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Location of Data on Disk Sector Having Unreadable ID

IP.com Disclosure Number: IPCOM000041959D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Agoglia, RJ: AUTHOR [+3]

Abstract

Diskette data storage files used with contemporary personal computers permit data to be written into sectors of a disk track defined by associated sector identity (ID) information stored on the disk, but require that when such IDs are written onto the disk, they are to be written always for an entire track rather than individual sectors. Furthermore, such file storage systems do not permit reading of data if the associated ID cannot be read. A recently developed IBM 5247 file storage system allows data to be read from a sector without reading an ID, permits writing of IDs for individual sectors and contains a "displacement" feature used for bypassing faulty sectors.

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Location of Data on Disk Sector Having Unreadable ID

Diskette data storage files used with contemporary personal computers permit data to be written into sectors of a disk track defined by associated sector identity (ID) information stored on the disk, but require that when such IDs are written onto the disk, they are to be written always for an entire track rather than individual sectors. Furthermore, such file storage systems do not permit reading of data if the associated ID cannot be read. A recently developed IBM 5247 file storage system allows data to be read from a sector without reading an ID, permits writing of IDs for individual sectors and contains a "displacement" feature used for bypassing faulty sectors. This article concerns a mechanism/scheme for using the recently developed system to sustain retrieval of data from sectors having unreadable IDs, with a high probability of successful retrieval. The present mechanism is a finite state logical machine described functionally as follows: 1. Each sector ID can be assigned one of four possible conditions: undisplaced, displaced once, displaced twice and unreadable. 2. When data is to be read, up to four IDs are read, starting at the expected/undisplaced location. 3. Attempts are made to read these IDs in the positional order: expected location, expected location +1, expected location -1, and expected location +2. The state sequence for controlling this order of "trial reading" selection is: State ID 0 Expected location 1 Expected location +1 2

Expected location -1 3 Expected location -1 4

Expected location +2 5 Expected location +2 6

Expected location +2 In order to avoid attempted access to a non-existent location, 2 is added to the state when the state is either 2 or 3 and the expected location is 0. 4. The condition of the last ID tried and the present state value determines the next state according to the following state matrix: 5. When enough information has been gathered to determine the location, the finite machine sets its state to one of the above values less than 0. 6.

Flags read from the expected location +1 are saved if the ID was readable. These fl...