X3T9.2/92-47r0
                                                  March 18, 1992

To:  X3T9.2 Membership

From:  Edward A. Gardner, Digital Equipment Corporation
       gardner@ssag.enet.dec.com

Subject:  Request for Sequential-Access Density Codes

Note:  The following request is for SCSI-3.  Since a draft SCSI-3 SSC
is not yet available, it refers to page and table numbers from SCSI-2
rev 10h.

Digital requests the following changes to Table 198:  Sequential
Access Density Codes, located on page 287 of SCSI-2 rev 10h.

1.  That table already defines density code 17h.  Please update the
    reference from X3B5/91-174 to X3B5/92-50, which is the most recent
    draft of the relevant tape format standard.

2.  Please add the following density code:

     Code  Width             Density                                
     Value mm (in)    Tracks bpmm    bpi  Code Type Reference   Note
     ----- ---------- ------ ------------ ---- ---- ----------- ----

     18h   12.7 (0.5)   112  1673 (42500) MFM  C    X3B5/92-50  1,4 

    This tape and format is identical to that currently identified by
    density code 17h except for an increased number of tracks.  It
    appears that code 18h is currently unassigned.  If so, we
    specifically request its assignment.

3.  The tape format described by X3B5/92-50 is undergoing active
    development, and we anticipate at least two, perhaps more, higher
    densities for the same media.  At present, densities for the same
    or similar media are assigned a block of adjacent density codes.
    For example, 01h-03h are 9-track tapes, 0Fh-12h are QIC tapes,
    0Ch-0Dh are HI-TC1 and TC2, and 14h-15h are two 8mm tape formats.

    With the above request, 17h-18h are different densities of
    identical media, and 16h is a slightly different but compatible
    media.  We request that several density codes beyond 18h be set
    aside for additional densities defined by the approved standard
    derived from X3B5/92-50.  Each density code definition would still
    be brought to and approved by X3T9.2.  However, for the duration
    of SCSI-3 development, X3T9.2 would not assign density codes
    19h-1Bh (for example) to any media incompatible with X3B5/92-50.

4.  A minor nit, the header line of Table 198 needs to be updated to
    properly reflect which density codes are reserved.  Rev 10h lists
    15h-7Eh as reserved, despite defining meanings for codes through
    17h.