<s>
A	O
screensaver	B-General_Concept
(	O
or	O
screen	B-General_Concept
saver	I-General_Concept
)	O
is	O
a	O
computer	B-Application
program	I-Application
that	O
blanks	O
the	O
display	O
screen	O
or	O
fills	O
it	O
with	O
moving	O
images	O
or	O
patterns	O
when	O
the	O
computer	O
has	O
been	O
idle	O
for	O
a	O
designated	O
time	O
.	O
</s>
<s>
The	O
original	O
purpose	O
of	O
screensavers	B-General_Concept
was	O
to	O
prevent	O
phosphor	O
burn-in	O
on	O
CRT	B-Device
or	O
plasma	O
computer	B-Device
monitors	I-Device
(	O
hence	O
the	O
name	O
)	O
.	O
</s>
<s>
Though	O
most	O
modern	O
monitors	O
are	O
not	O
susceptible	O
to	O
this	O
issue	O
(	O
with	O
the	O
notable	O
exception	O
of	O
OLED	B-Device
technology	O
,	O
which	O
has	O
individual	O
pixels	O
vulnerable	O
to	O
burnout	O
)	O
,	O
screensaver	B-General_Concept
programs	O
are	O
still	O
used	O
for	O
other	O
purposes	O
.	O
</s>
<s>
Screensavers	B-General_Concept
are	O
often	O
set	O
up	O
to	O
offer	O
a	O
basic	O
layer	O
of	O
security	O
by	O
requiring	O
a	O
password	O
to	O
re-access	O
the	O
device	O
.	O
</s>
<s>
Some	O
screensaver	B-General_Concept
programs	O
also	O
use	O
otherwise-idle	O
computer	O
resources	O
to	O
do	O
useful	O
work	O
,	O
such	O
as	O
processing	O
for	O
volunteer	B-Operating_System
computing	I-Operating_System
projects	O
.	O
</s>
<s>
As	O
well	O
as	O
computers	O
,	O
modern	O
television	O
operating	B-General_Concept
systems	I-General_Concept
,	O
media	O
players	O
,	O
and	O
other	O
digital	O
entertainment	O
systems	O
may	O
include	O
optional	O
screensavers	B-General_Concept
.	O
</s>
<s>
Before	O
the	O
advent	O
of	O
LCD	B-Device
screens	I-Device
,	O
most	O
computer	B-Device
screens	I-Device
were	O
based	O
on	O
cathode	B-Device
ray	I-Device
tubes	I-Device
(	O
CRTs	O
)	O
.	O
</s>
<s>
When	O
the	O
same	O
image	O
is	O
displayed	O
on	O
a	O
CRT	B-Device
screen	I-Device
for	O
long	O
periods	O
,	O
the	O
properties	O
of	O
the	O
exposed	O
areas	O
of	O
the	O
phosphor	O
coating	O
on	O
the	O
inside	O
of	O
the	O
screen	O
gradually	O
and	O
permanently	O
change	O
,	O
eventually	O
leading	O
to	O
a	O
darkened	O
shadow	O
or	O
"	O
ghost	O
"	O
image	O
on	O
the	O
screen	O
,	O
called	O
a	O
screen	B-General_Concept
burn-in	I-General_Concept
.	O
</s>
<s>
For	O
CRTs	O
used	O
in	O
public	O
,	O
such	O
as	O
ATMs	O
and	O
railway	O
ticketing	O
machines	O
,	O
the	O
risk	O
of	O
burn-in	B-General_Concept
is	O
especially	O
high	O
because	O
a	O
stand-by	O
display	O
is	O
shown	O
whenever	O
the	O
machine	O
is	O
not	O
in	O
use	O
.	O
</s>
<s>
Older	O
machines	O
designed	O
without	O
burn-in	B-General_Concept
problems	O
taken	O
into	O
consideration	O
often	O
display	O
evidence	O
of	O
screen	O
damage	O
,	O
with	O
images	O
or	O
text	O
such	O
as	O
"	O
Please	O
insert	O
your	O
card	O
"	O
(	O
in	O
the	O
case	O
of	O
ATMs	O
)	O
visible	O
even	O
when	O
the	O
display	O
changes	O
while	O
the	O
machine	O
is	O
in	O
use	O
.	O
</s>
<s>
In	O
these	O
applications	O
,	O
burn-in	B-General_Concept
can	O
be	O
prevented	O
by	O
shifting	O
the	O
position	O
of	O
the	O
display	O
contents	O
every	O
few	O
seconds	O
,	O
or	O
by	O
having	O
a	O
number	O
of	O
different	O
images	O
that	O
are	O
changed	O
regularly	O
.	O
</s>
<s>
Later	O
CRTs	O
were	O
much	O
less	O
susceptible	O
to	O
burn-in	B-General_Concept
than	O
older	O
models	O
due	O
to	O
improvements	O
in	O
phosphor	O
coatings	O
,	O
and	O
because	O
modern	O
computer	O
images	O
are	O
generally	O
lower	O
contrast	O
than	O
the	O
stark	O
green	O
-	O
or	O
white-on-black	O
text	O
and	O
graphics	O
of	O
earlier	O
machines	O
.	O
</s>
<s>
LCD	B-Device
computer	I-Device
monitors	I-Device
,	O
including	O
the	O
display	O
panels	O
used	O
in	O
laptop	B-Device
computers	I-Device
,	O
are	O
not	O
susceptible	O
to	O
burn-in	B-General_Concept
because	O
the	O
image	O
is	O
not	O
directly	O
produced	O
by	O
phosphors	O
(	O
although	O
they	O
can	O
suffer	O
from	O
a	O
less	O
extreme	O
and	O
usually	O
non-permanent	O
form	O
of	O
image	B-Device
persistence	I-Device
)	O
.	O
</s>
<s>
While	O
modern	O
screens	O
are	O
not	O
susceptible	O
to	O
the	O
issues	O
discussed	O
above	O
,	O
screensavers	B-General_Concept
are	O
still	O
used	O
.	O
</s>
<s>
As	O
screensavers	B-General_Concept
are	O
generally	O
expected	O
to	O
activate	O
when	O
users	O
are	O
away	O
from	O
their	O
machines	O
,	O
many	O
screensavers	B-General_Concept
can	O
be	O
configured	O
to	O
ask	O
users	O
for	O
a	O
password	O
before	O
permitting	O
the	O
user	O
to	O
resume	O
work	O
.	O
</s>
<s>
Some	O
screensavers	B-General_Concept
activate	O
a	O
useful	O
background	O
task	O
,	O
such	O
as	O
a	O
virus	B-Application
scan	I-Application
or	O
a	O
volunteer	B-Operating_System
computing	I-Operating_System
application	O
(	O
such	O
as	O
the	O
SETI	B-Application
@home	I-Application
project	O
)	O
.	O
</s>
<s>
The	O
first	O
screensaver	B-General_Concept
was	O
allegedly	O
written	O
for	O
the	O
original	O
IBM	B-Device
PC	I-Device
by	O
John	O
Socha	O
,	O
best	O
known	O
for	O
creating	O
the	O
Norton	B-Application
Commander	I-Application
;	O
he	O
also	O
coined	O
the	O
term	O
screen	B-General_Concept
saver	I-General_Concept
.	O
</s>
<s>
The	O
screensaver	B-General_Concept
,	O
named	O
scrnsave	O
,	O
was	O
published	O
in	O
the	O
December	O
1983	O
issue	O
of	O
the	O
Softalk	O
magazine	O
.	O
</s>
<s>
By	O
1983	O
a	O
Zenith	O
Data	O
Systems	O
executive	O
included	O
"	O
screen-saver	O
"	O
among	O
the	O
new	O
Z-29	O
computer	B-General_Concept
terminal	I-General_Concept
's	O
features	O
,	O
telling	O
InfoWorld	O
that	O
it	O
"	O
blanks	O
out	O
the	O
display	O
after	O
15	O
minutes	O
of	O
nonactivity	O
,	O
preventing	O
burned-in	O
character	O
displays	O
"	O
.	O
</s>
<s>
The	O
first	O
screensaver	B-General_Concept
that	O
allowed	O
users	O
to	O
change	O
the	O
activating	O
time	O
was	O
released	O
on	O
Apple	O
's	O
Lisa	B-Device
,	O
in	O
1983	O
.	O
</s>
<s>
The	O
Atari	O
400	O
and	O
800	B-Device
's	I-Device
screens	O
would	O
also	O
go	O
through	O
random	O
screensaver-like	O
color	O
changes	O
if	O
they	O
were	O
left	O
inactive	O
for	O
about	O
8	O
minutes	O
.	O
</s>
<s>
Prior	O
to	O
these	O
computers	O
,	O
games	O
for	O
the	O
1977	O
Atari	B-General_Concept
VCS/2600	I-General_Concept
gaming	O
console	O
such	O
as	O
Combat	O
and	O
Breakout	B-Application
,	O
included	O
color	O
cycling	O
in	O
order	O
to	O
prevent	O
burn-in	B-General_Concept
of	O
game	O
images	O
into	O
1970s-era	O
televisions	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
first	O
model	O
of	O
the	O
TI-30	B-Device
calculator	O
from	O
1976	O
featured	O
a	O
screensaver	B-General_Concept
,	O
which	O
consisted	O
of	O
a	O
decimal	O
point	O
running	O
across	O
the	O
display	O
after	O
30	O
seconds	O
of	O
inactivity	O
.	O
</s>
<s>
This	O
was	O
chiefly	O
used	O
to	O
save	O
battery	O
power	O
,	O
as	O
the	O
TI-30	B-Device
LED	O
display	O
was	O
more	O
power	O
intensive	O
than	O
later	O
LCD	B-Device
models	O
.	O
</s>
<s>
These	O
are	O
examples	O
of	O
screensavers	B-General_Concept
in	O
ROM	B-Device
or	O
the	O
firmware	B-Application
of	O
a	O
computer	O
.	O
</s>
<s>
Android	B-Application
4.2	I-Application
introduced	O
"	O
daydreams	O
"	O
,	O
screensavers	B-General_Concept
that	O
activate	O
while	O
the	O
device	O
is	O
docked	B-Operating_System
or	O
charging	O
.	O
</s>
<s>
In	O
2015	O
the	O
screensaver	B-General_Concept
"	O
Event	O
listeners	O
"	O
of	O
van	O
den	O
Dorpel	O
became	O
the	O
first	O
work	O
of	O
art	O
that	O
was	O
purchased	O
by	O
a	O
museum	O
(	O
Museum	O
of	O
Applied	O
Arts	O
,	O
Vienna	O
)	O
using	O
the	O
cryptocurrency	O
bitcoin	B-Protocol
.	O
</s>
<s>
Modern	O
graphics	O
technologies	O
such	O
as	O
3D	O
computer	O
graphics	O
have	O
allowed	O
a	O
wide	O
variety	O
of	O
screensavers	B-General_Concept
to	O
be	O
made	O
.	O
</s>
<s>
Screensavers	B-General_Concept
with	O
realistic	O
3D	O
environments	O
can	O
be	O
programmed	O
and	O
run	O
on	O
modern	O
computers	O
.	O
</s>
<s>
Screensavers	B-General_Concept
are	O
usually	O
designed	O
and	O
coded	O
using	O
a	O
variety	O
of	O
programming	O
languages	O
as	O
well	O
as	O
graphics	O
interfaces	O
.	O
</s>
<s>
Typically	O
the	O
authors	O
of	O
screensavers	B-General_Concept
use	O
the	O
C	B-Language
or	O
C++	B-Language
programming	I-Language
languages	I-Language
,	O
along	O
with	O
Graphics	B-Operating_System
Device	I-Operating_System
Interface	I-Operating_System
(	O
GDI	O
)	O
,	O
such	O
as	O
OpenGL	B-Application
(	O
"	O
Open	B-Application
Graphics	I-Application
Library	I-Application
"	O
,	O
which	O
works	O
on	O
many	O
,	O
if	O
not	O
most	O
,	O
platforms	O
capable	O
of	O
3D	O
rendering	O
)	O
,	O
or	O
alternatives	O
such	O
as	O
Microsoft	B-Application
DirectX	I-Application
(	O
which	O
is	O
limited	O
to	O
Microsoft	O
platforms	O
,	O
mainly	O
Microsoft	B-Application
Windows	I-Application
and	O
the	O
Microsoft	B-Operating_System
Xbox	I-Operating_System
)	O
,	O
to	O
craft	O
their	O
final	O
products	O
.	O
</s>
<s>
Several	O
OS	B-Operating_System
X	I-Operating_System
screensavers	B-General_Concept
are	O
created	O
and	O
designed	O
using	O
Quartz	B-Operating_System
Composer	I-Operating_System
.	O
</s>
<s>
The	O
screensaver	B-General_Concept
interfaces	O
indirectly	O
with	O
the	O
operating	B-General_Concept
system	I-General_Concept
to	O
cause	O
the	O
physical	O
display	O
screen	O
to	O
be	O
overlaid	O
with	O
one	O
or	O
more	O
graphic	O
"	O
scenes	O
"	O
.	O
</s>
<s>
The	O
screensaver	B-General_Concept
typically	O
terminates	O
after	O
receiving	O
a	O
message	O
from	O
the	O
operating	B-General_Concept
system	I-General_Concept
that	O
a	O
key	O
has	O
been	O
pressed	O
or	O
the	O
mouse	O
has	O
been	O
moved	O
.	O
</s>
<s>
If	O
the	O
system	O
detects	O
inactivity	O
lasting	O
longer	O
than	O
the	O
time	O
specified	O
in	O
the	O
control	O
panel	O
,	O
check	O
if	O
the	O
active	O
program	O
is	O
a	O
simple	O
program	O
(	O
and	O
not	O
another	O
screensaver	B-General_Concept
)	O
by	O
sending	O
the	O
"	O
WM_SYSCOMMAND	O
"	O
message	O
with	O
the	O
"	O
SC_SCREENSAVE	O
"	O
argument	O
.	O
</s>
<s>
If	O
the	O
program	O
calls	O
in	O
response	O
the	O
standard	O
system	O
function	O
(	O
DefWindowProc	O
)	O
,	O
the	O
screensaver	B-General_Concept
defined	O
in	O
the	O
control	O
panel	O
screen	O
runs	O
.	O
</s>
<s>
A	O
Windows	O
screensaver	B-General_Concept
is	O
a	O
regular	O
Portable	O
Executable	B-Application
(	O
PE	O
)	O
with	O
the	O
.scr	B-General_Concept
file	O
extension	O
.	O
</s>
<s>
This	O
enables	O
malware	O
authors	O
to	O
add	O
"	O
.scr	B-General_Concept
"	O
to	O
the	O
name	O
of	O
any	O
win32	B-Library
executable	B-Application
file	I-Application
,	O
and	O
thereby	O
increase	O
likelihood	O
that	O
users	O
of	O
Microsoft	B-Application
Windows	I-Application
will	O
run	O
it	O
unintentionally	O
.	O
</s>
<s>
In	O
addition	O
,	O
this	O
program	O
should	O
support	O
the	O
following	O
command	B-Application
line	I-Application
parameters	O
:	O
</s>
<s>
Runs	O
the	O
screensaver	B-General_Concept
.	O
</s>
<s>
Previews	O
the	O
screensaver	B-General_Concept
as	O
child	O
of	O
window	O
.	O
</s>
<s>
Windows	O
95	O
screensavers	B-General_Concept
must	O
handle	O
it	O
.	O
</s>
<s>
Under	O
macOS	B-Operating_System
,	O
screensavers	B-General_Concept
are	O
regular	O
macOS	B-Operating_System
application	O
bundles	O
with	O
the	O
.saver	O
file	O
extension	O
.	O
</s>
<s>
Internally	O
,	O
the	O
screensaver	B-General_Concept
must	O
define	O
a	O
class	O
that	O
is	O
subclass	O
of	O
ScreenSaverView	O
.	O
</s>
<s>
The	O
new	O
class	O
must	O
be	O
assigned	O
as	O
NSPrincipalClass	O
in	O
the	O
xcode	O
project	O
,	O
so	O
that	O
when	O
the	O
screensaver	B-General_Concept
is	O
launched	O
by	O
the	O
system	O
,	O
this	O
class	O
gets	O
instantiated	O
.	O
</s>
<s>
As	O
one	O
of	O
the	O
first	O
screensavers	B-General_Concept
appeared	O
in	O
8-bit	B-Device
Atari	I-Device
computers	O
,	O
forcing	O
systemic	O
color	O
changes	O
when	O
the	O
computer	O
is	O
idle	O
lasting	O
a	O
few	O
minutes	O
(	O
different	O
times	O
depending	O
on	O
the	O
model	O
)	O
,	O
stored	O
in	O
the	O
system	O
ROM	B-Device
of	O
the	O
computer	O
.	O
</s>
<s>
Monitors	O
running	O
screensavers	B-General_Concept
consume	O
the	O
same	O
amount	O
of	O
power	O
as	O
when	O
running	O
normally	O
,	O
which	O
can	O
be	O
anywhere	O
from	O
a	O
few	O
watts	O
for	O
small	O
LCD	B-Device
monitors	I-Device
to	O
several	O
hundred	O
for	O
large	O
plasma	O
displays	O
.	O
</s>
<s>
A	O
power-saving	O
mode	O
for	O
monitors	O
is	O
usually	O
part	O
of	O
the	O
power	O
management	O
options	O
supported	O
in	O
most	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
,	O
though	O
it	O
must	O
also	O
be	O
supported	O
by	O
the	O
computer	O
hardware	O
and	O
monitor	O
itself	O
.	O
</s>
<s>
Using	O
a	O
screensaver	B-General_Concept
with	O
a	O
flat	O
panel	O
or	O
LCD	B-Device
screen	I-Device
not	O
powering	O
down	O
the	O
screen	O
can	O
actually	O
decrease	O
the	O
lifetime	O
of	O
the	O
display	O
,	O
since	O
the	O
fluorescent	O
backlight	O
remains	O
lit	O
and	O
ages	O
faster	O
than	O
it	O
would	O
if	O
the	O
screen	O
is	O
turned	O
off	O
and	O
on	O
frequently	O
.	O
</s>
<s>
A	O
typical	O
LCD	B-Device
screen	I-Device
loses	O
about	O
50%	O
of	O
its	O
brightness	O
during	O
a	O
normal	O
product	O
lifetime	O
.	O
</s>
<s>
In	O
most	O
cases	O
,	O
the	O
tube	O
is	O
an	O
integral	O
part	O
of	O
the	O
LCD	B-Device
and	O
the	O
entire	O
assembly	O
needs	O
to	O
be	O
replaced	O
.	O
</s>
<s>
Thus	O
the	O
term	O
"	O
screen	B-General_Concept
saver	I-General_Concept
"	O
is	O
now	O
something	O
of	O
a	O
misnomer	O
–	O
the	O
best	O
way	O
to	O
save	O
the	O
screen	O
and	O
also	O
save	O
electricity	O
consumed	O
by	O
screen	O
would	O
simply	O
be	O
to	O
have	O
the	O
computer	O
turn	O
off	O
the	O
monitor	O
.	O
</s>
<s>
Screensavers	B-General_Concept
displaying	O
complex	O
3D	O
graphics	O
might	O
even	O
add	O
to	O
overall	O
power	O
draw	O
.	O
</s>
<s>
After	B-Operating_System
Dark	I-Operating_System
was	O
an	O
early	O
screensaver	B-General_Concept
for	O
the	O
Macintosh	B-Device
platform	O
,	O
and	O
later	O
PC/Windows	O
,	O
which	O
prominently	O
featured	O
whimsical	O
designs	O
such	O
as	O
"	O
flying	B-Operating_System
toasters	I-Operating_System
"	O
.	O
</s>
<s>
Perhaps	O
in	O
response	O
to	O
the	O
workplace	O
environment	O
in	O
which	O
they	O
are	O
often	O
viewed	O
,	O
many	O
screensavers	B-General_Concept
continue	O
this	O
legacy	O
of	O
whimsy	O
by	O
populating	O
the	O
idle	O
monitor	O
with	O
animals	O
or	O
fish	O
,	O
games	O
,	O
and	O
visual	O
expressions	O
of	O
mathematics	O
equations	O
(	O
through	O
the	O
use	O
of	O
fractals	B-Application
,	O
Fourier	B-Algorithm
transforms	I-Algorithm
or	O
other	O
means	O
)	O
as	O
in	O
the	O
Electric	B-Algorithm
Sheep	I-Algorithm
screensaver	B-General_Concept
.	O
</s>
<s>
At	O
least	O
one	O
screensaver	B-General_Concept
,	O
Johnny	B-General_Concept
Castaway	I-General_Concept
told	O
a	O
humorous	O
animated	O
story	O
over	O
many	O
months	O
.	O
</s>
<s>
The	O
ability	O
of	O
screensavers	B-General_Concept
to	O
divert	O
and	O
entertain	O
is	O
used	O
for	O
promotion	O
,	O
especially	O
to	O
build	O
buzz	O
for	O
"	O
event-based	O
"	O
products	O
such	O
as	O
feature	O
films	O
.	O
</s>
<s>
The	O
screensaver	B-General_Concept
is	O
also	O
a	O
creative	O
outlet	O
for	O
computer	O
programmers	O
.	O
</s>
<s>
The	O
Unix-based	O
screensaver	B-General_Concept
XScreenSaver	B-General_Concept
collects	O
the	O
display	O
effects	O
of	O
other	O
Unix	B-Application
screensavers	B-General_Concept
,	O
which	O
are	O
termed	O
"	O
display	O
hacks	O
"	O
in	O
the	O
jargon	O
file	O
tradition	O
of	O
US	O
computer	O
science	O
academics	O
.	O
</s>
<s>
On	O
older	O
versions	O
of	O
Microsoft	B-Application
Windows	I-Application
the	O
native	O
screensaver	B-General_Concept
format	O
had	O
the	O
potential	O
to	O
install	O
a	O
virus	O
when	O
run	O
(	O
as	O
a	O
screen	B-General_Concept
saver	I-General_Concept
was	O
just	O
an	O
ordinary	O
application	O
with	O
a	O
different	O
extension	O
)	O
.	O
</s>
<s>
When	O
any	O
file	O
with	O
the	O
file	O
suffix	O
"	O
.scr	B-General_Concept
"	O
was	O
opened	O
,	O
for	O
example	O
from	O
an	O
e-mail	O
attachment	O
,	O
Windows	O
would	O
execute	O
the	O
.scr	B-General_Concept
(	O
screensaver	B-General_Concept
)	O
file	O
automatically	O
:	O
this	O
had	O
the	O
potential	O
to	O
allow	O
a	O
virus	O
or	O
malware	O
to	O
install	O
itself	O
.	O
</s>
<s>
On	O
August	O
5	O
,	O
2006	O
,	O
the	O
BBC	O
reported	O
that	O
"	O
free	B-General_Concept
screensavers	I-General_Concept
"	O
and	O
"	O
screensavers	B-General_Concept
"	O
respectively	O
were	O
the	O
first	O
and	O
third	O
most	O
likely	O
search	O
terms	O
to	O
return	O
links	O
to	O
malware	O
,	O
the	O
second	O
being	O
BearShare	B-Protocol
.	O
</s>
<s>
By	O
launching	O
the	O
"	O
bubbles	O
"	O
screensaver	B-General_Concept
executable	B-Application
through	O
the	O
bubbles.scr	O
/p65552	O
command-line	B-Application
parameter	O
,	O
it	O
runs	O
as	O
desktop	O
wallpaper	O
,	O
the	O
bubbles	O
are	O
smaller	O
,	O
and	O
there	O
are	O
more	O
bubbles	O
on	O
screen	O
.	O
</s>
