<s>
A	O
random-access	O
memory	O
digital-to-analog	O
converter	O
(	O
RAMDAC	B-Device
)	O
is	O
a	O
combination	O
of	O
three	O
fast	O
digital-to-analog	O
converters	O
(	O
DACs	O
)	O
with	O
a	O
small	O
static	B-Architecture
random-access	I-Architecture
memory	I-Architecture
(	O
SRAM	O
)	O
used	O
in	O
computer	O
graphics	O
display	O
controllers	O
or	O
video	B-Device
cards	I-Device
to	O
store	O
the	O
color	B-Data_Structure
palette	I-Data_Structure
and	O
to	O
generate	O
the	O
analog	O
signals	O
(	O
usually	O
a	O
voltage	O
amplitude	O
)	O
to	O
drive	O
a	O
color	B-Device
monitor	I-Device
.	O
</s>
<s>
The	O
logical	O
color	O
number	O
from	O
the	O
display	O
memory	O
is	O
fed	O
into	O
the	O
address	O
inputs	O
of	O
the	O
SRAM	O
to	O
select	O
a	O
palette	B-Data_Structure
entry	I-Data_Structure
to	O
appear	O
on	O
the	O
data	O
output	O
of	O
the	O
SRAM	O
.	O
</s>
<s>
Each	O
component	O
value	O
is	O
fed	O
to	O
a	O
separate	O
DAC	O
,	O
whose	O
analog	O
output	O
goes	O
to	O
the	O
monitor	B-Device
,	O
and	O
ultimately	O
to	O
one	O
of	O
its	O
three	O
electron	O
guns	O
(	O
or	O
equivalent	O
in	O
non-CRT	O
displays	O
)	O
.	O
</s>
<s>
RAMDACs	B-Device
became	O
obsolete	O
as	O
DVI	B-Protocol
,	O
HDMI	B-Protocol
,	O
DisplayPort	B-Protocol
and	O
other	O
digital	O
interface	O
technology	O
became	O
mainstream	O
,	O
which	O
transfer	O
video	O
data	O
digitally	O
(	O
via	O
transition-minimized	B-Protocol
differential	I-Protocol
signaling	I-Protocol
or	O
low-voltage	B-Architecture
differential	I-Architecture
signaling	I-Architecture
)	O
and	O
defer	O
digital-to-analog	O
conversion	O
until	O
the	O
monitor	B-Device
's	O
pixels	O
are	O
actuated	O
.	O
</s>
<s>
The	O
size	O
of	O
each	O
DAC	O
of	O
the	O
RAMDAC	B-Device
is	O
6	O
to	O
10	O
bits	O
.	O
</s>
<s>
The	O
SRAM	O
acts	O
as	O
a	O
color	B-Data_Structure
lookup	I-Data_Structure
table	I-Data_Structure
(	O
CLUT	B-Data_Structure
)	O
.	O
</s>
<s>
In	O
fact	O
this	O
has	O
become	O
very	O
much	O
the	O
normal	O
mode	O
of	O
operation	O
of	O
a	O
RAMDAC	B-Device
since	O
the	O
mid-1990s	O
,	O
so	O
the	O
programmable	O
palette	B-Data_Structure
is	O
mostly	O
retained	O
only	O
as	O
a	O
legacy	O
feature	O
to	O
ensure	O
compatibility	O
with	O
old	O
software	O
.	O
</s>
<s>
In	O
many	O
newer	O
graphics	B-Device
cards	I-Device
,	O
the	O
RAMDAC	B-Device
can	O
be	O
clocked	O
much	O
faster	O
in	O
true	O
color	O
modes	O
,	O
when	O
only	O
the	O
DAC	O
part	O
without	O
the	O
SRAM	O
is	O
used	O
.	O
</s>
<s>
The	O
ability	O
to	O
drive	O
transitions	O
for	O
sharp	O
edges	O
usually	O
incurs	O
,	O
for	O
the	O
RAMDAC	B-Device
,	O
a	O
significant	O
requirement	O
in	O
excess	O
of	O
the	O
pixel	O
clock	O
.	O
</s>
<s>
As	O
of	O
2006	O
,	O
the	O
DAC	O
of	O
a	O
modern	O
graphics	B-Device
card	I-Device
runs	O
at	O
a	O
clock	O
rate	O
of	O
400MHz	O
.	O
</s>
<s>
However	O
,	O
video	B-Device
cards	I-Device
based	O
on	O
the	O
XGI	O
Volari	O
XP10	O
run	O
at	O
420MHz	O
DAC	O
.	O
</s>
<s>
The	O
highest	O
documented	O
DAC	O
frequency	O
ever	O
achieved	O
on	O
a	O
production	O
video	B-Device
card	I-Device
for	O
the	O
PC	O
platform	O
is	O
550MHz	O
,	O
set	O
by	O
by	O
Barco	O
.	O
</s>
<s>
The	O
term	O
RAMDAC	B-Device
did	O
not	O
enter	O
into	O
common	O
PC-terminology	O
until	O
IBM	O
introduced	O
the	O
IBM	B-Protocol
VGA	I-Protocol
display	B-Device
adapter	I-Device
in	O
1987	O
.	O
</s>
<s>
The	O
IBM	B-Protocol
VGA	I-Protocol
adapter	O
used	O
the	O
INMOS	O
G171	O
RAMDAC	B-Device
.	O
</s>
<s>
The	O
INMOS	O
VGA	B-Protocol
RAMDAC	B-Device
was	O
a	O
separate	O
chip	O
,	O
featured	O
a	O
256-color	O
(	O
8-bit	O
CLUT	B-Data_Structure
)	O
display	O
from	O
a	O
palette	B-Data_Structure
of	O
possible	O
values	O
,	O
and	O
supported	O
pixel-rates	O
up	O
to	O
approximately	O
30Mpix/s	O
.	O
</s>
<s>
As	O
clone	O
manufacturers	O
copied	O
IBM	B-Protocol
VGA	I-Protocol
hardware	O
,	O
they	O
also	O
copied	O
the	O
INMOS	O
VGA	B-Protocol
RAMDAC	B-Device
.	O
</s>
<s>
Advances	O
in	O
semiconductor	O
manufacturing	O
and	O
PC	O
processing-power	O
allowed	O
RAMDACs	B-Device
to	O
add	O
direct-color	O
operation	O
,	O
which	O
is	O
a	O
mode	O
of	O
operation	O
that	O
allows	O
the	O
SVGA-controller	O
to	O
pass	O
a	O
pixel	O
's	O
color-value	O
directly	O
to	O
the	O
DAC-inputs	O
,	O
thereby	O
bypassing	O
the	O
RAM	O
lookup-table	O
.	O
</s>
<s>
Another	O
innovation	O
was	O
Edsun	O
's	O
CEGDAC	O
,	O
which	O
featured	O
hardware-assisted	O
spatial	B-Algorithm
anti-aliasing	I-Algorithm
for	O
line/vector	O
draw-operations	O
.	O
</s>
<s>
By	O
the	O
early	O
1990s	O
,	O
the	O
PC	O
chip-industry	O
had	O
advanced	O
to	O
the	O
point	O
where	O
RAMDACs	B-Device
were	O
integrated	O
into	O
the	O
display	O
controller	O
chip	O
,	O
thus	O
reducing	O
the	O
number	O
of	O
discrete	O
chips	O
and	O
the	O
cost	O
of	O
video	B-Device
cards	I-Device
.	O
</s>
<s>
Consequently	O
,	O
the	O
market	O
for	O
standalone	O
RAMDACs	B-Device
disappeared	O
.	O
</s>
<s>
Today	O
,	O
RAMDACs	B-Device
are	O
still	O
manufactured	O
and	O
sold	O
for	O
niche	O
applications	O
,	O
but	O
in	O
obviously	O
limited	O
quantity	O
.	O
</s>
<s>
In	O
modern	O
PCs	O
,	O
the	O
RAMDAC(s )	O
are	O
integrated	O
into	O
the	O
display	O
controller	O
chip	O
,	O
which	O
itself	O
may	O
be	O
mounted	O
on	O
an	O
add-in-board	O
or	O
integrated	O
into	O
the	O
motherboard	O
core-logic	O
chipset	O
.	O
</s>
<s>
The	O
original	O
purpose	O
of	O
the	O
RAMDAC	B-Device
,	O
to	O
provide	O
a	O
CLUT-based	O
display-mode	O
,	O
is	O
rarely	O
used	O
,	O
having	O
been	O
supplanted	O
by	O
True	O
Color	O
display	O
modes	O
.	O
</s>
<s>
However	O
,	O
many	O
CAD	B-Application
and	O
video	O
editing	O
applications	O
use	O
hardware	B-Architecture
overlay	I-Architecture
,	O
combined	O
with	O
the	O
programmable	O
palette	B-Data_Structure
,	O
to	O
ensure	O
the	O
user	O
interface	O
does	O
not	O
disrupt	O
the	O
rendering	O
of	O
editing	O
window	O
.	O
</s>
