<s>
In	O
computing	O
,	O
a	O
server	O
is	O
a	O
piece	O
of	O
computer	B-Architecture
hardware	I-Architecture
or	O
software	O
(	O
computer	B-Application
program	I-Application
)	O
that	O
provides	O
functionality	O
for	O
other	O
programs	O
or	O
devices	O
,	O
called	O
"	O
clients.	O
"	O
</s>
<s>
This	O
architecture	B-Architecture
is	O
called	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
model	I-Operating_System
.	O
</s>
<s>
Servers	O
can	O
provide	O
various	O
functionalities	O
,	O
often	O
called	O
"	O
services	O
,	O
"	O
such	O
as	O
sharing	O
data	O
or	O
resources	B-General_Concept
among	O
multiple	O
clients	B-Protocol
or	O
performing	O
computations	O
for	O
a	O
client	B-Protocol
.	O
</s>
<s>
A	O
single	O
server	O
can	O
serve	O
multiple	O
clients	B-Protocol
,	O
and	O
a	O
single	O
client	B-Protocol
can	O
use	O
multiple	O
servers	O
.	O
</s>
<s>
A	O
client	B-Protocol
process	B-Operating_System
may	O
run	O
on	O
the	O
same	O
device	O
or	O
may	O
connect	O
over	O
a	O
network	O
to	O
a	O
server	O
on	O
a	O
different	O
device	O
.	O
</s>
<s>
Typical	O
servers	O
are	O
database	B-Application
servers	I-Application
,	O
file	B-Application
servers	I-Application
,	O
mail	B-Protocol
servers	I-Protocol
,	O
print	B-Application
servers	I-Application
,	O
web	B-Application
servers	I-Application
,	O
game	B-Application
servers	I-Application
,	O
and	O
application	B-Application
servers	I-Application
.	O
</s>
<s>
Client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
systems	O
are	O
usually	O
most	O
frequently	O
implemented	O
by	O
(	O
and	O
often	O
identified	O
with	O
)	O
the	O
request	B-Protocol
–	I-Protocol
response	I-Protocol
model	O
:	O
a	O
client	B-Protocol
sends	O
a	O
request	O
to	O
the	O
server	O
,	O
which	O
performs	O
some	O
action	O
and	O
sends	O
a	O
response	O
back	O
to	O
the	O
client	B-Protocol
,	O
typically	O
with	O
a	O
result	O
or	O
acknowledgment	O
.	O
</s>
<s>
Designating	O
a	O
computer	O
as	O
"	O
server-class	O
hardware	B-Architecture
"	O
implies	O
that	O
it	O
is	O
specialized	O
for	O
running	O
servers	O
on	O
it	O
.	O
</s>
<s>
This	O
often	O
implies	O
that	O
it	O
is	O
more	O
powerful	O
and	O
reliable	O
than	O
standard	O
personal	B-Device
computers	I-Device
,	O
but	O
alternatively	O
,	O
large	O
computing	B-Architecture
clusters	I-Architecture
may	O
be	O
composed	O
of	O
many	O
relatively	O
simple	O
,	O
replaceable	O
server	O
components	O
.	O
</s>
<s>
In	O
computing	O
,	O
"	O
server	O
"	O
dates	O
at	O
least	O
to	O
RFC	O
5	O
(	O
1969	O
)	O
,	O
one	O
of	O
the	O
earliest	O
documents	O
describing	O
ARPANET	O
(	O
the	O
predecessor	O
of	O
Internet	O
)	O
,	O
and	O
is	O
contrasted	O
with	O
"	O
user	O
"	O
,	O
distinguishing	O
two	O
types	O
of	O
host	B-Device
:	O
"	O
server-host	O
"	O
and	O
"	O
user-host	O
"	O
.	O
</s>
<s>
The	O
use	O
of	O
"	O
serving	O
"	O
also	O
dates	O
to	O
early	O
documents	O
,	O
such	O
as	O
RFC	O
4	O
,	O
contrasting	O
"	O
serving-host	O
"	O
with	O
"	O
using-host	O
"	O
.	O
</s>
<s>
The	O
Jargon	O
File	O
defines	O
""	O
in	O
the	O
common	O
sense	O
of	O
a	O
process	B-Operating_System
performing	O
service	O
for	O
requests	O
,	O
usually	O
remote	O
,	O
with	O
the	O
1981	O
(	O
)	O
version	O
reading	O
:	O
</s>
<s>
Strictly	O
speaking	O
,	O
the	O
term	O
server	O
refers	O
to	O
a	O
computer	B-Application
program	I-Application
or	O
process	B-Operating_System
(	O
running	O
program	O
)	O
.	O
</s>
<s>
On	O
a	O
network	O
,	O
such	O
a	O
device	O
is	O
called	O
a	O
host	B-Device
.	O
</s>
<s>
Alternatively	O
,	O
it	O
may	O
refer	O
to	O
a	O
computer	B-Application
program	I-Application
that	O
turns	O
a	O
computer	O
into	O
a	O
server	O
,	O
e.g.	O
</s>
<s>
For	O
instance	O
,	O
web	B-Application
servers	I-Application
"	O
serve	O
 [ up ] 	O
web	O
pages	O
to	O
users	O
"	O
or	O
"	O
service	O
their	O
requests	O
"	O
.	O
</s>
<s>
The	O
server	O
is	O
part	O
of	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
model	I-Operating_System
;	O
in	O
this	O
model	O
,	O
a	O
server	O
serves	O
data	O
for	O
clients	B-Protocol
.	O
</s>
<s>
The	O
nature	O
of	O
communication	O
between	O
a	O
client	B-Protocol
and	O
server	O
is	O
request	B-Protocol
and	I-Protocol
response	I-Protocol
.	O
</s>
<s>
In	O
principle	O
,	O
any	O
computerized	O
process	B-Operating_System
that	O
can	O
be	O
used	O
or	O
called	O
by	O
another	O
process	B-Operating_System
(	O
particularly	O
remotely	O
,	O
particularly	O
to	O
share	O
a	O
resource	O
)	O
is	O
a	O
server	O
,	O
and	O
the	O
calling	O
process	B-Operating_System
or	O
processes	O
is	O
a	O
client	B-Protocol
.	O
</s>
<s>
Thus	O
any	O
general-purpose	O
computer	O
connected	O
to	O
a	O
network	O
can	O
host	B-Device
servers	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
files	B-Operating_System
on	O
a	O
device	O
are	O
shared	O
by	O
some	O
process	B-Operating_System
,	O
that	O
process	B-Operating_System
is	O
a	O
file	B-Application
server	I-Application
.	O
</s>
<s>
Similarly	O
,	O
web	B-Application
server	I-Application
software	O
can	O
run	O
on	O
any	O
capable	O
computer	O
,	O
and	O
so	O
a	O
laptop	B-Device
or	O
a	O
personal	B-Device
computer	I-Device
can	O
host	B-Device
a	O
web	B-Application
server	I-Application
.	O
</s>
<s>
While	O
request	B-Protocol
–	I-Protocol
response	I-Protocol
is	O
the	O
most	O
common	O
client-server	B-Operating_System
design	O
,	O
there	O
are	O
others	O
,	O
such	O
as	O
the	O
publish	B-Operating_System
–	I-Operating_System
subscribe	I-Operating_System
pattern	I-Operating_System
.	O
</s>
<s>
In	O
the	O
publish-subscribe	B-Operating_System
pattern	I-Operating_System
,	O
clients	B-Protocol
register	O
with	O
a	O
pub-sub	O
server	O
,	O
subscribing	O
to	O
specified	O
types	O
of	O
messages	O
;	O
this	O
initial	O
registration	O
may	O
be	O
done	O
by	O
request-response	B-Protocol
.	O
</s>
<s>
Thereafter	O
,	O
the	O
pub-sub	O
server	O
forwards	O
matching	O
messages	O
to	O
the	O
clients	B-Protocol
without	O
any	O
further	O
requests	O
:	O
the	O
server	B-General_Concept
pushes	I-General_Concept
messages	O
to	O
the	O
client	B-Protocol
,	O
rather	O
than	O
the	O
client	B-Protocol
pulling	O
messages	O
from	O
the	O
server	O
as	O
in	O
request-response	B-Protocol
.	O
</s>
<s>
The	O
role	O
of	O
a	O
server	O
is	O
to	O
share	O
data	O
as	O
well	O
as	O
to	O
share	O
resources	B-General_Concept
and	O
distribute	O
work	O
.	O
</s>
<s>
A	O
server	B-Application
computer	I-Application
can	O
serve	O
its	O
own	O
computer	B-Application
programs	I-Application
as	O
well	O
;	O
depending	O
on	O
the	O
scenario	O
,	O
this	O
could	O
be	O
part	O
of	O
a	O
quid	O
pro	O
quo	O
transaction	O
,	O
or	O
simply	O
a	O
technical	O
possibility	O
.	O
</s>
<s>
Server	O
typePurposeClientsApplication	O
serverHosts	O
web	B-Application
apps	I-Application
(	O
computer	B-Application
programs	I-Application
that	O
run	O
inside	O
a	O
web	B-Application
browser	I-Application
)	O
allowing	O
users	O
in	O
the	O
network	O
to	O
run	O
and	O
use	O
them	O
,	O
without	O
having	O
to	O
install	O
a	O
copy	O
on	O
their	O
own	O
computers	O
.	O
</s>
<s>
Unlike	O
what	O
the	O
name	O
might	O
imply	O
,	O
these	O
servers	O
do	O
not	O
need	O
to	O
be	O
part	O
of	O
the	O
World	O
Wide	O
Web	O
;	O
any	O
local	B-General_Concept
network	I-General_Concept
would	O
do.Computers	O
with	O
a	O
web	O
browserCatalog	O
serverMaintains	O
an	O
index	O
or	O
table	O
of	O
contents	O
of	O
information	O
that	O
can	O
be	O
found	O
across	O
a	O
large	O
distributed	O
network	O
,	O
such	O
as	O
computers	O
,	O
users	O
,	O
files	B-Operating_System
shared	O
on	O
file	B-Application
servers	I-Application
,	O
and	O
web	B-Application
apps	I-Application
.	O
</s>
<s>
Directory	B-Application
servers	O
and	O
name	B-Protocol
servers	I-Protocol
are	O
examples	O
of	O
catalog	O
servers.Any	O
computer	B-Application
program	I-Application
that	O
needs	O
to	O
find	O
something	O
on	O
the	O
network	O
,	O
such	O
a	O
Domain	B-General_Concept
member	I-General_Concept
attempting	O
to	O
log	O
in	O
,	O
an	O
email	B-Protocol
client	I-Protocol
looking	O
for	O
an	O
email	O
address	O
,	O
or	O
a	O
user	O
looking	O
for	O
a	O
fileCommunications	O
serverMaintains	O
an	O
environment	O
needed	O
for	O
one	O
communication	O
endpoint	O
(	O
user	O
or	O
devices	O
)	O
to	O
find	O
other	O
endpoints	O
and	O
communicate	O
with	O
them	O
.	O
</s>
<s>
It	O
may	O
or	O
may	O
not	O
include	O
a	O
directory	B-Application
of	O
communication	O
endpoints	O
and	O
a	O
presence	O
detection	O
service	O
,	O
depending	O
on	O
the	O
openness	O
and	O
security	O
parameters	O
of	O
the	O
networkCommunication	O
endpoints	O
(	O
users	O
or	O
devices	O
)	O
Computing	O
serverShares	O
vast	O
amounts	O
of	O
computing	B-General_Concept
resources	I-General_Concept
,	O
especially	O
CPU	B-General_Concept
and	O
random-access	B-Architecture
memory	I-Architecture
,	O
over	O
a	O
network.Any	O
computer	B-Application
program	I-Application
that	O
needs	O
more	O
CPU	B-General_Concept
power	O
and	O
RAM	B-Architecture
than	O
a	O
personal	B-Device
computer	I-Device
can	O
probably	O
afford	O
.	O
</s>
<s>
The	O
client	B-Protocol
must	O
be	O
a	O
networked	O
computer	O
;	O
otherwise	O
,	O
there	O
would	O
be	O
no	O
client-server	O
model.Database	O
serverMaintains	O
and	O
shares	O
any	O
form	O
of	O
database	O
(	O
organized	O
collections	O
of	O
data	O
with	O
predefined	O
properties	O
that	O
may	O
be	O
displayed	O
in	O
a	O
table	O
)	O
over	O
a	O
network.Spreadsheets	O
,	O
accounting	B-Application
software	I-Application
,	O
asset	O
management	O
software	O
or	O
virtually	O
any	O
computer	B-Application
program	I-Application
that	O
consumes	O
well-organized	O
data	O
,	O
especially	O
in	O
large	O
volumesFax	O
serverShares	O
one	O
or	O
more	O
fax	O
machines	O
over	O
a	O
network	O
,	O
thus	O
eliminating	O
the	O
hassle	O
of	O
physical	O
accessAny	O
fax	O
sender	O
or	O
recipientFile	O
serverShares	O
files	B-Operating_System
and	O
folders	B-Application
,	O
storage	O
space	O
to	O
hold	O
files	B-Operating_System
and	O
folders	B-Application
,	O
or	O
both	O
,	O
over	O
a	O
networkNetworked	O
computers	O
are	O
the	O
intended	O
clients	B-Protocol
,	O
even	O
though	O
local	O
programs	O
can	O
be	O
clientsGame	O
serverEnables	O
several	O
computers	O
or	O
gaming	O
devices	O
to	O
play	O
multiplayer	O
video	O
gamesPersonal	O
computers	O
or	O
gaming	O
consolesMail	O
serverMakes	O
email	O
communication	O
possible	O
in	O
the	O
same	O
way	O
that	O
a	O
post	O
office	O
makes	O
snail	B-Application
mail	I-Application
communication	O
possibleSenders	O
and	O
recipients	O
of	O
emailMedia	O
serverShares	O
digital	O
video	O
or	O
digital	O
audio	O
over	O
a	O
network	O
through	O
media	O
streaming	O
(	O
transmitting	O
content	O
in	O
a	O
way	O
that	O
portions	O
received	O
can	O
be	O
watched	O
or	O
listened	O
to	O
as	O
they	O
arrive	O
,	O
as	O
opposed	O
to	O
downloading	O
an	O
entire	O
file	O
and	O
then	O
using	O
it	O
)	O
User-attended	O
personal	B-Device
computers	I-Device
equipped	O
with	O
a	O
monitor	O
and	O
a	O
speakerPrint	O
serverShares	O
one	O
or	O
more	O
printers	O
over	O
a	O
network	O
,	O
thus	O
eliminating	O
the	O
hassle	O
of	O
physical	O
accessComputers	O
in	O
need	O
of	O
printing	O
somethingSound	O
serverEnables	O
computer	B-Application
programs	I-Application
to	O
play	O
and	O
record	O
sound	O
,	O
individually	O
or	O
cooperativelyComputer	O
programs	O
of	O
the	O
same	O
computer	O
and	O
network	O
clients.Proxy	O
serverActs	O
as	O
an	O
intermediary	O
between	O
a	O
client	B-Protocol
and	O
a	O
server	O
,	O
accepting	O
incoming	O
traffic	O
from	O
the	O
client	B-Protocol
and	O
sending	O
it	O
to	O
the	O
server	O
.	O
</s>
<s>
Reasons	O
for	O
doing	O
so	O
include	O
content	O
control	O
and	O
filtering	O
,	O
improving	O
traffic	O
performance	O
,	O
preventing	O
unauthorized	O
network	O
access	O
or	O
simply	O
routing	O
the	O
traffic	O
over	O
a	O
large	O
and	O
complex	O
network.Any	O
networked	O
computerVirtual	O
serverShares	O
hardware	B-Architecture
and	O
software	O
resources	B-General_Concept
with	O
other	O
virtual	O
servers	O
.	O
</s>
<s>
It	O
exists	O
only	O
as	O
defined	O
within	O
specialized	O
software	O
called	O
hypervisor	B-Operating_System
.	O
</s>
<s>
The	O
hypervisor	B-Operating_System
presents	O
virtual	O
hardware	B-Architecture
to	O
the	O
server	O
as	O
if	O
it	O
were	O
real	O
physical	O
hardware	B-Architecture
.	O
</s>
<s>
Server	B-General_Concept
virtualization	I-General_Concept
allows	O
for	O
a	O
more	O
efficient	O
infrastructure.Any	O
networked	O
computerWeb	O
serverHosts	O
web	O
pages	O
.	O
</s>
<s>
A	O
web	B-Application
server	I-Application
is	O
what	O
makes	O
the	O
World	O
Wide	O
Web	O
possible	O
.	O
</s>
<s>
Each	O
website	O
has	O
one	O
or	O
more	O
web	B-Application
servers	I-Application
.	O
</s>
<s>
Almost	O
the	O
entire	O
structure	O
of	O
the	O
Internet	O
is	O
based	O
upon	O
a	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
model	I-Operating_System
.	O
</s>
<s>
High-level	O
root	B-Application
nameservers	I-Application
,	O
DNS	B-Protocol
,	O
and	O
routers	O
direct	O
the	O
traffic	O
on	O
the	O
internet	O
.	O
</s>
<s>
Hardware	B-Architecture
requirement	O
for	O
servers	O
vary	O
widely	O
,	O
depending	O
on	O
the	O
server	O
's	O
purpose	O
and	O
its	O
software	O
.	O
</s>
<s>
Servers	O
are	O
more	O
often	O
than	O
not	O
,	O
more	O
powerful	O
and	O
expensive	O
than	O
the	O
clients	B-Protocol
that	O
connect	O
to	O
them	O
.	O
</s>
<s>
Since	O
servers	O
are	O
usually	O
accessed	O
over	O
a	O
network	O
,	O
many	O
run	O
unattended	O
without	O
a	O
computer	B-Device
monitor	I-Device
or	O
input	O
device	O
,	O
audio	O
hardware	B-Architecture
and	O
USB	B-Protocol
interfaces	O
.	O
</s>
<s>
Many	O
servers	O
do	O
not	O
have	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
.	O
</s>
<s>
Remote	O
management	O
can	O
be	O
conducted	O
via	O
various	O
methods	O
including	O
Microsoft	B-Application
Management	I-Application
Console	I-Application
(	O
MMC	O
)	O
,	O
PowerShell	B-Application
,	O
SSH	B-Protocol
and	O
browser-based	B-Application
out-of-band	B-Application
management	I-Application
systems	O
such	O
as	O
Dell	O
's	O
iDRAC	O
or	O
HP	O
's	O
iLo	B-Device
.	O
</s>
<s>
Availability	O
would	O
have	O
to	O
be	O
very	O
high	O
,	O
making	O
hardware	B-Architecture
reliability	O
and	O
durability	O
extremely	O
important	O
.	O
</s>
<s>
Mission-critical	O
enterprise	B-Application
servers	I-Application
would	O
be	O
very	O
fault	B-General_Concept
tolerant	I-General_Concept
and	O
use	O
specialized	O
hardware	B-Architecture
with	O
low	O
failure	O
rates	O
in	O
order	O
to	O
maximize	O
uptime	B-Device
.	O
</s>
<s>
Servers	O
typically	O
include	O
hardware	B-Architecture
redundancy	O
such	O
as	O
dual	O
power	O
supplies	O
,	O
RAID	B-Architecture
disk	B-Device
systems	O
,	O
and	O
ECC	B-General_Concept
memory	I-General_Concept
,	O
along	O
with	O
extensive	O
pre-boot	B-Device
memory	O
testing	O
and	O
verification	O
.	O
</s>
<s>
Critical	O
components	O
might	O
be	O
hot	B-Device
swappable	I-Device
,	O
allowing	O
technicians	O
to	O
replace	O
them	O
on	O
the	O
running	O
server	O
without	O
shutting	O
it	O
down	O
,	O
and	O
to	O
guard	O
against	O
overheating	O
,	O
servers	O
might	O
have	O
more	O
powerful	O
fans	O
or	O
use	O
water	O
cooling	O
.	O
</s>
<s>
They	O
will	O
often	O
be	O
able	O
to	O
be	O
configured	O
,	O
powered	O
up	O
and	O
down	O
,	O
or	O
rebooted	O
remotely	O
,	O
using	O
out-of-band	B-Application
management	I-Application
,	O
typically	O
based	O
on	O
IPMI	O
.	O
</s>
<s>
Server	O
casings	O
are	O
usually	O
flat	O
and	O
wide	O
,	O
and	O
designed	O
to	O
be	O
rack-mounted	B-Application
,	O
either	O
on	O
19-inch	B-Application
racks	I-Application
or	O
on	O
Open	B-Application
Racks	I-Application
.	O
</s>
<s>
These	O
types	O
of	O
servers	O
are	O
often	O
housed	O
in	O
dedicated	O
data	B-Operating_System
centers	I-Operating_System
.	O
</s>
<s>
A	O
server	O
farm	O
or	O
server	B-Architecture
cluster	I-Architecture
is	O
a	O
collection	O
of	O
computer	B-Application
servers	I-Application
maintained	O
by	O
an	O
organization	O
to	O
supply	O
server	O
functionality	O
far	O
beyond	O
the	O
capability	O
of	O
a	O
single	O
device	O
.	O
</s>
<s>
Modern	O
data	B-Operating_System
centers	I-Operating_System
are	O
now	O
often	O
built	O
of	O
very	O
large	O
clusters	O
of	O
much	O
simpler	O
servers	O
,	O
and	O
there	O
is	O
a	O
collaborative	O
effort	O
,	O
Open	B-Operating_System
Compute	I-Operating_System
Project	I-Operating_System
around	O
this	O
concept	O
.	O
</s>
<s>
A	O
class	O
of	O
small	O
specialist	O
servers	O
called	O
network	B-Architecture
appliances	I-Architecture
are	O
generally	O
at	O
the	O
low	O
end	O
of	O
the	O
scale	O
,	O
often	O
being	O
smaller	O
than	O
common	O
desktop	O
computers	O
.	O
</s>
<s>
a	O
laptop	B-Device
.	O
</s>
<s>
In	O
contrast	O
to	O
large	O
data	B-Operating_System
centers	I-Operating_System
or	O
rack	O
servers	O
,	O
the	O
mobile	O
server	O
is	O
designed	O
for	O
on-the-road	O
or	O
ad	O
hoc	O
deployment	O
into	O
emergency	O
,	O
disaster	O
or	O
temporary	O
environments	O
where	O
traditional	O
servers	O
are	O
not	O
feasible	O
due	O
to	O
their	O
power	O
requirements	O
,	O
size	O
,	O
and	O
deployment	O
time	O
.	O
</s>
<s>
To	O
facilitate	O
portability	O
,	O
features	O
such	O
as	O
the	O
keyboard	B-Device
,	O
display	B-Device
,	O
battery	O
(	O
uninterruptible	O
power	O
supply	O
,	O
to	O
provide	O
power	O
redundancy	O
in	O
case	O
of	O
failure	O
)	O
,	O
and	O
mouse	O
are	O
all	O
integrated	O
into	O
the	O
chassis	O
.	O
</s>
<s>
On	O
the	O
Internet	O
,	O
the	O
dominant	O
operating	B-General_Concept
systems	I-General_Concept
among	O
servers	O
are	O
UNIX-like	O
open-source	B-Application
distributions	B-Application
,	O
such	O
as	O
those	O
based	O
on	O
Linux	B-Application
and	O
FreeBSD	B-Operating_System
,	O
with	O
Windows	B-Device
Server	I-Device
also	O
having	O
a	O
significant	O
share	O
.	O
</s>
<s>
Proprietary	O
operating	B-General_Concept
systems	I-General_Concept
such	O
as	O
z/OS	B-Application
and	O
macOS	B-Operating_System
Server	I-Operating_System
are	O
also	O
deployed	O
,	O
but	O
in	O
much	O
smaller	O
numbers	O
.	O
</s>
<s>
Specialist	O
server-oriented	O
operating	B-General_Concept
systems	I-General_Concept
have	O
traditionally	O
had	O
features	O
such	O
as	O
:	O
</s>
<s>
Advanced	O
backup	B-Protocol
facilities	O
to	O
permit	O
regular	O
and	O
frequent	O
online	O
backups	B-Protocol
of	O
critical	O
data	O
,	O
</s>
<s>
Advanced	O
detection	O
and	O
alerting	O
on	O
conditions	O
such	O
as	O
overheating	O
,	O
processor	O
and	O
disk	B-Device
failure	O
.	O
</s>
<s>
In	O
practice	O
,	O
today	O
many	O
desktop	O
and	O
server	O
operating	B-General_Concept
systems	I-General_Concept
share	O
similar	O
code	B-General_Concept
bases	I-General_Concept
,	O
differing	O
mostly	O
in	O
configuration	O
.	O
</s>
<s>
In	O
2010	O
,	O
data	B-Operating_System
centers	I-Operating_System
(	O
servers	O
,	O
cooling	O
,	O
and	O
other	O
electrical	O
infrastructure	O
)	O
were	O
responsible	O
for	O
1.1-1.5	O
%	O
of	O
electrical	O
energy	O
consumption	O
worldwide	O
and	O
1.7-2.2	O
%	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
Environmental	O
groups	O
have	O
placed	O
focus	O
on	O
the	O
carbon	O
emissions	O
of	O
data	B-Operating_System
centers	I-Operating_System
as	O
it	O
accounts	O
to	O
200	O
million	O
metric	O
tons	O
of	O
carbon	O
dioxide	O
in	O
a	O
year	O
.	O
</s>
