The PCI Special Interest Group has revealed plans to develop an external version of PCI Express to rival the likes of eSATA, USB 3.0, and Intel’s new Thunderbolt interconnect. The standard would be based on PCIe 3.0 technology, which will offer potential transfer speeds of up to 32Gbps, a significant boost from the PCIe 2.1 spec that's widely used today in PCs (internally) for connecting graphics cards, sound cards, and even solid-state drives.
Thunderbolt currently offers 10Gbps transfers, but Intel says it can scale up to 100Gbps in the future. With those speeds, USB 3.0 is already looking outdated, but then again it's the only standard gaining some traction.
Previously known as Light Peak, Thunderbolt was launched back in February using copper cabling instead of fiber optics as initially planned, and so far only Apple has adopted it for its latest MacBook Pro and iMac refreshes. Meanwhile, eSATA has seen a mild adoption in notebooks but its use is more limited compared both Thunderbolt and USB.
The initial proposal for external PCI Express 3.0 suggests using copper wires, with a maximum transfer distance of 3 meters, and the ability to support up to 20W of power delivery. That's double the 10W of power provided by Thunderbolt, and would be enough for external hard drives and other devices to run without the need for a separate power source -- though external graphics cards would certainly need one.
PCIe cables will be faster, cheaper, and thinner than Thunderbolt, but less functional, since the latter can be daisy-chained and carry DisplayPort data while external PCI Express cannot. The proposed standard is still in its early stages and won't be commercialized until at least mid-2013, so there's plenty of time for USB and Thunderbolt to battle it out.