When ATI launched the HD4870 graphics card, it surprised many with its blend of near high-end performance with mainstream prices. One of the most surprised seemed to be arch enemy Nvidia, which promptly started chopping prices to try to compete on the bang-for-buck front.

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So if one HD4870 is good, imagine how good two HD4870 cores on the same PCB might be. Welcome to the R700 - or, to you and me, the Radeon HD4870 X2.
From the outside the only apparent difference between the new HD4870 X2 and the previousHD3870 X2 is the pair of updated RV770 cores and faster GDDR5 memory, but under the skin there is a whole world of difference.

The HD4870 has the second generation PCI-E 2.0 x16 switch (PLX) as opposed to the PCI-E 1.1 of the previous generation X2, giving the HD4870 a much wider communication channel than before; twice as big, in fact, at 5GB/s (in each direction).