AMD / ATI Radeon Graphics
AMD purchased ATI Radeon in 2006 for 4.3 billion dollars. AMD & Radeon have always gone hand in hand but now even more so since 2006 the processor company now creates two separate products that work in harmony with one another. Radeon graphics give you the best bang for the buck when it comes to graphics cards vs the competitors Nvidia. Nvidia does have more powerful cards, but their cards in general are extremely more expensive easily making a budget gaming build impossible.
While this chart might not be the most update to date chart it does give you a feel for the speeds of cards. Whenever graphics cards are released you never really know who will come on top Nvidia or ATI usually Nvidia historically has been the best but ATI throws some powerhouse cards to beat Nvidia sometimes.
Crossfire is where link or “bridge” two graphics card together so that they both work together to process graphics. This allow your games to run faster, and your programs to run better. Radeon allows 4x16x PCI-E setup, but it is not recommended due to the extreme bandwidth limitation difference which will cause micro-stuttering. I myself have experienced this first hand with a pair of HD7770 in crossfire the first was in a 16x PCI-E slot while the second was in a 4x PCI-E slot I did get higher frames in my game but it skipped and simply made the games I played more frustrating to play due to the micro-stuttering. Always check to make sure the motherboard your buying can at least run two graphics cards in 8x by 8x which is almost as good as 16x by 16x. when you get down to 4x you enter a whole new world of problems assuming your going for high performance if not 4x is perfectly fine.