How are the Nikon D3100 and D90 different?

How are the Nikon D3100 and D90 different?

Added (1). I'm considering buying one of these and I'm not sure which to choose. Please don't suggest any other brands.

Http://www.dpreview.com/products/compare/side-by-side?products=nikon_d3100&products=nikon_d90

The D3100 is for beginners, the D90 for serious amateurs. If you have to ask get a d3100

Nikon D3100 is for beginners and Nikon D90 is for professionals or those who have good exposure to photography. Some of the basic differences are:
D90 is faster, has a bigger sensor, better image quality, longer battery life.
One more difference is that D90 comes with 18-105mm kit lens while D3100 comes with 18-55mm kit lens.
You will get more differences at the link below:
http://snapsort.com/...-Nikon_D90

The D3100 is an entry level DSLR the D90 is a more advanced model (though older). The principle difference is that the D90 has a focus motor in the body, so all Nikkor AF and AF-S lenses with autofocus with it.

The D3100 does not have a focus motor - so if you want to be able to autofocus your lenses, you HAVE to buy AF-S lenses.AF lenses will attach, but you need to manually focus them with this camera.

Personally, I would go with the D90. Although it's an older model, it has higher spec features not found on the entry level models (the focus motor, mentioned, and also the ability to control off camera flash wirelessly).