Editing PCI Express (section)

== Competing protocols ==
Other communications standards based on high bandwidth serial architectures include [[InfiniBand]], [[RapidIO]], [[HyperTransport]], [[Intel QuickPath Interconnect]], the [[Mobile Industry Processor Interface]] (MIPI), and [[NVLink]]. Differences are based on the trade-offs between flexibility and extensibility vs latency and overhead. For example, making the system hot-pluggable, as with Infiniband but not PCI Express, requires that software track network topology changes.{{citation needed|date=February 2021}}

Another example is making the packets shorter to decrease latency (as is required if a bus must operate as a memory interface). Smaller packets mean packet headers consume a higher percentage of the packet, thus decreasing the effective bandwidth. Examples of bus protocols designed for this purpose are RapidIO and HyperTransport.{{citation needed|date=February 2021}}

{{Clarify|date=September 2024|text=PCI Express falls somewhere in the middle,|reason=In the middle of *what*? What are the endpoints? Nothing above talks about device interconnects or routed network protocols; some discussion of routing was removed in a February 2019 edit, leaving this paragraph missing some context.}} targeted by design as a system interconnect ([[local bus]]) rather than a device interconnect or routed network protocol. Additionally, its design goal of software transparency constrains the protocol and raises its latency somewhat.{{citation needed|date=February 2021}}

Delays in PCIe 4.0 implementations led to the [[Gen-Z (consortium)|Gen-Z]] consortium, the CCIX effort and an open [[Coherent Accelerator Processor Interface]] (CAPI) all being announced by the end of 2016.<ref name="1Jwlv" />

On 11 March 2019, Intel presented [[Compute Express Link|Compute Express Link (CXL)]], a new interconnect bus, based on the PCI Express 5.0 physical layer infrastructure. The initial promoters of the CXL specification included: [[Alibaba Group|Alibaba]], [[Cisco]], [[Dell EMC]], [[Facebook]], [[Google]], [[Hewlett Packard Enterprise|HPE]], [[Huawei]], [[Intel]] and [[Microsoft]].<ref name="aJ00L" />