RAMDAC Speed

[Gamingphreek]

So for a long time i have noticed that the RAMDAC speed has been 400mhz.

First off, what exactly does RAMDAC do?

Second off, what would happen if NV/ATI upped that speed, or upped the quality?

-Kevin

 

[dug777]

i overclocked my RAMDAC









No idea i'm afraid.

*awaits a better response*

 

[dug777]

Some stuff is on google...

http://www.afterdawn.com/glossary/terms/ramdac.cfm

Does this mean DVI bypasses the RAMDAC?

 

[dug777]

and http://en.wikipedia.org/wiki/RAMDAC

it seems DVI bypasses the DAC lookup process...

 

[Gamingphreek]

Originally posted by: dug777
Some stuff is on google...

http://www.afterdawn.com/glossary/terms/ramdac.cfm

Does this mean DVI bypasses the RAMDAC?

I THINK the DAC might mean the same thing it does in Audio terms (Digital to Analog converter). So without reading those links yet, i guess it would make sense that it bypasses the RAMDAC.

-Kevin

 

[SpeedZealot369]

good question, I thought it had something to do with resolution/refresh rate?

 

[CP5670]

Yeah, it determines the maximums the card can support on an analog output. I think pretty much all cards made in the last two years or so have 400mhz RAMDACs, which top out at 20x15 at 85hz. There isn't much point in increasing it beyond that, as the fastest refreshing monitors out there also max out at the same level.

There is a short description here: http://en.wikipedia.org/wiki/RAMDAC

 

[Peter]

The DAC is the digital-analog converter that makes the RGB line voltage from pixel data. This conversion has a maximum speed for sharp voltage changes. This limits the pixel clock frequency - if you go above, things will start to get blurry.

The 350 to 400 MHz we have today are good for totally insane resolutions, not to worry. Most of us are running resolutions that are well below 200 MHz pixel clock.

 

[Steve]

Isn't 1920x1200@60Hz (32bit) transmitted at 165MHz?

 

[Matthias99]

Originally posted by: sm8000
Isn't 1920x1200@60Hz (32bit) transmitted at 165MHz?

1900 * 1200 * 60 * 3 (3 subpixels/pixel; the alpha information is only used internally) = ~410M subpixels/sec.

It's about 137M transmissions/sec. if you transmit the RGB values for each pixel in one burst. DVI works like this; I don't think VGA does (although it must be doing something to reduce the number of transmissions, since 2048x1536@85Hz is more like 800M subpixels/sec.)