CDB Control Byte, bits 6&7

Duncan Penman penman at
Thu Oct 6 21:31:13 PDT 1994

  In response to my note about tracking CD-ROM ATAPI commands in 
SCSI-3, Debbi Ast of NCR wrote:

          I would like to make a suggestion in response to the
          proposed changes to the SCSI-3 CD-ROM command set.  I
          would also like to see the READ TOC command updated in
          SCSI-3 with a 2 bit format field.   Many SCSI CDROM vendors
          (Sony, Matsushita, Hitachi...) have already added a 2 bit
          format field in the READ TOC command(byte 9, bits 6 & 7) to
          support multisession discs.  For compatibility, it would be
          nice to define this same location in the SCSI-3 spec.  Are
          there any implications with using this location?  Is this
          how it is mapped in the ATAPI version?

          Debbi Ast
          NCR Microelectronics
          debbi.ast at

  In SCSI-2, these 2 bits are defined as vendor-specific.  Quite reasonable 
for the CD-ROM drive manufacturers to use in this way.  The ATAPI mapping 
is direct..byte 9 of the CDB to byte 9 of the Command Packet.  The 
question in this is, Can we define a SCSI vendor-specific field to 
have a specific meaning for one device type?

  Would appreciate a bit of strategic guidance here before getting too 
deep into implementation alternatives.Received: from cc:Mail by CCMSMTP2.FTCollinsCO.NCR.COM
	id AA780266292; Thu, 22 Sep 94 13:28:09 MDT
Date: Thu, 22 Sep 94 13:28:09 MDT
Message-Id: <9408227802.AA780266292 at CCMSMTP2.FTCollinsCO.NCR.COM>
To: Duncan Penman <penman at>, scsi at WichitaKS.NCR.COM,
        atapi at
Subject: Re: Tracking ATAPI CD-ROM Cmds in SCSI-3
Status: RO

Duncan Penman
Zadian Technologies
penman at

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