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Method to Handle the Tape Turnaround for Serpentine Recording

IP.com Disclosure Number: IPCOM000124006D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Apr-05

Publishing Venue

IBM

Related People

Basham, RB: AUTHOR [+3]

Abstract

To support multi-track group tape formats, a means is needed to control track group changes. The wrap mark architecture described herein solves the track group change control problem.

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This is the abbreviated version, containing approximately 11% of the total text.

Method to Handle the Tape Turnaround for Serpentine Recording

       To support multi-track group tape formats, a means is
needed to control track group changes.  The wrap mark architecture
described herein solves the track group change control problem.

      In extending the 3480 tape architecture to accommodate multiple
track groups, a means was needed to change from the ending of data on
one track group to the start of data on another track group.  There
are two major aspects to this problem.  The first aspect is the need
to recognize reliably that data on one track has ended and it is time
to go to the next track group.  The second aspect is to overcome the
disorientation that occurs on a track group change and reliably find
the start of data on the next track group.

WRAP MARK FORMAT OVERVIEW

      The solution implemented covers only two track groups (called
in this article the odd tracks and the even tracks), but the
architecture is designed to support multiple track groups and the
implementation would need only minor changes to support multiple
track groups.

      To ensure the reliability of detecting the track change point
when reading, marks are used to manage the turnaround point.  The
turnaround point is that point where data ends on one track group and
begins on the next track group.  The track change control marks are
called wrap marks and have the same characteristics as tape marks or
tape format identification marks: they consist of patterns which can
be read and written much more reliably than data blocks.

      The tape format at turnaround point, where wrap marks are
located, is shown in Figure 1.

      The last block on a track group is followed by three wrap marks
each separated by an Inter-Block Gap (IBG).  The first wrap mark is
10 mm, the second wrap mark is 6 mm and the third wrap mark is
nominally 10 mm.  The third wrap mark may be up to 19 mm in length,
is requested by a write wrap mark Error Recovery Procedure (ERP).  If
the third wrap mark is longer, wrap mark four is also written longer
so that wrap mark three and wrap mark four are always written to the
same length.  Wrap mark six may also be up to 19 mm in length if
requested by an ERP to assure a good IBG between that wrap mark and
the first data block on the next track group.  These Wrap Marks
delimit the turnaround region for that tape (with its current data).
Data blocks have sequential block IDs around the turnaround point.
Wrap marks are written to tape after Logical End of Tape (LEOT) has
been reached, and the buffer has been emptied of all write data.  The
wrap marks have no block IDs, neither written on the tape nor implied
in the tape format.
SOLUTION TO THE TRACK CHANGE DISORIENTATION PROBLEM

      Given no compensation for disorientation, the last block
written on the odd tracks would be about 45 mm further out on tape
than the first block written on the odd tracks. This offset was
unacceptable.  The...