Quantum DLT 4000 Product Manual page 209

Density Code
This field should match the current density of the media, or will be set to zero if the
density is unknown.
00h - use default density
0Ah - 6667 bpi MFM serial cart. tape X3B5/86-199 (Read only)
16h - 10000 bpi MFM serial cart tape X3.193-1990 (Read only)
17h - 42500 bpi MFM serial cart tape X3B5/91-174 - 2.6 GB
18h - (Same as 17h but with 56 track pairs vs. 24) - 6.0 GB
19h - 62500 bpi, 64 track pairs, serial cart tape - 10/15 GB
1Ah - 81633 bpi, 64 track pairs, serial cart tape - 20/30 GB
7Fh - No change from previous density (NOP)
80h - 62500 bpi, 64 track pairs, serial cart tape-10/15 GB (without compression)
81h - 62500 bpi, 64 track pairs, serial cart tape-20/30 GB (with compression)
82h – 81633 bpi, 64 track pairs, serial cart tape - 20 GB (without compression)
83h – 81633 bpi, 64 track pairs, serial cart tape - 40 GB (with compression)
Number of Blocks
This MODE SENSE field will be sent as zero, indicating that all of the remaining
logical blocks on the tape will have the medium characteristics specified by the block
descriptor.
Block Length
This specifies the length in bytes of each logical block transferred over the SCSI bus.
A block length of zero indicates that the length is variable (specified in the I/O
command). Any other value indicates the number of bytes per block to use for read,
write and verify type commands that specify a "Fixed" bit of 1 (i.e., fixed block mode)
which also causes the transfer length in the CDB to be defined as a block count.
DLT4000/DLT4500/DLT4700 Cartridge Tape Subsystem 8-49
DLT4000 SCSI Interface