Pioneer SCSI-2 - Manual (Page 100)

Read CD-ROM Capacity
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2.21 Read CD-ROM Capacity (25h)
Operation code is (25h).
This command requests the drive to return physical parameters of the CD-ROM disc currently
loaded. The Logical Block Address, RelAdr (Byte 1, bit 0), and PMI (Byte 8, bit 0) parameters
are not supported and must be set to 0.
The drive sends the initiator the 8-byte data as shown in Table 2-3 in the data transfer phase.
Logical block address is the last logical block address on the disc.
Logical block length is the size of logical blocks in bytes.
The value of Logical Block Length returned depends on the block length set with a MODE
SELECT command. The default value of the block length is 2048 bytes. The CD-ROM drives
allow values of 2048 or 512 bytes to be set with an external switch on the drive.