Dynamic magnetic information storage or retrieval – General processing of a digital signal – In specific code or form
Patent
1978-07-17
1980-10-28
Canney, Vincent P.
Dynamic magnetic information storage or retrieval
General processing of a digital signal
In specific code or form
360 51, G11B 509
Patent
active
042310717
ABSTRACT:
Apparatus for reading data from a rotating magnetic disk whereon data has been recorded at either "single" or "double" density rate, or at both rates on different sectors of the same disk. Density rate information is used to control the frequency of a timing signal generated by a phase locked loop (PLL). The PLL times the reading of data according to a synchronizing signal recorded on the disk. To accommodate the bit shift associated with such plural density data recording, the phase locked loop is provided with a dual gain low pass filter. A high gain is used in the phase locked loop filter until lock-in is achieved, to increase acquisition range and reduce acquisition time; the gain of the loop filter is reduced upon acquisition, to provide a greater lock-in range and to reduce system sensitivity to bit shift of the data, thereby obviating the need for pre-compensation of the bit recording positions.
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"DNC File Memories" by H. J. McLaughlin, Instruments & Control Systems, 11/61, vol. 34, pp. 2063 through 2068.
Canney Vincent P.
Digital Equipment Corporation
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