Patent GB-891338-A (GB)
Title: Improvements in and relating to code converters
IPC: H03M7/00
Filed: 1958-08-06
Abstract: 891,338. Electric digital data storage apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. Aug. 6, 1958 [Aug. 8, 1957; Aug. 23, 1957], No. 25150/58. Class 106 (1). In an arrangement for converting an address from one coded representation to another addresses in the first form are stored at discrete locations of a data store identified by addresses, means are provided for scanning the locations in sequence and delivering information read from each in turn to a comparing device also receiving input signals in the first form, and output means actuated by agreement between the sensed address and the input signals for providing an output in the second form. The locations of the store are numbered in sequence and this number is the second form above referred to, or the " internal address." The first form of the address is a catalogue or serial number which may bear only an arbitary correspondence with the internal addresses. This form is termed the " external address " and the purpose of the invention is to convert the external address to the internal address so that read-out from the store may be under the control of an external address. In the form of Fig. 1 the store consists of a number of magnetic discs 11 mounted on rotatable shaft 12. Reading or writing heads 14 co-operate with either side of each disc, the heads being carried on arms 15 secured to shaft 16, the radial position of which is controlled by mechanism 17 to position the heads on the selected tracks of the discs 11. The tracks are concentrically arranged and the locations are numbered in sequence, any desired location being selected by the internal address selector 20 which stores the number of the desired address and at an appropriate time, by transference of switch contacts 21a, controls the positioning mechanism 17 to select the track indicated in the address. The address may also indicate the disc containing the desired data or when the data is read-out in parallel form from a number of discs it may indicate a storage position on each of a number of tracks. This indication is passed over line 22 to control further selection circuitry. A clock track disc 11a produces clock pulses which are amplified at 24 to produce A and B pulses, the latter lagging. Reference marks on disc 11a produce " start scan " signals on line 27 to indicate the start of all storage tracks. The external addresses are recorded in parallel form in one or more tracks of each disc. These tracks are first scanned and the signals derived are amplified at 38 and compared in comparator 39 with the contents of the external address register 30. The number of storage positions scanned before the comparator indicates agreement is the internal address, since this is the number of the desired location in the series along the track. Operation.-The external address is entered on line 31 into store 30 and a " scan control " signal is then applied from terminal 29 to the external address scan control 28. This signal transfers switch contacts 21a to contact the positioning mechanism 17 to the external address scan control, which positions the heads 14 on the external address tracks of the discs. If more than one track is used for the external addresses, the scan control 28 steps the heads to the next track after each revolution. The next start scan signal on line 27 resets counter 33 and opens gate 34 to allow the " A " clock pulses to pass to it. There is one pulse for each storage location and the value in the counter therefore corresponds to the internal address number. This count is applied via a converter 35 to the internal address selector which, when connected to the mechanism 17 positions the heads on the corresponding tracks. When the external address sensed agrees with that in the store 30 the comparator 39 closes gate 34 and transfers switch 21. The counter therefore receives no more pulses and the value therein, which is the internal address corresponding to the external address in the store 30, becomes effective to position the heads 14 on the corresponding address of the disc store. Entry of new external addresses.-A blank location in the external address track is detected by detector 41 which opens gate 43 to transfer the count in counter 33 to the register 45. The gate is closed by the next following " B " pulse to prevent more than one count being transferred. The signal from detector 41 also primes a trigger 46 which is set by the next start scan signal on line 27 to allow " A " pulses to pass through gate 47 to be subtracted from the value in register 45. When the value becomes zero, the blank external address locations are under the reading heads. The " B " pulses on line 26 are accordingly passed to the write matrix 52 to write into the blank location the address present in the store 30. The relay contacts 37a-37n are transferred for the writing process. Second embodiment.-In a modification (Fig. 2, not shown) both the external and the internal addresses are stored, being in corresponding positions on different groups of discs so that corresponding external and internal address are read simultaneously. As before the external addresses are read and compared with an external address entered in a store. The internal address sensed when agreement occurs is entered into a register and used to control the positioning mechanism for read-out of the desired data. New external addresses are entered serially, the next blank location being indicated by an internal address register. A counter is operated by clock pulses as before and its count is compared with the internal address register. An output therefore indicates that the blank position has been reached and the new external address is written into the appropriate tracks, the value in the internal address register is written into the internal address tracks and the value in this register is increased by one to indicate the address of the next blank internal address location. Specification 823,748 is referred to.