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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