<s>
A	O
merge	B-Device
module	I-Device
is	O
a	O
special	O
kind	O
of	O
Windows	B-Application
Installer	I-Application
database	O
that	O
contains	O
the	O
components	O
needed	O
to	O
install	O
a	O
discrete	O
software	O
bundle	O
.	O
</s>
<s>
A	O
merge	B-Device
module	I-Device
cannot	O
be	O
installed	O
alone	O
,	O
but	O
must	O
be	O
merged	O
into	O
a	O
standard	O
Windows	B-Application
Installer	I-Application
installation	O
during	O
the	O
creation	O
of	O
the	O
installation	O
.	O
</s>
<s>
Typically	O
,	O
a	O
merge	B-Device
module	I-Device
or	O
a	O
collection	O
of	O
merge	B-Device
modules	I-Device
related	O
by	O
dependencies	B-Application
,	O
installs	O
a	O
software	O
product	O
or	O
portion	O
of	O
a	O
product	O
at	O
runtime	O
.	O
</s>
<s>
The	O
purpose	O
of	O
merge	B-Device
modules	I-Device
is	O
to	O
let	O
you	O
add	O
self-contained	O
software	O
modules	O
to	O
multiple	O
installations	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
there	O
are	O
a	O
number	O
of	O
applications	O
that	O
require	O
a	O
specifically	O
configured	O
component	O
,	O
it	O
would	O
be	O
possible	O
to	O
create	O
a	O
merge	B-Device
module	I-Device
that	O
installs	O
and	O
configures	O
that	O
component	O
.	O
</s>
<s>
That	O
merge	B-Device
module	I-Device
could	O
then	O
be	O
added	O
to	O
the	O
installation	O
packages	O
of	O
each	O
product	O
that	O
required	O
that	O
particular	O
component	O
.	O
</s>
<s>
This	O
saves	O
the	O
effort	O
of	O
having	O
to	O
individually	O
add	O
the	O
necessary	O
files	O
,	O
registry	B-Protocol
entries	O
,	O
and	O
other	O
components	O
to	O
every	O
installation	O
.	O
</s>
<s>
It	O
also	O
saves	O
time	O
if	O
updates	O
are	O
needed	O
,	O
as	O
instead	O
of	O
updating	O
the	O
installations	O
for	O
all	O
applications	O
,	O
only	O
the	O
merge	B-Device
module	I-Device
is	O
updated	O
,	O
and	O
the	O
installations	O
only	O
need	O
to	O
be	O
rebuilt	O
.	O
</s>
<s>
Standard	O
merge	B-Device
modules	I-Device
have	O
a	O
.msm	O
file	O
extension	O
.	O
</s>
<s>
Some	O
merge	B-Device
modules	I-Device
may	O
be	O
configurable	O
merge	B-Device
modules	I-Device
.	O
</s>
<s>
Such	O
merge	B-Device
modules	I-Device
contain	O
certain	O
values	O
that	O
can	O
be	O
set	O
to	O
specify	O
how	O
the	O
module	O
behaves	O
in	O
your	O
installation	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
author	O
of	O
the	O
configurable	O
merge	B-Device
module	I-Device
may	O
allow	O
attributes	O
to	O
be	O
set	O
on	O
components	O
,	O
enable	O
or	O
disable	O
isolated	O
components	O
,	O
specify	O
a	O
bitmap	O
for	O
a	O
dialog	O
,	O
or	O
specify	O
how	O
a	O
custom	O
action	O
is	O
run	O
.	O
</s>
<s>
Configurable	O
merge	B-Device
modules	I-Device
are	O
supported	O
only	O
by	O
Windows	B-Application
Installer	I-Application
2.0	O
or	O
higher	O
.	O
</s>
<s>
There	O
exist	O
a	O
number	O
of	O
pre-created	O
merge	B-Device
modules	I-Device
which	O
install	O
commonly	O
used	O
Microsoft	O
software	O
packages	O
,	O
such	O
as	O
MDAC	B-Library
,	O
ActiveX	B-Application
controls	I-Application
,	O
MFC	B-Language
,	O
SAPI	B-Application
and	O
DCOM	B-Operating_System
.	O
</s>
