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Variable Sample Rate DASD Format

IP.com Disclosure Number: IPCOM000036902D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Greenberg, R: AUTHOR

Abstract

A direct-access storage device (DASD) disk surface format provides a high position sample rate to support fast seeking and settling. It allows for a lower sample rate during track-follow that is designed to eliminate write coupling problems between a data R/W (Read/Write) head and the dedicated servo head. The lower sample rate during track- follow also lowers the load on the servo control microprocessor, increasing the feasibility of using one micro to control both the interface and the servo.

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Variable Sample Rate DASD Format

A direct-access storage device (DASD) disk surface format provides a high position sample rate to support fast seeking and settling. It allows for a lower sample rate during track-follow that is designed to eliminate write coupling problems between a data R/W (Read/Write) head and the dedicated servo head. The lower sample rate during track- follow also lowers the load on the servo control microprocessor, increasing the feasibility of using one micro to control both the interface and the servo.

DASD products that employ a closed-loop position feedback system for controlling the actuator's motion typically require position information to be written on one or more of the disk surfaces. High performance DASD designs usually have one disk surface dedicated to providing position information. This is because obtaining high-access performance and high-track densities require precise radial position information on the head with many samples of this information per revolution.

The radial position information is used as feedback in the implementation of the 3 basic functions that a servo control loop provides. The first function, the track-follow phase, is used to move the R/W heads from an initial track number to within a half track of a final track destination. The third phase of control is the settle phase. This phase is evoked at the end of a seek phase to rapidly lock the position of the R/W heads over the final track destination. After the settle phase has moved the heads on track within a predetermined percent, the servo control switches to the track-follow phase.

The sample rate criter...