<s>
A	O
virtual	B-General_Concept
private	I-General_Concept
server	I-General_Concept
(	O
VPS	O
)	O
is	O
a	O
virtual	B-Architecture
machine	I-Architecture
sold	O
as	O
a	O
service	O
by	O
an	O
Internet	O
hosting	O
service	O
.	O
</s>
<s>
The	O
term	O
"	O
virtual	B-General_Concept
dedicated	I-General_Concept
server	I-General_Concept
"	O
(	O
VDS	O
)	O
also	O
has	O
a	O
similar	O
meaning	O
.	O
</s>
<s>
A	O
virtual	B-General_Concept
private	I-General_Concept
server	I-General_Concept
runs	O
its	O
own	O
copy	O
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
(	O
OS	O
)	O
,	O
and	O
customers	O
may	O
have	O
superuser-level	O
access	O
to	O
that	O
operating	B-General_Concept
system	I-General_Concept
instance	O
,	O
so	O
they	O
can	O
install	O
almost	O
any	O
software	O
that	O
runs	O
on	O
that	O
OS	O
.	O
</s>
<s>
However	O
,	O
as	O
virtual	O
servers	O
share	O
the	O
underlying	O
physical	O
hardware	O
with	O
other	O
VPSes	O
,	O
performance	O
may	O
be	O
lower	O
depending	O
on	O
the	O
workload	O
of	O
any	O
other	O
executing	O
virtual	B-Architecture
machines	I-Architecture
.	O
</s>
<s>
The	O
force	O
driving	O
server	B-General_Concept
virtualization	I-General_Concept
is	O
similar	O
to	O
that	O
which	O
led	O
to	O
the	O
development	O
of	O
time-sharing	B-General_Concept
and	O
multiprogramming	O
in	O
the	O
past	O
.	O
</s>
<s>
Although	O
the	O
resources	O
are	O
still	O
shared	O
,	O
as	O
under	O
the	O
time-sharing	B-General_Concept
model	O
,	O
virtualization	O
provides	O
a	O
higher	O
level	O
of	O
security	O
,	O
dependent	O
on	O
the	O
type	O
of	O
virtualization	O
used	O
,	O
as	O
the	O
individual	O
virtual	O
servers	O
are	O
mostly	O
isolated	O
from	O
each	O
other	O
and	O
may	O
run	O
their	O
own	O
full-fledged	O
operating	B-General_Concept
system	I-General_Concept
which	O
can	O
be	O
independently	O
rebooted	O
as	O
a	O
virtual	O
instance	O
.	O
</s>
<s>
Partitioning	O
a	O
single	O
server	O
to	O
appear	O
as	O
multiple	O
servers	O
has	O
been	O
increasingly	O
common	O
on	O
microcomputers	B-Architecture
since	O
the	O
release	O
of	O
VMware	B-Operating_System
ESX	I-Operating_System
Server	I-Operating_System
in	O
2001	O
.	O
</s>
<s>
The	O
physical	O
server	O
typically	O
runs	O
a	O
hypervisor	B-Operating_System
which	O
is	O
tasked	O
with	O
creating	O
,	O
releasing	O
,	O
and	O
managing	O
the	O
resources	O
of	O
"	O
guest	O
"	O
operating	B-General_Concept
systems	I-General_Concept
,	O
or	O
virtual	B-Architecture
machines	I-Architecture
.	O
</s>
<s>
These	O
guest	O
operating	B-General_Concept
systems	I-General_Concept
are	O
allocated	O
a	O
share	O
of	O
resources	O
of	O
the	O
physical	O
server	O
,	O
typically	O
in	O
a	O
manner	O
in	O
which	O
the	O
guest	O
is	O
not	O
aware	O
of	O
any	O
other	O
physical	O
resources	O
except	O
for	O
those	O
allocated	O
to	O
it	O
by	O
the	O
hypervisor	B-Operating_System
.	O
</s>
<s>
As	O
a	O
VPS	O
runs	O
its	O
own	O
copy	O
of	O
its	O
operating	B-General_Concept
system	I-General_Concept
,	O
customers	O
have	O
superuser-level	O
access	O
to	O
that	O
operating	B-General_Concept
system	I-General_Concept
instance	O
,	O
and	O
can	O
install	O
almost	O
any	O
software	O
that	O
runs	O
on	O
the	O
OS	O
;	O
however	O
,	O
due	O
to	O
the	O
number	O
of	O
virtualization	O
clients	O
typically	O
running	O
on	O
a	O
single	O
machine	O
,	O
a	O
VPS	O
generally	O
has	O
limited	O
processor	O
time	O
,	O
RAM	B-Architecture
,	O
and	O
disk	O
space	O
.	O
</s>
<s>
VPSs	O
may	O
be	O
used	O
to	O
decrease	O
hardware	O
costs	O
by	O
condensing	O
a	O
failover	B-General_Concept
cluster	I-General_Concept
to	O
a	O
single	O
machine	O
,	O
thus	O
decreasing	O
costs	O
whilst	O
providing	O
services	O
.	O
</s>
<s>
For	O
example	O
,	O
Windows	B-Device
Server	I-Device
2019	I-Device
requires	O
a	O
certificate	O
authority	O
and	O
a	O
domain	O
controller	O
to	O
exist	O
on	O
independent	O
servers	O
with	O
independent	O
instances	O
of	O
Windows	B-Device
Server	I-Device
.	O
</s>
<s>
This	O
is	O
because	O
additional	O
roles	O
and	O
features	O
add	O
areas	O
of	O
potential	O
failure	O
as	O
well	O
as	O
adding	O
security	O
risks	O
(	O
placing	O
a	O
certificate	O
authority	O
on	O
a	O
domain	O
controller	O
poses	O
the	O
potential	O
for	O
root	B-Application
access	I-Application
to	O
the	O
root	O
certificate	O
)	O
.	O
</s>
<s>
This	O
motivates	O
demand	O
for	O
virtual	B-General_Concept
private	I-General_Concept
servers	I-General_Concept
in	O
order	O
to	O
retain	O
conflicting	O
server	O
roles	O
and	O
features	O
on	O
a	O
single	O
hosting	O
machine	O
.	O
</s>
<s>
Also	O
,	O
virtual	B-Architecture
machine	I-Architecture
encrypted	O
networks	O
decrease	O
pass-through	O
risks	O
that	O
might	O
have	O
otherwise	O
discouraged	O
VPS	O
usage	O
as	O
a	O
hosting	O
server	O
.	O
</s>
<s>
Many	O
companies	O
offer	O
virtual	B-General_Concept
private	I-General_Concept
server	I-General_Concept
hosting	O
or	O
virtual	B-General_Concept
dedicated	I-General_Concept
server	I-General_Concept
hosting	O
as	O
an	O
extension	O
for	O
web	O
hosting	O
services	O
.	O
</s>
<s>
In	O
a	O
virtual	B-General_Concept
private	I-General_Concept
server	I-General_Concept
,	O
this	O
will	O
be	O
shared	O
bandwidth	O
and	O
a	O
fair	O
usage	O
policy	O
should	O
be	O
involved	O
.	O
</s>
