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3. Glossary and Conventions
3.1. Glossary
This section contains a glossary of special terms used in this standard.
Also see the glossaries for each device type in sections 8.4, 9.4, ..., 17.4.
active I/O process. An I/O process that is presently in execution (not
queued).
AEN. Asynchronous event notification (see 6.5.5).
AWG. American Wire Gauge.
byte. In this standard, this term indicates an 8-bit (octet) construct.
CA. Contingent Allegiance (see 6.6).
command descriptor block (CDB). The structure used to communicate commands
from an initiator to a target.
command queue. This term refers to the queue used to store the tagged I/O
processes (see 6.8.2).
connect. The initiator function that selects a target to establish a nexus
and to start an I/O process. The connection that results is an initial
connection.
connection. An initial connection or reconnection. A connection can only
occur between one initiator and one target.
contact. The electrically-conductive portion of a connector associated with a
single conductor in a cable.
current I/O process. The I/O process that is presently connected on the SCSI
bus.
disconnect. The action that occurs when an SCSI device releases control of
the SCSI bus, allowing it to go to the BUS FREE phase.
ECA. Extended Contingent Allegiance (see 6.7).
field. A group of one or more contiguous bits. Fields containing only one
bit are usually referred to as the xx bit instead of the xx field.
host adapter. A device which connects between a host system and the SCSI bus.
The device usually performs the lower layers of the SCSI protocol and normally
operates in the initiator role. This function may be integrated into the host
system.
initial connection. An initial connection is the result of a connect and it
exists from the assertion of the BSY signal in a SELECTION phase until the
next BUS FREE phase occurs.
initiator. An SCSI device (usually a host system) that requests an I/O
process to be performed by another SCSI device (a target).
invalid. An illegal (reserved) or unsupported bit, field, or code value.
I/O process. An I/O process consists of one initial connection and zero or
more reconnections, all pertaining to a single command or a group of linked
commands. More specifically, the connection(s) pertain to a nexus as defined
below in which zero or more command descriptor blocks are transferred. An I/O
process begins with the establishment of a nexus. An I/O process normally
ends with the BUS FREE phase following successful transfer of a COMMAND
COMPLETE or a RELEASE RECOVERY message. An I/O process also ends with the BUS
FREE phase following an ABORT, ABORT TAG, BUS DEVICE RESET, or CLEAR QUEUE
message or when a hard RESET condition or an unexpected disconnect occurs.
I_T nexus. A nexus which exists between an initiator and a target.
I_T_L nexus. A nexus which exists between an initiator, a target, and a
logical unit. This relationship replaces the prior I_T nexus.
I_T_R nexus. A nexus which exists between an initiator, a target, and a
target routine. This relationship replaces the prior I_T nexus.
I_T_x nexus. A nexus which is either an I_T_L or I_T_R 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.
I_T_x_y nexus. A nexus which is either an I_T_x or I_T_L_Q.
logical unit. A unit of data supplied or requested by an initiator.
logical unit. A physical or virtual peripheral device addressable through a
target.
logical unit number. An encoded three-bit identifier for the logical unit.
LSB. Least significant bit.
LUN. Logical unit number.
mandatory. The referenced item is required to claim compliance with this
standard.
mm. Millimeter.
ms. Millisecond.
MSB. Most significant bit.
nexus. A relationship that begins with the establishment of an initial
connection and ends with the completion of the I/O process. The relationship
may be restricted to specify a single logical unit or target routine by the
successful transfer of an IDENTIFY message. The relationship may be further
restricted by the successful transfer of a queue tag message.
ns. Nanosecond.
one. A true signal value or a true condition of a variable.
optional. The referenced item is not required to claim compliance with this
standard.
page. Several commands use regular parameter structures that are referred to
as pages. These pages are identified with a value known as a page code.
parameter. A structure containing one or more fields.
peripheral device. A physical peripheral device that can be attached to an
SCSI device, which connects to the SCSI bus. The peripheral device and the
SCSI device (peripheral controller) may be physically packaged together.
Often there is a one-to-one mapping between peripheral devices and logical
units, but this is not required. Examples of peripheral devices are: magnetic
disks, printers, optical disks, and magnetic tapes.
queue tag. The value associated with an I/O process that uniquely identifies
it from other queued I/O processes on the logical unit for the same initiator.
queued I/O process. An I/O process that is in the command queue and has not
begun execution.
reconnect. The act of reviving a nexus to continue an I/O process. A target
reconnects to an initiator by using the RESELECTION and MESSAGE IN phases
after winning arbitration. An initiator reconnects to a target by using the
SELECTION and MESSAGE OUT phases after winning arbitration (see 6.5.2).
reconnection. A reconnection is the result of a reconnect and it exists from
the assertion of the BSY signal in a SELECTION or RESELECTION phase until the
next BUS FREE phase occurs.
reserved. The term used for bits, fields, and code values that are set aside
for future standardization.
SCSI. Either SCSI-1 or SCSI-2.
SCSI-1. The Small Computer System Interface (X3.131-1986).
SCSI-2. The Small Computer System Interface - 2 (X3.131-198X).
SCSI address. The octal representation of the unique address (0-7) assigned
to an SCSI device. This address would normally be assigned and set in the
SCSI device during system installation.
SCSI ID. The bit-significant representation of the SCSI address referring to
one of the signal lines DB(7-0).
SCSI device. A host adapter or a target controller that can be attached to
the SCSI bus.
signal assertion. The act of driving a signal to the true state.
signal negation. The act of driving a signal to the false state or allowing
the cable terminators to bias the signal to the false state (by placing the
driver in the high impedance condition).
signal release. The act of allowing the cable terminators to bias the signal
to the false state (by placing the driver in the high impedance condition).
status. One byte of information sent from a target to an initiator upon
completion of each command.
target. An SCSI device that performs an operation requested by an initiator.
target routine. A target routine is an I/O process directed to a target, and
not to a logical unit.
third-party. When used in reference to COPY commands, third-party means a
COPY command issued to one device to perform a copy operation between two
other devices. When used in reference to RESERVE, or RELEASE commands, third-
party means a reservation made on behalf of another device (e.g., A processor
device requests that a direct-access device reserve itself for exclusive use
by a sequential-access device).
unexpected disconnect. A disconnection that occurs as a result of a protocol
error (see 5.1.1).
us. Microsecond.
vendor specific (VS). Something (e.g., a bit, field, code value, etc.) that
is not defined by this standard and may be used differently in various
implementations.
xx. Numbers that are not immediately followed by lower-case "b" or "h" are
decimal values. Large Numbers are not separated by commas or spaces (e.g.,
12345; not 12,345 or 12 345).
xxb. Numbers immediately followed by lower-case "b" are binary values.
xxh. Numbers immediately followed by lower-case "h" are hexadecimal values.
zero. A false signal value or a false condition of a variable.
3.2. Editorial Conventions
Certain words and terms used in this standard have a specific meaning beyond
the normal English meaning. These words and terms are defined either in the
glossary (see 3.1 and 8.4, 9.4, ..., 17.4) or in the text where they first
appear. Names of signals, phases, messages, commands, statuses, sense keys,
additional sense codes, and additional sense code qualifiers are in all
uppercase (e.g., REQUEST SENSE). Lower case is used for words having the
normal English meaning.
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