File name SA22-7085-1_370-XA_Principles_of_Operation_Jan87.pdf
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Principles of Operation
Publication Number File Number
Second Edition (January 1987)
This major revision obsoletes SA22-7085-0 and Technical Newslet-
ters SN22-0682 and SN22-0688.
For a summary of changes to the last edition, see the last
section of the Preface.
Except for minor style alterations, changes are identified by a
vertical line to the left of the change.
Changes are made periodically to the information herein; before
using this pUblication in connection with the operation of IBM
equipment, refer to the latest IBM System/370, 30xx, and 4300
Processors Bibliography, GC20-0001, for the editions that are
applicable and current.
References in this publication to IBM products, programs, or
services do not imply that IBM intends to make these available in
all countries in which IBM operates. Any reference to an IBM
program product in this publication is not intended to state or
imply that only IBM's program product may be used. Any func-
tionally equivalent program may be used instead.
Publications are not stocked at the address given below.
Requests for IBM publications should be made to your IBM repre-
sentative or to the IBM branch office serving your locality.
A form for readers' comments is provided at the back of this
publication. If the form has been removed, comments may be
addressed to IBM Corporation, Central Systems Architecture,
Department E57, PO Box 390, Poughkeepsie, NY, USA 12602. IBM may
use or distribute whatever information you supply in any way it
believes appropriate without incurring any obligation to you.
ec) Copyright International Business Machines Corporation 1983,
This publication provides, for reference and phrases appear, of necessity, earli-
purposes, a detailed definition of the er in the publication than the principal
machine functions performed by systems discussions explaining them. The reader
operating in the System/370 extended- who encounters a problem because of this
architecture (370-XA) mode. arrangement should refer to the index,
which indicates the location of the key
The publication applies only to systems description.
operating in the 370-XA mode. The IBM
System/370 Principles of Operation, The information presented in this publi-
GA22-7000, should be consulted regarding cation is grouped in 17 chapters and
the functions of the architecture which several appendixes:
apply to systems operating in the
System/370 mode. Chapter 1, Introduction, highlights some
of the major facilities of systems oper-