Tandberg Data SLR7-140 PROGRAMMER Manual page 51

Tandberg Data
The usage of the different fields varies slightly as a
function of the tape format used, but the following
general description is true for all tape formats.
The DCC (Data Compression Capable) bit is a status bit
that indicates
compression/decompression capabilities. The MLR Series
Drives are always
When transferring a Data Compression page with a MODE
SELECT command this bit must be set to one (it is not
changeable). When
retrieve the Data Compression page the value returned is
always one.
The DCE (Data Compression Enable) is a configuration bit
used to turn
restrictions apply when using SLR5 and DC9250 media. See
below for further details. The MODE SELECT command is
used to set/reset this bit. When a MODE SENSE command is
used to retrieve the Data Compression page the value
returned reflects the value set by the last MODE SELECT
command.
The DDE (Data Decompression Enable) bit is used in two
different ways depending on the tape format in use. See
the following sub-sections for further details.
The Compression Algorithm field is a configuration field
used to select a specific data compression algorithm to
be used when data are being compressed. The SLR Series
Drives support two values; A value of 3h selects the
ALDC algorithm. A value of 0h means " no algorithm se-
lected" . In this case the drive will not perform any
data compression. This means that in order to have data
compressed the
Compression Algorithm field must be set to 3h. The MODE
SELECT command is used to set a value in the Compression
Algorithm field. When a MODE SENSE command is used to
retrieve the Data Compression page the value returned in
this field reflects the value set by the last MODE
SELECT command.
The Decompression Algorithm field is a status field used
by the drive to report which compression algorithm that
was used when the data were written to a medium. The
value in this field is valid only after this data have
been read off the medium using a READ or VERIFY
A value of 3h indicates that the ALDC algorithm was used
(the data on the medium is compressed). A value of 0h
indicates that no algorithm was selected (the data on
the medium is not compressed). A MODE SENSE command can
be used to retrieve the Decompression Algorithm field.
This field is ignored by the MODE SELECT command.
1
VERIFY is not supported by SLR7 and SLR140
2-31 Tandberg SLR Product Line SCSI Functional Specifications
whether
compression/decompression
a MODE SENSE
data compression
DCE bit must be
About Tape Streamers
a device
capable.
command is used
on or off.
set to 1 and
1
command.
has
to
Some
the