Browse Prior Art Database

Dynamically Changing the Number of Times that a Sector of Data May Be Rewritten

IP.com Disclosure Number: IPCOM000123304D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 120K

Publishing Venue

IBM

Related People

Kulakowski, JE: AUTHOR [+3]

Abstract

There is a growing market for inexpensive optical media with sectors which can each be rewritten up to a maximum of Nmax times, where Nmax is a relatively low number, approximately 1,000. This includes phase change media used in Compact Disk Rewritable (CD-RW) data recording devices. It may also include Digital Versatile Disk (DVD) media. Decreasing the number of times that optical media may be rewritten can substantially decrease the cost of that data recording media. Furthermore, many customers may rewrite sectors infrequently and not want to pay additional cost for an unnecessarily high number of times that the sectors could be rewritten.

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Dynamically Changing the Number of Times that a Sector of Data May
Be Rewritten

   There is a growing market for inexpensive optical media with
sectors which can each be rewritten up to a maximum of Nmax times,
where Nmax is a relatively low number, approximately 1,000.  This
includes phase change media used in Compact Disk Rewritable (CD-RW)
data recording devices.  It may also include Digital Versatile Disk
(DVD) media.  Decreasing the number of times that optical media may
be rewritten can substantially decrease the cost of that data
recording media.  Furthermore, many customers may rewrite sectors
infrequently and not want to pay additional cost for an unnecessarily
high number of times that the sectors could be rewritten.

   Since the data and directory sectors have a finite number
of times that they can be rewritten, it becomes important to record
the number of times that each sector has been rewritten during use.
This permits the optical disk drive to relocate sectors when the
number of rewrites exceeds a threshold.  An example of tracking the
number of times a sector has been rewritten is taught in U.S. Patent
5,111,442.  In this patent, the number of times that sectors have
been rewritten is stored in a region of the optical disk not
accessible to the user.

   This paper describes a mechanism to include the number of
times that a sector was rewritten in the sector header itself,
rather than in a separate portion of the disk.  This saves on disk
space, as there are unused bytes in the sector header which can be
used.  By using the sector header itself for storing the number of
times that the sector has been rewritten means separate dedicated
disk space, specifically for tracking the number of rewrites of each
sector, is not needed.  It does mean that a sector must be read first
to obtain the number of times it has already been rewritten before
incrementing the number of rewrites by 1 and then rewriting that
sector.  This action would not introduce additional overhead if the
file was being updated, the sector having been previously read.  As
contrasted to the method taught by the '442 patent, which would
require first seeking to and accessing a table to determine the
number of rewrites of a sector and then updating that table.
Recording the number of writes in the sector header of each sector is
logistically simpler, as the information is contained within each
sector header rather in a table which requires a table lookup
function, table updating, and table ECC and/or CRC.

   Some inexpensive optical media may have sectors which can
only be rewritten a fraction of the maximum Nmax.  Thus, Nmax can be
altered for each piece of media, in order to account for differences
in media manufacturing quality, media age, media history of handling,
etc.  The Nmax used for removable media, such as found in library
applications, could be stored in a sector known to the data recording
device, such as sector 0.

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