command descriptor block—A structure used to communicate a command from an application client to a device server. Command structures of 6, 10, 12, or 16 bytes are used, but a new variable length command structure has recently been introduced.
completed command—A command that has ended by returning a status and service response of Task Com- plete or Linked Command Complete.
completed task—A task that has ended by returning a status and service response of Task Complete. The actual events comprising the Task Complete response are protocol specific.
confirmation—A response returned to an object, which signals the completion of a service request.
confirmed service—A service available at the protocol service interface, which requires confirmation of com- pletion. The confirmed service consists of the request and confirmation steps and optionally the indication and response steps.
contingent allegiance (CA)—An optional condition of a task set following the return of a CHECK CONDITION status. A detailed definition of contingent allegiance may be found in Section 4.4.2. (CA declared obsolete by SAM-4, ACA supported by SAM-4)
control mode page—The mode page that identifies the settings, and provides control, of several device server behaviors that may be of interest to an application client or may be changed by an application client. The complete definition of the Control mode page is found in the Seagate SCSI Command Reference Manual, Part number 100293068, or SPC-4.
current task—A task that is in the process of sending messages, sending status, transferring data, or transfer- ring command data to or from the initiator.
cyclic redundancy check (CRC)—An error detecting code used to detect the validity of data that has been transferred during the current data group.
data field—The portion of a data group that contains data bytes.
data group—A sequence of data bytes and the four pCRC bytes during a DT DATA IN PHASE or a DT DATA OUT PHASE that starts at the first byte of the DT DATA phase or at the first byte after the last pCRC byte.
data group transfer—Parallel transfers that transfer data and pCRC information using only data groups. The last four bytes of a data group transfer contain CRC information over the whole data group.
destination device—The SCSI device to which a service delivery transaction is addressed. See source device.
device server—An object within the logical unit which executes SCSI tasks according to the rules for task management described in clause 7 of ANSI SAM-4 document, T10/1683-D.
device service request—A request, submitted by an application client, conveying a SCSI command to a device server.
device service response—The response returned to an application client by a device server on completion of a SCSI command.
differential—A signalling alternative that employs differential (two complementary signals) drivers and receiv- ers to improve signal-to-noise ratios and increase maximum cable lengths.
disconnect—The action that occurs when a SCSI device releases control of the SCSI bus, allowing it to go to the BUS FREE PHASE.
domain—An I/O system consisting of a set of SCSI devices that interact with one another by means of a ser- vice delivery subsystem.
dormant (task state)—The state of a task that is prevented from starting execution due to the presence of cer- tain other tasks in the task set.
