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Stage to End of Track Plus One Record Disclosure Number: IPCOM000112046D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 43K

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This invention relates to the support of CKD on DASD arrays.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 70% of the total text.

Stage to End of Track Plus One Record

      This invention relates to the support of CKD on DASD arrays.

      The implementation of a CKD array requires the emulation of CKD
on a fixed block DASD or the acceptance of very large penalties in
the form of wasted device time, control unit overheads and DASD
space.  The emulation of CKD is most efficiently done through the use
of a RAM buffer (or cache), where the CKD track is mapped into the
RAM.  This mapping requires the uses of control information to
efficiently determine the mapping.  The alternative is to start at
the beginning of a track and decode the count fields of each record
until the desired record is found.  With the addition of suitable
control information most of the decoding time can be bypassed.  The
control information must be recorded on the DASD with the data, in
order that the CKD track can be properly processed by the controller.
There are two ways to record the information: as a single field at
one place on the track; or distributed with each block on the DASD,
where each block contains, in a fixed location, the control
information pertinent to the block.

      The embedding of the control information in each block is
disruptive to the normal flow of CKD information to and from the
system adapter (host channel).  This is because the control for CKD
emulation is not transmitted to the host.  The simpler solution is to
place the control information at the beginning or end of the CKD