<s>
A	O
persistent	B-Protocol
world	I-Protocol
or	O
persistent	B-Protocol
state	I-Protocol
world	I-Protocol
(	O
PSW	O
)	O
is	O
a	O
virtual	B-Application
world	I-Application
which	O
,	O
by	O
the	O
definition	O
by	O
Richard	O
Bartle	O
,	O
"	O
continues	O
to	O
exist	O
and	O
develop	O
internally	O
even	O
when	O
there	O
are	O
no	O
people	O
interacting	O
with	O
it	O
"	O
.	O
</s>
<s>
The	O
first	O
virtual	B-Application
worlds	I-Application
were	O
text-based	O
and	O
often	O
called	O
MUDs	B-Application
,	O
but	O
the	O
term	O
is	O
frequently	O
used	O
in	O
relation	O
to	O
massively	B-Protocol
multiplayer	I-Protocol
online	I-Protocol
role-playing	I-Protocol
games	I-Protocol
(	O
MMORPGs	B-Protocol
)	O
and	O
pervasive	O
games	O
.	O
</s>
<s>
Examples	O
of	O
persistent	B-Protocol
worlds	I-Protocol
that	O
exist	O
in	O
video	O
games	O
include	O
Battle	O
Dawn	O
,	O
EVE	O
Online	O
,	O
and	O
Realms	O
of	O
Trinity	O
.	O
</s>
<s>
A	O
persistent	B-Protocol
world	I-Protocol
can	O
be	O
achieved	O
by	O
developing	O
and	O
maintaining	O
a	O
single	O
or	O
dynamic	O
instance	O
state	O
of	O
the	O
game	O
world	O
that	O
is	O
shared	O
and	O
viewed	O
by	O
all	O
players	O
around	O
the	O
clock	O
.	O
</s>
<s>
The	O
persistence	B-Application
of	O
a	O
world	O
can	O
be	O
subdivided	O
into	O
"	O
game	O
persistence	B-Application
"	O
,	O
"	O
world	O
persistence	B-Application
"	O
and	O
"	O
data	B-Application
persistence	I-Application
"	O
.	O
</s>
<s>
Data	B-Application
persistence	I-Application
ensures	O
that	O
any	O
world	O
data	O
is	O
not	O
lost	O
in	O
the	O
event	O
of	O
computer	O
system	O
failure	O
.	O
</s>
<s>
World	O
persistence	B-Application
means	O
the	O
world	O
continues	O
to	O
exist	O
and	O
is	O
available	O
to	O
players	O
when	O
they	O
want	O
to	O
access	O
it	O
.	O
</s>
<s>
Game	O
persistence	B-Application
refers	O
to	O
the	O
persistence	B-Application
of	O
game	O
events	O
within	O
the	O
world	O
(	O
a	O
Groundhog	O
Day	O
MUD	B-Application
is	O
a	O
virtual	B-Application
world	I-Application
where	O
the	O
entire	O
(	O
game	O
)	O
world	O
is	O
reset	O
periodically	O
)	O
.	O
</s>
<s>
When	O
referring	O
to	O
a	O
"	O
persistent	B-Protocol
world	I-Protocol
"	O
,	O
world	O
and	O
game	O
persistence	B-Application
are	O
sometimes	O
used	O
interchangeably	O
.	O
</s>
<s>
The	O
persistence	B-Application
criterion	O
is	O
the	O
trait	O
that	O
separates	O
virtual	B-Application
worlds	I-Application
from	O
other	O
types	O
of	O
video	O
games	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
pervasive	O
games	O
share	O
the	O
persistence	B-Application
trait	O
with	O
virtual	B-Application
worlds	I-Application
.	O
</s>
<s>
An	O
example	O
of	O
a	O
pervasive	O
game	O
that	O
makes	O
heavy	O
use	O
of	O
a	O
virtual	B-Application
world	I-Application
is	O
Can	O
You	O
See	O
Me	O
Now	O
?,	O
where	O
street	O
runners	O
exist	O
in	O
a	O
virtual	B-Application
world	I-Application
while	O
simultaneously	O
running	O
around	O
the	O
real	O
physical	O
world	O
;	O
the	O
game	O
was	O
persistent	O
during	O
play	O
,	O
as	O
well	O
as	O
the	O
virtual	B-Application
world	I-Application
.	O
</s>
<s>
To	O
give	O
the	O
illusion	O
that	O
the	O
game	O
world	O
is	O
always	O
available	O
,	O
persistence	B-Application
can	O
be	O
simulated	O
.	O
</s>
<s>
This	O
can	O
be	O
achieved	O
by	O
scheduling	O
when	O
players	O
are	O
allowed	O
to	O
play	O
,	O
around	O
times	O
when	O
the	O
world	O
is	O
offline	O
,	O
or	O
as	O
in	O
the	O
Animal	B-Application
Crossing	I-Application
series	I-Application
,	O
having	O
the	O
game	O
generate	O
events	O
that	O
could	O
have	O
happened	O
during	O
the	O
period	O
of	O
inactivity	O
.	O
</s>
<s>
Aside	O
from	O
virtual	B-Application
worlds	I-Application
,	O
the	O
simulation	O
of	O
a	O
persistent	B-Protocol
world	I-Protocol
is	O
also	O
possible	O
in	O
single	O
player	O
games	O
.	O
</s>
<s>
In	O
Noctis	B-Application
,	O
players	O
are	O
advised	O
to	O
turn	O
off	O
the	O
game	O
while	O
refueling	O
because	O
it	O
takes	O
so	O
long	O
.	O
</s>
<s>
A	O
form	O
of	O
simulated	O
persistence	B-Application
referred	O
to	O
as	O
"	O
pseudo-persistence	O
"	O
has	O
been	O
used	O
in	O
both	O
video	O
games	O
and	O
pervasive	O
games	O
.	O
</s>
<s>
Pseudo-persistence	O
means	O
making	O
relevant	O
world	O
data	O
available	O
when	O
the	O
relevant	O
players	O
reconnect	O
to	O
the	O
world	O
instance	O
.	O
</s>
<s>
In	O
a	O
mobile	B-Application
game	I-Application
,	O
a	O
virtual	B-Application
world	I-Application
might	O
exist	O
on	O
a	O
distributed	B-Architecture
collection	O
of	O
mobile	O
devices	O
.	O
</s>
<s>
In	O
the	O
video	O
game	O
Destiny	B-Application
,	O
a	O
World	O
Server	O
provides	O
the	O
persistent	B-Protocol
world	I-Protocol
data	O
for	O
the	O
game	O
instances	O
(	O
called	O
"	O
bubbles	O
"	O
)	O
,	O
which	O
are	O
created	O
on	O
demand	O
as	O
a	O
number	O
of	O
players	O
are	O
matched	O
to	O
play	O
the	O
game	O
together	O
..	O
</s>
<s>
The	O
term	O
'	O
persistent	B-Protocol
world	I-Protocol
 '	O
is	O
frequently	O
used	O
by	O
players	O
of	O
Neverwinter	B-Application
Nights	I-Application
(	O
2002	O
)	O
and	O
Neverwinter	B-Application
Nights	I-Application
2	I-Application
(	O
2006	O
)	O
to	O
refer	O
to	O
MMORPG-like	O
online	O
environments	O
created	O
using	O
the	O
toolkit	O
.	O
</s>
<s>
The	O
first	O
multi-player	O
game	O
to	O
demonstrate	O
on-line	O
persistence	B-Application
was	O
the	O
text-based	O
MUD1	B-Protocol
written	O
in	O
1978	O
by	O
Rob	O
Trubshaw	O
and	O
Richard	O
Bartle	O
.	O
</s>
<s>
The	O
subsequent	O
decade	O
saw	O
many	O
on-line	B-Application
worlds	I-Application
clone	O
this	O
template	O
,	O
but	O
all	O
featured	O
variations	O
on	O
timed	O
resets	O
and	O
reboots	O
or	O
did	O
not	O
allow	O
players	O
to	O
retain	O
objects	O
within	O
the	O
game	O
other	O
than	O
running	O
point	O
totals	O
such	O
as	O
treasure	O
or	O
experience	O
points	O
as	O
a	O
marker	O
of	O
progress	O
.	O
</s>
<s>
Avalon	B-Application
:	I-Application
The	I-Application
Legend	I-Application
Lives	I-Application
can	O
be	O
considered	O
the	O
first	O
game	O
to	O
introduce	O
a	O
true	O
persistent	B-Protocol
state	I-Protocol
world	I-Protocol
in	O
1989	O
.	O
</s>
<s>
Avalon	B-Application
pioneered	O
the	O
ability	O
for	O
items	O
to	O
be	O
retained	O
by	O
the	O
player	O
whilst	O
offline	O
while	O
the	O
Avalon	B-Application
realm	O
at	O
large	O
continued	O
24/7	O
with	O
only	O
a	O
morning	O
backup	O
to	O
mark	O
the	O
world	O
pausing	O
briefly	O
.	O
</s>
<s>
It	O
is	O
currently	O
the	O
longest	O
running	O
online	O
virtual	B-Application
world	I-Application
.	O
</s>
