What is PCIe 4.0?

PCIe 4.0 is the 4th generation of the PCIe (Peripheral Component Interconnect Express) interface standard that is commonly used to connect graphics cards, hard disk drive host adapters, SSDs, Wi-Fi and Ethernet hardware to the motherboard. PCIe 4.0 was announced on 29 November 2011, by PCI-SIG (PCI Special Interest Group) - a group of more than 900 companies that maintains the conventional PCI specifications.

PCIe slots can be configured with one lane or multiples of four lanes, such as x1, x4, x8, x16 and each lane has the same maximum bandwidth for a version. PCIe 4.0 provides a bit rate of 16 GT/s which is approximately 2GB/s per single lane. This is double the bit rate of that provided by PCIe 3.0 - 8 GT/s which is approximately 1GB/s per single lane. Hence a PCIe 3.0 x8 interface can be replaced by a PCIe 4.0 x4 interface that provides the same amount of bandwidth. This increased bandwidth is due to the use of the OCuLink-2 hardware interface in version 4.0 as opposed to Intel’s Thunderbolt 3 used in version 3.0. OCuLink-2 is approximately 60% faster than Thunderbolt 3. PCIe 4.0 also operates at 16 GHz as opposed to 8 GHz of PCIe 3.0.

PCIe 4.0 maintains backward as well as forward compatibility in both software support and the mechanical interface used. Hence, PCIe 3.0 cards will work on motherboards that support PCIe 4.0, and PCIe 4.0 cards will also work on PCIe 3.0 motherboards, but they will be limited to the performance of the PCIe 3.0 interface. PCIe 4.0 also includes slight tweaks to improve flexibility, scalability and power consumption.