<s>
In	O
computing	O
,	O
a	O
data	B-Data_Structure
descriptor	I-Data_Structure
is	O
a	O
structure	O
containing	O
information	O
that	O
describes	O
data	O
.	O
</s>
<s>
Data	B-Data_Structure
descriptors	I-Data_Structure
may	O
be	O
used	O
in	O
compilers	B-Language
,	O
as	O
a	O
software	O
structure	O
at	O
run	O
time	O
in	O
languages	O
like	O
Ada	B-Language
or	O
PL/I	B-Language
,	O
or	O
as	O
a	O
hardware	O
structure	O
in	O
some	O
computers	O
such	O
as	O
Burroughs	B-Device
large	I-Device
systems	I-Device
.	O
</s>
<s>
Data	B-Data_Structure
descriptors	I-Data_Structure
are	O
typically	O
used	O
at	O
run-time	O
to	O
pass	O
argument	O
information	O
to	O
called	O
subroutines	O
.	O
</s>
<s>
HP	O
OpenVMS	B-Operating_System
and	O
Multics	B-Application
have	O
system-wide	O
language-independent	O
standards	O
for	O
argument	O
descriptors	O
.	O
</s>
<s>
Descriptors	O
are	O
also	O
used	O
to	O
hold	O
information	O
about	O
data	O
that	O
is	O
only	O
fully	O
known	O
at	O
run-time	O
,	O
such	O
as	O
a	O
dynamically	B-General_Concept
allocated	I-General_Concept
array	I-General_Concept
.	O
</s>
<s>
The	O
following	O
descriptor	O
is	O
used	O
by	O
IBM	O
Enterprise	O
PL/I	B-Language
to	O
describe	O
a	O
character	O
string	O
:	O
</s>
<s>
'	O
desc	O
type	O
 '	O
is	O
2	O
to	O
indicate	O
that	O
this	O
is	O
an	O
element	O
descriptor	O
rather	O
than	O
an	O
array	B-Data_Structure
or	O
structure	O
descriptor	O
.	O
</s>
<s>
'	O
flags	O
 '	O
indicate	O
the	O
encoding	O
of	O
the	O
string	O
,	O
EBCDIC	B-Language
or	O
ASCII	B-Protocol
,	O
and	O
the	O
encoding	O
of	O
the	O
length	O
of	O
varying	O
strings	O
.	O
</s>
<s>
Here	O
is	O
the	O
source	O
of	O
an	O
array	B-Data_Structure
descriptor	O
from	O
Multics	B-Application
.	O
</s>
<s>
The	O
definitions	O
include	O
a	O
structure	O
for	O
the	O
base	O
array	B-Data_Structure
information	O
and	O
a	O
structure	O
for	O
each	O
dimension	O
.	O
</s>
<s>
(	O
Multics	B-Application
ran	O
on	O
systems	O
with	O
36-bit	O
words	O
)	O
.	O
</s>
