This publication provides, for reference purposes, a
detailed definition of the machine functions per
formed by System/370.
The manual describes each function to the level of
detail that must be understood in order to prepare an
assembly language program that relies on that func
tion. It does not, however, describe the notation and
conventions that must be employed in preparing
such a program, for which the user must instead
refer to the appropriate assembly language manual,
such as the IBM System/360 Operating System
Assembly Language, GC28-6514.
The information in this publication is provided
principally for use by assembly language program
mers, although anyone concerned with the functional
details ofSystem/370 will find it useful.
Note that this manual is written as a reference
document and should not be considered to be an
introduction or a textbook for System/370. It as
sumes the user has a basic knowledge of data proc
essing systemsand, specifically, the System/370,
such as can be derived from the Introduction to
IBM Data Processing Systems,GC20-1684, and
the IBM System/370 System Summary, GA22-7001. Persons intending to use the information pre
sented here in preparing computer programs should, also become familiar with the publications dealing
with the programming language to be used. The lan
guage publications available in theSystem/370 Sys
tem Library, as well as all publications relating to
other aspects of the system, are listed and described
in the IBM System/370 Bibliography, GC20-0001. All facilities discussed in this manual are not nec
essarily available on every model of System/370.
Furthermore, in some instances the definitions have
been structured to allow for some degree of extensi
bility, and therefore certain capabilities may be
described or implied that are not offered on any
model. Examples of such capabilities are the provi
sions for the number of channel mask bits in the
control register, for the size of the processor ad
dress, and for the number ofCPUs sharing main stor
age. The allowance for this type of extensibility
should not be construed as implying any intention by
IBM to provide such capabilities. For information
about the characteristics and availability of fea-
tures on a specificSystem/370 model, use the func
tional characteristics manual for that model. The
availability of features onSystem/370 models is
summarized in the IBM System/370 System Sum mary, GA22-7001. Page of GA22-7000-4 Revised September 1, 1975
By TNL: GN22-0498
Preface
The information presented in this manual is
grouped into 14 chapters and several appendixes:
IBM System/370 highlights some of the major
features of System/370--particularly those that con
stitute advances beyond System/360.
System Organization describes the major group
ings within the system--the central processing unit,
main storage, and input/output--with some attention
paid to the composition and characteristics of those
groupings.
Program Execution explains the role of instruc
tions in program execution, looks in detail at instruc
tion formats, and describes briefly the use of the
program status word(PSW), of branching, and of
interruptions. It also details the aspects of program
execution on oneCPU as observed by channels or
anotherCPU. System Control describes in depth the facilities
for the switching of system status, for program pro
tection, for special externally initiated operations,
and for certain system enhancements. It deals specif
ically withCPU states, control modes, the PSW, control registers, protection, monitoring, program
event recording, timing facilities, resets, store status,
and initial program loading.
Dynamic Address Translation explains the opera
tion of the machine facility which, coupled with spe
cial programming support, makes the use of a virtual
storage possible in System/370. Dynamic address
translation (DAT) eliminates the need to assign a
program to a fixed location in real main storage and
thus reduces the addressing constraints on system
and problem programs.
Interruptions details theSystem/370 mechanism
that permits theCPU to change its state as a result
of conditions external to the system, within the sys
tem, or within theCPU itself. Six classes of interrup
tions are identified and described: machine-check
interruptions, program interruptions, supervisor-call
interruptions, external interruptions, input/output
interruptions, and restart interruptions.
Multiprocessing describes the facilities required
for the sharing of main storage by multipleCPUs and associated I/O. System Control Instructions contains detailed
descriptions of all of the instructions, except for theI/O instructions, that are available only to the con
trol program.
General Instructions contains detailed descrip
tions of all of the instructions in the standard in
struction set that are available to all programs.
detailed definition of the machine functions per
formed by System/370.
The manual describes each function to the level of
detail that must be understood in order to prepare an
assembly language program that relies on that func
tion. It does not, however, describe the notation and
conventions that must be employed in preparing
such a program, for which the user must instead
refer to the appropriate assembly language manual,
such as the IBM System/360 Operating System
Assembly Language, GC28-6514.
The information in this publication is provided
principally for use by assembly language program
mers, although anyone concerned with the functional
details of
Note that this manual is written as a reference
document and should not be considered to be an
introduction or a textbook for System/370. It as
sumes the user has a basic knowledge of data proc
essing systems
such as can be derived from the Introduction to
IBM Data Processing Systems,
the IBM System/370 System Summary, GA22-
sented here in preparing computer programs should
with the programming language to be used. The lan
guage publications available in the
tem Library, as well as all publications relating to
other aspects of the system, are listed and described
in the IBM System/3
essarily available on every model of System/370.
Furthermore, in some instances the definitions have
been structured to allow for some degree of extensi
bility, and therefore certain capabilities may be
described or implied that are not offered on any
model. Examples of such capabilities are the provi
sions for the number of channel mask bits in the
control register, for the size of the processor ad
dress, and for the number of
age. The allowance for this type of extensibility
should not be construed as implying any intention by
IBM to provide such capabilities. For information
about the characteristics and availability of fea-
tures on a specific
tional characteristics manual for that model. The
availability of features on
summarized in the IBM System/3
By TNL: GN22-0498
Preface
The information presented in this manual is
grouped into 14 chapters and several appendixes:
IBM System/3
features of System/370--particularly those that con
stitute advances beyond System/360.
System Organization describes the major group
ings within the system--the central processing unit,
main storage, and input/output--with some attention
paid to the composition and characteristics of those
groupings.
Program Execution explains the role of instruc
tions in program execution, looks in detail at instruc
tion formats, and describes briefly the use of the
program status word
interruptions. It also details the aspects of program
execution on one
another
for the switching of system status, for program pro
tection, for special externally initiated operations,
and for certain system enhancements. It deals specif
ically with
event recording, timing facilities, resets, store status,
and initial program loading.
Dynamic Address Translation explains the opera
tion of the machine facility which, coupled with spe
cial programming support, makes the use of a virtual
storage possible in System/370. Dynamic address
translation (DAT) eliminates the need to assign a
program to a fixed location in real main storage and
thus reduces the addressing constraints on system
and problem programs.
Interruptions details the
that permits the
of conditions external to the system, within the sys
tem, or within the
tions are identified and described: machine-check
interruptions, program interruptions, supervisor-call
interruptions, external interruptions, input/output
interruptions, and restart interruptions.
Multiprocessing describes the facilities required
for the sharing of main storage by multiple
descriptions of all of the instructions, except for the
trol program.
General Instructions contains detailed descrip
tions of all of the instructions in the standard in
struction set that are available to all programs.