<s>
Distributed	B-Operating_System
Component	I-Operating_System
Object	I-Operating_System
Model	I-Operating_System
(	O
DCOM	B-Operating_System
)	O
is	O
a	O
proprietary	B-Application
Microsoft	O
technology	O
for	O
communication	O
between	O
software	B-Architecture
components	I-Architecture
on	O
networked	O
computers	O
.	O
</s>
<s>
DCOM	B-Operating_System
,	O
which	O
originally	O
was	O
called	O
"	O
Network	O
OLE	B-Operating_System
"	O
,	O
extends	O
Microsoft	O
's	O
COM	B-Application
,	O
and	O
provides	O
the	O
communication	O
substrate	O
under	O
Microsoft	O
's	O
COM+	O
application	O
server	O
infrastructure	O
.	O
</s>
<s>
The	O
extension	O
COM	B-Application
into	O
Distributed	O
COM	B-Application
was	O
due	O
to	O
extensive	O
use	O
of	O
DCE/RPC	B-General_Concept
(	O
Distributed	O
Computing	O
Environment/Remote	O
Procedure	O
Calls	O
)	O
–	O
more	O
specifically	O
Microsoft	O
's	O
enhanced	O
version	O
,	O
known	O
as	O
MSRPC	B-General_Concept
.	O
</s>
<s>
In	O
terms	O
of	O
the	O
extensions	O
it	O
added	O
to	O
COM	B-Application
,	O
DCOM	B-Operating_System
had	O
to	O
solve	O
the	O
problems	O
of	O
:	O
</s>
<s>
Marshalling	B-Application
–	O
serializing	O
and	O
deserializing	O
the	O
arguments	O
and	O
return	O
values	O
of	O
method	O
calls	O
"	O
over	O
the	O
wire	O
"	O
.	O
</s>
<s>
Distributed	O
garbage	B-General_Concept
collection	I-General_Concept
–	O
ensuring	O
that	O
references	O
held	O
by	O
clients	O
of	O
interfaces	O
are	O
released	O
when	O
,	O
for	O
example	O
,	O
the	O
client	O
process	O
crashed	O
,	O
or	O
the	O
network	O
connection	O
was	O
lost	O
.	O
</s>
<s>
Combining	O
significant	O
numbers	O
of	O
objects	O
in	O
the	O
client	O
's	O
browser	B-Application
into	O
a	O
single	O
transmission	O
in	O
order	O
to	O
minimize	O
bandwidth	O
utilization	O
.	O
</s>
<s>
One	O
of	O
the	O
key	O
factors	O
in	O
solving	O
these	O
problems	O
is	O
the	O
use	O
of	O
DCE/RPC	B-General_Concept
as	O
the	O
underlying	O
RPC	O
mechanism	O
behind	O
DCOM	B-Operating_System
.	O
</s>
<s>
DCE/RPC	B-General_Concept
has	O
strictly	O
defined	O
rules	O
regarding	O
marshalling	B-Application
and	O
who	O
is	O
responsible	O
for	O
freeing	O
memory	O
.	O
</s>
<s>
DCOM	B-Operating_System
was	O
a	O
major	O
competitor	O
to	O
CORBA	B-Architecture
.	O
</s>
<s>
However	O
,	O
the	O
difficulties	O
involved	O
in	O
getting	O
either	O
of	O
these	O
technologies	O
to	O
work	O
over	O
Internet	O
firewalls	B-Application
,	O
and	O
on	O
unknown	O
and	O
insecure	O
machines	O
,	O
meant	O
that	O
normal	O
HTTP	B-Protocol
requests	I-Protocol
in	O
combination	O
with	O
web	B-Application
browsers	I-Application
won	O
out	O
over	O
both	O
of	O
them	O
.	O
</s>
<s>
Microsoft	O
,	O
at	O
one	O
point	O
,	O
attempted	O
to	O
remediate	O
these	O
shortcomings	O
by	O
adding	O
an	O
extra	O
http	B-Protocol
transport	O
to	O
DCE/RPC	B-General_Concept
called	O
ncacn_http	O
(	O
Network	O
Computing	O
Architecture	O
connection-oriented	O
protocol	O
)	O
.	O
</s>
<s>
DCOM	B-Operating_System
was	O
publicly	O
launched	O
as	O
a	O
beta	O
for	O
Windows	O
95	O
September	O
18	O
,	O
1996	O
.	O
</s>
<s>
As	O
part	O
of	O
the	O
initiative	O
that	O
began	O
at	O
Microsoft	O
as	O
part	O
of	O
Secure	O
Development	O
Lifecycle	O
to	O
re-architect	O
insecure	O
code	O
,	O
DCOM	B-Operating_System
saw	O
some	O
significant	O
security-focused	O
changes	O
in	O
Windows	O
XP	O
Service	O
Pack	O
2	O
.	O
</s>
<s>
In	O
response	O
to	O
a	O
security	O
vulnerability	O
reported	O
by	O
Tencent	O
Security	O
Xuanwu	O
Lab	O
in	O
June	O
of	O
2021	O
,	O
Microsoft	O
released	O
security	O
updates	O
for	O
several	O
versions	O
of	O
Windows	O
and	O
Windows	O
Server	O
,	O
hardening	O
access	O
to	O
DCOM	B-Operating_System
.	O
</s>
<s>
COMsource	O
is	O
a	O
Unix	O
based	O
implementation	O
of	O
DCOM	B-Operating_System
,	O
allowing	O
interoperability	O
between	O
different	O
platforms	O
.	O
</s>
<s>
Its	O
source	O
code	O
is	O
available	O
,	O
along	O
with	O
full	O
and	O
complete	O
documentation	O
,	O
sufficient	O
to	O
use	O
and	O
also	O
implement	O
an	O
interoperable	O
version	O
of	O
DCOM	B-Operating_System
.	O
</s>
<s>
COMsource	O
comes	O
directly	O
from	O
the	O
Windows	B-Device
NT	I-Device
4.0	O
source	O
code	O
,	O
and	O
includes	O
the	O
source	O
code	O
for	O
a	O
Windows	B-Protocol
NT	I-Protocol
Registry	I-Protocol
Service	I-Protocol
.	O
</s>
<s>
In	O
1995	O
,	O
Digital	O
and	O
Microsoft	O
announced	O
Affinity	O
for	O
OpenVMS	O
(	O
also	O
known	O
as	O
NT	O
Affinity	O
)	O
which	O
was	O
intended	O
to	O
allow	O
OpenVMS	O
to	O
serve	O
as	O
the	O
persistence	O
layer	O
for	O
Windows	B-Device
NT	I-Device
client-server	B-Operating_System
applications	I-Operating_System
.	O
</s>
<s>
As	O
part	O
of	O
this	O
initiative	O
,	O
an	O
implementation	O
of	O
the	O
Distributed	B-Operating_System
Component	I-Operating_System
Object	I-Operating_System
Model	I-Operating_System
(	O
DCOM	B-Operating_System
)	O
was	O
added	O
to	O
OpenVMS	O
Alpha	O
.	O
</s>
<s>
In	O
order	O
to	O
support	O
DCOM	B-Operating_System
,	O
VMS	O
was	O
provided	O
with	O
implementations	O
of	O
the	O
Windows	B-Protocol
Registry	I-Protocol
,	O
NTLM	O
authentication	O
,	O
and	O
a	O
subset	O
of	O
Win32	B-Library
APIs	I-Library
needed	O
to	O
support	O
COM	B-Application
.	O
</s>
<s>
DCOM	B-Operating_System
was	O
first	O
added	O
to	O
OpenVMS	O
V7.2-1	O
for	O
the	O
Alpha	O
.	O
</s>
<s>
A	O
similar	O
implementation	O
of	O
DCOM	B-Operating_System
was	O
added	O
to	O
Digital	B-Operating_System
Unix	I-Operating_System
as	O
part	O
of	O
the	O
AllConnect	O
program	O
.	O
</s>
<s>
TangramCOM	O
was	O
a	O
separate	O
project	O
from	O
Wine	O
,	O
focusing	O
on	O
implementing	O
DCOM	B-Operating_System
on	O
Linux-based	O
smartphones	O
.	O
</s>
