Whats the difference between PCI slots and PCI express because i dont know the difference?

 

Ive just got posted that the Nvidia 6600 PCI express wont work in a normal PCI slot so now im intergraded stuck.

 

If u could so kindly give me a price on a brand spanken new 5700 PCI only, that would be great

 

Thanks for your time

 

Kind regards Michael