Browse Prior Art Database

Index Decode Validity Check Circuit

IP.com Disclosure Number: IPCOM000046905D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Danen, JA: AUTHOR [+2]

Abstract

The proposed circuit is used to detect an error resulting from an erroneous decoding of either the index or the servo clock pulses, when reading data from a disk pack. If the index is erroneously decoded from the servo tracks, then sector boundaries will be calculated from an incorrect reference point, and data will be written in wrong locations on the disk and lost. This invention provides a high percentage of certainty that the index has been decoded properly. The building blocks of a fixed-blocked architecture file consist of sectors, tracks, and cylinders. A sector is the smallest separable set of data associated with an identifier. A track is all the data under one head at a given radius on the disk. A cylinder is all the data under all the heads at a given radius on the disk.

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Index Decode Validity Check Circuit

The proposed circuit is used to detect an error resulting from an erroneous decoding of either the index or the servo clock pulses, when reading data from a disk pack. If the index is erroneously decoded from the servo tracks, then sector boundaries will be calculated from an incorrect reference point, and data will be written in wrong locations on the disk and lost. This invention provides a high percentage of certainty that the index has been decoded properly. The building blocks of a fixed-blocked architecture file consist of sectors, tracks, and cylinders. A sector is the smallest separable set of data associated with an identifier. A track is all the data under one head at a given radius on the disk. A cylinder is all the data under all the heads at a given radius on the disk. For example, a cylinder has 14 tracks, a track comprises 50 sectors, and a sector includes 609 bytes. With a staggered-sector format, the sectors are located differently for each of the 14 tracks of each cylinder. This creates 700 different sector locations per cylinder. The first sector of the first track starts 43.5 bytes (the 1/14th of 609 bytes) after the index, and the first sector of each of the remaining 13 tracks is incremented by 43.5 bytes. The determination of the sector boundaries is accomplished by using the index which is decoded from the servotrack patterns as a reference point and then counting servo clock pulses which are also decode...