<s>
The	O
MIT	B-Device
Shared	I-Device
Memory	I-Device
Extension	I-Device
or	O
MIT-SHM	B-Device
or	O
XShm	B-Device
is	O
an	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
extension	O
for	O
exchange	O
of	O
image	O
data	O
between	O
client	O
and	O
server	O
using	O
shared	O
memory	O
(	O
usually	O
)	O
.	O
</s>
<s>
This	O
is	O
essentially	O
a	O
version	O
of	O
the	O
ximage	O
interface	O
where	O
the	O
actual	O
image	O
data	O
is	O
stored	O
in	O
a	O
SysV	B-Operating_System
shared	O
memory	O
segment	O
,	O
and	O
thus	O
need	O
not	O
be	O
transferred	O
across	O
the	O
socket	B-Protocol
to	O
the	O
X	B-Operating_System
server	O
.	O
</s>
<s>
These	O
are	O
two-dimensional	O
arrays	O
of	O
pixels	O
in	O
a	O
format	O
specified	O
by	O
the	O
X	B-Operating_System
server	O
,	O
where	O
the	O
image	O
data	O
is	O
stored	O
in	O
the	O
shared	O
memory	O
segment	O
.	O
</s>
<s>
Through	O
use	O
of	O
shared	O
memory	O
pixmaps	O
,	O
it	O
is	O
possible	O
to	O
change	O
the	O
contents	O
of	O
these	O
pixmaps	O
without	O
using	O
any	O
Xlib	B-Language
routines	O
at	O
all	O
.	O
</s>
<s>
Shared	O
memory	O
pixmaps	O
can	O
only	O
be	O
supported	O
when	O
the	O
X	B-Operating_System
server	O
can	O
use	O
regular	O
virtual	O
memory	O
for	O
pixmap	O
data	O
;	O
if	O
the	O
pixmaps	O
are	O
stored	O
in	O
the	O
on-board	O
memory	O
of	O
graphics	O
hardware	O
,	O
an	O
application	O
will	O
not	O
be	O
able	O
to	O
share	O
them	O
with	O
the	O
server	O
.	O
</s>
<s>
In	O
the	O
1.15	O
release	O
of	O
the	O
X.org	B-Operating_System
server	I-Operating_System
the	O
MIT-SHM	B-Device
extension	O
gains	O
two	O
additional	O
requests	O
:	O
'	O
X_ShmAttachFd	O
 '	O
and	O
'	O
X_ShmCreateSegment	O
 '	O
,	O
to	O
be	O
able	O
to	O
pass	O
shared	O
memory	O
through	O
file	O
descriptors	O
from	O
client	O
to	O
server	O
and	O
from	O
server	O
to	O
client	O
,	O
reducing	O
the	O
number	O
of	O
copy	O
operations	O
further	O
.	O
</s>
