EE Times writes fourth-gen PCIe will use a new connector but the specification will be backward compatible mechanically and electrically with today's 8GT Gen 3.
The big work ahead for the standard is in fine tuning the link and getting engineers to agree on its parameters. The work is significant because the greater speed translates into shorter reach generating some new costs for retimers in some systems such as servers which make heavy use of PCIe.Beyond this we'll likely need optical links as copper links have reached their limits in terms of performance.
The spec may be taking a bit longer to finish than previous PCIe generations. That’s understandable given the SIG chose to go for what they thought was the maximum possible data rate, squeezing copper links for all they could deliver, twice as much as in today’s Gen 3 products.
“We are getting 16G, something no one thought was possible a few years ago,” said Al Yanes, president of the PCI SIG in an interview with EE Times.