Technique for recording data on magnetic disks at plural densiti

Details Technique for recording data on magnetic disks at plural densiti Technique for recording data on magnetic disks at plural densiti

1978-07-17

1980-01-08

Canney, Vincent P.

Dynamic magnetic information storage or retrieval

General processing of a digital signal

In specific code or form

360 43, G11B 509

Patent

active

041830660

ABSTRACT:
A method and apparatus for recording data on a rotating magnetic disk at plural density rates on different areas of the disk is disclosed. The method is particularly useful in magnetic disk recording systems in which the header or control fields of the recorded information are recorded in "single" density FM recording and the data fields of the recorded information are in "double" density modified frequency modulation (MFM) code. The technique involves changing the conventional MFM coding rules to prevent certain data patterns from appearing to the data recording system read circuitry as part of the control fields. In particular, the data pattern 011110 is encoded according to the invention as a data pattern which consists of 000000 with synchronization bits between the first and second, third and fourth, and fifth and sixth data bits. This encoding modification prevents any misinterpretation of the data field as part of a control field. The data recording circuitry used to decode the MFM information is modified from the conventional decoding circuitry so that adjacent "zero" data bits having no synchronization bit between them are decoded as adjacent "one" bits. The original data stream is thereby recovered.

REFERENCES:
patent: 3789377 (1974-01-01), Norris
patent: 3815122 (1974-06-01), Schwartz et al.
patent: 4129888 (1978-12-01), Reinholtz

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