PCIe 4.0 is the fourth generation of the PCIe specification, which was released in 2017. It offers a significant increase in bandwidth, doubling the data transfer rate to 16 GT/s (gigatransfers per second) compared to PCIe 3.0. This increased bandwidth enables faster data transfer, reduced latency, and improved overall system performance.
PCIe 4.0 modifies the Link Training Status State Machine (LTSSM). A specific phase, , was enhanced to allow for more granular coefficient negotiation between the Root Complex (CPU/Chipset) and the Endpoint (Device). pcie specification 4.0 pdf download