<s>
In	O
IBM	B-Application
System/360	I-Application
through	O
present	O
day	O
z/Architecture	B-Device
,	O
an	O
address	B-Language
constant	I-Language
or	O
"	O
adcon	O
"	O
is	O
an	O
assembly	B-Language
language	I-Language
data	O
type	O
which	O
contains	O
the	O
address	B-General_Concept
of	O
a	O
location	O
in	O
computer	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
An	O
address	B-Language
constant	I-Language
can	O
be	O
one	O
,	O
two	O
,	O
three	O
or	O
four	O
bytes	O
long	O
,	O
although	O
an	O
adcon	O
of	O
less	O
than	O
four	O
bytes	O
is	O
conventionally	O
used	O
to	O
hold	O
an	O
expression	O
for	O
a	O
small	O
integer	O
such	O
as	O
a	O
length	O
,	O
a	O
relative	O
address	B-General_Concept
,	O
or	O
an	O
index	O
value	O
,	O
and	O
does	O
not	O
represent	O
an	O
address	B-General_Concept
at	O
all	O
.	O
</s>
<s>
Address	B-Language
constants	I-Language
are	O
defined	O
using	O
an	O
assembler	B-Language
language	I-Language
"	O
DC	O
"	O
statement	O
.	O
</s>
<s>
A	O
adcons	O
normally	O
store	O
a	O
four	O
byte	O
relocatable	O
address	B-General_Concept
,	O
however	O
it	O
is	O
possible	O
to	O
specify	O
the	O
length	O
of	O
the	O
constant	O
.	O
</s>
<s>
V	O
type	O
adcons	O
store	O
an	O
external	O
reference	O
to	O
be	O
resolved	O
by	O
the	O
link-editor	B-Application
.	O
</s>
<s>
'	O
Y	O
 '	O
adcons	O
can	O
directly	O
address	B-General_Concept
up	O
to	O
32K	O
bytes	O
of	O
storage	O
,	O
and	O
are	O
not	O
widely	O
used	O
since	O
early	O
System/360	B-Application
assemblers	B-Language
did	O
not	O
support	O
a	O
'	O
Y	O
 '	O
data	O
type	O
.	O
</s>
<s>
Early	O
DOS/360	B-Application
and	O
BOS/360	B-Application
systems	O
made	O
more	O
use	O
of	O
Y	O
adcons	O
,	O
since	O
the	O
machines	O
these	O
systems	O
ran	O
on	O
had	O
limited	O
storage	O
.	O
</s>
<s>
Q	O
address	B-Language
constants	I-Language
contain	O
not	O
actual	O
addresses	O
but	O
a	O
displacement	O
in	O
the	O
External	O
Dummy	O
Section	O
–	O
similar	O
to	O
the	O
Linux	O
Global	O
Offset	O
Table	O
(	O
see	O
Position-independent	B-Operating_System
code	I-Operating_System
)	O
.	O
</s>
<s>
A	O
J	O
adcon	O
is	O
set	O
by	O
the	O
linkage	O
editor	O
to	O
hold	O
the	O
cumulative	O
length	O
of	O
the	O
External	O
Dummy	O
Section	O
,	O
and	O
does	O
not	O
actually	O
contain	O
an	O
address	B-General_Concept
.	O
</s>
<s>
Other	O
types	O
of	O
address	B-Language
constants	I-Language
are	O
R	O
which	O
had	O
special	O
significance	O
for	O
TSS/360	B-Application
to	O
address	B-General_Concept
the	O
PSECT	O
,	O
and	O
S	O
,	O
which	O
stores	O
an	O
address	B-General_Concept
in	O
base-displacement	O
format	O
–	O
a	O
16	O
bit	O
value	O
containing	O
a	O
four	O
bit	O
general	O
register	O
number	O
and	O
a	O
twelve	O
bit	O
displacement	O
,	O
the	O
same	O
format	O
as	O
addresses	O
are	O
encoded	O
in	O
instructions	O
.	O
</s>
<s>
System	B-Device
z	I-Device
supports	O
types	O
AD	O
,	O
JD	O
,	O
QD	O
,	O
and	O
VD	O
,	O
which	O
represent	O
8	O
byte	O
(	O
doubleword	O
)	O
versions	O
of	O
types	O
'	O
A	O
 '	O
,	O
'	O
J	O
 '	O
,	O
'	O
Q	O
 '	O
,	O
and	O
'	O
V	O
 '	O
to	O
hold	O
64	O
bit	O
addresses	O
.	O
</s>
<s>
An	O
absolute	B-Language
expression	I-Language
can	O
be	O
completely	O
evaluated	O
at	O
assembly	O
time	O
and	O
does	O
not	O
require	O
further	O
processing	O
by	O
the	O
linkage	O
editor	O
.	O
</s>
<s>
A	O
relocatable	O
expression	O
is	O
one	O
that	O
contains	O
one	O
or	O
more	O
terms	O
that	O
require	O
relocation	B-Library
by	O
the	O
linkage	O
editor	O
when	O
the	O
program	O
ls	O
linked	O
,	O
for	O
example	O
,	O
in	O
the	O
following	O
code	O
'	O
ACON	O
 '	O
has	O
a	O
relocatable	O
nominal	O
value	O
.	O
</s>
