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Comprehensive Guide to Byte Command Descriptor Block (CBD) Structure

This document outlines the structure and components of the Byte Command Descriptor Block (CBD). It includes an in-depth analysis of the byte layout, detailing operation codes, logical unit numbers, transfer lengths, and control bits. Each section of the CBD format is explained, emphasizing the significance of parameters like Logical Block Addressing (LBA) and how they relate to device communication. Understanding the CBD structure is crucial for professionals involved in storage systems, as it directly impacts data handling and efficiency within storage protocols.

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Comprehensive Guide to Byte Command Descriptor Block (CBD) Structure

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  1. 6 Byte CBD +======-========-========-========-========-========-========-========-========+ | Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |Byte | | | | | | | | | |======+=======================================================================| | 0 | Operation code | |------+-----------------------------------------------------------------------| | 1 | Logical unit number | (MSB) | |------+------------------------------ ---| | 2 | Logical block address (if required) | |------+--- ---| | 3 | (LSB) | |------+-----------------------------------------------------------------------| | | Transfer length (if required) | | 4 | Parameter list length (if required) | | | Allocation length (if required) | |------+-----------------------------------------------------------------------| | 5 | Control | +==============================================================================+

  2. 10 Byte CBD +======-========-========-========-========-========-========-========-========+ | Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |Byte | | | | | | | | | |======+=======================================================================| | 0 | Operation code | |------+-----------------------------------------------------------------------| | 1 | Logical unit number | DPO | FUA | Reserved | REL | |------+-----------------------------------------------------------------------| | 2 | (MSB) | |------+--- ---| | 3 | | |------+--- Logical block address (if required) ---| | 4 | | |------+--- ---| | 5 | (LSB) | |------+-----------------------------------------------------------------------| | 6 | Reserved | |------+-----------------------------------------------------------------------| | 7 | (MSB) Transfer length (if required) | |------+--- Parameter list length (if required) ---| | 8 | Allocation length (if required) (LSB) | |------+-----------------------------------------------------------------------| | 9 | Control | +==============================================================================+

  3. 12 Byte CBD +======-========-========-========-========-========-========-========-========+ | Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |Byte | | | | | | | | | |======+=======================================================================| | 0 | Operation code | |------+-----------------------------------------------------------------------| | 1 | Logical unit number | DPO | FUA | Reserved | REL| |------+-----------------------------------------------------------------------| | 2 | (MSB) | |------+--- ---| | 3 | | |------+--- Logical block address (if required) ---| | 4 | | |------+--- ---| | 5 | (LSB) | |------+-----------------------------------------------------------------------| | 6 | (MSB) | |------+--- ---| | 7 | Transfer length (if required) | |------+--- Parameter list length (if required) ---| | 8 | Allocation length (if required) | |------+--- ---| | 9 | (LSB) | |------+-----------------------------------------------------------------------| |10 | Reserved | |------+-----------------------------------------------------------------------| |11 | Control | +==============================================================================+

  4. 16 Byte CBD

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