gates such as 189; the output of each OR gate is inverted in a circuit 191 and combined with the output of the associated AND gate in a further AND gate such as 190 whose output energizes a relay R. As shown, the circuit 182 for tape unit No. 1 (binary 001) has diodes at 3b, 2b, 1a; and the circuit for unit No. 7 (binary 111) has diodes at 3a, 2a, 1a, so that the inverter 191 is not required. The record and read commands, Figs. 3b and 3c, include, as well as the tapeselection code in 06, two " mode-of-operation " digits in 04 which determine whether the block address only, odd words (W1. . . W15) or even words (W2 . . . W16) are to be read from or recorded on the selected tape, and also include, in O0, the address of the J register to be used first. For a record operation, it is assumed that a block search has been made and that a maximum of eight words has been transferred from channels 111 to register J, Figs. 1 and 2; during the first programme counter step, circuit 183 energizes line PCS2 and thus, through contacts of the energized relay R, Fig. 11, record-control line W2 of the selected tape unit. The address in O0 of register H (always " O " in the embodiment described) is compared with the units octal digits of the arc addresses supplied to flip-flop Mw and, when agreement is detected, the first word from J is transferred to register E and " 2 " is entered into O0 of H. The next word (at address " 1 ") in J is then transferred to register F and the digits in E are transferred four at a time to flip-flops A1-A4 and then to L1-L4; register E includes a chain of four flip-flops in unit 114 which are by-passed every time a transfer takes place, to effect a right shift. The digit-representing outputs from L1-L4 are applied over lines T1-T4 to the recorder of the selected tape unit, the transfers and recording being synchronized with the movement of the tape by circuit 184 controlled by tape clock pulses Ct. When register E has been emptied it receives the word in F, and a test is made to determine whether further recording is required. If so, the word now in E is similarly transferred and recorded on the tape, and the word at address " 2 " in J is transferred to F. At the same time, " 1 " is added to the O0 content of H so that address " 3 " of J will be the next to be read out, and so on. When all the words in J have been recorded, circuit 173 detects that the O0 contents of the register H (now " 1 ") agree with that of register G, and the computer will step on to the next programme sequence. A read operation is similar, readcontrol line R2 of the selected tape unit being energized through PCS1, and the information flowing from the tape to L1-L4, A1-A4, E and J. The flip-flops A1-A4 operate as a shift register to enter binary digits serially into E, and the J address is transferred from O0 of H to O0 of G, so that register H can be used as a counter to indicate when eight words have been read from the selected tape.