Browse Prior Art Database

Flexible Disk Index Pulse Generation

IP.com Disclosure Number: IPCOM000049637D
Original Publication Date: 1982-Jul-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Frazier, GR: AUTHOR [+2]

Abstract

A hardware or software timer generates phantom index pulses at a rate slightly slower or faster than once per disk revolution depending on whether the flexible disk is being initialized, formatted, or read. This technique eliminates the need for electronics and hardware associated with sensing light through a hole in the disk to generate index marker pulses based on the position of the disk.

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Flexible Disk Index Pulse Generation

A hardware or software timer generates phantom index pulses at a rate slightly slower or faster than once per disk revolution depending on whether the flexible disk is being initialized, formatted, or read. This technique eliminates the need for electronics and hardware associated with sensing light through a hole in the disk to generate index marker pulses based on the position of the disk.

When reading data, the only purpose of the index pulse is to terminate the reading operation if the target identification field is not found. Thus, the hardware or software phantom index pulse timer generates the pulses at a rate slightly slower than once per disk revolution. The reading operation begins when the first index pulse is detected and terminates upon the detection of the next index pulse. If the data for which the controller is looking exists on the track, it will be found before the second index pulse.

The formatting of a track consists of a two-pass operation. For the first pass the phantom index pulses are generated such that a minimum of two complete revolutions occur before the index pulse is detected for the second time. During the first revolution, formatting proceeds in the normal manner in that identification fields, data fields, and gaps are written. After the last sector is formatted, the disk controller writes the final gap until the second index pulse is detected. Since this pulse is delayed by at least one revolution, the entire track is written over with a specific bit pattern that identifies a section of the disk as a gap. This first pass insures that no valid data or identification fields remain on that track.

For the second pass, the phantom index pulses are generated with the pulses spaced apart...