Browse Prior Art Database

Efficient Way to Detect Variable Sectors/Track Diskette Format

IP.com Disclosure Number: IPCOM000043541D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Hung, TC: AUTHOR

Abstract

Disclosed is a new approach which assures efficiency and error recovery support to determine any number of sectors per track by using a double detection algorithm for speed and reliability. In most cases, the first read to the primary media control record (MCR), which is required to determine the type of a diskette, will indicate the number of sectors per track with the minimum amount of time. When the primary MCR is bad, there is a way to tell in which physical sector the secondary MCR resides. This double detection algorithm is very efficient and applicable in most environments where different sector, track or cylinder configurations are to be supported.

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Efficient Way to Detect Variable Sectors/Track Diskette Format

Disclosed is a new approach which assures efficiency and error recovery support to determine any number of sectors per track by using a double detection algorithm for speed and reliability. In most cases, the first read to the primary media control record (MCR), which is required to determine the type of a diskette, will indicate the number of sectors per track with the minimum amount of time. When the primary MCR is bad, there is a way to tell in which physical sector the secondary MCR resides. This double detection algorithm is very efficient and applicable in most environments where different sector, track or cylinder configurations are to be supported. While many computers currently support a 512-bytes-per-sector/ double side-double density/8-sectors-per-track diskette, it is highly desirable to support both of 8- and 9-sectors-per-track formats because of foreseeably wide use of the latter format. Most computers designed along this line have a trial and error type of detection mechanism. That is, a read command is issued to track 0 sector 9, and if a bad return code indicating a wrong sector is received, then it is determined to be an 8-sectors- per-track diskette. However, this approach requires much overhead time for the normal adapter software to recalibrate, seek and retry the requested sector, thus contributing to loss of time whenever a diskette is inserted into a diskette drive. The basic design of the present approach is to provide a special requirement (SREQ) byte within the primary MCR, located at logical sector 0 which is common to all sectors-per-track formats, to indicate whether the diskette has an 8- or 9-sectors-per-track format. More particularly, the SREQ byte is initialized to hexadecimal 40 to indicate an 8-sectors-per-track format. A new value of hexadecimal 48 is added to indicate a 9-sectors-per-track format. The least significant 3 bits are not used and padded with binary zeros in this SREQ field. The most significant bits 0 to 4 are used to indicate the number of secto...