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ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCT DESCRIPTION MANUAL
Figure 6-2 shows the layout of the Reference and System area.
BOT
Continuous
Frames
Reference Area
...
SYSTEM AREA
Continuous
Frames
Figure 6-2
Reference and System Area Layout
I
..
I
Continuous
I
Frames
1
DATAAREA
I'"
The Reference area is the first collection of frames written on the tape after the BOT. It is a reference point
when determining the tape format and updating the System area. This area consists of 35 frames followed by
a band of between zero and ten frames. Because updating the System area may result in a physical position
of the new System area that is not identical to its previous physical position, this band allows a sufficient
tolerance to allow for variation. The Main Data area of all tracks in the Reference are set to zero.
System Area
The System area consists of:
o
The System Preamble, which allows the servo to synchronize before reading the System Log.
o
The Tape Log, which contains tape usage infonnation, including current usage error count. The
Tape Log in this format contains information for the entire tape.
o
The System Postamble, which consists of ten frames. Immediately following these frames is another
band of ten identical frames. These extra frames allow a position tolerance for updating the System
area.
During the cassette ejection sequence, the System area is updated. Because of this updating, the physical
length of the System area must remain constant.
Frame rewriting is not used on any frames in the System area. This factor could cause the Main Data area to
be incorrect; thus, the Main Data area is not used and is set to zero.
Because the Sub areas are repeated many times, the Sub area is used to store the usage information.
The frames following the System area allow the servo to resynchronize before it must read the Vendor
Group.
6-6
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