NAT vs Router

Hi everyone, I was asked this question and it kind of stomped me. Say there's traffic on the network with a good 20 pc's. Why is it better to have a NAT server implemented as opposed to just a router?

thanks

NAT
http://www.webopedia.com/TERM/N/NAT.html

Router
http://www.webopedia.com/TERM/r/router.html

Nat if you notice, does give us some protection from the internet wrong doers. And the way things are today, we need all the nelp we can get.

I use a router with nat in it for that very reason.

I know what they both mean..

I was inquring about the scenerio posted in the my main post. The answer given to me was.... one I.P address is being forwarded (NAT) in comparison to 20 individual i.ps (if a NAT wasn't being used)
We'll it's not really an answer, it was more of a hint to the correct answer.

Im assuming this saves a lot of congestion and free's up traffic on the network, when I gave this response I was incorrect. I also stated that NAT adds security, still not what he was looking for.

Im trying to find out more information on this and how a NAT has such a huge advantage in the above example.

Well, with NAT you can run unlimited (well, at least more than you'll ever need) hosts on the internal side of the router. If you have 20 computers then you'd have to have 20 public IP addresses, and each one costs money from your ISP. With NAT you only need one public IP and all the internal hosts use a private IP address.

And as stated previous, there is a lot of security to using it.

Although if you're setting up a router to route a public subnet in, it's trivial to block unsolicited incoming connections too. :) In either case, the security advantage is over letting the hosts connect directly to the ISP without something in the way.

The only advantage NAT gives you over regular routing is conservation of the public IP address space. And in practical terms, that advantage comes down to $ when you don't have to ask your ISP for a big allocation. :)