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4.1 Control/Sense Commands
4.1.3 READ CAPACITY (25)
Bit
Byte
7 6 5 4 3 2 1 0
0 X'25'
1 0 0 0 0 0 0 0 0
2 Logical Block Address (MSB)
3 Logical Block Address
4 Logical Block Address
5 Logical Block Address (LSB)
6 0 0 0 0 0 0 0 0
7 0 0 0 0 0 0 0 0
8 0 0 0 0 0 0 0 PMI
9 0 0 0 0 0 0 0 0
This command transfers information related to the disk drive's capacity and the
data block size to the INIT.
When bit 0 "PMI (partial medium indicator)" of CDB byte 8 is "0," the logical
block address and block length (byte length) of the final data block which is
accessible in the disk drive (user space) are transferred to the INIT. At this time,
the "Logical Block address" field in the CDB must specify zero.
When the "PMI" bit is "1," the logical block address and block length (byte
length) of data blocks which satisfy either of the following conditions is
transferred to the INIT.
• The data block on the track where the specified block exists, which is just
before the block where the first alternate sector processing (not including
defective block sector slip processing) is implemented. However, when
alternate sector processing is being implemented in the specified block, the
data block specified in the CDB.
• When no alternate sector processed data block exists in the track where the
specified block exists, the last data block in that track.
By using this command with the "PMI" bit specified as "1", the INIT can search
for usable data space continuously without being interrupted by data transfers for
alternate sector processing or switching of cylinders.
The format of the data transferred to the INIT by this command is shown in
Table 4.11.
C141-C013 151