SCSI Command Lengths
Originally the most significant 3 bits of a SCSI opcode specified the length of the CDB. However, when variable-length CDBs were created this correspondence was changed, and the entire opcode must be examined to determine the CDB length. The lengths are as follows:
| Opcode (hex ) | Length |
|---|---|
| 00h to 1Fh | 6 |
| 20h to 5Fh | 10 |
| 60h to 7Dh | reserved |
| 7Eh | variable (more than 16 bytes) |
| 7Fh | extended (variable length; may contain one or more CDBs) |
| 80H to 9Fh | 16 |
| A0h to BFh | 12 |
| C0h to FFh | vendor specific |
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