More Watts and Speed with PCI Express 3
Instead of resting on their laurels, the PCI-SIG (Peripheral Component Interconnect Special Interest Group), which controls PCI specifications, is working on PCI Express 3. This is likely because many of PCI-SIG’s members sell graphics cards, and they want to make sure you won’t hesitate to buy one because you don’t have the bandwidth.
PCI-E 3.0 will double PCI-E 2.0 speeds to 1 GB/s per lane, or 16 GB/s for a x16 graphics card slot. Part of the increase will come from increasing the signaling rate, or just turning up the clock because manufacturing improvements allow for it. The rest of the increase comes from leaving behind 8b/10b encoding. Like a SATA connection, PCI-E 1 and 2 would add 2-bits to every byte: PCI-E 3 won’t.
On the wattage side, little is known. There are, however, rumors that PCI-E 3 will include support not only for 300 watt cards, but will physically be able to support a 1.5 kilo card. That’s support in terms of holding it up without dropping it, and kilo in terms of grams. Such a card would be behemoth, being an unprecedented three slots wide. Low to lower-midrange cards use take up one slot. Upper-midrange cards take up two with bulky cooling. A triple-wide boggles the mind at first, but starts to make sense if one considers a double GPU card with a lot of cooling.
PCI-E 3 will be backwards compatible. You will be able to put a version 1, 2, or 3 card in any PCI-E slot (though getting enough watts to a top end-card, and keeping it from falling out, may be a problem) and vice-versa. The combination will be limited to the slower of the two though.