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TAPE FORMATS
Within one sub ID for a block of the sub data area, the
area
ID identifies the current area on tape and the
type of current frame, where:
0000
=
Device area
XOOI
= Reference area
XOI0
=
System area
XI00
=
Data area
XI0l
= EOD area
others are reserved
Above, X is 0 for Partition 1 and 1 for Partition 0 in a two-partition tape. For a single
data space tape, X is 1.
The various pack items represent different types of information such as, group count, filemark count, save-
set count, the absolute frame count, checksums, N-group reading counts, and ECC retries.
6.8 Group Structure
A group is made up of 22 data frames for a size of 126632 bytes and an optional ECC frame. Groups are
separated by zero or more amble frames. The 22 data frames contain host written data and index information.
Figure 6-5 shows the group structure.
ECC FRAME (ERROR CORRECTION CODE)
I_
ONE GROUP
-I
'( 22 DATA FRAMES, APPROXIMATELY 128 KBYTES)
Figure 6-5
Group Structure
Figure 6-6 compares a group in the DDS format without compression to a group in the DDS-DC format with
compression. As an example, a 3.2:1 compression ratio is depicted. The size and structure of the groups are
the same. However, the contents of the group are different in that the group in the DDS-DC format may
contain uncompressed records and entities.
6-11
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