IBM System/370 Operator's Reference Manual page 237

h
hard copy: A printed copy of machine output in a visually readable form, for ex·
ample, a printed recording of the messages displayed on the System/370 Model 125
video display unit.
hard stop: A condition, usually caused by an error, in which the CPU is stopped and
is not executing the microprogram .
.
I
IC (instruction counter): Hardware circuit which tells the central processor (CPU) the
main storage address at which it will find the next instruction to execute.
inclusive segments: Overlay segments in the same region that can be in main storage
simu Itaneously. .
index (data management): 1. A table in the catalog structure used to locate data
sets. 2. A table used to locate the records of an indexed sequential data set.
initial program loading (lPL): The initialization procedure which loads the nucleus and
begins normal operations.
initiator: The part of the job scheduler that selects jobs and job steps to be executed,
allocates input/output devices for them, places them under task control, and at
completion of the job, supplies control information for writing job output on a system
output unit.
input queue: A queue of job definitions in direct access storage, assigned to a job class
and arranged in assigned priority order, waiting to be processed.
input stream: Job· control statements entering the system; may also include input data.
installation: A particular computing system, in terms of the overall work it does and
the people who manage it, operate it, apply it to problems, service it, and use the
resu Its it produces.
interrupt: A break in the normal sequence ·of instruction execution. It causes an
automatic transfer to a preset storage location where appropriate action is taken.
invalid page: In S/370, a page that cannot be directly addressed by the dynamic
address translation feature of the central processing unit.
I/O area: An area (portion) of real storage into which data is read or from which data
is written; the term buffer is often used in place of I/O area.
I/O Trace (Input/Output Trace): A program that records I/O device activity for all or
a selected group of I/O devices.
10CS (input/output control system): A group of macro instruction routines provided
by I BM for handling the transfer of data between main storage and external storage
devices.
irrecoverable error: A hardware error which cannot be recovered from by the normal
hardware and retry procedures .
.
J
job: 1. A unit of work for the system from the standpoint of installation accounting
and control. A job consists of one or more job steps. 2. A collection of related
problem programs, identified in the input stream by a JOB statement followed by one
or more EXEC statements.
job control starernent: A control statement in the input stream that identifies a job or
defines its needs.
job library: A set of user· identified partitioned data sets used as the main source of
load modules for a given job.
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