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Alternate Sector Assignment

IP.com Disclosure Number: IPCOM000082345D
Original Publication Date: 1974-Nov-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Adams, TA: AUTHOR [+4]

Abstract

Alternate sectors are assigned to replace defective recording areas in a disk storage drive. A defect is any flaw in the disk surface which prevents successful recovery of data therefrom. The disk surface contains a predetermined number of concentric tracks and each track is divided into a predetermined number of sectors. Each sector has an address or ID field followed by a data field. A spare track or tracks provide spare sectors which are assigned to replace defective sectors. It is necessary, in this arrangement, to be able to rewrite the address or ID of the defective sector with the alternate address of the replacement sector and insure its recoverability.

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Alternate Sector Assignment

Alternate sectors are assigned to replace defective recording areas in a disk storage drive. A defect is any flaw in the disk surface which prevents successful recovery of data therefrom. The disk surface contains a predetermined number of concentric tracks and each track is divided into a predetermined number of sectors. Each sector has an address or ID field followed by a data field. A spare track or tracks provide spare sectors which are assigned to replace defective sectors. It is necessary, in this arrangement, to be able to rewrite the address or ID of the defective sector with the alternate address of the replacement sector and insure its recoverability.

In this instance, each track has sixty sectors. As seen in Fig. 1, sector 30 is physically between sectors 00 and 01 and sector 59 is the last sector in the track. The sector arrangement is not significant to the alternate sector assignment. Logical sector 50 of track 07 is considered to have a defect in its data field. This defect renders the sector defective; however, the ID field is recoverable. Had the ID field been defective, i.e., any defect within the first 20 bytes of region 1 in Fig. 2, the alternate sector ID would be written in the data field away from the defective ID field. The distance that the alternate sector ID is skewed away from the ID field depends upon the particular disk storage drive. The skewed ID field is shown as starting at byte 76, i.e., the ID field is skewed 64 bytes to the right.

Detection of the defect in sector 50, Fig. 1, invokes an alternate sector assignment program. This program locates the next available sector in spare or alternate track 04 by reading each sector ID field, starting at sector 00 and detecting a sector ID field having its flag byte equal to hexadecimal 00. In this instance, logical sector 01 of track 04 is t...