<s>
A	O
multiple-sync	O
(	O
multisync	B-General_Concept
)	O
monitor	B-Device
,	O
also	O
known	O
as	O
a	O
multiscan	O
or	O
multimode	O
monitor	B-Device
,	O
is	O
a	O
raster-scan	O
analog	O
video	O
monitor	B-Device
that	O
can	O
properly	O
synchronise	O
with	O
multiple	O
horizontal	B-General_Concept
and	O
vertical	O
scan	O
rates	O
.	O
</s>
<s>
They	O
are	O
generally	O
used	O
for	O
computer	B-Device
displays	I-Device
,	O
but	O
sometimes	O
for	O
television	O
,	O
and	O
the	O
terminology	O
is	O
mostly	O
applied	O
to	O
CRT	B-Device
displays	I-Device
although	O
the	O
concept	O
applies	O
to	O
other	O
technologies	O
.	O
</s>
<s>
Multiscan	O
computer	B-Device
monitors	I-Device
appeared	O
during	O
the	O
mid	O
1980s	O
,	O
offering	O
flexibility	O
as	O
computer	O
video	O
hardware	O
shifted	O
from	O
producing	O
a	O
single	O
fixed	O
scan	O
rate	O
to	O
multiple	O
possible	O
scan	O
rates	O
.	O
</s>
<s>
"	O
MultiSync	B-General_Concept
"	O
specifically	O
was	O
a	O
trademark	O
of	O
one	O
of	O
NEC	O
's	O
first	O
multiple-sync	O
monitors	O
.	O
</s>
<s>
Early	O
home	O
computers	O
output	O
video	O
to	O
ordinary	O
televisions	O
or	O
composite	O
monitors	O
,	O
utilizing	O
television	O
display	O
standards	O
such	O
as	O
NTSC	O
,	O
PAL	B-Language
or	O
SECAM	O
.	O
</s>
<s>
These	O
display	O
standards	O
had	O
fixed	O
scan	O
rates	O
,	O
and	O
only	O
used	O
the	O
vertical	O
and	O
horizontal	B-General_Concept
sync	I-General_Concept
pulses	O
embedded	O
in	O
the	O
video	O
signals	O
to	O
ensure	O
synchronization	O
,	O
not	O
to	O
set	O
the	O
actual	O
scan	O
rates	O
.	O
</s>
<s>
Early	O
dedicated	O
computer	B-Device
monitors	I-Device
still	O
often	O
relied	O
on	O
fixed	O
scan	O
rates	O
.	O
</s>
<s>
IBM	O
's	O
original	O
1981	O
PC	B-Device
,	O
for	O
instance	O
,	O
was	O
sold	O
with	O
a	O
choice	O
of	O
two	O
video	O
cards	O
(	O
MDA	B-Device
and	O
CGA	B-Device
)	O
which	O
were	O
intended	O
for	O
use	O
with	O
custom	O
IBM	O
monitors	O
which	O
still	O
used	O
fixed	O
scan	O
rates	O
.	O
</s>
<s>
The	O
CGA	B-Device
timings	O
were	O
identical	O
to	O
NTSC	O
television	O
,	O
whereas	O
the	O
MDA	B-Device
card	I-Device
used	O
a	O
custom	O
timing	O
for	O
higher	O
resolution	O
to	O
provide	O
better	O
text	O
quality	O
.	O
</s>
<s>
In	O
1984	O
,	O
IBM	O
's	O
EGA	B-Device
added	O
a	O
second	O
resolution	O
which	O
necessitated	O
the	O
use	O
of	O
a	O
monitor	B-Device
supporting	O
two	O
scan	O
rates	O
,	O
the	O
original	O
CGA	B-Device
rate	O
as	O
well	O
as	O
a	O
second	O
scan	O
rate	O
for	O
the	O
new	O
video	O
modes	O
.	O
</s>
<s>
This	O
monitor	B-Device
as	O
well	O
as	O
others	O
that	O
could	O
be	O
manually	O
switched	O
between	O
these	O
two	O
sync	O
rates	O
were	O
known	O
as	O
dual-scan	O
displays	O
.	O
</s>
<s>
The	O
NEC	O
Multisync	B-General_Concept
was	O
released	O
in	O
1985	O
for	O
use	O
with	O
the	O
IBM	B-Device
PC	I-Device
,	O
supporting	O
a	O
wide	O
range	O
of	O
sync	O
frequencies	O
including	O
those	O
for	O
CGA	B-Device
,	O
EGA	B-Device
,	O
various	O
extended	O
forms	O
of	O
those	O
standards	O
marketed	O
by	O
third	O
party	O
vendors	O
,	O
and	O
standards	O
yet	O
to	O
be	O
released	O
.	O
</s>
<s>
IBM	O
's	O
1987	O
VGA	B-Protocol
standard	O
,	O
in	O
turn	O
,	O
expanded	O
to	O
three	O
fixed	O
scan	O
rates	O
.	O
</s>
<s>
At	O
this	O
point	O
,	O
PC	B-Device
and	O
Mac	O
owners	O
with	O
multiple	O
graphics	O
cards	O
required	O
unique	O
monitors	O
for	O
each	O
of	O
them	O
,	O
and	O
by	O
the	O
late	O
80s	O
all	O
of	O
the	O
below	O
computer	O
video	O
standards	O
required	O
monitors	O
which	O
supported	O
a	O
small	O
number	O
of	O
specific	O
frequencies	O
:	O
</s>
<s>
VGA	B-Protocol
:	O
31.5kHz	O
horizontal	B-General_Concept
scan	O
,	O
60	O
or	O
70Hz	O
vertical	O
scan	O
.	O
</s>
<s>
No	O
support	O
for	O
CGA/EGA	O
timings	O
.	O
</s>
<s>
CGA/EGA	O
resolutions	O
are	O
transmitted	O
to	O
the	O
monitor	B-Device
at	O
VGA	B-Protocol
compatible	O
timings	O
.	O
</s>
<s>
After	O
1987	O
's	O
VGA	B-Protocol
.	O
</s>
<s>
the	O
IBM	O
market	O
began	O
to	O
develop	O
Super	O
VGA	B-Protocol
cards	I-Protocol
which	O
used	O
many	O
different	O
scan	O
rates	O
,	O
culminating	O
in	O
the	O
VBE	B-Device
which	O
established	O
standardized	O
methods	O
for	O
outputting	O
many	O
different	O
resolutions	O
from	O
one	O
card	O
,	O
eventually	O
becoming	O
the	O
Generalized	B-General_Concept
Timing	I-General_Concept
Formula	I-General_Concept
which	O
permitted	O
graphics	O
cards	O
to	O
output	O
arbitrary	O
resolutions	O
.	O
</s>
<s>
In	O
addition	O
to	O
these	O
higher	O
resolutions	O
and	O
frequencies	O
,	O
during	O
system	O
boot	O
on	O
systems	O
like	O
the	O
IBM	B-Device
PC	I-Device
,	O
the	O
display	O
would	O
operate	O
at	O
standard	O
low	O
resolution	O
,	O
such	O
as	O
the	O
PC	B-Device
standard	O
of	O
720x400	O
at	O
70Hz	O
.	O
</s>
<s>
A	O
monitor	B-Device
capable	O
of	O
displaying	O
at	O
both	O
resolutions	O
would	O
need	O
to	O
be	O
able	O
to	O
horizontally	O
scan	O
in	O
a	O
range	O
from	O
at	O
least	O
31	O
to	O
68kHz	O
.	O
</s>
<s>
This	O
was	O
superseded	O
by	O
VESA	O
's	O
Generalized	B-General_Concept
Timing	I-General_Concept
Formula	I-General_Concept
,	O
which	O
provided	O
a	O
standard	O
method	O
to	O
derive	O
the	O
timing	O
of	O
an	O
arbitrary	O
display	O
mode	O
from	O
its	O
sync	O
pulses	O
,	O
and	O
this	O
in	O
turn	O
was	O
superseded	O
by	O
VESA	O
's	O
Coordinated	B-General_Concept
Video	I-General_Concept
Timings	I-General_Concept
standard	O
.	O
</s>
<s>
Early	O
multisync	B-General_Concept
monitors	I-General_Concept
designed	O
for	O
use	O
with	O
systems	O
having	O
a	O
small	O
number	O
of	O
specific	O
frequencies	O
,	O
like	O
CGA	B-Device
,	O
EGA	B-Device
and	O
VGA	B-Protocol
,	O
or	O
built-in	O
Macintosh	O
graphics	O
,	O
supported	O
limited	O
fixed	O
frequencies	O
.	O
</s>
<s>
On	O
the	O
IBM	B-Device
PC	I-Device
,	O
these	O
were	O
signaled	O
from	O
the	O
graphics	O
card	O
to	O
the	O
monitor	B-Device
through	O
the	O
polarities	O
of	O
one	O
or	O
both	O
H	O
-	O
and	O
V-sync	O
signals	O
sent	O
by	O
the	O
video	O
adapter	O
.	O
</s>
<s>
Later	O
designs	O
supported	O
a	O
continuous	O
range	O
of	O
scan	O
frequencies	O
,	O
such	O
as	O
the	O
NEC	O
Multisync	B-General_Concept
which	O
supported	O
horizontal	B-General_Concept
scan	I-General_Concept
rates	I-General_Concept
from	O
15to	O
31kHz	O
derived	O
from	O
the	O
sync	O
signal	O
timing	O
rather	O
than	O
the	O
polarity	O
of	O
the	O
sync	O
signals	O
.	O
</s>
<s>
Modern	O
monitors	O
produced	O
using	O
the	O
VESA	O
frequency	O
standards	O
generally	O
support	O
arbitrary	O
scan	O
rates	O
between	O
specific	O
minimum	O
and	O
maximum	O
horizontal	B-General_Concept
and	O
vertical	O
rates	O
.	O
</s>
<s>
Most	O
modern	O
multiscan	O
computer	B-Device
monitors	I-Device
have	O
a	O
minimum	O
horizontal	B-General_Concept
scan	I-General_Concept
frequency	I-General_Concept
of	O
31kHz	O
.	O
</s>
<s>
In	O
both	O
multisync	B-General_Concept
and	O
fixed-sync	O
monitors	O
,	O
timing	O
is	O
important	O
to	O
prevent	O
image	O
distortion	O
and	O
even	O
damage	O
to	O
components	O
.	O
</s>
<s>
Most	O
modern	O
multiscan	O
monitors	O
are	O
microprocessor	B-Architecture
controlled	O
and	O
will	O
refuse	O
to	O
attempt	O
to	O
synchronise	O
to	O
an	O
unsupported	O
scan	O
rate	O
,	O
which	O
usually	O
protects	O
them	O
from	O
damage	O
.	O
</s>
<s>
The	O
multisync	B-General_Concept
concept	O
applies	O
to	O
non-CRT	O
monitors	O
,	O
such	O
as	O
LCDs	B-Device
,	O
but	O
is	O
implemented	O
differently	O
.	O
</s>
<s>
LCD	B-Device
monitors	I-Device
are	O
fixed-pixel	B-General_Concept
displays	I-General_Concept
,	O
where	O
the	O
number	O
of	O
rows	O
and	O
columns	O
displayed	O
on	O
the	O
screen	O
are	O
constant	O
,	O
set	O
by	O
the	O
construction	O
of	O
the	O
panel	O
.	O
</s>
<s>
When	O
the	O
input	O
signal	O
has	O
a	O
resolution	O
that	O
does	O
not	O
match	O
the	O
number	O
of	O
pixels	O
in	O
the	O
display	O
,	O
the	O
LCD	B-Device
controller	O
must	O
still	O
populate	O
the	O
same	O
number	O
of	O
image	O
elements	O
.	O
</s>
<s>
This	O
is	O
accomplished	O
either	O
by	O
scaling	O
the	O
image	O
up	O
or	O
down	O
as	O
needed	O
,	O
creating	O
a	O
picture	O
that	O
does	O
not	O
have	O
a	O
1:1	O
relationship	O
between	O
LCD	B-Device
image	O
elements	O
and	O
pixels	O
in	O
the	O
original	O
image	O
,	O
or	O
by	O
displaying	O
the	O
image	O
unscaled	O
in	O
the	O
center	O
of	O
the	O
monitor	B-Device
,	O
filling	O
the	O
spaces	O
on	O
all	O
sides	O
with	O
black	O
pixels	O
.	O
</s>
<s>
While	O
stand-alone	O
LCD	B-Device
monitors	I-Device
generally	O
accept	O
a	O
wide	O
range	O
of	O
horizontal	B-General_Concept
scan	I-General_Concept
rates	I-General_Concept
,	O
the	O
majority	O
of	O
LCDs	B-Device
accept	O
only	O
60Hz	O
to	O
75Hz	O
vertical	O
scan	O
rates	O
.	O
</s>
<s>
In	O
recent	O
years	O
,	O
LCD	B-Device
monitors	I-Device
designed	O
for	O
gaming	O
have	O
appeared	O
on	O
the	O
market	O
offering	O
vertical	O
scan	O
rates	O
of	O
120Hz	O
and	O
up	O
.	O
</s>
<s>
CRT	O
televisions	O
are	O
typically	O
designed	O
to	O
operate	O
only	O
with	O
the	O
video	O
standard	O
of	O
the	O
country	O
they	O
are	O
sold	O
in	O
(	O
PAL	B-Language
,	O
NTSC	O
,	O
SECAM	O
)	O
,	O
but	O
some	O
sets	O
,	O
particularly	O
broadcast	O
monitors	O
,	O
can	O
operate	O
on	O
multiple	O
standards	O
.	O
</s>
