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ARCHIVE PYTHON DDS-DC DA T DRIVES---PRODUCT DESCRIPTION MANUAL
Figure 6-3 illustrates the two-partition tape layout
~""----P1--------
__
"~.~"~--------------~------------~"~
DEVICE
AREA
I
BOM
EN DO
GROUP
AFC=l
BOT
DATA
EOD
SYNTHEnC
EOM
AFC=Pl
AFCMAX
Figure 6-3
Two-Partition Tape Layout
6.6 Data Storage Organization
DATA
EOD
I
I
EOT
EOM
The data storage organization of the DDS and DDS-DC formats is based on two considerations:
o
Individual track layout
o
Data groups
Like the audio format, the DDS and DDS-DC formats allocate 60 percent of each track
to
user data and ECC.
The remaining 40 percent is divided between automatic-track-finding (ATF) signals and the subcode area.
The ATF and subcode areas are collectively called subareas and are used to maintain information about the
location of data records, filemarks, and save set marks.
The data area on the tape is organized into groups. Each group is made up of a fixed number of frames and
has a fixed capacity. A group stores host written data, save-set marks, and fllemarks. In the DDS format, the
host written data consists of uncompressed records; in the DDS-DC format, the host written information may
consist of uncompressed records and entities.
Although a group has a fixed size in memory, each group does not necessarily contain the same number of
physical frames. Some frames may be rewritten because an error is detected by the Read-After-Write
process.
If a host record is larger than the space remaining in the group, the space is filled, and bytes not
accommodated are placed in the next group.
In the case where a group is not fully occupied by user data, the group is still written as the fixed logical size,
but the index reflects its actual contents.
6-8
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