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Browse Prior Art Database

Diskette Sector Look-Ahead

IP.com Disclosure Number: IPCOM000046355D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Crandall, DR: AUTHOR [+5]

Abstract

A diskette sector look-ahead mechanism is described for use in a multiple device I/O controller having both a diskette and a hard disk file connected thereto. Diskette latency while the diskette mechanism is searching for a desired record ties up the I/O controller and prevents data transfers to the hard disk file. This latency time can be as much as l67 milliseconds. The sector look-ahead mechanism described herein reduces this latency time to approximately 20 milliseconds, thus increasing data transfer performance for the hard disk file.

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Diskette Sector Look-Ahead

A diskette sector look-ahead mechanism is described for use in a multiple device I/O controller having both a diskette and a hard disk file connected thereto. Diskette latency while the diskette mechanism is searching for a desired record ties up the I/O controller and prevents data transfers to the hard disk file. This latency time can be as much as l67 milliseconds. The sector look-ahead mechanism described herein reduces this latency time to approximately 20 milliseconds, thus increasing data transfer performance for the hard disk file.

Heretofore, an I/O controller for handling both a diskette and a hard disk file had no means of predetermining the rotational position of the diskette when a command to the diskette mechanism was initiated. As a result, the diskette search for the target sector could take from just a few microseonds (if the target sector was near) to over l60 milliseconds (if the target sector was nearly a full revolution away). During this time, all processor data transfers to the hard disk file were suspended.

This problem is overcome by providing a means for monitoring the diskette rotational position by setting up a dummy operation to the diskette mechanism which causes a detectable condition when the target sector is located. The target sector for this dummy operation is set such that it will be found approximately 20 milliseconds prior to the true target sector for the processor I/O command. At this time, approx...