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File No. 5360-36
GY28-6661-5




Program Logic




OS Release 21




IBM System/3S0 Operating System
Initial Program Loader and
Nucleus Initialization Program

Program Number 360S-CI-535


This publication presents the internal logic of the
IBM System/360 Operating System Initial Program Loader
and Nucleus Initialization Program. The operation of
the Nucleus Initialization Program in each of the con-
trol program environments (MFT, MVT) is described in
the section dealing with the Nucleus Initialization
Program. Special initialization procedures for MVT
with Model 65 multiprocessing systems are included in
Appendix A. The ~ables, work areas, and control blocks
are illustrated in the publication, as well as flowcharts
illustrating the logic flow of the Initial Program Loader
and the Nucleus Initialization Program.
This program logic manual is directed to personnel
responsible for program maintenance. It can be used to
locate specific areas of the program, and it enables
the reader to relate these areas to the corresponding
program listings. Program logic information is not
necessary for program operation and use.
Sixth Edition (March, 1972)
This is a major revision of, and makes obsolete, GY28-
6661-q and its associated TNL GN27-1353. This edition
applies to Release 21 of the System/360 Operating Sys-
tem and to all subsequent releases until otherwise
indicated in new editions or Technical Newsletters. A
change is indicated by a vertical line to the left of
the change. Changes are continually being made to the
specifications herein; before using this publication in
connection with the operation of IBM systems, consult
the latest System/360 SRL Newsletter, GN20-0360, for
the editions that are applicable and current.

This publication was prepared for production using an IBM computer to
update the text and to control the page and line format. Page impres-
sions for photo-offset printing were obtained from an IBM 1Q03 Printer
using a special print train.
Copies of this and other IBM publications can be obtained through IBM
branch offices.
A form for reader's comments appears at the back of this publication.
Address any additional comments concerning the contents of this publica-
tion to IBM Corporation, programming Publications, Department 636
Neighborhood Road, Kingston, New York 12401


~ Copyright International Business Machines Corporation 1970,1971,1972
PREFACE




This publication describes the internal used in the publication, MFT refers to sys-
logic and theory of operation of the Ini- tems capable of multiprogramming with a
tial Program Loader, which brings in the fixed number of tasks, and MVT refers to
programs which become the control program systems capable of multiprogramming with a
nucleus, and the Nucleus Initialization variable number of tasks. MVT with Model
Program, which prepares those programs and 65 multiprocessing is not abbreviated in
the balance of main storage for operation this publication. An appendix is devoted
of the control program. to a detailed discussion of MVT with Model
65 multiprocessing.
The publication consists of eight major
sections. The Introduction presents an
overview of the purpose and functions of The reader of this publication should
the programs and introduces the major have a knowledge of the assembler language
topics presented in the manual. The sec- for System/360 and should be familiar with
tion, Initial Program Loader presents a the following publications:
detailed discussion of that program's
operation, including the use of tables,
work areas, and control blocks. The IBM System/360: principles of Opera-
address resolution procedure is described tion, GA22-6821
in detail as an adjunct to the listings of
the program. The Nucleus Initialization IBM System/360 Operating System:
Program section discusses the operation of Introduction, GC28-6534
that program and emphasizes the differences Assembler Language, GC28-6524
that exist for the different configurations MFT Guide, GC27-6939
of the control program. The Routine Lists MVT Guide, GC28-6720
section presents a summary of each of the
major IPL and NIP routines. The section In addition, information contained in
Tables and Work Areas contains illustra- other publications may prove helpful to
tions of the tables, work areas, and con- understanding these programs. These publi-
trol blocks used by the programs or ini- cations are:
tialized by the programs. The Flowcharts
section contains charts that diagram the IBM System/360 operating System:
logic flow of the Initial Program Loader Data Management Macro Instructions,
and the Nucleus Initialization Program. GC26-3794
Appendix A: Initialization for MVT with Data Management Services Guide,
Model 65 Multiprocessing describes the spe- GC26-3746
cial initialization procedures for the Messages and Codes, GC28-6631
Model 65 Multiprocessing System. Appendix Operator's Reference, GC28-6691
B: NIP Interface Routine describes the Programmer's Guide to Debugging,
special processing necessary to maintain GC28-6670
correct base addresses when NIP uses Service Aids, GC28-6719
subroutines. Storage Estimates, GC28-6551
System Control Blocks, GC28-6628
Throughout this publication, references system Generation, GC28-6554
to control program configurations are simp- MFT supervisor PLM, GY27-7236
lified by the use of abbreviations. When MVT supervisor PLM, GY28-6659




iii
SUMMARY OF AMENDMENTS


Release 21