Ans: DVI-D is a digital ONLY connection. The difference between Single Link and Dual Link is that each supports varying resolutions. DVI-D Single Link can support up to 1920 x 1080 at 60 Hz. DVI-D Dual Link can support up to 2048 x 1536 at 60 Hz. DVI cables are used with new video cards for higher resolution over VGA, they are also used with new digital TV’s and HD decoders.

DVI-D Dual Link:
Notice that the three rows of eight pins and that the "flat blade"contact seen to the left has no contacts above and below it.
Male (left) and female (right) version are shown below.

DVI-D Single Link:
Notice the three rows have two missing pins in the center and that the "flat blade" contact seen to the left has no contacts above and below it.