U.S. Philips Corporation

Miloslav Janak

Martin Ginsberg

Eduard J Tercic

Helmut Schonwald

Albrecht Reiners

Method and apparatus for dividing a track on a magnetizable information storage disc into sectors by writing sector identification information into the track. In order to optimize the storage capacity of a track on a magnetizable information storage disc the track is first filled with information bytes in response to the occurrence of the leading edge of an index pulse (a) derived from the disc in such manner that a predetermined number of bytes fill a portion (ix) of the track, followed alternately by sector identification bytes and further bytes defining the data field of the relevant sector in portions SK and DT respectively until the final group of sector identification bytes has been written into portion SKn, followed by further bytes into portion z until the leading edge of the next index pulse occurs. The (positive or negative) difference between the total number of bytes in the portions z+ix and the number of bytes in each of the data field portions (DT) is then determined and the write operation is then repeated in the same track with the number of bytes written in the data field portions modified in accordance with the difference determined, so that the difference is distributed uniformly over the various data field portions. The write operations are controlled by apparatus comprising counters which address a read-only memory containing the information bytes, an arithmetic unit for determining the difference, and a store storing the modified number of bytes to be written to define each data field.

Method and apparatus for dividing a track on a magnetizable information

During the reading of serial data signals, for example, from a so-termed magnetic floppy disc, a synchronized condition between the local oscillator of the reading device and the timing of the data stream must be reached as quickly as possible after the start of the read operation. When the initial synchronization has been reached, readjustment of phase and frequency may take place only slowly, because the instants at which the actual signal transitions occur may exhibit a large spread with respect to the nominal instants. Therefore, during a synchronization operation an element of a read clock pulse train is applied to the phase comparator at each status transition of the medium as well as at further instants. The data sample signal of the clock pulse generator is applied at twice the bit frequency to the other input of the phase comparator. As a result, during the synchronization operation the phase comparison is performed in a dense series, so that the low-pass filter connected to the output of the phase comparator may have a high cut-off frequency. Once the synchronization has been realized, the phase comparison is performed only once per data bit and, the low-pass filter is switched over to a lower cut-off frequency.

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Sunnyvale, CA, United States of America

Miloslav Janak