PCI Express 7.0 Finalized: Achieving 256 GByte/s Over Cable

The PCI Special Interest Group (PCI SIG) has officially completed the specifications for PCI Express 7.0, enabling data transfer rates of up to 256 GByte/s over cable connections. This new standard introduces enhanced options for both electrical and optical PCIe cable connections and lays the groundwork for future developments in PCIe 8.0.

With the completion of PCIe 7.0, developers can now download the specifications in version 1.0. Although various teams have already begun their development work, it is unlikely that commercially available products utilizing this new standard will emerge before 2028. This delay is reminiscent of the timeline for PCIe 6.0, which was introduced in 2022 but has not yet seen widespread implementation in consumer products.

The transition to PCIe 7.0 marks another significant leap in data transfer capabilities, effectively doubling the data rates compared to its predecessor. A single PCIe lane can now achieve 16 GByte/s in each direction, enabling a x16 configuration to support a total of 256 GByte/s in one direction and up to 512 GByte/s overall. In comparison, PCIe 6.0 allowed for maximum rates of 128 and 256 GByte/s.

PCIe 7.0 retains the four-level pulse amplitude modulation (PAM4) signaling method introduced with PCIe 6.0. This approach allows each transfer to convey two bits of data using four voltage levels, necessitating more sophisticated controller designs. However, both PCIe 6.0 and 7.0 maintain backward compatibility, ensuring that existing devices can still operate within the new framework.

Additionally, PCIe serves as the foundation for Compute Express Link (CXL), enabling the connection of additional memory modules and enhancing overall system performance.

Last year, PCI SIG announced the new CopprLink standard for electrical cable connections compatible with PCIe 5.0 and 6.0. This standard includes both internal and external versions, with the latter capable of bridging distances of up to two meters, making them suitable for connecting devices within server racks. Molex showcased CopprLink technology featuring PCIe 7.0 at this year's Computex, indicating that similar advancements will follow.

For longer connections, optical solutions using fiber optics have been available for years, though they have primarily relied on proprietary technologies. PCIe 6.0 and 7.0 aim to standardize an interface for optical connections, although specific connector types, wavelengths, and cable specifications are yet to be defined.

The PCIe External Cabling specification primarily facilitates connections for storage devices, utilizing the SFF-8614 (MiniSAS-HD) connector. Meanwhile, the older OCuLink standard has been limited to PCIe 3.0, supporting transfer rates of 8 Giga-transfers per second (GT/s).

At Computex, Phison introduced its first PCIe 6.0 controller for SSDs, named PT1601. Other companies, such as Astera Labs and Micron, have also showcased their PCIe 6.0 products, though no specific timelines for mass production have been disclosed. The first servers featuring PCIe 6.0 are expected to be released no earlier than 2026, with AMD planning to transition its Epyc platforms to support this standard, while Intel may incorporate PCIe 6.0 in its upcoming Xeon 7, also known as Diamond Rapids.

Furthermore, the PCI SIG has indicated that research into PCIe 8.0 has already commenced, with aspirations to double the data signaling rate to 256 Gigatransfers per second compared to PCIe 7.0.