Browse Prior Art Database

Performance Enhancement in Multilayer Compact Disk Read Only Memories

IP.com Disclosure Number: IPCOM000118267D
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 87K

Publishing Venue

IBM

Related People

Iminao, WI: AUTHOR [+5]

Abstract

While the performance of CD ROMs is substantially lower than other direct access devices, the CD ROM offers prodigious storage capacity. More recently, multilayered compact disks offer tremendous increases in capacity over standard single-layer disks. While certain applications will use this capacity fully, many applications will not. Disclosed are data formatting schemes that make use of the extra capacity to enhance the performance of the drive, i.e., the time required to retrieve an arbitrary data segment. In the following, it is assumed that the rotational speed of the disk is adjusted to yield a constant linear velocity for any particular track on the disk; however, the benefits of the formatting should apply similarly for disks whose rotational velocity is constant for all radii.

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Performance Enhancement in Multilayer Compact Disk Read Only Memories

      While the performance of CD ROMs is substantially lower than
other direct access devices, the CD ROM offers prodigious storage
capacity.  More recently, multilayered compact disks offer tremendous
increases in capacity over standard single-layer disks.  While
certain applications will use this capacity fully, many applications
will not.  Disclosed are data formatting schemes that make use of the
extra capacity to enhance the performance of the drive, i.e., the
time required to retrieve an arbitrary data segment.  In the
following, it is assumed that the rotational speed of the disk is
adjusted to yield a constant linear velocity for any particular track
on the disk; however, the benefits of the formatting should apply
similarly for disks whose rotational velocity is constant for all
radii.

      Any formatting method must reduce seek time, latency, and the
time for switching between layers.  Hence, an optimum format is
dependent on the maximum seek acceleration alpha, rotational speed V
sub 0, and maximum focus actuator acceleration of the drive.  For
single-layer disks where the amount of data to be written to the disk
is less than the total capacity, the radial position of the data that
results in the minimum average access time can be found analytically.
In terms of b = r sub min over r sub max, where r sub min is the
inner radius of the data band and r sub max is the outer radius,

      For CD parameters using a program to numerically calculate
average access times, it was found that the best method for
distributing data in a multilayered medium is as follows.  The first
layer has a complete copy of the original data; this layer has the
same format as the original single-layer disk.  Subsequent layers
also have complete copies of the original data but are arranged
differently.  If one differe...