What's the difference between an iPhone 4 and iPhone 4S?

Help, please! I've been looking for an iPhone and noticed there's a massive price difference between the 4 and 4S. Why are they so different? They look identical to me.

Http://www.apple.com/iphone/compare-iphones/

I know one of the differences is the 4S has Siri so you can do a lot more with voice control but I don't really know much else sorry you might want to check out the Apple website for more info.

I think that the 4s can have 4G internet and the other one can't

Looking at it on the surface.

Faster processor, more RAM, better graphics, Siri, better camera, speakers, battery life, etc are all improved on the 4S vs the 4