| June 23, 2010 |
3.3.4 Keywords
Several keywords are used to differentiate between different levels of requirements and options.
3.3.4.1expected: A keyword used to describe the behavior of the hardware or software in the design models assumed by this standard. Other hardware and software design models may also be implemented.
3.3.4.2mandatory: A keyword indicating items to be implemented as defined by this standard.
3.3.4.3may: A keyword that indicates flexibility of choice with no implied preference.
3.3.4.4N/A: A keyword that indicates a field is not applicable and has no defined value and should not be checked by the host or device.
3.3.4.5obsolete: A keyword indicating that the designated bits, bytes, words, fields, and code values that may have been defined in previous standards are not defined in this standard and shall not be reclaimed for other uses in future standards. However, some degree of functionality may be required for items desig- nated as “obsolete” to provide for backward compatibility.
Obsolete commands should not be used by the host. Commands defined as obsolete may be command aborted by devices conforming to this standard. However, if a device does not return command aborted for an obsolete command, then the device shall return command completion for the command.
3.3.4.6optional: A keyword that describes features that are not required by this standard. However, if any optional feature defined by the standard is implemented, the feature shall be implemented in the way defined by the standard.
3.3.4.7prohibited: A keyword indicating that an item shall not be implemented by an implementation.
3.3.4.8reserved: A keyword indicating reserved bits, bytes, words, fields, and code values that are set aside for future standardization. Their use and interpretation may be specified by future extensions to this or other standards. A reserved bit, byte, word, or field shall be cleared to zero, or in accordance with a future extension to this standard. The recipient shall not check reserved bits, bytes, words, or fields. Receipt of reserved code values in defined fields shall be treated as a command parameter error and reported by returning command aborted.
3.3.4.9retired: A keyword indicating that the designated bits, bytes, words, fields, and code values that had been defined in previous standards are not defined in this standard and may be reclaimed for other uses in future standards. If retired bits, bytes, words, fields, or code values are used before they are reclaimed, they shall have the meaning or functionality as described in previous standards.
3.3.4.10shall: A keyword indicating a mandatory requirement. Designers are required to implement all such mandatory requirements to ensure interoperability with other products that conform to this standard.
3.3.4.11should: A keyword indicating flexibility of choice with a strongly preferred alternative. Equivalent to the phrase “it is recommended”.
3.3.5 Numbering
A binary number is represented in this standard by any sequence of digits consisting of only the
A hexadecimal number is represented in this standard by any sequence of digits consisting of only the
8 | Working Draft Enhanced Disk Drive - 4 |