PCI-Express Gen 3 Standard Released Into The Wild

PCI-SIG, the organization in charge of maintaining and developing PCI-Express, has announced that the third version of the PCIe standard is finished and ready for implementation. The new standard is fully compatible with earlier PCIe cards; a Gen 1 or Gen 2 card will run perfectly in a PCIe 3.0 slot.

Just as PCIe Gen 2 offered double the performance of Gen 1, Gen 3 again offers twice the performance of Gen 2 (8GT/s). Unlike Gen 2, however, Gen 3 incorporates a number of additional changes to improve its efficiency. PCIe 1.1 and 2.0 both use an 8b/10b encoding scheme. This means that 8-bit words are mapped to 10-bit packets. This is part of why PCIe bandwidth numbers are quoted differently. Technically, an x1 PCIe Gen 2 slot is capable of transferring 500MB/s, but 20 percent of this is overhead. The actual data transfer peak is 400MB/s. Instead of using the previous 8b/10b scheme, PCIe Gen 3 switches to 128b/130b encoding. This reduces the amount of overhead bandwidth from 20 percent to less than two percent.

"Each new version of the PCIe spec has doubled the bandwidth of the prior generation,” said Nathan Brookwood, research fellow at Insight 64. "The latest group of PCIe architects and designers drove the standard forward while maintaining complete backward compatibility for Gen 1 and Gen 2 devices. Rarely has a standard advanced so non-disruptively through three major evolutionary cycles. The ability to pull this off demonstrates not only the ingenuity of the Gen 3 developers, but also the insight of those who defined the earlier versions in such an extensible manner."

Should You Care?

How much this impacts day-to-day computing depends on whether or not vendors make full use of the technology. Manufacturers will be quick to slap PCIe Gen 3 x16 slots on their motherboards, but this, ironically, is where it'll matter least. The additional bandwidth may benefit GPGPU and HPC computing but modern video cards almost certainly don't need the bandwidth, even in SLI.

The new standard could lower the cost of external graphics solutions.

PCIe Gen 3's greatest utility is at the x1 / x4 end of PCIe. An x1 Gen 3 slot would have up to 1GB/s of bandwidth—more than enough for today's PCIe SSD drives or budget video cards. Gen 3 could also be useful in notebooks, particularly if the external graphics market ever emerges as something more than the tiniest of niche markets. Before this can happen, OEMs would need to agree to build solutions. Six years after the introduction of PCIe, the number of x1 cards available remains pathetically small; NewEgg currently sells five x1 cards, 30 AGP cards, and 57 PCI cards.

Ultimately we'd like to see PCIe do for external video and x1 ports what USB 3.0 has done for external drives. Remove the performance penalty currently inherent to a small interface or external box and component arrangements can become much more flexible. This goes double for laptops, where an external graphics box is often the only thing a system would need to go from terrible game performance to something more acceptable.