PCIe

Peripheral Component Interconnect Express, commonly known as PCI Express and abbreviated as “PCIe”, is a high speed computer bus architecture which has become the industry standard for nearly all internal computer component connections.

PCIe provides the connections from a computer’s processor(s) and memory to other components and peripherals. This interface is a highspeed serial transport designed to replace older parallel bus architectures including PCI and ISA (Industry Standard Architecture). PCIe uses a point-to-point access bus that provides outstanding data transfer speed improvement over its predecessors. 

What Does PCIe Mean?

By the early 2000’s, demands on computing bandwidth by internal hardware and peripherals had led to the next generation of PCI, known as PCI Express, or PCIe. The biggest advantage of PCIe over conventional PCI is that it utilizes a serial interface, rather than the parallel interface used in PCI architecture. Another advantage is the use of individual, rather than shared busses, for each connected device.

PCIe Architecture

The breakthroughs included in PCI Express architecture have enabled substantially faster transfer rates, as compared to PCI, and each successive version of PCIe has continued to build upon these improvements. Whereas conventional PCI utilized common address, data and control lines, the point to point topology of PCIe provides separate links to each connected device, freeing each from the potential constraints of the others.

PCIe communication utilizes a mode of data transfer known as “packets”. The transaction layer of the PCIe port performs the task of packetizing and de-packetizing the data. This difference in electrical signaling inherent to PCIe vs. conventional PCI required distinct electronic and connector architecture to be developed, making PCIe slots incompatible with PCI cards.

PCIe Formats

A variety of formats have been developed for PCI Express, each with slightly different nomenclature. Understanding what these PCIe formats indicate in terms of size and version is essential information for understanding what expansion cards will (or will not) work with your system.

PCIe Versions

Since the introduction of PCIe 1.0 in 2002, successive versions have been introduced to meet the growing demands for more bandwidth and frequency. Version 1.0 had an available bandwidth of just under 8GB/sec for the combined 16 lanes of traffic. The frequency for PCIe 1.0 was 2.5 GHz. With each new version, the total bandwidth has doubled, while the frequency for PCIe 4.0, introduced in 2017, has increased to 16 GHz to go along with 64GB/sec of bandwidth. This “doubling” convention will continue with PCIe 5.0, to be released in 2019. Along with performance improvements, each version has provided new features and increased energy efficiency.

The Future of PCIe

The immediate future of PCI Express will be determined by the upcoming release of PCIe 5.0 in 2019. This new revision, like its predecessors, will double the available bandwidth of the current version 4.0. In addition to the performance upgrade, physical differences inherent to PCIe 5.0 will include shorter keys and integration of improved materials on the printed circuit board. PCIe 5.0 will remain backwards compatible with PCIe 3.0 and 4.0. For this reason, motherboards and adapter cards will not require immediate upgrades. As computer hardware designers and manufacturers continue to integrate PCIe into their latest offerings, the entrenched position of de facto standard becomes more secure.

Computing power and memory enhancements continue to evolve at breakneck speed. So far, the PCI Express bus has managed to keep pace, but the gap is narrowing. Data transfer innovations in the not-so-distant future may seem like a Hyperloop compared to our familiar and reliable bus, and necessarily so. Perhaps no computer technology plays as important a role in meeting the demand for speed and bandwidth, so the impetus on designers for ongoing breakthroughs in PCIe performance will continue into the foreseeable future.