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MODE SELECT
6.7.3. Data Compression Control Page (0Fh)
The drive supports the Data Compression Control Page which has the following format:
Bit
7
Byte
0
PS (0)
1
2
DCE
3
DDE
4
(MSB)
7
8
(MSB)
11
12
13
14
15
Note: If the drive does not support compression the drive will return Check Condition status, and the sense key will
be set to ILLEGAL REQUEST.
This page specifies the parameters for the control of the data compression capability of the drive.
DCE: A Data Compression Enable (DCE) bit of one indicates that data compression is enabled. When this bit is set,
data sent to the device by the initiator shall be processed using the selected compression algorithm before being
written to the medium. A DCE bit of ZERO indicates that data compression is disabled.
DCC: A Data Compression Capable (DCC) bit of one indicates that the drive supports data compression and shall
process data sent to it for transferal to the medium using the selected compression algorithm when the DCE bit is
one. A DCC bit of ZERO indicates that the device does not support data compression. This shall be a
non-changeable field. The SDX-800V has the capability to decompress data and will set this bit to a one.
DDE: A Data Decompression Enable (DDE) bit of one indicates that data decompression is enabled. The SDX-800V
will always decompress the data. Setting this bit to ZERO has no effect.
RED: The Report Exception on Decompression (RED) field indicates the device's response to a boundary condition
caused by a change in the format of recorded data from:
uncompressed to compressed or compressed to uncompressed
This field is not supported and should be always set to 00b.
Compression Algorithm: The compression algorithm field indicates the compression algorithm the drive will use to
process data sent to it by the initiator (if the DCE bit is one).
The SDX-800V supports the ALDC1 data compression algorithm which is identified by the value: 00 00 00 03h in the
compression algorithm field. A value of ZERO shall indicate that no compression algorithm is currently selected. Any
other values in this field will cause the drive to return a CHECK CONDITION status the sense key shall be set to
ILLEGAL REQUEST.
Decompression Algorithm: For MODE SELECT the decompression algorithm field indicates the decompression
algorithm selected by the initiator for use in subsequent decompression of data encountered on the medium.
The SDX-800V can decompress data recorded with the ALDC1 algorithm therefore this field can be set to 00 00 00
03h. However, the SDX-800V is capable of automatic recognition of the compression algorithm used to process the
data encountered on the medium. Therefore, the drive will override the value in the decompression field (if is set to
ZERO) for a subsequent read operation when ALDC1 compressed data is detected on the media.
For the MODE SENSE command, the decompression algorithm field reflects compression algorithm which was
used to process the data most recently encountered on the medium, during a read operation.
A value of ZERO shall indicate that the data encountered on the medium during the most recent read operation was
uncompressed.
SONY AIT-3Ex drive SDX-800V series Ver.1.0
Table 6-41: Data Compression Control Page
6
5
Reserved
DCC (1)
RED (00h)
Compression Algorithm (0003h)
Decompression Algorithm (0003h)
4
3
Page Code (0Fh)
Page Length (0Eh)
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
6.Command Specification
2
1
0
(LSB)
(LSB)
6-43
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