Patent GB-921161-A (GB)
Title: Data storage system
IPC: G11B5/596
Filed: 1959-11-24
Abstract: 921,161. Disc record apparatus; track-finding. INTERNATIONAL BUSINESS MACHINES CORPORATION. Nov. 24, 1959 [Nov. 24, 1958], No. 39930/59. Class 40(2). [Also in Group XIX] A transducer is located at a particular storage ocation first, by means of an address signal and then by a signal derived from the relative positions of the transducer and the required storage location. The invention is applied to the magnetic discs of a random access store of the kind described in Specification 823,748, although optical recording may also be used. With each disc 10 (Fig. 1) is associated a fixed timing transducer 30 and, on each side of the disc, a set of ganged transducers, comprising information transducers 21 and a control transducer 22, which are moved by an hydraulic piston acting on an arm 24, a signal indicative of the position of the arm being produced by a linear differential transformer 28. On each disc are outer information tracks, an inner synchronizing track comprising magnetized sectors 13 and " matrices " of sample groups 14 which comprise sectors of magnetized and unmagnetized areas shaped and patterned as shown in Fig. 2. The leading edge 15, relative to the transducer, of each sample group is magnetized. In the present embodiment, each matrix consists of two sample groups 14, one displaced from the other a distance equal to the distance between adjacent information tracks (Fig. 3), so that a fine selection of one of two adjacent tracks can be made. Operation (Fig. 4).-A signal indicative of the radius of the required track is fed to a coarse error indicator 32 from control circuitry 36 where it is compared with the signal from the linear differential transformer 29, the error being used to drive the hydraulic piston 31. Detection of a coarse null signal results in switch 33 being operated to start fine track selection. Circuitry 36 has been operated to determine which of the two sample groups 14 of a matrix is to be used and to determine which direction of movement of the ganged transducers is to be associated with error signals of specific polarity. Timing signals from the synchronizing track differentiate the two sample groups and a signal from the control transducer 22 due to the magnetized leading edge 15 of the selected sample group operates to start a crystal controlled oscillator generating timing pulses which coincide with signals derived from the control transducer passing the boundaries of magnetized and unmagnetized areas of the sample group. When the control transducer is positioned at the boundary of two adjacent rows of the sample group the ganged information transducers 21 are positioned directly over information tracks. After an interval of one radial column of a sample group, to allow the pulse generator to settle, the signals from the control transducer are passed to error sampler circuits to operate the hydraulic piston 31. In Fig. 3, if the control transducer is positioned along line W, the first signal received by the error sampler circuits will be positive due to transition between unmagnetized and magnetized areas of the sample group; if it is positioned along lines Y or Z the first signal will be negative. In this case it will have been determined that a positive signal will cause outward radial movement of the transducer. Movement will continue until a null signal issues, due to the transducer being positioned along line X. At this time the fine null detector 47 will operate the read and record circuits 38 associated with the information transducers 21.