Seagate Ultra 160 Product Manual page 21

I/O operation—An operation defined by an unlinked SCSI command, a series of linked SCSI commands or a
task management function.
I/O process—An I/O process consists of one initial connection or, if information units are enabled, the
establishment of a nexus, and a zero or more physical or logical reconnection all pertaining to a single task or
a group of tasks. An I/O process begins with the establishment of a nexus. If the SPI information unit transfers
are disabled, an I/O process normally ends with a Command Complete message. If information unit transfers
are enabled, an I/O process ends with a SPI L_Q information unit with the type field set to status and the Data
Length field set to zero.
I_T nexus—A nexus that exists between a SCSI initiator port and a SCSI target port.
I_T_L nexus—A nexus that exists between a SCSI initiator port, a SCSI target port, and a logical unit. This
relationship replaces the prior I T nexus.
I_T_L_Q nexus—A nexus between a SCSI initiator port, a SCSI target port, a logical unit, and a queue tag fol-
lowing the successful receipt of one of the queue tag messages. This relationship replaces the prior I T L
nexus.
iuCRC protection—The use of CRC to detect DT DATA PHASE data transmission errors during parallel trans-
fers. Contains CRC information covering all bytes transmitted in a SPI information unit.
layer—A subdivision of the architecture constituted by subsystems of the same rank.
linked CDB—A CDB with the link bit in the control byte set to one.
linked command—One in a series of SCSI commands executed by a single task, which collectively make up
a discrete I/O operation. In such a series, each command has the same task identifier, and all except the last
have the link bit in the CDB control byte set to one.
logical connect—Establishes an I_T_L_Q nexus using SPI L_Q information units.
logical disconnect—Reduces the current I_T_L_Q nexus to an I_T nexus.
logical reconnect—Reestablishes an I_T_L_Q nexus from an I_T nexus using SPI L_Q information units.
logical unit—a SCSI target port-resident entity which implements a device model and executes SCSI com-
mands sent by an application client.
logical unit number—A 64-bit identifier for a logical unit.
logical unit option—An option pertaining to a logical unit, whose actualization is at the discretion of the logical
unit implementor.
logical unit reset— A logical unit action in response to a logical unit reset event in which the logical unit per-
forms the operations described in SCSI Architecture Model-4.
lower level protocol—A protocol used to carry the information representing upper level protocol transactions.
mandatory—The referenced item is required to claim compliance with a standard.
media information—Information stored within a SCSI device which is non-volatile (retained through a power
cycle) and accessible to a SCSI initiator port through the execution of SCSI commands.
multidrop—A characteristic of the SCSI bus that allows SCSI devices to be connected to the SCSI bus with-
out disrupting the electrical path between the terminators.
multimode single-ended (MSE)—A signalling alternative for LVD SCSI devices that combines LVD SCSI and
single-ended SCSI (see SPI-5, SCSI parallel interface electrical characteristics) drivers and receivers to allow
operation when SE SCSI devices are present on the bus.
Parallel SCSI Interface Product Manual, Rev. A 7