What are PCIe Connectors?

By Amy Goetzman | November 01, 2022

Meet the Connector: PCIe Connectors

Peripheral Component Interconnect Express (PCle), also called PCI Express, is a high-performance and high-bandwidth serial communication I/O interconnect bus standard. Interconnects that meet the PCIe standard include mezzanine and board-to-board connectors, over-the-board solutions, high-speed edge card sockets that support 1, 4, 8, and 16 PCIe links, and PCIe optical cable assemblies.

PCIe connector on motherboard (image courtesy of Keysight Technologies)

PCIe is a layered protocol consisting of a transaction layer, a physical layer (subdivided into logical and electrical sublayers), and a data link layer (subdivided to include a media access control sublayer).

The PCIe link is built around dedicated unidirectional couples of serial (1-bit), point-to-point connections known as lanes. Every device connected to a motherboard with a PCIe link has its own point-to-point connection. (The earlier PCI connection was a bus-based system in which the devices competed for a bidirectional, 32-bit or 64-bit parallel bus.) PCIe significantly improves system throughput, scalability, and flexibility at lower cost than traditional bus-based interconnects.

Amphenol Communication Solutions’ SAS/PCIe 5.0 (U.2 & U.3) connectors comes with 32 GT/s (PCIe lanes) and 24 Gb/s (SAS lanes) speeds to meet the demands of next-generation servers. The 68-position, SAS/PCIe receptacle and header enables implementation of high-speed Serial Attached SCSI (SAS) hard disk drive (HDD) interface as well as Peripheral Component Express (PCIe)-based devices. The molded guide post allows the device plug and receptacle to self-align during the mating process.

The first version of PCIe, 1.0a, was introduced in 2003 as a replacement for bus-based communication architectures such as PCI, PCI Extended (PCI-X), and Accelerated Graphics Port (AGP). It featured a per-lane data rate of 250 Mb/s and a transfer rate of 2.5 gigatransfers per second (GT/s). Each subsequent generation of PCIe has doubled the I/O bandwidth with new release every three years. The most recent iteration, the PCIe6.0 specification, was released in January 2022.

Image 2 PCIe bandwidth growth across generations

Features of PCIe 6.0 include:

64 GT/s raw data rate and up to 256 GB/s via x16 configuration
Pulse Amplitude Modulation with 4 levels (PAM4) signaling
Lightweight Forward Error Correct (FEC) and Cyclic Redundancy Check (CRC) mitigate the bit error rate increase associated with PAM4 signaling

Flit (flow control unit) based encoding supports PAM4 modulation and enables more than double the bandwidth gain
Updated Packet layout used in Flit Mode to provide additional functionality and simplify processing
Maintains backwards compatibility with all previous generations of PCIe technology

PCIe 7.0 specification is targeted for member release in 2025 and is anticipated to accommodate a 128 GT/s raw bit rate and up to 512 GB/s bi-directionally via x16 configuration.

Molex’s NearStack PCIe Connector System and Cable Assemblies for next-gen servers were developed with the Open Compute Project. They use new direct-attached cable technology to improve signal integrity while lowering insertion loss and signal latency. Direct-to-contact twinax termination eliminates paddle cards within the cable assembly. Unlike competing cable jumpers, NearStack uses a fully automated wire termination process, which improves manufacturing efficiencies, repeatability, and signal integrity.

Design Notes

Standardization: PCl Express was initially proposed by Intel and further developed by the Peripheral Component Interconnect Special Interest Group (PCI-SIG), which continues to maintain and develop the standard.

Samtec’s PCIe solutions

Markets, Sectors, and Applications

Key markets include Automotive, Datacom/Telecom, Industrial, Military/Aerospace

Applications include artificial intelligence/machine learning, data center, high-performance computing, and IoT. PCIe is the common motherboard interface for PC graphics cards, hard disk drive host adapters, solid state drives, Wi-Fi, and Ethernet hardware connections.