Browse Prior Art Database

Method to Avoid Long Head Switch Times

IP.com Disclosure Number: IPCOM000115259D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Pollock, JR: AUTHOR

Abstract

Disclosed is a method to avoid long head switch times, that is, pair up two Head Disk Assembly (HDA) in parallel using spindle sync and add switch control logic to logically map sequential heads to alternating HDAs and issue seeks to both HDAs. In this way the next sequencial head is always ready to read or write immediately after a head switch since it is on a different HDA.

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Method to Avoid Long Head Switch Times

      Disclosed is a method to avoid long head switch times, that is,
pair up two Head Disk Assembly (HDA) in parallel using spindle sync
and add switch control logic to logically map sequential heads to
alternating HDAs and issue seeks to both HDAs.  In this way the next
sequencial head is always ready to read or write immediately after a
head switch since it is on a different HDA.

      The use of dual element Magneto Resistance (MR) Read/Write
heads, rotary actuators, and fine track pitch in advanced Direct
Access Storage Device (DASD) has resulted in significantly longer
head switch times (40 &mu.  sec to 800 &mu.  sec) than previous
generation.  Combined with increased data rate and rotation speed the
result is a significant loss in DASD performance during head
switching.  Examples of such drives are the IBM Type 0664 models P10
and P11 3.5" Winchester Drives.

      The proposed method reduces the head switch time for sequencial
head stepping from 800 &mu.  sec to under 40 &mu.  sec.

      Two HDAs are paired up in parallel using spindle sync.  Logical
heads are located on alternating HDAs such that the other HDA is
always positioned to read or write the next sequencial head.  The
table in Figure illustrates one possible physical to logical head
mapping for an HDA with 15 heads.

      An additional benefit is that sequencial cylinder operations
can be performed without any missed revolutions.  Thi...