SCSI Command - SCSI Command Lengths

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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