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6.Command Specification MODE SELECT
6-46 SONY AIT-5 drive SDX-1100V series Ver.1.0
6.7.3. Data Compression Control Page (0Fh)
The drive supports the Data Compression Control Page which has the following format:
Table 6-45: Data Compression Control Page
Bit
Byte
7 6 5 4 3 2 1 0
0 PS (0) Reserved Page Code (0Fh)
1 Page Length (0Eh)
2 DCE DCC (1) Reserved
3 DDE RED (00h) Reserved
4 (MSB) Compression Algorithm (0003h)
7 (LSB)
8 (MSB) Decompression Algorithm (0003h)
11 (LSB)
12 Reserved
13 Reserved
14 Reserved
15 Reserved
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 will 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 will
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 will be a
non-changeable field. The SDX-1100V 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-1100V 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 will 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-1100V 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 will 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 will 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-1100V can decompress data recorded with the ALDC1 algorithm therefore this field can be set to 00 00
00 03h. However, the SDX-1100V 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 will indicate that the data encountered on the medium during the most recent read operation was
uncompressed.