CD-ROM Capacities & Last Sector(s) reading Questions

Gary_Peterson at Gary_Peterson at
Thu Jun 22 09:02:04 PDT 1995


CEO document contents:  
Date:    6/22/95 

To:      Ron Roberts, SCSI-3/MMC Technical Editor
         rkroberts at

         John Lohmeyer, X3T10 Chair
         john.lohmeyer at

CC:      SCSI Reflector
         scsi at

From:    Gary S. Peterson, Data General Corp.
         Gary_Peterson at

Re:      CD-ROM Capacities and Last Sector(s) Data Access

    A series of issues have surfaced concerning the format, readability, and
access to the last data sector(s) on CD-ROM media generated from CD-Writer

1.  The description of the CD-ROM Read Capacity command (SCSI-2, section
    14.2.8, pages 294-295) spells out that if the "lead out track" (following
    end of data/audio) of the CD is in audio format, the LBA returned by the
    read capacity command is only valid for seek operations, and may or may not
    be a readable LBA, since the LBA may be in a "transition area". This
    section also implies that if the lead out is encoded as data, the LBA
    returned can be used as the last valid LBA that is readable on the CD.

    The above statements are further supported in table 236 of the SCSI-2
    specification, particularly in notes 10 and 11 of that table, that point
    out that the read capacity command derives its last LBA information from
    the TOC data, which can be inexact by 75 LBA's if the lead out track is
    audio.  Section 14.1.1 note 171 and Section 14.4.16 also support the
    limitations of the read capacity's returned LBA.

    We interpret this to mean that when the "lead-out track" of a CD is audio,
    the LBA returned by the Read Capacity command from a CD-ROM reader is
    permitted (by SCSI) to be an inexact address by as many as +/- 75 LBA's,
    and cannot be reliably used to determine the last, readable LBA on the
    media. Is our interpretation correct?

2.  Further attempts to determine where the end of readable data is on CD-ROM
    media have shown that if the "lead out area" is encoded in audio format, it
    is possible for the last 'n' last sectors of the data that had been written
    to the media to become unreadable. The value of 'n' varies from device to
    device, although we have seen it as high at 2 sectors. When a read of any
    of these 'n' sectors is attempted, the device reports a medium error, with
    various ASC values. This is resulting in data loss, as these sectors
    contains the last data information written to the CD-ROM media.

    Is this a problem that has been seen elsewhere in the industry?

    Also, is this a SCSI-2/SCSI-3 spec violation? I can't seem to find a
    chapter and verse that seems to have violated, but I can't accept that SCSI
    would allow such a thing to happen.

Any comments, suggestions, or clarifications would be welcome.

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