Browse Prior Art Database

Latency Reduction for CD-ROM and CLV Disks

IP.com Disclosure Number: IPCOM000122541D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Ng, SW: AUTHOR

Abstract

Disclosed is a data replication technique for reducing the average latency for Compact Disk-Read Only Memory (CD-ROM) and other Constant Linear Velocity (CLV) disks.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Latency Reduction for CD-ROM and CLV Disks

      Disclosed is a data replication technique for reducing
the average latency for Compact Disk-Read Only Memory (CD-ROM) and
other Constant Linear Velocity (CLV) disks.

      One known method for reducing the latency of Constant Angular
Velocity (CAV) disks is to duplicate the data by dividing each track
into two halves, repeating in the second half data that is stored on
the first half [*].  CD-ROM uses the CLV approach, wherein the disk
rotates at a variable speed depending on the radial position of the
head in order to maintain a constant linear velocity of the disk sur
face relative to the head. Additionally, CLV disks do not have
concentric circular tracks as in CAV disks. Instead, data are written
on one single contiguous spiral track, subdivided into many fixed
length sectors. Therefore, the data replication method for latency
reduction for CAV disks cannot be directly applied to the CD-ROMs and
CLV disks.

      In a CLV disk, such as the CD-ROM, the rotation speed of the
disk is inversely proportional to the distance of the head from the
center of the disk.  As a result, the average rotational latency of
an I/O access is dependent on the location of the desired record. The
technique proposed here will also try to even out this disparity.
This is accomplished by repeating each record a different number of
times depending on its location on the disk.

      Let RI be the inner radius of the recording band, RO be the
outer radius and let F = RO/RI.  The recording band is then
partitioned into B sub-bands, where B is the smallest integer greater
than or equal to (F...