Which is better VGA or DVI-D?
How VGA works: The digital image data in your video card RAM is first converted to an analog signal through the card’s RAMDAC (RAM Digital to Analog Converter), which is then sent over the analog VGA cable to the LCD monitor, where the monitor re-converts the analog signal back to digital for display. Personally, I don’t see the point of converting the video signal from digital to analog then back to digital again, so I use DVI preferentially. DVI is all-digital, directly from the video card RAM all the way to the monitor. No signal conversion to analog. By itself, which output you use has no effect on the speed of your computer.
