DVI connections come in a few flavors:
DVI-A:
Analog video is carried on 4 pins on the left side of the connector. This connection is what allows HD15-DVI adapters. A cable that is DVI-A only will not transmit a digital signal.
DVI-D single link:
Digital video is carried on 12 pins in the middle of the connector. Maximum bandwith is around
[email protected] (That's off the top of my head, but it's in that ballpark)
DVI-D dual link:
Digital video is carried on all 24 pins on the right side of the connector. Maximum bandwidth is around
[email protected] (Again, somewhere in that ballpark...double check these figures before basing a purchase on them)
DVI-I single link:
Has both 12 of the 24 digital pins and the 4 analog ones, and can transmit either a single link digital signal or an analog one.
DVI-I dual link:
Same as above, but with all 24 digital pins and dual link bandwidth capability.