Browse Prior Art Database

Selective Placement of Small/Large Files on CD-ROM and Magneto-Optical Media

IP.com Disclosure Number: IPCOM000116164D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 93K

Publishing Venue

IBM

Related People

Goldfeder, ME: AUTHOR [+4]

Abstract

CD-ROM media is Constant Linear Velocity (CLV) rather than Constant Angular Velocity (CAV). This means that CD-ROM media spins slower in its angular velocity when the head is at the outer radius of the media than when the head is at the inner radius of the media. This can be seen by the following equation from planar rigid body dynamics, that linear velocity equals angular velocity times radius. Linear Velocity = Angular Velocity * Radius (1)

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Selective Placement of Small/Large Files on CD-ROM and Magneto-Optical
Media

      CD-ROM media is Constant Linear Velocity (CLV) rather than
Constant Angular Velocity (CAV).  This means that CD-ROM media spins
slower in its angular velocity when the head is at the outer radius
of the media than when the head is at the inner radius of the media.
This can be seen by the following equation from planar rigid body
dynamics, that linear velocity equals angular velocity times radius.
  Linear Velocity = Angular Velocity * Radius          (1)

This slower angular velocity, when the head is at the outer radius of
the CD-ROM media, produces a substantially longer average latency
(time
for a half-revolution), which could reduce random read performance.

      We propose files to be written to CD-Recordable (CD-R), or
CD-rewritable, media be cached until the files destined for that CD-R
media reach the capacity of the target media.  This caching could be
done to DASD.

      At this point, we desire that the small files be written near
the inner radius of the disk.  The large files would be written near
the outer radius of the disk.  The idea here is to have the small
files, which are the most sensitive to latency overhead, at the
portion of the CD-R disk having the smallest latency.  The large
files, which are the least sensitive to latency overhead, would be at
the outer radius of the disk.

      Small files written on CD-R would have the "inside track" for
performance reasons.  The read effective data rate is defined as the
following for a file of X kilobytes.
                                       X
  Read Effective Data Rate = ----------------------           (2)
                             Seek + Latency + X/SDR
  Where:  X       = file size in kilobytes
          Seek    = time to seek to file
          Latency = time for a 1/2 revolution of the disk
          SDR     = spin data rate (data rate as seen by the laser)

      For small files, the term X/SDR in the denominator is virtually
zero.  Hence, for small files, the read effective data rate is given
by eqn.(3).  In eqn. (3), we see that by reducing the latency, the
small-file read effective data rate will rise.  The latency will be
reduced by a factor of two by storing a file near the inner radius of
the CD-Recordable media versus the outer radius.
                                   X
  Read Effective Data Rate = --------------                   (3)
  (small files)              Seek + Latency

      For large files, the term X/SDR in the denominator dominates
the seek and latency terms.  Hence, for large files, th...