<s>
Application	B-Operating_System
virtualization	I-Operating_System
is	O
a	O
software	O
technology	O
that	O
encapsulates	O
computer	B-Application
programs	I-Application
from	O
the	O
underlying	O
operating	B-General_Concept
system	I-General_Concept
on	O
which	O
they	O
are	O
executed	O
.	O
</s>
<s>
A	O
fully	O
virtualized	B-General_Concept
application	O
is	O
not	O
installed	O
in	O
the	O
traditional	O
sense	O
,	O
although	O
it	O
is	O
still	O
executed	O
as	O
if	O
it	O
were	O
.	O
</s>
<s>
The	O
application	O
behaves	O
at	O
runtime	O
like	O
it	O
is	O
directly	O
interfacing	O
with	O
the	O
original	O
operating	B-General_Concept
system	I-General_Concept
and	O
all	O
the	O
resources	O
managed	O
by	O
it	O
,	O
but	O
can	O
be	O
isolated	O
or	O
sandboxed	O
to	O
varying	O
degrees	O
.	O
</s>
<s>
In	O
this	O
context	O
,	O
the	O
term	O
"	O
virtualization	B-General_Concept
"	O
refers	O
to	O
the	O
artifact	O
being	O
encapsulated	O
(	O
application	O
)	O
,	O
which	O
is	O
quite	O
different	O
from	O
its	O
meaning	O
in	O
hardware	B-General_Concept
virtualization	I-General_Concept
,	O
where	O
it	O
refers	O
to	O
the	O
artifact	O
being	O
abstracted	O
(	O
physical	O
hardware	O
)	O
.	O
</s>
<s>
Full	O
application	B-Operating_System
virtualization	I-Operating_System
requires	O
a	O
virtualization	B-General_Concept
layer	O
.	O
</s>
<s>
Application	B-Operating_System
virtualization	I-Operating_System
layers	O
replace	O
part	O
of	O
the	O
runtime	B-Device
environment	I-Device
normally	O
provided	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
layer	O
intercepts	O
all	O
disk	O
operations	O
of	O
virtualized	B-General_Concept
applications	O
and	O
transparently	O
redirects	O
them	O
to	O
a	O
virtualized	B-General_Concept
location	O
,	O
often	O
a	O
single	O
file	O
.	O
</s>
<s>
Application	B-Operating_System
virtualization	I-Operating_System
allows	O
applications	O
to	O
run	O
in	O
environments	O
that	O
do	O
not	O
suit	O
the	O
native	O
application	O
.	O
</s>
<s>
For	O
example	O
,	O
Wine	B-Application
allows	O
some	O
Microsoft	B-Application
Windows	I-Application
applications	O
to	O
run	O
on	O
Linux	B-Application
.	O
</s>
<s>
Application	B-Operating_System
virtualization	I-Operating_System
reduces	O
system	O
integration	O
and	O
administration	O
costs	O
by	O
maintaining	O
a	O
common	O
software	O
baseline	O
across	O
multiple	O
diverse	O
computers	O
in	O
an	O
organization	O
.	O
</s>
<s>
Lesser	O
integration	O
protects	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
other	O
applications	O
from	O
poorly	O
written	O
or	O
buggy	O
code	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
it	O
provides	O
memory	O
protection	O
,	O
IDE-style	B-Application
debugging	O
features	O
and	O
may	O
even	O
run	O
applications	O
that	O
are	O
not	O
written	O
correctly	O
,	O
for	O
example	O
applications	O
that	O
try	O
to	O
store	O
user	O
data	O
in	O
a	O
read-only	O
system-owned	O
location	O
.	O
</s>
<s>
Isolating	O
applications	O
from	O
the	O
operating	B-General_Concept
system	I-General_Concept
has	O
security	O
benefits	O
as	O
well	O
,	O
as	O
the	O
exposure	O
of	O
the	O
virtualized	B-General_Concept
application	O
does	O
not	O
automatically	O
entail	O
the	O
exposure	O
of	O
the	O
entire	O
OS	O
.	O
</s>
<s>
Application	B-Operating_System
virtualization	I-Operating_System
also	O
enables	O
simplified	O
operating	B-General_Concept
system	I-General_Concept
migrations	O
.	O
</s>
<s>
Applications	O
can	O
be	O
transferred	O
to	O
removable	B-Device
media	I-Device
or	O
between	O
computers	O
without	O
the	O
need	O
of	O
installing	O
them	O
,	O
becoming	O
portable	B-Application
software	I-Application
.	O
</s>
<s>
Application	B-Operating_System
virtualization	I-Operating_System
uses	O
fewer	O
resources	O
than	O
a	O
separate	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Not	O
all	O
computer	B-Application
programs	I-Application
can	O
be	O
virtualized	B-General_Concept
.	O
</s>
<s>
Some	O
examples	O
include	O
applications	O
that	O
require	O
a	O
device	B-Application
driver	I-Application
(	O
a	O
form	O
of	O
integration	O
with	O
the	O
OS	O
)	O
and	O
16-bit	B-Device
applications	O
that	O
need	O
to	O
run	O
in	O
shared	O
memory	O
space	O
.	O
</s>
<s>
Anti-virus	B-Application
programs	I-Application
and	O
applications	O
that	O
require	O
heavy	O
OS	O
integration	O
,	O
such	O
as	O
WindowBlinds	B-Application
or	O
StyleXP	B-Application
are	O
difficult	O
to	O
virtualize	B-General_Concept
.	O
</s>
<s>
Moreover	O
,	O
in	O
software	O
licensing	O
,	O
application	B-Operating_System
virtualization	I-Operating_System
bears	O
great	O
licensing	O
pitfalls	O
mainly	O
because	O
both	O
the	O
application	B-Operating_System
virtualization	I-Operating_System
software	O
and	O
the	O
virtualized	B-General_Concept
applications	O
must	O
be	O
correctly	O
licensed	O
.	O
</s>
<s>
While	O
application	B-Operating_System
virtualization	I-Operating_System
can	O
address	O
file	O
and	O
Registry-level	O
compatibility	O
issues	O
between	O
legacy	O
applications	O
and	O
newer	O
operating	B-General_Concept
systems	I-General_Concept
,	O
applications	O
that	O
do	O
n't	O
manage	O
the	O
heap	B-General_Concept
correctly	O
will	O
not	O
execute	O
on	O
Windows	O
Vista	O
as	O
they	O
still	O
allocate	O
memory	O
in	O
the	O
same	O
way	O
,	O
regardless	O
of	O
whether	O
they	O
are	O
virtualized	B-General_Concept
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
specialist	O
application	O
compatibility	O
fixes	O
(	O
shims	B-General_Concept
)	O
may	O
still	O
be	O
needed	O
,	O
even	O
if	O
the	O
application	O
is	O
virtualized	B-General_Concept
.	O
</s>
<s>
Technology	O
categories	O
that	O
fall	O
under	O
application	B-Operating_System
virtualization	I-Operating_System
include	O
:	O
</s>
<s>
Application	B-Application
streaming	I-Application
.	O
</s>
<s>
Packages	O
are	O
usually	O
delivered	O
over	O
a	O
protocol	O
such	O
as	O
HTTP	O
,	O
CIFS	B-Operating_System
or	O
RTSP	B-Protocol
.	O
</s>
<s>
Remote	B-Protocol
Desktop	I-Protocol
Services	I-Protocol
(	O
formerly	O
called	O
Terminal	B-Protocol
Services	I-Protocol
)	O
is	O
a	O
server-based	O
computing/presentation	O
virtualization	B-General_Concept
component	O
of	O
Microsoft	B-Application
Windows	I-Application
that	O
allows	O
a	O
user	O
to	O
access	O
applications	O
and	O
data	O
hosted	O
on	O
a	O
remote	O
computer	O
over	O
a	O
network	O
.	O
</s>
<s>
Remote	B-Protocol
Desktop	I-Protocol
Services	I-Protocol
sessions	O
run	O
in	O
a	O
single	O
shared-server	O
operating	B-General_Concept
system	I-General_Concept
(	O
e.g.	O
</s>
<s>
Windows	B-Device
Server	I-Device
2008	I-Device
R2	I-Device
and	O
later	O
)	O
and	O
are	O
accessed	O
using	O
the	O
Remote	B-Protocol
Desktop	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
Desktop	B-Protocol
virtualization	I-Protocol
software	O
technologies	O
improve	O
portability	O
,	O
manageability	O
and	O
compatibility	O
of	O
a	O
personal	O
computer	O
's	O
desktop	O
environment	O
by	O
separating	O
part	O
or	O
all	O
of	O
the	O
desktop	O
environment	O
and	O
associated	O
applications	O
from	O
the	O
physical	O
client	O
device	O
that	O
is	O
used	O
to	O
access	O
it	O
.	O
</s>
<s>
A	O
common	O
implementation	O
of	O
this	O
approach	O
is	O
to	O
host	O
multiple	O
desktop	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
instances	O
on	O
a	O
server	O
hardware	O
platform	O
running	O
a	O
hypervisor	O
.	O
</s>
<s>
This	O
is	O
generally	O
referred	O
to	O
as	O
"	O
virtual	B-Protocol
desktop	I-Protocol
infrastructure	I-Protocol
"	O
(	O
VDI	O
)	O
.	O
</s>
