<s>
Video	B-Protocol
Graphics	I-Protocol
Array	I-Protocol
(	O
VGA	B-Protocol
)	O
is	O
a	O
video	B-General_Concept
display	I-General_Concept
controller	I-General_Concept
and	O
accompanying	O
de	O
facto	O
graphics	O
standard	O
,	O
first	O
introduced	O
with	O
the	O
IBM	B-Device
PS/2	I-Device
line	O
of	O
computers	O
in	O
1987	O
,	O
which	O
became	O
ubiquitous	O
in	O
the	O
IBM	B-Device
PC	I-Device
compatible	O
industry	O
within	O
three	O
years	O
.	O
</s>
<s>
The	O
term	O
can	O
now	O
refer	O
to	O
the	O
computer	O
display	O
standard	O
,	O
the	O
15-pin	O
D-subminiature	B-Protocol
VGA	B-Protocol
connector	I-Protocol
,	O
or	O
the	O
640×480	B-General_Concept
resolution	O
characteristic	O
of	O
the	O
VGA	B-Protocol
hardware	O
.	O
</s>
<s>
VGA	B-Protocol
was	O
the	O
last	O
IBM	O
graphics	O
standard	O
to	O
which	O
the	O
majority	O
of	O
IBM	B-Device
PC	I-Device
compatible	O
computer	O
manufacturers	O
conformed	O
,	O
making	O
it	O
the	O
lowest	O
common	O
denominator	O
that	O
virtually	O
all	O
post-1990	O
PC	B-Device
graphics	O
hardware	O
can	O
be	O
expected	O
to	O
implement	O
.	O
</s>
<s>
IBM	O
intended	O
to	O
supersede	O
VGA	B-Protocol
with	O
the	O
Extended	B-Device
Graphics	I-Device
Array	I-Device
(	O
XGA	B-Device
)	O
standard	O
,	O
but	O
failed	O
.	O
</s>
<s>
Instead	O
,	O
VGA	B-Protocol
was	O
adapted	O
into	O
many	O
extended	O
forms	O
by	O
third	O
parties	O
,	O
collectively	O
known	O
as	O
Super	O
VGA	B-Protocol
,	O
then	O
gave	O
way	O
to	O
custom	O
graphics	B-Architecture
processing	I-Architecture
units	I-Architecture
which	O
,	O
in	O
addition	O
to	O
their	O
proprietary	O
interfaces	O
and	O
capabilities	O
,	O
continue	O
to	O
implement	O
common	O
VGA	B-Protocol
graphics	I-Protocol
modes	O
and	O
interfaces	O
to	O
the	O
present	O
day	O
.	O
</s>
<s>
The	O
VGA	B-Protocol
analog	O
interface	O
standard	O
has	O
been	O
extended	O
to	O
support	O
resolutions	O
of	O
up	O
to	O
2048×1536	O
and	O
even	O
higher	O
in	O
special	O
applications	O
.	O
</s>
<s>
The	O
color	B-Data_Structure
palette	I-Data_Structure
random	B-Architecture
access	I-Architecture
memory	I-Architecture
(	O
RAM	B-Architecture
)	O
and	O
its	O
corresponding	O
digital-to-analog	O
converter	O
(	O
DAC	O
)	O
were	O
integrated	O
into	O
one	O
chip	O
(	O
the	O
RAMDAC	B-Device
)	O
and	O
the	O
cathode-ray	B-Device
tube	I-Device
controller	O
(	O
CRTC	O
)	O
was	O
integrated	O
into	O
a	O
main	O
VGA	B-Protocol
chip	O
,	O
which	O
eliminated	O
several	O
other	O
chips	O
in	O
previous	O
graphics	O
adapters	O
,	O
so	O
VGA	B-Protocol
only	O
additionally	O
required	O
external	O
video	O
RAM	B-Architecture
and	O
timing	O
crystals	O
.	O
</s>
<s>
This	O
small	O
part	O
count	O
allowed	O
IBM	O
to	O
include	O
VGA	B-Protocol
directly	O
on	O
the	O
PS/2	B-Device
motherboard	O
,	O
in	O
contrast	O
to	O
prior	O
IBM	B-Device
PC	I-Device
modelsPC	O
,	O
PC/XT	B-Device
,	O
and	O
PC	B-Device
ATwhich	O
required	O
a	O
separate	O
display	O
adapter	O
installed	O
in	O
a	O
slot	O
in	O
order	O
to	O
connect	O
a	O
monitor	O
.	O
</s>
<s>
Unlike	O
the	O
graphics	O
adapters	O
that	O
preceded	O
it	O
(	O
MDA	B-Device
,	O
CGA	B-Device
,	O
EGA	B-Device
and	O
many	O
third-party	O
options	O
)	O
there	O
was	O
initially	O
no	O
discrete	O
VGA	B-Protocol
card	I-Protocol
released	O
by	O
IBM	O
.	O
</s>
<s>
The	O
first	O
commercial	O
implementation	O
of	O
VGA	B-Protocol
was	O
a	O
built-in	O
component	O
of	O
the	O
IBM	B-Device
PS/2	I-Device
,	O
in	O
which	O
it	O
was	O
accompanied	O
by	O
256KB	O
of	O
video	O
RAM	B-Architecture
,	O
and	O
a	O
new	O
DE-15	O
connector	O
replacing	O
the	O
DE-9	O
used	O
by	O
previous	O
graphics	O
adapters	O
.	O
</s>
<s>
IBM	O
later	O
released	O
the	O
standalone	O
IBM	B-Device
PS/2	I-Device
Display	O
Adapter	O
,	O
which	O
utilized	O
the	O
VGA	B-Protocol
but	O
could	O
be	O
added	O
to	O
machines	O
that	O
did	O
not	O
have	O
it	O
built	O
in	O
.	O
</s>
<s>
The	O
VGA	B-Protocol
supports	O
all	O
graphics	O
modes	O
supported	O
by	O
the	O
MDA	B-Device
,	O
CGA	B-Device
and	O
EGA	B-Device
cards	O
,	O
as	O
well	O
as	O
multiple	O
new	O
modes	O
.	O
</s>
<s>
The	O
640×480	B-General_Concept
16-color	O
and	O
320×200	O
256-color	O
modes	O
had	O
fully	O
redefinable	O
palettes	B-Data_Structure
,	O
with	O
each	O
entry	O
selected	O
from	O
an	O
18-bit	O
(	O
262,144	O
-color	O
)	O
gamut	O
.	O
</s>
<s>
The	O
other	O
modes	O
defaulted	O
to	O
standard	O
EGA	B-Device
or	O
CGA	B-Device
compatible	O
palettes	B-Data_Structure
and	O
instructions	O
,	O
but	O
still	O
permitted	O
remapping	O
of	O
the	O
palette	B-Data_Structure
with	O
VGA-specific	O
commands	O
.	O
</s>
<s>
As	O
the	O
VGA	B-Protocol
began	O
to	O
be	O
cloned	O
in	O
great	O
quantities	O
by	O
manufacturers	O
who	O
added	O
ever-increasing	O
capabilities	O
,	O
its	O
640×480	B-General_Concept
,	O
16-color	O
mode	O
became	O
the	O
de	O
facto	O
lowest	O
common	O
denominator	O
of	O
graphics	O
cards	O
.	O
</s>
<s>
By	O
the	O
mid	O
1990s	O
,	O
a	O
640×480×16	O
graphics	O
mode	O
using	O
the	O
VGA	B-Protocol
memory	O
and	O
register	O
specifications	O
was	O
expected	O
by	O
operating	O
systems	O
such	O
as	O
Windows	B-Application
95	I-Application
and	O
OS/2	O
Warp	O
3.0	O
,	O
which	O
provided	O
no	O
support	O
for	O
lower	O
resolutions	O
or	O
bit	O
depths	O
,	O
or	O
support	O
for	O
other	O
memory	O
or	O
register	O
layouts	O
without	O
additional	O
drivers	O
.	O
</s>
<s>
Well	O
into	O
the	O
2000s	O
,	O
even	O
after	O
the	O
VESA	O
standard	O
for	O
graphics	O
cards	O
became	O
commonplace	O
,	O
the	O
"	O
VGA	B-Protocol
"	O
graphics	O
mode	O
remained	O
a	O
compatibility	O
option	O
for	O
PC	B-Device
operating	O
systems	O
.	O
</s>
<s>
For	O
example	O
,	O
high	O
resolution	O
modes	O
with	O
square	O
pixels	B-Algorithm
are	O
available	O
at	O
768×576	O
or	O
704×528	O
in	O
16	O
colors	O
,	O
or	O
medium-low	O
resolution	O
at	O
320×240	O
with	O
256	O
colors	O
.	O
</s>
<s>
Alternatively	O
,	O
extended	O
resolution	O
is	O
available	O
with	O
"	O
fat	O
"	O
pixels	B-Algorithm
and	O
256	O
colors	O
using	O
,	O
e.g.	O
</s>
<s>
400×600	O
(	O
50Hz	O
)	O
or	O
360×480	O
(	O
60Hz	O
)	O
,	O
and	O
"	O
thin	O
"	O
pixels	B-Algorithm
,	O
16	O
colors	O
and	O
the	O
70Hz	O
refresh	O
rate	O
with	O
e.g.	O
</s>
<s>
"	O
Narrow	O
"	O
modes	O
such	O
as	O
256×224	O
tend	O
to	O
preserve	O
the	O
same	O
pixel	B-Algorithm
ratio	O
as	O
in	O
e.g.	O
</s>
<s>
320×240	O
mode	O
unless	O
the	O
monitor	O
is	O
adjusted	O
to	O
stretch	O
the	O
image	O
out	O
to	O
fill	O
the	O
screen	O
,	O
as	O
they	O
are	O
derived	O
simply	O
by	O
masking	O
down	O
the	O
wider	O
mode	O
instead	O
of	O
altering	O
pixel	B-Algorithm
or	O
line	O
timings	O
,	O
but	O
can	O
be	O
useful	O
for	O
reducing	O
memory	O
requirements	O
and	O
pixel	B-Algorithm
addressing	O
calculations	O
for	O
arcade	O
game	O
conversions	O
or	O
console	O
emulators	O
.	O
</s>
<s>
The	O
PC	B-Device
version	O
of	O
Pinball	B-Application
Fantasies	I-Application
has	O
the	O
option	O
to	O
use	O
non-standard	O
modes	O
"	O
high	O
res	O
"	O
modes	O
,	O
such	O
as	O
640x350	O
,	O
allowing	O
it	O
to	O
display	O
a	O
larger	O
portion	O
of	O
the	O
pinball	O
table	O
on	O
screen	O
.	O
</s>
<s>
VGA	B-Protocol
also	O
implements	O
several	O
text	O
modes	O
:	O
</s>
<s>
80×43	O
or	O
80×50	O
,	O
with	O
an	O
8×8	O
font	O
grid	O
,	O
with	O
an	O
effective	O
resolution	O
of	O
640×344	O
or	O
640×400	O
pixels	B-Algorithm
.	O
</s>
<s>
As	O
with	O
the	O
pixel-based	O
graphics	O
modes	O
,	O
additional	O
text	O
modes	O
are	O
possible	O
by	O
programming	O
the	O
VGA	B-Protocol
correctly	O
,	O
with	O
an	O
overall	O
maximum	O
of	O
about	O
100×80	O
cells	O
and	O
an	O
active	O
area	O
spanning	O
about	O
88×64	O
cells	O
.	O
</s>
<s>
One	O
variant	O
that	O
is	O
sometimes	O
seen	O
is	O
80×30	O
or	O
80×60	O
,	O
using	O
an	O
8×16	O
or	O
8×8	O
font	O
and	O
an	O
effective	O
640×480	B-General_Concept
pixel	B-Algorithm
display	O
,	O
which	O
trades	O
use	O
of	O
the	O
more	O
flickery	O
60Hz	O
mode	O
for	O
an	O
additional	O
5	O
or	O
10	O
lines	O
of	O
text	O
and	O
square	O
character	O
blocks	O
(	O
or	O
,	O
at	O
80×30	O
,	O
square	O
half-blocks	O
)	O
.	O
</s>
<s>
Unlike	O
the	O
cards	O
that	O
preceded	O
it	O
,	O
which	O
used	O
binary	O
TTL	B-General_Concept
signals	O
to	O
interface	O
with	O
a	O
monitor	O
(	O
and	O
also	O
composite	O
,	O
in	O
the	O
case	O
of	O
the	O
CGA	B-Device
)	O
,	O
the	O
VGA	B-Protocol
introduced	O
a	O
video	O
interface	O
using	O
pure	O
analog	O
RGB	O
signals	O
,	O
with	O
a	O
range	O
of	O
0.7	O
volts	O
peak-to-peak	O
max	O
.	O
</s>
<s>
In	O
conjunction	O
with	O
a	O
18-bit	O
RAMDAC	B-Device
(	O
6-bit	O
per	O
RGB	O
channel	O
)	O
,	O
this	O
produced	O
a	O
color	O
gamut	O
of	O
262,144	O
colors	O
.	O
</s>
<s>
The	O
original	O
VGA	B-Protocol
specifications	O
follow	O
:	O
</s>
<s>
Vertical	O
blank	O
interrupt	O
(	O
Not	O
all	O
clone	B-General_Concept
cards	O
support	O
this	O
.	O
)	O
</s>
<s>
The	O
intended	O
standard	O
value	O
for	O
the	O
horizontal	O
frequency	O
of	O
VGA	B-Protocol
's	O
640×480	B-General_Concept
mode	O
is	O
exactly	O
double	O
the	O
value	O
used	O
in	O
the	O
NTSC-M	O
video	O
system	O
,	O
as	O
this	O
made	O
it	O
much	O
easier	O
to	O
offer	O
optional	O
TV-out	B-Device
solutions	O
or	O
external	O
VGA-to-TV	O
converter	O
boxes	O
at	O
the	O
time	O
of	O
VGA	B-Protocol
's	O
development	O
.	O
</s>
<s>
It	O
is	O
also	O
at	O
least	O
nominally	O
twice	O
that	O
of	O
CGA	B-Device
,	O
which	O
also	O
supported	O
composite	O
monitors	O
.	O
</s>
<s>
All	O
derived	O
VGA	B-Protocol
timings	O
(	O
i.e.	O
</s>
<s>
those	O
which	O
use	O
the	O
master	O
25.175	O
and	O
28.322MHz	O
crystals	O
and	O
,	O
to	O
a	O
lesser	O
extent	O
,	O
the	O
nominal	O
31.469kHz	O
line	O
rate	O
)	O
can	O
be	O
varied	O
by	O
software	O
that	O
bypasses	O
the	O
VGA	B-Protocol
firmware	O
interface	O
and	O
communicates	O
directly	O
with	O
the	O
VGA	B-Protocol
hardware	O
,	O
as	O
many	O
MS-DOS	O
based	O
games	O
did	O
.	O
</s>
<s>
However	O
,	O
only	O
the	O
standard	O
modes	O
,	O
or	O
modes	O
that	O
at	O
least	O
use	O
almost	O
exactly	O
the	O
same	O
H-sync	O
and	O
V-sync	O
timings	O
as	O
one	O
of	O
the	O
standard	O
modes	O
,	O
can	O
be	O
expected	O
to	O
work	O
with	O
the	O
original	O
late-1980s	O
and	O
early-1990s	O
VGA	B-Protocol
monitors	I-Protocol
.	O
</s>
<s>
Third-party	O
"	O
multisync	O
"	O
CRT	B-Device
monitors	I-Device
were	O
more	O
flexible	O
,	O
and	O
in	O
combination	O
with	O
"	O
super	O
EGA	B-Device
"	O
,	O
VGA	B-Protocol
,	O
and	O
later	O
SVGA	O
graphics	O
cards	O
using	O
extended	O
modes	O
,	O
could	O
display	O
a	O
much	O
wider	O
range	O
of	O
resolutions	O
and	O
refresh	O
rates	O
at	O
arbitrary	O
sync	O
frequencies	O
and	O
pixel	B-Algorithm
clock	O
rates	O
.	O
</s>
<s>
For	O
the	O
most	O
common	O
VGA	B-Protocol
mode	O
(	O
640×480	B-General_Concept
,	O
60Hz	O
,	O
non-interlaced	B-Device
)	O
,	O
the	O
horizontal	O
timings	O
can	O
be	O
found	O
in	O
the	O
HP	O
Super	O
VGA	B-Protocol
Display	O
Installation	O
Guide	O
and	O
in	O
other	O
places	O
.	O
</s>
<s>
640×400	O
@	O
70Hz	O
is	O
traditionally	O
the	O
video	O
mode	O
used	O
for	O
booting	O
VGA-compatible	O
x86	B-Operating_System
personal	B-Device
computers	I-Device
that	O
show	O
a	O
graphical	O
boot	O
screen	O
,	O
while	O
text-mode	O
boot	O
uses	O
720×400	O
@	O
70Hz	O
.	O
</s>
<s>
This	O
convention	O
has	O
been	O
eroded	O
in	O
recent	O
years	O
,	O
however	O
,	O
with	O
POST	O
and	O
BIOS	O
screens	O
moving	O
to	O
higher	O
resolutions	O
,	O
taking	O
advantage	O
of	O
EDID	B-General_Concept
data	O
to	O
match	O
the	O
resolution	O
to	O
a	O
connected	O
monitor	O
.	O
</s>
<s>
640×480	B-General_Concept
@	O
60Hz	O
is	O
the	O
default	O
Windows	O
graphics	O
mode	O
(	O
usually	O
with	O
16colors	O
)	O
,	O
up	O
to	O
Windows	O
2000	O
.	O
</s>
<s>
It	O
remains	O
an	O
option	O
in	O
XP	O
and	O
later	O
versions	O
via	O
the	O
boot	O
menu	O
"	O
low	O
resolution	O
video	O
"	O
option	O
and	O
per-application	O
compatibility	O
mode	O
settings	O
,	O
despite	O
Windows	O
now	O
defaulting	O
to	O
1024×768	B-General_Concept
and	O
generally	O
not	O
allowing	O
any	O
resolution	O
below	O
800×600	B-General_Concept
to	O
be	O
set	O
.	O
</s>
<s>
The	O
need	O
for	O
such	O
a	O
low-quality	O
,	O
universally	O
compatible	O
fallback	O
has	O
diminished	O
since	O
the	O
turn	O
of	O
the	O
millennium	O
,	O
as	O
VGA-signalling-standard	O
screens	O
or	O
adaptors	O
unable	O
to	O
show	O
anything	O
beyond	O
the	O
original	O
resolutions	O
have	O
become	O
increasingly	O
rare	O
.	O
</s>
<s>
320×200	O
at	O
70Hz	O
was	O
the	O
most	O
common	O
mode	O
for	O
VGA-era	O
PC	B-Device
games	O
,	O
with	O
pixel-doubling	O
and	O
line-doubling	O
performed	O
in	O
hardware	O
to	O
present	O
a	O
640x400	O
at	O
70Hz	O
signal	O
to	O
the	O
monitor	O
.	O
</s>
<s>
The	O
Windows	O
95/98/Me	O
LOGO.SYS	O
boot-up	O
image	O
was	O
320x400	O
resolution	O
,	O
displayed	O
with	O
pixel-doubling	O
to	O
present	O
a	O
640x400	O
at	O
70Hz	O
signal	O
to	O
the	O
monitor	O
.	O
</s>
<s>
The	O
standard	O
VGA	B-Protocol
monitor	I-Protocol
interface	O
is	O
a	O
15-pin	O
D-subminiature	B-Protocol
connector	I-Protocol
in	O
the	O
"	O
E	O
"	O
shell	O
,	O
variously	O
referred	O
to	O
as	O
"	O
HD-15	B-Protocol
"	O
,	O
"	O
DE-15	O
"	O
and	O
"	O
DB-15	B-Protocol
"	O
.	O
</s>
<s>
Because	O
VGA	B-Protocol
uses	O
low-voltage	O
analog	O
signals	O
,	O
signal	O
degradation	O
becomes	O
a	O
factor	O
with	O
low-quality	O
or	O
overly	O
long	O
cables	O
.	O
</s>
<s>
Solutions	O
include	O
shielded	O
cables	O
,	O
cables	O
that	O
include	O
a	O
separate	O
internal	O
coaxial	O
cable	O
for	O
each	O
color	O
signal	O
,	O
and	O
"	O
broken	O
out	O
"	O
cables	O
utilizing	O
a	O
separate	O
coaxial	O
cable	O
with	O
a	O
BNC	B-Protocol
connector	I-Protocol
for	O
each	O
color	O
signal	O
.	O
</s>
<s>
BNC	O
breakout	O
cables	O
typically	O
use	O
five	O
connectors	O
,	O
one	O
each	O
for	O
Red	O
,	O
Green	O
,	O
Blue	O
,	O
Horizontal	B-General_Concept
Sync	I-General_Concept
,	O
and	O
Vertical	O
Sync	O
,	O
and	O
do	O
not	O
include	O
the	O
other	O
signal	O
lines	O
of	O
the	O
VGA	B-Protocol
interface	O
.	O
</s>
<s>
The	O
VGA	B-Protocol
color	O
system	O
uses	O
register-based	O
palettes	B-Data_Structure
to	O
map	O
colors	O
in	O
various	O
bit	O
depths	O
to	O
its	O
18-bit	O
output	O
gamut	O
.	O
</s>
<s>
It	O
is	O
backward	B-General_Concept
compatible	I-General_Concept
with	O
the	O
EGA	B-Device
and	O
CGA	B-Device
adapters	O
,	O
but	O
supports	O
extra	O
bit	O
depth	O
for	O
the	O
palette	B-Data_Structure
when	O
in	O
these	O
modes	O
.	O
</s>
<s>
For	O
instance	O
,	O
when	O
in	O
EGA	B-Device
16-color	O
modes	O
,	O
VGA	B-Protocol
offers	O
16	O
palette	B-Data_Structure
registers	O
,	O
and	O
in	O
256-color	O
modes	O
,	O
it	O
offers	O
256	O
registers	O
.	O
</s>
<s>
Each	O
palette	B-Data_Structure
register	O
contain	O
a	O
3×6	O
bit	O
RGB	O
value	O
,	O
selecting	O
a	O
color	O
from	O
the	O
18-bit	O
gamut	O
of	O
the	O
DAC	O
.	O
</s>
<s>
These	O
color	B-Data_Structure
registers	I-Data_Structure
are	O
initialized	O
to	O
default	O
values	O
IBM	O
expected	O
to	O
be	O
most	O
useful	O
for	O
each	O
mode	O
.	O
</s>
<s>
For	O
instance	O
,	O
EGA	B-Device
16-color	O
modes	O
initialize	O
to	O
the	O
default	O
CGA	B-Device
16-color	O
palette	B-Data_Structure
,	O
and	O
the	O
256-color	O
mode	O
initializes	O
to	O
a	O
palette	B-Data_Structure
consisting	O
of	O
16	O
CGA	B-Device
colors	O
,	O
16	O
grey	O
shades	O
,	O
and	O
then	O
216	O
colors	O
chosen	O
by	O
IBM	O
to	O
fit	O
expected	O
use	O
cases	O
.	O
</s>
<s>
After	O
initialization	O
they	O
can	O
be	O
redefined	O
at	O
any	O
time	O
without	O
altering	O
the	O
contents	O
of	O
video	O
RAM	B-Architecture
,	O
permitting	O
palette	B-Device
cycling	I-Device
.	O
</s>
<s>
The	O
CPU	O
interface	O
combines	O
the	O
4	O
planes	O
in	O
the	O
same	O
way	O
,	O
a	O
feature	O
called	O
"	O
chain-4	O
"	O
,	O
so	O
that	O
each	O
the	O
pixel	B-Algorithm
appears	O
to	O
the	O
CPU	O
as	O
a	O
packed	O
8-bit	O
value	O
representing	O
the	O
palette	B-Data_Structure
index	O
.	O
</s>
<s>
The	O
video	O
memory	O
of	O
the	O
VGA	B-Protocol
is	O
mapped	O
to	O
the	O
PC	B-Device
's	O
memory	O
via	O
a	O
window	O
in	O
the	O
range	O
between	O
segments	O
0xA0000	O
and	O
0xBFFFF	O
in	O
the	O
PC	B-Device
's	O
real	B-Application
mode	I-Application
address	O
space	O
(	O
A000:0000	O
and	O
B000:FFFF	O
in	O
segment:offset	O
notation	O
)	O
.	O
</s>
<s>
MDA	B-Device
or	O
Hercules	B-Device
)	O
and	O
a	O
color	O
adapter	O
such	O
as	O
the	O
VGA	B-Protocol
,	O
EGA	B-Device
,	O
or	O
CGA	B-Device
installed	O
in	O
the	O
same	O
machine	O
.	O
</s>
<s>
At	O
the	O
beginning	O
of	O
the	O
1980s	O
,	O
this	O
was	O
typically	O
used	O
to	O
display	O
Lotus	B-Application
1-2-3	I-Application
spreadsheets	O
in	O
high-resolution	O
text	O
on	O
a	O
monochrome	O
display	O
and	O
associated	O
graphics	O
on	O
a	O
low-resolution	O
CGA	B-Device
display	I-Device
simultaneously	O
.	O
</s>
<s>
Several	O
debuggers	O
,	O
like	O
Borland	O
's	O
Turbo	B-Application
Debugger	I-Application
,	O
D86	B-Application
and	O
Microsoft	O
's	O
CodeView	B-Application
could	O
work	O
in	O
a	O
dual	O
monitor	O
setup	O
.	O
</s>
<s>
Either	O
Turbo	B-Application
Debugger	I-Application
or	O
CodeView	B-Application
could	O
be	O
used	O
to	O
debug	O
Windows	O
.	O
</s>
<s>
There	O
were	O
also	O
DOS	B-Device
device	O
drivers	O
such	O
as	O
ox.sys	O
,	O
which	O
implemented	O
a	O
serial	O
interface	O
simulation	O
on	O
the	O
monochrome	O
display	O
and	O
,	O
for	O
example	O
,	O
allowed	O
the	O
user	O
to	O
receive	O
crash	O
messages	O
from	O
debugging	O
versions	O
of	O
Windows	O
without	O
using	O
an	O
actual	O
serial	O
terminal	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
use	O
the	O
"	O
MODE	O
MONO	O
"	O
command	O
at	O
the	O
DOS	B-Device
prompt	O
to	O
redirect	O
the	O
output	O
to	O
the	O
monochrome	O
display	O
.	O
</s>
<s>
"	O
Unchaining	O
"	O
the	O
256KB	O
VGA	B-Protocol
memory	O
into	O
four	O
separate	O
"	O
planes	O
"	O
makes	O
VGA	B-Protocol
's	O
256KB	O
of	O
RAM	B-Architecture
available	O
in	O
256-color	O
modes	O
.	O
</s>
<s>
Single-color	O
polygon	O
filling	O
could	O
be	O
accelerated	O
due	O
to	O
the	O
ability	O
to	O
set	O
four	O
pixels	B-Algorithm
with	O
a	O
single	O
write	O
to	O
the	O
hardware	O
.	O
</s>
<s>
The	O
video	O
adapter	O
could	O
assist	O
in	O
copying	O
video	O
RAM	B-Architecture
regions	O
,	O
which	O
was	O
sometimes	O
faster	O
than	O
doing	O
this	O
with	O
the	O
relatively	O
slow	O
CPU-to-VGA	O
interface	O
.	O
</s>
<s>
The	O
use	O
of	O
multiple	O
video	O
pages	O
in	O
hardware	O
allowed	O
double	O
buffering	O
,	O
triple	O
buffering	O
or	O
split	O
screens	O
,	O
which	O
,	O
while	O
available	O
in	O
VGA	B-Protocol
's	O
320×200	O
16-color	O
mode	O
,	O
was	O
not	O
possible	O
using	O
stock	O
Mode	O
13h	O
.	O
</s>
<s>
Most	O
particularly	O
,	O
several	O
higher	O
,	O
arbitrary-resolution	O
display	O
modes	O
were	O
possible	O
,	O
all	O
the	O
way	O
up	O
to	O
the	O
programmable	O
limit	O
of	O
800×600	B-General_Concept
with	O
16colors	O
(	O
or	O
400×600	O
with	O
256	O
colors	O
)	O
,	O
as	O
well	O
as	O
other	O
custom	O
modes	O
using	O
unusual	O
combinations	O
of	O
horizontal	O
and	O
vertical	O
pixel	B-Algorithm
counts	O
in	O
either	O
color	O
mode	O
.	O
</s>
<s>
Software	O
such	O
as	O
Fractint	B-Application
,	O
Xlib	B-Language
and	O
ColoRIX	O
also	O
supported	O
tweaked	O
256-color	O
modes	O
on	O
standard	O
adaptors	O
using	O
freely-combinable	O
widths	O
of	O
256	O
,	O
320	O
,	O
and	O
360pixels	O
and	O
heights	O
of	O
200	O
,	O
240	O
and	O
256	O
(	O
or	O
400	O
,	O
480	O
and	O
512	O
)	O
lines	O
,	O
extending	O
still	O
further	O
to	O
384	O
or	O
400	O
pixel	B-Algorithm
columns	O
and	O
576	O
or	O
600	O
(	O
or	O
288	O
,	O
300	O
)	O
.	O
</s>
<s>
However	O
,	O
320×240	O
was	O
the	O
best	O
known	O
and	O
most	O
frequently	O
used	O
,	O
as	O
it	O
offered	O
a	O
standard	O
40-column	O
resolution	O
and	O
4:3	O
aspect	O
ratio	O
with	O
square	O
pixels	B-Algorithm
.	O
</s>
<s>
Standard	O
VGA	B-Protocol
monitors	I-Protocol
had	O
a	O
fixed	O
line	O
scan	O
(	O
H-scan	O
)	O
rate	O
"	O
multisync	O
"	O
monitors	O
being	O
,	O
at	O
the	O
time	O
,	O
expensive	O
raritiesand	O
so	O
the	O
vertical/frame	O
(	O
V-scan	O
)	O
refresh	O
rate	O
had	O
to	O
be	O
reduced	O
in	O
order	O
to	O
accommodate	O
them	O
,	O
which	O
increased	O
visible	O
flicker	B-General_Concept
and	O
thus	O
eye	O
strain	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
highest	O
800×600	B-General_Concept
mode	O
,	O
being	O
otherwise	O
based	O
on	O
the	O
matching	O
SVGA	O
resolution	O
(	O
with	O
628	O
total	O
lines	O
)	O
,	O
reduced	O
the	O
refresh	O
rate	O
from	O
60Hz	O
to	O
about	O
50Hz	O
(	O
and	O
832×624	O
,	O
the	O
theoretical	O
maximum	O
resolution	O
achievable	O
with	O
256kb	O
at	O
16	O
colors	O
,	O
would	O
have	O
reduced	O
it	O
to	O
about	O
48Hz	O
,	O
barely	O
higher	O
than	O
the	O
rate	O
at	O
which	O
XGA	B-Device
monitors	O
employed	O
a	O
double-frequency	O
interlacing	O
technique	O
to	O
mitigate	O
full-frame	O
flicker	B-General_Concept
)	O
.	O
</s>
<s>
These	O
modes	O
were	O
also	O
outright	O
incompatible	O
with	O
some	O
monitors	O
,	O
producing	O
display	O
problems	O
such	O
as	O
picture	O
detail	O
disappearing	O
into	O
overscan	O
(	O
especially	O
in	O
the	O
horizontal	O
dimension	O
)	O
,	O
vertical	O
roll	O
,	O
poor	O
horizontal	B-General_Concept
sync	I-General_Concept
or	O
even	O
a	O
complete	O
lack	O
of	O
picture	O
depending	O
on	O
the	O
exact	O
mode	O
attempted	O
.	O
</s>
<s>
Due	O
to	O
these	O
potential	O
issues	O
,	O
most	O
VGA	B-Protocol
tweaks	O
used	O
in	O
commercial	O
products	O
were	O
limited	O
to	O
more	O
standards-compliant	O
,	O
"	O
monitor-safe	O
"	O
combinations	O
,	O
such	O
as	O
320×240	O
(	O
square	O
pixels	B-Algorithm
,	O
three	O
video	O
pages	O
,	O
60Hz	O
)	O
,	O
320×400	O
(	O
double	O
resolution	O
,	O
two	O
video	O
pages	O
,	O
70Hz	O
)	O
,	O
and	O
360×480	O
(	O
highest	O
resolution	O
compatible	O
with	O
both	O
standard	O
VGA	B-Protocol
monitors	I-Protocol
and	O
cards	O
,	O
one	O
video	O
page	O
,	O
60Hz	O
)	O
in	O
256	O
colors	O
,	O
or	O
double	O
the	O
horizontal	O
resolution	O
in	O
16-color	O
mode	O
.	O
</s>
<s>
Several	O
companies	O
produced	O
VGA	B-Protocol
compatible	O
graphic	O
board	O
models	O
.	O
</s>
<s>
Super	O
VGA	B-Protocol
(	O
SVGA	O
)	O
is	O
a	O
display	O
standard	O
developed	O
in	O
1988	O
,	O
when	O
NEC	O
Home	O
Electronics	O
announced	O
its	O
creation	O
of	O
the	O
Video	O
Electronics	O
Standards	O
Association	O
(	O
VESA	O
)	O
.	O
</s>
<s>
SVGA	O
enabled	O
graphics	O
display	B-General_Concept
resolutions	I-General_Concept
up	O
to	O
800×600	B-General_Concept
pixels	B-Algorithm
,	O
36%	O
more	O
than	O
VGA	B-Protocol
's	O
maximum	O
resolution	O
of	O
640×480	B-General_Concept
pixels	B-Algorithm
.	O
</s>
<s>
Extended	B-Device
Graphics	I-Device
Array	I-Device
(	O
XGA	B-Device
)	O
is	O
an	O
IBM	O
display	O
standard	O
introduced	O
in	O
1990	O
.	O
</s>
<s>
Later	O
it	O
became	O
the	O
most	O
common	O
appellation	O
of	O
the	O
1024768	O
pixels	B-Algorithm
display	B-General_Concept
resolution	I-General_Concept
.	O
</s>
