Browse Prior Art Database

Method to Overcome the Problems of using Fixed Frequency Oscillator to Write Variable Length Data on DASD

IP.com Disclosure Number: IPCOM000115304D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Pollock, JR: AUTHOR

Abstract

Disclosed is a method to overcome the problem of storing variable length records on low cost fixed block Direct Access Storage Device (DASD) by dividing the track into equal sectors and providing a means to remove any tolerance accumulation at the start of each sector.

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This is the abbreviated version, containing approximately 64% of the total text.

Method to Overcome the Problems of using Fixed Frequency Oscillator
to Write Variable Length Data on DASD

      Disclosed is a method to overcome the problem of storing
variable length records on low cost fixed block Direct Access Storage
Device (DASD) by dividing the track into equal sectors and providing
a
means to remove any tolerance accumulation at the start of each
sector.

      In current DASD that supports variable length records (i.e.,
Count Key Data (CKD), it has been a requirement that the clock used
for writing data be synchronized with the disk rotation.  This has
been required due to the small speed variations inherent in a
spinning disk.  Speed variations can cause a small record following a
long one to be overwritten when updating the earlier larger record.
A
less expensive DASD could be produced/used if a simpler fixed
frequency
oscillator could be used to clock the write data.

      The proposed method allows the use of low cost fixed block DASD
for variable length record (i.e., CKD) storage.

      To compensate for the variable speed of the disk motor, a
re-synchronization technique is employed to remove the tolerance
build-up at fixed positions around the disk.  Referring to the
Figure, a large record is divided into smaller pieces such that no
single write accumulates more tolerance in the plus direction than
can be absorbed by a fixed gap.  This is accomplished by dividing the
disk into a fixed number of equal "sectors".  At eac...