<s>
The	O
program	B-Device
status	I-Device
word	I-Device
(	O
PSW	O
)	O
is	O
a	O
register	O
that	O
performs	O
the	O
function	O
of	O
a	O
status	B-General_Concept
register	I-General_Concept
and	O
program	B-General_Concept
counter	I-General_Concept
,	O
and	O
sometimes	O
more	O
.	O
</s>
<s>
This	O
article	O
only	O
discusses	O
the	O
PSW	O
in	O
the	O
IBM	B-Application
System/360	I-Application
and	O
its	O
successors	O
,	O
and	O
follows	O
the	O
IBM	O
convention	O
of	O
numbering	O
bits	O
starting	O
with	O
0	O
as	O
the	O
leftmost	O
(	O
most	O
significant	O
)	O
bit	O
.	O
</s>
<s>
Contained	O
within	O
the	O
PSW	O
are	O
the	O
two	O
bit	O
condition	B-General_Concept
code	I-General_Concept
,	O
representing	O
zero	O
,	O
positive	O
,	O
negative	O
,	O
overflow	O
,	O
and	O
similar	O
flags	O
of	O
other	O
architectures	O
 '	O
status	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
Conditional	B-General_Concept
branch	I-General_Concept
instructions	O
test	O
this	O
encoded	O
as	O
a	O
four	O
bit	O
value	O
,	O
with	O
each	O
bit	O
representing	O
a	O
test	O
of	O
one	O
of	O
the	O
four	O
condition	B-General_Concept
code	I-General_Concept
values	O
,	O
23	O
+	O
22	O
+	O
21	O
+	O
20	O
.	O
</s>
<s>
In	O
the	O
early	O
instances	O
of	O
the	O
architecture	O
(	O
System/360	B-Application
and	O
early	O
System/370	O
)	O
,	O
the	O
instruction	O
address	O
was	O
24	O
bits	O
;	O
in	O
later	O
instances	O
(	O
XA/370	O
)	O
,	O
the	O
instruction	O
address	O
was	O
31	O
bits	O
plus	O
a	O
mode	O
bit	O
(	O
24	O
bit	O
addressing	O
mode	O
if	O
zero	O
;	O
31	O
bit	O
addressing	O
mode	O
if	O
one	O
)	O
for	O
a	O
total	O
of	O
32	O
bits	O
.	O
</s>
<s>
In	O
the	O
present	O
instances	O
of	O
the	O
architecture	O
(	O
z/Architecture	B-Device
)	O
,	O
the	O
instruction	O
address	O
is	O
64	O
bits	O
and	O
the	O
PSW	O
itself	O
is	O
128	O
bits	O
.	O
</s>
<s>
On	O
all	O
but	O
360/20	B-Device
,	O
the	O
PSW	O
has	O
the	O
following	O
formats	O
.	O
</s>
<s>
S/360	B-Application
Extended	O
PSW	O
format	O
only	O
applies	O
to	O
the	O
360/67	B-Device
with	O
bit	O
8	O
of	O
control	O
register	O
6	O
set	O
.	O
</s>
