Difference between D & G in camera lenses?

I want a 50mm f/1.4 lens for my Nikon D3100. My choices are 50mm f1.4 D & 50mm f1.4G. What is the difference? Which would be best for my D3100?

The D lenses are an older design. There's not autofocusing motor in the lens. It has a pin that links to the autofocus motor in the camera body, if the body has one. The D3100 does not. The D lens also has a mechanical aperture ring that is useful for working with older film SLR bodies. The DSLR has no need for it, unless it is being adapted to another brand of camera, which is not worth the trouble anyway.

The G lens is also AF-S. Being a G lens means it has no mechanical aperture ring, and it gets its aperture setting from the camera electronics. (According to Ken Rockwell, "G" stands for "gelded".) Being AF-S it has its own autofocus motion, and just interacts with the body electronically. It is compatible with your D3100.

D won't autofocus with your camera - G will.

Save yourself some serious bucks and get the 50mm f/1.8 G. You will never tell the difference. Also, just what are you getting in the 1.4?
http://www.adorama.com/...f18-or-f14