Diference betwen default Windows and Radius autentification

I have confgiured , for my 70-291 , a DC with routing and access role , and I'm am
, what's the diference betwen . RADIUS and Windows authentification ? can someone expliain me ?
Thank's ! :P

Thank's ! :P
Optimism is an occupational hazard of programming: feedback is the treament. (Kent Beck)
Comments
RADIUS authentication uses a RADIUS server to determine if and what access a login should get. Now the RADIUS server in turn could use AD to get information to authenticate and authorize the RRAS login.
IAS is essentially a RADIUS server service that comes with Windows 2K/2K3 and can optionally be installed and used.
Also, on very large networks, you can also have a radius proxy forward authentication requests to multiple Raidus servers for load balancing/fault tolerance.
IAS is Microsoft's implementation of Radius.