Exabyte EXB-8505 8mm - Manual (Page 51)

Gap Bytes
A gap byte is a byte containing undefined data that the tape drive uses
to fill empty space in a physical block. The tape drive may
automatically write gap bytes in the following cases:
At the end of a write operation.
Before writing a filemark.
Before writing a setmark (EXB-8505 or EXB-8505XL only).
When it is physically impossible to start the next logical block in
the physical block because less than three bytes are available.
(This is because the two-byte header and at least one data byte
must be present in the first physical block before the logical block
can spill over to a second physical block.)
Figure 2-10 shows how gap bytes can be used to fill empty space at
the end of a physical block. Gap bytes cannot be accessed by any SCSI
command.
256 bytes 256 bytes 256 bytes 250 bytes
Header, 2 logical blocks, header, 2 logical blocks, and 2 gap bytes
2-byte headers 2 gap bytes 14-byte header
Figure 2-10 Gap bytes (one physical block)
May 1994 EXB-8205 and EXB-8505 2-15
(Standard and XL)
2 Recording Format