<s>
The	O
IBM	B-Device
System/360	I-Device
architecture	I-Device
is	O
the	O
model	O
independent	O
architecture	B-General_Concept
for	O
the	O
entire	O
S/360	B-Application
line	O
of	O
mainframe	B-Architecture
computers	I-Architecture
,	O
including	O
but	O
not	O
limited	O
to	O
the	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
.	O
</s>
<s>
The	O
elements	O
of	O
the	O
architecture	B-General_Concept
are	O
documented	O
in	O
the	O
IBM	B-Application
System/360	I-Application
Principles	O
of	O
Operation	O
and	O
the	O
IBM	B-Application
System/360	I-Application
I/O	O
Interface	O
Channel	O
to	O
Control	O
Unit	O
Original	O
Equipment	O
Manufacturers	O
 '	O
Information	O
manuals	O
.	O
</s>
<s>
The	O
System/360	B-Device
architecture	I-Device
provides	O
the	O
following	O
features	O
:	O
</s>
<s>
A	O
standard	O
instruction	B-General_Concept
set	I-General_Concept
,	O
including	O
fixed-point	O
binary	O
arithmetic	O
and	O
logical	O
instructions	O
,	O
present	O
on	O
all	O
System/360	B-Application
models	O
(	O
except	O
the	O
Model	B-Device
20	I-Device
,	O
see	O
below	O
)	O
.	O
</s>
<s>
A	O
commercial	O
instruction	B-General_Concept
set	I-General_Concept
,	O
adding	O
decimal	O
arithmetic	O
instructions	O
,	O
is	O
optional	O
on	O
some	O
models	O
,	O
as	O
is	O
a	O
scientific	O
instruction	B-General_Concept
set	I-General_Concept
,	O
which	O
adds	O
floating-point	B-Algorithm
instructions	O
.	O
</s>
<s>
The	O
universal	O
instruction	B-General_Concept
set	I-General_Concept
includes	O
all	O
of	O
the	O
above	O
plus	O
the	O
storage	O
protection	O
instructions	O
and	O
is	O
standard	O
for	O
some	O
models	O
.	O
</s>
<s>
The	O
Model	B-Device
44	I-Device
provides	O
a	O
few	O
unique	O
instructions	O
for	O
data	O
acquisition	O
and	O
real-time	O
processing	O
and	O
is	O
missing	O
the	O
storage-to-storage	O
instructions	O
.	O
</s>
<s>
However	O
,	O
IBM	O
offered	O
a	O
Commercial	O
Instruction	B-General_Concept
Set	I-General_Concept
"	O
feature	O
that	O
ran	O
in	O
bump	O
storage	O
and	O
simulated	O
the	O
missing	O
instructions	O
.	O
</s>
<s>
The	O
Model	B-Device
20	I-Device
offers	O
a	O
stripped-down	O
version	O
of	O
the	O
standard	O
instruction	B-General_Concept
set	I-General_Concept
,	O
limited	O
to	O
eight	O
general	O
registers	O
with	O
halfword	O
(	O
16-bit	O
)	O
instructions	O
only	O
,	O
plus	O
the	O
commercial	O
instruction	B-General_Concept
set	I-General_Concept
,	O
and	O
unique	O
instructions	O
for	O
input/output	O
.	O
</s>
<s>
The	O
Model	B-Device
67	I-Device
includes	O
some	O
instructions	O
to	O
handle	O
32-bit	O
addresses	O
and	O
"	O
dynamic	O
address	O
translation	O
"	O
,	O
with	O
additional	O
privileged	O
instructions	O
to	O
provide	O
virtual	O
memory	O
.	O
</s>
<s>
Memory	O
(	O
storage	O
)	O
in	O
System/360	B-Application
is	O
addressed	O
in	O
terms	O
of	O
8-bit	O
bytes	O
.	O
</s>
<s>
The	O
original	O
architecture	B-General_Concept
of	O
System/360	B-Application
provided	O
for	O
up	O
to	O
224	O
=	O
16,777,216	O
bytes	O
of	O
memory	O
.	O
</s>
<s>
The	O
later	O
Model	B-Device
67	I-Device
extended	O
the	O
architecture	B-General_Concept
to	O
allow	O
up	O
to	O
232	O
=	O
4,294,967,296	O
Twice	O
the	O
size	O
of	O
the	O
later	O
System/370	B-Device
bytes	O
of	O
virtual	O
memory	O
.	O
</s>
<s>
System/360	B-Application
uses	O
truncated	O
addressing	O
similar	O
to	O
that	O
of	O
the	O
UNIVAC	B-Operating_System
III	I-Operating_System
.	O
</s>
<s>
In	O
the	O
case	O
of	O
System/360	B-Application
the	O
base	O
address	O
is	O
contained	O
in	O
one	O
of	O
15A	O
specification	O
of	O
general	O
register	O
0	O
yield	O
a	O
base	O
address	O
of	O
zero	O
rather	O
than	O
the	O
register	O
content	O
.	O
</s>
<s>
The	O
S/360	B-Application
architecture	B-General_Concept
defines	O
formats	O
for	O
characters	O
,	O
integers	O
,	O
decimal	O
integers	O
and	O
hexadecimal	B-Device
floating	I-Device
point	I-Device
numbers	O
.	O
</s>
<s>
Character	O
and	O
integer	O
instructions	O
are	O
mandatory	O
,	O
but	O
decimal	O
and	O
floating	B-Device
point	I-Device
instructions	O
are	O
part	O
of	O
the	O
Decimal	O
arithmetic	O
and	O
Floating-point	B-Algorithm
arithmetic	I-Algorithm
features	O
.	O
</s>
<s>
Floating	B-Algorithm
point	I-Algorithm
numbers	I-Algorithm
are	O
only	O
stored	O
as	O
fullword	O
or	O
doubleword	O
values	O
on	O
older	O
models	O
.	O
</s>
<s>
On	O
the	O
360/85	B-Device
and	O
360/195	O
there	O
are	O
also	O
extended	O
precision	O
floating	B-Algorithm
point	I-Algorithm
numbers	I-Algorithm
stored	O
as	O
quadwords	O
.	O
</s>
<s>
Instructions	O
in	O
the	O
S/360	B-Application
are	O
two	O
,	O
four	O
or	O
six	O
bytes	O
in	O
length	O
,	O
with	O
the	O
opcode	O
in	O
byte	O
0	O
.	O
</s>
<s>
Instructions	O
must	O
be	O
on	O
a	O
two-byte	O
boundary	O
in	O
memory	O
;	O
hence	O
the	O
low-order	O
bit	O
of	O
the	O
instruction	B-General_Concept
address	I-General_Concept
is	O
always	O
0	O
.	O
</s>
<s>
The	O
64-bit	O
PSW	O
describes	O
(	O
among	O
other	O
things	O
)	O
the	O
address	O
of	O
the	O
current	B-General_Concept
instruction	I-General_Concept
being	O
executed	O
,	O
condition	B-General_Concept
code	I-General_Concept
and	O
interrupt	B-Application
masks	I-Application
.	O
</s>
<s>
+	O
PSW	O
format	O
Bits	O
Contents	O
Explanation	O
0-7	O
System	O
Mask	O
bits	O
0-5	O
:	O
enable	O
channels	O
0-5	O
,	O
bit	O
6	O
:	O
enable	O
all	O
remaining	O
channels	O
,	O
bit	O
7	O
:	O
enable	O
External	O
interruptions	O
(	O
timer	O
,	O
interrupt	B-Application
key	O
,	O
and	O
external	O
signal	O
)	O
PoOps	O
8-11	O
Protection	O
key	O
CPU	O
protection	O
key	O
to	O
compare	O
against	O
storage	O
protection	O
keys	O
12	O
ASCII	O
mode	O
enable	O
ASCII	O
mode	O
for	O
packed	O
decimal	O
instructions	O
,	O
never	O
used	O
by	O
IBM	O
softwareBecause	O
the	O
design	O
of	O
the	O
S/360	B-Application
occurred	O
simultaneously	O
with	O
the	O
development	O
of	O
ASCII	O
,	O
IBM	O
's	O
ASCII	O
support	O
did	O
not	O
match	O
the	O
standard	O
that	O
was	O
ultimately	O
adopted	O
.	O
</s>
<s>
Load	O
Program	O
Status	O
Word	O
(	O
LPSW	O
)	O
is	O
a	O
privileged	O
instruction	O
that	O
loads	O
the	O
Program	O
Status	O
Word	O
(	O
PSW	O
)	O
,	O
including	O
the	O
program	O
mode	O
,	O
protection	O
key	O
,	O
and	O
the	O
address	O
of	O
the	O
next	B-General_Concept
instruction	I-General_Concept
to	O
be	O
executed	O
.	O
</s>
<s>
The	O
architecture	B-General_Concept
defines	O
5	O
classes	O
of	O
interruption	O
.	O
</s>
<s>
An	O
interruption	O
is	O
a	O
mechanism	O
for	O
automatically	O
changing	O
the	O
program	O
state	O
;	O
it	O
is	O
used	O
for	O
both	O
synchronousThe	O
S/360	B-Application
literature	O
does	O
not	O
use	O
the	O
terms	O
fault	O
or	O
trap	B-Application
and	O
asynchronous	B-Operating_System
events	O
.	O
</s>
<s>
There	O
are	O
two	O
storage	O
fields	O
assigned	O
to	O
each	O
class	O
of	O
interruption	O
on	O
the	O
S/360	B-Application
;	O
an	O
old	O
PSW	O
double-word	O
and	O
a	O
new	O
PSW	O
double-word	O
.	O
</s>
<s>
This	O
generally	O
replaces	O
the	O
instruction	B-General_Concept
address	I-General_Concept
,	O
thereby	O
effecting	O
a	O
branch	O
,	O
and	O
(	O
optionally	O
)	O
sets	O
and/or	O
resets	O
other	O
fields	O
within	O
the	O
PSW	O
,	O
thereby	O
effecting	O
a	O
mode	O
change	O
.	O
</s>
<s>
The	O
S/360	B-Application
architecture	B-General_Concept
defines	O
a	O
priority	O
to	O
each	O
interruption	O
class	O
,	O
but	O
it	O
is	O
only	O
relevant	O
when	O
two	O
interruptions	O
occur	O
simultaneously	O
;	O
an	O
interruption	O
routine	O
can	O
be	O
interrupted	O
by	O
any	O
other	O
enabled	O
interruption	O
,	O
including	O
another	O
occurrence	O
of	O
the	O
initial	O
interruption	O
.	O
</s>
<s>
An	O
I/O	O
interruptionPoOps	O
occurs	O
at	O
the	O
completion	O
of	O
a	O
channel	O
program	O
,	O
after	O
fetching	O
a	O
CCW	O
with	O
the	O
PCI	O
bit	O
set	O
and	O
also	O
for	O
asynchronous	B-Operating_System
events	O
detected	O
by	O
the	O
device	O
,	O
control	O
unit	O
or	O
channel	O
,	O
e.g.	O
,	O
completion	O
of	O
a	O
mechanical	O
movement	O
.	O
</s>
<s>
On	O
360/65	O
,	O
360/67	B-Device
and	O
360/85	B-Device
the	O
Protection	O
Exception	O
and	O
Addressing	O
Exception	O
interruptions	O
can	O
be	O
imprecise	O
,	O
in	O
which	O
case	O
they	O
store	O
an	O
Instruction	O
Length	O
Code	O
of	O
0	O
.	O
</s>
<s>
In	O
particular	O
,	O
an	O
operation	O
exception	O
is	O
recognized	O
when	O
a	O
program	O
is	O
written	O
for	O
an	O
optional	O
feature	O
,	O
e.g.	O
,	O
floating	B-Device
point	I-Device
,	O
that	O
is	O
not	O
installed	O
.	O
</s>
<s>
An	O
execute	O
exceptionPoOps	O
is	O
recognized	O
when	O
the	O
operand	O
of	O
an	O
EXECUTE	B-General_Concept
instruction	I-General_Concept
(	O
EX	O
)	O
is	O
another	O
EXECUTE	B-General_Concept
instruction	I-General_Concept
.	O
</s>
<s>
An	O
exponent	O
overflow	O
exceptionPoOps	O
is	O
recognized	O
when	O
the	O
characteristic	O
in	O
a	O
floating-point	B-Algorithm
arithmetic	I-Algorithm
operation	O
exceeds	O
127	O
and	O
the	O
fraction	O
is	O
not	O
zero	O
.	O
</s>
<s>
An	O
exponent	O
underflow	O
exceptionPoOps	O
is	O
recognized	O
when	O
the	O
characteristic	O
in	O
a	O
floating-point	B-Algorithm
arithmetic	I-Algorithm
operation	O
is	O
negative	O
and	O
the	O
fraction	O
is	O
not	O
zero	O
.	O
</s>
<s>
A	O
significance	O
exceptionPoOps	O
is	O
recognized	O
when	O
the	O
fraction	O
in	O
a	O
floating-point	B-Algorithm
add	O
or	O
subtract	O
operation	O
is	O
zero	O
.	O
</s>
<s>
A	O
floating-point	B-Algorithm
divide	O
exceptionPoOps	O
is	O
recognized	O
when	O
the	O
fraction	O
in	O
the	O
divisor	O
of	O
a	O
floating-point	B-Algorithm
divide	O
operation	O
is	O
zero	O
.	O
</s>
<s>
A	O
Supervisor	B-Operating_System
Call	I-Operating_System
interruptionPoOps	O
occurs	O
as	O
the	O
result	O
of	O
a	O
Supervisor	B-Operating_System
Call	I-Operating_System
instruction	I-Operating_System
;	O
the	O
system	O
stores	O
bits	O
8-15	O
of	O
the	O
SVC	O
instruction	O
as	O
the	O
Interruption	O
Code	O
.	O
</s>
<s>
interruption	O
occurs	O
as	O
the	O
result	O
of	O
certain	O
asynchronous	B-Operating_System
events	O
.	O
</s>
<s>
Channels	O
have	O
their	O
own	O
instruction	B-General_Concept
set	I-General_Concept
,	O
and	O
access	O
memory	O
independently	O
of	O
the	O
program	O
running	O
on	O
the	O
CPU	O
.	O
</s>
<s>
On	O
the	O
smaller	O
models	O
(	O
through	O
360/50	B-Device
)	O
a	O
single	O
microcode	O
engine	O
runs	O
both	O
the	O
CPU	O
program	O
and	O
the	O
channel	O
program	O
.	O
</s>
<s>
There	O
are	O
three	O
types	O
of	O
channels	O
on	O
the	O
S/360	B-Application
:	O
</s>
<s>
This	O
is	O
intended	O
for	O
devices	O
in	O
which	O
there	O
is	O
a	O
mechanical	O
delay	O
after	O
completion	O
of	O
data	O
transfer	O
,	O
e.g.	O
,	O
for	O
seeks	O
on	O
moving-head	O
DASD	B-Application
.	O
</s>
<s>
The	O
block	O
multiplexer	O
channel	O
was	O
a	O
late	O
addition	O
to	O
the	O
System/360	B-Device
architecture	I-Device
;	O
early	O
machines	O
had	O
only	O
byte	O
multiplexer	O
channels	O
and	O
selector	O
channels	O
.	O
</s>
<s>
The	O
block	O
multiplexor	O
channel	O
was	O
also	O
available	O
on	O
the	O
later	O
System/370	B-Device
computers	O
.	O
</s>
<s>
Conceptually	O
peripheral	O
equipment	O
is	O
attached	O
to	O
a	O
S/360	B-Application
through	O
control	O
units	O
,	O
which	O
in	O
turn	O
are	O
attached	O
through	O
channels	O
.	O
</s>
<s>
However	O
,	O
the	O
architecture	B-General_Concept
does	O
not	O
require	O
that	O
control	O
units	O
be	O
physically	O
distinct	O
,	O
and	O
in	O
practice	O
they	O
are	O
sometimes	O
integrated	O
with	O
the	O
devices	O
that	O
they	O
control	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
architecture	B-General_Concept
does	O
not	O
require	O
the	O
channels	O
to	O
be	O
physically	O
distinct	O
from	O
the	O
processor	O
,	O
and	O
the	O
smaller	O
S/360	B-Application
models	O
(	O
through	O
360/50	B-Device
)	O
have	O
integrated	O
channels	O
that	O
steal	B-General_Concept
cycles	I-General_Concept
from	O
the	O
processor	O
.	O
</s>
<s>
Peripheral	O
devices	O
are	O
addressed	O
with	O
16-bitBecause	O
of	O
the	O
limits	O
on	O
the	O
channel	O
number	O
,	O
S/360	B-Application
and	O
early	O
S/370	B-Device
software	O
only	O
used	O
12	O
bits	O
to	O
store	O
device	O
addresses	O
.	O
</s>
<s>
If	O
the	O
selection	O
returns	O
to	O
the	O
channel	O
then	O
no	O
control	O
unit	O
accepted	O
the	O
command	O
and	O
SIO	O
returns	O
Condition	B-General_Concept
Code	I-General_Concept
3	O
.	O
</s>
<s>
In	O
this	O
way	O
,	O
an	O
entire	O
load	O
module	O
may	O
be	O
read	O
and	O
relocated	O
while	O
utilizing	O
only	O
one	O
EXCP	B-Application
,	O
and	O
possibly	O
only	O
one	O
revolution	O
of	O
the	O
disk	O
drive	O
.	O
</s>
<s>
Attention	O
is	O
a	O
special	O
condition	O
,	O
and	O
requires	O
specific	O
operating	O
system	O
support	O
,	O
and	O
for	O
which	O
the	O
operating	O
system	O
has	O
a	O
special	O
attention	O
tableThe	O
OS	O
uses	O
the	O
attention	O
index	O
in	O
a	O
Unit	B-Application
Control	I-Application
Block	I-Application
(	O
UCB	O
)	O
as	O
an	O
index	O
into	O
the	O
attention	O
table	O
.	O
</s>
<s>
The	O
meaning	O
of	O
the	O
high	O
order	O
six	O
or	O
four	O
bits	O
,	O
the	O
modifier	O
bits	O
,	O
M	O
in	O
the	O
table	O
above	O
,	O
depends	O
upon	O
the	O
type	O
of	O
I/O	O
device	O
attached	O
,	O
see	O
e.g.	O
,	O
DASD	B-Application
CKD	B-Application
CCWs	I-Application
.	O
</s>
<s>
A	O
noteworthy	O
deviation	O
from	O
the	O
architecture	B-General_Concept
is	O
that	O
DASD	B-Application
use	O
Sense	O
command	O
codes	O
for	O
Reserve	O
and	O
Release	O
,	O
instead	O
of	O
using	O
Control	O
.	O
</s>
<s>
The	O
S/360	B-Application
has	O
four	O
I/O	O
instructions	O
:	O
Start	O
I/O	O
(	O
SIO	O
)	O
,	O
Test	O
I/O	O
(	O
TIO	O
)	O
,	O
Halt	O
I/O	O
(	O
HIO	O
)	O
and	O
Test	O
Channel	O
(	O
TCH	O
)	O
.	O
</s>
<s>
The	O
B1	O
(	O
base	O
)	O
and	O
D1	O
(	O
displacement	O
)	O
fields	O
are	O
used	O
to	O
calculate	O
the	O
cuu	O
(	O
channel	O
and	O
device	O
number	O
)	O
;	O
bits	O
8-15	O
of	O
the	O
instructions	O
are	O
unused	O
and	O
should	O
be	O
zero	O
for	O
compatibility	O
with	O
the	O
S/370	B-Device
.	O
</s>
<s>
It	O
may	O
also	O
store	O
a	O
CSW	O
,	O
in	O
which	O
case	O
it	O
completes	O
with	O
condition	B-General_Concept
code	I-General_Concept
1	O
.	O
</s>
<s>
It	O
may	O
also	O
store	O
a	O
CSW	O
,	O
in	O
which	O
case	O
it	O
completes	O
with	O
condition	B-General_Concept
code	I-General_Concept
1	O
.	O
</s>
<s>
The	O
architecture	B-General_Concept
of	O
System/360	B-Application
specified	O
the	O
existence	O
of	O
several	O
common	O
functions	O
,	O
but	O
did	O
not	O
specify	O
their	O
means	O
of	O
implementation	O
.	O
</s>
<s>
System	O
Reset	O
is	O
not	O
guaranteed	O
to	O
correct	O
parity	O
errors	O
in	O
general	O
registers	O
,	O
floating	B-Device
point	I-Device
registers	O
or	O
storage	O
.	O
</s>
<s>
This	O
process	O
is	O
sometimes	O
known	O
as	O
Booting	B-Operating_System
.	O
</s>
<s>
The	O
Interrupt	B-Application
keyPoOps	O
causes	O
an	O
external	O
interruption	O
with	O
bit	O
25	O
set	O
in	O
the	O
External	O
Old	O
PSW	O
.	O
</s>
<s>
Two	O
modes	O
are	O
defined	O
by	O
the	O
architecture	B-General_Concept
:	O
</s>
<s>
Three	O
selections	O
are	O
defined	O
by	O
the	O
architecture	B-General_Concept
:	O
</s>
<s>
The	O
Set	O
IC	O
=	O
PoOps	O
sets	O
the	O
instruction	B-General_Concept
address	I-General_Concept
portion	O
of	O
the	O
PSW	O
from	O
the	O
Data	O
Switches	O
or	O
the	O
Address	O
Switches	O
,	O
depending	O
on	O
the	O
model	O
.	O
</s>
<s>
Stop	O
on	O
instruction	B-General_Concept
address	I-General_Concept
compare	O
is	O
present	O
on	O
all	O
models	O
,	O
but	O
stop	O
on	O
data	O
address	O
compare	O
is	O
only	O
present	O
on	O
some	O
models	O
.	O
</s>
<s>
On	O
some	O
models	O
,	O
e	O
,	O
g.	O
,	O
the	O
S/360	B-Device
-85	I-Device
,	O
the	O
alignment	O
requirements	O
for	O
some	O
problem-state	O
instructions	O
were	O
relaxed	O
.	O
</s>
<s>
The	O
floating-point	B-Algorithm
arithmetic	I-Algorithm
feature	O
provides	O
4	O
64-bit	O
floating	B-Device
point	I-Device
registers	O
and	O
instructions	O
to	O
operate	O
on	O
32	O
and	O
64	O
bit	O
hexadecimal	B-Device
floating	I-Device
point	I-Device
numbers	O
.	O
</s>
<s>
The	O
360/85	B-Device
and	O
360/195	O
also	O
support	O
128	O
bit	O
extended	O
precision	O
floating	B-Algorithm
point	I-Algorithm
numbers	I-Algorithm
.	O
</s>
<s>
If	O
the	O
interval	O
timer	O
feature	O
is	O
installed	O
,	O
the	O
processor	O
decrements	O
the	O
word	O
at	O
location	O
80	O
( 	O
 '	O
50'X	O
)	O
at	O
regular	O
intervals	O
;	O
the	O
architecture	B-General_Concept
does	O
not	O
specify	O
the	O
interval	O
but	O
does	O
require	O
that	O
value	O
subtracted	O
make	O
it	O
appear	O
as	O
though	O
1	O
were	O
subtracted	O
from	O
bit	O
23	O
300	O
times	O
per	O
second	O
.	O
</s>
<s>
The	O
System/360	B-Device
Model	I-Device
20	I-Device
is	O
radically	O
different	O
and	O
should	O
not	O
be	O
considered	O
to	O
be	O
a	O
S/360	B-Application
.	O
</s>
<s>
The	O
System/360	B-Device
Model	I-Device
44	I-Device
is	O
missing	O
certain	O
instructions	O
,	O
but	O
a	O
feature	O
allowed	O
the	O
missing	O
instructions	O
to	O
be	O
simulated	O
in	O
hidden	O
memory	O
thus	O
allowing	O
the	O
use	O
of	O
standard	O
S/360	B-Application
operating	O
systems	O
and	O
applications	O
.	O
</s>
<s>
Some	O
models	O
have	O
features	O
that	O
extended	O
the	O
architecture	B-General_Concept
,	O
e.g.	O
,	O
emulation	O
instructions	O
,	O
paging	O
,	O
and	O
some	O
models	O
make	O
minor	O
deviations	O
from	O
the	O
architecture	B-General_Concept
.	O
</s>
<s>
The	O
multisystem	O
feature	O
on	O
the	O
S/360	B-Application
-65	O
which	O
modifies	O
the	O
behavior	O
of	O
the	O
direct	O
control	O
feature	O
and	O
of	O
the	O
Set	O
System	O
Mask	O
(	O
SSM	O
)	O
instruction	O
.	O
</s>
<s>
Some	O
deviations	O
served	O
as	O
prototypes	O
for	O
features	O
of	O
the	O
S/370	B-Device
architecture	B-General_Concept
.	O
</s>
