okay so what is the diffrence between a gtx 580 classified that has a 384bit
and a
gtx 680 256bit
forgive me if its a stupid question but i am a Nobist to graphics cards and need a educational answer
Thank You!

gtx 680 256 memory bus is clocked at 6000mhz the 580 was at 4000mhz a 680 at 256 has similar memory bandwith as a gtx 580 clocked at 4000 mhz on a 384 bit interface. so there really isnt much difference between the gtx 580 and 680 memory one has more lanes but is slower and the other has less lanes but is faster equaling out to about the same.

If you are looking for any better analysis then this I would say either Pm lephron or wait until he sees this post and responds.  His post are always full of the little details that make it right.

if money is not an issue, the 680 beats the 580 everywhere.

here watch this in full screen 580 v 680 1080 p ultra settings  neat to see the differences
http://www.eurogamer.net/videos/battlefield-3-1080p-dx11-ultra-settings-gtx-580-vs-gtx-680-video

Only the memory bandwidth matters, that is the rate that the GPU places a scene in your Vram buffer temporarily before it goes to your display.
 
The math is simple: 
interface width x effective frequency ÷ 8 bits per byte = bandwidth.
 
GTX680 reference  : 256-bit x 6.008GHz ÷ 8 bits per byte = 192.26GB/s
GTX580 ClassUltra : 384-bit x 4.212GHz ÷ 8 bits per byte = 202.18GB/s 
 
In many cases, a high frequency can compensate for the smaller interface resulting is very similar bandwidth.  We can say GK104 used the bandwidth better if the performance is better than the GF110 despite lower bandwidth.  A more extreme example would be comparing the 512-bit interface of the G200 with GF100/GF110's interfaces, the older high-end cards have slow Vram and their GPU's were just slower and didn't use the space, so to speak. 
 
This is why I suggest you ignore the "bit-interface" size unless you do the math and find the bandwidth number, otherwise the interface size itself is useless.  You can't just say the lower interface is slower without knowing the actual bandwidth number.   Always consider the big picture.

Gratz on another BR