<s>
In	O
computing	O
,	O
virtualization	B-General_Concept
or	O
virtualisation	B-General_Concept
(	O
sometimes	O
abbreviated	O
v12n	B-General_Concept
,	O
a	O
numeronym	O
)	O
is	O
the	O
act	O
of	O
creating	O
a	O
virtual	O
(	O
rather	O
than	O
actual	O
)	O
version	O
of	O
something	O
at	O
the	O
same	O
abstraction	O
level	O
,	O
including	O
virtual	B-Architecture
computer	I-Architecture
hardware	B-Architecture
platforms	O
,	O
storage	B-General_Concept
devices	I-General_Concept
,	O
and	O
computer	B-Architecture
network	I-Architecture
resources	O
.	O
</s>
<s>
Virtualization	B-General_Concept
began	O
in	O
the	O
1960s	O
,	O
as	O
a	O
method	O
of	O
logically	O
dividing	O
the	O
system	O
resources	O
provided	O
by	O
mainframe	B-Architecture
computers	I-Architecture
between	O
different	O
applications	O
.	O
</s>
<s>
An	O
early	O
and	O
successful	O
example	O
is	O
IBM	O
CP/CMS	B-Application
.	O
</s>
<s>
Hardware	B-General_Concept
virtualization	I-General_Concept
or	O
platform	B-General_Concept
virtualization	I-General_Concept
refers	O
to	O
the	O
creation	O
of	O
a	O
virtual	B-Architecture
machine	I-Architecture
that	O
acts	O
like	O
a	O
real	O
computer	O
with	O
an	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Software	O
executed	O
on	O
these	O
virtual	B-Architecture
machines	I-Architecture
is	O
separated	O
from	O
the	O
underlying	O
hardware	B-Architecture
resources	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
computer	O
that	O
is	O
running	O
Arch	O
Linux	O
may	O
host	O
a	O
virtual	B-Architecture
machine	I-Architecture
that	O
looks	O
like	O
a	O
computer	O
with	O
the	O
Microsoft	B-Application
Windows	I-Application
operating	I-Application
system	I-Application
;	O
Windows-based	O
software	O
can	O
be	O
run	O
on	O
the	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
In	O
hardware	B-General_Concept
virtualization	I-General_Concept
,	O
the	O
host	B-Operating_System
machine	I-Operating_System
is	O
the	O
machine	O
that	O
is	O
used	O
by	O
the	O
virtualization	B-General_Concept
and	O
the	O
guest	O
machine	O
is	O
the	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
The	O
words	O
host	O
and	O
guest	O
are	O
used	O
to	O
distinguish	O
the	O
software	O
that	O
runs	O
on	O
the	O
physical	O
machine	O
from	O
the	O
software	O
that	O
runs	O
on	O
the	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
The	O
software	O
or	O
firmware	B-Application
that	O
creates	O
a	O
virtual	B-Architecture
machine	I-Architecture
on	O
the	O
host	O
hardware	B-Architecture
is	O
called	O
a	O
hypervisor	B-Operating_System
or	O
virtual	B-Operating_System
machine	I-Operating_System
monitor	I-Operating_System
.	O
</s>
<s>
Different	O
types	O
of	O
hardware	B-General_Concept
virtualization	I-General_Concept
include	O
:	O
</s>
<s>
Full	B-Architecture
virtualization	I-Architecture
–	O
Almost	O
complete	O
simulation	O
of	O
the	O
actual	O
hardware	B-Architecture
to	O
allow	O
software	O
environments	O
,	O
including	O
a	O
guest	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
and	O
its	O
apps	O
,	O
to	O
run	O
unmodified	O
.	O
</s>
<s>
Paravirtualization	O
–	O
The	O
guest	O
apps	O
are	O
executed	O
in	O
their	O
own	O
isolated	O
domains	O
,	O
as	O
if	O
they	O
are	O
running	O
on	O
a	O
separate	O
system	O
,	O
but	O
a	O
hardware	B-Architecture
environment	O
is	O
not	O
simulated	O
.	O
</s>
<s>
Hardware-assisted	B-General_Concept
virtualization	I-General_Concept
is	O
a	O
way	O
of	O
improving	O
overall	O
efficiency	O
of	O
virtualization	B-General_Concept
.	O
</s>
<s>
It	O
involves	O
CPUs	O
that	O
provide	O
support	O
for	O
virtualization	B-General_Concept
in	O
hardware	B-Architecture
,	O
and	O
other	O
hardware	B-Architecture
components	O
that	O
help	O
improve	O
the	O
performance	O
of	O
a	O
guest	O
environment	O
.	O
</s>
<s>
Hardware	B-General_Concept
virtualization	I-General_Concept
can	O
be	O
viewed	O
as	O
part	O
of	O
an	O
overall	O
trend	O
in	O
enterprise	O
IT	O
that	O
includes	O
autonomic	B-Architecture
computing	I-Architecture
,	O
a	O
scenario	O
in	O
which	O
the	O
IT	O
environment	O
will	O
be	O
able	O
to	O
manage	O
itself	O
based	O
on	O
perceived	O
activity	O
,	O
and	O
utility	B-Operating_System
computing	I-Operating_System
,	O
in	O
which	O
computer	O
processing	B-General_Concept
power	I-General_Concept
is	O
seen	O
as	O
a	O
utility	O
that	O
clients	O
can	O
pay	O
for	O
only	O
as	O
needed	O
.	O
</s>
<s>
The	O
usual	O
goal	O
of	O
virtualization	B-General_Concept
is	O
to	O
centralize	O
administrative	O
tasks	O
while	O
improving	O
scalability	B-Architecture
and	O
overall	O
hardware-resource	O
utilization	O
.	O
</s>
<s>
With	O
virtualization	B-General_Concept
,	O
several	O
operating	B-General_Concept
systems	I-General_Concept
can	O
be	O
run	O
in	O
parallel	O
on	O
a	O
single	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
.	O
</s>
<s>
Using	O
virtualization	B-General_Concept
,	O
an	O
enterprise	O
can	O
better	O
manage	O
updates	O
and	O
rapid	O
changes	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
applications	O
without	O
disrupting	O
the	O
user	O
.	O
</s>
<s>
"	O
Ultimately	O
,	O
virtualization	B-General_Concept
dramatically	O
improves	O
the	O
efficiency	O
and	O
availability	O
of	O
resources	O
and	O
applications	O
in	O
an	O
organization	O
.	O
</s>
<s>
Hardware	B-General_Concept
virtualization	I-General_Concept
is	O
not	O
the	O
same	O
as	O
hardware	B-Architecture
emulation	B-Application
.	O
</s>
<s>
In	O
hardware	B-Architecture
emulation	B-Application
,	O
a	O
piece	O
of	O
hardware	B-Architecture
imitates	O
another	O
,	O
while	O
in	O
hardware	B-General_Concept
virtualization	I-General_Concept
,	O
a	O
hypervisor	B-Operating_System
(	O
a	O
piece	O
of	O
software	O
)	O
imitates	O
a	O
particular	O
piece	O
of	O
computer	B-Architecture
hardware	I-Architecture
or	O
the	O
entire	O
computer	O
.	O
</s>
<s>
Furthermore	O
,	O
a	O
hypervisor	B-Operating_System
is	O
not	O
the	O
same	O
as	O
an	O
emulator	B-Application
;	O
both	O
are	O
computer	O
programs	O
that	O
imitate	O
hardware	B-Architecture
,	O
but	O
their	O
domain	O
of	O
use	O
in	O
language	O
differs	O
.	O
</s>
<s>
A	O
snapshot	O
is	O
a	O
state	O
of	O
a	O
virtual	B-Architecture
machine	I-Architecture
,	O
and	O
generally	O
its	O
storage	B-General_Concept
devices	I-General_Concept
,	O
at	O
an	O
exact	O
point	O
in	O
time	O
.	O
</s>
<s>
A	O
snapshot	O
enables	O
the	O
virtual	B-Architecture
machine	I-Architecture
's	O
state	O
at	O
the	O
time	O
of	O
the	O
snapshot	O
to	O
be	O
restored	O
later	O
,	O
effectively	O
undoing	O
any	O
changes	O
that	O
occurred	O
afterwards	O
.	O
</s>
<s>
This	O
capability	O
is	O
useful	O
as	O
a	O
backup	B-Protocol
technique	O
,	O
for	O
example	O
,	O
prior	O
to	O
performing	O
a	O
risky	O
operation	O
.	O
</s>
<s>
Virtual	B-Architecture
machines	I-Architecture
frequently	O
use	O
virtual	B-Application
disks	I-Application
for	O
their	O
storage	O
;	O
in	O
a	O
very	O
simple	O
example	O
,	O
a	O
10-gigabyte	O
hard	B-Device
disk	I-Device
drive	I-Device
is	O
simulated	O
with	O
a	O
10-gigabyte	O
flat	B-Application
file	I-Application
.	O
</s>
<s>
Thus	O
,	O
the	O
entire	O
stack	O
of	O
snapshots	O
is	O
virtually	O
a	O
single	O
coherent	O
disk	O
;	O
in	O
that	O
sense	O
,	O
creating	O
snapshots	O
works	O
similarly	O
to	O
the	O
incremental	B-General_Concept
backup	I-General_Concept
technique	O
.	O
</s>
<s>
Other	O
components	O
of	O
a	O
virtual	B-Architecture
machine	I-Architecture
can	O
also	O
be	O
included	O
in	O
a	O
snapshot	O
,	O
such	O
as	O
the	O
contents	O
of	O
its	O
random-access	B-Architecture
memory	I-Architecture
(	O
RAM	B-Architecture
)	O
,	O
BIOS	B-Operating_System
settings	I-Operating_System
,	O
or	O
its	O
configuration	O
settings	O
.	O
</s>
<s>
"	O
Save	O
state	O
"	O
feature	O
in	O
video	B-Device
game	I-Device
console	I-Device
emulators	B-Application
is	O
an	O
example	O
of	O
such	O
snapshots	O
.	O
</s>
<s>
The	O
snapshots	O
described	O
above	O
can	O
be	O
moved	O
to	O
another	O
host	B-Operating_System
machine	I-Operating_System
with	O
its	O
own	O
hypervisor	B-Operating_System
;	O
when	O
the	O
VM	O
is	O
temporarily	O
stopped	O
,	O
snapshotted	O
,	O
moved	O
,	O
and	O
then	O
resumed	O
on	O
the	O
new	O
host	O
,	O
this	O
is	O
known	O
as	O
migration	O
.	O
</s>
<s>
However	O
,	O
in	O
this	O
case	O
,	O
the	O
VM	O
continues	O
operation	O
from	O
the	O
last-known	O
coherent	O
state	O
,	O
rather	O
than	O
the	O
current	O
state	O
,	O
based	O
on	O
whatever	O
materials	O
the	O
backup	B-Protocol
server	O
was	O
last	O
provided	O
with	O
.	O
</s>
<s>
A	O
video	B-Device
game	I-Device
console	I-Device
emulator	B-Application
is	O
a	O
program	O
that	O
allows	O
a	O
personal	B-Device
computer	I-Device
or	O
video	B-Device
game	I-Device
console	I-Device
to	O
emulate	O
a	O
different	O
video	B-Device
game	I-Device
console	I-Device
's	O
behavior	O
.	O
</s>
<s>
Video	B-Device
game	I-Device
console	I-Device
emulators	B-Application
and	O
hypervisors	B-Operating_System
both	O
perform	O
hardware	B-General_Concept
virtualization	I-General_Concept
;	O
words	O
like	O
"	O
virtualization	B-General_Concept
"	O
,	O
"	O
virtual	B-Architecture
machine	I-Architecture
"	O
,	O
"	O
host	O
"	O
and	O
"	O
guest	O
"	O
are	O
not	O
used	O
in	O
conjunction	O
with	O
console	O
emulators	B-Application
.	O
</s>
<s>
Nested	O
virtualization	B-General_Concept
refers	O
to	O
the	O
ability	O
of	O
running	O
a	O
virtual	B-Architecture
machine	I-Architecture
within	O
another	O
,	O
having	O
this	O
general	O
concept	O
extendable	O
to	O
an	O
arbitrary	O
depth	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
nested	O
virtualization	B-General_Concept
refers	O
to	O
running	O
one	O
or	O
more	O
hypervisors	B-Operating_System
inside	O
another	O
hypervisor	B-Operating_System
.	O
</s>
<s>
Nature	O
of	O
a	O
nested	O
guest	O
virtual	B-Architecture
machine	I-Architecture
does	O
not	O
need	O
not	O
be	O
homogeneous	O
with	O
its	O
host	O
virtual	B-Architecture
machine	I-Architecture
;	O
for	O
example	O
,	O
application	B-Operating_System
virtualization	I-Operating_System
can	O
be	O
deployed	O
within	O
a	O
virtual	B-Architecture
machine	I-Architecture
created	O
by	O
using	O
hardware	B-General_Concept
virtualization	I-General_Concept
.	O
</s>
<s>
Nested	O
virtualization	B-General_Concept
becomes	O
more	O
necessary	O
as	O
widespread	O
operating	B-General_Concept
systems	I-General_Concept
gain	O
built-in	O
hypervisor	B-Operating_System
functionality	O
,	O
which	O
in	O
a	O
virtualized	B-General_Concept
environment	O
can	O
be	O
used	O
only	O
if	O
the	O
surrounding	O
hypervisor	B-Operating_System
supports	O
nested	O
virtualization	B-General_Concept
;	O
for	O
example	O
,	O
Windows	B-Device
7	I-Device
is	O
capable	O
of	O
running	O
Windows	B-Application
XP	I-Application
applications	O
inside	O
a	O
built-in	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Furthermore	O
,	O
moving	O
already	O
existing	O
virtualized	B-General_Concept
environments	O
into	O
a	O
cloud	B-Architecture
,	O
following	O
the	O
Infrastructure	B-General_Concept
as	I-General_Concept
a	I-General_Concept
Service	I-General_Concept
(	O
IaaS	B-General_Concept
)	O
approach	O
,	O
is	O
much	O
more	O
complicated	O
if	O
the	O
destination	O
IaaS	B-General_Concept
platform	O
does	O
not	O
support	O
nested	O
virtualization	B-General_Concept
.	O
</s>
<s>
The	O
way	O
nested	O
virtualization	B-General_Concept
can	O
be	O
implemented	O
on	O
a	O
particular	O
computer	B-General_Concept
architecture	I-General_Concept
depends	O
on	O
supported	O
hardware-assisted	B-General_Concept
virtualization	I-General_Concept
capabilities	O
.	O
</s>
<s>
If	O
a	O
particular	O
architecture	O
does	O
not	O
provide	O
hardware	B-Architecture
support	O
required	O
for	O
nested	O
virtualization	B-General_Concept
,	O
various	O
software	O
techniques	O
are	O
employed	O
to	O
enable	O
it	O
.	O
</s>
<s>
Over	O
time	O
,	O
more	O
architectures	O
gain	O
required	O
hardware	B-Architecture
support	O
;	O
for	O
example	O
,	O
since	O
the	O
Haswell	B-Device
microarchitecture	I-Device
(	O
announced	O
in	O
2013	O
)	O
,	O
Intel	O
started	O
to	O
include	O
VMCS	O
shadowing	O
as	O
a	O
technology	O
that	O
accelerates	O
nested	O
virtualization	B-General_Concept
.	O
</s>
<s>
Virtual	B-Architecture
machines	I-Architecture
running	O
proprietary	O
operating	B-General_Concept
systems	I-General_Concept
require	O
licensing	O
,	O
regardless	O
of	O
the	O
host	B-Operating_System
machine	I-Operating_System
's	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
installing	O
Microsoft	B-Application
Windows	I-Application
into	O
a	O
VM	O
guest	O
requires	O
its	O
licensing	O
requirements	O
to	O
be	O
satisfied	O
.	O
</s>
<s>
Desktop	O
virtualization	B-General_Concept
is	O
the	O
concept	O
of	O
separating	O
the	O
logical	O
desktop	O
from	O
the	O
physical	O
machine	O
.	O
</s>
<s>
One	O
form	O
of	O
desktop	O
virtualization	B-General_Concept
,	O
virtual	O
desktop	O
infrastructure	O
(	O
VDI	O
)	O
,	O
can	O
be	O
thought	O
of	O
as	O
a	O
more	O
advanced	O
form	O
of	O
hardware	B-General_Concept
virtualization	I-General_Concept
.	O
</s>
<s>
Rather	O
than	O
interacting	O
with	O
a	O
host	O
computer	O
directly	O
via	O
a	O
keyboard	O
,	O
mouse	O
,	O
and	O
monitor	O
,	O
the	O
user	O
interacts	O
with	O
the	O
host	O
computer	O
using	O
another	O
desktop	O
computer	O
or	O
a	O
mobile	O
device	O
by	O
means	O
of	O
a	O
network	O
connection	O
,	O
such	O
as	O
a	O
LAN	B-General_Concept
,	O
Wireless	B-Architecture
LAN	I-Architecture
or	O
even	O
the	O
Internet	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
host	O
computer	O
in	O
this	O
scenario	O
becomes	O
a	O
server	B-Application
computer	I-Application
capable	O
of	O
hosting	O
multiple	O
virtual	B-Architecture
machines	I-Architecture
at	O
the	O
same	O
time	O
for	O
multiple	O
users	O
.	O
</s>
<s>
As	O
organizations	O
continue	O
to	O
virtualize	B-General_Concept
and	O
converge	O
their	O
data	O
center	O
environment	O
,	O
client	B-Protocol
architectures	O
also	O
continue	O
to	O
evolve	O
in	O
order	O
to	O
take	O
advantage	O
of	O
the	O
predictability	O
,	O
continuity	O
,	O
and	O
quality	O
of	O
service	O
delivered	O
by	O
their	O
converged	B-General_Concept
infrastructure	I-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
companies	O
like	O
HP	O
and	O
IBM	O
provide	O
a	O
hybrid	O
VDI	O
model	O
with	O
a	O
range	O
of	O
virtualization	B-General_Concept
software	O
and	O
delivery	O
models	O
to	O
improve	O
upon	O
the	O
limitations	O
of	O
distributed	B-Architecture
client	I-Architecture
computing	I-Architecture
.	O
</s>
<s>
Selected	O
client	B-Protocol
environments	O
move	O
workloads	O
from	O
PCs	B-Device
and	O
other	O
devices	O
to	O
data	O
center	O
servers	O
,	O
creating	O
well-managed	O
virtual	O
clients	O
,	O
with	O
applications	O
and	O
client	B-Protocol
operating	O
environments	O
hosted	O
on	O
servers	O
and	O
storage	O
in	O
the	O
data	O
center	O
.	O
</s>
<s>
For	O
users	O
,	O
this	O
means	O
they	O
can	O
access	O
their	O
desktop	O
from	O
any	O
location	O
,	O
without	O
being	O
tied	O
to	O
a	O
single	O
client	B-Protocol
device	O
.	O
</s>
<s>
Since	O
the	O
resources	O
are	O
centralized	O
,	O
users	O
moving	O
between	O
work	O
locations	O
can	O
still	O
access	O
the	O
same	O
client	B-Protocol
environment	O
with	O
their	O
applications	O
and	O
data	O
.	O
</s>
<s>
For	O
IT	O
administrators	O
,	O
this	O
means	O
a	O
more	O
centralized	O
,	O
efficient	O
client	B-Protocol
environment	O
that	O
is	O
easier	O
to	O
maintain	O
and	O
able	O
to	O
more	O
quickly	O
respond	O
to	O
the	O
changing	O
needs	O
of	O
the	O
user	O
and	O
business	O
.	O
</s>
<s>
Another	O
form	O
,	O
session	O
virtualization	B-General_Concept
,	O
allows	O
multiple	O
users	O
to	O
connect	O
and	O
log	B-General_Concept
into	I-General_Concept
a	O
shared	O
but	O
powerful	O
computer	O
over	O
the	O
network	O
and	O
use	O
it	O
simultaneously	O
.	O
</s>
<s>
With	O
multiseat	B-Operating_System
configuration	I-Operating_System
,	O
session	O
virtualization	B-General_Concept
can	O
be	O
accomplished	O
using	O
a	O
single	O
PC	O
with	O
multiple	O
monitors	O
,	O
keyboards	O
,	O
and	O
mice	O
connected	O
.	O
</s>
<s>
Thin	B-Device
clients	I-Device
,	O
which	O
are	O
seen	O
in	O
desktop	O
virtualization	B-General_Concept
,	O
are	O
simple	O
and/or	O
cheap	O
computers	O
that	O
are	O
primarily	O
designed	O
to	O
connect	O
to	O
the	O
network	O
.	O
</s>
<s>
They	O
may	O
lack	O
significant	O
hard	B-Device
disk	I-Device
storage	I-Device
space	I-Device
,	O
RAM	B-Architecture
or	O
even	O
processing	B-General_Concept
power	I-General_Concept
,	O
but	O
many	O
organizations	O
are	O
beginning	O
to	O
look	O
at	O
the	O
cost	O
benefits	O
of	O
eliminating	O
“	O
thick	O
client	B-Protocol
”	O
desktops	O
that	O
are	O
packed	O
with	O
software	O
(	O
and	O
require	O
software	O
licensing	O
fees	O
)	O
and	O
making	O
more	O
strategic	O
investments	O
.	O
</s>
<s>
Desktop	O
virtualization	B-General_Concept
simplifies	O
software	O
versioning	O
and	O
patch	O
management	O
,	O
where	O
the	O
new	O
image	O
is	O
simply	O
updated	O
on	O
the	O
server	O
,	O
and	O
the	O
desktop	O
gets	O
the	O
updated	O
version	O
when	O
it	O
reboots	O
.	O
</s>
<s>
Moving	O
virtualized	B-General_Concept
desktops	O
into	O
the	O
cloud	B-Architecture
creates	O
hosted	O
virtual	O
desktops	O
(	O
HVDs	O
)	O
,	O
in	O
which	O
the	O
desktop	O
images	O
are	O
centrally	O
managed	O
and	O
maintained	O
by	O
a	O
specialist	O
hosting	O
firm	O
.	O
</s>
<s>
Benefits	O
include	O
scalability	B-Architecture
and	O
the	O
reduction	O
of	O
capital	O
expenditure	O
,	O
which	O
is	O
replaced	O
by	O
a	O
monthly	O
operational	O
cost	O
.	O
</s>
<s>
Operating-system-level	O
virtualization	B-General_Concept
,	O
also	O
known	O
as	O
containerization	B-General_Concept
,	O
refers	O
to	O
an	O
operating	B-General_Concept
system	I-General_Concept
feature	O
in	O
which	O
the	O
kernel	B-Operating_System
allows	O
the	O
existence	O
of	O
multiple	O
isolated	O
user-space	B-Operating_System
instances	O
.	O
</s>
<s>
Such	O
instances	O
,	O
called	O
containers	O
,	O
partitions	O
,	O
virtual	O
environments	O
(	O
VEs	O
)	O
or	O
jails	O
(	O
FreeBSD	B-Language
jail	I-Language
or	O
chroot	B-Application
jail	I-Application
)	O
,	O
may	O
look	O
like	O
real	O
computers	O
from	O
the	O
point	O
of	O
view	O
of	O
programs	O
running	O
in	O
them	O
.	O
</s>
<s>
A	O
computer	O
program	O
running	O
on	O
an	O
ordinary	O
operating	B-General_Concept
system	I-General_Concept
can	O
see	O
all	O
resources	O
(	O
connected	O
devices	O
,	O
files	O
and	O
folders	O
,	O
network	B-General_Concept
shares	I-General_Concept
,	O
CPU	O
power	O
,	O
quantifiable	O
hardware	B-Architecture
capabilities	O
)	O
of	O
that	O
computer	O
.	O
</s>
<s>
Containerization	B-General_Concept
started	O
gaining	O
prominence	O
in	O
2014	O
,	O
with	O
the	O
introduction	O
of	O
Docker	B-Language
.	O
</s>
