Logical block address

Logical block address
The logical block addresses on a logical unit or within a volume or partition shall begin with block zero and be contiguous up to the last logical block of that logical unit or within that volume or partition.

It specifies where to start the transfer.

• A six-byte CDB may contain a 21-bit LOGICAL BLOCK ADDRESS field. 
• The ten-byte and the twelve-byte CDBs may contain 32-bit LOGICAL BLOCK ADDRESS fields.
• The sixteen-byte CDB has two formats: one allows a 32-bit LOGICAL BLOCK ADDRESS field and 
• the other allows a 64-bit LOGICAL BLOCK ADDRESS field . 

LOGICAL BLOCK ADDRESS fields in additional parameter data have their length specified for each occurrence.