Seagate SCSI Interface Product Manual page 19

SCSI Interface Product Manual, Rev. J 5
initiator—A SCSI device containing application clients which originate device service and task management
requests to be processed by a target SCSI device.
interconnect subsystem—One or more physical interconnects which appear as a single path for the transfer
of information between SCSI devices in a domain.
intersymbol interference (ISI)—The effect of adjacent symbols on the symbol currently being received.
in transit—Information that has been sent to a remote object but not yet received.
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 reconnections, all pertaining to a single task or a group of tasks.
An I/O process begins with the establishment of a nexus. An I/O process normally ends with the Bus Free
phase if the quick arbitrate method is disabled. If the quick arbitrate method is enabled, the I/O process
normally ends with a QA Request message.
I T nexus—A nexus that exists between an initiator and a target.
I T L nexus—A nexus that exists between an initiator, a target, and a logical unit. This relationship replaces the
prior I T nexus.
I T L Q nexus—A nexus between an initiator, a target, a logical unit, and a queue tag following the successful
receipt of one of the queue tag messages. This relationship replaces the prior I T L nexus.
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 unit—A target-resident entity which implements a device model and executes SCSI commands 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.
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 an initiator through the execution of SCSI commands.
multidrop—A characteristic of the SCSI bus that allows SCSI devices to be connected to the SCSI bus without
disrupting the electrical path between the terminators.
multimode single-ended (MSE)—A signalling alternative for multimode SCSI devices that employs MSE driv-
ers and receivers to allow multimode SCSI devices to operate when SE SCSI devices are present on the bus.
nexus—A relationship between an initiator and a target, logical unit, or queue tag that begins with an initial
connection and ends with the completion of the associated I/O process. This relationship is formed as the
result of a task.
object—An architectural abstraction or "container" that encapsulates data types, services, or other objects that
are related in some way.
peer-to-peer protocol service—A service used by an upper level protocol implementation to exchange infor-
mation with its peer.
peer entities—Entities within the same layer.
pending task—A task that is not a current task.